Flash Light Charging Circuit

Discussion in 'General Electronics Chat' started by rishiraj01, Jan 12, 2010.

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  1. rishiraj01

    Thread Starter New Member

    Jan 10, 2010
    1.)Referring to the schematic attached - Br1 is a fill-wave bridge rectifier that charges photoflash capacitors C1 and C2.

    2.) Upon apllying a high-voltage pulse to the external electrode of the flash-fube (F1), the xenon gas in the tube get ionised thus providing a path for C1 & C2 to quickly discharge through D5,D6 and F1 - the energy being dissipated in the form of a flash of light (Energy dissipated - 0.5 X C X V^2) (where C = effective capacitance of C1 and C2 in parallel i.e 4400uF; V is the voltage to which C1 & C2 are charged)

    3.) I intend to vary the voltage to which C1,C2 get charged by using a Triac (operated by an opto-triac as shown). (Can provide more details of the controlling circuit if required - but my query here is of a different nature)

    4.) Have added another bridge rectifier (Br2) that charges C3 and C4 to the peak of mains AC ( i.e about 1.414 X 230V = 325 V)
    This voltage (Vb) is also applied to the terminals of the flash tube and these two capacitors also discharge through F1 as it fires.

    5.) The bulk of the energy is provided by C1 abd C2 , while C3 and C4 merely serve to provide a boost voltage to ensure proper firing of F1 in case Va is very low.

    6.) With the introduction of D5 and D6 I am presuming that Va and Vb woudl be isolated from each other and would have differenrt values. However, it seems that C1 and C2 somehow get charged to the same voltage as C3 , C4 even if the triac is switched off.

    7.) What is this happening? Why doesn't the voltmeter read different values of Va and Vb ?
  2. SgtWookie


    Jul 17, 2007
    This is not a safe circuit. You must include a transformer for isolation from mains power.
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