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Old 23rd May 2002, 08:45 PM   #1
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Default Regulators for digital circuits

From checking out the schematics I noticed that most designs are using IC based regulators in digital circuits. I've been using LT 1085 and 1033 regulators in my recent projects but currently I'm looking for something better, preferably discreet circuit. Any suggestions?
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Old 23rd May 2002, 09:29 PM   #2
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LT1762 at <20uV noise, a 17dB improvement over LT1085. 150mA.

LT1964 for negative. <30uV, 200mA.

These are so cheap, small and require so little in the way of support components that you can place a lot of them throughout a board, close to the chips you are powering.

Look through the rest of Linear's catalog; there are some higher power chips that still provide better noise performance than LT1085.
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Old 23rd May 2002, 10:56 PM   #3
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Default Discrete regulators

I have some ideas for you, but not enough time today. Hold on, ok?

Jocko
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Old 24th May 2002, 02:04 AM   #4
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Glad I got you interested, Jocko.

Tiroth, how they compare sonically to LT1085?
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Old 24th May 2002, 03:40 AM   #5
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Put up some of the design parameters you think are important to your application, and stuff like current draw might help, too. I'll keep track, but may miss some stuff while out trying to make a buck.

Jocko
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Old 24th May 2002, 05:35 AM   #6
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I'm building CD transport based on Philips CD PRO 2 module. Servo decoder and DAC voltage is 5V with 250mA max, motors and actuators 9V, 200mA with 750mA for 2 sec. I also include separate DAC based probably on PCM1704 with +/- 5V requirements. The most important parameter to me is the sound of the supply.

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Old 24th May 2002, 02:38 PM   #7
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Question Multiples regulators ?

This is a little bit out of topic, but I was wondering if overall performance of digital audio boards would be improved if we assign one regulator for each IC on a board...

What I have in mind is a preregulator with heavy cap filtering (ripple and RF rejection) and ferrite-beaded on both input and output. This output is distributed all over the board. As close as possible to each IC on board, the preregulated voltage enters a local regulator through a ferrite bead (or an inductance) and a light bypassing ('lytic cap + SMT ceramic cap). Output connected to the supply pin(s) of the IC, with a "Goudreau triplet" (120uF/25V/Panasonic HFQ -or FC- // with stacked SMT 0612 ultra low inductance 270nF/Z5U and 10nF/X7R ceramic caps)...

Has someone here already tried this configuration ? Sould we use high quality local regs, or is the 78LXX series good enough in this config to do a nice job ?

Oh, for the "Goudreau triplet", see here
(Pete Goudreau has done a wonderful job in the 90's improving the performance of Parts Connection's Dacs. A worthwhile reading Click the image to open in full size.)
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Old 24th May 2002, 03:39 PM   #8
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That's what I did in my recent DAC. Ea. IC has it's own separate PS from the start: transformer, soft recovery diodes and filter caps. I have total 8 transformers with 16 separate winding altogether and 64 soft recovery diodes.
On the board there are 1000uF HFQ in parallel with .22u caps as close to ea. chip as possible. Active regulators are LT1085 and 1033. I went as far as providing separate regulators for dgital and analog section of PCM1704 DACs which are also paralleled.
This had a quite noticable improvement with better definition and tighter bass.
Overall the sound is exceptional.
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Old 24th May 2002, 04:42 PM   #9
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WOW!!! Monster design !

Did you use the 1000uF HFQ in input or output of the regs ? Both ? Any ferrite/inductance ?

And did you use toroids for yout transformers? I was told they are too wideband for digital (Noise can pass through, back and forth between xformers)...
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Old 24th May 2002, 04:44 PM   #10
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Default Separate regulators

Have one large supply, and smaller regs next to each part.

By parameters, I was refering to transient response; impedance-how low and over what bandwidth; regulation. Stuff like that.

Jocko
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