Switching Voltage Regulator question

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60amp_relay
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Switching Voltage Regulator question

Post by 60amp_relay » Sat Sep 04, 2010 5:56 am

I'm trying to figure out which parts I need to make a switching +5V voltage regulator. Up to this point, I've always used an LM7805 linear regulator, which works great at low currents. But the current draw on my latest project is around 0.8A. The LM7805 generates too much heat in this situation, and can't consistently maintain +5V without active cooling. So I'm looking at building a switching regulator around an LM2575.

The schematic for the LM2575T-5 lists 4 external components: 2 caps, 1 inductor, and 1 diode. The caps are easy, but I'm not sure about the other two parts. What kind of inductor and diode do I need to get? When I look for inductors, I find everything from ferrite beads, to RF chokes, to toroid inductors. Which of these does a switching regulator work with? For the diode, does it need to be anything special? Zener, schottky, etc?

gm
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Re: Switching Voltage Regulator question

Post by gm » Sat Sep 04, 2010 6:41 am

Take a look at the data sheet. Under "Test Circuit and Layout Guidelines" it tells you how to size the inductor and gives recommended manufacturers and part numbers. Same with the diode.

HTH,

gm

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leon_heller
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Re: Switching Voltage Regulator question

Post by leon_heller » Sat Sep 04, 2010 7:55 am

Nat Semi has a very useful on-line design facility for their switchers, that will tell you what to use. Make sure you use their suggested PCB layout, unless you really know what your are doing; switchers are rather fussy.
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tecoist
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Re: Switching Voltage Regulator question

Post by tecoist » Sat Sep 04, 2010 10:04 am

60amp_relay wrote:Which of these does a switching regulator work with? For the diode, does it need to be anything special? Zener, schottky, etc?
Yes, the diode needs to be something special. The datasheet includes suggested Schottky diode part numbers, suggested inductors from several vendors, and a nice discussion of capacitor parameters. All the information you need is in the datasheet, and they explain why they recommend their choices. It's a good read.

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