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Click image to see the larger schematics
Description:
The figure shows the circuit, shamelessly copied off the datasheet provided by Microchip.
I have been more inventive with the parts. I had to get a modern P channel MOSFET from Texas Instruments because old hard drive boards were seriously deficient in this one critical component.
However, using the parts as specified would be necessary to get 1. A more compact layout 2. higher efficiency.
As it is, my circuit is small enough to fall off the desk and be lost among the crud on the floor. I feel an increase in efficiency to 90% would be wonderful, but three points less is good enough.
This small integrated circuit has a maximum tolerable input of around 12 volts. It has terminals for driving external power devices, and that makes it more versatile.
For example, replacing that inductor with a transformer and arranging things so that the bulk of the power and voltage is handled by a second hefty transistor and diode can make this little circuit control a power supply operating off the rectified mains.
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