0-30V Stabilized Power Supply

[Tarkul]

Hey umm does anyone that has a working supply did a voltage table for the nodes on the circuit? It would be of great help. Thanks in advance

 

[audioguru2]

Hey umm does anyone that has a working supply did a voltage table for the nodes on the circuit? It would be of great help. Thanks in advance

It is a very simple circuit. Tell us which version you made and the problem you have with it and we will tell you the voltages that should be measured and what might cause your problem.

For example the output of U1 is always 11.2V. The output of U2 is about 1.7V higher than the output voltage.

 

[Tarkul]

I made the version that is in the page http://www.electronics-lab.com/projects/power/003/. My problem is that the LED is always 'on', and the output voltage steadily declines. The only component taht gets a bit hot is the transistor 2n2219 (Q2) after having it connected 1 minute. The circuit doesn't respond to any of the potentiometers or the trimmer. The rectified/filtered voltage is 36V DC.

 

[audioguru2]

I made the version that is in the page http://www.electronics-lab.com/projects/power/003/. My problem is that the LED is always 'on', and the output voltage steadily declines. The only component taht gets a bit hot is the transistor 2n2219 (Q2) after having it connected 1 minute. The circuit doesn't respond to any of the potentiometers or the trimmer. The rectified/filtered voltage is 36V DC.

Check that the -5.6V supply is actually -5.6V.

U3 is the current regulator that detects the voltage across R7 that is caused by load current and compares it to the voltage of the current-setting pot which goes from almost 0V to +1.92V. Since the (+) input of U3 connects to the current setting pot then its voltage is usually higher than the voltage across R7 so the output of U3 is high and then the LED is turned off and D9 does not reduce the output voltage. Check the pins and parts connected to U3.

The 2n2219 is much too small for this project and will over-heat if the output is set to a low voltage or is shorted with the current set high. A BD139 transistor should be used with a real heatsink.

The original project uses TL081 opmps that have an absolute max total supply of 36V. In your circuit U2 and U3 also have the -5.6V supply so their total supply is too high at 41.6V and maybe they are destroyed or maybe they will fail soon. Use MC33071 or TLE2141 opamps that are rated at 44V.

 

[redwire]

PicMaster,  How come R1 and R2 in your sketch  have signifcantly different values than the revised parts list?

 

[PicMaster]

PicMaster,  How come R1 and R2 in your sketch  have signifcantly different values than the revised parts list?

Sorry that's my fault I missed those 2 values I can see that they should be 2K2 and 82R, Thanks for pointing that out, I will recheck the rest of the values,

I presume that everything else is ok ?
PCB is about 80% laid out and routed I will post as soon has it is done.

Thanks

 

[bugmenot1]

Have any chance to make the RedWire circuit mod work with 30A?
Maybe change only the transformer (30Vx30A) and the retify diodes, number of power transistors and wire diameter?
I suggest Redwire to put in the beginning of the topic the most recent files so that we don't need to seek for the whole topic that today is with 18 pages. Please include the Eagles files too (.sch and .brd)

 

[audioguru2]

To get a 30A output then the output transistors must dissipate a total of 1,188W at times.
Liquid nitrogen will be needed to cool them.

The driver transistors also must be many. Opamp U2cannot drive many driver transistors so a pre-driver transistor or a few of them and a pre-pre-driver transistor must be used. Then the max output voltage will be reduced.

If you are a good circuit designer you could use a switching pre-regulator to reduce the heat.

 

[redwire]

PicMaster,  You have other mistakes on your board.    R12 and R11 form a voltage divider.  Your board  seems to have errors in this area. 

 

[redwire]

bugmenot,          I have been meaning to do that for a while and I strongly agree it would be more helpful than searching through 20 pages.  When I first posted, I had some info on my computer at work, some at home and some I had to gather from other posters since the site crashed.      I'll try to round up the parts and put them in a zip file.  A continuing  problem is that my Eagle file is double sided and a pain to make at home. 

 

[PicMaster]

PicMaster,  You have other mistakes on your board.    R12 and R11 form a voltage divider.  Your board  seems to have errors in this area.   

Thanks for that I did spot that one, This has now been corrected, Aslo ZD3 has been reomved has it is not needed,

Thanks
Picmaster

 

[Tarkul]

Hey. Ive beentrying to fix the circuit. The problem now is that the ooutput voltage is steady at -0.5V!!! The good news is that the current limitng LED is now off... Voltage of D7 is -0.7V voltage of U2(out) is zero u3 is 32V and u1 is 8.3, D8 is at -5.6V.
Thanks a lot audioguru

 

[mendimano1]

Hi Audioguru, as i sead earlier i have decided to build the modified version with this parts list and schematic, please if you have any new ideas and version to post it beafore i have start to buy parts, rgr

PS_Parts_List_10-11-09.pdf

 

[audioguru2]

Hey. Ive been trying to fix the circuit. The problem now is that the output voltage is steady at -0.5V!!! The good news is that the current limitng LED is now off... Voltage of D7 is -0.7V

D7 is a 5.6V zener diode. Its voltage should be -5.6V so maybe you installed it backwards and maybe D5 and D6 are installed backwards.

voltage of U2(out) is zero

U2 will not work properly without a -5.6V supply. The output from U2 should go from about +1V to about +32V in your circuit.

u3 is 32V

It is low because your 24VAC transformer voltage is too low.

u1 is 8.3, D8 is at -5.6V.

The output of U1 should be +11.2V (the 5.6V from D8 times a gain of two). R4 should be changed to 1k.
D8 should be a 5mA zener diode (BZX79C5V6).

 

[effenberg0x0]

For the 3A version, R7 is 0R47 10W. I got 0R27 10W units. If i put two of them in series I get 0R54 and better heat dissipation (two components instead of one). But what would be the downsides?

 

[audioguru2]

The original circuit with 0.47 ohms had a max current of about 4.1A which is too much for most of the parts.
With 0.54 ohms the max current before calibrating will be about 3.5A before calibrating.

 

[Tarkul]

Hey audioguru, i inverted de D7 zener, but still gives me bellow 1V. Maybe I ought to change the diode. Just one question. I had some 6A rectifying diodes, which I used for the rectifying part. Do you think this can be the source of the error? The diodes only say
6 A 4    
UTL
So Im not sure of their code.
Thanks again

 

[audioguru2]

So Im not sure of their code.

Then throw them away and use good diodes that are very inexpensive.

 

[effenberg0x0]

The original circuit with 0.47 ohms had a max current of about 4.1A which is too much for most of the parts.
With 0.54 ohms the max current before calibrating will be about 3.5A before calibrating.

The original is 0R47 5W. Your's (fixed 3A version) is also 0R47, but 10W.
Do you think two 0R27 10W in series is still too little and risky?

Thanks,
Effenberg

 

[audioguru2]

The original is 0R47 5W. Your's (fixed 3A version) is also 0R47, but 10W.
Do you think two 0R27 10W in series is still too little and risky?

The original circuit had many parts overloaded. For example its current was not calibrated so when set to max it was typically 4.1A (it could be higher if you have parts on the wrong side of their tolerance). So the poor little 0.47 ohm/5W resistor was dissipating 7.9W and was almost incandescent. If the current was calibrated for 3A max then the 5W resistor dissipated 4.23W and was still extremely hot.

Your 0.27 ohm resistors total 0.54 ohms and if the current is calibrated for 3a then each resistor dissipates 2.43W which is fine for a 5W resistor and is a waste for a 10W resistor.