Simple 220V Diac Controlled LED Flasher Circuit

This is perhaps the easiest method to create a flashing light using an LED with AC power.

The circuit is a simple way to flash one or more LEDs using high voltage DC derived from the mains power.

It can serve as a mains indicator or a simulated flasher.

Circuit Working:

Parts List:

The circuit utilizes a diac for the LEDs alternate switching.

The diac is commonly employed in pulse generator circuits to trigger SCRs and triacs.

Under low voltage, the diac acts as an open circuit allowing only a minimal current.

However, when the voltage reaches the diacs breakdown threshold, it conducts a significant current.

Typically, a 35V DC voltage is necessary to reach this threshold.

Unlike an SCR a diac conducts in both directions.

In this setup a commonly available DB3 diac is used.

Diode D1 rectifies AC to generate high voltage DC while resistor R1 safely controls the DC to operate the diac and LED.

Normally, the LED remains off.

When the capacitor charges completely the diac reaches the threshold voltage and triggers supplying current to the LED causing it to light up.

Resistor R2 limits the LED current to a safe level of 30mA.

As the diac conducts, capacitor C1 discharges reducing the diacs breakdown voltage and turning off the LED.

This charging and discharging cycle of C1 creates the flashing effect.

The flash rate is determined by the value of C1 with higher values yielding a slower flash rate and vice versa.

If the diacs threshold is not reached with the specified value of R1 reduce it to 10k, but ensure its wattage is increased to 5W.

Formula:

Here are some relevant formula to take into account when dissecting the 220V Diac Controlled LED Flasher Circuit.

Time Constant (τ):

This formula establishes the duration of the circuits capacitor C1 charging and discharging, which in turn influences the LEDs flash rate.

The following formula is used to get the time constant:

τ = RC

where:

• τ tau is the time constant in seconds
• R is the resistance in ohms of resistor R1
• C is the capacitance in farads of capacitor C1

Because component tolerances vary, the actual flash rate may range significantly from the estimates provided by these calculations.

Here are a few more things to think about:

The capacitor C1 voltage rating needs to be greater than the AC line voltage peak.

The resistor R2 sets a safe limit on the amount of current that passes through the LED.

When the voltage of the capacitor hits its breakdown value, the Diac DB3 functions as a trigger switch and permits current to flow to the LED.

When dealing with this circuit, it is crucial to use caution because high voltage is involved.

It is advisable to leave work to a licensed electrician if you are uncomfortable handling mains electricity.

How to Build?

To build a Simple 220V Diac Controlled LED Flasher below mentioned are the assembling steps:

Safety First:

• Ensure you are familiar with working with high voltage circuits and take necessary precautions.
• Do not touch any parts of the circuit when it is connected to mains power.

Component Placement:

• Place the components on a suitable circuit board or project enclosure.
• Arrange them according to the circuit diagram.

Wiring:

• Connect one terminal of the AC mains power source to one terminal of diode D1.
• Connect the other terminal of diode D1 to one terminal of resistor R1.
• Connect the other terminal of resistor R1 to one terminal of the diac.
• Connect the other terminal of the diac to the anode longer lead of the LED.
• Connect the cathode shorter lead of the LED to one terminal of resistor R2.
• Connect the other terminal of resistor R2 to one terminal of capacitor C1.
• Finally, connect the other terminal of capacitor C1 back to the other terminal of the AC mains power source.

Testing and Adjustment:

• Double check all connections for correctness.
• Place the circuit in the shock proof case.
• Connect the circuit to the mains power and observe the LED flashing.
• Adjust the value of R1 if necessary to achieve the desired flash rate as described in the original text.

Safety Measures:

• Ensure the circuit is enclosed in a shock proof case and that no parts are exposed when connected to mains power.

Note:

• This circuit is directly connected to high voltage AC and lacks galvanic isolation.
• Exercise extreme caution when handling the circuit.
• Enclose it in a shock proof case and avoid touching any points when it is connected to the mains.

Conclusion:

In conclusion, the Simple 220V Diac Controlled LED Flasher is a simple circuit that uses common components to create a flashing LED indicator using AC mains voltage.

With careful assembly and attention to safety precautions, this circuit can serve as a useful mains indicator or mock flasher for various applications.

References:

Datasheet Diac DB3