Power-On Reset Circuit
Électronique / Electronic

Do you know what a reset circuit does?

it activates other circuits and detects any power fluctuations in order to prevent malfunctions.

In this project, we change the supply voltage to the circuit with the switch.

The power to the display portion of the circuit is on or logic high when the switch is set to position A; it is off when the switch is at position B.

The LED display shows 1 when the circuit has been reset. Let's start experimenting.

First, complete the wiring and set the switch to position B.

Now, with the switch set to B, the power reset circuit operates under 6V, and the three LEDs light dimly.

The LED display is off, meaning that the display circuit is not activated. Now, set the switch to position A.

You can see the three LEDs light brightly because the supply voltage has been changed to 9V. For a moment the LED display still shows no change, indicating that the circuit is being reset.

After a short interval, the LED displays 1 to show that the circuit has finished resetting and now it is stabilized.

Set the switch to position Β to switch the power back to 6V.

You will see the 1 on the LED disappear, because now the display circuit is off.

Look at the schematic as you read the following.

The operational amplifier acts as a comparator. The negative (-) terminal receives the reference voltage of about 5.4V.

When the switch is at position B, the positive ( + ) terminal receives about 4.1 V so the comparator does not allow the display to light.

When you use position A to switch to the 9V supply, the 100 uF capacitor causes the comparator's positive (+) terminal voltage to gradually increase to about 6V.

When this voltage exceeds the reference voltage of 5.4V, the LED display lights 1.

When you set the switch to B, the voltage at the amplifier's positive ( + ) terminal discharges through the diode, so the voltage is reduced immediately to 4.1V.

Although this circuit seems very simple (consisting of only one operational amplifier), it is very complex and important for later use.








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