Ground Isolation

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Errr, Say I've got a 100uH torroid and then a 100uF Al electro cap as an input filter on the power lines going into a low noise preamp. Power is feed from a switching supply +\-15V at 2/1 amp.

Am I in trouble?

Inside the box is a 2 ohm resistor that is the sense element for a current limit...a bipolar turns off a FET if the voltage drop is greater than 0.6 or so...

George H.

but it

worse.

But the size of the bang isn't proportional to volts, rather energy.

They looked like a slo-mo flash bulb. Like I said, it only happened once and we never found the cause (it was during manufacturing final test, so something was likely miswired).

but it

worse.

Belt & suspenders: you could add an R and a diode.

• ---+---[L]---+-------+---------------------------o o | | | "pesky power switch" > \ --- | | o /_\ [100uF] [R] | | | | [Load] | | | | Gnd --+---------+-------+-----------------------------+

RE: "Am I in trouble?" We all are - Murphy prevails. :-(

Fortunately, Joerg can provide the correct sound effects. :-)

Ed

but it

worse.

Depends on how fast power is turned on and off. Off is usually slow because caps are being depleted. But if it came on in, say, 200usec you'd see overshoot and then ringing up to 25V. Most likely you'll hear some popcorn noises from inside and that could be followed by a wee "amperage scent". Possibly also some anatomical changes in the opamps, such as little craters :-)

With 2ohms it'll probably be ok but ... you have to watch out for the spike on the FET in case it "snaps" off within a few microseconds. If the resistor were an ohm or less you'd see a few volts of overshoot when it turns back on, the lower the resistor the higher that overshoot.

If your email address is valid and you know your way around LTSpice I can send you a sim file.

--
Regards, Joerg

http://www.analogconsultants.com/

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but it

worse.

Yup, but usually more volts leads to more energy of the destructive kind. I had this happen at 900V when I was a kid and that made a large blob of molten metal, some of it hissing out of the box. Then the

230V/16A breaker came, and dad was not enthused at all because he was watching soccer. [...]

--
Regards, Joerg

http://www.analogconsultants.com/

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Joerg wrote:

The way GM has shed divisions, you might think that. Oldsmobile: April 29, 2004 Pontiac: November 2, 2010

In China (an emerging market, in case I have to point that out), Buicks are very popular, however.

but it

worse.

My point is that an inductor can only store what the supply will give it. Low-power supplies => small "phuts".

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Wow, Thanks Joerg, email is gherold@teachspin(dot)com

I've been playing around with LTspice on and off for a year or three. Previously I was using 'electronics workbench'...

Perhaps I should monitor the power lines while I open and close the various power supply connections.

George H.

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things worse.

what

I had briefly tried EWB at a company but find LTSpice better, and it's the standard nowadays. This sim is just a few parts, should be in your email box now.

That, too, but most of all your load because that's what would more likely die.

--
Regards, Joerg

http://www.analogconsultants.com/

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but it

things worse.

True, but a small phut often triggers a latch-up or some other more nasty effect, the power rail has plenty of available amps or the reserves of a large electrolytic ... *BANG*

--
Regards, Joerg

http://www.analogconsultants.com/

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Many people over here like them as well. A friend who drive a Ford truck has a Buick Regal as a passenger car, wouldn't want to have any other one.

--
Regards, Joerg

http://www.analogconsultants.com/

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Use another domain or send PM.

pins, but it

things worse.

That's the point. Our entire system is less than 12W (and that's twice what I'd like it to be). There isn't any *BANG* available in the entire thing. A small *phut* is all that's available. ;-)

pins

pins, but it

things worse.

How many uF is the electrolytic in there? And what's its ESR?

--
Regards, Joerg

http://www.analogconsultants.com/

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Use another domain or send PM.

pins

the

pins, but it

things worse.

A lot of little tantalums. No aluminum (until recently they have had crappy reflow profiles). Sure they go bang it stuffed backwards, but so does a Black Cat; no harm done (unless there is some real power behind them).

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EWB was very limited.. well I had a student copy that someone gave me for free. I switched to LT spice, soon after finding SED.

" That, too, but most of all your load because that's what would more likely die."

Yeah I thought of yanking the power lines under full load. (only ~0.2

-0.3 Amps)

More later if 'bad' thing appear.

George H.

pins

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out what

EWB was crap, and their marketing was less than honest.

John