CIRCUIT060086

Comparators can be used in an ORing configuration to choose between different sources. With a relatively simple circuit and smart switches, the comparator can be used to always maintain a supply voltage to the load. For low voltage applications, comparators have a better edge over diodes because there is no voltage drop. This circuit is designed for a system connected to a wall outlet with an incorporated backup battery. If the main power is ever cut, then the back up battery will supply power to the load to ensure the device is always on. The switch network on the left side of the circuit is used to model the LDO output.

• LDO output:
  • R1 = 200 Ω
  • C1 = 47 µF
  • C3 = 100 nF
• Supply voltages:
  • V1 = 5 V
  • V2 = 5 V
• Resistors:
  • R2 = 1 kΩ
  • R3 = 1 MΩ
  • R6 = 10 kΩ