The bipolar transistor is a good switching device because of its large transconductance Gm.
A single NPN transistor can be used as a switch for energizing or powering off the load resistor connected between the collector and the positive supply.
One problem with the simple switch circuit discussed above is the fact that a stray capacitance exists between the transistor's collector and its grounded emitter, such that the switch-off time of the transistor is slower than its switch-on time.
This is because during switch-off, this stray capacitance has to charge first through the load resistor before the load current stops.
During switch-on, on the other hand, this stray capacitance needs to discharge to ground, which is easily accomplished by the conducting transistor.
The slower charging up of the stray capacitance compared to its quick discharging is the reason why the switch-off of the circuit is slower than its switch-on.
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The bipolar transistor is a good switching device because of its large transconductance Gm.
A single NPN transistor can be used as a switch for energizing or powering off the load resistor connected between the collector and the positive supply.
One problem with the simple switch circuit discussed above is the fact that a stray capacitance exists between the transistor's collector and its grounded emitter, such that the switch-off time of the transistor is slower than its switch-on time.
This is because during switch-off, this stray capacitance has to charge first through the load resistor before the load current stops.
During switch-on, on the other hand, this stray capacitance needs to discharge to ground, which is easily accomplished by the conducting transistor.
The slower charging up of the stray capacitance compared to its quick discharging is the reason why the switch-off of the circuit is slower than its switch-on.
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