Electronics > Beginners

DIY 0-30V 0-3A ...Again

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Richard Crowley:

--- Quote from: Mate_Well on January 06, 2019, 03:00:15 pm ---•Actually, i was very interested in this project some time ago, after digging into it, i found there is a great document ( in French and it is not idealy translated but it is understandable into english), it has very nice measurements, facts, and additions to ithttp://electronics-lab.com/community/applications/core/interface/file/attachment.php?id=42970 (it has the most stable part list/diagram from all that are floating arround, i hope this will help out (also  i did not tryed to build it yet) :D


•I will also try to make it much more powerfull with more powerfull transformer, which leads to more powerfull opamps, and other parts, air coling and such, i will do it long time from now on (i need to save up for the parts sadly)  :scared:

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Microcheap:
I am well aware of the limitation of this circuit but I've assembled this project over a decade ago when I started learning electronics, and the psu still works, of course I never pushed it to its limits, I think the only time was when I left it overnight recharging an old lead acid battery at around 13V@2A, and it survived. The only thing I remember I had to replace 1 or 2 times were transistors Q2 and/or Q4 but I was using Chinese knock-off transistors with improper heat-sink.

Back to the original question, have you checked Q1, R13 and R14 already? As Audioguru pointed, Q1 must be off, test the Vbe of Q1, it should be lower than 0.7V (I measured 0.2V in my board, with R13=10k and R14=1k5).

Mate_Well:
•Any chance the u3 is damaged, or has wrong pins conection (could be caused by putting the chip in 180°rotated also) ?

link fixed

IanB:

--- Quote from: Richard Crowley on January 06, 2019, 03:49:01 pm ---
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I am able to download it from Google docs, however it is 5 MB so it is too big to attach here.

Jwillis:
Hello folks.sorry for not getting back sooner.
All the information you guys provided is a great help.

--- Quote from: Mate_Well on January 06, 2019, 03:00:15 pm ---•Actually, i was very interested in this project some time ago, after digging into it, i found there is a great document ( in French and it is not idealy translated but it is understandable into english), it has very nice measurements, facts, and additions to it https://drive.google.com/open?id=1qaKc0H9951NUQiRNrA4dNyz8iehMwrSn (it has the most stable part list/diagram from all that are floating arround, i hope this will help out (also  i did not tryed to build it yet) :D


•I will also try to make it much more powerfull with more powerfull transformer, which leads to more powerfull opamps, and other parts, air coling and such, i will do it long time from now on (i need to save up for the parts sadly)  :scared:

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Thank you  Mate_Well ,I'll call a friend to see if she can translate that PDF file for me.
I'm currently testing  the ops to see which one failed .The voltage adjust is fine but lost current control.I suspect U3 as you mentioned .


--- Quote from: Cliff Matthews on January 06, 2019, 04:10:10 am ---Note: the garbage pots from Banggood could be a source of a lot trouble (at least they were for me).
I cut-and-pasted a side-by-side schematic to help future modders.

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Cliff Matthews I had the same problem at the start and changed those to 2W 10K for testing.


So I pulled all the Ops to measure the voltages at pin 4 and pin 7 in relation to output ground.For U1 I can't identify a true zero point to compare the values of pin 4 which should be negative and pin 7 which should be positive for any of the Ops .So from what I understand the TL081 requires a supply of 7 V ~ 36 V, ±3.5 V ~ 18 V  (single or dual) So I just took a reading pin 4 to pin 7 and got 33.8Vdc.Since pin 4 looks like it gets a variable voltage off of U3 pin 2.That's of course a guess on my part. Taking a reading at pin 4 on U1 from ground gives 0Vdc.Pin 7 I measure 33.5Vdc.
For U2 pin 4 reads from output negative for pin 4  -5.1Vdc and pin 7 33.8Vdc . Across from pin 4 to pin 7 is 38.9Vdc.Which is to high.
For U3 pin 4 reads from output negative for pin 4   -5.1Vdc and pin 7 33.8Vdc. Across from pin 4 to pin 7 is 38.9Vdc.Which is also to high.
Since the additive values of pin 4 and pin 7 can't exceed 36 V,I wondering if theirs any reason why I can't  incorporate  zener regulators for U1 ,U2 and U3 to bring  pin7  voltage down so the additive voltage of pin 4 and pin 7 won't exceed 36 V ? Could even bring D7 down as well since it really only needs to be >3.5V



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