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0-30 Vdc Stabilized Power Supply


Sallala
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audioguru, thanks.

When you said that they are in this thread, did you mean scattered, or in one place, if they are in one place(plz link) or if anybody is willing to put them in one place?, I can remake the circuit, list all the changes and upload for future viewers.

If the answer is no, then I'm off to read,and I'll post as soon as possible my result.

greeting

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;D thanks! audioguru  ;D

I can't buy:- TIP31A, but I can TIP33C, and (BC548,2N2219).

                  - OPA445AP, but I can TL081CN (C=operating temperature 0=>+70,
                                                                    N=DIP8 package).
Are they good substitution? 

Under two paralleled 2N3055, just to connect B-B, E-E, C-C or something else.

Thanks a lot.

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I can't buy:- TIP31A, but I can TIP33C, and (BC548,2N2219).

A huge difference.
The BC548 has a max current rating of only 100mA and max power rating of only 625mW.
A 2N2219 has a max current rating of only 800mA and a max power rating with a clip-on heatsink of only 1.6W.
The recommended TIP31A has a max current rating of 3A, a max power rating of 40W and a max voltage rating of 60V.
A TIP33C has a max current rating of 10A, a max power rating of 80W and a max voltage rating of 100V. It can replace the TIP31A but it costs more.

A TIP31A costs $.68US each and a TIP33C costs $1.80US at Digikey.
There are many BDxxx european transistors that are the same as a TIP31A.

I can't buy - OPA445AP, but I can TL081CN.

The TL081 has a max supply voltage rating of 36V. The OPA445 has a max voltage rating of 90V.

With a 30VAC transformer, with no load current on the project the positive supply will be 43VDC and the negative supply will be 5.6V. Therefore the total supply voltage for the opamps is 48.6V and even opamps rated for a 44V supply won't be good enough.

Under two paralleled 2N3055, just to connect B-B, E-E, C-C or something else

No. The transistors are not exactly the same. One will have more current gain.

Each 2N3055 transistor has its own 0.33 ohm resistor in series with its emitter to equalize their current gains so they share the current better.
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Multisim might not understand how the negative 5.6V supply works.


I replaced TLE2141CP with OPA445 (I try many others OP amp but 100% work only OPA445) and replace 24VAC TR with 30VAC to get max voltage 30V and now, in simulation PSU work. Both V and I regulation work perfect.  But I have next problem. If I measure output with osciloscope I get 20kHz oscilating about 200mV AC. Where can be problem? If I replace output 10uF capacitator with 100uF, oscilating is now pretty low in uV. But this is not right way.... Can somebody help please?
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Hi,

I have made the standard PSU from the projects page, and am after some help with troubleshooting.

the few changes in parts

-TL081 for HA17741, which seem similar.
-C1 is a 4700uF / 63V
-C4 i used two 53nF
-Q2 is a TIP31C, with bent legs to fit the original PCB design
-Resistors are half watt, R1 1W, R7 5W
-D7, D8 is a 5v6 zener tho im not sure the power rating, i can check if the problem seems to point to this
-transfo is 72VA, 24VAC output
-RV1 . ther is some confustion about this, 100ohm trimmer resistor, not a 100k trimpot? still not really sure what the difference is.

The problem seems to be the current regulation.

I can't seem to get more then 50mA out of the PSU.

I can run a LED at 2V draws about 40mA.

25V bulb that is spose to run at 750mA  i think, measures 33ohm, i donno if you can measure the expected current like that ? :o Draws about the same at 50mA if i set the voltage at 25V before load it goes to 8V with this bulb on it. There is a faint light.

Also a 3A load, voltage drops to 0.1V or so

Current pot at full off . volts measures -0.06 and the LED is on. if i turn (current pot) it up 10% or so the voltage goes up to 0 which is when the LED turns off. This is with no load.

volt pot at 100%
Voltage at the output is 32.00V
C1 33.8V
D8 5.7V

I have read both this thread and the 5A+ mod thread and i did find a few things around page 20 and some interesting things around page 76 but not really anything the same as the problem i have

Im just after it to actually work right before i change a few things which i do plan on.

Thankx for any help.

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Hi Tinny,
Welcome to our forum. ;D
Your project has a few problems:
1) the 741 opamps have a positive supply of 33.8V as you measured plus a negative supply of 5.6V for a total of 39.4V. Their absolute maximum voltage allowed is only 36V so maybe they are broken.
2) Your transformer has only a 72VA output rating. Then it is overloaded if the output current is more than only about 2.1ADC.
3) The TL081 needed a value for RV1 of 100k in series with 270k to the negative supply.
Your 741 opamp needs 10k for RV1 in series with a wire to the negative supply. Look at its datasheet.
RV1 is a trimmer pot that is small and is adjusted with a small screwdriver. 100 ohms is much too low.

You said that you cannot get more than 50mA from the project. When you try more than 50mA for a load is the current pot set to max and does the LED light to show that it is regulating the current?

The current regulation depends on U3, D9 and the values of  R7, R17, R18, R21 and P2.
R7 is supposed to be 0.47 ohms which is less than half of one ohm. If it is 30 ohms instead then the current regulation will be about 50mA max.

Measure the voltage at pin 4 of U2 and U3. It is supposed to be -5.6V.

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C5. C6 and C9 keep the output from oscillating.


Ok thank you. I have one more question  :) It is impossible to buy OPA445 in my country and TI dont send free samples for me. I can buy LM143 (SG143) OP amp.  Will those op amps work or I must change some parts?   
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The old LM143 and SG143 are very slow and their output voltage swing is limited. Their offset voltage adjustment is different. The circuit would need many changes for them to be used.


