Photosensitive Relay

Thread Starter

haditya

Joined Jan 19, 2004
220
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
 

Battousai

Joined Nov 14, 2003
141
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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