I need a manual for calculating RCD-snubber circuit for my led driver with Vac=180-265, Vled=33-36V and Iled=0.35A. Now I use a TVS snubber, but it is VERY hot.
Help me please
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The RCD snubber will have to dissipate as much as the TVS snubber unless you let the ring voltage rise higher (caused by the leakage inductance). Then the power must get dissipated elsewhere such as core loss in the transformer or avalanche in the MOSFET. If you can measure how much power is being dissipated in the TVS diode you can easily calculate the R value needed. One way to do this is measure the temperature of the diode then run DC current through the diode to match the temperature and use the voltage and current to figure out how much power is being dissipated. Another method would be to pick a capacitor and resistor and then measure the voltage across the capacitor. At this power level, provided the leakage inductance isn't excessively high, I might start with a 330-1000 pF capacitor and a 100 Kohm one to two watt resistor. The capacitor should be a film or COG/NPO if ceramic. At low input voltage, in your case 180 VAC, watch the voltage on the capacitor/resistor and adjust from there.
Calculating how much power it needs to dissipate is not trivial. You need to know the leakage inductance of the transformer to calculate the dissipation needed. The other part that makes this a bit more complicated is the switching current changes as the input voltage changes (power factor correction does this).