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
>
> --
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