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Old 30th July 2013, 02:21 PM   #1
Koenjer is offline Koenjer  Netherlands
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Default LT1963 - Pre Regulation

Hi there,

After reading the linear-audio test about different powersupply's, i'd like to test the LT1963 in my preamp.

The preamp needs +18v and -18v. Rotel puts in 7818/7918 as standard regulators.
And the input voltage on the 78/79 is around 22volt.

The LT1963 has a maximum input of 20v.
Is it wise to use the 7818 as a pre regulator and after that let the LT1963 regulating around 17v?

Or are there any other better solutions?
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Old 30th July 2013, 05:31 PM   #2
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Use diodes in series to drop out 2v or so? //Maybe use mosfet, one common type mosfet should dropout enough voltage.
How do you plan to regulate negative rail then?
Is the trafo with dual secondaries? If it is, use the regulator you wanted to with both rails, something like in attached schematic. (Don't pay attention to missing elements and using LM317 macro.)
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Last edited by Headbanger; 30th July 2013 at 05:50 PM.
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Old 31st July 2013, 08:27 PM   #3
sonidos is offline sonidos  United States
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LT3015 is negative reg. I am working on 317/337 to drop enough voltage to safely provide the appropriate Vin to 1963/3015
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Old 3rd August 2013, 11:02 PM   #4
agdr is offline agdr  United States
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Originally Posted by sonidos View Post
LT3015 is negative reg. I am working on 317/337 to drop enough voltage to safely provide the appropriate Vin to 1963/3015
That setup works really well. I'm using it on this project

A version of an O2 Desktop Amp (ODA) (schematic is first picture, power supply section at the top)

with the 317/337 pre-regulators set up to produce +/-18.5Vdc, then the LT1963A/LT3015 produce +/-16Vdc (and +/-7Vdc, two switch positions) as the final regulators.

The LT LDO's only need around 0.5Vdc drop, so for the OP's circuit he could do the same and set the pre-regs at 18.5Vdc. That would still leave 3.5V across the LM's, which is probably about the minimum. I usually try for at least 5V across them to hit all the datasheet ripple specs.
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