How do I calculate resistor sizes for capacitors?

Thread Starter


Joined May 16, 2013
I'm extremely new to all of this (I'm learning as I go!) and I've decided to build a 300V Xenon Strobe for fun and as a learning experience. I will be building it according to the diagram below, with a 12V to 300V step-up converter, a bank of 6x 300V capacitors totaling 60uF (Cs), and with a 300V 0.22uF trigger capacitor (Ct).

Now, the diagram calls for a resistor between the input voltage and the 0.22uF trigger capacitor. How do I calculate what size resistor I need? I have searched for hours and can't find anything that explains this. Also, do I need a resistor on each of the 6x 10uF main capacitors (Cs)?

Thank you for the help!!



Joined Oct 2, 2009
The purpose of resistor R1 is to charge the trigger capacitor Ct.

The product of R1 x Ct is approx. the time it will take to recharge the capacitor once the trigger button is released.

Try 100kΩ for R1.

You do not need resistors for the storage capacitors. 60μF will give you a weak flash but might be ok for a continuous strobe light. Typical photo flashes use 300μF/300V caps.