1.Schematic and Working :
The heart of this light bulb is a very small 4 legged IC QX5252F. It works very similar to"Joule Thief "circuit.
But the advantage of using this chip is that ,it does not require a bulky and heavy toroid.It do the same job using only a simple inductor, single AA / AAA battery and a LED.
Most of the solar garden light uses this small intelligent chip.I came across these ICs when one of my Instructable friend talk me about this and send the data sheet and information.
Pin-1 -> Solar panel positive terminal
Pin-2 -> Battery positive terminal and one leg of Inductor
Pin-3 -> All ground ( Solar panel,Battery and LED negative terminal)
Pin-4 -> Other leg of Inductor
You can downlod the QX5252F data sheet
2.Bread board testing :
Before soldering the Circuit,It is always a good idea to prototype any circuit on a breadboard. This lets you check to make sure that all of your components are working perfectly.
Make the circuit on your bread bard as per the schematic.The LED should not glow if the circuit is correct.
To simulate the dark condition,cover the solar panel with your palm.Now the LED should glow.
3. Output Waveform and Observations :
To check the performance of the circuit, I remove the LED and hook up my Oscilloscope probe.
The output is not a steady DC voltage but a voltage that fluctuates rapidly.In my case the frequency is around
184.5 KHz. The peak to peak voltage is nearly 7.28 V and the average value is around 1.0 to 1.20V.
Note : If you try to measure the voltage by a normal meter,it will show near to your battery voltage.Because your meters only measure the average value of a fluctuating voltage
4. Parts Selections :
1. Battery :
You can use any AA or AAA rechargeable battery.As per my experience I can sayeneloopbatteries are the best one.They are sold in pre-charged condition, so that you can use it directly after purchasing just like an standard alkaline battery.It can be reused up to 2100 times. When they weren't in use,could hold their charge for a lot longer than traditional NiMh battery.It can hold 70% charge after 5years of use.
For more details on eneloop batteries click here
Though a standard alkaline AA battery also works,but you can not charge the battery from solar power.
2. Solar panel :
Rating : A 2V solar panel is perfect for charging a AA NiMh battery (1.2v).Along with solar panel voltage,the current rating is also very important.Higher the current rating quicker the battery will charge.
I used a 2V,150mA solar panel.Choose according to your choice.
Size : Be sure during buying that the size of the panel is perfect to sit over the lid.In my case it is 55.1x55.1x3.59mm
3. Inductor :
The LED brightness can be controlled by using different values of inductor.
As per data sheet LED Power =( 2* Vbat / L )* 10^-6
As per my observation 33uH and 47uH works good for these 0.5W straw hat LED.
You can also try with other value and let me know which value works good for you.
I used a 0.5W stray hat white LED.It produce very bright light.I can say a single LED with fully charged battery is enough for basic lighting need.For specification of the LED I used is shown in the above picture.
You can also use a standard white LED but it will not produce sufficient light.
5. DIY Kit :
Made a DIY kit to help the society.
It will useful in the following areas
1. In rural area to replace the harmful kerosene lamp
2.Disaster management (Flood, Earth Quake etc )
4.STEM Education for child ( The entire kit will be distributed in school,student will assemble it and use their own creation to make an enclosure from waste materials )
Others steps can be found from my Instructables page