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Solar charger problem.

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al98

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Hi,

I am trying to make my own solar powered garden light using a 4.5v 60mA solar panel incorporating a comparator with hystereis. The circuit works well, as the light level falls to a certain threshold the LED turns on.

My problem is as the battery slowly decreases the turn on time of the comparator drifts. I was thinking of using a zener diode to establish a constant reference voltage to the input of the comparator but since the desired turn on time of the solar panel is so low at around 0.15v a zener cant be used to establish a threshold.

I don’t know how clear this is but can anyone suggest anything?

Thanks.
 

laktronics

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Hi,

You should use the output from the standby battery to generate the reference. Use a high value resistor divider network ( to reduce the lading on the battery) and generate about 0.15V and connect to the comparator input as reference. Since the comparator input has high input resistance, it will not practically load the divider network.

Regards,
Laktronics
 

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