Check sibling questions

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

Answer

A p-n junction diode is formed by combining a p-type and a n-type semiconductor.

  • 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 .
  • AC current becomes DC when it stops changing directions in a set period of time. That is, DC current has a constant direction .
  • A rectifier that produces an output signal with frequency as double than the input frequency is known as a full wave rectifier

The diagram is as given below:

Full wave rectifier-01.jpg

 

  • The input is given across the primary coil .
  • The secondary coil of the transformer receives the signal
  • Output is taken across resistor R L

(a) In the positive cycle of the input AC waveform:

POSITIVE CYCLE OF THE INPUT AC WAVEFORM.jpg

  • Diode D1 is forward biased - it acts as a short circuit
  • Diode D2 is reversed biased - it acts as an open circuit 

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

 

(b) In the negative cycle of the input AC waveform:

NEGATIVE CYCLE OF THE INPUT AC WAVEFORM.jpg

  • Diode D1 is reversed biased - it acts as a open circuit
  • Diode D2 is forward biased - it acts as an short circuit 

Hence, current flows through  R L 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 DC 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.

FULL WAVE RECTIFIER- DC OUTPUT.jpg

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Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 12 years. He provides courses for Maths and Science at Teachoo.