Diac controlled LED Flasher

Diac Controlled LED Flasher

This is probably the simplest idea to generate flashing light from an LED using AC. The circuit is relatively the simple way of flashing one or more LEDs from a high voltage DC obtained from Mains. This can be used as a Mains indicator or Mock flasher.

The circuit uses a diac for the alternate switching of LED. The diac is usually used in pulse generator circuits to trigger SCR and Triac. If a low voltage passes through a diac, it simply behaves like an open circuit and only very low current passes through it. But if the voltage increases to the breakdown threshold of the diac, it will pass heavy current. Usually 35 volt DC is required to attain the threshold level of diac. Unlike SCR, diac conduct in both the directions. In the circuit, a commonly available DB3 diac is used. Diode D1 rectifies AC and generates a high volt DC. Resistor R1 safely controls the DC to operate diac and LED.

Normally LED will be OFF. When the capacitor charges fully, diac gets the threshold voltage and fires. This provides current to LED and it lights. Resistor R2 makes the LED current to a safer value of 30 mA. When the diac conducts, C1 discharges and again the breakdown voltage of diac decreases and LED turns off. Thus the charging/discharging cycles of C1 makes the LED flashing. The value of C1 determines the flash rate. Higher values give slow flash rate and vice versa. If the threshold level of diac is not obtained using the given value of R1, reduce it to 10K, but its wattage should be increased to 5 watts.

Caution The circuit is directly connected to high volt AC and there is no galvanic isolation. Take utmost care while handling the circuit. Enclose it in a shock proof case. Do not touch any points when it is connected to Mains.

Diac controlled Flasher Circuit

Diac controlled LED Flasher


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  • Wagner Lip

    It will be wise to install a 270k to 1M ohms resistor in parallel to the capacitor, to discharge it automatically after removing power. Also, if the disc, the Led or R2 opens the parallel with the 100V capacitor, it will explodes, since the voltage over it will increases above 250V. It would wise to use a higher voltage capacitor.

  • Rajeev

    Caution:- Capacitor C1 remains charged even after power supply is switched off!

  • Dorni

    I love this circuit

  • Nidhu

    Sir,instead of led,is it possible to connect transistor based astable multivibrator flasher circuit?
    Plz reply?

  • Judith S. Randa

    Since LEDs are small, durable and require little power they are used in hand held devices such as flashlights. LED strobe lights or camera flashes operate at a safe, low voltage, as opposed to the 250+ volts commonly found in xenon flashlamp-based lighting. This is particularly applicable to cameras on mobile phones, where space is at a premium and bulky voltage-increasing circuitry is undesirable. LEDs are used for infrared illumination in night vision applications including security cameras. A ring of LEDs around a video camera, aimed forward into a retroreflective background, allows chroma keying in video productions.

  • Sivanand

    Instead of diac any transistor (collector emitter breakdown voltage )can be used.

  • shafiq

    perfact 4 those who r at the abinitio ov electronics……. its dry run to b ok…

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