Transistor as switch | Transistor Application note

This Transistor application note covers basic description on Transistor Switch. The circuit diagram is mentioned.

transistor switch

Figure shows NPN transistor circuit used as switch. As we know that a circuit which can turn on or off current in it is known as switching circuit.

A transistor can be used as electronic switch. Operating a transistor as switch means operating it either in cut-off or saturation mode. When transistor is cut-off, it works as open switch. When transistor is saturated it works as closed switch.

The DC voltage connected to the transistor terminals is referred as bias voltage. When negative voltage is applied to this NPN transistor it operates in cut-off region. When positive voltage is applied to this NPN transistor it operates in saturation region.

When transistor is switched on, collector current Ic is increased from Ico to Ic(sat.). When transistor is switched off, Ic is decreased from Ic(sat) to Ico. Due to this Ico which is minority carrier leakage current, transistor does not function as ideal switch. For high speed switch applications, transistor based switch is superior to other switch types.

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