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Old 1st November 2006, 08:52 PM   #1
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Default power regulators

What are people using these days for power regulation for national 3886/3875 parts? Are most of you guys doing linear stuff? Has anyone played with more efficient designs? Thx,

D
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Old 2nd November 2006, 12:43 AM   #2
Leolabs is offline Leolabs  Malaysia
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try some LDO regulators such as the 1085 series.
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Old 2nd November 2006, 07:24 AM   #3
Bob0513 is offline Bob0513  United States
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I am pretty sure that most people do not regulate the power for LM3886/LM3875 designs.
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Old 2nd November 2006, 07:33 AM   #4
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Yes, I realize a lot of people don't, but for those who do, what do they use? I don't want to enter the endless debate about whether or not you should regulate your supply (I'm an electrical egineer so folklore doesn't do it for me). The LDO mentioned above looks somewhat interesting. Has anyone ever tried to utilizing the adjustable version of the part to create a +-35V supply using a transformer that spits out 38ish volts? Thanks,

D
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Old 2nd November 2006, 07:41 AM   #5
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Also, the ds for that LDO seems a little strange. On one hand the application circuit states that it's adjustable from 1.2V-15V. The Abs max ratings state taht you can have a 29V input to output voltage differential... Regardless, this part doesn't look like it can give the requisite power output to drive the 3886 to it's maximum potential...
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Old 2nd November 2006, 07:58 AM   #6
AndrewT is offline AndrewT  Scotland
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Hi,
or try capacitance multiplier.

Even substitute a Zener for the final R to create a follower regulator (no feedback).

Or a series combination of R + Z for the final R, produces a two slope regulator that follows a proportion of the input voltage and still retains some regulation and lowish output impedance.
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Old 2nd November 2006, 08:05 AM   #7
Dag is offline Dag  Sweden
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Old 2nd November 2006, 06:57 PM   #8
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The LM338 is capable of delivering 5A. If you have a split secondary transformer and run with seperate rectifiers you can actualy get away with using this regulator for both the + and - rail. I'm working on a desing right now that uses these in front of a pair of OPA549's that amplify +5V from a REF01 voltage reference. The output of the posotive rail is fed to the inverting input of another OPA549 which is set to a gain of 1, and gives you your negative supply. It will automattically track the posotive supply voltage. If you add a pass transistor or two to the LM338 you can get this to deliver at least 10A which is the rated output of the OPA549. The beauty of using an opamp in the supply is that the PSRR helps to further reduce any noise from the regulators.

I attached my current schematic. As you will see I haven't used pass transistor to boost the current handling for the LM338 but it should be a relatively simple addition. This is based somewhat on the power supply for the Gilmore headphone amp over at Headwize. I have just about finished designing the boards and can post them later if anyone is interested.



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Old 2nd November 2006, 08:00 PM   #9
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If the output current of regulators seem to be unsatisfactory for your requirements then paralleling voltage regulators can be a sollution.
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Old 2nd November 2006, 09:32 PM   #10
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I'm currently experimenting with TIs UC3834.

I'm working on a 10A design (per rail, per amp) for a BPA configuration of 4 LM4780.

It's a pretty good ic and until now with good results on regulation. I've tried a complete solution with 9A load using torroids and reserve caps 10000uf followed by regulation using this device. The ripple rejection is not very good but usually it is well absorbed by the IC.

Regarding regulation drop-out is possibly the best hi current device i've tested. Even using a beasty power darlington at full current (10A) drop out is below 2V which is very hard to achieve if not impossible with LM338s (tested several different configurations, 2 LM338s, pass transistors, diodes etc. min drop out at full load was 4-5V).

It's not the simplest design, and if you want to use the numerous safety features that has on it you need to select very carefully the component values around it.

You can find details of the device here: http://focus.ti.com/docs/prod/folders/print/uc3834.html

Also you can have a look at my post regarding hi current regulation and the design of this power supply.

32V 8A Regulated PSU Schematics
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