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0-30V Stabilized Power Supply

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To make a negative power supply you make the project and use the + output as ground and use the GND output as the negative output. Its transformer must be completely separate from the positive supply project transformer but they can use a single transformer with two completely separate windings.

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audioguru, I mounted transistors on heatsink and tryed PSU. I shorted its output and measure current. At voltage set to 30V and current regulation pot set to highest value, I calibrated it to max current 3A. But when I get near the minimum setting of current adjustment pot, it took about 5-10A. I quickly powered it off to prevent any damage. Why is that? Current regulation doesn't work fine. At highest value of current adjustment pot, I measured 3A, then I was slowly turning it down. Current was always not less than 2,96A at same voltage (30V). But when I got near minimum, LED turned on and that happend (5-10V). What could be wrong with my current regulation?
PS.: I forgot to mention, that I used 25k for RV2 instead of 20k...does this makes any difference?
PPS.: We talked about D8, if you remember. I used BZX85C instead of BZX79C and you said that BZX85C regulates porely. I don't have BZX79C, but I have BZX55C. Can I use it?
PPPS.: Is it possible, that one of D7 diodes in series is faulted, becouse voltage drop across theese two is just 400mv..(they are not shorted, I checked)...

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Hi Fikic,
In order for the current regulator to limit the current when the output is shorted then the anode of D9 must go very close to ground which causes the output voltage to be very close to ground which limits the current.
Then the output of U3 must go down to about -0.7V. A TLE2141 or MC34071 opamp was selected for U2 because it has an output that goes down almost to ground and has inputs that work at ground. If one of these opamps is used for U3 then a negative supply for it of only -1.3V is fine. But if an ordinary opamp is used for U3 then it needs about -5.6V for its negative supply and the 10V zener that feeds it its positive voltage might need to be changed to a higher voltage.

Did you not use a TLE2141 or MC34071 opamp for U3?
Is your negative supply not working at -1.3V?

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Good evening. I have collected your scheme, voltage regulation is working well, up to 25 volts regulated (24 volt transformer). But the current regulation does not work at all. In fire diode current limit on the output of 5 volts and the current order of 20 mA. removing the current limit mode, the output from the power supply to 12 amps ...
Tell me what could be and how to configure the boundary current. Podstroichnye resistors do not change anything from the current output. I have a resistor to 20k U2 set the maximum output voltage. But when you switch current limit voltage below 5 volts drop failed. Thank you for your help.

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I shorted its output and measure current. At voltage set to 30V and current regulation pot set to highest value, I calibrated it to max current 3A. But when I get near the minimum setting of current adjustment pot, it took about 5-10A. I quickly powered it off to prevent any damage. Why is that?

Current regulation doesn't work fine. At highest value of current adjustment pot, I measured 3A, then I was slowly turning it down. Current was always not less than 2,96A at same voltage (30V). But when I got near minimum, LED turned on and that happend (5-10V). What could be wrong with my current regulation?

The LED is supposed to turn on when the current regulation is beginning to reduce the output voltage.
If it is calibrated to begin current regulation when the output current is 3.0A then its should begin current regulation at less output current when the current adjustment pot is turned down.
When the current adjustment pot is turned down to minimum Then the output current should be no more than a few mA.

Did you always have the voltage set to 30V? Then if you have a 10 ohm load for 3A at 30V, the output voltage should drop to 1.0V when the load is 0.33 ohms.

Maybe you have the terminals of the pots connected backwards.  


PS.: I forgot to mention, that I used 25k for RV2 instead of 20k...does this makes any difference?

No.

PPS.: We talked about D8, if you remember. I used BZX85C instead of BZX79C and you said that BZX85C regulates porely. I don't have BZX79C, but I have BZX55C. Can I use it?

Didn't you look at its datasheet? It is tested at 5mA like the BZX79C so it is perfect.

PPPS.: Is it possible, that one of D7 diodes in series is faulted, becouse voltage drop across theese two is just 400mv..(they are not shorted, I checked)...

Something is wrong with your -1.3V supply. Each diode should have a voltage of 0.65V to 0.7V so their total is supposed to be -1.3V to -1.4V. That is the cause of your problem.

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Ok, I replaced D7 (two diodes) and it doesn't make any difference, so this is not the case. Diodes are fine. Voltage drop across both of them is just about 400mV.  ???
Can you pleeeeease take a look at my schematic and PCB, becouse I don't see any mistake now..please..

dokumentacija.zip

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Hi Fikic,
Your schematic is correct. Your pcb is an Eagle file that I cannot open because I do not use Eagle.
Check the values of R2, R3, C2 and C3. Replace diodes D5 and D6.


PCB is not Eagle, it's Kicad..I will send you pdf..

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Are there some safety measures for shortening the +/- outputs of the PSU? Also where is apropriate to put a fuse before the regulator and how much A to be? And one more question. The Voltage regulator is working perfect. The current regulator also work, but when the potenciometer is nearly at the beggining (few mAs) the current limit led lit and the voltage goes to almost 0V ( with 15-16V regulated for example). So is there something wrong with the current regulator or it's normal?

