Variable chopper cct. for charging portable accumulator - has variably-pulsed transistor switch between charging vehicle and accumulator for warning lights

The variable chopper circuit for charging a portable warning light accumulator from a motor vehicle electric system, has a transistor switch connected by its emitter to the vehicle positive terminal and by its collector over a choke to the accumulator. The accumulator negative terminal is connected directly to the vehicle negative terminal. The accumulator is bridged by a capacitor and the transistor collector is coupled to the negative pole via a diode which allows the choke current to dissipate, to prevent voltage spikes appearing as the transistor switches off. The transistor is pulled on and off by a square wave whose frequency and duty cycle depend on the difference between a reference voltage and the accumulator charging voltage. The reference voltage is adjustable to allow the use of different supply voltages.