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: The present invention relates to emergency systems used in buildings, and particularly to emergency lighting systems whose function is to provide emergency illumination in the event of failure of primary (e.g. mains) power supply. As such systems must have the ability to operate correctly in any emergency it is necessary to ensure, by regular checking, that the emergency capability is maintained at all times. In an emergency lighting system the emergency capability is usually provided by a back-up power supply, which switches in on failure of the main power supply. Regular checks of the back-up power supply are required to make sure that it is capable of functioning in times of emergency. In the present invention, to facilitate the checking procedure, each emergency unit has a self-contained testing facility. This testing facility is operative to perform regular checks on the capability of the back-up supply.

Abstract: An emergency lighting system comprising a central monitoring and control unit, a plurality of single point lighting units and a communication system linking all of these units and being configured with a loop topology. Addressing of single point units around the loop is achieved via a protocol whereby a first address is issued by the central unit to the first unit in the loop. This first unit then stores this address as its own and increments the address number before passing it on to the next unit in the loop and so on. When the last unit in the loop finally passes its own incremented address number back to the central unit this provides the central unit with the necessary information to determine the number of single point units in the system.

Abstract: The battery charger employs integrator means and current switch means in combination with a control circuit whereby the control circuit receives a synchronizing signal at the start of each cycle as determined by a cyclical supply or pulse generator as well as information about the state of the integrator means which is compared with the predetermined average current such information determining the required control signals for the integrator means and current switch means so as to maintain the value of the average charging current substantially constant throughout the charging time. Current sense means being provided to sense the current flow through battery and supply the integrator means with said sensed current.

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.