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

Metal Oxide Semiconductor FET, abbreviated as MOSFET, It is one of the most important transistors. It was used in Micro computer 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.

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

When the gate of MOSFET have a positive voltage , it will attract electrons to region below to 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.

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 make 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 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 same first.

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

How to test it
My son test this circuit on a breadboard, it worked.

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 is 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

Hope friends may like and enjoy.


  1. syed.s February 26, 2013 Reply
  2. aj March 6, 2013 Reply
  3. admin March 7, 2013 Reply
  4. admin March 7, 2013 Reply
  5. aj March 12, 2013 Reply
  6. aj March 12, 2013 Reply
  7. EM123 October 6, 2017 Reply
  8. zahid October 16, 2017 Reply

Add a Comment

Your email address will not be published. Required fields are marked *