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0-30V Stabilized Power Supply


redwire
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Guest Guber1

Hi, I have built the original circuit placed on the web page and at first it works ok, but the other day I turned it on and suddenly it smell burned, after that the output is always 34V for every position of the potentiometer, later i have seen this post and read about all the udpates make to the original circuit, now i don't if the original circuit has some mistakes and how to fix it, because now with the board already made I have to change a lot of things.

Thanks.

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Guest Big zee

Hi there
I tride to do it 4 times
On 4 pcb but the dc gives me 33 volt
And the transformer 25.1 volt and 1.1 amp

The 3rd tl081 gets hot and i hear some thing then i unblog it
After tring that agin its sems fine but the volt still 33 volt
And p1 and p2 and rv1 dosent chang the volt just the LED
All the parts are correct and there are no shorts at all

Is thes fake or what ?

Thx.

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Hi there
I tride to do it 4 times
On 4 pcb but the dc gives me 33 volt
And the transformer 25.1 volt and 1.1 amp

The 3rd tl081 gets hot and i hear some thing then i unblog it
After tring that agin its sems fine but the volt still 33 volt
And p1 and p2 and rv1 dosent chang the volt just the LED
All the parts are correct and there are no shorts at all

Is thes fake or what ?

Since you are using TL081 opamps and a 25V transformer then I guess you made the original project that has problems:
1) Your transformer is probably 27V with no load then its peak voltage is 27V x 1.414= 38.2V and the bridge rectifier reduces it to 36.8V as the positive unregulated supply to the opamps. The opamps also have a negative 5.6V supply so the opamps are powered with a total of 36.8V + 5.6v= 42.4V. But their absolute maximum allowed total supply is only 36V so they fail soon.

2) Many parts in the original project are overloaded and fail soon.

I fixed the project as shown on many threads about it in the forum by using opamps that are rated for a 44V total supply and reducing the negative supply to -1.3V.

Since your output is always 33V then maybe opamp U2 is destroyed by having a supply that is too high or the pins on the driver transistor or the output transistors (yes, the improved circuit users two output transistors to share the heat) are connected backwards so that the transistor that is connected wrong is simply a 5V zener diode from the positive supply voltage that is reducing the 38V to 33V. 
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Guest Big zee

yes i did the original
and no one says any thing in the original about the problems

so
how can i  fix it
where is the last update

thx.

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yes i did the original
and no one says any thing in the original about the problems

The original project is an old kit. DO NOT BUY THE KIT!

so how can i  fix it
where is the last update

Look in the list of topics in the forum for Projects Q/A for two or three threads about the fixed version.

can i use the original PCB?

Many parts are larger (so they do not overheat) and some wiring is different.
Many people posted a revised pcb design in the forum.

Here is the latest schematic and parts list:

post-1706-14279144537666_thumb.gif

post-1706-14279144538022_thumb.png

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Guest nida

Hi, I have build my PCB.I checked the circuit without load so I get 30V at the output.
I have full wave transformer not centre tape 24VAC,5A.(Does it affect the circuit?)
What is current limiting and how it works in this circuit?
I have connected a load of 100ohms 10W so i get 23V and 0.23A at output so Is it correct?
I get 11.8V at the output of U2 and 28.2V at the output of U3.
what voltages should be maintain at the inputs of ICS (U1,U2 and U3)? 

Waiting for your reply...

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Hi, I have build my PCB.I checked the circuit without load so I get 30V at the output.
I have full wave transformer not centre tape 24VAC,5A.(Does it affect the circuit?)

The transformer must be 28V or 30V for the output to be regulated at 30VDC.
At 3A your output will be about 26V and will not be regulated because it will be full of ripple because the voltage from your transformer is too low.

What is current limiting and how it works in this circuit?

The circuit does not have simple current limiting. Instead it has accurate current regulation.
R7 senses the load current and feeds the sense voltage to the (-) input of opamp U3. The current setting pot P2 sends its voltage to the (+) input of U3. Then U3 amplifies the difference to turn on Q3 and the LED to indicate that current regulation is reducing the output voltage through D9. The output voltage is reduced to the amount that accurately produces the current set by the current-setting pot.

