Designing a high current (10A) voltage buffer

Add a * BreakdownVolts ^2 in there. For a given sized MOSFET, the on resistance increases as something near the square of the breakdown voltage.

If you make a P-IGBT, the bipolar part of the device is NPN. This suggests that there should be a different situation in the IGBT. The MOSFET and the bipolar parts are always the compliment type.

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MooseFET
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(I just realized that I was talking about one configuration, common source output but was thinking of the more usual common drain output.)

(snip)

Of course, that won't work as stated, because the opamp output is inverted (at least at low frequencies), compared to the MOSFET output. So capacitive feedback around the opamp to the + input is positive feedback, not negative feedback. Duh! So with a common source output stage, an additional inversion is needed to make use of the opamp output as negative feedback, or that feedback has to be connected to the - input, in some way.

Reply to
John Popelish

Hmm - I guess I can see that noise could cause problems with the D. When would a PID controller be better than just a PI?

But this doesn't seem right - let's say the op-amp is magically outputting the correct voltage to the FET. The differential term will output zero, and thus the P term will drop to zero, and since there's no I or D, the output to the FET will be zero. Or am I forgetting something? Something isn't adding up...

So, if I were to need higher bandwidth, how would I go about changing the circuit?

Thanks,

-Michael

Reply to
Michael

As an update to my original post - after cracking open my analog signal processing textbook, I came up with the below:

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Functionality is the same (besides that I tweaked the PID gains). Thing is - now all the gains are dependent on one another. Any way to change that? As far as I can tell you really need about 5 OAs to make a PID controller with individually adjustable gains.

-Michael

Reply to
Michael
[too much stuff]

Look, before diving into all that PID theory, why don't you first spec what your current booster has to deliver, bandwith-wise? You may get what you want from one opamp, one MOSFET, and three or four discrete parts without any math. If you need more performance and have the cash you might want to look at Apex's line of high-current opamps.

With a circuit that is capable of burning in excess of 100 watts, you also may have to think of overcurrent and overtemperature protection.

robert

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Robert Latest

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