dark activated switch

Thread Starter

conntaxman

Joined Oct 30, 2009
12
Im looking for a cir. for a Dark activated switch, using a TIP120 Darlington Transistor. Im making a 10 LED flood light , the LED will draw about 1 amp. I have some of the tip120 and they say its good for 5 amp. I'll be using a 12dc battery to run the system.I really don't want to use a relay with a coil.I'll be using a cds cell or could use led's to detect the light.
I looked on google and cant find a cir. and I don't play around enought to make a cir, so I will leave that up to the wisords. LOL
tks
John
 

Wendy

Joined Mar 24, 2008
23,457
You will need a good heat sink on the transistor, it can be a clip on if it is not enclosed.



You didn't specify the current specs on the LEDs, which will also affect R2's value. I figure a nominal value for R3-6 is 20ma, which would mean those resistors are around 100Ω, and R2 would be around 1KΩ. You may have to go as low as 47Ω for R3-6 due to using a Darlington.

If the LEDs are 1A parts, which is unlikely, I would change the driver circuit entirely.

R1 is around 100KΩ.

I would use either 9 or 12 LEDs, if you must use 10 LEDs then remove D9 and D12, then recalculate R5 and R6 to match.
 

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Wendy

Joined Mar 24, 2008
23,457
OP specified the part, you plan on using the part the OP specified. Works that way in industry too.

A MOSFET would be better, agreed.
 

Thread Starter

conntaxman

Joined Oct 30, 2009
12
You will need a good heat sink on the transistor, it can be a clip on if it is not enclosed.



You didn't specify the current specs on the LEDs, which will also affect R2's value. I figure a nominal value for R3-6 is 20ma, which would mean those resistors are around 100Ω, and R2 would be around 1KΩ. You may have to go as low as 47Ω for R3-6 due to using a Darlington.

If the LEDs are 1A parts, which is unlikely, I would change the driver circuit entirely.

R1 is around 100KΩ.

I would use either 9 or 12 LEDs, if you must use 10 LEDs then remove D9 and D12, then recalculate R5 and R6 to match.
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Hi Bill. the LED F.C. is 1 amp x 12vdc. You are using a 555. could I replace that with the TIP120 Darlington tran. why i want to use this is because i have some and no sence to not use .But if I can find another cir, i'll use that. Some one said use a mosf.
I just want a cir to build the light im making, all or most cir, that I find are using relays, and i dont want those.
tks
John
 
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