Contents
How can I use BJT as a switch?
The function of the transistor is to amplify the signal. The three terminals of BJT are base, emitter and collector. BJT is either a PNP transistor or NPN transistor based on the doping type of the three terminals. Using the transistor as a switch is the simplest application of transistors.
Can a transistor be used to switch AC?
Transistor currents The small base current controls the larger collector current. A transistor amplifies current and can be used as a switch, as explained on this page. With suitable resistors (and capacitors for AC) a transistor can amplify voltage such as an audio signal but this is not yet covered by this website.
How is a BJT transistor used as a switch?
A switch consists of a BJT transistor that is alternately driven between the saturation and cutoff regions. A simple version of the switch is shown in figure 1. When the input equals -Vin , the base-emitter junction is reverse biased or off so no current flows in the collector.
Why is the base of a BJT not connected to the base?
In the above figures, the base of either BJT is not connected to a suitable voltage, and no current is flowing through the base. Consequently, the transistor cannot turn on. Perhaps, the simplest thing to do would be to connect a switch between the base and collector wires of the transistor as in figure (a) below.
How is a BJT used as an example?
Using a BJT as a Switch: An Example. Remember that the controlled current through a transistor must go between collector and emitter. Since it is the current through the lamp that we want to control, we must position the collector and emitter of our transistor where the two contacts of the switch were.
What is the saturation voltage of a BJT switch?
In practice, even in cutoff there is some leakage current through the transistor. Also, in saturation, there is always some voltage dropped across the transistor’s internal resistance. Typically, this will be between 0.2 and 0.4 V in saturation depending on the collector current and size of the device.