GB1236979A - Improvements relating to battery charging apparatus - Google Patents

Abstract

1,236,979. Charging batteries. ELECTRIC POWER STORAGE Ltd. 23 July, 1969 [24 July, 1968], No. 35324/68. Heading H2H. A battery is charged from a pulsating supply and a control circuit includes an arrangement for modifying the charge in response to the voltage assumed by the battery during intervals between the charging pulses. In the circuit of Fig. 1, a battery 10 is charged from an A.C. supply 11 by way of a main transistor 12 and a half-wave rectifying diode 13. The base-emitter circuit of a further transistor 20 is connected across the battery 10 and supply 11 so that during charging it is biased off, but when the battery voltage exceeds the supply voltage it is turned on and a capacitor 25 is charged to a voltage depending directly on the battery voltage. When the battery approaches its fully charged state, the capacitor voltage becomes sufficient to break down a Zener diode 27 so that a transistor 26 conducts and tends to turn off the transistor 12 and thus reduce the charging current. The circuit may be provided with a more elaborate sensing and trigger circuit including transistors connected in cascade, Fig. 2 (not shown), and may also include a current control device which compares the voltage drop across a resistor in the charging circuit with a Zener diode and adjusts the conductivity of the main transistor accordingly.