A circuit arrangement for protecting the remainder of a plurality of parallely operated transistors in the event any one of the transistors fails in a shorted condition. An open circuited failure has no adverse effect upon the operating circuit. Each transistor includes a "slow" turn-off diode with respect to the period of the input drive signal, coupled in series between a common input signal-feed point and the base of the transistor to which it is connected. The diodes are poled to block the collector B+ supply potential appearing at the base of the respective shorted transistor, thus preventing the B+ supply potential from being applied to the base of the remaining transistors. Additionally, a respective fusister is connected in series between each emitter and the load circuit line in order to thereafter remove the failed transistor from the circuit and to balance the transistor currents during normal operation.

Parallel transistor protection circuit

THE CIRCUIT INCLUDES AN ARRANGEMENT FOR PROVIDING ELECTRICAL DISCHARGE MACHINING ACROSS ONE OR MORE GAPS WITH POWER PULSES DERIVED FROM A COMMON POWER SUPPLY. EACH MACHINING GAP INCLUDES AN ELECTRONIC SWITCH AND HAS ASSOCIATED WITH IT A SHUNT DIODE OF BLOCKING POLARITY TO PREVENT GAP INDUCTANCE FROM BREAKING DOWN THE ASSOCIATED SWITCH. WHEN SEVERAL ELECTRONIC SWITCHING MEANS ARE USED, THEY ARE EACH CONNECTED THROUGH AN ISOLATING DIODE TO A COMMON PULSE GENERATOR OR TRIGGERING MEANS FOR TURNING THEM ON AND OFF AT THE SAME TIME. ALSO IN- CLUDED IN EACH GAP CIRCUIT IS A SERIES DIODE OF A POLARITY TO A PASS POWER PULSES TO THE GAP WITH A DETECTOR MEANS CONNECTED ACROSS THE SERIES DIODE FOR PROVIDING AN INDICATION OF COMPONENT FAILURE IN THE ASSOCIATED GAP CIRCUIT WHEN SEVERAL SWITCHES ARE CONNECTED IN PARALLEL.

Dalton R Verner

Papers

Multiple gap electrical discharge machining circuit