Basic Question regarding transistors

S

sandmanjack

New Member
I understand how transistors work, and how they apply to calculations in a computer, and what not, but i am confused as to how, in a computer, the transistors are actually turned on. I know they need to have power supplied to the input, but what allows power to go to the input? I greatly appreciate any help that can be provided.
 
Well power is supplied to the CPU by the motherboard and PSU, you have voltage regulation and such on the board to make sure everything gets the right voltage
 
A transistor uses a small voltage on one terminal to control the amount of current flowing between the other terminals. The input is the small voltage. You can use it with other components like resistors and capacitors to control analog voltages as in audio amplifiers, power supplies etc or in digital control where it is turning devices or other electronics on or off.

They replaced tubes (valves) which did the same thing but needed a lot of space and power, and produced a lot of heat.

In a computer (the digital side) the transistors are embedded in the integrated circuits but do the same thing. A transistor output turned "Off" could represent a 0, "On" a 1 (or vice versa depending). By stringing transistors together in certain ways you can perform simple mathematic functions. Lots make a microprocessor.
 
i understand all that, but what i am asking is, physically, how does a transistor's input get changed from enough voltage for it to be on, to off. As in, what physically happens to make the transistors input change.
 
To answer your question exactly as asked, you simply apply enough voltage to turn it on (a certain minimum is required and usually comes from another part of the circuitry). If the output of the transistor is across two rails at 0 and 5V, then you apply somewhere between 0 and 5V to the base or gate connection.

Take a look at the link tremmor suggested which shows typical circuits. If you want to get into the more detailed physics of the semiconductor and doping processes, try this link, the "How a Junction Transistor Works" paragraph.

Here's another link that gives an example with numerical voltage data and shows some simple transistor logic.
 
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sandmanjack said:
i understand all that, but what i am asking is, physically, how does a transistor's input get changed from enough voltage for it to be on, to off. As in, what physically happens to make the transistors input change.
Click to expand...

Most people don't care. Its related to the chemistry or architecture of the component. In another sense its if no voltage is applied to the base it has a high resistance. A negative or positive voltage could allow it to conduct changing the resistance. Not many interested in or unless isolating a problem at a component level. Not always easy to understand unless looking from a oscilloscope. I doubt if you will understand that either.
cheers......
 
99.99999% of the time, transistors are driven by other transistors - but that's not going to enlighten you very much. So where does it all start? In a computer it all starts with the ones and zeros stored in memory. These are transfered to the working parts of the computer over various busses at various rates (by clock circuits). Of course, it required transistors to write the ones and zeros to the memory as well. Theoretically, when you push the power button, you send the initial one or zero to the system that gets the whole mess started.
 
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