Simple Time Delay Circuit for DC Power

This Simple Time Delay Circuit for DC Power uses an SCR.

It is a really useful circuit that can be used in lots of different ways.

The way it works is quite easy to understand.

Sometimes, you need to wait a little bit before turning on a device or circuit.

This Simple Time Delay Circuit for DC Power gives you a delayed output after a set amount of time once you turn on the power.

It is great for cases where you want to turn on devices one after another or to prevent sudden spikes in current.

Input DC supply can be maximum 24V.

Circuit Working:

Parts List:

The working of this circuit diagram is quite simple.

This circuit uses a special part called an SCR (Silicon Controlled Rectifier), which works like a switch to control when the output happens.

When you first turn on the power the capacitor C2 starts to fill up with energy through R2.

The amount of energy in C2 decides when the SCR will turn on.

At the beginning the SCR is turned OFF so no power goes to the output.

As C2 fills up it gets to a point where a little bit of current can flow through D3 and R2 which makes the SCR turn on.

Once the SCR is on, it lets power flow to the output.

Capacitor C1 and resistor R1 help keep everything steady and stop any accidental triggers.

D1 and D2 make sure the circuit works properly by stopping any unwanted current from flowing.

Formulas with Calculations:

The delay time T is determined mainly by the capacitor C2 and resistor R2.

It follows the charging equation:

T = R2 × C2 × ln(Vth / (Vcc – Vth))

where,

• Vth is the SCR gate trigger voltage from ~0.7V for TIC106D
• Vcc is the supply voltage
• R2 is the charging resistor 100k
• C2 is the capacitor 10uF
• In() is the natural logarithm function

For example:

Assuming a 12V supply:

T = 100k × 10uF × ln(0.7 / (12 – 0.7))

T = 100k × 10uF × ln(0.7 / 11.3)

T = 100k × 10uF × (-2.33)

T = 2.33 seconds

This means the output will be delayed by about 2.33 seconds after applying power.

How to Build:

To build a Simple Time Delay Circuit for DC Power following steps are required to be followed:

• Gather all the components as mentioned in the above circuit diagram
• Connect diode D1 and resistor R2 in parallel
• Connect diode D3 cathode to one end of of resistor R2 and diode D1 and anode of diode D3 connect to GATE pin of SCR.
• Connect the anode pin of SCR to supply input pin
• Connect anode pin of SCR to one end of resistor R2 and diode D1 and other end connect to cathode of diode D2
• Connect the K pin of SCR to delayed output pin.
• Connect resistor R1 and capacitor C1 in parallel one end between anode of diode D3 and GATE pin of SCR and other end connect to K pin of SCR
• Connect capacitor C2 one end to anode of diode D3 and other end connect to GND

Conclusion:

This Simple Time Delay Circuit for DC Power is helpful in various situations where devices need to turn on one after the other.

You can change the delay time by adjusting the values of the resistor and capacitor.

The SCR provides a steady switching system, which makes the circuit dependable and effective.

References:

A simple delay ON circuit