Abstract: A high frequency electronic ballast which comprises a variable frequency oscillator (1) having its frequency controlled by inputs (10 to 15). The oscillator (1) providing complementary outputs (16, 17) which controls an inverter (4) via a driver circuit (3). The inverter output is a source for a transformer or choke (5) which directly drives a gas discharge lamp (6). In this way the frequency of operation and hence the illumination of the lamp (6) can be changed by changing the driver (3) frequency by direct control (10 to 15) of the oscillator (1) and the lamp voltage is maintained substantially constant while reducing its current flow.

Abstract: A power supply control system suitable for controlling and protecting batteries used in such systems by causing the automatic disconnection of the battery from a load when either the battery voltage has dropped to a preset level or when the load has open circuited. Disconnection of the load ensures that the battery does not undergo any further discharge (except self discharge) and the load can only be reconnected to the battery when a main supply (charging means) is reapplied and removed again or by use of additional circuitry from an external switch, and then only when load is present and battery voltage is above the preset level.