Simple Automatic Battery Backup Circuit

Battery Backup circuit, is useful for Burglar alarm systems, security camera flashing circuits and many more.

This circuit provides an alternate voltage source if the mains voltage failed. It is quite simple to wireup and effective to do. The 9V rechargeable battery gets charged if the main voltage is available, through the resistor R1.

The battery will discharges and take the load in no time, where the input voltage (12V) drops to zero.

The circuit mainly consisting of a Voltage Regulator IC 7809. The pin out of 7809 ic is shown below:-
Battery voltage backup circuit
  • 7809 IC regulates the input voltage to charge the Rechargeable battery.

  • The capacitor C1 filters the input ripples (if any).

  • Resistor R1 limits the time to charge up the Battery.

  • Diodes D1 and D2 switches the circuit for two modes (with and without mains voltage)

Battery voltage backup circuit


IC 7809

R1 100 ohms

D1 1N4001

D2 1N4001

C1 0.1mF

Post a Comment

  1. hi. I am looking for a battery backup circuit to charge a 7.4 rechargeable battery. it fine if 12v input is connected, but when there is no 12v input I need the 7.4v to switch on. can I use the above circuit. just I have to replace the 9v battery with a 7.4v battery(5200Ah). please advise

  2. Could the circuit be easily modified to discharge to 9V battery when the input voltage drops below +8V?