Turn-off circuit for gate turn-off thyristors and transistors using snubber energy

Claim 2

A semiconductor device turn-off circuit comprising a power semiconductor device having a pair of load terminals and a control terminal for controlling switching of said device between a conducting state and a non-conducting state blocking voltage, a polarized snubber circuit comprising a series-connected snubber diode and snubber capacitor connected between said load terminals and operative to store energy in said snubber capacitor as the rate of rise of voltage across said device is limited, and a turn-off circuit for selectively utilizing said stored snubbEr capacitor energy to generate a turn-off control current pulse to achieve switching of said device to the nonconducting state, said turn-off circuit comprising a controlled solid state switch and inductive energy storage means connected across said snubber capacitor to form a series resonant circuit, means for rendering conductive said controlled solid state switch for a predetermined interval to transfer said stored energy to said inductive energy storage means, said inductive energy storage means and a series-connected blocking diode being coupled between said control terminal and one load terminal such that discharge of said inductive energy storage means forward biases said blocking diode and generates said turn-off pulse, and an impedance connected between said control terminal and one load terminal for circulating excess energy.

Claim 3

The combination according to claim 1 wherein said inductive energy storage means is an inductor, and said blocking diode is connected between said inductor and said control terminal.

Claim 4

The combination according to claim 1 wherein said semiconductor device is connected in a power circuit between a pair of supply lines, and said inductive energy storage means is a transformer having a primary winding in series with said controlled solid state switch and snubber capacitor, said blocking diode further being connected between said primary winding and control terminal, said transformer having a magnetically coupled secondary winding connected in series with a diode between said supply lines to return a portion of the excess energy to the supply.

Claim 5

The combination according to claim 1 wherein said inductive energy storage means is a transformer having magnetically coupled primary and secondary windings, and said primary winding is connected in series with said controlled switch device and snubber capacitor, said blocking diode and secondary winding being connected between said control terminal and one load terminal.

Claim 6

The combination according to claim 4 wherein said semiconductor device is connected in a power circuit between a pair of supply lines, and said transformer has a magnetically coupled third winding connected in series with a diode between said supply lines to return a portion of said excess energy to the supply.

Claim 7

A turn-off circuit for a gate turn-off thyristor comprising a gate turn-off thyristor device having anode and cathode terminals and a gate terminal for controlling switching of said device between a conducting state and a non-conducting state blocking voltage, a polarized snubber circuit comprising a series-connected snubber diode and snubber capacitor connected between said anode and cathode terminals and operative to store energy in said snubber capacitor as the rate of rise of voltage across said device is limited upon switching to the non-conducting state, said snubber diode having a polarity to be reverse biased and trap the stored energy upon switching of said device to the conducting state, and a turn-off circuit for selectively utilizing said stored snubber capacitor energy to generate a turn-off current pulse, said turn-off circuit comprising a controlled solid state device and inductive energy storage means connected across said snubber capacitor to form a series resonant circuit, means for rendering conductive said controlled solid state switch for a predetermined interval to transfer said stored energy to said inductive energy storage means, said inductive energy storage means and a series-connected blocking diode being coupled between said gate and cathode terminals such that discharge of said inductive energy storage means forward biases said blocking diode and generates said turn-off current pulse to achieve switching of said device to the non-conducting state.

Claim 8

A turn-off circuit for a gate turn-off thyristor comprising a gate turn-off thyristor device having anode and cathode terminals and a gate terminal for controlling switching of said device between a conducting state and a non-conducting state blocking voltage, a polarized snubber circuit comprising a series-connected snubber diode and snubber capacitor connected between said anode and cathode terminals and operative to store energy in said snubber capacitor as the rate of rise of voltage across said device is limited upon switching to the non-conducting state, said snubber diode having a polarity to be reverse biased and trap the stored energy upon switching of said device to the conducting state, and a turn-off circuit for selectively utilizing said stored snubber capacitor energy to generate a turn-off current pulse, said turn-off circuit comprising a controlled solid state device and inductive energy storage means connected across said snubber capacitor to form a series resonant circuit, means for rendering conductive said controlled solid state switch for a predetermined interval to transfer said stored energy to said inductive energy storage means, said inductive energy storage means and a series-connected blocking diode being coupled between said gate and cathode terminals such that discharge of said inductive energy storage means forward biases said blocking diode and generates said turn-off current pulse to achieve switching of said device to the non-conducting state.