Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Bruce Griffiths wrote: Don Collie wrote: I`ve always wondered about noise from batteries - please tell us more Bruce!! [also wondered about noise from the electrolytic action of aluminium, and tantalum electrolytic capacitors, and wondered if the reference bypass capacitor in a 723 should be a plastic dielectric type, rather than electrolytic]. ...Don C. Further reference on battery noise: http://smirc.stanford.edu/papers/JAP_04_Electrode_Noise.pdf Above paper actually has some theoretical predictions. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY From: Tom Clifton [EMAIL PROTECTED] Subject: Re: [time-nuts] Parallel voltage regulators Date: Fri, 26 Oct 2007 17:19:45 -0700 (PDT) Message-ID: [EMAIL PROTECTED] ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY This has been a fascinating and educational thread! I have always been aware of noise coming from switching regulators - just have Argo or Speclab look at your laptop's sound card with no input signal and there is plenty to look at until you go to battery power. I had never considered diode switching noise in linear supplies, nor birdies from an assortment of logic devices - though I am a believer in healthy distribution of bypass capacitors... They are sharp and unsteady oscillation is common, even on an old analogue synthesizer for instance. You can reduce it by putting bypass caps over the rectifying diodes. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY There is a concept in temperature control called feed-forward. In this case you would sample the supply line with an inverting amplifier and use it to increase the oven drive signal as the line voltage decreases. The goal is to keep the integral term from changing as the line voltage changes. It is not as easy as it sounds. Bill Hawkins ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Surely there will be an improvement in oven temparature regulation, by using a regulated supply, but whether or not this improvment is marginal or significant would have to be determined either by experiment [my favourite], or calculation. As you say Chuck : it`s eliminating [or reducing the effect of] one variable in the equation. Cheers,Don. - Original Message - From: Chuck Harris [EMAIL PROTECTED] To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, October 26, 2007 12:29 PM Subject: Re: [time-nuts] Parallel voltage regulators ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY The simple answer is if the heater supply in unregulated, and the supply changes, it will take a little while before the heater control loop can compensate. While this is happening, the oven temperature will be slightly wrong, and the crystal frequency will be offset. Voltage regulation adds one more level of isolation to the oven temperature from changes in raw supply voltage. -Chuck Harris Matt Ettus wrote: ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY This may be a bit late in this [strangely contentious] discussion, but I have to ask why you need to regulate the heater voltage? If the voltage varies, the control loops will adjust accordingly. Unless the input voltage is higher than some safe range for the heater circuitry. Matt ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY - Original Message - From: Bruce Griffiths [EMAIL PROTECTED] To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Friday, October 26, 2007 12:36 PM Subject: Re: [time-nuts] Parallel voltage regulators ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Magnus Danielson wrote: From: Bruce Griffiths [EMAIL PROTECTED] Subject: Re: [time-nuts] Parallel voltage regulators Date: Thu, 25 Oct 2007 17:42:51 +1300 Message-ID: [EMAIL PROTECTED] Don Collie wrote: Hi Tom, If you really want to regulate the oven`s supply voltage, my National Voltage Regulator handbook shows that the LM317T will supply over 2 Amps, with an input/output differential of between 5, and 12.5 Volts. A single one of these should do the job OK. Cheers!,.Don Collie jnr. Never rely on typical specs always use the minimum spec which is 1.5A not quite enough. You want design-margin. Some of that toll will be in less than optimum heating, some will be in less heating in the first place (compared to upper limit) and for a power regulating aspect, headroom allows better regulations. In one design we had to parallel the regulators since the regulator the designer put in just barely was able to regulate the CPU core voltage. It worked, but at just rebooted at some vauge point an the memory tests. What actually happend was that as soon as it started to actually do anything, the regulator was running at its limit and output voltage dropped as the current was rising and the voltage supervision pulled the RESET. That's what you get from reading the typical reading on the CPU current and match that with the maximum rating of the power regulator. A no margin design. That designer had a few more flaws which was creeping around in that design, but let's not bring that can of worms open here. :) The 5A LM338 will be just fine. Infact, you can pull 8A out of it under certain conditions. Cheers, Magnus Hej Magnus The LM338 thermal design is also much easier (it has a much lower junction to case thermal resistance than an LM317) especially if the circuit is intended to operate over wide temperature (0 -40C or more) and mains voltage ranges (+-10% or more). The alleged problem with the high short circuit current is easily solved by using diodes with adequate current ratings in conjunction with a fuse to protect the transformer if it isnt rated to produce an 8A dc output. The startup current of the load (rubidium standard) may also vary with temperature and /or input voltage. Either find the manufacturers specifications or allow adequate margins. Worst case design is desirable even for one off circuits especially if the circuit is published. When the design is publicly available one is in effect transferring the production run problems associated with a marginal design to many individuals rather than a single factory or production line. Bruce I don`t think the higher current created when a fuse is used instead of near-instantaneous current limiting is alleged, but rather a real problem that can cause damage further down the line. Fast acting current limiting is preferable to all but the fastest fuses that are designed to protect semiconductors. Current limiting plus thermal shutdown in the regulator will protect both load, and regulator [and resovior capacitor, and diodes, and transformer] Commonly available fuses won`t give much protection to the load - especially the delay types often necessary with large filter capacitors. A precision, proven, high performance, low noise regulator like the 723 using an external pass transistor [or preferably a darlington], to avoid chip heating, and a well bypassed reference would be a lovely solution. Cheers!,Don C. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Don Collie wrote: Bruce I don`t think the higher current created when a fuse is used instead of near-instantaneous current limiting is alleged, but rather a real problem that can cause damage further down the line. Fast acting current limiting is preferable to all but the fastest fuses that are designed to protect semiconductors. Current limiting plus thermal shutdown in the regulator will protect both load, and regulator [and resovior capacitor, and diodes, and transformer] Commonly available fuses won`t give much protection to the load - especially the delay types often necessary with large filter capacitors. A precision, proven, high performance, low noise regulator like the 723 using an external pass transistor [or preferably a darlington], to avoid chip heating, and a well bypassed reference would be a lovely solution. Cheers!,Don C. One can always use more than one fuse (one in the mains wiring and another between the reservoir caps and the regulator input), only one of which needs to be a slow blow type. An LM350 has a more tightly specified current limit than earlier 3 terminal regulators. Powering a load from an unregulated supply as suggested also offers little load protection, however if the load isnt faulty then close current limiting wont be necessary. However it is always useful when testing to have close control of the short circuit load current if at all possible. If this is required then a 3 terminal regulator by itself will not suffice. However a low power small signal npn transistor to sense the voltage drop across a current sensing resistor in the load return lead can be used to pull down the regulator adjust terminal when the transistor turns on limiting the maximum load voltage to around 1.2V in this situation which will limit the current in most loads but not in a short circuit. The only way to add control of the regulator short circuit current being to use an electronic current limiter in series with the regulator input, however this increases the regulator dropout voltage significantly as well as the circuit complexity. The only problem with the 723 for a beginner is they are much more complicated to wire up and too easy to destroy when probing if care isnt taken. Also with modern high gain transistors a darlington pass element isnt really necessary for a load current of a couple of amps. The commercial open frame linear supplies dont use them even with a 3A load current. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY I do have some experience with temperature controlled ovens. I found that a long term plot of the temperature while using an unregulated supply on the oven heater showed small random variations due to voltage variations. When the oven heater was put on a regulated supply the line became flat. The problem here seems to be during the heat up cycle. The voltage doesn't need to be regulated during that time. You might try sensing the error signal and when it is outside of the linear control range you could switch in a parallel transistor and resistor to handle the warm-up current and it would switch out when the oven has stabilized at the lower current. Regards. Max. K 4 O D S. Email: [EMAIL PROTECTED] Transistor site http://www.funwithtransistors.net Vacuum tube site: http://www.funwithtubes.net Music site: http://www.maxsmusicplace.com To subscribe to the fun with tubes group send an email to, [EMAIL PROTECTED] - Original Message - From: Bill Hawkins [EMAIL PROTECTED] To: 'Discussion of precise time and frequency measurement' time-nuts@febo.com Sent: Friday, October 26, 2007 1:21 AM Subject: Re: [time-nuts] Parallel voltage regulators There is a concept in temperature control called feed-forward. In this case you would sample the supply line with an inverting amplifier and use it to increase the oven drive signal as the line voltage decreases. The goal is to keep the integral term from changing as the line voltage changes. It is not as easy as it sounds. Bill Hawkins ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.503 / Virus Database: 269.15.11/1094 - Release Date: 10/26/2007 8:50 AM ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Considering the efficiency and easy availability of switchmode supplies these days, I would never bother with a linear regulator in a new design. For instance national has a series of switch mode regulators (LM25xx) which just requires a coil and a diode more than the usual LM78xx types. If you are worried about noise from the swichmode, you can add more filtering to the output. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [EMAIL PROTECTED] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Poul-Henning Kamp wrote: Considering the efficiency and easy availability of switchmode supplies these days, I would never bother with a linear regulator in a new design. For instance national has a series of switch mode regulators (LM25xx) which just requires a coil and a diode more than the usual LM78xx types. If you are worried about noise from the swichmode, you can add more filtering to the output. That is a recipe for disaster if one wants a really low noise oscillator. This is particularly true if one is a beginner. Reducing the output noise of a switching regulator to 100uV rms or less is neither easy nor simple. