Driving small high voltage inverter module.

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John_A_Brown
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Posted by John_A_Brown: Wed. Feb 6, 2013 - 09:32 AM
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I have a small high voltage inverter module (produces a few KV). I have no info, apart from the fact that it draws 25mA at 4V. The whole thing is potted, and has nothing written on it(it's from China!).
I'd ultimately like to drive this from two AVR outputs in parallel, but to start with I thought I'd use a transistor, and make some measurements (scope style, looking for nastiness that might need supressing).
Anyone care to help me guess what would be a best guess for driving this - I was thinking of adding a flywheel diode at the least - or any pointers to similar devices (could be for electroluminescent backlights or similar).

John

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Learning and Information, General Electronics
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valusoft
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Posted by valusoft: Wed. Feb 6, 2013 - 10:15 AM
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John_A_Brown wrote:
... (could be for electroluminescent backlights or similar).

John

.. or maybe an electrostatic painting system ...

Ross McKenzie ValuSoft Melbourne Australia

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John_A_Brown
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Posted by John_A_Brown: Wed. Feb 6, 2013 - 12:05 PM
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Indeed.

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Bronze Markbobgardner
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Posted by bobgardner: Wed. Feb 6, 2013 - 01:02 PM
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I use a lot of the ERG EL inverters. 3 terminal... 5V, gnd, and 140VAC out. Just turn up the 5V on a lab power supply and watch ther output?

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John_A_Brown
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Posted by John_A_Brown: Wed. Feb 6, 2013 - 01:22 PM
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bobgardner wrote:
I use a lot of the ERG EL inverters. 3 terminal... 5V, gnd, and 140VAC out. Just turn up the 5V on a lab power supply and watch ther output?

More interested in the switch on/switch off performance. Back EMF, that sort of thing.

However, having wired it up now and run it 1 second on, 1 second off rinse and repeat, there doesn't seem to be anything much in the way of spikes. Noisy, but fairly low level stuff.

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DocJC
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Posted by DocJC: Wed. Feb 6, 2013 - 02:09 PM
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Quote:
to drive this from two AVR outputs in parallel

That's a subject that has come up a time or two.

The interesting question is does one add any load balancing circuitry, or just figure that at the low currents involved, with two ports adjacent to each other on the chip die, in whatever technology is used these days, the outputs will self balance the current draw.

JC

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John_A_Brown
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Posted by John_A_Brown: Wed. Feb 6, 2013 - 06:02 PM
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Since the total current requirement is listed as 25mA, and the I/Os are rated at 20mA, I think it should be OK. IIRC, FETs have a positive temperature coefficient, so the outputs SHOULD self balance.

John

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jgmdesign
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Posted by jgmdesign: Wed. Feb 6, 2013 - 07:13 PM
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Why not use an external FET and not worry about killing the AVR pins? Boardspace/cost?

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John_A_Brown
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Posted by John_A_Brown: Wed. Feb 6, 2013 - 07:44 PM
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Cost.

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Plons
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Posted by Plons: Wed. Feb 6, 2013 - 08:09 PM
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John, if you add 47 Ohm in series with each of the two driving pins, that should be sufficient to keep things balanced. And low cost ;)

One of the fabulous things of AVR's, amongst many others, is their fantastic drive :)

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John_A_Brown
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Posted by John_A_Brown: Wed. Feb 6, 2013 - 10:56 PM
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Plons wrote:
John, if you add 47 Ohm in series with each of the two driving pins, that should be sufficient to keep things balanced. And low cost ;)

One of the fabulous things of AVR's, amongst many others, is their fantastic drive :)

Nard


Thanks for the suggestion, but I work out that'll be 0.6V drop. This may not be acceptable.

John

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Bronze Marktheusch
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Posted by theusch: Thu. Feb 7, 2013 - 02:16 AM
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Quote:

but I work out that'll be 0.6V drop.

Now, I'm just an old bit-pusher. But then you are talking of drawing [relatively] high current from the pin ... "Figure 29-70.ATmega88PA: I/O Pin Output Voltage vs. Source Current (VCC = 5 V)"

Quote:

Cost.

A bit confusing. Are you going to make a zillion of these? Building in a component without a datasheet?

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John_A_Brown
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Posted by John_A_Brown: Thu. Feb 7, 2013 - 08:32 AM
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theusch wrote:
Quote:

but I work out that'll be 0.6V drop.

Now, I'm just an old bit-pusher. But then you are talking of drawing [relatively] high current from the pin ... "Figure 29-70.ATmega88PA: I/O Pin Output Voltage vs. Source Current (VCC = 5 V)"

Quote:

Cost.

A bit confusing. Are you going to make a zillion of these? Building in a component without a datasheet?

25mA, as stated earlier. Maybe I did my calcs wrong.

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John_A_Brown
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Posted by John_A_Brown: Thu. Feb 7, 2013 - 11:31 AM
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Having thought about this, I will probably stick a FET in there.
They are cheap enough.

Thanks for all the suggestions and advice.

John

Four legs good, two legs bad, three legs stable.

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