MOSFET-based DC regulator
Bobb Fwed
Posts: 1,119
I am using this piece on a project I am working on: MCP73862 (datasheet). It uses a very ingenious design with it's regulation. It uses a p-channel MOSFET for voltage regulation. This means almost no wasted energy for down-stepping voltages. A linear regulator outputting 1A will draw 1A (plus overhead) no matter what the input voltage. This design allows the input current to scale with the voltage thus netting a similar wattage (in and out). The IC (above) is setup to do up to 1.25A, but I am very confident the regulator could do much more (seeing as there is relatively low heat dissipation (practically none at 1.25A) with a good MOSFET).
Does anybody know if there are regulators (say, in a TO-220 package) that are designed like this? The benefits are massive, way less power consumption (especially if using a high voltage input, or high current output), and almost no heat generation. With a high voltage (55V or higher), 17mOhm MOSFET, it should be simple enough to control a 55V input at 10A. Some hefty capacitors would be very helpful on the output, but if the controlling frequency is high enough and power noise shouldn't be a problem.
I have parts ordered (mainly the p-channel mosfets) and I am going to attempt to make a propeller object to mimic the function of the regulator. It shouldn't be too difficult, a couple resistors to set the voltage and some CTR work should be able to do with fairly well.
Any info on an existing regulator that works this way could save me some work (though it won't--I'm going to try to do it myself anyway). Or any input on design or easy implementation would be helpful.
EDIT: fixed datasheet link (should have tested it when I created the link).
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April, 2008: when I discovered the answers to all my micro-computational-botherations!
Post Edited (Bobb Fwed) : 5/30/2009 8:38:58 AM GMT
Does anybody know if there are regulators (say, in a TO-220 package) that are designed like this? The benefits are massive, way less power consumption (especially if using a high voltage input, or high current output), and almost no heat generation. With a high voltage (55V or higher), 17mOhm MOSFET, it should be simple enough to control a 55V input at 10A. Some hefty capacitors would be very helpful on the output, but if the controlling frequency is high enough and power noise shouldn't be a problem.
I have parts ordered (mainly the p-channel mosfets) and I am going to attempt to make a propeller object to mimic the function of the regulator. It shouldn't be too difficult, a couple resistors to set the voltage and some CTR work should be able to do with fairly well.
Any info on an existing regulator that works this way could save me some work (though it won't--I'm going to try to do it myself anyway). Or any input on design or easy implementation would be helpful.
EDIT: fixed datasheet link (should have tested it when I created the link).
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April, 2008: when I discovered the answers to all my micro-computational-botherations!
Post Edited (Bobb Fwed) : 5/30/2009 8:38:58 AM GMT
Comments
-Phil
If what I'm working on works correctly, I think I could make something that size. I wouldn't use the Prop for a long term solution, but rather a CMOS logic IC an opamp and a couple resistors should do the job. But that's just speculation until I build one (maybe Monday).
I also expect (as I said above) a much high current rating, as well as a fairly wide voltage input range. The voltage will probably be limited by whatever method I use to get a reference voltage.
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April, 2008: when I discovered the answers to all my micro-computational-botherations!
Post Edited (Bobb Fwed) : 5/29/2009 9:38:17 PM GMT
Looking at that IC, it uses the P-Channel MOSFET in a series linear regulator. Look at the power dissipation calculations on Page 18/19 of the data sheet. The MOSFET is simply working as a resistor and chucking the heat out into the package. Worst case, with a one-cell load and a 12V input the package is going to try and dissipate 9.75 watts and go into its internal thermal throttling mode.
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"VOOM"?!? Mate, this bird wouldn't "voom" if you put four million volts through it! 'E's bleedin' demised!
Bobb, if you want to do a switching regulator from scratch, you might want to check out National's "Simple Switcher" product line.
-Phil