User Manual

Required parts: Solar cell, BC557 transistor, 4K7 resistor (yellow, purple, red, gold),

yellow led, battery holder for two AAA batteries,

How it works: When the sun shines, a current

flows from the (+) of the solar cell via the

Emitter/Base of the transistor trough the

batteries and back to the solar cell. This is the

Base current, indicated with the dotted line. In

our example, the Base current will also charge

our batteries. The fact that there is a current

flowing between Emitter and Base causes the

transistor to turn on and fully conduct, as if it

were a switch. Hence, a current can flow from

the solar cell via the transistor Emitter/Collector

and resistor to the led and back to the solar cell.

This current causes the led to light (solid line).

SOLAR CELL

BC557

4K7

or an ge led

For advanced users:

The led turns off when the batteries are removed. Why ?

In the simple battery charge circuit, there was a diode to prevent

discharging of the batteries in low light condition. In this circuit, it has

been omitted. Why ?