Regulator to replace LT1940? - diyAudio
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Old 29th May 2008, 02:17 AM   #1
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Location: Los Angeles
Default Regulator to replace LT1940?

Hi,

I'd like to build a linear psu to replace a 5VDC 2a walwart that feeds an LT1940 dual step down, switching voltage regulator that generates a 3.3 and 1.2 VDC.

I could use an LT1121 for the 3.3V, but haven't worked with 1.2VDC. Any suggestions on a reg so I can toss the LT1940. This powers a cpu in squeezebox and am told that the tolerances must be pretty tight.

thanks!
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Old 29th May 2008, 02:33 AM   #2
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I don't understand why you're making it so complicated. I have a Squeezebox too. You just need another 5V, 2A wallwart. Just get the Elpac that everyone else uses. Why create a "clean" linear supply for something that has switching regulators, anyway?
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Old 29th May 2008, 02:42 AM   #3
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Hi, I don't use anything inside the SB except the cpu and logic. I don't use the dac or analog stage, and I'm planning to do away with the display. So I only need to power the cpu (1.2v) and logic (3.3v). I'd like to do away with the switching reg that powers these. I'm searching for a linear reg to power the 1.2v
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Old 29th May 2008, 03:36 AM   #4
Stocker is offline Stocker  United States
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Diodes. They drop voltage. If you can regulate to 1.9-ish and slap a diode on there, you're done.

Just a thought.
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Old 29th May 2008, 06:30 AM   #5
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The LT1940 is rated for 1.4A, so you need to meet that spec. Go to Digikey and search for a 1.2V regulator with 1.5A or more.

The LT1121 is rated for 150mA. Is that enough, when the original part is rated for 1.4A?
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Old 29th May 2008, 07:46 AM   #6
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LP3892? PSRR and regulation specs are pretty good too.

LT1121 is definitely underspeced. Use the ubiquitous LM317, or pretty much anything else really.
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