Simple UPS

  1. Input: The input to the UPS circuit is the mains AC voltage, which is typically at a higher voltage level.
  2. Transformer (T1): The transformer steps down the mains voltage to 12V AC. This step-down voltage is required because most electronic devices and circuits operate at lower voltages.
  3. Rectification (B1): The rectifier bridge (B1) converts the 12V AC into unregulated DC voltage. A rectifier bridge is a configuration of diodes that converts AC into pulsating DC.
  4. Smoothing (C1): The output from the rectifier bridge is pulsating DC. The capacitor C1 acts as a filter and smoothens the pulsating DC into a relatively stable DC voltage.
  5. Battery Charging: During times when the mains supply is available, the battery is charged via diode D3. Diode D3 ensures that the charging current flows from the rectifier output to the battery and prevents the battery from discharging back into the circuit.
  6. Voltage Regulation (IC): The regulated 5V DC is obtained using a voltage regulator IC. The voltage regulator IC ensures that the output voltage remains stable at 5V, even if the input voltage fluctuates.
  7. Output during Mains Mode: When the mains supply is available, the regulator IC gets its supply via diode D5. The 12V and 5V DC outputs are available at the output terminals.
  8. Output during Battery Mode: If the mains supply is not available (power outage), the battery supplies current to the regulator IC and to the 12V DC terminal through diode D4. Diode D3 blocks the reverse flow of current during battery mode, preventing the battery from discharging through the charging circuit.
  9. Filtering (C2 and C3): Capacitors C2 and C3 act as additional filters to further smoothen the output voltage and reduce any ripples or noise in the DC supply.

It's important to ensure that the components used in the circuit, such as diodes, capacitors, and the voltage regulator IC, are appropriately rated to handle the expected currents and voltages. Additionally, proper protection circuits and charging control mechanisms may be necessary to ensure the safe and efficient operation of the UPS and battery charging process.

Circuit diagram with Parts list.


Simple UPS Circuit Diagram



  • 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.