# PWM Solar Charger Circuit

## A request for a solar pwm solar battery charger circuit made by one of the user is discussed below, an appropriate circuit design for the same may be seen at the bottom of the article.

I have been reading your posts for hours upon hours looking for the exact design or how I can put multiple circuits together to create a safe autonomous solar charger. I see a lot of good partial circuits, but what makes it hard on putting them together is that you use the 555 timer for a PWM signal. I will not be interested in using the LM555 but rather the TMS320C2000 MCU Experimenter Kit that has an F28x controlCARD, http://www.ti.com/lit/ml/sprufr5f/sprufr5f.pdf ,and digitally create the varying PWM signals depending on solar radiance. Thus I will need to monitor the voltage levels of the solar panel, battery bank, and the 5V device to charge with the MCU.

I would like to change the PWM converter to a buck converter. Also The solar panel I will be building will have about a 2.5V output that I need to boost to 5V. As far as amperage output goes I would say possibly 1 amp Max. But testing will have to be done to ultimately calculate that. I don’t see the amperage varying more than +/- 0.5 amps. Guess components that would be able to handle a 2 amp load would be sufficient?

The reason I’m making a solar panel with 2.5V output boosted to 5V, and correct me if I am wrong, is to have as much amperage as possible to the device. Each solar chip has an open cell voltage of 0.52V and a short circuit current of 75 mA. If I didn’t boost the voltage and made a 5V solar panel would I have more current or less current?

I will be charging an internal bank of two 3.7V Li-Ion batteries that have an Ah rating of 2.6 Ah each; as well as a 5V device hooked up to the solar charging unit.

I would like to have automatic charging of both the internal batt bank(with an indicator circuit, red(0-33%), yellow(34-67%), green(68-100%) and the connect 5V device simultaneously for charging. When the batt bank is fully charged the circuit should trickle charge the batts maintaining voltage, while continuing to charging the 5V device. Then trickle charge/cut off the 5V device when it’s fully charged until it is removed.

If there is no sun out or not enough sun, then I would like the internal battery bank to discharge. The battery bank will either supplement the low solar voltage or be the sole source of power(like at night) to charge the 5V device.

Definitely need overload protection as to not send current back into the circuitry of the device.

This PWM Solar Charger Circuit must be completely autonomous and safe as to protect the circuit and the 5V device.

The proposed solar pwm charger may be seen in the following design: