How transistor behaves as a switch?
With a zero signal applied to the Base of the transistor it turns “OFF” acting like an open switch and zero collector current flows. With a positive signal applied to the Base of the transistor it turns “ON” acting like a closed switch and maximum circuit current flows through the device.
Can a transistor act as switch and amplifier?
By turning a small input current into a large output current, the transistor acts like an amplifier. But it also acts like a switch at the same time. When there is no current to the base, little or no current flows between the collector and the emitter. Turn on the base current and a big current flows.
When a transistor is used as a switch?
One of the most common uses for transistors in an electronic circuit is as simple switches. In short, a transistor conducts current across the collector-emitter path only when a voltage is applied to the base. When no base voltage is present, the switch is off. When base voltage is present, the switch is on.
How can BJT be used as a switch?
The transistor can be used as a switch if biased in the saturation and cut-off regions. This allows current to flow (or not) in other parts of a circuit. Because a transistor’s collector current is proportionally limited by its base current, it can be used as a sort of current-controlled switch.
When does a transistor act as a switch?
The transistor operates as a Single Pole Single Throw (SPST) solid state switch. When a zero input signal applied to the base of the transistor, it acts as an open switch.
Why are transistor switches used in logic gates?
However, high power devices such as motors, solenoids or lamps, often require more power than that supplied by an ordinary logic gate so transistor switches are used.
What’s the difference between a transistor and a NPN switch?
The equations for calculating the Base resistance, Collector current and voltages are exactly the same as for the previous NPN transistor switch. The difference this time is that we are switching power with a PNP transistor (sourcing current) instead of switching ground with an NPN transistor (sinking current).
How does a transistor work in cut off mode?
To operate the device in cut off mode, We should connect reverse biasing voltage to both junctions. Therefore, in this operating condition, the current can not flow between the collector and emitter terminal due to open circuit between these terminals. In the saturation region, the transistor remains in full-on mode.