Simple MOSFET Timer Circuit

Have anyone heard about MOSFETs?

This little component is gaining popularity in electronics because it performs specific tasks better than older components.

This article explains how to use a MOSFET to create a cool timer circuit.

Due to MOSFETs outstanding results this timer can be very accurate and delay actions for quite a bit of time.

What is MOSFET Timer Circuit:

While building a delay or timer circuit a MOSFET timer circuit often functions as a switching element when used with other parts.

Because they are often used as electronic switches MOSFETs are semiconductor devices that are suitable for various kinds of timing applications.

Circuit Working:

Parts List:

The circuit functions when the push button is pressed and released.

The MOSFET is powered by the energy stored in the 100uF capacitor which collects the 12V supply.

The capacitors stored voltage triggers the MOSFET allowing it to enter its conducting condition.

The relay then gets triggered by the MOSFET, starting the circuits operational phase.

After activation a regulated discharge of the 100uF capacitor begins with the 10M resistor.

When the voltage across the capacitor falls below 5V it indicates that the stored energy has been used up.

The MOSFET then starts to change into a non-conductive condition.

In order to turn off the relay the MOSFET currently shuts off its power supply.

The 100uF capacitor and the 10M resistor work together to control how long the MOSFET and relay stay active.

Advantages of MOSFET Implementation:

The MOSFETs almost endless gate capacitance is its unique benefit.

Because of this feature the timing mechanism is closely monitored because the 100uF capacitor cannot discharge through the MOSFET gate.

Even up to 50M of resistance is used because of the high gate impedance.

Because of its adaptability the MOSFET timer circuit can handle extremely long delay periods which makes it perfect for applications seeking high timing accuracy.

Formulas:

The basic resistor capacitor RC circuit time constant (τ) is calculated with the formula below.

Even though it is often referred to as the delay time its easier to consider as a unique time constant that impacts the charging and discharging behavior of the capacitor.

T = R * C

here,

• T (τ) represents the time constant of the circuit in seconds (s).
• R represents the resistance of the resistor in ohms Ω, here R = 10MΩ (10 million ohms).
• C represents the capacitance of the capacitor in farads F, here C = 100µF (microfarads).

Calculation:

• Convert microfarads to Farads: 100µF = 0.000 1F
• Apply the formula: T = R * C = 10MΩ × 0.000 1F = 0.1 seconds

Therefore the time constant of your RC circuit with a 10MΩ resistor and 100µF capacitor is approximately 0.1 seconds.

How formula works:

The duration required for the voltage across the capacitor Vc to reach around 63.2% of the applied voltage source Vs during charging or to drop to 36.8% of Vs while discharging is indicated by the time constant (τ).

It does not indicate how long it takes for the supply voltage or the voltage to reach 0V.

Note:

This formula is just an estimate and is predicated on suitable components.

Real capacitors may experience leakage current whereas resistors may experience minor differences in tolerance.

For basic RC charging and discharging applications this technique is useful.

According to the specific application complicated circuits could require different calculations.

Understanding the time constant is necessary to figure out how RC circuits operate in various types of applications, including timers, filters and signal coupling.

How to Build:

To build a Simple MOSFET Timer Circuit follow the following steps:

• Collect all the required components listed above.
• Identify the pins of the N channel enhancement type MOSFET.
• It typically has three pins: Gate, Source and Drain.
• Place the MOSFET on the breadboard and connect it as follows:
• Connect the MOSFETs gate pin between 10M resistor and a bush button.
• The MOSFETs source pin should be connected to ground.
• Connect the MOSFETs drain pin to one end of the 12V relay.
• Positive end of the capacitor connect to MOSFETs gate pin and to ground.
• Connect one end of the 10M resistor to the MOSFETs gate pin and other to ground.
• Connect one coil pin of relay to 12V positive source.
• And other coil pin of 12V relay to the drain pin of MOSFET
• Connect diode 1N4007 between MOSFETs drain pin and 12V positive supply.

Test the Circuit

• Press and release the push button to start the circuit.
• Keep and eye on the relay activation and deactivation based on the timing measured by the capacitor and resistor values.

Circuit Operation:

• Pressing the push button charges the capacitor.
• The MOSFET is activated by powering the relay.
• The capacitor discharges through the resistor calculating the timing.
• When the voltage across the capacitor drops below 5V the MOSFET deactivates turning off the relay.

Conclusion:

This simple timer circuit based on MOSFETs provides an illustration of an advanced timing solution with particular advantages.

This circuit provides stability and adaptability in timing applications by using the features of MOSFETs and carefully choosing component values by making it a useful tool in electrical tasks which require for long delay durations.

References:

Delayed start with RC and MOSFET