Hi All.
Anyone able to help with this small LDR circuit please?

I am building/have built, this simple photo switch for the instrument lights on my m/bike to turn the lights off during the day.
I am using J3Y smd transistors and 5730 SMD leds.
The cuircuit works fine for one led but when I connect all 4 it dies.( It's cooking the transistors I think)
I am aiming for 130mA and 3.1v on the led from a 12v source.
I am using a 500k photo resistor(LDR)(variable resistor in schematic) at around 70% for lights on.


TIA.
Darren.

 

So your one LED is pulling 142 mA. adding 3 more will pull 4*142 mA. How did you come to select 60 ohms as your current limiting resistor value? I'm guessing your LEDs have a Vf of something like 2V and your resistors should be something like 470.

Do you understand how to select the right resistor value for your LEDs? And, if your transistor didn't go first, your LEDs wouldn't last very long.

 

Hi Philba.
Thanks for your reply.
As mentioned the vf is 3v and trying to achieve 130mA.
In the electrodroid app it suggest 67R for these values.

 

False alarm.
Apparently it is still working. Just my phone light is not enough. In daylight it's working awesome.
Thanks.

 

Hello,

What is the exact details of the used leds?
Here is a comparison between some chinese leds and branded leds:
http://led-obzor.com/led/smd-led-3528-5050-5630-5730

Bertus