Electronics > Beginners

150w DC Load project (low cost, med difficulty)

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ogden:

--- Quote from: Mechatrommer on March 03, 2018, 06:29:12 am ---using 4X 120A mosfet in a 5A dummy load is kinda nuts imho, its kinda mosfet-toss-phobic design.

--- End quote ---

It looks so, but it is not. When you use switching mosfet in linear mode, nasty things (hot spots) can happen on it's die. If you pick smallish mosfet, most likely it will make just quiet puff. What's worse - they die short!

[edit] Reading: http://www.ixyspower.com/images/tech-papers/Article_Linear_Power_MOSFETs_2007.pdf

alex-sh:

--- Quote from: Cliff Matthews on March 02, 2018, 07:04:49 pm ---
--- Quote from: blackdog on March 02, 2018, 06:50:25 pm ---Hi,

I see several problems in his design, the AD8630 is a nice opamp, but like almost all other chopper or auto zero opamps, it is not suitable for driving capacitive loads...
Take the output of U7D, 100 Ohm and then 100nF to mass, you must be kidding ...  :-DD
Look in the datasheet on page 10 and figure 25, above 100pF it is inherent instable, 500pF load 90% overshoot TADA!!!

And also the output section 2K2 resistor for a gate input who is 14nF  |O
Probably the circuit is stable for DC use, say for testing batteries, but if you have a load that is not constand, the entire output section can not keep up with it.
In the Netherlands we say: as slow as a snail on a tar barrel.
The AC otput impedance of this current source is low, even in the low frequencies, and likely to get easily generated, during error conditions.

Kind regards,
Blackdog

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Just measured my 4 IXFK90n20's at 24.5nF.. I think I'd need a costly PA to drive each one!! There's no free ticket is there?


Should not be that high. IXFK90N20Q-ND is rated 6800pF @ 25V
Did you manage to complete your DC load?

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