Re: Is this a gate/drain capacitance problem?

Andrew Holme wrote:

I'm using a power FET in a TO-220 case, simply because that was all I
had, but I'm wondering if swapping to a low power FET will cure this?



It'll have a lower drain-gate capacitance.  Do you get the same thing if you
replace the FET with a small capacitor?

Two alternatives that spring to mind:
1. PNP BJT switching +28V on/off

Is that any better than just switching the 28V on/off? This wsll under some circumsttances be used with a HP 8920A noise figure meter

http://www.tucker.com/java/jsp/doorway_partnoH-P8970A_invid4751.htm

which I assume will switch the 28V on, wait for any transients to settle, make a measurement, switch the 28V off, waith for transients to settle etc.

The noise figure meter will supply its own switched 28V supply.

However, for some other uses, a fixed 28V supply and a TTL annd/or CMOS compatible input would be nice.

2. NPN BJT with base to +5V; emitter (via series resistor) is TTL input;
collector to R / L junction

Is that likely to be better? There is no 5V inside, but I could derrive one. from 28V.

.

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