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automatic Solar Lamp

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I would like to make a garden solar lamp that automatically turn on when the sun goes down. I tryed first with a transistor s9013 npn (seen on youtube), but it restricted the current, i suspect because of the internal resistance of the transistor.

I decided to try the use of an Op amp as comparator, with a low internal resistance P channel Mosfet. I don't have much experience with these components, and the best way of learning is trying right?

So see below my circuit. My problem is that it seem to work fine when the battery is full but the solar charging doesn't seem to be very efficient (the charge light does turn ON) and the battery looses it's charge fast, leading to a weired blinking LED.

would anyone see a problem with my circuit explaining that?

thank you very much for your help




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The battery is powering the opamp and LED when the solar panel is dark. You did not say a part number for the opamp, Mosfet or driver so we do not know if they will work from only 3.2V to 4.2V.

The 3W LED might use a current of 3W/4.2V= 0.7A and maybe your opamp is actually an audio power amp that has a high current. Then the battery is drained in a few hours.


You learn by reading the datasheets and selecting parts that work together, not by having errors and more errors. 

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I read the datasheets and I don't see why they wouldn't work together, but i'm no expert.

the mosfet is a  SSM3J352F,LF , the opAmp is  LMV321LICT , I got them both from digikey. They are super small and were tricky to weld, I can't exclude that I fried them when I welded. I did 3 lamps and they all show the same behavior, and I think it's unlikely that they are all fried, specially as they work when the battery is charged.

should I put a resistor to the opAmp VCC pin? i'm afraid it will decrease even more the voltage...

concerning the driver it is a 3W LED driver from aliexpress : https://fr.aliexpress.com/item/3W-LED-driver-16MM-DC3-7V-1-Mode-LED-Flashlight-Driver-for-CREE-XRE-Q5-XPE/32627605064.html?spm=a2g0s.9042311.0.0.654f6c37kYHKsp

does anybody have another idea for this circuit? something energy efficient to get the battery last the longest possible.

Thank you very much for your help



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