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Turning Transistors On and Off

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I know that turning on the transistor is easy enough if you apply power to the base. But i wanted to know is it possible to turn off the transistor has already been switched on and how?

Or is it just as simple as taking away the power from the base
 

k7elp60

Active Member
I know that turning on the transistor is easy enough if you apply power to the base. But i wanted to know is it possible to turn off the transistor has already been switched on and how?

Or is it just as simple as taking away the power from the base
Yes that simple
 

Hero999

Banned
It depends on what course you've done?

An SCR can't be turned off as easily, the cathode current needs to drop below the minimum holding current before it turns off.
 

MikeMl

Well-Known Member
Most Helpful Member
If you are interested in how rapidly the transistor turns off, it is a little more complicated. In addition to the resistor that feeds current into the base, there should also be a resistor from base to ground to help discharge the base to emitter capacitance. The transistor turns off faster if there is an Ohmic path to from base to emitter or base to ground.
 
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Hero999

Banned
If the output driving the transistor is push-pull such as a microcontroller, a 555 or a logic gate, you don't need a base-emitter resistor to make it turn off quickly because it will short it anyway.
 

CafeLogic

New Member
BJT yes that simple, amplifies current, no current into the base, then no current from collector to emitter. Mosfet no, will stay on for indeterminate amount of time till charge leaks out. To turn off, for N mosfet, pull the gate to ground. If you are interested in turning things off fast, most of the time u want to be using a mosfet. If you must use a BJT, then lookup a baker clamp.
 
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