I have connected a load of 100ohms 10W so i get 23V and 0.23A at output so Is it correct?

only if the output voltage is set to 23V and the current-setting is set higher than 0.23A, or if the voltage is set higher than 23V and the current-setting is at 0.23A.

I get 11.8V at the output of U2

U2, the driver transistor and the output transistors have a voltage gain of R12/R11 (plus one) that is changed a little by the voltage calibration pot. They amplify the 0V to 11.2V from the voltage setting pot up to 30.0V so the voltage gain should be 2.67857 times.
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Hi,

I'm new to the forum and also looking for the revised printout of the PCB. Can someone please post a link to this.

Thanks.

if you are unable to find the pcb you will be unable to make it also, use search read at least 20 last pages then you will now what issues can ocure in making progress
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i couldn't find tle2141 or mc34071  :-[
is there other options ?

The TLE2141 is made by Texas Instruments who is the largest semiconductor manufacturer in the world.
The MC34071 is made by Motorola/Freescale Semi who is also a very large semiconductor manufacturer.

They were chosen because their maximum total allowed supply is 44V and they have inputs that work at very low voltages so the negative supply voltage can be only -1.3V.

Go to www.farnell.com and click on the flag of your country because they supply electronic parts all over the world.
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im working on the new one but i already did the old one 4 times can i still use the old one if i used lower volt like 20

The calculations are simple:
A 20VAC transformer might produce 22VAC without a load. Its peak voltage will be 22V x 1.414= 31V and the bridge rectifier will charge the positive main filter capacitor to +29.6V.
The TL081 opamps have a maximum allowed total supply of 36V and they still need the negative -5.6V supply so their total supply will be 35.6V which is fine.

The tiny old 2N2219 driver transistor will probably still overheat especially when its obsolete heatsink might not still be available. The pins and heatsink for a modern BD139 driver transistor will not fit on the original pcb.
You can calculate how big the heatsink and fan for a single 2N3055 must be since its maximum dissipation will be very high at 79W.
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Guest Big zee

how can i make it the best PS by adding -30 volt to the circuit and dual linear pontesiometer for the voltage

so it will be -30 . 0 . +30

can the IC power the -30 to add IC4 ?

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how can i make it the best PS by adding -30 volt to the circuit and dual linear pontesiometer for the voltage

so it will be -30 . 0 . +30

can the IC power the -30 to add IC4 ?

There is no IC4 in the circuit.
Nothing in the project is grounded.

If you want a negative supply then use one of these projects and use the positive output as 0V. Then the "0V" output is the negative output.

Then make a second project to produce the positive output voltage with its "0V" used normally as 0V and the positive output is the positive output.
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Guest Big zee

And use the same circuit?
Caps trnsistiors and diodes ?

What about the transformer ? And the bridge ?

And the output +30 0 0 -30
The 2 zeroes conected to same point ?
+30 0 -30
Not
+30 0 0 -30

Thx.

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And use the same circuit?
Caps trnsistiors and diodes ?
What about the transformer ? And the bridge ?

Make two completely separate circuits. Even separate transformers and separate bridge rectifiers.
The first circuit can make 0V to +30V and the second circuit can make 0V to -30V.

And the output +30 0 0 -30
The 2 zeroes conected to same point ?
+30 0 -30
Not
+30 0 0 -30

Yes, you can connect the positive output of the second one to the 0V of the first one.
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  • 2 weeks later...

Could you provide calculation, what mains AC input fuse should I use (for 230V, 50Hz country)?

When the output current is 3ADC then the power is 38V plus 2V of rectifier drops x 3A= 120W.
Since your mains is 230VAC then 120W uses 230V/120W= 1.92A AC. Use a 2.5A fuse.

Furthermore, someone in this forum recommended ("P.S. use PTC! They limit the output current in case of a transistor melt down") using PTC thermo fuses, if I remember.. Any recommendations on using them?

I have never seen a PTC thermo fuse. I do not know how accurate they are.
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