Photosensitive Relay

Discussion in 'General Electronics Chat' started by haditya, Jan 19, 2004.

  1. haditya

    Thread Starter Senior Member

    Jan 19, 2004
    220
    0
    dear sir,
    i m a student of electronics and have a doubt in photosensitive relay circuit using SZIKLAI CONNECTION (COMPLEMENTARY DARLINGTON PAIR).. using BC147(NPN) SK100(PNP) and a LDR (connected between base and Vcc) using voltage divider bias.
    i need to know when which transistor is in cut off and in saturation in regard to light falling on the LDR.
    THANKING YOU

    Aditya
     
  2. Battousai

    Senior Member

    Nov 14, 2003
    141
    44
    If the light illuminating the ldr is sufficient to raise the output voltage of the ldr (the input to the darlington pair) above the supply voltage of the darlington pair you may knock the first transistor into saturation because the base-collector diode will become forward biased.

    The output voltage of the ldr would have to be pretty high to knock the second transistor into saturation.
     
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