987,002. Converting. WESTINGHOUSE BRAKE & SIGNAL CO. Ltd. Jan. 14, 1964 [Jan. 21, 1963], No. 2498/63. Heading H2F. [Also in Division H3] An inverter is alternately operating and quiescent for periods of time equal to several cycles of the inverter. In the Figure a 50 c/s supply S is rectified by a bridge rectifier 1, filtered by the elements 2, 3, 4 and fed to a storage capacitor 10. A controlled rectifier 7 (of the type which is rendered conductive on application of a firing pulse and only rendered non-conducting when the current tends to reverse) inductance 6 and capacitor 5 are connected in series forming an oscillatory circuit. When the rectifier 7 is fired this circuit attempts to oscillate, and the rectifier is turned off leaving the capacitor 5 charged. The circuit comprising the load 9, inductance 8 and the capacitor 5 is also oscillatory, having a natural frequency which is high relative to that of the first oscillatory circuit, and the energy stored in the capacitor 5 is dissipated at the higher frequency in the load. Control circuit.-The source S also supplies a bridge rectifier 31 in the control circuit. The transistor 13, where collector and emitter electrodes are connected through resistor 18 across the bridge 31, has its base connected through resistors 12 and 15 to both A.C. lines. Consequently whenever the bridge 31 is conducting transistor 13 conducts, and it is only non-conducting at the cross-over points of the supply S. When transistor 13 conducts the voltage drop across resistor 18 is such that diode 19 is reverse biased. Capacitor 21 charges through resistor 20 from the stabilized supply provided by resistor 22 and capacitor 23. When transistor 13 becomes non-conducting diode 19 can conduct, and the capacitor 21 discharges rapidly through resistors 18 and 23. Consequently a sawtooth waveform with a frequency of twice the supply frequency appears at the junction of capacitor 21 and resistor 20. This sawtooth waveform is opposed by a direct control voltage from 33, and when the resultant is negative transistor 25 conducts. A blocking oscillator comprising transistor 26, transformer 28, capacitor 27 and resistor 30 runs as long as the base of the transistor 26 is sufficiently negative, that is when transistor 25 is not conducting. Firing pulses are therefore produced from a variable point in each half cycle of the supply S, until the end, and the average power in the load depends on the control voltage at 33. There may be a feedback system from the load 9 to the control voltage source 33.