What does the diode have the influence on the switching power supply ?
In switching power supplies, the main function of diodes is rectification. According to the frequency of the alternating current in the rectifier circuit, the rectifier circuit in the switching power supply can be divided into a primary rectification circuit (low frequency rectification) and a secondary rectification circuit (high frequency rectification).
Among them, the primary rectification circuit refers to the rectification of the mains alternating current (frequency is 50Hz or 60Hz), and the secondary rectification circuit refers to the rectification of high-frequency alternating current (the frequency is tens of kHz to hundreds of kHz or even higher). The principles of the primary rectification circuit and the secondary rectification circuit both use the unidirectional conductivity of the diode to convert the alternating current into a unidirectional pulsating direct current, but they have different requirements for the diode parameters. When selecting a diode for a primary rectification circuit, power loss and reverse blocking capability are mainly considered, that is, the forward voltage drop UF and reverse current IR in the diode parameters should be as small as possible.
When choosing a diode for a secondary rectification circuit, in addition to considering the forward voltage drop UF and the reverse current IR to be small, the reverse recovery time trr must meet the needs of the circuit, and the reverse recovery time becomes a priority for selecting diode parameters. Fast recovery diodes and Schottky diodes are commonly used diodes in switching power supply circuits.
The converter transforms the DC voltage or current into a high-frequency square wave voltage or current. After being stepped up or down by the transformer, it is rectified and smoothed to become a DC voltage or current. An output rectification and filtering circuit is provided at the output end of the transformer. The voltage after DC conversion is rectified and filtered to obtain a stable output. Because the rectifier diode has a reverse recovery time, it will cause a large peak current at the moment of turn-on, which not only increases its own power consumption, but also makes the switch tube flow through an excessive surge current, which increases the power at the moment of turn-on. consumption.
Generally, fast recovery diodes or Schottky diodes are used as rectifier diodes. When reverse voltage is applied to both ends of the output rectifier diodes, a large surge current will also be generated due to the charge stored in the diodes. There is a lot of noise. An RC loop is connected in parallel to the rectifier diode, which can absorb the above-mentioned interference and effectively prevent surges.
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