0-30 Vdc Stabilized Power Supply

[LEECH666]

Hi audioguru,

I didn't even notice that this (*click*) post was from 2007.

No wonder the parts list doesn't match!

I am having trouble finding the right documents though. Couldn't find the parts list anywhere in the last 12-13 pages. And I think others will have this problem too.You partly solved my problem, as you just posted the right parts list again.

[Question removed, I really should learn to read your answers properly.]

Thank you for your quick help.

Cheers,
Florian


//EDIT:

Sorry I made a mistake, I was actually talking about this resistor.
http://tinyurl.com/2wg733q

I got 0.33 Ohm confused with 0.47 Ohm, I tried to fix my mistake in the first post by editing it but I didn't edit the link to the resistor and overlooked one of the mistakes.
But anyway you already answered my question.

Thanks again.

 

[abdulwaheed]

I really enjoyed the blog

 

[sorin0306]

hi
I have stimulate your circuit with multisim.
the test value are this:
RL=35 ohm

but a have some problem with the stability!!!
is this normal? ???
thanks!

View attachment 41209

 

[mendimano1]

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.

Dear Audiguru can you tell me is this changes  that you have posted in a latest parts lists ( R1=2.2Kohm , R11=27Kohm, R15=100Ohm, R18=33Kohm, R22=3,9Kohm)
are aplicable for 5 Ampers version of power supply

old values for this rezistors are ( R1=3.9Kohms, R11=10Kohm, R15=(there is no),  R18=20Kohm R22=1.2Kohm)

 

[audioguru2]

R7 is 0.47 ohms for 3A max and is 0.27 ohms for 5A max. All other resistor values do not get changed.
Of course for a max of 5A you need a 28V/200VA transformer (7.14A).

 

[mendimano1]

And what about R15 ? where is placed this resistor? in my schematic i dont have R15.

View attachment 41210

 

[audioguru2]

R15 was used on the original circuit but is not used anymore.

 

[belisimo]

Hi after finishing my power supply the U2 was overheating. I eliminated Q1 so it was ok, but the output was going from 22v to 2v and then goes up to 22v. i cant reulate it with RV1 and i cant controll the current. Can anyone halp me?

Sorry for my bad english

 

[audioguru2]

Opamp U2 drives transistor Q2 which drives transistors Q4 and Q5.
When the output load current is 3A then the max base current into the combined Q4 and Q5 is 86mA. Then the max base current into Q2 is about 1.7mA. Then the max output current from opamp U2 is only 1.7mA which will barely make it a little warm, not hot.

When there is less output current the ouput current from U2 is less.
When there is no output current then there is no output current from U2. Its idle current will make it a little warm.

If the C and E pins of Q2, Q4 or Q5 are connected backwards then they draw much more current than they should which will make them and/or U2 very hot. Look at the pins on the datasheets for the transistors.

 

[kankki]

Hello everyone!  8)

I am having some trouble with this circuit. I have milled out a PCB according to the schematic I attached. (it's from Eagle). Soldered everything up and it kind of works.

The current limiting is acting weird though. Seems like there is some hysteresis on it. When I set the current limit to e.g. 0.5A you have to go to 1A for the current limiting to kick in. After that it works just fine. But if I then wind the current limit up and down again I have the same problem.

The large heatsink on the board are for the flyback diodes and the smaller one for the BD139. The transistors and large heatsink is gonna be mounted outside the chassi.

I have also tried with a .47ohm shunt resistor.

Does anyone know what could be causing this problem?  ???

Any help would be greatly appreciated.  ;D (maybe this has been answered before, but I couldn't find an answer)

View attachment 41267

View attachment 41268

View attachment 41269

 

[audioguru2]

Hi Kankki,
Your schematic is normal so I don't see anything wrong with the current regulation.
When the output current tries to exceed the setting of the current pot then the circuit should reduce its output voltage so that the current stays at the setting.

You probably have an error or short on your pcb around the current control opamp.

You changed all the Rx, Cx and Ux numbers so it is difficult to compare your circuit with all the other schematics.

