Author Topic: Chinese 0-30v 3a psu issues  (Read 5197 times)

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Offline m3vuvTopic starter

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Chinese 0-30v 3a psu issues
« on: September 10, 2019, 10:07:10 pm »
just built this kit,schematic attached,it works fine but if i turn it off when its in cc mode i get a brief spike on the output,in cv mode its fine,is this normal?,if so it there a fix bar chucking it in the bin?,regards m3vuv
« Last Edit: September 11, 2019, 07:13:42 am by Simon »
 

Offline RIKRIK

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Re: chinky 0-30v 3a psu issues
« Reply #1 on: September 10, 2019, 10:42:35 pm »
This reminds me of the old school power supplies , lm358 http://www.electronics-lab.com/project/0-30v-laboratory-power-supply/ , I'd say it's a keeper, have you tried turning the current and voltage fully down on power off, apart from that, have a tinker with it, for hobbyist electronics it should be fine. Fingers crossed .
 

Offline ledtester

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Re: chinky 0-30v 3a psu issues
« Reply #2 on: September 10, 2019, 11:37:00 pm »
This looks like the 2ma-3A, 30V power supply kit that has been much discussed on this forum.

Have a look at this thread and, in particular, the comments by Audioguru:

https://www.eevblog.com/forum/beginners/bangood-psu-enhancements/
 

Offline m3vuvTopic starter

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Re: chinky 0-30v 3a psu issues
« Reply #3 on: September 10, 2019, 11:44:11 pm »
if the current and voltage are turned fully down it wont do it as its then not in cc mode,its only in cc mode that it does it.
 

Offline floobydust

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Re: chinky 0-30v 3a psu issues
« Reply #4 on: September 11, 2019, 12:45:19 am »
It's a design issue unless you assembled the kit wrong. The original design was copied from 1978 (Practical Electronics 1978 October) and used LM741's.
https://www.eevblog.com/forum/beginners/0-30v-0-3a-psu-audiogurus-version/msg2239764/#msg2239764
R13, R14 were changed for better control of switch on/off spikes, I think 160R and 12k in Rev. 7

Normally, when power is switched off, C3 discharges first then Q1 turns on to shut off the output, until C1 is discharged. But under load, C1 can discharge first so the +ve rail sags and the op-amp outputs a nasty blip. The PSU needs an output off switch, or undervoltage lockout added.

« Last Edit: September 11, 2019, 02:06:07 am by floobydust »
 
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Offline Audioguru again

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Re: chinky 0-30v 3a psu issues
« Reply #5 on: September 11, 2019, 01:59:56 am »
You show the schematic of the old Greek kit that has many parts overloaded and wrongly uses TL081 opamps that have a problem where the output goes as high as it can when an input voltage becomes too close to the negative supply voltage. TR1 shorts the voltage driver opamp output to prevent it happening when the power is turned off.

Recently Banggood and other Chinese companies sell their copy of the kit.
 

Online wraper

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Re: chinese 0-30v 3a psu issues
« Reply #6 on: September 11, 2019, 02:23:03 am »
Try increasing C3 capacitance so negative rail holds voltage longer on turning off and see what happens. Most likely it happens because negative rail discharges faster than positive rail.
« Last Edit: September 11, 2019, 07:13:58 am by Simon »
 

Offline m3vuvTopic starter

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Re: Chinese 0-30v 3a psu issues
« Reply #7 on: September 11, 2019, 10:19:47 am »
Hi i increased c8 to 100uf,all it does is delay the spike on switch off,still the same just happens a moment after switch off.
 

Offline xavier60

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Re: Chinese 0-30v 3a psu issues
« Reply #8 on: September 11, 2019, 11:06:34 am »
Try replacing R14 with a zener diode with the same voltage as D7. Hopefully it will cause Q1 to mute early enough.
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 

Offline m3vuvTopic starter

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Re: Chinese 0-30v 3a psu issues
« Reply #9 on: September 11, 2019, 12:11:04 pm »
i think ive sorted it,i replaced q2 with a bd139,only issue is now max volys out is only about 12v,thats running a 5watt bulb,voltage over c1 holds at 27v under those conditions,i suspect q1 is faulty.
 

Offline m3vuvTopic starter

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Re: Chinese 0-30v 3a psu issues
« Reply #10 on: September 11, 2019, 02:06:05 pm »
well i changed q4 for a 3055,still no voltage spikes but only just over 9 volts out into a 21 watt bulb,any ideas?
 

