Synthetic Test Circuit (STC) system for thyristor valve of current-type High Voltage Direct Current (HVDC) typically consists of a low-voltage high-current and high-voltage low-current source. In order to provide the isolation between each source, STC comprises the auxiliary valve that has same or over the voltage and current rating of test thyristor valve. To ensure that auxiliary valve is turned off, the auxiliary source to apply reverse voltage to auxiliary valve at turn-off instant is used. This paper describes of new high-current source for minimizing turn-off time of auxiliary valve. The proposed system consists of two chopper, auxiliary valve, auxiliary IGBT, diode, resistor, and capacitor. Based on the computer simulation and the experiment with scaled hardware system, proposed system is conformed validity.