Making a pin sink?

[kevj]

The “bridge to Vcc” resistor is needed cause transistors ain’t perfect. There is always a leakage current from B to C that needs come from somewhere. If you don’t provide a source for it then it comes from E to B, which is real base current, which makes the device begin to turn on, which increases current out the collector, which burns power, which heats the device, which increases the B to C leakage that needs come from somewhere …

Outstanding! Thank you Ernie - that actually helps a lot - I'm much more clear now. Total lightbulb moment.

[mister_e]

while i can't 100% agree with explanation for a simple G.P. NPN/PNP, i will suggest you a simple test... configure an I/O as input,and measure the voltage between it and GND.. what do you get?

What's the trip point of a transistor?

[kevj]

a) a simple G.P. NPN/PNP

b) configure an I/O as input,and measure the voltage between it and GND.. what do you get?

c) What's the trip point of a transistor?

a) What is a G.P. ???

b) With the power on or off?

c) Don't know.

d) Can I buy a vowel?

[ErnieM]

The last one is easy!

c) What's the trip point of a transistor?

It's a trick question. Transistors are analog devices; they don't have anything like a well-defined trip point.


And I'll go out on a limb here and guess "GP" is General Purpose.