audioguru Posted February 2, 2012 Report Share Posted February 2, 2012 Measuring the setting of current regulation is complicated because the voltage at the current-setting pot is the 11.2V voltage reference divided plus the voltage across R7. Quote Link to comment Share on other sites More sharing options...
josko Posted February 2, 2012 Report Share Posted February 2, 2012 So it should be voltage between (-) output of supply and P2 (+ input of U3) or am I wrong? Quote Link to comment Share on other sites More sharing options...
Sparkington Posted February 5, 2012 Report Share Posted February 5, 2012 Ok just finish building the power supply, I had to make a new PCB but this project has taught me a lot. so I didnt mind.I use the TL081 but use a LM7809 to drop the voltage down, use a 30V 3Amp transformer and the Power supply outputs 25 volts which isnt bad :D Thanks for all the inputs into this thread it help to better my design :) Here's a couple of photos.[img width=680 height=510][img width=680 height=510]No room left for the amp meter to be install inside the case, so stuck it on the side :D Quote Link to comment Share on other sites More sharing options...
mmojtabaa Posted March 4, 2012 Report Share Posted March 4, 2012 I am Iranian. And I've closed the project. Much higher.thanks youYou can just see you herewww.dehnokit.blogfa.com Quote Link to comment Share on other sites More sharing options...
audioguru Posted March 4, 2012 Report Share Posted March 4, 2012 I am Iranian. And I've closed the project. Much higher.thanks youYou can just see you herewww.dehnokit.blogfa.comYou built the original project that used old parts that were overloaded so it is not reliable.This improved version uses modern parts operating within their maximum limits. Quote Link to comment Share on other sites More sharing options...
Tompa Posted April 7, 2012 Report Share Posted April 7, 2012 Hi week ago i finished this PSU ( with latest part list). I have one problem, with current regulation; ammeter shows me some current ( when i connect something) but i cant regulate it ( current), LED light up when i turn potentiometer to the max, then voltage drops. Voltage regulation works fine... Maybe i wrong connected ammeter ( I attached picture how i connect it).sry for my english...TY Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 7, 2012 Report Share Posted April 7, 2012 Hi Tompa,Since your current meter is in series with the load then its resistance reduces voltage regulation at the load. It will be better to use a voltmeter to measure the voltage across R7 which shows the amount of output current without reducing the voltage regulation.When the current control is turned to minimum then the current regulation begins when the current is a few mA.When the current control is turned to maximum then the current regulation begins when the current is 3.0A.The current regulator reduces the output voltage until the load current is what is set by the current control. When regulating the current then the LED should light to warn you that the output voltage is being reduced. Quote Link to comment Share on other sites More sharing options...
Guest Posted April 30, 2012 Report Share Posted April 30, 2012 Been lurking around here for a while, I built this power supply over the course of a few years and it's served me well in it's half completed state (need to build the DMM project here to finish it).However, for some reason, at times, Q1 will turn on (this should turn on only on powerdown?) and start cooking U2 (output drops to 0.15v at any setting). If left off for a day, it will work properly again until it randomly occurs again.Pin 6 of U2 measures 42.9vD5 measures 0.3v instead of -6.1vD7 measures ~0.2v instead of -5.74vThe electrolytic caps C1, C2, C3 and C7 are not damaged and show the proper capacitance.Swapping the TLE2141s around confirms that the chips are not damaged as it works properly for a while.Could having a 10k pot for RV1 instead of 5k be the cause?I'm otherwise completely stumped as I've measured all parts of the -5.6v negative supply and they all check out fine.EDIT: Added diagram of PSU version I'm using Quote Link to comment Share on other sites More sharing options...
audioguru Posted April 30, 2012 Report Share Posted April 30, 2012 Q1 was used when the opamps were TL081 because they had the problem called "Phase Inversion" where the output would suddenly go high when the input became within a few volts of the negative supply (that happens when the power is turned off).The TLE2141 opamps do not have this problem because they work perfectly when their input is at the same voltage as the negative supply.The circuit with the TLE2141 opamps was changed so that the negative supply is only -1.3V so that their total supply was never more than their max allowed supply of 44V.If your negative supply is -5.6V then U2 will have a total supply of about 48V which might blow it up.Maybe your negative supply is too low because R2 or C2 is bad.You have pin 4 of U3 connected to the power input ground instead of to the negative supply.Its output must be able to swing at least -0.8V (that is why the new negative supply is -1.3V) so tha D9 can reduce the input of U2 to 0V when the output is shorted. Quote Link to comment Share on other sites More sharing options...
