Circuit Schematic Power Supply Failure Indicator using IC LM741

PowerSupply. - Here is Circuit Schematic Power Supply Failure Indicator using IC LM741. Many circuits, especially digital systems such as random access memories and digital clocks, must have a continuous power supply to ensure correct operation. If the supply to a RAM is interrupted then the stored information is lost, as is the time in the case of a digital clock.

The supply failure indicator described here will sense the interruption of the power supply and will light a LED when the supply is restored, thus informing the microprocessor user that the information stored in RAM is garbage and must be re-entered, and telling the digital clock owner that  his clock must be reset to the correct time.
Figure 1. Schematic Power Supply Failure Indicator using IC LM741
(Source: www.electronicecircuits.com)

When the supply is initially switched on the inverting input of IC1 is held at 0.6V below positive supply by D2. Pressing the reset button takes the non-inverting input of IC1 to positive supply potential, so the output of IC1 swings high, holding the non-inverting input high even when the reset button is released. LED D1 is therefore not lit.

Component List

  • R1 100kΩ
  • R2 10kΩ
  • R3 10kΩ
  • R4 680Ω
  • C1 10nF (103)
  • D1 LED
  • D2 1N4148
  • IC1 741
  • PB1 Push Button Switch
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