Many electronics circuits and projects for learning in simple ways.

Surge protection circuit for power supplies

The surge protection circuit is important. If there is a thunderstorm, the power goes out or the extreme power surges.

Sometimes, our electrical appliances may damage easily. A little high voltage surge may make it loses.

We can protect this problem with this circuit. When we switch on the appliances. The circuit will delay turning on it.

For example, we set the timer for 3 seconds. After 3 seconds the circuit will turn on load right now.

Simple surge protection circuit using SCR


Simple surge protection circuit using SCR

This is a special circuit. It uses SCR that working like the relay. It is a good idea. Because of 2 advantages! First, fast switch on-off. Second, use low current in a trigger.
But it may difficult than a relay.

How the circuit works
In the circuit, the voltage of the power supply into the Supply voltage in the terminal.

The circuit is working. But the SCR is still stopping. Why?

The input current flows through R1 to charges to C1. In the first time, the voltage across C1 is 0V. After that, the voltage will rise up partially.

Until C1 is fully charged. So, the voltage across it is “high” state.

The current will flow through ZD1 to trigger the gate of the SCR. It turns on to connect the supply voltage input to output Delayed supply out.

Why we use it
ZD1—6V Zener diode will limit the voltage to gate of SCR, not too over!
D1,D2—diodes—protect the spike voltage backward.
C1—to set time delay.
R2 and C2 in parallel—reduce the noise to gate of SCR.

While SCR is working it may be hot. It requests a large heat sink.

‘Small surge protector for AC load’ »

Parts you will need
SCR1—TIC106D, 5A 400V SCR Thyristor; Quantity:1
D1,D2—1A 50V diodes; Quantity:2
ZD1—6V 0.5W Zener Diode; Quantity:1
R1,R2—100K 0.5W Resistors; Quantity:2
C1—22uF 50V Electrolytic capacitor; Quantity:1
C2—1uF 50V Electrolytic capacitor; Quantity:1

‘Surge protection using CD4011’ »

Time Delay for Relay using CD4011

This Post Has 6 Comments

  1. This circuit will not work, when switched on the relay will stay on forever.
    Pin 3 is shorted to ground, it will damage the IC !
    The other output gates pins shorted to ground will damage the IC too !

  2. PLEASE WHAT VALUE OF VOLTS OF CAPACITORS?

    1. Hi, again
      For this circuit, I not sure it is in you want. Do you want the spike voltage protection for your machine?
      Please wait for me. I will try to check my circuit for you.

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