In order that a transistor acts as switch, a larger positive potential is applied across its:

Explanation

Using a transistor as a switch is the simplest application of the device. A transistor can be extensively used for switching operations, either for opening or closing a circuit. On the other hand, the basic concept behind the operation of a transistor as a switch relies on its mode of operation. Generally, the low-voltage DC is turned on or off by transistors in this mode.Both PNP and NPN transistors can be utilised as switches. A basic terminal transistor can be handled differently from a signal amplifier by biasing both NPN and PNP bipolar transistors with an "ON / OFF" static switch. One of the main uses of the transistor to transform a DC signal "ON" or "OFF" is solid-state switches.Some devices, including LEDs, only require several milliamperes of DC voltages at the logical level and can be directly controlled via the logical gate output. High-power devices such as generators, solenoids or lamps usually need more power to use transistor switches than the usual logic gate..