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.