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Poul-Henning Kamp wrote: Considering the efficiency and easy availability of switchmode supplies these days, I would never bother with a linear regulator in a new design. For instance national has a series of switch mode regulators (LM25xx) which just requires a coil and a diode more than the usual LM78xx types. If you are worried about noise from the swichmode, you can add more filtering to the output. That is a recipe for disaster if one wants a really low noise oscillator. This is particularly true if one is a beginner. Reducing the output noise of a switching regulator to 100uV rms or less is neither easy nor simple. http://www.linear.com/pc/downloadDocument.do?id=4159 In this document, Linear Technology's Application Note 70, a switchmode power supply design is presented with less than 100uV output noise, and little RFI. This is achieved by using a switch controller which has controlled output switch slewing, allowing a trade-off between EMI/RFI and efficiency. Methods to measure and control PSU noise are also discussed (IMHO, the EMI sniffer probe in Section J is particularly interesting). BTW: contrary to popular belief, linear PSUs are NOT inherently noise-free. The cap charging current spikes through the rectifier diodes can produce plenty of EMI/RFI. JDB [not claiming it's easy, just pointing out one route that could be taken] -- LART. 250 MIPS under one Watt. Free hardware design files. http://www.lartmaker.nl/ ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Switchmode regulators really are risky for use in a low noise environment. Even if you can reduce input and output conducted noise to acceptable levels, the opportunity for magnetic coupling from the inductor to adjacent wiring is bad news. This can be very tough to find and eliminate, particularly if the controller frequency varies with load. Toroidal inductors are superior, but lead dress/routing can still result in unwanted coupling. Pete ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Pete wrote: Switchmode regulators really are risky for use in a low noise environment. Even if you can reduce input and output conducted noise to acceptable levels, the opportunity for magnetic coupling from the inductor to adjacent wiring is bad news. This can be very tough to find and eliminate, particularly if the controller frequency varies with load. Toroidal inductors are superior, but lead dress/routing can still result in unwanted coupling. Pete ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. Using a series resonant topology for the switching power supply can be helpful in reducing EMI. However even then one has to be careful to use the correct form of resonant converter to achieve low noise. Whilst such regulators can easily be designed they are not commonly available off the shelf. The design and construction of such a regulator isnt a task for a beginner. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY J.D. Bakker wrote: Poul-Henning Kamp wrote: Considering the efficiency and easy availability of switchmode supplies these days, I would never bother with a linear regulator in a new design. For instance national has a series of switch mode regulators (LM25xx) which just requires a coil and a diode more than the usual LM78xx types. If you are worried about noise from the swichmode, you can add more filtering to the output. That is a recipe for disaster if one wants a really low noise oscillator. This is particularly true if one is a beginner. Reducing the output noise of a switching regulator to 100uV rms or less is neither easy nor simple. http://www.linear.com/pc/downloadDocument.do?id=4159 In this document, Linear Technology's Application Note 70, a switchmode power supply design is presented with less than 100uV output noise, and little RFI. This is achieved by using a switch controller which has controlled output switch slewing, allowing a trade-off between EMI/RFI and efficiency. Methods to measure and control PSU noise are also discussed (IMHO, the EMI sniffer probe in Section J is particularly interesting). BTW: contrary to popular belief, linear PSUs are NOT inherently noise-free. The cap charging current spikes through the rectifier diodes can produce plenty of EMI/RFI. JDB [not claiming it's easy, just pointing out one route that could be taken] However this isnt a recommended approach for a beginner and you can easily do much better with a well designed linear regulator. The EMI due to diode reverse recovery and charging the reservoir capacitor is exacerbated by the modern tendency to leave parts out of designs, particularly if one doesn't understand their purpose. A shunt capacitor across the input of a bridge rectifier or a capacitor in parallel with each of the rectifier diodes can help by reducing the area of the radiating EMI loop. However some damping may also be required. Another problem with using switching regulators can arise when using an input filter with the regulator. Since the input power is to a first approximation independent of the input voltage, for frequencies from dc to an upper limit determined by the switching frequency the regulator has a negative resistance input characteristic. This means that undesired oscillations are possible if the input filter design doesn't take this into account. This situation can easily arise when the load is another switching regulator (eg when powering a Z3815 from a switching regulator usually Ok when powered by a switchmode power supply, but if one decides to add a filter between the switchmode power supply and the Z3815 one may just create an interesting power oscillator instead of a quieter input supply). Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY In a message dated 10/26/2007 14:59:29 Pacific Daylight Time, [EMAIL PROTECTED] writes: That is a recipe for disaster if one wants a really low noise oscillator. This is particularly true if one is a beginner. Reducing the output noise of a switching regulator to 100uV rms or less is neither easy nor simple. I Agree, it get's even worse when several independent switchers are on the PCB, with similar switching frequencies. This can generate beat frequencies that vary over time, temperature and from board to board. NEC Tokin makes a ferrous sheet material that is very good at shielding switching regulator noise - both electro, and magnetic components. When trying to get noise floors approaching -160dBc/Hz the RS-232 transmitter on the Fury GPSDO can be used as an example of a potential interference: The RS-232 transceiver chip generates the RS-232 level signals from a 3.3V DC input rail using switched-capacitor voltage doublers. There are no inductors or flyback diodes involved. The switching currents involved are very small (orders of magnitude smaller than a switchmode power supply), 0.1uF caps are used as charge reservoirs. Even so, the current spikes generated in the RS-232 transceiver are enough to create a couple of low measurable spurs at around -120 to -130dBc/Hz on the output spectrum of the 10MHz sine wave. This happens even though we have allocated a separate 3.3V regulator for the RS-232 chip, and have extensive power supply filtering in front of the regulator and before the transceiver chip. There are no switching regulator power supplies at all on the Fury PCB for this reason. To completely remove the spurs we added a mode to disable the transceiver's DC-DC switching regulator (Quiet Mode). That takes care of the spurs. bye, Said ** See what's new at http://www.aol.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Great idea!!,Don C. - Original Message - From: Max Robinson [EMAIL PROTECTED] To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Saturday, October 27, 2007 10:07 AM Subject: Re: [time-nuts] Parallel voltage regulators ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY I do have some experience with temperature controlled ovens. I found that a long term plot of the temperature while using an unregulated supply on the oven heater showed small random variations due to voltage variations. When the oven heater was put on a regulated supply the line became flat. The problem here seems to be during the heat up cycle. The voltage doesn't need to be regulated during that time. You might try sensing the error signal and when it is outside of the linear control range you could switch in a parallel transistor and resistor to handle the warm-up current and it would switch out when the oven has stabilized at the lower current. Regards. Max. K 4 O D S. Email: [EMAIL PROTECTED] Transistor site http://www.funwithtransistors.net Vacuum tube site: http://www.funwithtubes.net Music site: http://www.maxsmusicplace.com To subscribe to the fun with tubes group send an email to, [EMAIL PROTECTED] - Original Message - From: Bill Hawkins [EMAIL PROTECTED] To: 'Discussion of precise time and frequency measurement' time-nuts@febo.com Sent: Friday, October 26, 2007 1:21 AM Subject: Re: [time-nuts] Parallel voltage regulators There is a concept in temperature control called feed-forward. In this case you would sample the supply line with an inverting amplifier and use it to increase the oven drive signal as the line voltage decreases. The goal is to keep the integral term from changing as the line voltage changes. It is not as easy as it sounds. Bill Hawkins ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.503 / Virus Database: 269.15.11/1094 - Release Date: 10/26/2007 8:50 AM ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Well, there is another trick of the control trade, used to bring batch process reactors up to the desired temperature in a hurry. At first, you turn on full heat for an experimentally determined time. You turn it off at the end of that time, before the oven has reached final temperature. You leave it off for an experimentally determined time while the oven coasts up to the peak temperature. If you've done it right, the peak temperature is the oven setpoint. Then you preset the oven controller to its normal output. This is the value that you read when the output is settled out from a plain old startup. Now the controller is at its setpoint, and the output is at its operating point. Turn on the oven supply regulator and enjoy relatively stable control. This method is considerably faster than letting the controller respond to the turn on transient by oscillating its way into steady state. Bill Hawkins -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Max Robinson Sent: Friday, October 26, 2007 4:08 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Parallel voltage regulators ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY I do have some experience with temperature controlled ovens. I found that a long term plot of the temperature while using an unregulated supply on the oven heater showed small random variations due to voltage variations. When the oven heater was put on a regulated supply the line became flat. The problem here seems to be during the heat up cycle. The voltage doesn't need to be regulated during that time. You might try sensing the error signal and when it is outside of the linear control range you could switch in a parallel transistor and resistor to handle the warm-up current and it would switch out when the oven has stabilized at the lower current. Regards. Max. K 4 O D S. Email: [EMAIL PROTECTED] Transistor site http://www.funwithtransistors.net Vacuum tube site: http://www.funwithtubes.net Music site: http://www.maxsmusicplace.com To subscribe to the fun with tubes group send an email to, [EMAIL PROTECTED] - Original Message - From: Bill Hawkins [EMAIL PROTECTED] To: 'Discussion of precise time and frequency measurement' time-nuts@febo.com Sent: Friday, October 26, 2007 1:21 AM Subject: Re: [time-nuts] Parallel voltage regulators There is a concept in temperature control called feed-forward. In this case you would sample the supply line with an inverting amplifier and use it to increase the oven drive signal as the line voltage decreases. The goal is to keep the integral term from changing as the line voltage changes. It is not as easy as it sounds. Bill Hawkins ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.5.503 / Virus Database: 269.15.11/1094 - Release Date: 10/26/2007 8:50 AM ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY This has been a fascinating and educational thread! I have always been aware of noise coming from switching regulators - just have Argo or Speclab look at your laptop's sound card with no input signal and there is plenty to look at until you go to battery power. I had never considered diode switching noise in linear supplies, nor birdies from an assortment of logic devices - though I am a believer in healthy distribution of bypass capacitors... Now if Sears only sold Diehard batteries that put out 3.3 volts... __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Tom Clifton wrote: This has been a fascinating and educational thread! I have always been aware of noise coming from switching regulators - just have Argo or Speclab look at your laptop's sound card with no input signal and there is plenty to look at until you go to battery power. I had never considered diode switching noise in linear supplies, nor birdies from an assortment of logic devices - though I am a believer in healthy distribution of bypass capacitors... Now if Sears only sold Diehard batteries that put out 3.3 volts... Even batteries have noise, some types have more than others. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Don Collie wrote: Great idea!!,Don C. Now all you need is a current limited bypass switch to protect the load. Such a switch is relatively easy to implement. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
