0-30 Vdc Stabilized Power Supply

[audioguru2]

I ordered from tI TLE2141 and now i replace the integrates. I also replace the 2n2219 with Tip31. now what resistor i must replace?

It sounds like you made the original circuit that has many problems. A few years ago we discussed why a BD139 transistor works better than a TIP31.

Why don't you make the latest corrected version that is talked about in this forum and its shematic and parts list have been posted many times?????

 

[Lester Jeffries]

I  never hear of this type of power supply before, how far have you gotton?

Moderator edit: Spam removed.

 

[lacusta]

Hello,
First, sorry for my english... :-[
I am new to electronics-lab forum and a beginner. I've built this power supply and now I have a problem. When I connect Q4, the output is 17V . When Q4 isn't connected the output depends on p1 and it varies from 0V to 34.6V. With Q4 conected the voltage at pin 6 of U2 is around 0V. The voltage at pin 6 of U3 is always the same as voltage across R1 and with voltage between point 7 and point 4. I've short-circuited the output without q4 and the led not lit. Help me please!

P.S. I used this circuit diagram> http://www.electronics-lab.com/projects/power/001/index.html because I 'have built it some time ago.

 

[audioguru2]

Maybe you have the base and emitter pins of Q4 connected backwards.
With Q4 removed then the output comes from R16. But the current through R16 is very low and might not be enough current to light the LED when the output is shorted.

 

[lacusta]

My first 2n3055 has burned out. I used a new one but IT WAS BROKEN. I checked the voltage at pin 6 of U1 ad it was 11.27V (no Q4). The voltage across R5 and R6 is 5.6V. Audioguru, would you like to tell me what checks should I do to see if something else has broken?

 

[audioguru2]

My first 2n3055 has burned out.

The original project has no calibration so its max output current is too high at about 4.1A. Then if the output is shorted the 2N3055 transistor must dissipate 131W which will cause it to overheat even if its heatsink is huge.
Maybe the current regulator circuit in your project does not work so the current and power dissipation are higher.

I checked the voltage at pin 6 of U1 ad it was 11.27V (no Q4). The voltage across R5 and R6 is 5.6V.

Perfect.

Audioguru, would you like to tell me what checks should I do to see if something else has broken?

With the voltage setting pot turned up to maximum, U2 and the output transistors will try to amplify the 11.2V reference to 34.4V at the output of the project. But 34.4V is not possible if there is any output current since the transformer is too small. The max output is about 25V at 3A with lots of ripple.

 

[lacusta]

Thankyou very much audioguru for helping me. I shorted the output , the new and good 2n3055 burned instantly but it was cold! I don't know what to measure so that I could see if the current regulator works.

If I will not be able to fix my actually power supply, I think I will build the power supply from bellow. 28 V, 4 A transformer is good?
http://www.electronics-lab.com/forum/index.php?topic=7317.1512

 

[audioguru2]

The current regulation works by U3 comparing the voltage across R7 caused by the load's current with the voltage across the current-setting pot and its series resistor.
When the current in the load exceeds the set amount then the output of U3 goes low which turns on the LED and reduces the output voltage until the current in the load equals the set amount.
R7 is listed as 0.47 ohms in the original parts list but 3A needs about 0.35 ohms which is not a standard resistor value. A calibration trimpot is used in the latest version.

 

[kankki]

Hello! I have just hooked up a working prototype on a breadboard. Everything seems to be in order. Current limiting works and all.

I have some problems though. There seems to be some 50hz junk on top of the output. Is that supposed to be there? Also some high frequency stuff. It's about 10mV pk-pk. Does the breadboard bring in some stray capacitance perhaps?

Also when I attach a computer speaker that draws about 250mA peak the output voltage varies like half a volt!   That's unacceptable  Anybody know what that might be about? :-\

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[audioguru2]

It must be made on a pcb.
The long connection wires and tracks on a breadboard are antennas that pickup mains hum (your 50Hz junk). The high capacitance between the wire ands tracks on a breadboard cause capacitive coupling which causes ringing and oscillation (your high frequency stuff).

The voltage at the output normally changes about 3mV from no load to a 3A load.

 

[kankki]

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

 

[audioguru2]

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.

 

[kankki]

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 

 

[forp]

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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[audioguru2]

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.

 

[forp]

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.

 

[Hero999]

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.

 

[forp]

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.

 

[LEECH666]

[No message]

 

[audioguru2]

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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