So while making my robot I came across some 18650 lithium ion cells. I designed and made a working charger for pairs of them wired in parallel.
Because of the much greater complexity of making a series cell charger, I would like to power my robot from these cells wired in parallel, at 3.7v - 4.2v.
To accomplish this, I want to make a boost converter to convert the 3.7v to something like 8-8.5v. Current draw would be about 2 amps maximum.
How do I make a boost converter? I've searched around, and can't figure it out. There's plenty on upping 1.5v to 3v, but none on the voltages I need.
Also, is an inductor necessary? I've got plenty of NPN and PNP transistors for use, as well as 4 555 timers if those would work.
In most cases a switching setup-up converter is used for such applications. One example: http://www.onsemi.com/pub_link/Collateral/NCV33163-D.PDF. An inductor is needed to get higher voltages than you have on the input. Most of the switching converters can be configured for step-up and step-down circuits and have quite a broad voltage range.
I should clarify, as my original question wasn't phrased very well. I know how to make the boost converter circuit, I just need some help figuring out which values to use on the components.
liquidlightning:
I should clarify, as my original question wasn't phrased very well. I know how to make the boost converter circuit, I just need some help figuring out which values to use on the components.
I doubt anyone could just toss out component values without seeing the circuit.
http://www.daycounter.com/Calculators/Switching-Converter-Calculator.phtml
will give you all the equations needed.
Building boost converters is not a trivial task, and you really need to know what you are doing.
The inductor is a critical part, and you need the right sort of ferrite with a sufficiently high current rating to ensure
that core saturation does not occur under worse state conditions.
ie maximum current draw at the output with mininum input voltage.
That's not a usable circuit unless you just want to create some high-voltage sparks or something like that. You need an oscillator and some feedback to control the pulse-width and output voltage... You either need a boost regulator chip, or a ship-load of more components!