I`ve always wondered about noise from batteries - please tell us more Bruce!! [also wondered about noise from the electrolytic action of aluminium, and tantalum electrolytic capacitors, and wondered if the reference bypass capacitor in a 723 should be a plastic dielectric type, rather than electrolytic]. ...Don C. - Original Message - From: Bruce Griffiths [EMAIL PROTECTED] To: Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Saturday, October 27, 2007 1:57 PM Subject: Re: [time-nuts] Parallel voltage regulators ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Tom Clifton wrote: This has been a fascinating and educational thread! I have always been aware of noise coming from switching regulators - just have Argo or Speclab look at your laptop's sound card with no input signal and there is plenty to look at until you go to battery power. I had never considered diode switching noise in linear supplies, nor birdies from an assortment of logic devices - though I am a believer in healthy distribution of bypass capacitors... Now if Sears only sold Diehard batteries that put out 3.3 volts... Even batteries have noise, some types have more than others. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Don Collie wrote: I`ve always wondered about noise from batteries - please tell us more Bruce!! [also wondered about noise from the electrolytic action of aluminium, and tantalum electrolytic capacitors, and wondered if the reference bypass capacitor in a 723 should be a plastic dielectric type, rather than electrolytic]. ...Don C. Don A plastic dielectric capacitor for the reference bypass is best (X7R ceramic may also be usable) as the leakage is lower as is the noise. Yes electrolytics are noisy especially at low frequencies. Aluminium electros can be noisier than tantalum electros. NIST prefer plastic bypass caps paralleled by ceramic caps to bypass the base of their RF isolation amplifiers. Battery noise links: http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normalid=ELLEAK010500013201idtype=cvipsgifs=yes http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normalid=ELLEAK010500013201idtype=cvipsgifs=yes Note the high excess noise of the carbon resistors favoured by some audio nuts. http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel2/3499/10330/00483923.pdf?arnumber=483923 There is also a more accessible article somewhere, I'll try to find it. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Don Collie wrote: I`ve always wondered about noise from batteries - please tell us more Bruce!! [also wondered about noise from the electrolytic action of aluminium, and tantalum electrolytic capacitors, and wondered if the reference bypass capacitor in a 723 should be a plastic dielectric type, rather than electrolytic]. ...Don C. Here's another reference - at least you can check this yourself with a suitable low noise preamp. http://www.tnt-audio.com/clinica/regulators_noise4_e.html Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Don Collie wrote: Bollocs, Bruce! If National say it will do it, you can bet that it will. An LM338K will do the job too, but in my opinion it`s overkill, and in the event of a short circuit on the output of the regulator the current for the LM338 will only be limited to [...he gets the book..] 8 Amps [Typ], as against 2.2 Amp [Typ] for the LM317T. This would probably be too much for the transformer, rectifiers, and smoothing capacitor, effectively meaning that you would have no current limiting. If the input/output differential was kept in the range of 5 to 10 Volts, while the oven was stabilising, and the LM317 had an adequate heatsink, it would do the job nicely [and cheaper too!] Actually, it wouldn`t matter if the oven supply went unregulated while the temperature was stabilising, because you wouldn`t be using it for measurements during this time anyway - or is that a bit radical!? All the best!,..Don. - Original Message - From: Bruce Griffiths [EMAIL PROTECTED] To: Don Collie [EMAIL PROTECTED]; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Thursday, October 25, 2007 5:42 PM Subject: Re: [time-nuts] Parallel voltage regulators Show me where that is actually guaranteed on the datasheet. Only the inexperienced and the gullible fall into the trap of assuming every regulator (or any other device) will meet its typical specs. The designer of this particular regulator actually cautions against this cavalier approach to design. If you worried about the transformer a simple fuse (resettable or otherwise) will surely cure that problem. