Switch transistor

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Switch transistor

The shape of the switch transistor is the same as that of the common triode. It works in the cut-off area and the saturation area, which is equivalent to the cut-off and conduction of the circuit. It is widely used in all kinds of switching circuits, such as switching power supply circuit, driving circuit, high frequency oscillation circuit, analog-to-digital conversion circuit, pulse circuit and output circuit.

Circuit diagram

The load resistance is directly connected between the collector and the power supply of the triode, which is on the circuit of the main current of the triode. The input voltage Vin controls the opening and closing action of the triode switch. When the triode is in the open state, the load current is blocked, otherwise, when the triode is in the closed state, the current can flow.

In detail, when Vin is of low voltage, there is no current at the base, so there is no current at the collector, so there is no current at the load connected to the collector, which is equivalent to the opening (closing) state of the switch. At this time, the triode works in the cut-off area.

Similarly, when Vin is of high voltage, the collector will flow through a larger amplification current due to the flow of base current, so the load circuit will be turned on, which is equivalent to the closing (connection state) of the switch. At this time, the triode is working in the saturation area