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Old 13th December 2007, 07:18 AM   #1
zei is offline zei  Sweden
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Default LM3X7 Supply

I made this from some schematic i found.

Is it correct? any flaws?

Something that can be improved?

Click the image to open in full size.


Best regards
/Zei
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Old 13th December 2007, 12:13 PM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
add the low value compensation capacitors specified by the manufacturer and fit them VERY close to the regulator pins.

Disconnect the smoothing capacitor zero volts line from the ground sense line of the regulator.
Take the smoothing cap zero volt line direct to the output ground point.

R3 may need to be lowered to 120r to ensure sufficient current flow through the regulator if the output draws zero current.

What does the manufacturer say about protection diodes across C5 & C6?
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Old 13th December 2007, 12:16 PM   #3
SY is offline SY  United States
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47k for the voltage set resistor seems rather large.
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Old 13th December 2007, 06:35 PM   #4
zei is offline zei  Sweden
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Thanx Andrew for the input.

I,ll look into your suggestions and also see if i can understand the datasheet.


Thanx SY, i,ll recheck the values.


/Zei
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Old 13th December 2007, 07:36 PM   #5
zei is offline zei  Sweden
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Caps (0,1uF) for improved ripple rejection i,ll add directly to the pins "under the board".

Quote:
Disconnect the smoothing capacitor zero volts line from the ground sense line of the regulator.
This i do not understand and could find anything similar in the datasheet so for now,, i did nothing like that.

Protection diods across C5, C6 is not needed for this application AFAIK..

Trimmer pots are 4k7 and not 47k.. thanx for pointing that out

Thanx for support !

/Zei
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Old 14th December 2007, 08:56 AM   #6
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by zei
Disconnect the smoothing capacitor zero volts line from the ground sense line of the regulator.
Take the smoothing cap zero volt line direct to the output ground point.

This i do not understand and could find anything similar in the datasheet so for now,, i did nothing like that.
because almost everyone uses software to draw the schematics and the software assumes that wires have zero impedance.
Do not connect any current carrying wire to the voltage sense part of the regulator. This applies to both the +ve voltage sense and the -ve voltage sense.
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Old 16th December 2007, 09:51 PM   #7
Gordy is offline Gordy  United Kingdom
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Diodes accross your R3 and R4 as hinted at by AndrewT.

Refer to http://cache.national.com/ds/LM/LM117.pdf , Page 9, Figure 3.
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Old 17th December 2007, 04:34 AM   #8
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Does your transformer has dual secondaries?

Gajanan Phadte
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Old 17th December 2007, 05:28 AM   #9
gootee is online now gootee  United States
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Quote:
Originally posted by AndrewT
Disconnect the smoothing capacitor zero volts line from the ground sense line of the regulator.
Take the smoothing cap zero volt line direct to the output ground point.
Quote:
Originally posted by zei

...
This i do not understand and could find anything similar in the datasheet so for now,, i did nothing like that.
...
/Zei
It's important. I tried to explain the underlying concepts in Post #178, here:

http://www.diyaudio.com/forums/showt...855post1376855
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Old 17th December 2007, 09:08 AM   #10
zei is offline zei  Sweden
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Thanx for the hints.

I,ll read some more and see if i can understand the meaning of it.

/Z
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