# High(er) Current AC Flasher Circuit

I'm trying to develop a flasher circuit for an aircraft warning light like the one shown at https://flightlight.com/products/obstruction-lights-controls-faa-l-810/. The light will be powered with normal 120VAC providing 15 amps. I'd like to use transistors (BJTs, MOSFETS, thyristors, DIACs, TRIACs, etc.) to cause the light to flash (turn on and off at a given frequency).

Along those lines, I found several examples of transistor-based flasher circuits online, such as this one: https://www.electroschematics.com/4488/diac-controlled-led-flasher/ However, those circuits seem to all be intended for use in powering LEDs, which, I assume, have a lower current draw than the light I'm intending to use. Along those lines, I have a couple of questions:

1/ Will the circuit I linked to above work with the light I'm powering? If so, what modifications do I have to make to accommodate the higher current levels in the light I'm using?

2/ If this circuit does work, how do I modify the frequency of the flashing? I know it's possible to control that frequency by changing the values of the resistors and capacitor, but I don't remember the formula to do so.

3/ In the diagram for the circuit I found, it looks like the capacitor voltage has been set to 100V, presumably due to the value of the resistors. How do I calculate the voltage for that capacitor for a different resistor value?

• Have you looked at the electronic flasher units that were used in cars? while 12v it may give you a stable design... – Solar Mike Dec 9 '18 at 21:24

The circuit you linked to is for low power use. The 10uF capacitor provides little energy. All the current for the load (the led) goes through the diac, which has limited capability.

For higher power you may want to look at strobe lights. They work on the same principle as far as the timing goes, but the timing circuit triggers a SCR that them conducts and discharges a much larger capacitor through a xenon flash tube.

http://www.free-electronic-circuits.com/circuits/strobe-light.html

This is a basic circuit. It will give a lot more output than the led circuit but still may be underpowered for your application. This is a simple circuit and a professional design would be a bit more involved because of the power required and the reliability needed for the application.

It is recommended that pulse grade capacitors be used. Photoflash capacitors are designed to discharge into flash tubes but they are not designed for the repetitive cycles that a strobe uses.

With higher powers it is desirable to have an inductor in series with the flash tube to control the peak current at the start of a discharge cycle.

There is a lot of engineering that goes into this type of device. (or there should be) There is a lot of information available on the internet, some of it is very good.