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I agree with Tony. If Bf is found to affect switching speed, we need to see the test circuit .ASC that you are using, because it's probably not the optimum.

On 03/04/2025 09:26, jacfev via groups.io wrote:

My question is multiple:
1. What are the influential spice parameters that optimize the switching speed?
To my knowledge, it's mainly Bf that seems to be the most important for increasing the switching speed, which I vary like this:
.step param X LIST 100 150 200 250 300
.model myModel AKO: 2N2222 NPN (Bf={X})
2. What measurement (equation) can be used to measure the speed?
3. What circuit should I use to compare the switching speed results as a function of the influential parameter?

This is not such a simple question. What are your parameters for switching speed? Presumably rise and fall times? How about delays times? You can still have fast rise and fall times, but with a significant delay time if the transistor is driven into saturation.

I would say that Bf is not one of the most influential parameters for speed. More important are the internal capacitances: Cje and Cjc, and transit times: Tf and Tr. Tr sets the reverse recovery time, i.e. charge storage in the base region on switch off - this is critical in saturated BJT switching circuits.

To assess the speed, you need to .MEAS the rise and fall times at the output, and the turn-on and turn-off delay times referenced to the input source waveform.

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Regards,
Tony