Question

Explain with a proper diagram how an ac signal can be converted into dc(pulsating) signal with an output frequency double the input frequency using the PN junction diode. Give its input and output waveforms.

Accepted Answer

A $p - n$ junction diode allows current to pass only when it is forward biased. This property is used to rectify alternating voltages and the circuit used for this purpose is called a rectifier. $A C$ current becomes $D C$ when it stops changing directions in a set period of time.

The input is given across the primary coil.

The secondary coil of the transformer receives the signal.

Output is taken across resistor $R$

$(a)$ In the positive cycle of the input $A C$ waveform:

Diode $D_{1}$ is forward biased-it acts as a short circuit.

Diode $D_{2}$ is reversed biased-it acts as an open circuit.

Hence, current flows through $R$ and is observed as output.

$(b)$ In the negative cycle of the input $A C$ waveform:

Diode $D_{1}$ is reversed biased-it acts as an open circuit.

Diode $D_{2}$ is forward biased-it acts as a short circuit.

Hence, current flows through $R$ and is observed as output.

You may notice that the direction of current in the first case is clockwise, while the second case is anti-clockwise.

The current produced is $D C$ because the direction of the current in the load resistor in both cases is the same.

Since, the no. of cycles per second has doubled, a full wave rectifier produces an output with double the input frequency.

Explain with a proper diagram how an ac signal can be converted into dc(pulsating) signal with an output frequency double the input frequency using the PN junction diode. Give its input and output waveforms.

Important Questions on Sample Paper 2

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