Please see the attached image.
I wish to make a switching "front end" for a LINEAR regulator circuit. The linear regulator will be a conventional LM-317 with booster transistor design.
The switching front end is meant to "roughly" control the unregulated INPUT to the linear regulator to minimize power dissipation at low output voltages.
Note: the whole thing (setting the output voltage of the linear side, current and voltage monitoring, control of the switching front end, etc..) will all be done with an Arduino.
Imagine an adjustable power supply of 1.2 to 15 or 18 volts DC at 10 amps or more. Of course the linear regulator needs at least 22 to 25 volts input to account for the regulator losses. Now, setting the regulator to a low voltage like 3.3 and drawing 10 amperes causes the regulator to dissipate over 200 watts!
I expect the switching "front end" to track the output voltage setting (all Arduino controlled) and provide "just enough" for the linear regulator to work without heating the entire house!
I'm not all that great with this type of circuit design, so I would really appreciate any input from you all.
Is anything blatantly wrong? Is there a better way to do it? Are the components I specified really needed? Did I leave out anything that is needed? Should I use a resistor or diode to snub the inductor so it doesn't "snap back" and injure the MOSFET? How should I calculate the best value for the inductor? What is the best PWM frequency to use for this - and why? Should the inductor be air core, iron core or ferrite core? And why?
Note: I made a circuit like this already for a power supply project and I'm not happy with the way it works. The MOSFET seems to get much warmer than I expected (switching time problem?) and a "teensy" bit of switching noise seems to get through to the output, despite the amazing AC rejection capability of the LM-317.
Comments please. Thank you!