A diode is a semiconductor device build with a combination of two P-N junction semiconductor materials, they have main applications at AC to DC rectifier circuits.

 

But in the electronic circuit, they have been used as electrical switches, the biasing property of the diode is utilized here to works the diode as a switch.

 

Almost all the diode types could function as a switch, but in this post, we try to explain about diode as a switch. The diode types such as pin diode and Zener diodes are used as a switch in some circuits, but the operation behind that is different from p-n junction diode operation.

We include the operations behind the switching of diode types and factors that are responsible for the fast switching operation of diodes at the circuits.

 

P-N junction diode as a switch

The p-n junction diodes are considered as one of the main diode types at whole electronic, we call it as p-n junction because a combination of P-type and N-type semiconductor materials are joined together to form a p-n junction.

The connection procedure of diode is called forward biasing and reverse biasing of the diode, that means when batteries +VE is connected to p-type and –VE is connected to n-type is called forward biasing of diode and +VE is connected to n-type and –VE is connected to p-type is called reverse bias.

 

The diode is an electrical switching process is happened between forward and reverse biasing of the diode.

Diode as a switch circuit diagram

Diode as a switch circuit diagram
Diode as a switch circuit diagram

 

In the above figure, we can see the diode is connecting between forward and reverse biasing network, this circuit is the best way to explain the switching operation of the diode in a circuit.

The first half of the circuit is the forward biasing network, so at that time circuit will act as a closed circuit.

 

And the second half of the circuit is the reverse biasing network, at that time circuit will act as an open circuit.

This is how the change over between forward to reverse and reverse to forward biasing makes the diode works as a switch.  

Explain the working of diode as a switch

working of diode as a switch
working of diode as a switch
  • The switching over between forward to reverse and vice versa will be happened at the diode by, when a specific voltage passes, the resistance at the diode increase will make the diode is reverse biased and acts as an open switch.
  • At the same time the voltage may be below the reference voltage value, the diode resistance decreases and it will make the diode into the forward biased mode, which will act as a closed switch.

Diode as a switch theory

The main theory behind the working of the diode as a switch is the transient response, as when we changing the biasing condition at the diode, the device will change equilibrium position this is called the transient response.

The transient response time will be responsible for the switching speed of the diode types.

Other than this many more factors are responsible for the switching operation of the diode.

Pin diode as a switch

Pin diode as a switch
Pin diode as a switch

The figure above indicates the RF switches using pin diode, the pin diode is considered as the fast switching element, this fast switching property of a diode is due to its semiconductor material layer arrangement.

The pin diode has +p, ‘I’ intrinsic layer, an –N layer, when we used it at RF switching applications, the pin diode biased with high or low impedance device state and also depending on the level of stored charges in the i-region.

Zener diode as a switch

The working operation behind the Zener diode as a switch is almost the same as the p-n junction diode, but the technical features of the Zener diode are way different from than conventional diode.

The normal operation of the Zener diode is a reverse biased condition, construction wishes Zener had narrow width of the depletion layer, and this will make the Zener diode works in the faster-switching operation.

The Zener diode has a narrow depletion layer than the avalanche diode, this will make the Zener diode a better electrical switch.

Factors that affect diode switching

  • Diode capacitance
  • Diode resistance
  • Doping concentration
  • Depletion width

Diode as a switch uses

  • High speed rectifying switch
  • High-speed switching circuits
  • RF receiver
  • Automotive applications
  • Relay driving
  • Telecommunication applications
  • Reverse current and discharge protection
  • SMPS
  • Logic gates
  • Clipper circuits
  • Clamper circuits

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