High frequency cathode heater supply for a microwave source

摘要

A high frequency cathode heater supply for a microwave source includes a SMPS inverter (13) and an isolation transformer (12) having a primary winding (122) arranged to be powered by the SMPS inverter, a monitor winding (123) passing through primary core assemblies of the primary winding and a secondary winding (121) arranged for connection to the cathode heater (11). A current monitor (141) is arranged to monitor a current in the primary windings. Signal processing modules (14, 131, 132) are arranged to receive a first input signal from the monitor winding (123) indicative of a voltage Vh across the cathode heater (11) and a second input signal from the current monitor (141) indicative of a current through the cathode heater. The signal processing modules are arranged to output a control signal to the SMPS inverter to control power supplied to the cathode heater dependent on a monitored resistance of,or monitored power supplied to, the cathode heater as determined from the first input signal and the second input signal.