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY - Original Message - From: Bruce Griffiths [EMAIL PROTECTED] To: Don Collie [EMAIL PROTECTED]; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Thursday, October 25, 2007 7:20 PM Subject: Re: [time-nuts] Parallel voltage regulators Don Collie wrote: Bollocs, Bruce! If National say it will do it, you can bet that it will. An LM338K will do the job too, but in my opinion it`s overkill, and in the event of a short circuit on the output of the regulator the current for the LM338 will only be limited to [...he gets the book..] 8 Amps [Typ], as against 2.2 Amp [Typ] for the LM317T. This would probably be too much for the transformer, rectifiers, and smoothing capacitor, effectively meaning that you would have no current limiting. If the input/output differential was kept in the range of 5 to 10 Volts, while the oven was stabilising, and the LM317 had an adequate heatsink, it would do the job nicely [and cheaper too!] Actually, it wouldn`t matter if the oven supply went unregulated while the temperature was stabilising, because you wouldn`t be using it for measurements during this time anyway - or is that a bit radical!? All the best!,..Don. - Original Message - From: Bruce Griffiths [EMAIL PROTECTED] To: Don Collie [EMAIL PROTECTED]; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Thursday, October 25, 2007 5:42 PM Subject: Re: [time-nuts] Parallel voltage regulators Show me where that is actually guaranteed on the datasheet. Only the inexperienced and the gullible fall into the trap of assuming every regulator (or any other device) will meet its typical specs. The designer of this particular regulator actually cautions against this cavalier approach to design. If you worried about the transformer a simple fuse (resettable or otherwise) will surely cure that problem. Bruce Hi Bruce, I`ve got the National Semiconductor Corporation Voltage Regulator Handbook [1982]. On page 3-3, the leftmost graph shows the LM117/217/317 as having its current limit, with a junction temperature of 125 degrees Centigrade, at 2.25 Amps over the input/output differential of 5 to 10 Volts. The point being, that if you use a higher current regulator, you loose the advantage of the regulator`s current limiting, and perhaps, its thermal shutdown protection as well. A fuse *might* protect the semi`s down the line, but often it`s the semi`s that fail before the fuse, and the peak current that might flow before the fuse blows might be many times the current limit of the regulator [which is nearly instantaneous], and if so, damaging, so it is wise to run these regulators near their current limit, just as you would set the current limit on a bench supply to just above the working current. I find your use of the emotive words inexperienced, gullible, and cavalier saddening. Wishing you well,Don. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Don Collie wrote: Hi Bruce, I`ve got the National Semiconductor Corporation Voltage Regulator Handbook [1982]. On page 3-3, the leftmost graph shows the LM117/217/317 as having its current limit, with a junction temperature of 125 degrees Centigrade, at 2.25 Amps over the input/output differential of 5 to 10 Volts. The point being, that if you use a higher current regulator, you loose the advantage of the regulator`s current limiting, and perhaps, its thermal shutdown protection as well. A fuse *might* protect the semi`s down the line, but often it`s the semi`s that fail before the fuse, and the peak current that might flow before the fuse blows might be many times the current limit of the regulator [which is nearly instantaneous], and if so, damaging, so it is wise to run these regulators near their current limit, just as you would set the current limit on a bench supply to just above the working current. I find your use of the emotive words inexperienced, gullible, and cavalier saddening. Wishing you well,Don. The graphs are only typical, read the actual printed specifications. You need to be more skeptical and question your assumptions. If you want a lower current limit regulator use an LM350. However you have identified one problem in applying 3 terminal regulators, the rather wide tolerances associated with the current limit circuitry. A 723 regulator can be easily designed to have a much narrower spread for the current limit. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY From: Bruce Griffiths [EMAIL PROTECTED] Subject: Re: [time-nuts] Parallel voltage regulators Date: Thu, 25 Oct 2007 13:51:47 +1300 Message-ID: [EMAIL PROTECTED] ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Magnus Danielson wrote: It is not that hard to acheive 2 A at 24 V after all. The old uA723 and variants would probably do the trick good enought for you with external transitor(s). I recommend to at least include fold-back for over-current protection, but adding an over-voltage in form of a crow-bar setup isn't too hard either. The point of the crow-bar is to cause fold-back and if that fails, blow the fuse, so include a fuse on the unregulated supply side. Cheers, Magnus Hej Magnus Using a 723 correctly configured with a low pass filter on the reference is a very low noise regulator solution with its output noise at least 20dB lower than that produced by a typical 3 terminal regulator. Most of the OEM open frame linear supplies use 723 regulators with external (to the 723) series pass transistors. These regulators have varying degrees of sophistication, some even use a zener plus emitter follower preregulator for the LM723. Some foolishly omit bleeder resistors across the reservoir capacitors which can lead to damage when making connections after powering the supply on and then off as the residual energy stored in the reservoir capacitors is more than sufficient to destroy the 723 should the output terminals be shorted. While the 723 isn't the highest degree of sofistication these days, it does alow for building more or less complete linear regulators. In another hobby of mine they are in plentiful use and provide stable enought regulation. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Magnus Danielson wrote: From: Bruce Griffiths [EMAIL PROTECTED] Subject: Re: [time-nuts] Parallel voltage regulators Date: Thu, 25 Oct 2007 17:42:51 +1300 Message-ID: [EMAIL PROTECTED] Don Collie wrote: Hi Tom, If you really want to regulate the oven`s supply voltage, my National Voltage Regulator handbook shows that the LM317T will supply over 2 Amps, with an input/output differential of between 5, and 12.5 Volts. A single one of these should do the job OK. Cheers!,.Don Collie jnr. Never rely on typical specs always use the minimum spec which is 1.5A not quite enough. You want design-margin. Some of that toll will be in less than optimum heating, some will be in less heating in the first place (compared to upper limit) and for a power regulating aspect, headroom allows better regulations. In one design we had to parallel the regulators since the regulator the designer put in just barely was able to regulate the CPU core