Electronic – How is a transistor’s input changed from on to off and vice versa

logic-gatestransistors

I am currently diving deeper into electronics and have been researching silly to find an answer to the one question that is not clear to me.

I am still unsure how a transistor's input is changed from on to off and vice versa without a moving part or a physical action such as a keyboard key click or a mouse click. I think this due to the fact the computer is still running background programs and tasks without in physical action.

The only way that I may of thought of is that current is constantly running throughout the computer and it uses logic gates to change the input signal but in my mind this contradicts the idea of a transistor being that it has an "input" which can be changed.

I have noticed that all examples of this online that I have found whilst researching are always using physical switches of some sorts but this doesn't explain how a computer can still work without a physical action.

Any clarification to clear my confusion or links to where I can find out more on how transistors receive an input without a physical action would be much appreciated!

Best Answer

You're going from very low level (how does a transistor switch on) to very high level (processes running in the back ground of a PC) in a single leap. This is not really advisable. If you want to study electronics then best not to start with understanding a whole PC.

If your question is really "how does electronics keep doing different things when there is no external input" (this is a legitimate question - "how does it move from one state to the next entirely on it's own - surely at some point it would have to stop...").

Then this might be what you want:

All chips like microcontrollers / processors etc, which keep 'running' have one thing in common (besides being powered) - and that's a clock source.

This is a circuit that, when voltage is applied, keeps changing from 1 to 0 periodically, without any outside intervention. This is like a heart beat which allows all sequential processing right up to the background process running on your PC.

If you look up all the low level sub systems of a 'computer' (counters, shift registers, latches etc) you'll find they all need a clock to run.

https://en.wikipedia.org/wiki/Crystal_oscillator

https://en.wikipedia.org/wiki/Electronic_oscillator