Ken is correct that the circuit is unable as soon as I lose USB power. I can power via battery or USB but switching from USB to battery locks everything up or the circuit reboots.
On Wed, Mar 6, 2019 at 1:09 PM [email protected] < [email protected]> wrote: > Forrest, I added the VXO7805-500 between the battery and the board and > now the board appears to > be working reliably from battery. It's always worked fine via USB. Can you > explain why going from 12V > down to 5V makes the circuit work reliably? When the AZ2117 was reducing > voltage was it also reducing > the amps going through as well? > > I like the TPPM0301 but yes, I could use a few more mA. Also, I'd like a > wider temperature > range. I found another 500mA version but it has the same 0-70C operating > range. > > > > On Sat, Mar 2, 2019 at 1:15 PM Chuck McCown <[email protected]> wrote: > >> I never looked at the data sheet until Forrest noticed the thermal >> problem. >> Surface mount. I use similar packages in some products. My pcb is >> double >> sided with large lands with a bazillion vias perforating it trying to use >> the PCB as a heatsink. It sucks for any real amount of heat. I am able >> to >> get rid of about 5 watts without turning things brown and having the >> parts >> unsolder themselves. >> >> In your case, the reg has a thermal shutdown circuit so you never got to >> the >> obvious smoke and self disassembly clues. >> >> The data sheet says you can flow -20C air over it at 8 watts... >> Just spray it with freon and you are good to go! >> >> >> -----Original Message----- >> From: Forrest Christian (List Account) >> Sent: Saturday, March 02, 2019 10:23 AM >> To: AnimalFarm Microwave Users Group >> Subject: Re: [AFMUG] OT: EE Consultant >> >> Like Chuck said, pretty much any switchmode regulator aka buck >> converter aka dc-dc converter. This is where you end up with >> cost/benefits - there are fully integrated ones out there which are >> expensive but easy. A quick mouser search turns up a VXO7805-500 as >> an example. You can also do all of the design yourself, which is >> where datasheets come in handy. >> >> Note that this isn't going to be a drop in replacement since the USB >> voltage isn't going to be enough to power this with the switch method >> you are using. I'd reccomend setting this up so the bat goes >> directly into the regulator (it might even be reverse polarity >> protected, if not add a diode on the input to protect it). This >> would then have a 5V out which you would then feed into the rest of >> your circuit. This would require that you rearrange a bit of >> everything else. >> >> If I was designing it I would probably try to use something like a >> TPPM0301 which does all of the switching and regulating for you on the >> 3.3V side - You'd feed the USB into the 5Vcc pin, feed the output of >> the regulator described above into the 5Vaux pin, then take your >> output out of the 3.3Vout pin, ignoring the GND. However, if you >> really need 2.2W this particular part won't be enough, and you might >> actually have to add a 3.3V switcher as well since 2.2W is around >> 750mA and that's pretty beefy for a linear regulator of any sort. On >> the other hand, if you meant 2.2W currently at 12V, then this might be >> be fine. >> >> This pretty much neuters your source identification leds though. And >> the monitoring stuff to go with it. There's ways around this as >> well. >> >> Depending how much you want to share, I will say that the eevblog >> forum is a really good resource for this type of stuff. They also >> have a jobs board if you're looking for someone who might just take >> this off your hands. >> >> On Sat, Mar 2, 2019 at 7:22 AM [email protected] >> <[email protected]> wrote: >> > >> > USB is preferred input so the battery isn't drawn down during normal >> > operation. I'm drawing >> > about 2.2W under normal operation. Is there another chip you'd >> recommend >> > other than >> > the AZ2117? >> > >> > On Sat, Mar 2, 2019 at 3:51 AM Forrest Christian (List Account) >> > <[email protected]> wrote: >> >> >> >> Oh this is an easy answer. >> >> >> >> At 12V, the AC2117 is dropping about 8 of those volts. >> >> 8V*400mA=3.2W. Thermal resistance to the heatsink on this part is >> >> 100C/W. So with a room temperatureish heatsink at 30*C, you're going >> >> to end up with a junction temperature of 100C/W * 3.6W = 320C + 30*C >> >> = 350C. This is above the absolute maximum operating temperature >> >> range of 150*C. >> >> >> >> The most you can draw through this with an 8V drop and an appropriate >> >> heatsink not exceeding 150*C (I'm assuming it gets a bit warm) is 150C >> >> - 50C = 100C. 100C/W means this part can dissipate at most 1W with >> >> an adequate heatsink. This equates to 1W/8V = 125mA max with a 12V >> >> input voltage. >> >> >> >> If you don't have an adequate heatsink or the temperature gets higher >> >> this is even lower, since the rating without a heatsink is 125C/W. >> >> >> >> Note that this isn't a problem off of USB because the AZ2117 doesn't >> >> drop