voltage. It worked, but at just rebooted at some vauge point an the memory tests. What actually happend was that as soon as it started to actually do anything, the regulator was running at its limit and output voltage dropped as the current was rising and the voltage supervision pulled the RESET. That's what you get from reading the typical reading on the CPU current and match that with the maximum rating of the power regulator. A no margin design. That designer had a few more flaws which was creeping around in that design, but let's not bring that can of worms open here. :) The 5A LM338 will be just fine. Infact, you can pull 8A out of it under certain conditions. Cheers, Magnus Hej Magnus The LM338 thermal design is also much easier (it has a much lower junction to case thermal resistance than an LM317) especially if the circuit is intended to operate over wide temperature (0 -40C or more) and mains voltage ranges (+-10% or more). The alleged problem with the high short circuit current is easily solved by using diodes with adequate current ratings in conjunction with a fuse to protect the transformer if it isnt rated to produce an 8A dc output. The startup current of the load (rubidium standard) may also vary with temperature and /or input voltage. Either find the manufacturers specifications or allow adequate margins. Worst case design is desirable even for one off circuits especially if the circuit is published. When the design is publicly available one is in effect transferring the production run problems associated with a marginal design to many individuals rather than a single factory or production line. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Hi Tom I dont think you need the resistors these are current limited and the sense is inside the chip so the resistors dont do anything (you are thinking of a negative feedback effect). All that happens in paralled operation is that one may take the majority of the current til it current limits and the rest is provided by the other. They will need heat sinking. You can get Hi-power versions of these fixed regs as well or use one of them to drive a big transistor (the 2N2955 PNP used to be a popular choice up to 5A) for the series control. You may ned to lift the common leg with a diode to allow for the e-b drop on the pass transistor if you use an NPN. Cheers de Alan G3NYK - Original Message - From: Tom Clifton [EMAIL PROTECTED] To: time-nuts@febo.com Sent: Thursday, October 25, 2007 12:33 AM Subject: [time-nuts] Parallel voltage regulators A question for those that might know (or have an opinion)... I have in hand an LPRO rubidium reference that requires 1.7 amps at 24 volts while the oven warms, dropping to 500ma while it runs. Can I parallel three or four 7824 TO220 style 1 amp regulators with a quarter ohm half watt equalizing resistor on the output of each one? At maximum load there would be a quarter volt drop across the resistors and the LPRO is stated to be ok running on 16 to 32 volts. Tom __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Alan Melia wrote: Hi Tom I dont think you need the resistors these are current limited and the sense is inside the chip so the resistors dont do anything (you are thinking of a negative feedback effect). All that happens in paralled operation is that one may take the majority of the current til it current limits and the rest is provided by the other. They will need heat sinking. You can get Hi-power versions of these fixed regs as well or use one of them to drive a big transistor (the 2N2955 PNP used to be a popular choice up to 5A) for the series control. You may ned to lift the common leg with a diode to allow for the e-b drop on the pass transistor if you use an NPN. Nonsense look at the circuit. The base emitter drop of the pnp booster just increases the composite regulator dropout voltage. No diodes required to compensate Vbe drops. However this circuit is unreliable without current limiting of the PNP collector current. These days its simpler to use an LM338. Cheers de Alan G3NYK Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Magnus Danielson wrote: It is not that hard to acheive 2 A at 24 V after all. The old uA723 and variants would probably do the trick good enought for you with external transitor(s). I recommend to at least include fold-back for over-current protection, but adding an over-voltage in form of a crow-bar setup isn't too hard either. The point of the crow-bar is to cause fold-back and if that fails, blow the fuse, so include a fuse on the unregulated supply side. Cheers, Magnus Hej Magnus Using a 723 correctly configured with a low pass filter on the reference is a very low noise regulator solution with its output noise at least 20dB lower than that produced by a typical 3 terminal regulator. Most of the OEM open frame linear supplies use 723 regulators with external (to the 723) series pass transistors. These regulators have varying degrees of sophistication, some even use a zener plus emitter follower preregulator for the LM723. Some foolishly omit bleeder resistors across the reservoir capacitors which can lead to damage when making connections after powering the supply on and then off as the residual energy stored in the reservoir capacitors is more than sufficient to destroy the 723 should the output terminals be shorted. