PicMaster

Hi all I have redrawn the schematic again and I've managed to find some time and finial got round to lay out a single side PCB 75mm X 100mm, Now I have checked the schematic over and for checking and checking it over I'm 99% sure it is correct and can't see anything for looking, I'm ready for the next stage to etch the PCB and get it built up, But before I do that I would like a second opinion to make sure the schematic is 100% correct this will help me to save waisting time and money on the PCB'S. Some of the values may be incorrect, So far I've mainly focused on the connections, The Values and be corrected later and I can draw up the parts lsit. Once I know the schematic is 100% correct I know the PCB will be 100% has I've ran the DRC rule check without any errors. I will then share the PCB layout for everyone. This will also cause less confusion over which layout is correct if I uploaed cerytime corrections where made if any Thanks Power_supply_V1.pdf

You could have a look here ;D, I think it's based on the same circuit but the all the information is free and you can obtain all the files you need to build it. I would say there is infringement on copyrights hs all the info is published on his web site http://ironbark.bendigo.latrobe.edu.au/~rice/lc/

Here is a single version which you can make a dual tracking psu http://www.velleman.eu/downloads/0/manual_k7200.pdf

Hopefully with a bank holiday here I might get chance to have a look, I shall have a run over the PCB with a scope when the voltage shoot's up and see why the R20 is messing around with the current, I know it should not but it does I can get upto 8amps by messing around with that. I have checked my schematic against yoour and to me it's correct, Can you just double check it got me jsut incase it's wrong thanks mosffet_power_supply.pdf

It stayed at 22V, what I shall do is move the zener diode like drawing above, and investigate more when I get some spare time

I have done a bit more playing and something is not right, When I adjust R20 the amps do adjust I know you said it should not. The other thing I noticed instead of using a resistor has a load I used a 12V fan I set the voltage to 12.56V the fans runs OK then if I turn down the current pot to the Min the fans starts to slow down then stop on turning the current back up the fan spins mega fast, So I tried it again this time with a multimeter set up and I measured the voltage and it went up to 22volts ??? and that even without the voltage pot adjusted only the current Now I'm not sure but it could be my fault I used IFRP3710 Mosfets has these are the only one I add at the time. could this be causing the problem ? to much gate capacitance ? I shall have a look through my bigger junk box for different types ;D

This is quite simple to do, use your friend called Google ;D There are plenty in the net

Hero Can you explain a little how the current limit side of thigs work and about the role of R20 just has so I cna get a better understanding of how the circuit works cheers

This was before I changed the resistors to 82K&10K with a 0.1R shunt, The max current is 4.36Amps and altering tR20 does not effect the current readings now but I thought the output voltage was limited to 32V but I get 35V. Is this correct ? I will investigate some more but can't understand why I get 16amps(to scared to leave it on for more than 2 seconds to see if it drops). Could this be-caused by me changing the shunt resistor I know you said it should have no effect, But really i can't go any further with all the other tests until I find out why or what is causing high amps

I changed the resitor values to 82K&10K this give me a max current of 4.36A Not sure if it is me me, Put when I alter R20 the current does not seem stable and I get higher amps out put. I have got R20 set about half way current pot set near minimum voltge set to 15V then when I switxh on a .1R load the output current goes upto 16amps I turned if off quickly, I set R20 back to min and tired it again and I thought it was ok, But when I turned off the power supply then turned it back on and the same thing 16amps. It only does this once after that it does not seem to do it again until I turn off/on the Power. I opened up the sim version on the PC and I noticed that is does the same in there but because it's a sim prog it's goes to 66amps but it does drop off down to it's normal current draw, I do not have the guts to let it run long enough in real life Any ideas Why this should be happening

I did have a 3k & 160k but with a .1R restor the current has you was low now I have stll got the 160k and a 22k but judging what you said a 82k &10k should be better with the .1R so if The voltage was set to 5v darwing say 10mA I still should be able to alter the voltages before the voltage drop sorry it's a quick reply but got to go out

What is the lowest current you cna set it to ? My V-Ref is 4.05V and the maxium voltage is 35V. The lowest current I can go to is 123MA, The center tap of the curent pot reads 103MV This enables the ouput to go to 35V, If I set it the center of the pot reads 33MV the max out I can only obtain 13.60V

I realised that after I typed it. The reason why the current was reading higher and funny readings was down to my meter(not my fluke one). I brought home my spare meter from work(another fluke meter) I used that to measure the current and the other fluke for the voltage readings. Your right I get right I was only getting .699ma. So I now know not to trust cheap meters well it was not that cheap 40quid from maplin (that may be why ;D) I shall work out the calculations now so I get the right resistors to obtain the right current until next time I place an order so I can get the 15mr resistor. So now I know that I'm getting some where Because I have to wait for the wife to get tired and go to bed it's a bit on the late side and you know the brain does not function as well ;D, EDIT: Right I have worked out R7 = 22k R6 160K a gain of gain of 7.27 = 5.63A. I dropped in some 22K for R7 & R8 but this seems to throw the voltage readings out and the current pot to max to get 20V with the voltage pot on max. Do I have to just change R7 to 22k and leave R8 3K ? You bare with me if I seem a little thick or slow analogue is not my strongest point

