Switching Power Supply RCD Spike Absorption Circuit Principle Analysis
To the switching power supply using a ramp wave to compensate for the role of the transistor, this article talks about the role of R4,D1,C6 and the principle. Take you to analyse the role of each component of the switching power supply.
4 resistor, D1 diode, C6 capacitor is a spike absorption circuit, because it is a resistor-capacitor-diode circuit, referred to as RCD absorption circuit. So why add a spike absorption circuit? It is because it is necessary to protect the MOS tube over-voltage breakdown, and limit the peak voltage to the MOS tube withstand voltage. So that the MOS tube can work safely, so how does it work.
As a result of transformer production will have a certain leakage inductance, what is the leakage inductance, is the turns ratio of the transformer and winding coils generated in the transformer work primary energy can not be completely transferred to the secondary, then due to inductance will produce a reverse electromotive force, resulting in a reverse voltage and the superposition of the supply voltage generates a voltage spike, this voltage will be more than the value of the withstand voltage of the MOS, the breakdown of the MOS tube.
So you need to join the spike absorption circuit, in the transformer primary coil, in order to absorb the coil generated by the reverse electromotive force, joined the RCD absorption circuit, RCD work process, when the MOS tube conduction, the voltage flows through the transformer primary coil, charging the coil, when the MOS tube is closed, the inductor generates a reverse electromotive force, the transformer secondary voltage output through the diode, due to leakage of primary coil, can not be fully transferred to the secondary, the excess. Can not all be transferred to the secondary, the excess energy will be superimposed with the supply voltage, resulting in a spike voltage, the spike voltage through the diode D1 on the capacitor C6 charging, in the MOS conductive again, the capacitor C6 on the voltage through the resistor R4 discharge, the excess energy through the resistor to consume, the RCD of a work cycle is complete, continue to cycle the next cycle.
Here the diode selection of fast recovery diode, resistance and capacitance according to the circuit debugging to determine the parameters, the size of the resistor value, the greater the absorption of energy, which will affect the efficiency, their purpose is to consume the circuit to produce excess energy, can not consume the circuit's own energy, which affects the primary electromotive force, the transfer of electromotive force to the secondary is less, reducing the conversion efficiency. Resistor value is too large, in the discharge, the discharge rate is slow, the spike voltage will fall slowly, the spike voltage will exceed the MOS tube withstand voltage, resulting in MOS tube breakdown. So the value of the resistor is selected in the circuit debugging, debugging with an oscilloscope to see the waveform of the MOS tube D-pole, you can clearly see the spike voltage, change the resistor can change the spike voltage, capacitance can also change the magnitude of the spike voltage, and resistors with the use of the ultimate goal, is to absorb the spike voltage, excess energy, can not consume the circuit energy.
Absorption circuit has three kinds, one is RCD, a TVS transient suppression diode accelerated recovery diode composition, there is a voltage regulator diodes and fast recovery diode Tube, each of which has its own advantages and disadvantages, the RCD circuit is used more, the latter two are also often seen. Switching power supply