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Tom Clifton [EMAIL PROTECTED] wrote: A question for those that might know (or have an opinion)... I have in hand an LPRO rubidium reference that requires 1.7 amps at 24 volts while the oven warms, dropping to 500ma while it runs. Can I parallel three or four 7824 TO220 style 1 amp regulators with a quarter ohm half watt equalizing resistor on the output of each one? At maximum load there would be a quarter volt drop across the resistors and the LPRO is stated to be ok running on 16 to 32 volts. Tom, Most of the oven circuits will tolerate a significant sag in potential during warm-up as long as the supply doesn't cut out. I've often run OCXO's and Rb's off a wimpy bench supply when my high current bench supply has been otherwise occupied. But if you want more current, the typical way to get a 3-terminal regulator to put out more than spec'ed is to place a big PNP power transistor across the input and output. You'll find the details in the datasheets of many parts (e.g. LM340). Also, check out the National AN-103 app note. It's old but it's still full of useful info. I refer you, at least for a laugh, to page 20 of Linear's AN-83: http://www.linear.com/pc/downloadDocument.do?id=4172 (Despite what others have posted, *some* 3-terminal regulators *can* be paralleled. The LT1083 can be -- checkout the datasheet -- but, nota bene, in the suggested circuit the ballast resistance is on the order of 0.01 ohms, not 0.25 ohms. But it isn't the best idea.) -ch ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Thanks for all the good feedback! Looks like the LM388 is the way I'm to go. Got to toddle off to the local surplus shop in the morning to see what they have in the goodie bin. If they don't have it eBay is full of them. Tom __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY christopher hoover wrote: Tom, Most of the oven circuits will tolerate a significant sag in potential during warm-up as long as the supply doesn't cut out. I've often run OCXO's and Rb's off a wimpy bench supply when my high current bench supply has been otherwise occupied. But if you want more current, the typical way to get a 3-terminal regulator to put out more than spec'ed is to place a big PNP power transistor across the input and output. You'll find the details in the datasheets of many parts (e.g. LM340). Also, check out the National AN-103 app note. It's old but it's still full of useful info. I refer you, at least for a laugh, to page 20 of Linear's AN-83: http://www.linear.com/pc/downloadDocument.do?id=4172 (Despite what others have posted, *some* 3-terminal regulators *can* be paralleled. The LT1083 can be -- checkout the datasheet -- but, nota bene, in the suggested circuit the ballast resistance is on the order of 0.01 ohms, not 0.25 ohms. But it isn't the best idea.) -ch Tom The trouble with these circuits, as the designers will tell you, is that they were developed when the pnp power transistors had lower fts than their modern incarnations. Thus some engineering development is required to cure the oscillations that occur when a modern pnp with high ft is connected to boost the current output. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Hi Tom: When I had that problem a work around was to parallel a battery with the power supply (using a diode). The battery supplies the extra current while the oven warms up. If the power supply voltage is a little higher than the battery voltage when the oven is warmed up then the diode disconnects the battery. A resistor shunting the diode will then set a small charging current. Have Fun, Brooke Clarke http://www.PRC68.com http://www.precisionclock.com http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Cam Tom Clifton wrote: Thanks for all the good feedback! Looks like the LM388 is the way I'm to go. Got to toddle off to the local surplus shop in the morning to see what they have in the goodie bin. If they don't have it eBay is full of them. Tom __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Hi Tom, If you really want to regulate the oven`s supply voltage, my National Voltage Regulator handbook shows that the LM317T will supply over 2 Amps, with an input/output differential of between 5, and 12.5 Volts. A single one of these should do the job OK. Cheers!,.Don Collie jnr. - Original Message - From: Tom Clifton [EMAIL PROTECTED] To: time-nuts@febo.com Sent: Thursday, October 25, 2007 12:33 PM Subject: [time-nuts] Parallel voltage regulators ); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY A question for those that might know (or have an opinion)... I have in hand an LPRO rubidium reference that requires 1.7 amps at 24 volts while the oven warms, dropping to 500ma while it runs. Can I parallel three or four 7824 TO220 style 1 amp regulators with a quarter ohm half watt equalizing resistor on the output of each one? At maximum load there would be a quarter volt drop across the resistors and the LPRO is stated to be ok running on 16 to 32 volts. Tom __ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Don Collie wrote: Hi Tom, If you really want to regulate the oven`s supply voltage, my National Voltage Regulator handbook shows that the LM317T will supply over 2 Amps, with an input/output differential of between 5, and 12.5 Volts. A single one of these should do the job OK. Cheers!,.Don Collie jnr. Never rely on typical specs always use the minimum spec which is 1.5A not quite enough. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Parallel voltage regulators
); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY Bollocs, Bruce! If National say it will do it, you can bet that it will. An LM338K will do the job too, but in my opinion it`s overkill, and in the event of a short circuit on the output of the regulator the current for the LM338 will only be limited to [...he gets the book..] 8 Amps [Typ], as against 2.2 Amp [Typ] for the LM317T. This would probably be too much for the transformer, rectifiers, and smoothing capacitor, effectively meaning that you would have no current limiting. If the input/output differential was kept in the range of 5 to 10 Volts, while the oven was stabilising, and the LM317 had an adequate heatsink, it would do the job nicely [and cheaper too!] Actually, it wouldn`t matter if the oven supply went unregulated while the temperature was stabilising, because you wouldn`t be using it for measurements during this time anyway - or is that a bit radical!? All the best!,..Don. - Original Message - From: Bruce Griffiths [EMAIL PROTECTED] To: Don Collie [EMAIL PROTECTED]; Discussion of precise time and frequency measurement time-nuts@febo.com Sent: Thursday, October 25, 2007 5:42 PM Subject: Re: [time-nuts] Parallel voltage regulators Don Collie wrote: Hi Tom, If you really want to regulate the oven`s supply voltage, my National Voltage Regulator handbook shows that the LM317T will supply over 2 Amps, with an input/output differential of between 5, and 12.5 Volts. A single one of these should do the job OK. Cheers!,.Don Collie jnr. Never rely on typical specs always use the minimum spec which is 1.5A not quite enough. Bruce ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
