Thanks a lot for the circuit, Russell.

Russell McMahon wrote:
>>I am looking for a schematic for a known good high-current [1+ amps]
>>MOSFET driver built from discrete components. Any help appreciated.
>
>
> The attached driver cct works well in many applications.
>
> As shown, D1 limits the minimum gate voltage to a diode drop above ground.
> This is immaterial for all except exceptionally low Vth FETs. Most FETs are
> completely unenhanced at under 1 volt gate drive.
>
> For a lower negative going drive, remove D1 and add a PNP transistor,
> emitter to Q8 emitter, base to Q6 collector, collector to ground.
> (essentially a mirror of Q8).
>
> In both cases drive current is essentially Vsupply/R4.
>
> Z2 is essential for soundness of sleep. Mount as electrically close to FET
> as possible
> Some people use a reverse Schottky diode there and write rude things about
> using zeners BUT I have had extremely good results as shown. Z2 voltage
> should be slightly higher than maximum drive voltage.
>
> Q6 & Q8 (and the PNP, if used*) need to have enough current capability to
> meet your needs. I use BC337 ** for this with excellent results up to as
> little as a few 1 uS gate drive pulse width. Faster than that and you are
> going to have to experiment with "speed up" capacitors etc.
>
>
>         Russell McMahon
>
>
> * If PNP is used as above, then Q6 needs carry far less max current.
> ** BC337/BC327 nominally rated at 500 mA. Good for 1A plus pulse at reduced
> beta.
>
>
>
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>
>
> ------------------------------------------------------------------------
>

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Martin Klingensmith
http://infoarchive.net/
http://nnytech.net/

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