7.2V Battery Replacement Power Supply For Camcorders

This circuit lets an external 12V SLA battery power a camcorder which normally has an inbuilt 7.2V battery. Such batteries can now be very difficult or expensive to obtain for earlier model camcorders. In essence, the circuit is a standard LM317 adjustable regulator with resistors R1 & R2 set to provide 7.2V (depending on the accuracy of the 1.25V internal reference). If the resulting output voltage is low, it can be increased by reducing the 130 resistor and vice versa. The circuit can be assembled on to the Eliminator PC board or the simple DC power supply PC board. The regulator should be fitted with a flag heatsink. Note that the circuit should be disconnected from the battery when not in use, otherwise its quiescent current (from the LED and regulator) will flatten the SLA battery.

Circuit diagram: