LM338 power supply pcb, I want to make on for personal use - Page 2 - diyAudio
Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 2nd January 2014, 03:41 AM   #11
diyAudio Member
 
sofaspud's Avatar
 
Join Date: Nov 2005
Location: San Antonio
I wouldn't connect the heatsink to ground. I would leave it with a direct connection to the LM338 tab (Vout) for better heat transfer.
__________________
It is error only, and not truth, that shrinks from enquiry. - Thomas Paine
  Reply With Quote
Old 2nd January 2014, 03:43 AM   #12
Trileru is offline Trileru  Romania
diyAudio Member
 
Join Date: Dec 2010
Ok, that makes sense. And it isn't too heavy to worry about mechanical security.
Thank you!

The rest, does it seem ok?
  Reply With Quote
Old 2nd January 2014, 04:05 AM   #13
diyAudio Member
 
sofaspud's Avatar
 
Join Date: Nov 2005
Location: San Antonio
If mechanics are an issue, you can make holes and pads to solder the pins; just don't have them connect to anything.
Looking back over things...
I don't know what purpose R1 serves. I'd remove it, and remove R3B. Using 120Ω at R3 provides a good idle load for the regulator.
__________________
It is error only, and not truth, that shrinks from enquiry. - Thomas Paine
  Reply With Quote
Old 2nd January 2014, 05:26 AM   #14
Trileru is offline Trileru  Romania
diyAudio Member
 
Join Date: Dec 2010
R1 is used to discharge the reservoir capacitors when I turn off the supply. I made a test on breadboard and it was useful to be able to dial in from r3 as well.
  Reply With Quote
Old 2nd January 2014, 03:27 PM   #15
Trileru is offline Trileru  Romania
diyAudio Member
 
Join Date: Dec 2010
I've removed R3B in this version, and also made the single sided board smaller so it fits 5cmx10cm. Also I moved some capacitors further from the heatsink.

How can I make the isolated pads on the heatsink?


edit:

I just realized that I must note +/GND on the output connector, as they are reversed from single sided to double sided. So if anyone plans on doing the boards please measure before connecting the output of the board.
Attached Images
File Type: png brd.png (35.8 KB, 99 views)
File Type: png sch.png (11.7 KB, 99 views)
File Type: png brd ds.png (33.0 KB, 98 views)
File Type: png sch ds.png (11.1 KB, 96 views)
Attached Files
File Type: zip lm338 regulator V1.3.zip (100.2 KB, 8 views)
File Type: zip lm338 regulator double sided V1.2.zip (100.3 KB, 3 views)

Last edited by Trileru; 2nd January 2014 at 03:31 PM.
  Reply With Quote
Old 4th January 2014, 02:13 AM   #16
Trileru is offline Trileru  Romania
diyAudio Member
 
Join Date: Dec 2010
I've made some changes to the double sided board.
I've been reading some more and found a discussion regarding LT1085. Some people have found that larger (330uF) ADJ capacitor gave better results so I increased the footprint of this capacitor and the output capacitor just to be safe. Also I've rearranged some output components. I've removed completely the input/output connectors as I'm probably going to solder my cables directly to the board.
The ta2020 has it's own power reservoir caps (also bypassed with lower values, but I'm going to test this as well). Is it worth to add a 0.1uF film cap on the output of this regulator as well? I guess I do have some space left there, especially if I remove the snubber
I've added R.LOAD resistor of 300 ohm that will serve as a load for the regulator. Should keep it at 45-55mA in my 13.5V-16V range. I moved the LED on the input side of the regulator. I could have moved the positive connection hole next to the negative one but I prefer the trace as short as possible.
Also I am not yet sure about the reservoir caps, should I leave all three or better a larger one and a smaller one? Something like 6800uF and 100uF.
Attached Images
File Type: png brd.png (56.2 KB, 89 views)
File Type: png sch.png (18.4 KB, 36 views)
  Reply With Quote
Old 5th January 2014, 02:19 AM   #17
diyAudio Member
 
sofaspud's Avatar
 
Join Date: Nov 2005
Location: San Antonio
Your circuit doesn't need R.LOAD.
The regulator will impress a 1.25V reference voltage across R1. Ohm's Law then says that will be a little over 10mA flowing through R1. That current also flows through the specified R2 value to set the desired regulated output voltage. The point is, that 10mA is already an adequate idle current for the regulator.
I am glad to see you add a series LED to your bleeder resistor. The voltage on the filter caps should be only about 18VDC; is bleeding the charge really necessary?
The ADJ capacitance? I can't quite put my finger on it, but I recall there being the possibility of performance degradation with over-sized caps used there. I think 47μF is the upper limit. I can't recall where I got this info, though. NatSemi app notes, perhaps.
__________________
It is error only, and not truth, that shrinks from enquiry. - Thomas Paine
  Reply With Quote
Old 5th January 2014, 04:07 AM   #18
Trileru is offline Trileru  Romania
diyAudio Member
 
Join Date: Dec 2010
I've put that load resistor as someone on another forum asked me if there's enough current flowing to keep the regulator stable if no load is present so I wanted to make sure. Also it seems to keep the regulator into a more linear zone if there's no load.
Also I've skimmed through this topic: Another look at the LM317 and LM337 regulators
And it seems they got the best results with adj capacitor of 330uF, but also they are using a LT1085, which should be similar to LT1084 that I'm also planning to test on this board.
I'm only trying to keep options open. I may decide to not solder some components, but I like the idea of it being able to be used with more regulators (LM317, LM337, LT1084, LT1085 etc).
I now have a few issues left. One of them is if I keep three reservoir capacitors or should I use two different sizes ? I'm currently thinking of putting a 4700uF and something like 1000uF or 470uF. The other problem is that I cannot solder the pins of the heatsink. If I use another similar heatsink that has electrical connection on it's pins and I ground it, it does a weird thing and it clears the copper around it's outline (and inside the footprint). I've attached a picture to get an idea.
Attached Images
File Type: png brd.png (63.3 KB, 14 views)
  Reply With Quote
Old 5th January 2014, 04:37 AM   #19
diyAudio Member
 
Join Date: Aug 2013
Quote:
Originally Posted by Trileru View Post
I've put that load resistor as someone on another forum asked me if there's enough current flowing to keep the regulator stable if no load is present so I wanted to make sure. Also it seems to keep the regulator into a more linear zone if there's no load.
Hello there ...
You're right about including a min. current draw (about 100mA) at the regulator output, you could either use a load resistor or a LED.

Quote:
Originally Posted by Trileru View Post
Also I've skimmed through this topic: Another look at the LM317 and LM337 regulators
And it seems they got the best results with adj capacitor of 330uF, but also they are using a LT1085, which should be similar to LT1084 that I'm also planning to test on this board.
I'm only trying to keep options open. I may decide to not solder some components, but I like the idea of it being able to be used with more regulators (LM317, LM337, LT1084, LT1085 etc).
Here 're a quote from the national datasheet....

Quote:
The adjustment terminal can be bypassed to ground on the LM138 to improve ripple rejection. This bypass capacitor prevents ripple from being amplified as the output voltage is increased. With a 10 μF bypass capacitor 75 dB ripple rejection is obtainable at any output level. Increases over 20 μF do not appreciably improve the ripple rejection at frequencies above 120 Hz. If the bypass capacitor is used, it is sometimes necessary to include protection diodes to prevent the capacitor from discharging through internal low current
paths and damaging the device.
In general, the best type of capacitors to use are solid tantalum. Solid tantalum capacitors have low impedance even at high frequencies. Depending upon capacitor construction, it takes about 25 μF in aluminum electrolytic to equal 1 μF solid tantalum at high frequencies. Ceramic capacitors are also good at high frequencies; but some types have a large decrease in capacitance at frequencies around 0.5 MHz. For this reason, 0.01 μF disc may seem to work better than a
0.1 μF disc as a bypass.
That gives a pretty good idea about the value of the adjustment bypass capacitor and that its performance depends more on the capacitor type.

Quote:
Originally Posted by Trileru View Post
The other problem is that I cannot solder the pins of the heatsink. If I use another similar heatsink that has electrical connection on it's pins and I ground it, it does a weird thing and it clears the copper around it's outline (and inside the footprint). I've attached a picture to get an idea.
You need to route the ground connection to the heatsink (the yellow wire) .

Best regards.
  Reply With Quote
Old 5th January 2014, 04:41 AM   #20
Trileru is offline Trileru  Romania
diyAudio Member
 
Join Date: Dec 2010
If I route it it is ok, but I wanted it to go on the ground plane, and not clear the ground plane around it. That way it was easier and I had a hefty ground plane in that area. Even so I might route it to the nearest ground connection, and use that vertical area to separate the ground plane from the input side from the ground plane of the output side, and just use the lower connection to complete the circuit between both ground planes. As I read that is good practice as it keeps the noise out from the output area ground.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
lm338 regulated power supply bego2 Power Supplies 7 11th October 2012 02:34 PM
Using LM338 and LM337 for 250VA supply camus Power Supplies 2 10th February 2012 05:26 PM
Regulated PSU PCB available for LM338? jmillerdoc Chip Amps 1 3rd March 2011 04:30 AM
Does this power supply make any sense to you? Cassiel Tubes / Valves 14 17th June 2009 06:18 PM
PCB: LM338 Regulated Snubberized PSU yusuf Power Supplies 7 27th March 2007 02:45 PM


New To Site? Need Help?

All times are GMT. The time now is 02:38 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2