Patent ID: 7233507

Claim:
A non-dissipative Saturable Reactor (SR) snubber circuit for a high voltage main switch of a boost converter comprising: an inductor winding placed on a special saturable magnetic core to form a saturable reactor; said saturable reactor connected at one end thereof to a drain terminal of said main switch and output end of an input inductor of said boost converter, and an other end of said saturable reactor connected to an anode terminal of main diode of said boost converter; a charging diode, having an anode terminal connected to said one end of said saturable reactor; a charging capacitor, having one end connected to a cathode terminal of said charging diode and an other end of said charging capacitor connected to a source terminal of said main switch; a resonant inductor, having one end connected to said cathode terminal of said charging diode; a blocking diode, having an anode terminal connected to an other end of said resonant inductor; a resonant capacitor, having one end connected to a cathode terminal of said blocking diode and an other end of said resonant capacitor connected to said other end of said saturable reactor; a discharging diode, having an anode terminal connected to said cathode terminal of said blocking diode and a cathode terminal of said discharging diode connected to a cathode terminal of said main diode; a clamping diode, having an anode terminal connected to said drain terminal of said main switch; a zener diode, having an anode terminal connected to said cathode terminal of said main diode and a cathode terminal of said zener diode connected to a cathode terminal of said clamping diode; wherein said main switch is a semiconductor current bi-directional switching device, capable of conducting the current in both directions while in an ON state, and sustaining voltage in one direction while in an OFF state; wherein said semiconductor switching device turns ON and OFF at high switching frequency; wherein after said main switch is turned ON, a reverse current starts to flow through said main diode driving said saturable reactor quickly out of saturation, and increased inductance of said saturable reactor limits said reverse current of said main diode to a low value to cause said main diode stop conducting; wherein after said main switch is turned OFF, charging capacitor is charged to the level of output voltage of said boost converter, said resonant capacitor is fully discharged to zero, and all current from said input inductor flows through said saturable reactor and said main diode; whereby high voltage spikes on the input high voltage switching transistor of the boost converter are eliminated and EMI noise is much reduced while converter efficiency is improved with the lower voltage rated devices with lower ON-resistance.