Whadda WSEDU02, Инструкция по сборке

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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
BC55 7
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 ?