Author Topic: Banggood PSU Enhancements  (Read 62438 times)

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Offline Kleinstein

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Re: Banggood PSU Enhancements
« Reply #50 on: March 17, 2018, 03:44:10 pm »
The first step in troubleshooting is usually a visible inspection. So check if all solder joints are done and diodes the right way around.

A nest step would than be to measure voltages following the supply. A first point could be something like just after the rectifier, than maybe the negative supply and voltage at the OPs.

Be aware that the cheap PSU kit gives too much supply voltage to the OPs if the intended 24 v transformer is used. So a 16-20 V transformer would be the more suitable choice and the resulting maximum output voltage lower. Depending on the voltage used, chances are the OP dis not like it. So a broken OP is a likely fault with a 24 V transformer.  So as a bonus you get an example for fault finding.
 

Offline Cliff Matthews

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Re: Banggood PSU Enhancements
« Reply #51 on: March 17, 2018, 04:12:08 pm »
The voltages you gave are referenced to 0V (-) from the rectifier? I've no idea where the -24v would come from if you used the same reference.. Tell us about your transformer setup and perhaps why you didn't start the project using 18 Vac as described earlier in the thread.
 

Offline wrongtwins

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Re: Banggood PSU Enhancements
« Reply #52 on: March 17, 2018, 07:00:00 pm »
Hi Kleinstein,

Thanks for the info.  I have already check all the solder joints and diodes.  i will mesure de voltage and trace it back were it's stop.  Can i replace the OP ?

Cliff,

I have comme alone this thread only todays.  I have follow the intruction from instructables/DIY-bench-power-supply. So i have used  110v 24VA 2Amp for the power supply.   i will print the circuits and begin meseauring along the circuits to see where can be the probleme.  And i will poste some picture of my setup.

Or do you sigest to us another  board/option.  I preffer to keept what i have already.

Thanks

p.s. English is not my primary language
« Last Edit: March 17, 2018, 07:50:55 pm by wrongtwins »
 

Offline Kleinstein

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Re: Banggood PSU Enhancements
« Reply #53 on: March 17, 2018, 07:49:10 pm »
The kit is more suitable for a 18 V or similar transformer - the 24 V from the instructions is too high.  24 VA and 2 A would mean a 12 V AC transformer. This should be OK and not deliver too much voltage. It could be more on the low side so that the negative supply might not have enough current. This would be relatively easy to fix by using a smaller value for R2.

IF needed one can replace the OP with a different type to work with a little higher voltage. But first one should check a few more points, like the supply to the OPs. This should be something around -5 V and a positive voltage around 20-30 V depending on the transformer. More would be a risk to damage the supplied OPs.

Seeing -28 V at the SD1047 would be kind of odd as there should be no -28 V on the circuit - it could indicate a problem with the negative supply, like a wrong diode where the 5.x V Zener is supposed to be. This in turn would have a good chance to fry the OPs.
 
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Offline wrongtwins

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Re: Banggood PSU Enhancements
« Reply #54 on: March 17, 2018, 08:21:19 pm »
Kleinstein,

i have 30V at PIN7 on each IC.  I cannot fin the -5V any were ?  And my R2/R3 are hot ?  I notice D12 is not working to. 

Thanks for your help.

 

Offline Cliff Matthews

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Re: Banggood PSU Enhancements
« Reply #55 on: March 17, 2018, 08:48:10 pm »
  ..So i have used  110v 24VA 2Amp for the power supply
We assume you are connecting the PCB directly to an AC to AC transformer. Are you?
Do not connect DC to the PCB or it will not function as intended.
What DC voltage do you measure between pin 4 and 7 of all 3 op amps?
One of them (U1) should be less, and all should be under 35v DC for stable operation.
 

Offline wrongtwins

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Re: Banggood PSU Enhancements
« Reply #56 on: March 17, 2018, 09:01:32 pm »
Yes i use a Avalanche Transfo 12vac-0-12vac 2Amp.

I have -29.4v, -29.7v and -30.2v.

 

Offline Cliff Matthews

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Re: Banggood PSU Enhancements
« Reply #57 on: March 17, 2018, 09:51:42 pm »
It looks like the charge pump circuit is not working. Using pin 4 on U1 as a positive reference, you should see 5v less to pin 4 of the other two IC's (this is established from the junction of R3 and D7). What did you mean by Avalanche? A photo helps...
 

Offline wrongtwins

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Re: Banggood PSU Enhancements
« Reply #58 on: March 17, 2018, 10:15:26 pm »
It's the company that made the transfo.

For pin4 i have 0v with the other IC.  I have mesure D7 and got 0v ref to ground.  I have remove it from the circuit to test it and i have 0.700 my diode tester.

