The RC snubber issue for the secondary-side rectifier diode in Flyback converters 1

When discussing the RC snubber absorption for the secondary-side rectifier diode in a Flyback circuit, using an RCD snubber yields better results than an RC snubber for handling such spikes. With an RCD snubber, the rectifier diode's peak voltage can be suppressed lower (with appropriate parameter matching, the spikes can be completely absorbed, making them almost invisible). Additionally, the snubber losses are smaller. After testing, you'll be pleasantly surprised—diodes can be surface-mounted (fast-switching diodes like the 1N4148 work well if parameters are suitable), and both resistors and capacitors can also be surface-mounted.diode

The RCD absorption design here can be understood as follows: To absorb oscillation spikes, capacitor C must have sufficient capacitance so that the voltage across the capacitor does not become too high after absorbing the spike energy. To balance the energy stored on the capacitor, resistor R must dissipate the leakage inductance energy stored in capacitor C. Therefore, the ideal parameter configuration is when the energy dissipated by the resistor equals the energy in the leakage inductance spike (at this point, the voltage at capacitor C's terminals equals Uin/N + Uo). Since there are many uncertainties in the leakage inductance spike energy, calculation methods are often ineffective. Hence, the following introduces an experimental approach for designdiode

Select a larger capacitor (e.g., 100nF) as capacitor C, and choose a fast-recovery diode (e.g., 1N4148) with a voltage rating >1.5(Uin/N+Uo) for D;

2. You can select a smaller resistor, such as a 10K, 1W resistor, as the absorbing R;diode

3. Gradually increase the load and observe the voltage at the C terminal of the capacitor and the peak voltage of the rectifier tubediode