0-30V Stabilized Power Supply

[audioguru]

why do I need 3 Transistors for a 5 amp supply?
I checked the datasheet for the MJ11015, and it states it can handle 200W.
From my calculations, I get : 30V * 5 Amps = 150 W...
I should say one transistor is enough...

It can dissipate 200W if its case is cooled to 25 degrees C somehow (liquid nitrogen spraying on a huge heatsink?).

Your math is wrong. The load dissipates 150W not the output transistor.
The 30VAC transformer has a peak voltage of 42.4V. The rectifier bridge drops 2V and the main filter capacitor might have ripple as low as 1V. The current-sense resistor has 1.4V. Then the output transistor has a collector voltage of 38V and dissipates 38V x 5A= 190W.

The heat from the transistor will heat the heatsink so the case of the transistor will be hotter than 25 degrees C so you must reduce the power to keep the transistor from over-heating.
With a huge heatsink, one 200W transistor will be at its max temperature dissipating 120W. With a huge heatsink and a noisy fan the transistor might survive power of 150W.

But do you want to risk operating one transistor at its absolute max rating when adding a second or 3rd transistor is best?

[Holt]

Excuse me.. about the schematic in 0-30V w/ 3A power supply..

can anybody post the new schematic and PCB image and the size of the PCB??

I saw a comment regarding the proj. And I hesitated starting on the project because of the comment by "IVAN" i think.. can anybody post the correct schem. DIAGram and PCB pls..? as soon as possible? tnx very much!!...

The newest schematics and parts list must be this one (Dec 09)

http://www.electronics-lab.com/forum/index.php?topic=19066.msg87803#msg87803

The newest pcb design must be tesseract

[kikitron]

Hi!

4 years ago i builded this project with OPA445 with upgraded parts to 5A and it is working fine. I used 4 pieces of 2N3055 in parallel, for R7 i used 2 pieces of 0,56 ohm/9W in parallel, for C1 i used 2 pieces of 10.000uF/50V.

I desided to build a new one and i dont know if i will use version with OPA445 or new TLE2141.

Did anyone tryed to upgrade this new version to 5A?

[lysium]

Hi audioguru,

just finished soldering all the component using old schematic + old pcb layout with OPA445 and 25Vac 6.25A toroid. but there is a problem the output can not be adjust? and the U1 is slightly hotter than the others. do you have test point what the voltage should be at that point so i can check it.

and R2 and R3 is really hot around 40-60 celsius is this normal?

thanks

[audioguru]

just finished soldering all the component using old schematic + old pcb layout with OPA445 and 25Vac 6.25A toroid. but there is a problem the output can not be adjust? and the U1 is slightly hotter than the others. do you have test point what the voltage should be at that point so i can check it.

U2 has a variable input voltage of 0V to +11.2V from the voltage adjustment pot. U2, Q2 and Q4 make an amplifier with a voltage gain determined by R11 and R12 so the gain is 3.074 times. Q2 and Q4 are emitter-followers with a base to emitter voltage of about +0.7V when the load current is low so the output voltage of U2 should be +1.4V higher than the output voltage of the project.

You forgot to say what the output voltage of your project is stuck at.
Usually the pins of Q2 or Q4 are connected backwards.

R2 and R3 is really hot around 40-60 celsius is this normal?

Many other parts in the original parts list also get much too hot because they are too small.
R2 should be 2W and R3 should be 1/2W.

thanks

[DD1WKS]

@audioguru:
i will build the power supply with the old PCB and schematic,
i change the tl081 to tle2141 and change also the other stuff
about your list (http://www.electronics-lab.com/forum/index.php?topic=19066.msg87814#msg87814)

is that correct?

and excuse my bad English

Thanks

Wolfgang

[audioguru]

@audioguru:
i will build the power supply with the old PCB and schematic,
i change the tl081 to tle2141 and change also the other stuff
about your list (http://www.electronics-lab.com/forum/index.php?topic=19066.msg87814#msg87814)

is that correct?

You have the latest parts list but the latest schematic  and pcb are different to the original one.
Here is the latest schematic that goes with the parts list you found.

[lysium]

U2 pin 3 0V to +11.2V checked, U1 pin 6 +11.27V, but when i put the Q1 U2 become Hot so right now i disconnect Q1. i have  swap the BCE of Q1 but the U2 still hot.



i can not measure output voltage because i disconnect Q1 and Q2. but at collector Q4 is 30.5V



i use the part list for the OPA445 as you post at the beginning of this thread. R2 82Ω 3W and R3 220Ω 1/2W


thanks

[audioguru]

U2 pin 3 0V to +11.2V checked, U1 pin 6 +11.27V, but when i put the Q1 U2 become Hot so right now i disconnect Q1. i have  swap the BCE of Q1 but the U2 still hot.

Q1 is used when the U2 opamp is a TL081. Q1 is not needed when the U2 is almost any other opamp.
I think your Q1 is turned on all the time because something is wrong with your negative -5.6V supply.

I can not measure output voltage because I disconnect Q1 and Q2. But at collector Q4 is 30.5V.

With Q2 disconnected, R16 should turn off Q4. The collector of Q4 is supposed to be connected to the positive unregulated supply (about +36V with your transformer). The emitter of Q4 is the output which should be 0V when Q2 is removed.

R2 and R3 is really hot around 40-60 celsius is this normal?

I think something is wrong with your negative -5.6V supply. Measure it.

