In the schematic on this page,
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the power transistor is connected power supply to emiter, collecter to output. Doesn't current flow from collector to emiter in an NPN transistor?
Transistor question
Dec 11, 2005
6 Replies
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The schematic is correct...
A positive voltage on the base will cause current to flow from the base to the emitter and into ground. When this happens, a large current will also flow from the
12 volt supply through the coil and transistor and into ground.Think about the circuit using conventional current, from + to - rather than electron flow.
PS. heat sink that 2N3055 very well!
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Yes.
The collector is indeed positive wrt the emitter. See that " + " before the 12V ?
It would be conventional practice to say that the emitter is connected to ground and the positive suply is connected to the collector load btw.
Graham
The little arrow in the symbol always points in the direction of
*conventional current flow* which is (historically) from positive to negative. This is the opposite of electron flow, which is what we are *really* concerned with. So the arrows in these symbols basically point the 'wrong' way.
"What is now proved was once only imagin\'d" - William Blake
Thnks, I have a small peltier cooler and a heat sink should use both?
P.S. the peltier is just a small 1.5v one, should i use a voltage divider or is there some better way to divide the voltage by eight?
Since a peltier is run on current, a series resistor is the simplest way to regulate the current. But you will be wasting 7/8ths of the power that way. A more efficient way (but a more complicated one) would be to use a buck switching regulator, that converts power to power. So, for example 8 volts @ .1 amp (.8 watt) in, would become
1.5 volts @ 5.333 amps out, minus switch and inductor losses. Losses might be 10 to 20% of the output power. There are some integrated circuits that do most of the work for this sort of thing. You just add and inductor, a couple capacitors, and, perhaps a Schottky diode.See simple switchers under switching regulators at:
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Here is a tutorial on buck switching regulators:
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As an aside from what Paul.has mentioned, You could also say that the arrow always points to the N-material in semiconductors. This is especially helpful when dealing with JFET or MOSFET devices when determining channel type.This the way I learned it anyway. Thought this might be helpful to know.
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