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Posted on 21 May 2020

Basic Operating Modes of Power Semiconductors

 

With the exception of a few special applications, power semiconductors are used predominantly in switching applications. Their switching sequences are either inductive (current-impressed) or capacitive (voltage-impressed).

A switch used in an inductive circuit can actively turn on at any given time. For an infinitely short switching time, no power losses occur in the switch.

If the circuit is live, turn-off is not possible without conversion of energy. For this reason, the switch can only turn off without any energy conversion if the current is zero. This is called passive turn-off, because the switching moment is dependent on the current flow in the circuit. A switch that is subject to these switching conditions is called a zero-current switch (ZCS).

If voltage is applied at the switch terminals directly, turn-on is only free from energy loss if the voltage is zero. This is called passive turn-on, since the voltage flow through the switch is determined by the outer circuit. If voltage is applied, active turn-off is not possible without conversion of energy.

Active turn-off, in contrast, is possible at any time in a capacitive circuit. For an infinitely short switching time, no power losses occur in the switch. Switches that operate under these switching conditions are called zero-voltage switches (ZVS).

In summary, the operating mode of power semiconductors determines fundamental rules and working principles of all types of power electronic circuits. Operating modes are characterised by active and passive switching processes or inductive and capacitive commutation, respectively.

 

For more information, please read:

 Four Types of Switching Processes

Power Electronic Switches: Neutral Switches

Power Electronic Switches: Zero Voltage Switching and Zero Voltage Resonant Switches

 

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