Online wraper

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Re: Chinese 0-30v 3a psu issues
« Reply #11 on: September 11, 2019, 02:20:06 pm »
BD139 has different pinout. So most likely that's the reason of 'fix' and becoming broken. You just assembled it incorrectly. Also BD139 is not a right part to go there.
 

Offline xavier60

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Re: Chinese 0-30v 3a psu issues
« Reply #12 on: September 11, 2019, 04:43:52 pm »
Measuring the voltage drop across R15 will indicate how much current U2 is supplying to drive the output stage and how much current gain there is.
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 

Offline m3vuvTopic starter

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Re: Chinese 0-30v 3a psu issues
« Reply #13 on: September 12, 2019, 06:36:06 am »
its not the wrong pinout!!
 

Offline m3vuvTopic starter

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Re: Chinese 0-30v 3a psu issues
« Reply #14 on: September 13, 2019, 12:11:48 pm »
For what its worth if i lift one leg of R11 and one leg of C9,it still behaves the same,voltage adjusts to a max of about 9v and the current limit still works.
 

Offline Ysjoelfir

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Re: Chinese 0-30v 3a psu issues
« Reply #15 on: September 13, 2019, 12:48:13 pm »
Is that still the same PSU discussed back in your thread from april?
https://www.eevblog.com/forum/projects/chinky-psu-kit/msg2369598/#msg2369598
Greetings, Kai \ Ysjoelfir
 

Offline m3vuvTopic starter

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Re: Chinese 0-30v 3a psu issues
« Reply #16 on: September 13, 2019, 06:29:28 pm »
same design but a new unit,seem fine just cant ger any output above 9v.
 

Offline xavier60

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Re: Chinese 0-30v 3a psu issues
« Reply #17 on: September 13, 2019, 08:29:41 pm »
While an op-amp is in control of a loop, its input pins will measure the same voltage.
HP 54645A dso, Fluke 87V dmm,  Agilent U8002A psu,  FY6600 function gen,  Brymen BM857S, HAKKO FM-204, New! HAKKO FX-971.
 

Offline m3vuvTopic starter

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Re: Chinese 0-30v 3a psu issues
« Reply #18 on: September 13, 2019, 08:49:13 pm »
well i removed q1 and tested it,it was sort of leaky in all directions,it now outputs to about 27v,the strange thing is now both the current and volt pot seem to adjust the output,the amp pot seems to vary the voltage less smoothly than the volt pot tho,the cc led is still working but back to a spike on turn off with the cc led lit,starting to tear my hair out with this now!.
 

Offline m3vuvTopic starter

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Re: Chinese 0-30v 3a psu issues
« Reply #19 on: September 13, 2019, 08:59:00 pm »
pin 2 of u sits at 7.63 volt in cv mode,pin 3 at 24.75,then in cc mode with the led lit pin 2 sits at 1.042v and pin 3 at 1.032.
 

Offline m3vuvTopic starter

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Re: Chinese 0-30v 3a psu issues
« Reply #20 on: September 13, 2019, 08:59:40 pm »
those last readings were from u3 pins btw.
 

Offline m3vuvTopic starter

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Re: Chinese 0-30v 3a psu issues
« Reply #21 on: September 13, 2019, 09:11:09 pm »
i changed d9 and its fixed it,cheers everyone,its been a pain but feel ive learnt something,it was the comment about both  op amp inputs beeing equal if there in the loop led me too it,many thanks all.,also the spike hs gone in cc mode at turn off too.
 

Offline m3vuvTopic starter

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Re: Chinese 0-30v 3a psu issues
« Reply #22 on: September 13, 2019, 10:20:17 pm »
well maybe i spoke too soon,just noticed i cant get the output below 35mv,rv1 does nothing,earler i dis swap c3 for a 100uf from a 47uf,is that the cause?,cheers Paul m3vuv.
 

Offline Ysjoelfir

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Re: Chinese 0-30v 3a psu issues
« Reply #23 on: September 13, 2019, 10:22:19 pm »
You do notice that there is an edit function implemented into this forum software?
Greetings, Kai \ Ysjoelfir
 

Offline m3vuvTopic starter

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Re: Chinese 0-30v 3a psu issues
« Reply #24 on: September 13, 2019, 11:59:52 pm »
in a word no i didnt,anyway swapped u2 and it goes down to 3mv,think thats good enough for me.
 


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