audioguru Posted January 11, 2006 Report Share Posted January 11, 2006 Did the circuit make about -5.6V? If it was much less then Q1 will turn on when it shouldn't. Quote Link to comment Share on other sites More sharing options...
Tedy Posted January 11, 2006 Report Share Posted January 11, 2006 Voltage across D7 is 0.71V :o Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 11, 2006 Report Share Posted January 11, 2006 Isn't D7 installed backwards? Quote Link to comment Share on other sites More sharing options...
Tedy Posted January 11, 2006 Report Share Posted January 11, 2006 that colored ring is pointing to ground (0V) ???Here are some more measurments on -5.6V elements:Ud5=266mVUr2=0VUd6=420mVUr3=5mVUr14=-220mV (common of instrument was on Q1 base)Uc2=40V (common of instrument was on negative of cap.)Uc3=650mV (common of instrument was on negative of cap.) Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 12, 2006 Report Share Posted January 12, 2006 Hi Tedy,Your Zener dagram is confusing. It shows the polarity of ordinary diodes, not zener diodes.Your D7 is installed correctly. D5 also has its cathode to ground.Your lowest voltage is at C3, maybe it is shorted.Do you have a 4-diode full-wave-bridge rectifier for D1 to D4?Is the transformer's terminal #2 on my sketch accidently grounded? Quote Link to comment Share on other sites More sharing options...
Tedy Posted January 12, 2006 Report Share Posted January 12, 2006 HiI have checked C3 and it is not shorted, yes I have 4 rectifier diodes.My D5 is also installed corectly.Transformers terminal #2 is not grounded. Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 12, 2006 Report Share Posted January 12, 2006 Well, there isn't much remaining:R2 or C2 are open or the wrong value.D5 or D6 not working or backwards.Shorted diode in the bridge rectifier.Broken trace or shorted traces on the pcb.??? Quote Link to comment Share on other sites More sharing options...
Tedy Posted January 12, 2006 Report Share Posted January 12, 2006 Shorted diode in the bridge rectifier.That was it, thanks ;DIt was cold joint at D1 :-[ Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 12, 2006 Report Share Posted January 12, 2006 Hi Tedy,Great! You fixed it. ;D Quote Link to comment Share on other sites More sharing options...
rodrigo.j.p Posted January 25, 2006 Report Share Posted January 25, 2006 the output of my power supply remains always in 30V the input+ of U2 have regulation of 0,3 - 11,2 V but your output remains in 30V sorry for my English but i'm from brazil and my English is very bad ;D Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 25, 2006 Report Share Posted January 25, 2006 Hi again Rodrigo,Before your supply's problem was that its output voltage was too low. Now it is too high. What happened that changed it?Is Q2 or Q4 shorted?What is the output voltage of U2 when the voltage control pot is turned down? It is normal for it to go low but U2 will overheat if left for much time. Quote Link to comment Share on other sites More sharing options...
rodrigo.j.p Posted January 26, 2006 Report Share Posted January 26, 2006 I find that the problem is in the U2 because your output is not gradual in the input - of u2 i have 10,5V and the input + i have 0V to 11,3V q2 and q4 is OK Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 26, 2006 Report Share Posted January 26, 2006 Hi Rodrigo,The input voltage to U2 should change smoothly from 0V to about 11.2V from the voltage adjust pot. Without a load, U2's output voltage should change smoothly from about 1.2V to about 36V (if the supply voltage is high enough) since Q2 and Q4 are emitter-followers and since R11 and R12 apply negative feedback to U2 so that the output stage has a gain of 3.1.U2 has a gain of 200 thousand so its inputs should have just about exactly the same voltages. Since yours has its - input voltage too low at 10.5V then it is trying to force its output as low as it can. Replace U2 and turn off the power if it gets hot.Which opamp did you use for U2? Quote Link to comment Share on other sites More sharing options...
rodrigo.j.p Posted January 26, 2006 Report Share Posted January 26, 2006 U2 = TL-081i replace them but the problem continued. Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 26, 2006 Report Share Posted January 26, 2006 Hi Rodrigo,Check the pins on Q2 or Q4. If its base is connected to +30V where its collector is supposed to be then the output voltage will stay at max. Quote Link to comment Share on other sites More sharing options...
rodrigo.j.p Posted January 27, 2006 Report Share Posted January 27, 2006 the pins are corect Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 27, 2006 Report Share Posted January 27, 2006 Hi Rodrigo,It is time to troubleshoot your project:1) Remove R15 (1k or 100 ohms), R12 (56k), C6 (100pF) and C9 (100pF).2) Temporarily connect the 56k resistor where C9 was.3) Turn on the power without a load and measure if the output pin 6 of U2 goes smoothly from 0V to 35V when the voltage adjustment pot is turned.4) Measure the project's output voltage, it should be 0V.If U2's output works properly then it is fine.If the project's output has high voltage then either Q2, Q4 or both are bad. Quote Link to comment Share on other sites More sharing options...
rodrigo.j.p Posted January 29, 2006 Report Share Posted January 29, 2006 i go see this but now i don't have many time :) :) :) Quote Link to comment Share on other sites More sharing options...
rodrigo.j.p Posted February 5, 2006 Report Share Posted February 5, 2006 i have a new project and he is perfect thanks for your help Quote Link to comment Share on other sites More sharing options...
vjedlicka Posted February 8, 2006 Report Share Posted February 8, 2006 Hi all,I am going to build this PSU. I cannot get any of the opamps mentioned in this forum (OPA445, MC34071AP, TLE2141CP)Can I use NE5534 instead?Thanks for advice.Vaclav Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 8, 2006 Report Share Posted February 8, 2006 The NE5534 is for a closed-loop gain of 3 or more without an extra capacitor as compensation, has diodes between its inputs and has an opposite voltage for its input offset adjustment. I wouldn't want to modify the circuit and pcb to use it. Quote Link to comment Share on other sites More sharing options...
vjedlicka Posted February 9, 2006 Report Share Posted February 9, 2006 Thanks a lot for the quick response!How about LF356N?Vaclav Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 9, 2006 Report Share Posted February 9, 2006 The LF356N also has an unusual offset adj. voltage and its max supply is only 36V.Look at www.datasheetarchive.com for more. Quote Link to comment Share on other sites More sharing options...
mix Posted February 12, 2006 Report Share Posted February 12, 2006 Hello,I build the original 30V x 3A PSU and it works pefectly, but after some (test ;D) short circuits the output fall to 0V. Searching I found Q2 transistor (2N2218A) damaged. This happened two times and I don't know what is the problem ???.Somebody can help me?Thanks!PS: sorry for English ;D Quote Link to comment Share on other sites More sharing options...
audioguru Posted February 12, 2006 Report Share Posted February 12, 2006 Hi Mix,Welcome to our forum. ;DWhen the project's output is shorted or set to a low voltage at 3A. Q2 has about 32V across it and up to 100mA through it. That is heating of 3.2W. A little 2N2218A will be at its absolute max internal temperature with about only 1.5W with the clip-on tiny heatsink recommended in the original project.That is why I recommend using a real little power transistor like a TIP31A that has a metal tab for bolting to a real heatsink. Quote Link to comment Share on other sites More sharing options...
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