Power on delay circuit and Surge protector without transformer

These are Power on delay circuit. It uses the contact of relay acts as a switch. When we enter an AC main to this circuit. The circuit will delay working.

While It reduces a surge current protection with a fuse. Same as current will gradually flow into the first period.

Delay turn on the moitor

Currently, we use the same computer. Most are connected to an outlet with a switch to turn off with the easier to use.

But when we turn off the switch, plug it in short strokes will be. Surge current flows into. This may result in damage and lost a hard drive.

Therefore require a delay for a while. It is time to turn on itself, which will help prevent hard disk the damage.

Simple monitor turn on delay circuit
The simple delay turn on the monitor circuit

This circuit can be used with 220-volt house power. by contact of the relay switch to acting.

When 220-volt power input to the circuit, the lower the voltage to 220 volts to 15 Volts, with R1, R2, C1, and C2 current limiting it to about 41 milliamps.

And C Partners diodes ZD1 limited pressure it to 15 volts and Direct Optical Fire through D1,. D2 and C3 to the party circuit.

There will be current through R3 to charge C4, which takes time to charge and when the C4 charge fully to make a current flowing into pin B of Q1.

The Q1 runs and drive currents to RY1 switch contacts touch. Each per 220-volt power to the monitor acts C4 delay.

If you want a long delay, it added the C4, but if you want to delay it a little to reduce the C4.

The Diode-D3 prevents reverse voltage from the coil of a relay. Which may be damaged to the circuit.

How to build this project

This project is not used many components so can assemble on the universal PCB board. The wiring and various components to look out carefully for the polarity of the electrolytic capacitors, Diodes, Transistor, and relay are correct.

The components List

0.25W Resistors, tolerance: 5%
R1: 470Ω 1W
R2: 150K 0.5W
R3: 3.3K ¼W
C1: 0.01uF 250V_Polyester
C2: 0.33uF 250V_Polyester
C3, C4: 470uF 16V_Electrolytic
D1-D3_1N4007_1000V 1A Diodes
ZD1_Zener diode 15V 1W
RY_Relay 12V see text
The universal PCB board.


Surge protector using delay system

Power failure, voltage drop, power surge, but do not worry when has this circuit. Sometimes when raining and maybe windy, until a power failure and the power lower or a flashing lights switch in a short period. And causes the power surges severe. until may cause electrical, such as TV, refrigerator, computer, or other damage.

Which is normally protected by the appliance is turned off. But maybe the power failure period, In a different time, Cause you to lose time to stand to turn on-off more often.

As has electronics in the heart, Cannot ignore this problem

We should have a system time delay. When a power failure, Then, not long typical power. This system is not connected to the AC line to the electrical appliances. But it will time delay is a period of time, when the surging electrical away, the power system will continue to electrical appliances again. Our electrical appliances are so safe. Without the worries. this surge protector circuit builds simple and cheap as ever.

Small surge protector using delay system by C1815

How this circuit works

First, not have a 220 volt AC power into this circuit, The relay contacts-RY1 is connected to NC terminals. As shown in a circuit figure below. Thus, making electrical appliances is not working. But after the powering the primary coil of the transformer T1 and then the secondary coil has AC voltage is 9 Volt, next it is So is rectified from AC to DCV by diodes D1-D4 and is filtered voltage with smooth by C1.
These parts are VR1, R1and R2 helps to divide the voltage to bias current to transistor Q1. But it was not until

How to delays

The C2 as acts the delay, by it, will store slowly charged, until enough to Q1 works. The VR1 is used to adjust the time delay. (Time delay is electrical appliances, do not run immediately, After the AC line flowing into this circuit.) when Q1 and Q2 transistors work. Contacts of the relay is switched to the NO. electrical appliances are ready to works now. In the event of a power failure the relay contact is connected to the NC, RY1a cut off electrical appliances out of ac line power. For the D5 to protect the transistor from the operation of the relay.

The parts of this circuit

  • Q1: NIO, a transistor number is 2SC458 or 2SC828 or 2SC945 or 2SC1815 or other NPN transistor small size.
  • Q2: 2SC1061 or BD139 or TIP31, NPN medium transistor size
  • R1: 220K  0.25W Resistor
  • R2: 68K 0.25W Resistor
  • VR1: 220K Trimpot
  • D1-D5: OID is diode 1A 50V to 1A 1,000V For example 1N4001,1N4002 to 1N4007
  • C1: 470uF 25V, Electrolytic Capacitors
  • C2: 100uF 25V, Electrolytic Capacitors
  • RY1: Relay 9V coil,  contact 3A 250V
  • T1:  0.5A 9V Transformer

How to make

This project is easy to make so contain all parts into the perforated board that small size.
I know that you can build them for beginners. But you should always fine and be careful in check circuit diagram always before you insert ac line onto this circuit.
I hope you to enjoy this project.

We recommended others delay circuits

Related Posts


I always try to make Electronics Learning Easy.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Close Menu