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0-30 Vdc Stabilized Power Supply


Sallala
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Okay :) What about the large voltage fluctuations under load? Are they because of the breadboard too?

Yes.
The Mickey Mouse contacts on a breadboard have poor contact so they have resistance. With a load of 250mA and a voltage change of 0.5V then the resistance is 0.5/0.25= 2 ohms. A soldered wire has a resistance of 0.001 ohms or less.
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Yes.
The Mickey Mouse contacts on a breadboard have poor contact so they have resistance. With a load of 250mA and a voltage change of 0.5V then the resistance is 0.5/0.25= 2 ohms. A soldered wire has a resistance of 0.001 ohms or less.


Oh, okay
Thanks for the help  :)
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Hi guys,
Sad day last week, I shorted my 6yr old power supply yesterday by connecting a 12v cordless drill pack battery to the psu without double checking the polarity.

The power supply was set to 14.5v and current is limited to 14mA, I wanted to do cell balancing the battery pack by manual overcharging. And poof the psu died just like that. There's no sign of burn, I turn the voltage knob up but it would not go beyond 9volts.

I checked the circuit, D11 1N4001 is blown, I replaced it. Everything else seems okay, I dont know how to check the TL081 op amps. I am using a 24v 3A 72VA transformer, I wonder how the TL081s survived for so long since you guys suggest changing to MC34071.

Very sad for me since this power supply has been with me and helping me with my daily stuff almost everyday. I need to get it back up again.

I am so surprise to find Audioguru still posting after so many many years! I have to find time to digest this 112 pages forum...

Vincent.

EDIT: After reading the last few pages of this post, I decided that my original 2004 circuit psu is not reliable, I will have to rebuild the psu with the updated schematics and parts.

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Hi Forp,
I am sorry to hear that your project blew up.
I am retired so every day is a Saturday and I do whatever I want, whenever I want.

I made many projects on Veroboard (stripboard) but I have never mounted all parts on the copper side like you did.

Opamp U2 controls the output voltage because it is an amplifier driving emitter-follower Q2 which drives the output emitter-follower Q4. The gain of the amplifier is 3.07 times.
I don't see your Q2, maybe it has failed because the original transistor was a very weak one with almost no cooling. Replace it with a BD139 transistor mounted on a pretty big heatsink.

The input of opamp U2 is the 0V to 11.2V from the voltage-setting pot. The voltage setting pot is fed 11.2V from opamp U1.

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Hello audioguru,

Thank you for your time and reply. It helped me a lot understanding how those opamp works. I am into microcontrollers, never had much chance working with opamps.

I learned to mount components on the non copper-side in highschool but then after many years of flipping, checking, flipping, soldering, checking I got tired of it, so I improvise. This is basically treating the through hole components as surface mount components. It has it's advantages and disadvantages. Firstly, there is risk of leads shorting to the copper tracks. Other than that I can't think of anything else which is bad. If you have enough experience of PCB prototyping I don't see why you can't do it properly.

The advantages outweight the risk. By mounting the components directly on the copper side, you are looking at the interconnects. You can actually see all the circuitry including the tracks which has been cut to allow different electrical path together with the components. Flipping the board around increase confusion. When completed, to reduce risk of shorting, I spray a thick layer of varnish on the board as a conformal coating. This creates a electrical barrier between the exposed leads and copper tracks.

My Q2 2n2219 and 3 other larger capacitors are mounted on the other side of the board. I will check Q2 later and see if it's the failing part. I will report back soon.



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If you mount components on the copper side, you should cover the long leads with insulation to prevent them from short circuiting on the tracks.

I don't see what's so hard about mounting them on the non-copper side. I don't even bother planning all of the connections. I just roughly lay out the board, so the components are roughly the same place as is on the schematic (looking at it from the board side), tack them into place (just solder enough of the leads to secure them the right place), solder the links (ticking off each connection on the schematic as I go), check the board, completely solder the components and check again before cutting the unneeded tracks. Before applying the power, I give the board a final check over, looking carefully for solder bridges, dry joints and checking against the schematic again.

In short I disagree with putting all the components on the copper side. I think the risks of it blowing up outweigh the perceived benefits of saving time (I'd question that too, I don't see how it's any quicker). What's better for you to spend a little bit longer and it work first time or it blowing up and you have to replace lots of expensive components?

There's nothing wrong with mounting the odd component on the copper side, but it should only be done when the non-copper side is already full and there isn't space for it.

I don't use much stripboard nowadays, I breadboard it and make proper PCB, once I'm happy with it.

I'd also question whether the traces on the stripboard are thick enough to carry 3A, without overheating.

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You are right regarding the risk, but if you work with lots of surface mount component then you will have to mount them on the copper side.

Audioguru - you saved my power supply. It is indeed the Q2 2n2219. I removed it and did a simple Base-Collector, Base-Emitter junction test on diode setting, it's open. I replaced with a new 2n2219, sorry that's what I got on hand, it's all good and working again.

I will have to rebuild a new version someday when I have time.

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  • 2 weeks later...

Hi Florian Leech,
You have a very old parts list (about 5 years old) that does not match the latest schematic (about 1.5 years old) you found.
The latest parts list was posted on this website somewhere hundreds of times.

The zener diode and calibration trimpots do not have numbers yet.

With a current of 3.0A then R7 (0.47 ohms) dissipates 4.23W. A 5W resistor will be extremely hot so use a 10W resistor. I have never seen a 9W resistor but it will be fine.
The calibration trimpot's value and the resistor in series with it were selected with 0.47 ohms for R7.

The latest parts list uses TLE2141 or MC34071 opamps.

I fixed the original project that was a mess of errors, did not work properly and was not reliable.

