Circuit 2

This project uses the components
from a
Solar Light circuit 2.

The Solar Garden Light can be bought for less than $5.00!!
No kits for this project are available.

These are the pages on SOLAR CHARGERS:

1. Solar Charger
2. Solar Light
3. 5v Solar Power Supply - Circuit 1
4. 5v Solar Power Supply - Circuit 2 - this page
5. Solar Charger - Push Pull circuit 
6. Solar 5v Supply using 2 Garden Lights

See also an article on hand-cranked generator

5v Solar Power Supply Circuit - 2

This project uses components from a Solar Garden Light with a circuit similar to Circuit 2 in our Solar Garden Light project.
These lights can be bought for less than $5.00 in most $2.00 shops or similar shops that sell general household items.
We are also using the housing for this project as we could not buy the case, battery, solar panel and electronics for $5.00 in an electronics shop.
We have already described the operation of the Solar Circuit - 2, and shown that it will produce peaks of more than 40v if the LED is removed from the circuit.
We can use this characteristic to produce a 5v power supply suitable for a microcontroller project or an amplifier or FM transmitters etc.
The circuit we have designed will produce a 5v output @ 15mA. If a higher current is drawn, the output voltage will drop to 4v @ 15mA.
The components we have added are shown in grey in the diagram above.
All you have to do is remove the LED from the circuit and add a signal diode, electrolytic and 3 LEDs.
If you add three red LEDs, the maximum voltage will be 5.1v.
This can be called a zener reference output and as soon as a load is connected to the circuit, the voltage will drop and the LEDs will turn off.
The LEDs are a safety feature to prevent the output voltage rising to 40v!
Do not remove the LEDs as the voltage will rise and if you connect them to the fully charged electrolytic, they will be damaged.

The operation of the circuit has already been covered in the Solar Garden Light article.
The added signal diode rectifies the pulses to charge the electrolytic.
The LEDs provide a maximum output voltage by using their accurate voltage of 1.7v per LED (for a red LED) to create a 5v supply.
Other LEDs can be used to create a supply up to 20v or more.
As the voltage increases, the current you can draw from the circuit decreases.

The purpose of the diode between the battery and the circuit is to prevent "back-leakage." When light is not falling on the solar panel and the battery is charged, some current may leak through the panel and discharge the battery. You have to find out if the panel you are using has a slight resistance (back-resistance) when in the dark. The 220k biases the BC 557 off when light falls on the photo resistor as any slight conduction of the BC 557 will turn on the BC 338 very slightly and discharge the battery.

In future articles we will present a microcontroller project and an FM transmitter that uses this solar power supply.
Keep returning, as the links will be added to the top of this page.

Colin Mitchell