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Light Dependant Circuit

vick5821

Jan 22, 2012
700
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Jan 22, 2012
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700
Anything wrong with this circuit ?? I constructed it but seems not working. One more question, can I replace the 558 PNP transistor with 557 PNP ?? Thank you

LightDependantCircuit_zps680ae702.png
 

MrEE

Apr 13, 2012
84
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Apr 13, 2012
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Based on this circuit, it looks to me that the intention is to turn the LED on when it gets dark. I recommend inserting a base resistor on Q1 (1k to 4.7k).
A BC557 works as well. It just has a higher Vce rating (45 V, vs. 30V)
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
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The first thing I would do is insert a base resistor as suggested above (between the base of Q1 and the collector of T1).

The next thing I would do is remove the LDR. The LED should turn on. If it doesn't then you may have wired something up incorrectly.

Check very carefully that you have selected the correct transistors, they are in the right place, and that you have identified base, collector, and emitter correctly. These are probably the easiest things to muck up.

What voltage is your power source?

Incidentally, we would normally designate transistors as either T or Q, so you would have T1 and T2, or Q1 and Q2. This is a minor point -- since they do have different names and designations so it's not confusing (just odd).
 

Terrance

Feb 4, 2011
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Feb 4, 2011
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my opinion is that you put R2 in between LED and LDR and then open the circuit and watch, is it work?
i hope you like my opinion!
 
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