Simple time Delay Circuit using MOSFET

My son wants to know more about MOSFET. I recommend trying to create a Long Duration Time Delay circuit. He said is easier than transistors can output power and good for switching and amplifier.

1. OFF After Delay circuit using MOSFET

2. ON After Delay using MOSFET

The Metal Oxide Semiconductor FET abbreviated as MOSFET. It is one of the most important transistors.

We use them in Microcomputer Memory to put a large number of MOSFETs on the Silver of Silicon.

Because MOSFETs are easy to make, they are small and eat a lot less. So new types of Power MOSFETs are very useful.

Normally, I will use the MOSFET as a good switch and amplify the sound very well.


The working of the MOSFET

I recommend the son to use the MOSFET-IRF540N number. Because of high performance, cheap, easy to use. It works like a transistor but has different legs.

The internal structure of N-MOSFET compared to NPN
And P-MOSFET compared to the PNP.

When the gate of MOSFET has a positive voltage, it will attract electrons to the region below the gate. The current flow the source and Drain to higher as the gate voltage.

Below, when use MOSFET to drive a lamp. We use less voltage to the gate, the lamp is much brighter if we use the gate voltage higher.

Also, we can use MOSFET is a simple liner dimmer.

Linear Light Dimmer circuit using Power MOSFET

Linear Light Dimmer circuit using Power MOSFET

When we adjust the value of R2(variable resistor) down. A Lamp will dim, too. This circuit uses N-Channel Power MOSFET.

We connect R1, R2, and R3 in a voltage divider form. If the low voltage across the gate of MOSFET. It causes it runs less. And the current flows to load is lower, too.

Is it easy? Yes, you can use load is a lamp or coil. If you use a 6V power supply. You can use light bulbs of 4V to 6V.

Anyway, back to learn to continue:

OFF After Delay circuit using MOSFET

We press S2 (push bottom switch) to Close. The current will flow to charge in C1, Now it voltage drop across the Gate is voltage battery (9V). It makes the MOSFET works, the current flow pass through Source to Drain of MOSFET, the buzzer it will active sound.


Then we release S1(OPEN) The buzzer will active sound. After C1 discharges internally or through R1 (optional), Q1 turns off and silences the buzzer. The long Time delay possible control by C1 and R1, 100uF for an hour.

If the time is very long but we need to stop ahead of time. We put S2 to reset or short circuit the current in C1 is Zero the same first.

OFF-delay MOSFET with LED load

NOTE: The Load we use Piezobuzzer (or portable radio, Light, LED, etc.). Do not exceed the power rating of Q1. Use the R2 series resistor to reduce the current through Q1 and the load. Below we test it using LED as load.

How to test it

My son tests this circuit on a breadboard, it worked.

The OFF After Delay circuit on Breadboard using MOSFET

Parts will you need

Q1: IRF540N, TO-220 MOSFET N-Channel 33A 100V
C1: 100µF 25V, Electrolytic Capacitors
R1: 10M, 1/4W Resistors tolerance: 5%
R2: 390 ohms, 1/4W Resistors tolerance: 5%
BZ1: Piezoelectric Transducer
LED1: LED as you want


1. Apply 9V battery to the circuit
2. Measure Voltage across C1 now is Zero
3. Press S1 voltage C1 is about 9V same battery
4. LED1 will light up
5. Time passes, Voltage C1 decreases gradually
6. When the voltage drops below 3V LED1, it will gradually dimmer. Until LED1 is completely extinguished.
7. During that, we press S2, it gives LED1 to go down as a reset.

On After Delay with MOSFET

This is ON After Delay circuit. Above We use MOSFET as in the circuit for Delay switch that easy more than the transistor.

Now, we add Q2 to inverts the status of Q1. Thus the buzzer sounds after the time delay is complete.


How it works

When we press S1(CLOSE), an electric bell will not loud suddenly, also above circuit now the C1’s voltage as hight so Q1 MOSFET active. The voltage across Drain -Source is zero.

The Q2 NPN transistor does not have bias current to Base so no current pass through Collector-Emitter. Thus electronics bell no sound.

Next, We released S1, but still no sound.

Over time, gradually. The MOSFET gradually less work. So voltage Drain-Source is higher.

It makes Q2 active,the base is biased to control the large current to Collector-Emitter to the buzzer sound up.

Note: The R2 resistors keep for decrease the popularity of an electric bell, R1 add keep for decrease the time down and decrease the noise give MOSFET. The Q2 use 2N2222 or BC549 or C1815 all NPN transistors

Parts will you need

Q1: IRF540N, TO-220 MOSFET N-Channel 33A 100V
Q2: 2N2222, 75V 0.6A TO-18 NPN transistor
C1: 100µF 25V, Electrolytic Capacitors
R1: 10M, 1/4W Resistors tolerance: 5%
R2: 390 ohms, 1/4W Resistors tolerance: 5%
BZ1: Piezoelectric Transducer

I hope friends may like it and enjoy it.

Sharing is caring!

JLCPCB - Only $2 for PCB Protytpe(Any Color)

With 600,000+ Customers Worldwide, 10,000+ PCB Orders Per Day

Up to $20 shipping discount on first order now:

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.

newest oldest most voted
Notify of

#On After Delay with MOSFET

I want adjustable 1sec to 55sec on delay timer circuit pls help me anyone


#On After Delay with Mosfet

what kind of switch is the “S2″ in AFTER DELAY with MOSFET circuit” ??


#On After Delay with Mosfet

another question.. what value of your R1 in the diagram??


#On After Delay with MOSFET

I have already tested this circuit using BUZZER or LED as a load.. but it seems that it does not have any delay or the ascending sound of the buzzer.. is it okay if i use 12v source?? please do answer it as soon as possible sir..

THANK yOU.. GOD bless


Can you send the picture of the mounted circuit from top please?


he its very helpful blog please keepit


#Off after delay
Do we really need to use the piezoelectric transducer?

Close Menu