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Transistor question

L

Lord Garth

Jan 1, 1970
0
ngdbud said:
In the schematic on this page,

http://www.freeinfosociety.com/electronics/schematics/powersupply/pictures/555ignitioncoildriver.jpg

the power transistor is connected power supply to emiter, collecter to
output. Doesn't current flow from collector to emiter in an NPN
transistor?

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!
 
P

Pooh Bear

Jan 1, 1970
0
ngdbud said:
In the schematic on this page,

http://www.freeinfosociety.com/electronics/schematics/powersupply/pictures/555ignitioncoildriver.jpg

the power transistor is connected power supply to emiter, collecter to
output. Doesn't current flow from collector to emiter in an NPN
transistor?

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
 
P

Paul Burridge

Jan 1, 1970
0
In the schematic on this page,

http://www.freeinfosociety.com/electronics/schematics/powersupply/pictures/555ignitioncoildriver.jpg

the power transistor is connected power supply to emiter, collecter to
output. Doesn't current flow from collector to emiter in an NPN
transistor?

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.
 
N

ngdbud

Jan 1, 1970
0
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?
 
J

John Popelish

Jan 1, 1970
0
ngdbud said:
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:
http://www.national.com/catalog/0,4567,74,00.html

Here is a tutorial on buck switching regulators:
http://www.national.com/appinfo/power/files/f5.pdf
 
L

Lacy

Jan 1, 1970
0
Paul Burridge said:
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.


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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