The volume and weight of magnetic elements account for a large proportion in switching power supply, and the development direction of switching power supply is small in size, light in weight and low in cost. High-frequency can effectively reduce the volume and weight of magnetic elements, that is, the higher the working frequency of switching devices, the smaller their volume and weight.In traditional DCOC converters, switching devices work in the hard switching state.
The disadvantages of hard switches are as follows:
(1) Relatively large loss in the opening and closing process;
(2) Emotional cut-off:
When there is a sensitive device in the circuit, the switch device will be turned off, a high voltage peak will be induced, which will damage the switch device easily.
(2) Capacitive opening problem:
When the switching device is opened under high voltage, all the energy in the junction capacitance of the switching device will be consumed on the device, which will easily damage the switching device due to overheating.
(3) Diode reverse recovery problem:
When the diode changes from conduction to cut-off, there is a reverse recovery time. During this time, the diode is still in the conduction clearance state. If the switch device connected in series is opened immediately, a large impulse current will be generated and the switch device is easy to be damaged.
Due to the above disadvantages of hard switches, the improvement of working frequency of switching devices is limited. Before soft switching technology comes out, the switching loss of power switching devices is very large.In order to make up for the shortage of hard switch, soft switch technology is proposed.
(4) Emotional cut-off:
When there is a sensitive device in the circuit, the switch device will be turned off, a high voltage peak will be induced, which will damage the switch device easily.

SUKI
2020-7-15
 

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