One of the best threads evar glad it's 'free' to lurk. -- On Thu, Mar 7, 2019 at 7:17 PM Ken Hohhof <af...@kwisp.com> wrote:
> Kudos to Forrest, he zeroed right in on the problem. > > I had blinders on, and focused on the control circuitry instead of the > regulators. > > > > Plus you were in a great position to evaluate consultants, already knowing > part of the answer. > > > > > > *From:* AF <af-boun...@af.afmug.com> *On Behalf Of *canopy--- via AF > *Sent:* Thursday, March 7, 2019 6:01 PM > *To:* Forrest Christian (List Account) <li...@packetflux.com> > *Cc:* can...@believewireless.net <p...@believewireless.net>; AnimalFarm > Microwave Users Group <af@af.afmug.com> > *Subject:* Re: [AFMUG] OT: EE Consultant > > > > Forrest, you rock! Per your suggestion, I reached out to eevblog to find > someone that could help. > > One guy that responded recognized the thermal problem you described. He > was the only one that > > brought it up. Upon looking at my design, he explained why a few other > problems were happening. > > > > I've had several others look at it in the past and not one noticed the > problem with that chip. Thanks > > again for your insight and suggestions. > > > > Chuck and Ken, you both helped me realize the design was flawed even when > some other "experts" > > just recommended tweaking it. > > > > I just wish I had reached out to the list sooner. I keep forgetting the > depth and breadth of knowledge here. > > > > On Wed, Mar 6, 2019 at 1:55 PM Forrest Christian (List Account) < > li...@packetflux.com> wrote: > > Simplified mental picture statement: a linear regulator like the > AZ2117 works by burning off excess voltage as heat. > > Assume you have a circuit which takes 500mA @ 3V. If you want to > feed it with 12V, and use a linear regulator, the circuit is still > going to take 500mA but at 12V, with 500mA@9V being turned into heat > by the linear regulator and 500mA@3V being turned into heat by your > circuit. > > 500mA x 9V = 4.5W. > > Each type of case can dissipate (or get rid of) a certain amount of > power. The AZ2117 couldn't get rid of power quickly enough so it > overheated. It happened to have over temperature protection so it > shut down. Less sophisticated regulators will destroy themselves. > > The VXO8705-500 is a switchmode regulator, which effectively works > like the following: > > Assume you have a circuit which takes 500mA@3V. If you want to feed > it with 12V, and use a switchmode regulator, the switchmode regulator > very quickly turns the power on for 25% of the time, and off for 75% > of the time, making an average of 12V*25%=3V. The average current > used at 12V will also be cut in a quarter, so you'd have 125mA@12V. > Because it's switching it on and off there is very little heat > generated. > > On Wed, Mar 6, 2019 at 11:11 AM canopy--- via AF <af@af.afmug.com> 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 <ch...@wbmfg.com> 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 can...@believewireless.net > >> <p...@believewireless.net> 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) > >> > <li...@packetflux.com> 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 can...@believewireless.net > >> >> <p...@believewireless.net> 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 <ch...@wbmfg.com> 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 <af...@kwisp.com> 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 <af-boun...@af.afmug.com> On Behalf Of Mark Radabaugh > >> >> >> Sent: Tuesday, February 26, 2019 9:09 AM > >> >> >> To: AnimalFarm Microwave Users Group <af@af.afmug.com> > >> >> >> 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 <af...@kwisp.com> 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 <af-boun...@af.afmug.com> On Behalf Of > >> >> >> can...@believewireless.net > >> >> >> Sent: Tuesday, February 26, 2019 8:33 AM > >> >> >> To: AnimalFarm Microwave Users Group <af@af.afmug.com> > >> >> >> Subject: [AFMUG] OT: EE Consultant > >> >> >> > >> >> >> Having an issue with a circuit design, anyone know a good > electrical > >> >> >> engineer they can > >> >> >> recommend? > >> >> >> -- > >> >> >> AF mailing list > >> >> >> AF@af.afmug.com > >> >> >> http://af.afmug.com/mailman/listinfo/af_af.afmug.com > >> >> >> > >> >> >> > >> >> >> -- > >> >> >> AF mailing list > >> >> >> AF@af.afmug.com > >> >> >> http://af.afmug.com/mailman/listinfo/af_af.afmug.com > >> >> >> > >> >> >> > >> >> >> > >> >> >> ________________________________ > >> >> >> -- > >> >> >> AF mailing list > >> >> >> AF@af.afmug.com > >> >> >> http://af.afmug.com/mailman/listinfo/af_af.afmug.com > >> >> >> > >> >> >> -- > >> >> >> AF mailing list > >> >> >> AF@af.afmug.com > >> >> >> http://af.afmug.com/mailman/listinfo/af_af.afmug.com > >> >> > > >> >> > -- > >> >> > AF mailing list > >> >> > AF@af.afmug.com > >> >> > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > >> >> > >> >> > >> >> > >> >> -- > >> >> - Forrest > >> >> > >> >> -- > >> >> AF mailing list > >> >> AF@af.afmug.com > >> >> http://af.afmug.com/mailman/listinfo/af_af.afmug.com > >> > > >> > -- > >> > AF mailing list > >> > AF@af.afmug.com > >> > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > >> > >> > >> > >> -- > >> - Forrest > >> > >> -- > >> AF mailing list > >> AF@af.afmug.com > >> http://af.afmug.com/mailman/listinfo/af_af.afmug.com > >> > >> > >> -- > >> AF mailing list > >> AF@af.afmug.com > >> http://af.afmug.com/mailman/listinfo/af_af.afmug.com > > > > -- > > AF mailing list > > AF@af.afmug.com > > http://af.afmug.com/mailman/listinfo/af_af.afmug.com > > > > -- > - Forrest > > -- > AF mailing list > AF@af.afmug.com > http://af.afmug.com/mailman/listinfo/af_af.afmug.com >
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