I remember when I was in my early twenties thinking the same thing. I was so proud when I build my PWM power supply using a bipolar transistor (I would be surprised if a MOSFET worked any different). It was a big disappointment to learn by way of a burnt finger that it dissipated as much heat/power as a linear regulator. Also, The power dissipation even in a PWM circuit should be across a big assed resistor not the transistor. It will allow you to use a smaller transistor which will run cooler and hopefully last longer.
You need to use the wonders of inductors in the form of buck/boost or transformers to keep from making Just Another Linear Amplifier (JALA if you like acronyms) -joe On Monday 25 July 2011 18:06:10 Frank Bemelman wrote: > Dissipation is relative small with a pwm driven transistor. > > ----- Original Message ----- > From: "Tidak Ada" <[email protected]> > To: <[email protected]> > Sent: Monday, July 25, 2011 10:38 PM > Subject: RE: [neonixie-l] Nixie Tube Power Supply: 0..300V @ 30mA max. > > > Hi, > > > > Did you realize the power dissipation in the transistor? > > Better is to use a tranformer with several taps in a circuit like this. > > > > eric > > > > -----Original Message----- > > From: [email protected] [mailto:[email protected]] On > > Behalf Of jb-electronics > > Sent: maandag 25 juli 2011 19:00 > > To: [email protected] > > Subject: Re: [neonixie-l] Nixie Tube Power Supply: 0..300V @ 30mA max. > > > > Hi, > > > > thanks for the hint. See the reviewed circuit: > > > > http://www.jb-electronics.de/tmp/400v_adjustable.png > > > > Yes, the feedback loop will be included, I forgot to mention that my > > power supply will have both a volt- and amperemeter built in. > > > > This way I will be able to check the voltage, as well as to completely > > shut > > off the PWM stage when the current is too high. Is this safe? > > > > Does anyone know a good PNP transistor for this purpose? > > > > Regards, > > Jens > > > > Am 25.07.2011 18:08, schrieb Frank Bemelman: > >> I would (at least) add some feedback. Voltage divider and opamp to > >> compare against set value. > >> Without feedback, the cap would charge to 400V in no time. > >> Plus a current limiting resistor of 1K in series with the emitter, > >> which makes a lousy protection but still better than nothing. > >> > >> ----- Original Message ----- From: "jb-electronics" > >> <[email protected]> > >> To: <[email protected]> > >> Sent: Monday, July 25, 2011 5:11 PM > >> Subject: Re: [neonixie-l] Nixie Tube Power Supply: 0..300V @ 30mA max. > >> > >>> Hi, > >>> > >>> thanks a lot for all these replies. I am not an engineer, so I am not > >>> familiar with power supply circuitry. > >>> > >>> These modules on Ebay are nice, but I would like to build my own > >>> meters around that supply, that would be a waste of these units I > >>> think. They are a tad too powerful for me as well ;-) > >>> > >>> I like the PWM idea because it is so simple: Why not rectify some AC > >>> (after two transformers of course) to say 400V. Then use some suited > >>> PNP transistor (which would that be?) that switches the +400V on and > >>> off, and then a cap to smoothen the signal. Probably a rather Spartan > >>> design yet, any improvements? I can tell it is not protected against > >>> shorts. > >>> > >>> http://www.jb-electronics.de/tmp/400v_adjustable.png > >>> > >>> The maximum current is then limited by the transformers that are > >>> used, isn't it? > >>> > >>> Thanks again, > >>> Jens > >>> > >>> Am 23.07.2011 02:36, schrieb Charles MacDonald: > >>>> On 11-07-22 06:51 AM, Tidak Ada wrote: > >>>>> The background is this: I would like to build a universal power > >>>>> supply that can be used to drive all kinds of display devices: VFD > >>>>> tubes with their 50-60V anode voltage, as well as larger Nixie > >>>>> tubes with 300V anode voltage and 25mA current. > >>>>> > >>>>> > >>>>> Any other ideas are quite welcome, too. > >>>> > >>>> Do you really want to BUILD such an item? They are common on test > >>>> benches and with fewer test benches using High Voltage devices, they > >>>> are found in surplus. > >>>> > >>>> I recently got a nice looking unit with 1-400 volts at about 100ma > >>>> as a science lab item. Dial the voltage limit, Dial the current > >>>> limit. I have not tried it with an audio amp yet, but it should run > >>>> fine for Nixie use. > >>>> > >>>> For example have a look at Ebay > >>>> Item number: 230649564649 > >>>> Item number: 150634915051 > >>>> > >>>> > >>>> > >>>> If you want to look at the OLD school way, My old school test bench > >>>> as a Stark Regulated supply, which is one of the schematics at > >>>> Pacific TV tubes site. It uses a 6l6 as a pass regulator. The C > >>>> supply would cover your VFD requirements. This was surplus from an > >>>> Old High School lab. > >>> > >>> -- > >>> You received this message because you are subscribed to the Google > >>> Groups "neonixie-l" group. > >>> To post to this group, send an email to [email protected]. > >>> To unsubscribe from this group, send email to > >>> [email protected]. > >>> For more options, visit this group at > >>> http://groups.google.com/group/neonixie-l?hl=en-GB. > > > > -- > > You received this message because you are subscribed to the Google Groups > > "neonixie-l" group. > > To post to this group, send an email to [email protected]. > > To unsubscribe from this group, send email to > > [email protected]. > > For more options, visit this group at > > http://groups.google.com/group/neonixie-l?hl=en-GB. -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to [email protected]. To unsubscribe from this group, send email to [email protected]. 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