The simple solar garden lights (made in China) often consist of only 1 LED, 1 small solar panel and 1 (1,2V) NiCd or NiMh battery. This circuit shows how you can “boost” this circuit by switching a power LED on. This power LED is supplied by a seperate (more powerful) solar cell, that charges a more powerful battery. A BD 139 and a BC 547 work as current amplifiers (Darlington). Of course you can also make it in such a way that the garden light, when it becomes dark, switches something else on, e.g. with a 5 volt print relay instead of the power LED. Possibly you need a series resistor to the relay (with voltages higher than 4 Volt, value between 20 and 100 Ohm, depends on the coil resistance from the relay). More simple transistor circuits in my book “Schematics 1″, available on the Lulu website. Content: www.lulu.com/content/ 4734386.
nb: “treasure voltage” = treshold voltage
nb: The reason that I used an LDR is that these garden lights are high frequency oscillators (like the joule thief). So it is an oscillating system and every external influence (even tiny influences) can damp the oscillator and stops its oscillation. So I took the “sure” way to make the circuit work. Perhaps a very slight coupling via a small value capacitor can replace the LDR and drive the Darlington properly. I encourage everyone to experiment and publish a circuit on a YT channel.
Post time: Jun-13-2017