Advice wanted - regulated PSU for Vin 42 V / Vout 25-40 V - diyAudio
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Old 15th February 2007, 02:16 PM   #1
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Question Advice wanted - regulated PSU for Vin 42 V / Vout 25-40 V

I want to build kinda "universal amplifier PSU", adjustable from 25 to 40 volts and giving enough current to drive GC, MyRev, Symasym and others. I got a pair of 30 V / 240 VA dual secondary transformers and no clue. What regulator is recommended? All I found is the LM317HV, but it doesn´t give enough current ...

Don´t want to spend so much for transformers anymore.

Thanks.
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Old 15th February 2007, 02:21 PM   #2
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Look on the LM317 datasheet for how to add pass transistors to boost current.

Given the cost and heatsinking required for this project, I would just build a simple fixed unregulated PSU from a 100VA 2x25V transformer. There's rarely any need to have any more voltage than this just for testing.
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Old 15th February 2007, 02:36 PM   #3
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Thank you, richie00boy. But it´s not meant for testing only.
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Old 15th February 2007, 02:40 PM   #4
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Well even more reason to build a simple fixed unregulated supply then. Just build it with the most voltage whatever circuit you anticipate to use in the future will take.
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Old 15th February 2007, 02:59 PM   #5
blmn is offline blmn  Brazil
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Try LM338 (5A regulator). It must be enough.

[url]http://www.datasheet4u.com/html/L/M/3/LM338_STMicroelectronics.pdf.html

Best regards,
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Old 15th February 2007, 03:13 PM   #6
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Hi,
an advantage of a regulated supply is flexibility for testing prototype circuits.

I see the main advantage as adjustable current limit.

For power amp duty, stay with unregulated.
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Old 15th February 2007, 03:17 PM   #7
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@ blmn: Vout of LM338 is 32 V max. ...

@ richie00boy: And what¢¥s about lower voltages then? For example a LM3875 with 4 §Ù load is ~25 V. A MyRev takes ~34 V. A Sysmasym ~36 V. And so on ...

In the future I don¢¥t want to burn money for all the transformers, that¢¥s in the back of my mind.
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Old 15th February 2007, 03:20 PM   #8
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Just build a 25V supply then. The other amps will still work perfectly fine with this voltage.

The heatsinking cost, size and messing about building a powerful enough regulated supply might as well be spent on a new unregulated PSU for each amp as you need it.
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Old 15th February 2007, 03:31 PM   #9
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@ blmn: Vout of LM338 is 32 V max. ...
Put a 10V zener from the "Adjust" pin to ground. This will float the reg., making it 11.2-42V instead of 1.2-32V.

-Casey
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Old 15th February 2007, 03:32 PM   #10
blmn is offline blmn  Brazil
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No,

VDiff for LM338 is 35V, If properly designed, fits OK for your needs.

It must be a problem in case of short-circuits, but, since you don´t need less than 25V, you can pre-regulate or drop the voltage to achieve what you want.

But, for linear power supplies, is not a easy task achieve well regulated 40V from more or less 43 volts. The transformer must be very good. For this level of voltage I sugest you work in non regulated mode. A switch to bypass the regulator could work.

Best regards,
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