Transistors?

hey Ardy forum.

Just a simple question. Am I correct in understanding that a transistor changes the voltage/amperage of a current? If that's true, what are the limits? For instance, you turn 5v @ .200amp into 12v @ 2amps? How about 200amp? What are the limits?

http://knol.google.com/k/electronic-circuits-design-for-beginners-chapter-8#

Spanman:
http://knol.google.com/k/electronic-circuits-design-for-beginners-chapter-8#

Yea I got about half way through it before it went over my head.

a transistor changes the voltage/amperage of a current?

No a transistor is like a valve, a small current flow in the base makes a larger current flow in the collector / emitter.
The ratio of these two currents is the gain. o for example if you have 2mA flowing in the base with a transistor that has a gain of 80 there will be 2 * 80 = 160mA flowing in the collector providing the resistances around the rest of the circuit allow that much to flow.

Grumpy_Mike:

a transistor changes the voltage/amperage of a current?

No a transistor is like a valve, a small current flow in the base makes a larger current flow in the collector / emitter.
The ratio of these two currents is the gain. o for example if you have 2mA flowing in the base with a transistor that has a gain of 80 there will be 2 * 80 = 160mA flowing in the collector providing the resistances around the rest of the circuit allow that much to flow.

That makes sense! So it's kind of like a relay with no moving parts?

Well a relay is an all on or all off device. Where as a transistor can continuously control a flow of current from a much smaller one.
Think of it as a valve, a small turn controls a lot of flow.

Grumpy_Mike:
Well a relay is an all on or all off device. Where as a transistor can continuously control a flow of current from a much smaller one.
Think of it as a valve, a small turn controls a lot of flow.

Ok, I'm getting there slowly. So the Transistor doesn't really amplify a current. It just has the ability to allow the current to reach it's maximum potential? It's not generating power from somewhere is it?

transistor can continuously control a flow of current from a much smaller one.

This why transistors can AMPLIFY.... small signal in - bigger signal out... amplification.

But you cannot magically create current from nothing unless you are talking about power sources like batteries.

The valves that Mike was referring to are what our colonial cousins on the west side of the pond would call a faucet

jack

Another way of thinking about it is that a transistor is a variable resistor where the knob is turned by the base current flow.

Well the root of the name 'transistor' is 'transfer of resistance'. It means that higher resistance representive by the base/emitter junction can control the lower resistance of the emitter/collector junction.

Lefty