Voltage regulator
Introduction
A story
Imagine you could only eat purple-colored fruit - fruit of any other color would give you a stomachache. If you lived in a place where plums trees were everywhere, this wouldn't be too terrible, since you'd always have food to eat when you needed it. But if you lived in a place that only had a few plum trees, you'd have to walk back and forth to get plums at that spot every day, and worry about traveling because you might get hungry while you're in place without plums. If you came across a new fruit - say, grapes - you'd have to take the time to check out whether its color was purple enough for you to eat...
Now imagine that
Now imagine that someone came to you and said "
maybe some grapevines in the town, yo
The XO is designed for children in developing nations - kids who may not live with easy access to a reliable power grid they can charge their laptops from. In these sorts of conditions, the ability to plug any power source (a solar panel, a diesel generator, a car battery, etc.) into a computer and have it "just work" and charge it greatly expands the types of conditions under which the XO can be used. Think of it this way; it's like being able to eat a wide variety of foods (and get energy from them) as opposed to only being able to eat (for example) purple-colored fruit.
Actually, most laptops can only "eat purple-colored fruit," in the sense that you have to provide a very precise voltage and amperage into them to have them charge properly (and not explode). The XO is already
The XO is already designed to accept power from a wide range of inputs
Why
- power into xo without frying
Requirements
Input
We used this information on possible power input to guide out input requirements for the voltage regulator:
| Attribute | Bicycle Power [David Gordon Wilson. "Bicycling Science: Third Edition" The MIT Press. Cambridge, MA. 2004] | Cow Power [1] | Solar Power [http://wiki.laptop.org/go/Product_News#Solar_Panels} | Car Battery |
|---|---|---|---|---|
| Voltage | ~15V steady, 60V max | 12V steady | 14-17V steady | 12.7V steady |
| Current | 20A max | 10A steady | 0.35-3.6A steady | Adjustable |
| Power | 40-200W steady, 400W max | ~120W steady | 5-60W steady | - |
Steady State Requirements
- 17-18V
- 10A
Design Requirements
- 60V
- 20A
Output
- (single) XO power input - ideal is 18V at 0.944A. (Laptop can accept 17W maximum, 11-25V and 2Amax but lower current = lower resistance losses.)
- "overflow" wattage should get switched out to another place - by default some sort of dissipator (whonkin' power resistors with a big heatsink?) that's easily bypassed in favor of something useful like a battery.
Parts
Current recommended
The current recommended voltage regulator is a L200.
- Digikey: 497-1382-5-ND ($1.92 USD each when purchased individually)
- datasheet (pdf)
- application notes (pdf)
Benefits
- can handle up to 60V, which is around the surge you'd expect when you start up a human-powered source (for instance, the spike from a bike-power generator when you start to pedal)
Open questions
- what is its behavior at spikes over 60V? constant input?