Guest Posted May 2, 2012 Report Share Posted May 2, 2012 Thanks for the advice audioguru, it's much appreciated.Looks like I'm going to have to remove a few components and correct a mistake on the PCB. (U3 gets it's "negative" supply from the 0v rail which doesn't seem right.) Quote Link to comment Share on other sites More sharing options...
Guest Posted May 7, 2012 Report Share Posted May 7, 2012 Finally, fixed the problems with my PSU and updated it to the latest (March 2009?) version.Turns out that the trace from the AC supply to R2 was intermittent, causing the negative supply to fail.The output was very low due to the trace out of the base of Q2 being broken.Next, a digital multimeter to finish off the PSU.Thanks again audioguru! Quote Link to comment Share on other sites More sharing options...
Alf_Melmok Posted May 12, 2012 Report Share Posted May 12, 2012 Hi All!What do you think about this version of the scheme?But i have only 19,8VAC transformer. Can i use this scheme having replaced U4 on 7818, D13 on 2,4v zener? Will it work? Is this scheme reliable? (sorry for my english) Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 12, 2012 Report Share Posted May 12, 2012 What do you think about this version of the scheme?But i have only 19,8VAC transformer. Can i use this scheme having replaced U4 on 7818, D13 on 2,4v zener? Will it work? Is this scheme reliable?Since your voltages are very low, many resistor values will need to be re-calculated.You do not need to use U4 and D13 since without them the unregulated positive supply is only +26V which is fine for a TL071 or TL081 opamp.With U4 and D13 the maximum output voltage will be only about +14.4V. Without U4 and D13 the maximum output voltage will be about +20V.If U5 is a -5V regulator then it will not work (it is not needed anyway) since its input voltage is too low. Quote Link to comment Share on other sites More sharing options...
Alf_Melmok Posted May 12, 2012 Report Share Posted May 12, 2012 Since your voltages are very low, many resistor values will need to be re-calculated.Can you help me?You do not need to use U4 and D13 since without them the unregulated positive supply is only +26V which is fine for a TL071 or TL081 opamp.I want to limit the input voltage. If the line voltage change. So that the output has always been a 20V.With U4 and D13 the maximum output voltage will be only about +14.4V. Without U4 and D13 the maximum output voltage will be about +20V.Just in this scheme, the output voltage 30VDC (U4+D13=30,2V). I decided if I'm have 20V, then i need replace the U4 and D13 (18+2,4=20,4V). I was wrong? The output voltage of 20V was enough for me.If U5 is a -5V regulator then it will not work (it is not needed anyway) since its input voltage is too low. It also surprised me. I think D7 not needed. Am I right?Or, maybe, you advise me another way in my situation. I read this and some similar forum almost 2 weeks and dont know what to do. Thank you anyway. Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 12, 2012 Report Share Posted May 12, 2012 Can you help me?Too much trouble. Use the proper 28VAC or 30VAC transformer and the proper opamps.I want to limit the input voltage. If the line voltage change. So that the output has always been a 20V.I don't know why your input voltage changes, mine does not change.A TIP3055 at 3A has a maximum base-emitter voltage loss of 1.7V.A BD139 at 110mA has a maximum base-emitter voltage loss of 0.8V.The 1k series base resistor R15 feeding the BD139 has a maximum voltage loss of 1.5V.Opamp U2 has a maximum voltage loss of about 3.3V and you are powering it with only +20.4V.Then the maximum output voltage can be as low as +13.1V when calculated properly. I decided if I'm have 20V, then i need replace the U4 and D13 (18+2,4=20,4V). I was wrong? The output voltage of 20V was enough for me.You forgot to see the voltage losses on the datasheets.The corrected and improved circuit here has an output of +30V at 3A when its unregulated positive supply is +37.6V from a rectified 28VAC transformer.I decided if I'm have 20V, then i need replace the U4 and D13 (18+2,4=20,4V). I was wrong?Yes you are wrong.I think D7 not needed. Am I right?No.D7 is a negative 5.6V regulator. It was needed in the original project. Your additional 5V regulator U5 is not needed. Quote Link to comment Share on other sites More sharing options...