What is the charge pump circuit ?

Thanks
« Last Edit: March 17, 2018, 10:40:50 pm by wrongtwins »
 

Offline Zero999

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Re: Banggood PSU Enhancements
« Reply #59 on: March 17, 2018, 10:58:34 pm »
It's the company that made the transfo.

For pin4 i have 0v with the other IC.  I have mesure D7 and got 0v ref to ground.  I have remove it from the circuit to test it and i have 0.700 my diode tester.

What is the charge pump circuit ?

Thanks
https://www.google.co.uk/search?q=charge+pump+circuit&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjC6YW_uvTZAhUDI8AKHWgOBY0Q_AUICigB&biw=1920&bih=953
 
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Offline Cliff Matthews

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Re: Banggood PSU Enhancements
« Reply #60 on: March 18, 2018, 12:53:31 am »
I think you could visualize how C3 charges to become the -5.6v rail in this way.. C2 charges on the negative half cycles, and during the positive half cycles, C2 and the transformer add together (like batteries) to reduce charge on C3 even more (or.. with reference to the 0v rail). Not a lot of current available, but it's enough to establish a negative rail for the op-amps. (I've seen others forward bias 2 or 3 diodes instead of the zener so the op-amps don't release the magic smoke.. but I think a TL431 would make it more temperature stable).
*restored GIF animation*
« Last Edit: August 25, 2018, 12:12:06 am by Cliff Matthews »
 
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Offline Kleinstein

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Re: Banggood PSU Enhancements
« Reply #61 on: March 18, 2018, 09:00:11 am »
That R2 is getting a little hot is kind of normal. One could reduce that by making C2 and R2 smaller, but this would be more like the last polish, the original circuit should be working in this respect too. D7 is required to limit the negative voltage. The TL081 needs something around -3 V to work around ground at the input. There can be even a slightly negative input voltage. As the TL081 can react with phase reversal the OPs should get at least around -4 V to work well. Even this might require to more extra diodes to limit the possible negative voltage at the OPs input. So just 2 or 3 forward diodes don't sound right if the original TL081 is used, it may be OK with other OPs (like MC34071).

A 700 mV forward voltage is OK for a zener diode - so it is not burnt. The more important voltage would be the reverse voltage - especially to make sure it is not mixed up with a normal diode, that might look very similar.

Measuring 0 V across D7 indicates a short to ground somewhere else. This could also be a damages part.
 

Offline Calambres

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Re: Banggood PSU Enhancements
« Reply #62 on: March 18, 2018, 10:23:24 am »
I've got two of these kits for a symmetric supply project. Both work OK but for some reason I cannot set the zero voltage with the trimmer in none of them.
Both were thoroughly checked and both fail miserably when trying to set 0V.

Any clues on this failure?

Offline Cliff Matthews

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Re: Banggood PSU Enhancements
« Reply #63 on: March 18, 2018, 05:52:45 pm »
@Calambres, maybe this is similar to @wrongtwins problem (talvez). Read post #57. What voltage do you see?
 
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Offline wrongtwins

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Re: Banggood PSU Enhancements
« Reply #64 on: March 18, 2018, 07:53:19 pm »
I have donne somme reading on the board :

Like i said U1, U2, U3 have 30v from pin7 to 4.  i have 30V at R1, 0V at R2 (heat on the ressistor), D5 3.2V, D6 2.7V, R3 5.8V.  At Q3 i have 30 v emitter(1), 30v base(2) and 0V at Collector and  0V at R22/D12.  I have 30V at pin 3 U3 and i have a lot of heat on U3 ?  I think my probleme is arround there ? 
 

Offline Cliff Matthews

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Re: Banggood PSU Enhancements
« Reply #65 on: March 19, 2018, 05:43:54 pm »
U3 should not get hot.. replace. An age-old problem: 5.6v is too much for the negative rail and 24vac pushes things to the limit.
Most who take this cct seriously, will opt for higher Vcc in op-amps (MC340xx or etc..) or settle with 18vac on the transfo.
IMO, Banggood and other sellers should encourage buyers to assemble and test in two stages.
« Last Edit: March 19, 2018, 06:18:11 pm by Cliff Matthews »
 
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Offline wrongtwins

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Re: Banggood PSU Enhancements
« Reply #66 on: March 19, 2018, 06:04:37 pm »
Ok,

I will replace all of them with  MC34071/tle2141 ?
« Last Edit: March 19, 2018, 06:11:14 pm by wrongtwins »
 

Offline Cliff Matthews

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Re: Banggood PSU Enhancements
« Reply #67 on: March 19, 2018, 06:27:56 pm »
Yes, I'd socket them.. still something wrong in charge pump, since U2 and U3 are getting the negative rail from somewhere. Lift one end of D7 and test to see if it's shorted in both directions.. R2 heat might be explained too.
 