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Hi, I need your help.
I built this project (last version with MC34071). I tried to run the power supply in this morning. I measured the input voltage before insert the op amps in the sockets. The AC voltage was 30V, but the DC voltage was more than 50V, about 55Vdc.
I used two caps 6800uF/63V in parallel. I changed them with one 15000uF, but no modification. I measured with , two different digital multimeters with the same value. What is wrong?
Please help and excuse my english.

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Are there some safety measures for shorting the +/- outputs of the PSU?

If the output is shorted then the current regulator limits the current to its setting. all the parts should be rated and cooled so they do not get too hot.

Also where is apropriate to put a fuse before the regulator and how much A to be?

the fuse should be in series with the high voltage power on/off switch. Use a slow-blow fuse rated for a draw of 150W.

The Voltage regulator is working perfect. The current regulator also work, but when the potenciometer is nearly at the beggining (few mAs) the current limit led lit and the voltage goes to almost 0V ( with 15-16V regulated for example). So is there something wrong with the current regulator or it's normal?

Your opamp U3 has a high input offset voltage. Null it with a pot (like at U2) or increase the value of R17.

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I measured the input voltage before insert the op amps in the sockets. The AC voltage was 30V, but the DC voltage was more than 50V, about 55Vdc.

The peak voltage is 30V x 1.414= 42.4V and the bridge rectifier reduces it to 41.0V with no load.
Maybe your filter capacitor was charged to a higher voltage. R1 should slowly discharge it.

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The peak voltage is 30V x 1.414= 42.4V and the bridge rectifier reduces it to 41.0V with no load.
Maybe your filter capacitor was charged to a higher voltage. R1 should slowly discharge it.

Thank you Audioguru for your replay. I know the peak voltage should be around 42 Vdc, but I don't understand what is wrong. The filter capacitor is ok, it's discharged by R1. Could be the bridge rectifier defective ?  I measured the negative voltage ,too. It was 1.47 Vdc. It's ok or it's too high?

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How exactly to null it? I'm using PicMaster's schematic and there isn't R17. What value it should be?

R17 is R16 on my schematic They are both laid out the same order so you can cross referaence from the original version. If I get time I will correct my version so it's the same has the original

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How exactly to null it?

I said to null the input offset voltage of the opamp in the current regulator circuit exactly the same as it is done with the opamp that is in the output voltage amplifier. With a trimpot and resistor between pin 1 and pin 5 of the opamp.
I'm using PicMaster's schematic and there isn't R17. What value it should be?

Again we are sorry that PicMaster changed all the parts designation numbers. R17 on my schematic is 33 ohms. If its value is increased a little then the current regulator will stay off without a load.

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I said to null the input offset voltage of the opamp in the current regulator circuit exactly the same as it is done with the opamp that is in the output voltage amplifier. With a trimpot and resistor between pin 1 and pin 5 of the opamp.

Again we are sorry that PicMaster changed all the parts designation numbers. R17 on my schematic is 33 ohms. If its value is increased a little then the current regulator will stay off without a load.

So, what value should I use, 68 ohms or ?

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Hi Audioguru

I seem to be having a problem, I've just finished the second board and while testing, C7 explodes into pieces about a 1 or 2 seconds after I power up, I replaced it and the same thing happened again. The transformer is the same one I use on my other board, so it can't be it.

any idea where I can start? as I can test without powering it up?

When I powered it up the 2nd time, I had my meter on the output, and it seemed to sit at about 30V.

C7 where 10uF 50V electrolytic.

Thanks

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I remember now why I created a new BOM is that some of the parts do not exist now like the .33R power transistors resistors . I will check that all the values are correct and I have decided to leave my version has it is, After all it is so simple to cross reference between the two drawings and BOM but I can't see the reason or nay need to, Has I built my PSU off my version including the bom. I will correct the last sheet which is the Assembly drawing

morpheous87  I would try 47R then 51R and just increase it a little until it works, I never had this trouble with mine

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morpheous87  I would try 47R then 51R and just increase it a little until it works, I never had this trouble with mine


May be there is something wrong with U3 oamp. I'll try first with a new one, then increasing the resistor's value.

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Hi Audioguru

I seem to be having a problem, I've just finished the second board and while testing, C7 explodes into pieces about a 1 or 2 seconds after I power up, I replaced it and the same thing happened again. The transformer is the same one I use on my other board, so it can't be it.

any idea where I can start? as I can test without powering it up?

When I powered it up the 2nd time, I had my meter on the output, and it seemed to sit at about 30V.

C7 where 10uF 50V electrolytic.

Thanks


Ok, found the fault, didn't fit the header for the off board LED, which one the the legs acts as a "via"

Will get new caps tomorrow and test again.

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