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Old 29th January 2005, 04:47 AM   #1
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Unhappy 5 volt version of the Updated super regulator.

I have the latest version of the J/D super regulator from Audio Xpress but I don't know how to get the lower voltages out of it.I'm trying to get 5 vdc and 7vdc.I changed the reference diode from the LM329 to a TL 431.The voltage drops but doesn't go below 7.8vdc.What changes do I need to make to get 5 and 7 vdc.Thanks for any help in advance.

Mike
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Old 29th January 2005, 01:56 PM   #2
moamps is offline moamps  Croatia
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Hi,
The regulator you're referring to was designed for the input voltage of about 15V. To make it suitable for 5V, a lot of changes need to be done first, IMO. The schematic below shows how I would make the necessary modifications.
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Milan
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Old 30th January 2005, 04:45 AM   #3
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Did you change the zener diode to the left of the 10 ohm resistor?I made the other changes you made to 4.99k to 1k and the 499r to 470r.I got 7.5vdc.Any more suggestions?

Mike
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Old 30th January 2005, 11:39 AM   #4
moamps is offline moamps  Croatia
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Hi,

The value of the zener diode should equal the value of the reference voltage at the + input of the regulator IC. The reference voltage should be lower than the output voltage (about half its value) from the regulator.
If your zener diode is 6.8V, it's not possible to get voltage lower than 7.4V at the regulator output. In many cases it may be possible to short the zener, which you may try as well to see what happens.
Also, in your case, the + power terminal of the regulator IC should be connected before the regulator transistor.
Could you post the schematic you're using to make things easier for me to visualize?

Regards,
Milan
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Old 30th January 2005, 03:41 PM   #5
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This is what I'm using.
Mike
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Old 30th January 2005, 04:05 PM   #6
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Mike, do you have a connection between the supply star gnd and the sense ground group at the right?

Jan Didden
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Old 30th January 2005, 04:44 PM   #7
moamps is offline moamps  Croatia
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5V reg, part two
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Old 30th January 2005, 05:44 PM   #8
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Moamps, why don't you feed the 825 from the prereg output, is there a voltage level issue? I thought the 825 works fine with lower supply, and it would improve the line rejection.

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Old 30th January 2005, 05:57 PM   #9
moamps is offline moamps  Croatia
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Quote:
Originally posted by janneman
... why don't you feed the 825 from the prereg output, is there a voltage level issue?
Hi Jan,

You're right - there is a voltage level issue indeed. I'm not sure that the voltage at the prereg out is high enough for the regulator IC to work properly. The voltage at the prereg out exceeds the output voltage by about 2.5V, which is in this case only about 7.5V. However, Mike might also try out what you're suggesting and let us know if it works.

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Milan
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Old 30th January 2005, 06:31 PM   #10
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Yes. With that zener in the opamp output, it doesn't have to swing more than some 2V BELOW Vout (=5V), so I see no need for a highish opamp supply voltage. The 825 is fully spec'd for 10V total supply, so that would be the min prereg output voltage to allow the 825 to be fed from the stable and clean prereg instead of the raw supply. And in that case the zener could go, and that ugly elcap as well, setting Vout of the opamp almost smack in the middle of that 10V (5.6V actually, +/- a dB. )

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