much voltage, so even at 1V of drop, you'd only have >> >> 1V*400mA=400mW of power dissipation, and the unit should be able to >> >> handle this even without a heatsink. >> >> >> >> ALSO: Could you clarify here if the USB is the preferred input? If >> >> not, one could rip out IC2, R26, R3 and Q1 and replace it with another >> >> diode. >> >> ALSO: Not sure why the indicator leds are done the way they are - they >> >> probably work, but seems like overkill. >> >> >> >> On Fri, Mar 1, 2019 at 12:14 PM [email protected] >> >> <[email protected]> wrote: >> >> > >> >> > Schematics attached. The main issue I'm having is when powered via >> USB, >> >> > everything works fine. When powered via a 12V car battery, the >> >> > chips seem to not have enough power. There are two comparator >> circuits, >> >> > one to monitor USB/Batt and report how the unit is being powered. >> >> > The 2nd actually provides the power. One chip will occasionally draw >> >> > ~150-400ma of power causing the board to lock up. Chips are powered >> >> > via Vin. >> >> > >> >> > What I don't understand is why everything works perfectly on USB but >> >> > has issues when powered via 12V. >> >> > >> >> > On Tue, Feb 26, 2019 at 11:53 AM <[email protected]> wrote: >> >> >> >> >> >> Circle of stability, miller capacitance all good stuff. >> >> >> >> >> >> From: Mark Radabaugh >> >> >> Sent: Tuesday, February 26, 2019 9:48 AM >> >> >> To: AnimalFarm Microwave Users Group >> >> >> Subject: Re: [AFMUG] OT: EE Consultant >> >> >> >> >> >> Oh sure, now you probably want me to believe transistors have >> states >> >> >> other than off and on. >> >> >> >> >> >> Mark >> >> >> >> >> >> On Feb 26, 2019, at 11:20 AM, Ken Hohhof <[email protected]> wrote: >> >> >> >> >> >> > And good luck finding an analog circuit guy anymore ;-) >> >> >> >> >> >> That’s what I was. Not much demand, that’s why I’ve been doing >> other >> >> >> things for over 20 years. Actually made the switch to engineering >> >> >> management in the 80’s but still did some design work for another >> 10 >> >> >> years because all the engineers wanted to do digital and processor >> >> >> designs. I still have the books, the brain is rusty though. >> >> >> >> >> >> I tried to convince the new engineers that high speed digital >> design >> >> >> meant knowing analog, RF and microstrip techniques, but they >> weren’t >> >> >> buying it. Getting their products through regulatory emissions >> >> >> testing did give them a bit of religion. >> >> >> >> >> >> I still remember laying out PCBs using red and blue tape. >> >> >> >> >> >> From: AF <[email protected]> On Behalf Of Mark Radabaugh >> >> >> Sent: Tuesday, February 26, 2019 9:09 AM >> >> >> To: AnimalFarm Microwave Users Group <[email protected]> >> >> >> Subject: Re: [AFMUG] OT: EE Consultant >> >> >> >> >> >> Yep - I’m qualified to answer some things and would be totally lost >> on >> >> >> others. EE has become a huge field with many many disciplines. >> >> >> >> >> >> And good luck finding an analog circuit guy anymore ;-) >> >> >> >> >> >> Mark >> >> >> >> >> >> >> >> >> On Feb 26, 2019, at 9:56 AM, Ken Hohhof <[email protected]> wrote: >> >> >> >> >> >> Analog? Digital? Even with those there tend to be specialties >> like >> >> >> emissions, safety, PLD/ASIC design, microprocessor/microcontroller, >> >> >> RF, etc. Or do you need a generalist? >> >> >> >> >> >> From: AF <[email protected]> On Behalf Of >> >> >> [email protected] >> >> >> Sent: Tuesday, February 26, 2019 8:33 AM >> >> >> To: AnimalFarm Microwave Users Group <[email protected]> >> >> >> Subject: [AFMUG] OT: EE Consultant >> >> >> >> >> >> Having an issue with a circuit design, anyone know a good >> electrical >> >> >> engineer they can >> >> >> recommend? >> >> >> -- >> >> >> AF mailing list >> >> >> [email protected] >> >> >> http://af.afmug.com/mailman/listinfo/af_af.afmug.com >> >> >> >> >> >> >> >> >> -- >> >> >> AF mailing list >> >> >> [email protected] >> >> >> http://af.afmug.com/mailman/listinfo/af_af.afmug.com >> >> >> >> >> >> >> >> >> >> >> >> ________________________________ >> >> >> -- >> >> >> AF mailing list >> >> >> [email protected] >> >> >> http://af.afmug.com/mailman/listinfo/af_af.afmug.com >> >> >> >> >> >> -- >> >> >> AF mailing list >> >> >> [email protected] >> >> >> http://af.afmug.com/mailman/listinfo/af_af.afmug.com >> >> > >> >> > -- >> >> > AF mailing list >> >> > [email protected] >> >> > http://af.afmug.com/mailman/listinfo/af_af.afmug.com >> >> >> >> >> >> >> >> -- >> >> - Forrest >> >> >> >> -- >> >> AF mailing list >> >> [email protected] >> >> http://af.afmug.com/mailman/listinfo/af_af.afmug.com >> > >> > -- >> > AF mailing list >> > [email protected] >> > http://af.afmug.com/mailman/listinfo/af_af.afmug.com >> >> >> >> -- >> - Forrest >> >> -- >> AF mailing list >> [email protected] >> http://af.afmug.com/mailman/listinfo/af_af.afmug.com >> >> >> -- >> AF mailing list >> [email protected] >> http://af.afmug.com/mailman/listinfo/af_af.afmug.com >> >
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