DC/DC Voltage boost from solar panel

Discussion in 'The Projects Forum' started by russpatterson, Feb 12, 2010.

1. russpatterson Thread Starter Member

Feb 1, 2010
351
16
I'm starting a project to do a DC/DC boost from a solar panel. I want to make small panels, ~16 watts, with the .5V, 4A cells you can get for cheap on eBay. So my voltage out of the panel will be around 3.7v ~ 4.5V. I plan to run this through a filter cap and power my PIC and logic.

I plan to use the PWM on the PIC to boost the voltage so that I can use the panel to drive motors, charge batteries, etc. I know there are DC/DC boost IC's but I've already need the PIC for other functions and I want to learn the ins and outs of voltage conversion. I need to be able to vary the output voltage from about 10V to 18V depending on the load and available current coming from the panel. So current would vary from around .8A to 1.6A.

I've done a bunch of reading about boost converters, inductors and magnetic fields. So the basic circuit will look like this:

Where I'm confused is where to start as far as what specs I need for the inductor and what PWM frequency to start at. Do I vary the duty cycle on the PWM or just the frequency? How do I spec the diode and cap too?

It seems if I use a higher frequency I can use a smaller inductor?

If anyone can point me at some information so I can learn what values are necessary for the voltages and currents I'd really appeciate it. Thanks!

2. SgtWookie Expert

Jul 17, 2007
22,183
1,728
Here's a great page for you:
http://www.dos4ever.com/flyback/flyback.html

You'll learn a lot going through these experiments. Start with the inductor test bench, then the boost converter, then go on to the flyback converter.

3. russpatterson Thread Starter Member

Feb 1, 2010
351
16
Thanks! This is great.

4. russpatterson Thread Starter Member

Feb 1, 2010
351
16
I bread boarded up the boost converter and was able to step up my 12V battery to over 100V but I need to figure out what I'm looking at on the scope. I want to understand what my scope will look like when I'm saturating the inductor and just generating heat by running current through the inductor to ground.

This picture is using a 1.5mH inductor, 100Khz, 50% duty cycle; it outputs 42V with a 100K ohm load.

Here's one with all the same setup but a 33% duty cycle. Where's the voltage spike coming from when I close the switch?

What should the scope look like when the circuit is setup optimally?