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 >
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