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LT Dual Tracking 3A Regulated Power Supply 1.25V to 20V
LT Dual Tracking 3A Regulated Power Supply 1.25V to 20V
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Old 24th April 2009, 07:49 PM   #51
marce is offline marce  United Kingdom
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Nice looking boards.
Something I didnt notice on the artworks, the heat sink pin looks close to the power track, be careful of any shorts when you assemble the PCB.
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Old 24th April 2009, 08:06 PM   #52
Mr Evil is offline Mr Evil  United Kingdom
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Quote:
Originally posted by marce
Nice looking boards.
Something I didnt notice on the artworks, the heat sink pin looks close to the power track, be careful of any shorts when you assemble the PCB.
Not only the pins, but the heatsinks themselves look like they will touch some tracks. The anodizing on most heatsinks is thin, and should not be relied on for electrical insulation.
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Old 24th April 2009, 08:37 PM   #53
okapi is offline okapi  United States
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thanks for the comments.

I did notice the heatsink sitting on the power track and was a bit annoyed. Live and learn i guess. Not sure where else i could have run the power track though. I might have been able to squeeze it around the other side of the heat sink pin if i pushed everything towards the center but then my heatsinks wouldn't be as close to the edge of the board.

I will likely stick a thermal pad between the heatsink and the board unless there is a better way? Maybe a coat of paint.

The problem with a thermal pad is that it is thick enough to offset the heatsink from the regulator. I would have to raise the regulator to compensate. Since i went out of my way to keep the parts as close as possible to the regulator i find this solution unpleasant as well.
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Old 25th April 2009, 05:14 PM   #54
marce is offline marce  United Kingdom
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Some thin insulation, not paint. This is unfortenatley part of the fun of PCB design. General tecnique with PTH components and heatsinks, is find out what potential the heatsink pad on the device is at, it is usualy connected to a pin internaly. Then have a copper flood the size of the heatsink connected to that signal, that way you know your safe. It happens, and quite often it isn't obvious till you first assemble the board. Another way is to add the heatsink outline to your component outline, then you have an indication on the board when your laying out where the heatsink is.
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Old 22nd May 2009, 04:47 AM   #55
ccschua is offline ccschua  Malaysia
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I am newbie to the power supplies . I am using the LM 3x7 series for the tda1541a DAC analog output stage. pls take a look

I wonder R11, C29, C24 suitable for the purpose of driving a simple transimpedance amplifier.

Further thots on this matter, I will try to put in charge transfer supply by ECDesigns before LM 3x7 and also put in TL431 shunt after LM3x7. What is your view ?
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Old 23rd May 2009, 02:22 PM   #56
okapi is offline okapi  United States
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Quote:
Originally posted by ccschua
I am newbie to the power supplies . I am using the LM 3x7 series for the tda1541a DAC analog output stage. pls take a look

I wonder R11, C29, C24 suitable for the purpose of driving a simple transimpedance amplifier.

Further thots on this matter, I will try to put in charge transfer supply by ECDesigns before LM 3x7 and also put in TL431 shunt after LM3x7. What is your view ?

I would implement the LM3x7 series as recommended in the data sheet or i would do this:

http://www.diyaudio.com/forums/showt...37#post1833337
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Old 9th July 2010, 03:33 AM   #57
Norfindel is offline Norfindel  Argentina
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Quote:
Originally Posted by okapi View Post
In the data sheet for the LT1033 negative adjustable regulator there is a typical application schematic for a tracking regulator that i am interested in but don't understand. I like the simplicity of the design as all the tracking regulators i am familiar with use opamps.

here is the schematic from the data sheet

LT Dual Tracking 3A Regulated Power Supply 1.25V to 20V


here is the more common implementation as well as the formula for calculating resistor values to set the output voltage.

LT Dual Tracking 3A Regulated Power Supply 1.25V to 20V


my two questions are:

1. how do you adapt the formula to calculate resitor values for the tracking regulator?

2. how does the circuit match a voltage change at the output of one regulator in the other regulator?
Very interesting circuit!
I simulated it, and i think that it works like this:
Ir1 and Ir5 are always going to be 12mA, because of the 1.2v across that resistors. That's all the available current, and it's going down thru the resistor network.

R3 is connected to the top of R2 and the bottom of R5, so whatever r3 you use, Vr3 = Vr2+Vr4 = 2*Vr2 = 2*Vr4.

That means, that with r3=r2=r4, Ir3 is going to be 2*Ir2.

Ir1=Ir2+Ir3=Ir2+2*Ir2=Ir2*(1+2)=Ir2*3

So, in this case, Ir2 = Ir1/3, while in a standard circuit, all the current from R1 flows thru R2. This has the effect of dividing R2 by 3.

Then, by reducing R3 further, more current goes there, instead of thru R2 and R4, reducing the voltage drop there, and thus, the output voltage.
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