[lysium]

Q1 is used when the U2 opamp is a TL081. Q1 is not needed when the U2 is almost any other opamp.
I think your Q1 is turned on all the time because something is wrong with your negative -5.6V supply.

so i just remove the Q1, R13, R14, R15, D10 correct?

I think something is wrong with your negative -5.6V supply. Measure it.

is it in D7 i have to measure the -5.6V?

thank's

[audioguru]

so i just remove the Q1, R13, R14, R15, D10 correct?

No.
Remove only Q1, R13 and R14.

is it in D7 i have to measure the -5.6V?

Yes.

[kvakva]

In original schematic, what is the "role" of R16 and D10?
Thanx!

[audioguru]

R16 bypasses any leakage current in Q4 when it gets hot to turn it off when it is supposed to conduct a small current.
D10 discharges C7 when the output voltage suddenly is reduced and there is no load.

[lysium]

Q1, R13, R14 remove now and the output at emitter Q4 +29.8V collector +31.5V

without load (remove all ICs) it is -5.6V. with load (all component) except Q1, R13, R14 is -2.1V

thanks

[audioguru]

You have a serious problem with your -5.6V supply. Replace R2 and C2.

[lysium]

You have a serious problem with your -5.6V supply. Replace R2 and C2.

just replace R2 with higher watt, 5W and C2 with branded one still -2.1V with full load. output still stuck at 28.5V.
R7 because i have difficulties to find one so i use 4 1Ω parallel is it problem?

thanks

[halentech]

Why do not use cheap LF356? I have one channel power supply made with those OPAMPs and works great. I think, that those are good alternative for MC34071 and TLE2141

[halentech]

What's conclusion is about this modification:


Received the following email from Ivan on 02/2010:

    Ok. I bulid your project about a day ago. Mounted all the parts on the pcb and then concluded that there is some serious problems in this schematics. First, 2N3055 will overheat, so you have to connect two of them in parallel with emitter resistors 0.1ohm/5w. Second, maximal voltage between '+' and '-' of TL081 is 36VDC.If you connect them as it is shown in this circuit diagram that voltage will be about 45VDC, so they will burn down immediately. To fix this problem you have to reconnect all pins number 7 of U1, U2 and U3, emitter of Q3 and 'upper' end of R19 to out of an 7809 with 18V zener diode between 'common' pin and '-' of 3300uF cap, and input of 7809 connect to '+' of the same cap. Now, on pin number 7 and mentioned parts you'll have 27VDC, and total voltage will be 32.6VDC. Third, instead of using 3300uF, use 4700 or 6800uF/63VDC to reduce the ripple on higher currents (2-3A). The rest of the circuit is perfect. I like it cause it is so inexpensive and easy to make with those simple reconstructions i mentioned.

[tesseract]

@jeroenj_1989

I use 3x MJ11016 Transistors. I used 3 Transistors because i need 5A.  The powertransistors on heatsink. The transistors are paralell copuled. And so i have on the PCB only 3 conections.

[audioguru]

just replaced R2 with higher watt, 5W and C2 with branded one still -2.1V with full load. output still stuck at 28.5V.

The opamps should draw only a small amount of current from the negative supply. Your U2 or U3 opamp draws too much. Find it and look at how it is connected wrongly.

R7 because i have difficulties to find one so i use 4 1Ω parallel is it problem?

R7 should be 1.92V/3A= 0.64 ohms. The original project had a max putput current of 1.92V/0.47 ohms= 4.1A which is too high.
We use 0.47 ohms then calibrate for a max current of 3A.
With 0.25 ohms then your max current is 1.92V/0.25 ohms= 7.68A which is much too high.

[audioguru]

Why do not use cheap LF356? I have one channel power supply made with those OPAMPs and works great. I think, that those are good alternative for MC34071 and TLE2141

The MC34071 or TLE2141 opamps are used in the latest version because their max allowed supply is 44V and their inputs work at their negative supply voltage which is 0V for U2. these opamps do not need q1 to short their output when the mains power is turned off.

the TL081 opamp in the original project and the LF356 that you are talking about have a max allowed supply of only 36v and they need a -5.6V supply because their inputs do not work if their voltage is close to the negative supply voltage. They need Q1 because they have the Opamp Phase Inversion problem.

[audioguru]

What's conclusion is about this modification:

Received the following email from Ivan on 02/2010

Maybe Ivan did not see our modified circuit.
The original project has many problems. It does not produce 30V at 3A (its max is 25V at 3A) and many of its parts get too hot so it is unreliable. Its little transformer is overloaded.

Ivan's modification is not needed because the transformer voltage could be reduced to do the same thing. The driver and output transistors are emitter-followers so with Ivan's 27V positive supply the max output from his project is only about 20V or less.

[halentech]

The MC34071 or TLE2141 opamps are used in the latest version because their max allowed supply is 44V and their inputs work at their negative supply voltage which is 0V for U2. these opamps do not need q1 to short their output when the mains power is turned off.

the TL081 opamp in the original project and the LF356 that you are talking about have a max allowed supply of only 36v and they need a -5.6V supply because their inputs do not work if their voltage is close to the negative supply voltage. They need Q1 because they have the Opamp Phase Inversion problem.

But LF356 has 44V power supply, so it is usable for this project. As I say, I used those opamps in this psu before and withouth problem at all.

[audioguru]

The datasheet from the inventor, National Semiconductor shows the expensive LF156 with a max supply of 44V and the cheap LF356 with a max supply of only 36V.

[GabrielRR]

Hi audioguru,

After this suggestions made by you and the others, what's the best and final circuit. By the way and what about tesseract's circuit, it seems quite simple...

Thank's in advance