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Posted on 03 May 2019

Four Types of Switching Processes

 

 

 

 

 

 

 

For current and voltage characteristics related to semiconductors and the associated power losses, it is possible to distinguish between four types of switching processes: hard switching, soft switching, resonant switching and neutral switching.

Hard turn-on is characterized by a total commutation voltage drop over the current-carrying switch at a current commutation time. In case of hard turn-off, the voltage increases up to the value of the commutation voltage while the current continues flowing, before it drops. Both processes cause high power loss peaks in the switch.

In the case of soft turn-on of a zero-current switch (ZCS), the switch voltage will drop relatively fast to the forward voltage drop value if inductance is sufficiently high, before the current increases. Active turn-off will initialize soft turn-off of a zero-voltage switch (ZVS). The switch current commutates to the parallel capacitance. The voltage only increases if the capacitance is sufficiently high and when the current has reached a low value. Dynamic losses are reduced when soft switching is used.

The term resonant turn-on is used if a zero current switch is turned on at that moment when the current to be commutated almost drops to zero. Switching losses are still reduced compared to soft switching. On the other hand, reference to resonant turn-off of a zero voltage switch applys if the commutation voltage almost drops to zero during the turn-off process. With both processes, switching losses are reduced compared to soft turn-off of the zero-voltage switch, but at the expense of losing one control option.

If the switch voltage and the switch current are zero at the moment of switching, this is called neutral switching. This is the case with the application of diodes. The various switching processes are therefore characterized by different current and voltage conditions as well as switching losses.

 

For more information, please read:

Power Electronic Switches: Neutral Switches

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

An Advantage of Hard Switching

 

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