Simple Triac Flasher Circuit

Building a circuit to switch a regular lightbulb on and off is described in the article.

Using a knob the lights blinking speed can be changed from about two to 10 times per second.

What is a Triac Flasher Circuit:

An electrical circuit known as a triac flasher circuit is designed to make a connected load with mainly an incandescent bulb which light frequently or flashingly.

The Triac a semiconductor device that regulates the flow of AC current is the essential part of this kind of circuit.

Triac flasher circuits are often used for indications, ornamental lighting and many other application that requires for a repeated flashing effect.

Circuit Working:

Parts List:

After the mains input AC is rectified by the 1N4004 diode the signal that results is sent to a variable RC network stage.

This stage has an electrolytic capacitor that when fully charged, causes the diac DB3s breakdown voltage.

The triac triggers when the capacitor discharges through the diac.

The connected bulb flashes as a result of this firing sequence generating a dazzling flash and then the lamp goes off.

The lighting phase is followed by a delay that is controlled by the 100k potentiometer.

During this time the lamp pulses before shutting out as the capacitor starts to recharge near the diacs breakdown limit.

Through a continuous cycle of discharge, triggering, lighting, delay and recharge the lamp is able to flash at the frequency that is set.

The circuits 1k resistor is essential in establishing the current threshold at which the triac is designed to activate.

This component helps in adjusting the circuits operating qualities.

Details of the connection:

Triac BT136s MT1 terminal is connected to the mains AC phase creating a series connection with a 40 watt lightbulb.

The triacs MT2 terminal is connected to the neutral.

A 1N4004 diode and a 6.8k resistor are also used to connect the phase to a 100k potentiometer.

A 220uF capacitor connects the potentiometers opposite end to the neutral.

A diac is then connected to this potentiometer capacitor junction.

Through a 1k preset the opposite end of the diac is connected to the triacs gate.

Ability to adjust:

The main device that controls the flashing rate of the bulb throughout a broad frequency range is the 100k potentiometer.

The flashing rate can be carefully adjusted with the help of the 1k preset.

Formulas and Calculations:

To regulate the switching of the triac BT136 the above circuit depends on the charging and discharging duration of capacitor C1.

One of the key factors controlling the flash rate is the time constant (τ) which has the following calculation:

Time Constant (τ):

The time constant (τ) expressed in seconds (s) is the product of resistance R and capacitance C.

Before charging or discharging it shows how long it takes for the voltage across the capacitor to reach a specific percentage or around 63% of the total value.

The time constant formula is:

τ = RC

The circuits important parts to calculate the time constant is:

• Resistor R = R1 100k
• Capacitor C = C1 220µF

Calculating the Approximate Flash Rate:

Calculate the time constant (τ):

τ = R1 * C1 = 100,000 Ω * 220 x 10^-6 F = 22 seconds

Note:

This is the time constant for a single charging or discharging cycle of the capacitors.

Actual flash rate includes the cycles of charging and discharging.

Flash Rate Estimation:

If the charging and discharging times match with a simple estimation for the flash rate (f) than the ratio will be around twice the time constant (2τ).

This enables a single flash cycle to fully charge and discharge the capacitor.

Flash Rate (f) Estimation:

f = 1 / (2τ) = 1 / (2 * 22 s) = 0.022 Hz

Converting Frequency to Flash Period:

The frequency or number of cycles per second is indicated by the flash rate which is 0.022 Hz.

By calculating the flash period T which is the ratio frequency is to provide a sense of the flash timing in seconds between flashes.

Flash Period (T):

T = 1 / f = 1 / 0.022Hz = 45.5 seconds

How to Build:

To build a Simple Triac Flasher Circuit following steps are required for connections:

Triac Relationships:

• The triac BT136s MT1 a terminal should be connected to the mains AC phase.
• Connect the triacs MT2 terminal to the neutral.

Network of Diodes and Resistors:

• Using a 1N4004 diode and a 6.8k resistor connect the mains AC phase to a 100k potentiometer.
• Use a 220uF capacitor to connect the potentiometers other end to the neutral.

Diac Link:

• Connect one end of the diac to the potentiometer capacitor junction.
• Using a 1k preset resistor connect the diacs other end to the triacs gate.

Lamp Attachment:

• Connect a 40 watt lightbulb in series with the triacs MT1 terminal.
• The bulbs other end should be connected to the neutral.

Source of Power:

• With the correct polarity connect the circuit to the primary power source.

Modifications:

• The 100k potentiometer is used to control the bulbs flashing rate.
• Use the preset resistor of 1k to fine tune the flashing rate.

Safety Measures:

• Turn off the power while working on the circuit.
• Check connections again to make sure they match with the requirements.
• Make use of insulated instruments.
• Ask an experienced person for advice if you are unsure about any step or component.

Conclusion:

When working with electronic circuits particularly the ones that involve mains power safety should always come first.

In case one is unsure think about seeking advice from a specialist or an experienced electronics hobbyist.

References:

Datasheet BT136