How do I calculate resistor sizes for capacitors?

Discussion in 'General Electronics Chat' started by Randy13, May 24, 2013.

  1. Randy13

    Thread Starter New Member

    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!!

  2. MrChips


    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.
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
    This is the page , but dose not suggest any values to start with, try a 1Meg preset and trim it to suit...