Four pin BJT IC?

Hello there,

I am trying to re-engineering a pretty basic circuit for a solar cell outdoor lamp. It's just a diode, resistor, a battery and the solar cell. But it has a four pin IC which I guess is a BJT? Maybe some sort of Darlington configuration? Hope you can shed some light on it.

My immediate guess is that the battery supplies through the resistor current to diode, and the transistor is used to plug in the solar cell when it is not providing current.

I have uploaded a picture of the PCB here:

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Thank you

A solar garden light uses a voltage stepup circuit usually using an inductor (that looks like a resistor) to stepup the 1.2V from the battery to light a 3.5V white or colours-changing LED. The voltage stepup circuit is turned on and off by a circuit that detects ambient light usually using an LDR but some detect light on the solar panel.

The 4 pin chip has to produce 3.6v, detect sunlight via the solar cell and possibly have a diode between solar cell and battery to prevent discharge.
Since there is only 1 inductor, the 4 pin chip has an oscillator.

The following circuit uses a transistor to turn on the oscillator:
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This circuit employs an oscillator to produce the high voltage:
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You will have to combine the features of the two circuits.

If the resistor looking component indeed is an inductor, I am a bit puzzled about why there is only 1.3V across the diode?

The diode blocks the battery from discharging into the solar panel in the dark.

Uh, I'm sorry for the confusion, I meant the white LED - not the diode. There's a 1.3V drop across the LED.

You cannot accurately measure the voltage across the LED because it is pulsing on and off at a frequency that is too high for a meter to measure. The voltage of a white LED when it is turned on is about 3.6V.

That is of cource true, dunno why I didn't though of that. I will have my probes back for my scope next week I hope, and I'll have a look at it.

Thank you