Re: Battery Backed external power supply

<steve.jones@xxxxxxxxxxxxx> wrote in message
> We have a small unit which has a external power supply of 7V. This unit
> draws around 100mA. We have been asked to supply some sort of battery
> backup for it. There is no ups to hand so what we are looking for is a
> DC small DC supply 7 to 15V which can power the unit from the mains and
> keep powering the unit for around 2 hours on power fail.

This can be setup really simple: feed your circuit from tha 15V (must be
higher than battery voltage) supply through a diode. Also connect a 12
lead-gel battery to the circuit through another diode. When the power fails,
the battery takes over. You can trickle-charge the battery from the power
supply as well though a suitable resistor.