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What is the component Q4in this schematic? (lemmy.world)

submitted 8 months ago by [email protected] to c/[email protected]

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This is from a module I'm using and I don't understand this part of it. https://files.waveshare.com/upload/3/3c/RP2040-Touch-LCD-1.28.pdf

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[–] [email protected] 2 points 8 months ago (1 children)

I should have been clear about which resistor. I was talking about R18 as current limiter to the presumed load on the header. That way if the header gets shorted or the load has too high a draw at 3V3 you don't blow the transistor.

R20 is probably a weak pull down resistor to keep the transistor off until the microcontroller comes online.

As far as the transistor I was thinking it was probably a 2N7000. That's my goto in this kind of circuit.

Depending on the spefic microcontroller the pins can default to a very week high even when off. Enough to activate a 2N7000. I've had motors briefly engage using a PIC and a 2N7000 when the system is turned on without a pull down resistor.