 

[kankki]

Oh ,okay I'm gonna try and look for errors on the PCB 

 

[gogo2520]

Hello
  I am going to give this one a try( finally ) I have been reading the thread for about two years now.  I already have two good bench top power supplies but I have a cnc  machine project coming up and I want to build its own power supply.  A variable supply would work perfect, because  I plan on testing out different size motors. The blog on cnc machines re sparked my interest.  Hobbies are illnesses you know and I don't plane on getting well soon.
have fun :
gogo

 

[kankki]

Hello again. I've taken a closer look at the PCB and fixed up some suspicious looking solder joints and so. I haven't gotten it working yet, rather it became worse  : Heh.

I don't know what I did but now the CC LED is always on and it only becomes slightly brighter when the current is limited. Something wrong with Q3?

And I still have the hysteresis problem.. I've noticed something though. It seems that in order for the current limiting to kick in the output voltage needs to rise to (the normal point where it would start to drop + forward voltage of a diode, about .6 volts.) Then it starts limiting the current and works until I turn I raise the current limit again. Could it have something to do with D9?

I've attached my schematic with the original schematics component names so it's easier to see. I'm also attaching my board layout.

Again, I'd really appreciate some help  

Oh, and the 20k pot isn't connected to GND it's connected to "before shunt-gnd". A drawing mistake  :-[

View attachment 41271

View attachment 41272

 

[gogo2520]

I put this post up so people will know what were talking when it comes to the two different power supply threads. To bad we can't rename  them one and two or old and new
gogo

 

[audioguru2]

U3 is supposed to have a DC voltage gain of typically 220000. Maybe it is bad or C4 is leaky.
Maybe U3 is a counterfeit IC that cannot reduce its output voltage as low and and does not have inputs that work at such a low voltage as a real TLE2141 opamp.

When U3 is not regulating the current then its (+) input is higher than its (-) input so its output is high which turns off transistor Q3 and reverse-biases D9.

When the load current in R7 produces a voltage at the (-) input of U3 that is slightly higher than the voltage at the current-setting pot P2 which is the (+) input of U3 then the output voltage of U3 should drop which turns on transistor Q3 which turns on the LED, and diode D9 causes the voltage at the input of opamp U2 to drop. Then the output voltage drops low enogh that the current in the load is reduced to the setting of the current-setting pot.

Sorry, I didn't look at your pcb. U do dat. 

 

[kankki]

Thanks for the reply! I fiddled around with my board a  bit and lo and behold- the hysteresis thing just disappeared. Hope it ain't intermittent. The LED is still acting weird. Gonna do more research on that tomorrow.

One thing though. Is there supposed to be a ~2v drop across the pass transistors when they are fully open? I measured the base voltage when they are supposed to be fully open and it was around 1.1v.

Is the On-resistance that high on the TIP3055's that I'm using 

Anyways thanks for the help so far

 

[audioguru2]

I fiddled around with my board a  bit and lo and behold- the hysteresis thing just disappeared.

Good. you fixed it.

Is there supposed to be a ~2v drop across the pass transistors when they are fully open? I measured the base voltage when they are supposed to be fully open and it was around 1.1v.

Doors and windows open and close. But transistors turn on and turn off.

The output transistors are not fully turned on in this circuit because the opamp U2 cannot drive its output voltage high enough. U2, Q2 and the output transistors have a combined voltage loss of as high as 5V.

Is the On-resistance that high on the TIP3055's that I'm using  ?

A Mosfet has an on-resistance but a transistor has a voltage loss.
The datasheet for the 2N3055 transistor shows a max voltage loss of about 1.7V. The driver transistor Q2 has an additional voltage loss, opamp U2 has an additional voltage loss and current-sensing resistor R7 also has an additional voltage loss. Extra voltage must be provided when the mains electricity voltage is a little low.
So for an unregulated positive supply of typically 37.6VDC, the max regulated output is only 30.0VDC.

 

[kankki]

Thanks a lot for the help! 

 

[redwire]

gogo2520,  

I would not have an objection if you labled this thread "old"  and the other one "new"  or part 1 and part 2.     I started the other  tread when this one was  lost.  It was meant to be a continuation of the original thread.  Having 2 out there  is confusing to new posters.   The this one could be available for viewing but closed for posting.