Switch mode regulator. Sent from my iPhone
> On Mar 2, 2019, at 7:21 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
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