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Offline Calambres

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Re: Banggood PSU Enhancements
« Reply #68 on: March 20, 2018, 10:15:00 am »
@Calambres, maybe this is similar to @wrongtwins problem (talvez). Read post #57. What voltage do you see?
With positive reference in pin 4 of U1, I see 5.162V in both pin 4 of U2 and U3.

No matter how much I fiddle with the trimmer, the zero adjustment won't vary at all...

What DC voltage do you measure between pin 4 and 7 of all 3 op amps?
One of them (U1) should be less, and all should be under 35v DC for stable operation.
U1: 31.22V
U2: 35.18V
U3: 35.18V

All this measurements with:

- Input:   25.7V AC. The xfrmr is 220V to 23V, 4.2A toroidal. As I have a mains out of 240V, the output is a bit higher.
- Output: 27.8V DC (maximum) @ 1.462A.
« Last Edit: March 20, 2018, 11:00:26 am by Calambres »
 

Offline Cliff Matthews

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Re: Banggood PSU Enhancements
« Reply #69 on: March 20, 2018, 11:58:38 am »
The measured 5.162v difference between op amps showed the zener is regulating, but after you measure op-amp voltages with a 3.96v disparity..  :-//  (was the later measurement under load?). If the transformer has 25.7VAC during load tests, it could be 27-28VAC with no-load.. so rectified, that 36v could fry TL081's (considering where they came from..) without even considering the other two op-amps at 36v + 5.16v across them.

If you want to continue testing with this transformer, a quick way to drop 5 or 6 volts would be with a Variac, or as a noisy last resort, a light dimmer on the primary side - be careful of mains..

*Oops, an updated post (I saw your earlier version). At ~1.5amps out you'll have 1.5v drop on R7, so the +rail is 32.7v! (V(U1) + Vr7). So you have 5.16v more (37.8v) on U2 and U3 under load, and likely 39v with no load.. Any smoke happening?
« Last Edit: March 20, 2018, 01:06:57 pm by Cliff Matthews »
 
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Offline Calambres

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Re: Banggood PSU Enhancements
« Reply #70 on: March 20, 2018, 04:08:57 pm »
...Any smoke happening?...

No... it works OK. The only complain I have with this kit is that the zero volt trimmer is not working at all...and as I said in a previus post, I've got two of these kits and the trimmer issue is happening in both of them!

I've got somewhere a couple of 4A 18V AC toroidal transformers. I'm going to use them just in case and/or swap the Op Amps for some uA741 or LM741 (not the "C" version).

Offline Zero999

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Re: Banggood PSU Enhancements
« Reply #71 on: March 20, 2018, 04:27:25 pm »
...Any smoke happening?...

No... it works OK. The only complain I have with this kit is that the zero volt trimmer is not working at all...and as I said in a previus post, I've got two of these kits and the trimmer issue is happening in both of them!

I've got somewhere a couple of 4A 18V AC toroidal transformers. I'm going to use them just in case and/or swap the Op Amps for some uA741 or LM741 (not the "C" version).
Perhaps the trimmer potentiometers are bad. Have you tried replacing them with a decent brand?
 
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Offline Calambres

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Re: Banggood PSU Enhancements
« Reply #72 on: March 20, 2018, 04:42:41 pm »
No, but I'll give it a go!

Offline Calambres

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Re: Banggood PSU Enhancements
« Reply #73 on: March 21, 2018, 11:44:51 am »
Perhaps the trimmer potentiometers are bad. Have you tried replacing them with a decent brand?
No, but I'll give it a go!

Nope!... both trimmers are good  :-//

On the other hand, I've seen other's reports with the same issue: the trimmers do nothing to set the zero volts.

Offline IanMacdonald

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Re: Banggood PSU Enhancements
« Reply #74 on: March 21, 2018, 12:39:15 pm »
Just my ten cents worth but using a single TO248 for this kind of power level is indeed stretching the thermal capability of the package. No matter how large the heatsink, internal temperature difference between chip and case will be the issue. Two would be more sensible.

Also, in any lab PSU running the opamps from the main supply rail and directly controlling an emitter follower output stage, is neither robust nor efficient. Apart from limiting the max output to ~30V, if any spike or reverse voltage gets onto that rail from a load, pop go their clogs.  Better to drive a C-E transistor from the opamp output, that in turn driving a PNP or P-channel output stage. That isolates the opamps from any nastiness on the PSU output, and has the bonus of a near-zero minimum volt drop instead of wasting a good volt or two of output. 
 


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