Snubber circuit for H.F. bridge converter

Claim 1

A high-frequency bridge converter circuit for converting a direct-current input voltage to a high-frequency alternating-current output voltage, comprising (a) a plurality of current-conducting first switching devices (T 1 -T 4 ) each including a control electrode and a pair of power circuit electrodes; (b) means connecting said first switching devices to define a four-armed bridge circuit having a pair of input terminals adapted for connection across a direct-current voltage source, and a pair of output terminals adapted for connection across a load, the power circuit electrodes of first and second pairs of said first switching devices T 1 , T 2 , T 3 , T 4 ) being connected in series to define first and second current paths extending in the same direction between said input terminals, respectively, said output terminals being located at the junctions between the switching devices of each pair, respectively, said bridge circuit also including (1) a plurality of capacitors (C 1 -C 4 ) connected across the power circuit electrodes of said switching devices, respectively; (2) a plurality of blocking diodes (D 1 -D 4 ) connected across said switching devices, respectively; and (3) first control means (BD 1 -BD 4 ) for alternately switching the pairs of first switching devices contained in diagonally opposite arms (T 1 , T 4 ; T 2 , T 3 ) of said bridge circuit between oppositely conducting and non-conducting conditions, respectively, said first control means being operable to cause one arm to be conductive at a time (t 5 ,t 8 ) delayed from the time (t 4 ,t 7 ) at which the other arm is caused to be non-conductive, respectively, and; (c) snubber circuit means connected between said bridge output terminals for controlling the discharging of said capacitors during the operation of said first switching devices, respectively, said snubber circuit means including (1) an inductor (L 1 ) connected at one end with one of said output terminals, (2) means including a pair of parallel-connected oppositely-poled second switching means with reverse blocking characteristics (SD 1 , SD 2 ) connecting the other end of said inductor with the other output terminal, and (3) second control means (GD 1 , GD 2 ) for operating said second switching means to connect in series with said inductor those capacitors (C 1 , C 4 ; C 2 , C 3 ) that are charged when the state of conduction of the arms of said bridge circuit is reversed, respectively, said second control means being operable at the times (t 4 , t 7 ) at which the arms are switched to their non-conductive conditions, respectively.