Thank you for super-quick answer! So what now? I find next Ha7-2645-5 OP, but best is OPA445 isnt it?
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Where are you where common parts are not available?

Come over to this part of the world where everything is available.

Czech Republic - Europe, Alll distributors of electronics parts doesnt have OPA445, and if I want to buy them, i  must buy 100+ pieces... :-( Iam not crazy.
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Thx for the info audioguru,

it seems the PSU works better with the correct value at R7 0.47 and not 47ohm

now that i can run it over 50mA, looks like i will have to find some better cooling for this power transistor :p 15V at 2A for a few mins and the whole heatsink is pritty hot. small heatsink tho

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That is why I recommend using two output transistors on two separate heatsinks to share the heat.
A 24V transformer is used like in the original project. Then it is set to a low output voltage and set to 3A or its output is shorted. Then the 2N3055 output transistor must dissipate 32V x 3A= 96W. It can dissipate 115W if its case id held at 25 degrees C somehow, but a huge heatsink isn't good enough without also having a fan or liquid nitrogen.

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Hi,

I've just finished making this PSU, and even tho it seems to run ok. a bit hot atm but ill pick up some bigger heatsinks soon enough. I want to learn a bit more about how it works.

eg

How to work out how much heat things might generate and what heatsink is going to work best

D8 is a 5v6 zener but seems to have around 5.8V. will it change much if i find a way to make it the correct voltage? and why, D7 isn't quite right either.

Is ther a way to work out the efficency of a circut ?

This might be a bit off topic but if somone can point me to some info about this kind of theroy.

I have checked out the theroy article forum. well i still am :p

Thanks

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How to work out how much heat things might generate and what heatsink is going to work best

Heat is caused by power dissipation. Power= volts x amps. You have a 24VAC transformer that has a peak voltage of 40.0V. The rectifiers will drop it to an unfiltered positive supply of 38.0VDC at full output current. If your transformer is rated at 120VA then it will be able to supply the 40V peak voltage to the rectifiers at an average current of 3A.

If the voltage is set low and the current is set at 3A then the output transistor will have 38V across it and 3A through it. Then its power dissipation is 38V x 3A= 114W.

The datasheet for a 2N3055 power transistor rates it at 115W when its chip is at its max allowed temperature and its case is held at only 25 degrees C somehow. If its case gets warm then its chip will have over-temperature and it will fail. You cannot buy a heatsink that holds the case of a transistor at 25 degrees C. The transistor will get warm and cannot dissipate its full rated power.

Heatsinks are rated in "degrees rise per watt" where a very big one will have a rating of 1 degree temperature rise per watt. A 2N3055 transistor mounted on one without an insulator will be able to dissipate a max power of 56.7W when its chip is at its max allowed temperature.
A fan would allow more power to be dissipated.

D8 is a 5v6 zener but seems to have around 5.8V. will it change much if i find a way to make it the correct voltage? and why, D7 isn't quite right either.

Most zener diodes have a tolerance of 5%. Then the voltage for 5.6V ones could be from 5.32V to 5.88V. It doesn't matter in this project because the pots have a tolerance of 20%.

Is ther a way to work out the efficency of a circut ?

Efficiency is defined as the ratio of the power output divided by the power input.
If you short the output when it is set to 3A then its efficiency is zero.
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It is too bad that you can't get stuff in your country.

I just order parts from a neighbor country (USA) online and they are delivered to me the next morning.


I can buy: LF356N, OP37, OP07, NE5534. It is possible to use one ot those?

EDIT: I can buy OPA604 - 48V supply voltage
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You can look up the spec's for those old opamps to see if they will fail with a supply voltage from this project that is higher than the max voltage allowed for them.
The OP37 and NE5534 are de-compensated and therefore would oscillate in this circuit.

Since you cannot get modern parts then use a transformer with a lower voltage like 20VAC which would give a unregulated positive supply to the opamps of 29VDC without a load, plus the negative supply of 5.6VDC so they will have a total supply of 34.6V which is less than the 36V max allowed for ordinary opamps.
The project will then have a max output voltage at 3A of current of only about 20VDC.

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I just find out about multimmeter with Atmega8 and I'll do soon. After that i find out about this 0-30vcc psu and I see that is perfect for mai multimmeter  :) but is something that i dont like :
-with 24Vca transformer the Vcc result will be 34Vcc
-D5-D6-C3-R3-D7 make a negative -5,6V power unit
U3 and U2 are bouth powered between +34 and -5.6. Is'nt that 39.6 ? Is'nt that dangerous for TL081 who has 36 (+/-18in datasheet) up limit ? Or maybe something I dont get'it . Thk's

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i find out about this 0-30vcc psu and I see that is perfect for mai multimmeter  :) but is something that i dont like :
-with 24Vca transformer the Vcc result will be 34Vcc
-D5-D6-C3-R3-D7 make a negative -5,6V power unit
U3 and U2 are bouth powered between +34 and -5.6. Is'nt that 39.6 ? Is'nt that dangerous for TL081 who has 36 (+/-18in datasheet) up limit ?

Yes, the opamps have a supply voltage that is higher than their max allowed voltage. They will fail.
Some of the parts get too hot. They will also fail.

That is why I recommend using OPA445AP high voltage opamps, then the transfomer's voltage can be increased to 30VAC so the project's output voltage can reach 30VDC at a current of 3A.

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