This circuit provides up to 20 V output from a 12-V automotive supply, to enable constant current charging o
f Nicad battery assemblies up to about 18 V total. VI forms a square-wave oscillator, Dl and D2, coupling this square wave to the 12-V battery supply to obtain over 20 Vdc. If this is not needed, SI is left open. Ql forms a current regulator to determine the charging rate of the rechargeable battery. R4 is selected from the table or it can be switched with a rotary selector switch.