Alf_Melmok Posted May 12, 2012 Report Share Posted May 12, 2012 You are right, i forgot about the voltage losses.In my country mains voltage change from 200 to 240 very often (In rare cases, even is worse (phase is not uniformly loaded)). That's why i want to limit the input voltage.It's a vicious circle. In my country i can't buy op amp that you recommend. So that i can't use 28VAC transformer. And i can't find 28-30VAC transformer. I can't find another scheme similar PSU. I just want this power supply with 20V transformer. :'(Thanks for your help Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 12, 2012 Report Share Posted May 12, 2012 Here in Canada my inexpensive mains electricity is 120V. Sometimes it surges very high to 121V and sometimes it drops very low to 119V. It fails maybe every 2 or 3 years for a moment during a thunderstorm.There are many electronic parts distributors here that have ANYTHING and EVERYTHING at a good price.If I order a part by phone or online before 8:00PM then it is delivered to me the next morning.Maybe in your country you should do gardening instead of electronics. Quote Link to comment Share on other sites More sharing options...
Alf_Melmok Posted May 13, 2012 Report Share Posted May 13, 2012 I envy you. But it's not funny. By our standards in the electrical network there shall be 220V +20 % -20 %. You can calculate how much it turns out (176-264 It's normal :o). All of our electronics designed for this. Quote Link to comment Share on other sites More sharing options...
asdewq Posted May 26, 2012 Report Share Posted May 26, 2012 hey guys i need some helpi've built this psu project from the first schematic (the original) with the tl081 and everything and it didn't burn up immediately after being switched on as suggested by some i tried testing the circuit and the current limitation/regulation works fine but voltage regulation does not and im wondering if anyone has had the same problem or if someone has a suggestion as to how to fix this problem this is a great project and i need this psu for some other projects and i've spent quite a lot of money on parts (electronics parts are still a bit expensive where i live) and i would hate it this build was a waste of time and money please help and thank you in advance Quote Link to comment Share on other sites More sharing options...
asdewq Posted May 26, 2012 Report Share Posted May 26, 2012 after about two more hours of tinkering with the psu i finally got some kind of reaction on the output of the psu but now i can only get either 0V or 31V nothing in betweenany suggestions? Quote Link to comment Share on other sites More sharing options...
audioguru Posted May 27, 2012 Report Share Posted May 27, 2012 The input to the output amplifier is 0V to +11.2V from the voltage adjust pot.The output amplifier is simply opamp U2 with the driver transistor and output transistor as emitter-followers boosting the output current. The output amplifier has R11 (27k) and R12 (56k) for over-all negative feedback which sets the gain too high at (56k/27k) + 1= 3.074. Then the output should be able to go from 0V to (11.2V x 3.074=) 34.4V if the unregulated DC voltage is high enough.Maybe you have the pins on the driver transistor or output transistor mixed up so that they are on-off switches instead of emitter-followers. Quote Link to comment Share on other sites More sharing options...
asdewq Posted June 2, 2012 Report Share Posted June 2, 2012 Solved it. I accidentaly put the wrong transistor in the wrong place.Just one more thing. I tested one circuit (I built two) by shorting the output to see the max current rating and it put out almost 5 amps. Those 5 amps burned through the rectifier diodes but everything else was fine. Did you get 5 amps as max current on the output? Quote Link to comment Share on other sites More sharing options...
audioguru Posted June 2, 2012 Report Share Posted June 2, 2012 Yes, the original project was missing calibration trimpots to reduce the maximum output voltage to 30.0V and the maximum output current to 3.0A.The modified circuit has the calibration trimpots added and uses a high current rectifier bridge module that can be bolted to a heatsink. Quote Link to comment Share on other sites More sharing options...
asdewq Posted June 2, 2012 Report Share Posted June 2, 2012 Would you mind posting a link to the modified circuit? Quote Link to comment Share on other sites More sharing options...
audioguru Posted June 4, 2012 Report Share Posted June 4, 2012 Would you mind posting a link to the modified circuit?I have looked it up on my hard drive and posted it on one of the many threads about the modified circuit hundreds of times.Here they are again: Quote Link to comment Share on other sites More sharing options...
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