Why not use a linear voltage regulator? Because it dumps waste heat. We are all about not putting unecessary heat in our computers, right?
As for the cost... it might be a bit more expensive to do the PWM. You'd need (to duplicate my version):
3 56K resistors - $0.99
1 5K resistor - $0.99
1 10K pot linear taper - $2.49
1 0.47uF capacitor - $0.99
1 555 timer chip - $1.49
1 741 opamp chip - $0.89
1 NPN transistor - $0.69
1 IRF510 transistor - $1.99
1 diode - $2.49
1 proto board - $3.99
Total: $17
To build a linear voltage regulation system, you would need:
1 proto board - $3.99
1 LM317 - $1.99
1 resistor (I can't remember what value) - $0.99
1 10K pot linear taper - $2.49
1 heatsink - $1.59
Total: $11.05
Prices are from Radio Shack, which is more expensive than most, but very available. With the above prices, you will also be left with a number of leftover components when building the PWM circuit. As for the linear voltage regulator, not much savings was it?
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