Diode Power Loss Calculation

How to Calculate Power Dissipation of Diode?


Before proceeding further just remember the following points about the diode:

  1. When the diode is forward biased ( Anode is positive with respective to cathode), it will allow the current through it.
  2. When the diode is reverse biased ( Cathode terminal is positive with respective to anode terminal), it will block the current flow.

When the current flows through the diode some part of the current will be wasted as heat energy. It is known as Power Loss.
In this short post let us see about How to Calculate Diode Power loss...

Power - Definition:
The rate at which work is done in an electric circuit is called Electric power.
P = VI   watts

From the above definition,
The rate at which work is done in moving electrons in the diode depends upon,

  1. How many electrons are to be moved (Which is decided by the applied forward voltage)
  2. The speed at which electrons are to travel ( which is decided by the forward current flows through the circuit)

Formula for Diode Power Dissipation Calculation:

Power Dissipation = Vf x If    watts

Vf = Forward voltage drop across the diode
If = Forward current flows through the diode

Example Diode Loss Calculation:

Halfwave_rectifier_circuitTo understand properly, consider the above simple circuit.
The forward current(If) has to be calculated using the formula I = V/R . [Remember that,  Ohms law V = IR]

The forward voltage drop corresponding to the forward current will be available in the diode datasheet. This information is available in the Vf vs If graph.


Power Dissipation Calculation of Zener Diode:

We know that the zener diode will be connected in reverse bias manner as shown in the following circuit.
Zener_voltage_regulatorConsider the above example circuit. To calculate the power loss occurred in the zener diode, we can not use the previously mentioned formula.

For this, the power loss is

P = VZ x IR

Vz = Zener Voltage
IR = Reverse leakage current

Point to Remember:
For the same forward current (If), the forward voltage drop (Vf) will be less in Schottky diode than normal P-N junction diode. Consequently the power loss will be less in schottky diode.

Read More:

Diode Bridge Rectifier Circuit Tutorial
Power Diode Basics
How Zener Diode works as a Voltage Regulator?

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1 Response

  1. azzam omer says:

    How to calculate the thermal resistance for these types of diodes including the freewheeling diode ..towards finding the temperature rise for diode.. thanks

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