gEDA-user: mosfet design help

[phil at plastitar.com]

carzrgr8 at optonline.net wrote:
> volts.  Maybe in my design, since the drive voltage is over the max, I 
> can simply use resistor dividers to get the gate voltage to a reasonable 
> level.  It may change the turn on time though.

It's not turn-on time you have to worry about it's the relationship of 
when this circuit turns on wrt your power amp.  A divider will give you 
a scaled-down version of what your PA output voltage, but since your 
inverter has its own thresholds, there's nothing to say that it's output 
will resemble it's input (the original wave you're monitoring).

If this is an audio amp, and if the ckt we're talking about in the 
feedback loop, it will cause some distortion since your comparator or 
feedback device is getting bad info on what the output of the amp is 
doing.  If it were a linear amp, you'd say this intuitively--here it's 
not so obvious because it's digital.

Unfortunately, the 500kc output from your power amp is not going to be 
very square, and it's transitions will be ramps, thus making your 
problems all about turn-on thresholds.  You may want to use the divider 
scheme to drop the voltage levels, but then a small feedback loop around 
an opamp trigger that'll hard-switch your feedback signal with good time 
alignment to the original.

best, phil