This is the circuit diagram of a simple UPS that can deliver 12V unregulated and 5V regulated DC. The transformer T1 steps down the mains voltage to 12V AC and then the bridge B1 rectifies it. The rectified signal is smoothed by the capacitor C1.When the mains supply is available the battery will be charged via diode D3 and the regulator IC gets supply via diode D5. 12V and 5V DC will be available at the output terminals. When mains supply is not available the battery supplies current to the regulator IC and to the 12V DC terminal through diode D4.Also, the diode D3 blocks reverse flow of current during battery mode. Capacitors C2 and C3 acts as filters.
Notes:
- Assemble the circuit on a good quality PCB.
- The transformer T1 can be a 230V AC primary, 12V secondary,3A step-down transformer.
- The bridge B1 can be a 2A bridge. If such a bridge is not available, make one using four 1N4007 diodes.
- The capacitor C1 must be rated at least 25V.
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