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Hi audioguru,

I didn't even notice that this (*click*) post was from 2007.

No wonder the parts list doesn't match!

I am having trouble finding the right documents though. Couldn't find the parts list anywhere in the last 12-13 pages. And I think others will have this problem too.You partly solved my problem, as you just posted the right parts list again.

[Question removed, I really should learn to read your answers properly.]

Thank you for your quick help.

Cheers,
Florian


//EDIT:

Sorry I made a mistake, I was actually talking about this resistor.
http://tinyurl.com/2wg733q

I got 0.33 Ohm confused with 0.47 Ohm, I tried to fix my mistake in the first post by editing it but I didn't edit the link to the resistor and overlooked one of the mistakes.
But anyway you already answered my question.

Thanks again.

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  • 2 weeks later...

Hi Florian Leech,
You have a very old parts list (about 5 years old) that does not match the latest schematic (about 1.5 years old) you found.
The latest parts list was posted on this website somewhere hundreds of times.

The zener diode and calibration trimpots do not have numbers yet.

With a current of 3.0A then R7 (0.47 ohms) dissipates 4.23W. A 5W resistor will be extremely hot so use a 10W resistor. I have never seen a 9W resistor but it will be fine.
The calibration trimpot's value and the resistor in series with it were selected with 0.47 ohms for R7.

The latest parts list uses TLE2141 or MC34071 opamps.

I fixed the original project that was a mess of errors, did not work properly and was not reliable.


Dear Audiguru can you tell me is this changes  that you have posted in a latest parts lists ( R1=2.2Kohm , R11=27Kohm, R15=100Ohm, R18=33Kohm, R22=3,9Kohm)
are aplicable for 5 Ampers version of power supply

old values for this rezistors are ( R1=3.9Kohms, R11=10Kohm, R15=(there is no),  R18=20Kohm R22=1.2Kohm)
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  • 1 month later...

Opamp U2 drives transistor Q2 which drives transistors Q4 and Q5.
When the output load current is 3A then the max base current into the combined Q4 and Q5 is 86mA. Then the max base current into Q2 is about 1.7mA. Then the max output current from opamp U2 is only 1.7mA which will barely make it a little warm, not hot.

When there is less output current the ouput current from U2 is less.
When there is no output current then there is no output current from U2. Its idle current will make it a little warm.

If the C and E pins of Q2, Q4 or Q5 are connected backwards then they draw much more current than they should which will make them and/or U2 very hot. Look at the pins on the datasheets for the transistors.

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Hello everyone!  8)

I am having some trouble with this circuit. I have milled out a PCB according to the schematic I attached. (it's from Eagle). Soldered everything up and it kind of works.

The current limiting is acting weird though. Seems like there is some hysteresis on it. When I set the current limit to e.g. 0.5A you have to go to 1A for the current limiting to kick in. After that it works just fine. But if I then wind the current limit up and down again I have the same problem.

The large heatsink on the board are for the flyback diodes and the smaller one for the BD139. The transistors and large heatsink is gonna be mounted outside the chassi.

I have also tried with a .47ohm shunt resistor.

Does anyone know what could be causing this problem?  ???

Any help would be greatly appreciated.  ;D (maybe this has been answered before, but I couldn't find an answer)

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Hi Kankki,
Your schematic is normal so I don't see anything wrong with the current regulation.
When the output current tries to exceed the setting of the current pot then the circuit should reduce its output voltage so that the current stays at the setting.

You probably have an error or short on your pcb around the current control opamp.

You changed all the Rx, Cx and Ux numbers so it is difficult to compare your circuit with all the other schematics.

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Hello
  I am going to give this one a try( finally ) I have been reading the thread for about two years now.  I already have two good bench top power supplies but I have a cnc  machine project coming up and I want to build its own power supply.  A variable supply would work perfect, because  I plan on testing out different size motors. The blog on cnc machines re sparked my interest.  Hobbies are illnesses you know and I don't plane on getting well soon.
have fun ::)
gogo

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Hello again. I've taken a closer look at the PCB and fixed up some suspicious looking solder joints and so. I haven't gotten it working yet, rather it became worse  ::) Heh.

I don't know what I did but now the CC LED is always on and it only becomes slightly brighter when the current is limited. Something wrong with Q3?

And I still have the hysteresis problem.. I've noticed something though. It seems that in order for the current limiting to kick in the output voltage needs to rise to (the normal point where it would start to drop + forward voltage of a diode, about .6 volts.) Then it starts limiting the current and works until I turn I raise the current limit again. Could it have something to do with D9?

I've attached my schematic with the original schematics component names so it's easier to see. I'm also attaching my board layout.

Again, I'd really appreciate some help  :)

Oh, and the 20k pot isn't connected to GND it's connected to "before shunt-gnd". A drawing mistake  :-[

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U3 is supposed to have a DC voltage gain of typically 220000. Maybe it is bad or C4 is leaky.
Maybe U3 is a counterfeit IC that cannot reduce its output voltage as low and and does not have inputs that work at such a low voltage as a real TLE2141 opamp.

When U3 is not regulating the current then its (+) input is higher than its (-) input so its output is high which turns off transistor Q3 and reverse-biases D9.

When the load current in R7 produces a voltage at the (-) input of U3 that is slightly higher than the voltage at the current-setting pot P2 which is the (+) input of U3 then the output voltage of U3 should drop which turns on transistor Q3 which turns on the LED, and diode D9 causes the voltage at the input of opamp U2 to drop. Then the output voltage drops low enogh that the current in the load is reduced to the setting of the current-setting pot.

Sorry, I didn't look at your pcb. U do dat. 

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