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0-30V Stabilized Power Supply


redwire
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Without a load a 28V transformer will be 29VAC and a 30V transformer will be 31VAC.
The peak voltage of 31VAC is 43.8V and the bridge rectifier drops the unregulated DC to 42.4VDC.

The absolute max allowed voltage for the latest recommended opamps is 44V.

Your 57VDC is 14.6V higher than normal. Maybe your transformer AC voltage is too high or maybe it is extremely cheap and its voltage is too high with no load then drops when loaded because it uses cheap thin wire with too much resistance. Measure it.

With 42.4VDC a 2.2k resistor draws only 19.3mA so a decent quality 30VAC transformer voltage will rise to maybe 30.9VAC.

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The transformer is just fine, it's a 30$ 150VA toroidal transformer. It's good quality. Something else was the problem. I have found it. I have integrated a multimeter on the same board, I have mounted a 7824, a 7812 and a 7805 for the uC and the LCD display. It wasn't a good solution. When I was connecting the display, the output voltage was rising quickly, so i've bought a 5W 20V zener diode and a 5W 220 Ohms resistor for voltage regulation. This way it worked just perfectly.

Now I have another problem. I have shorted the output to see the value of the current and I think I blew it. Now the output voltage is 39.6V, no matter what. Are the MC34071s blown? Or one of them?

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I have shorted the output to see the value of the current and I think I blew it. Now the output voltage is 39.6V, no matter what. Are the MC34071s blown? Or one of them?

U1 is simply an 11.2V reference voltage so it has nothing to do with current in the output.
U3 is used as a comparator to sense the voltage across R7 which represents the output current and compares it with the voltage set by the current-settingh pot. If the sensed current is too high then the output of U3 pulls down D9 to reduce the output voltage which should reduce the output current.
U2 is in the output amplifier circuit. D9 reduces its input voltage of U2 if the output current gets too high.

I think the driver transistor Q2 is shorted or the output transistors are shorted maybe because their heatsaink is too small and they got too hot. 
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You forgot to add a heatsink to the BD139 driver transistor.
When the output is shorted then it will dissipate 1.5W if the output transistors have typical current gain or 5.5W if they have minimum current gain.
Without a heatsink it is at its max allowed temperature with a dissipation of 1.2W.

U2 will be very hot when the BD139 becomes shorted.   

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Problem solved. I have replaced the BD139 and added a heat sink. Now it works great.
Thank you for your help and for the design.

Just one more thing. My current limiting LED stays on all the time, though the current is not limited. When it goes into limiting stage, the LED lights brighter. What could I do to turn it off when it is not needed to be on? Voltage divider made out of 10K and 1K resistors? I have unconnected the LED and measured 19VDC on the pins in normal stage, 29VDC in current limit.

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My current limiting LED stays on all the time, though the current is not limited. When it goes into limiting stage, the LED lights brighter.

U3 and Q3 are a switch that is on or off, never half-way. Maybe you used an opamp for U3 that is different from a TLE2141 or MC34071?

I marked the current regulator circuit with notes that explain how it works:

post-1706-14279144427349_thumb.png

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The output of U3 and Q3 should never turn the LED on dimly.
Maybe if the current-setting pot is at minimum, there is no load and U3 has a fairly high input offset voltage then the LED will be turned on. R17 sets the amount of minimum current regulation so it can be increased to 47, 56 or 68 ohms to increase the minimum current setting which will turn off the LED.

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Hello :) I'm Kirill from Ukraine. Help me please, I have a trouble with 0...30V Stabilized Power Supply.  I've just finished upgrading construction from original circuit to new one (with new TLE2141 opamps and trimpots connections fixed and BD139 instead of 2n2219). I have transformer rated 30V, 6A and 10mFx63V capacitor for C1. And I've got such problem: voltage regulation works fine, except that fact, that I can't establish zero output voltage when Vreg pot is set to 0 - I have about 25 mV on output terminals. But that fact doesn't bother me: I suspect that trimpot I used is slightly poor :) Other thing drives me mad: output current never rises more, than 1.2 A :( It seems that current limiting part working correct, because under the load LED glows only when current limiting pot is at 1/3 of full range from minimum (1/3 - it's exactly ~1.2 A), than it fades, just like source has out from current limiting mode. But the output current still remains 1.2 A. For more clean scene: I set output voltage to 35V, and set current limiting threshold to 0 - LED switches on, as it supposed to. Then I connect load - 5 Ohms resistor to output and increase current limiting threshold. Voltage on the load rises to about 6 Volts, and current, respectively, to 1.2 A. Voltage at U3 pin 3 = 0.56V, as it should be. LED switches off, but voltage and current still remains the same, even if current limiter is set to max, as though something else limiting the output current %) Any ideas?

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C7 is an electrolytic capacitor on the output. electrolytic capacitors have dielectric absorption where they store a voltage for a while. Try using a film capacitor instead then adjust the input offset voltage trimpot on u2 for an output of 0v when the voltage pot is at zero.

If the BD139 or the output transistors have their pins connected wrong (emitter and collector reversed) then their current gain is very low which reduces the max output current.

R7 senses the output current. Its voltage is compared to the setting of the current pot by U3.
The output of U3 goes only low enough to turn on Q3 and the LED and to reduce the output voltage through D9. With a very high load current or shorted output then the output of U3 might go 0.7V below 0V so that D9 can reduce the output voltage almost to 0V. 

