ARC discharge supply component protection circuitry

Abstract

In a mercury bombardment ion engine, the discharge supply is a high current, low voltage supply that maintains an arc or discharge inside the engine. The output of the power supply is commandable and the response to this command is current, Ina 30 cm ion engine the supply provides up to 45 volts at ~13 amperes and is referenced at ~1100 volts above ground. Due to the engine discharge characteristics, a very slow feedback control loop is required. A high speed current limit must therefore be used to protect the components in the power conditioner, in this case a pulse width modulated bridge inverter. A high speed cycle-bycycle current limit circuit which allows the inverter to continue running in an overcurrent condition is used to protect the inverter. The high speed current sensing allows the inverter to be turned off each half cycle before the current in the primary of the inverter exceeds a safe level. This permits the inverter to continue to provide current into a discharge or a fault condition, until the feedback control system can actively control the current.