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Old 29th December 2013, 12:23 AM   #1
Trileru is offline Trileru  Romania
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Default LM338 power supply pcb, I want to make on for personal use

Hello,


I'm planning on doing a lm338 snubberized power supply. I want to use it for a ta2020 amp and another one for a tda7297 amp. I guess the supply voltage should be about 13.5V and 16V respectively.
I made the schematic in Eagle but I got lost at pcb layout. I haven't done any pcb and I don't know what's best as far as parts layout, spacing, trace width etc. I plan on making it myself with one of the few methods available so I'm looking for a single sided pcb. Also I want to add the option of two parallel resistors for the resistors that set the voltage for lm338. I guess it's nice to have the option of dialing the voltage as close as possible. I'm planning on using the to-220 version. Also at this moment I'm oscillating between lm338 and lt1084. Current requirement is about 2-3A maximum so any should do. The LT1084 needs a 22uF tantalum or 150uF electrolytic on the output as that's part of the frequency compensation network. I guess a 5mm lead spacing on that capacitor would enable me to add either a 1uF tantalum for lm338 either 22uF tantalum or 150uF electrolytic.
I don't care about it being super miniaturized. I prefer to limit the capacitor's exposure to heat (if any) from the heatsink. Also I saw some versions with a transistor somewhere on the adjust pin, any idea what that's used for? I'd modify the schematic for nicer functions
Also I want to use TO-220 MUR860 diodes, do they need any kind of heatsink? I can add the small ones directly on them, or else space them out more to make room for larger individual heatsinks?
So basically I'd like some help from anyone willing, with the schematic/pcb layout.
I've attached the schematic I've used and the pcb layout with autorouter


p.s. I'm planning on using Panasonic FR for main reservoir capacitors. I don't think that I want to bypass them with smaller ones.
Attached Images
File Type: png schematic.png (4.1 KB, 351 views)
Attached Files
File Type: zip lm338 regulator.zip (100.3 KB, 16 views)
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Old 29th December 2013, 09:19 PM   #2
Trileru is offline Trileru  Romania
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No one?
I'm thinking this to be for everyone who wants to make one at home, single sided. I haven't seen any pcb layout for LM338, with MUR860 diodes and parallel resistors.
I've also seen some layouts with most of the copper on the circuit itself, there were only small lines delimiting the traces themselves. Is that a better way to design a power supply pcb?
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Old 1st January 2014, 07:59 PM   #3
Trileru is offline Trileru  Romania
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I've made some changes. I also added power planes. Is this good?

edit:
I'd like to connect the heatsink's pins to the ground plane, and also the holes in the corners, I want to ground them at install.
Attached Images
File Type: png pcb.png (29.7 KB, 296 views)
File Type: png sch.png (9.0 KB, 288 views)

Last edited by Trileru; 1st January 2014 at 08:02 PM.
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Old 1st January 2014, 10:38 PM   #4
Trileru is offline Trileru  Romania
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I've added pads to the corner holes so I can ground them with the case, but I don't know how to add solder pads to the heatsink pins. I wish to ground it as well. Also for mechanical security.
This design can be used by anyone besides commercial purposes

Any feedback? Did I do something wrong here?


edit:

I've tried connecting the heatsink to ground in the schematic but I can't, the wire won't "stick" to it Like it has no electrical connection.
Attached Images
File Type: png pcb.png (37.6 KB, 273 views)
File Type: png sch.png (12.6 KB, 260 views)
Attached Files
File Type: zip lm338 regulator.zip (106.7 KB, 7 views)
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Old 2nd January 2014, 12:52 AM   #5
Trileru is offline Trileru  Romania
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I also did a two layer version.
I also tried to get it as small as possible.
There are only three mounting holes, but they are aligned and should hold the board in place. I think I might try a pcb making service for this one.
Everyone can use them for personal purposes, not for commercial use.
I accept any suggestions regarding both versions.
I'm planning on using them somewhere in the area of 13-16V output at about 3A maximum 4A.
Attached Images
File Type: png pcb.png (33.3 KB, 57 views)
File Type: png sch.png (11.2 KB, 51 views)
Attached Files
File Type: zip lm338 regulator double sided.zip (100.3 KB, 0 views)
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Old 2nd January 2014, 01:37 AM   #6
Trileru is offline Trileru  Romania
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And another update on the single sided version.
I rearranged the components similar to the double sided version. Also made it smaller.
Attached Images
File Type: png pcb.png (37.1 KB, 47 views)
File Type: png sch.png (11.7 KB, 47 views)
Attached Files
File Type: zip lm338 regulator.zip (100.2 KB, 6 views)
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Old 2nd January 2014, 02:07 AM   #7
esgigt is offline esgigt  Netherlands
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Hi Trileru,

Looking at the schematic I found two 1 Meg resistors which puzzled me. But perhaps you can enlighten me...

Both are parallel to other resistors (120 Ohms and 1k2 Ohms). But since resistors are notorious sources of noise I doubt their use in this schematic. On the other hand I might have missed their relevance.

Regards,
Edwin
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Old 2nd January 2014, 02:21 AM   #8
Trileru is offline Trileru  Romania
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Hello Edwin,

I put those resistors there so you can use another one in parallel to dial in the voltage as close as possible to your needs. I just noted it 1M as that would keep the total value close to the other resistor. For me I would just use whatever resistor needed in place for 1M to dial in the voltage. Same goes for both voltage divider resistors. Although it's recommended to use 120ohm resistor for R3, one could use a slightly lower/higher value to get the desired result. I guess if you don't want to use two resistors you could leave that spot unconnected.

I made a small revision by replacing C5 with a larger pin spacing for both variants. Also I've adjusted the silkscreen notations by adding the LT1084 possibility.
The schematic is almost the same but in some cases C5 is called at 20uF and the output capacitor needs to be 150uF electrolytic or 22uF tantalum. The footprint should match any I think.

Also for diodes 1N4002 can be used, I just didn't find them in the library, and also IC1 is not actually a LM338 in the eagle schematic, but something else in the same package. It was the only one I found that had a vertical mounting position for pcb layout. That shouldn't matter as I kept the package integrity.
Attached Images
File Type: png pcb.png (37.4 KB, 47 views)
File Type: png sch.png (11.8 KB, 44 views)
File Type: png pcb ds.png (33.6 KB, 47 views)
File Type: png sch ds.png (11.4 KB, 42 views)
Attached Files
File Type: zip lm338 regulator V1.2.zip (100.4 KB, 6 views)
File Type: zip lm338 regulator double sided V1.1.zip (100.3 KB, 2 views)
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Old 2nd January 2014, 02:40 AM   #9
esgigt is offline esgigt  Netherlands
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Trileru, thanks for explaining their use.
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Old 2nd January 2014, 02:41 AM   #10
Trileru is offline Trileru  Romania
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Join Date: Dec 2010
I tried to make the last thing that bugged me, add solder pads to the heatsink holes. But I ended up in trouble at DRC check with heatsink's hole size not matching the pad's hole size etc.
I would need some assistance with this problem. What can I do so I can solder the heatsink's pins to ground?
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