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Logic gate output won't go low enough to turn off NPN transistor

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David Hess:

--- Quote from: Infraviolet on June 09, 2023, 07:58:32 pm ---I'm not keen on the capacitor in parallel to the 1K resistor because that causes some further ripples on the base signal which translate to extra ripples in the output, and a clean signal is quite important for my application.
--- End quote ---

If a clean signal is important, then emitter switching is the way to go.  This means driving the emitter with the output of the gate instead of the base and driving the base with a low impedance fixed voltage, usually ground but it could be something else.

Reference level pulse generators work this way to produce very clean output pulses.

bdunham7:

--- Quote from: Benta on June 10, 2023, 12:14:21 am ---Sorry, but whacking a transistor base through 100 ohms is easy for anyone. Especially at only 500 kHz. Not impressed.

--- End quote ---

I didn't post it because I thought it was a Nobel-worthy accomplisment, but rather because it clearly documented the differences in performance (for that case) in the three clamp configurations and had nice pictures to boot.  He clearly had the same sort of issues as the OP even with only a 100R (total) base resistor.

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