Xenon Flash Circuit

This Xenon flash circuit for creating photographic flash. It consist of 2 stages. High voltage inverter for creating 200 - 300V and trigger stage to trigger the flash.

This circuit produces dangerous high voltages. Be careful and do everything at your own risk. Author accepts no responsibilty for any harm to your health or your property. Do not look directly to flash tube when it is triggered it can cause temporary blindness.

1x Flash capacitor (100 - 200uF, 300 - 400V electrolytic capacitor)

1x 5-20nF high voltage capacitor

1x 100kΩ resistor

1x 2.2kΩ resistor

1x NPN switching transistor (I've used 2SD965 but bd139 and similar can be used)

1x 1 nF ceramic capacitor

1x Push button

1x 47Ω resistor

1x SCR (I've used BT152)

1x High voltage, high speed diode FR107, UF4007 or similar

1x Xenon Flash Tube

1x Hv voltage transformer

1x Trigger transformer

Photos of flash capacitor, flash tube with reflecctor, HV transformer and trigger transformer is given respectively.

The inverter is very similar to the well known joule thief with addition of a capacitor in parallel to the transformer. The transformer is from camera which I took flash tube, trigger transformer and flash capacitor. But you can make the transformer yourself using ferrite core and some enameled copper wire (primary 10-15 turns in each shoulder and secondary with 350-400 turns). This inverter is choosen because of its simplicity and I don't want to make new transformer (If I made the transformer from scratch I've probably used royer oscillator or similar)

Check the winding direction in secondary when connecting to the diode and and capacitor because this inverter switches the transformer into one polarity and in the other polarity voltage just overshoots inductively, voltage in one polarity is higher than the other polarity. For minimum capacitor charge time connect transformer in right polarity.

This boosted voltage is then used for charching 2 high voltage capacitor through rectifier.

The flash succesfuly fires above 220-230V so adding zener (or series of zener diodes with overall zener voltage of about 250V), resistor and led to indicate when flash is ready can be beneficial and eliminates the risk of overcharging flash capacitor.

The trigger circuit consist of trigger transformer, SCR and resistor. Trigger transformer can be homemade or can be bought or can be found in old disposable cameras. It is a special transformer with pins common, low and high voltage. Low voltage pin has very low resistance of 0.5 to 1Ω and high voltage winding has a resistance of 20 to 30Ω usually. This transformer constructed using a ferrite rod in middle and the winding are wound over it layer by layer to prevent internal arcs. High voltage winding has approximately 500 turns and low voltage winding has 20 - 30 turns and and one end of each winding is joined.

In this type of transformers you need to discharge a capacitor to low voltage pin to create very high (several kilovolts) very short duration voltage spike. Because 200 - 300V is not enough to ionize xenon gas (which is inert and have very high resistance). This trigger pulse is given between flash tube envelope and one of its terminals. This trigger pulse ionizes the xenon in the the flash tube. Then 300V from flash capacitor can discharge to ionized xenon (which has very low resistance) and creates the flash. This type of triggering is called external triggering. Here is an article about external triggering and flash tubes in general.

https://en.wikipedia.org/wiki/Flashtube#External_triggering

The SCR is used as a momentary switch (a pulse in it's gate opens the SCR until current disappears). If you have a switch which can handle high voltage you can replace SCR with a switch.