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Hello,

I also have а couple of questions. First, the original article states:

In order to make it possible for U2 to control the output voltage down to 0 V, it is necessary to provide a negative supply rail and this is done by means of the circuit around C2 & C3. The same negative supply is also used for U3. As U1 is working under fixed conditions it can be run from the unregulated positive supply rail and the earth.


But in the improved schematic (latest version) pin 4 of U2 is connected to ground ("-" pin of C1). Is this done on purpose or by oversight?

Second, what is the behaviour of the output voltage when the power is switched off with Q1 removed from the schematic? Is any harm to put Q1 back?

Thanks.
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1) The original article states:



But in the improved schematic (latest version) pin 4 of U2 is connected to ground ("-" pin of C1). Is this done on purpose or by oversight?

The original circuit had a few serious problems. It used TL081 opamps that need a 5.6V negative supply for their inputs to work properly and its absolute maximum allowed total supply was only 36V. The project used a 24V transformer which produced an unregulated +32V which is not high enough for the output to be 30V at 3A, its max output might be only +25V. Without a load the 24V transformer might produce +34V so the opamps operate with a total of 34V + 5.6V= 39.6V which is higher than their max allowed total supply voltage.

TLE2141 and MC34071 opamps were selected for the fixed version because their maximum total supply is 44V and their inputs work perfectly without a negative supply voltage. Without a load and with a 30VAC transformer the total supply for U2 is +42.4V so it will be fine. A 28VAC transformer can be used instead and the supply for U2 will be +39.6V which gives more headroom. It is easy for the output to produce +30V at 3A.

2) What is the behaviour of the output voltage when the power is switched off with Q1 removed from the schematic? Is any harm to put Q1 back?

TL081 opamps have a problem called Opamp Phase Inversion where the output suddenly goes high if an input voltage becomes too close (within a few volts) to their negative supply voltage. The negative supply in this project was small so it collapsed first when the power was turned off which caused the output voltage of U2 to rise which caused the output voltage of the project to rise. Q1 was used to short the output of U2 to 0V when the negative supply begins to drop so the output voltage could not rise.
The new opamps do not have this problem so Q1 is not needed.
U3 needs to have a small -1.3V negative supply so that its output in series with D9 can go low enough to cause an output voltage of close to 0V when the output of the project is shorted. 

post-1706-14279144434202_thumb.png

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TL081 opamps have a problem called Opamp Phase Inversion where the output suddenly goes high if an input voltage becomes too close (within a few volts) to their negative supply voltage. The negative supply in this project was small so it collapsed first when the power was turned off which caused the output voltage of U2 to rise which caused the output voltage of the project to rise. Q1 was used to short the output of U2 to 0V when the negative supply begins to drop so the output voltage could not rise.
The new opamps do not have this problem so Q1 is not needed.
U3 needs to have a small -1.3V negative supply so that its output in series with D9 can go low enough to cause an output voltage of close to 0V when the output of the project is shorted. 

There was a video posted on some page of this tread, where output voltage raise briefly. And that was with these new opamps. That's why I was thinking to put back Q1.
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There was a video posted on some page of this thread, where output voltage raise briefly. And that was with these new opamps. That's why I was thinking to put back Q1.

If the output capacitor C7 is electrolytic then it has "dielectric absorption" which causes the output voltage to rise with no load if the project is powered or not. A film capacitor will not do that. An output load resistor can discharge a film C7 when the power is turned off.

When the positive supply drops when the power is turned off then there is a low voltage where U2 does not control the output anymore. I think then Q1 also will not have enough voltage to work.
Try it to see.
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Is it necessary for the elements "REV3" make a new board? Can I use the old PCB, but it does not plug in Q1, R13, etc.

There have been many pcb designs for the various versions. The original pcb used parts that were too small so they overheated. Some of the newer larger parts do not fit on it.
The latest schematic (REV 3) has calibration trimpots added.
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HELLO

Today I spent 4 hours (more/less) that I reviewed all 90 pages of this topic.

And I think it would be good to put all good things (in my opinion) in 1 place.

That's why I made ​​a zip file containing the following items.

zip file contains:

folder:
- audio (audioguru schmatic and part list)
- EL_PS6_redwire ( redwires pcb (which is made in EAGLE), part list, some pics)
- tesseract (his version of PSU)
- picmaster (his version of PSU)
- pictures ( PSUs images of those who made ​​it (fly3rman,gfrotti,surubel, and some others)


and some other stuff(pictures) like:
-diffrece betwen audioguru and redwire project (difference _red_audio)
-0-30V current regulator at 3A
-0-30V current regulator at zero
-0-30V reference circuit
-0V - 30V Redwire's schematic
-0V-30V latest current regulator
-0V-30V power supply

Download link (10.05 MB):
https://rapidshare.com/files/394978044/PSU.rar

or

https://rapidshare.com/files/3793630850/PSU.zip

PS. If someone thinks that there is unnecessary (false) things feel free to warn us/me. Or maybe something needs to be added

Sry for my bad english... :/

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Thanks Tompa.
I downloaded your RAR file and tried to extract its files with Windows XP and I got 116 errors.
The RAR file is 10.5MB.

It extracted one folder named PSU. Inside the PSU folder is more folders:
Audio (empty)
PICmaster_str50 (empty)
tesseract_str27 (empty)
EL-PS6_redwire  Inside is more folders:
Borad (empty)
Plocica_PDF_holt_26str (empty)
red_multimeter (empty)

pictures Inside is more folders:
fly3rman-str83 (empty)
gfrotti_str64 (empty)
surubel_str66 (empty)

tesseract_str27 (empty)

I rarely use RAR so I don't know what to do.

 

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