![]() ![]() The 3 cm x 3 cm one from this example generated 2.7 volts in full sunlight with a short circuit current of 17 mA. Which also means the solar panel can be a cheaper low voltage version. The use of a single AAA NiCd rechargeable cell keeps the cost down. The circuit pulses the small inductor to step up the voltage to drive the LED in a similar way as a Joule Thief circuit. The YX8018 is more or less just a gated oscillator which runs at approximately 200 KHz driving an open drain NMOS switch ( output on pin1 ). The YX8018 comes in a 4 pin transistor style TO-94 package and the pin configuration is shown here: The complete circuit is shown in figure 2. ![]() Inside the example I deconstructed was a single 1.25 volt 100 mAh AAA NiCd cell and a small PCB with the LED, a 220 uH inductor, and a four pin voltage boosting integrated circuit marked YX8018. The LED comes on when it gets dark and the solar panel is no longer able to charge the battery, so there has to be some sort of control circuit inside to do this. A typical most inexpensive example, as shown in figure 1, costs as little as $1.00 but maybe up to $2.00 each. Looking from the outside, they generally consist of a small solar panel to charge a battery and a high brightness white LED. ![]() Solar rechargeable LED garden or pathway stake lights have become very inexpensive and common place. You can file this blog entry under exploring interesting bits of electronics hidden in everyday household items much like these two previous entries on using coin cell batteries and flickering LED candles. ![]()
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