Diode as a Switch

Several semiconductor devices can be operated as electronic switchwes as they can work in ON state OFF state.

Examples are Semiconductor Diodes, BJTs,FETS and UJTS.

Diode as a Switch ON state

If we connect the semiconductor diode in Forward bias,diode acts as short circuit with some forward resistance rf, the current if flows to bulb and it will switch ON.

Diode as a Switch OFF state

If we connect the semiconductor diode in Reverse bias,diode acts as open circuit with linfinity reverse resistance rr  so, the bulb in OFF state for ideal diode.But for practical diode, diode shows high resistance rr  only the minority charge carrier current ir flows to bulb, which  is in micro amps.Which is not enough to turn on a device and it will switch off the output device bulb.