Yep!
I can see that :)
Anytime I was working with small TO-223 voltage regulators I would
sometimes forget the heatsink and things would get HOT LOL.
On 3/2/2019 2:49 AM, Forrest Christian (List Account) 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?
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