I've add another hour on it and Finlay getting some where, I found out where I went wrong. I checked my schematic against the original very thing check out OK. I then studied the values and foot prints, I got incorrect values on R12 68K instead of 33K and R14 15K instead of 56K so the swap over voltage is working correct now ;D Then onto the foot prints I selected the wrong foot print for U5 which explains the V-Ref voltage to be all over the place. So I now get 4.0V at V-Ref all the time ;D, The output voltage is smoother and more accurate readings. I started to look at the current side now, It's still not quite there I used a 0.1R for the load and can vary the current I get to 1.25A then it jumps to 3.25amps turn it up a bit more then back down 1.25A I can get to 3amps then when R21 is at it max the current is back down to 1.25A Now I think is caused by me having a incorrect value pot 10L instead of 100K and R5 .1R instead of 15mr ? Silly me I've read about the calculations you posted. I shall look into that next time, Then once I'm happy that the current side is working correct I shall see about carrying out the other stuff you talked about.

I wondered where you went to. With it been Mothers day I think that it would be better left for today ;D

I removed the 2 resistors and I did forget to say U5 as well It was the same if it running from U5 or the exteranl PSU set for 4.1V with common GND No when running off U5 The goes up and down due to the V-Ref voltage not been stable from the external PSU set for 4.1V I only get 2.6amps max I will still carry on in looking and more testing I'm not giving up yet, I class this has a minor set back, But the PSU seems to work well in the sim program ???

But looking at the schematic U3 if feed by +10V -1.3V supply if I'm looking at correct and U1,U3 are fed form the high plus side of power supply(41V), I was not sure if this would affect the operation of it if it all was in one chip which would maje a smaller neater design well I think so any way

Just a quick question Is there any reason why you could not use the quad vesrin of the TLE2141 instead of the three op-amps, Or would this have the effect the operation of U3 ?

Right I have done a bit more testing. I will try and explain the best I can. I found out where I went wrong, It was on the connections from the transformer(my fault). V-Ref I can only get 2.6V out of it. and the max output voltage was 23V. Also if I connected a load it went lower 2.1V. So here is what I did, Removed R18 and R14 connect my other PSU to V-Ref(on the top end of the pot) which was set to 4.1V, This then enables the PSU to goto 0 - 35V, To limit the voltage I turned V-Ref PSU to 3.63V which give a max Voltage ouput of 32V. but what I did notice is that when the PSU gets to 7V my meter displays OL (and the high voltage symbol) only for a split second well enough for my eyes to see it, Then volatge contiues to rise upto 32V So something is telling me that the swap over is happening at 7V not 12V, My second test was I measured the current draw on V-ref line and it read 180MA. the current pot has to be turn up slighty to get the full 32V, the center of the pot read 333mv to obtain the full voltage with out no load. I can veary the current from 0-2.6amps with a 0.1R(R5) shunt and a 0.1R load but the PSU was set for 5V I did not want to risk higer voltage yet. Is the 2.6amps due to the act that the shunt resistor R5 is 0.1R ? This was the way I set my velleman power supply up at 5V using a 0.1R has the load and can vart the full 5amps (8A max), So I think that the mosfet PSU should work in the same manner. The velleman PSU was a good desing it makes you wonder why they stoped selling it. Hope you can understand what I'm trying to say, ask any questions and I will try and explain in more detail a bit by bit. I might be early in saying this or even thinking about it, I'm beging to have doubts about the stability and the smoothness of the operation of the voltage control/current, (really I should not think this yet but can't help it) BTW, I have double checked my PCB for any errors and shorts everything checks out oK

There must be ishall look into it and go over the rest of the pcb,I have just tested the v-ref 4.31v no load connected and both pots at 0 I turned the voltage to 10.v v-f ref went down to 2.8v I then placed a 1A load and with the current turned to max the v-ref semms to be jumping up and down,I then placed my a .1R resistor turned current pot to max and I only get 1.2A which mens v-ref is only 1.2v the v-ref components seem to be getting warm, I shall look into just in case it's me but do you think that the v-ref circuit is up to thr job ?

It was R20 100K. I shall change it and start to carry out the tests above

Sorry what I meant is I shall carry out the test on M1 with a 1A load on it. Make sure M1 is off below 12V. Youre not boring me I'm finding this very interesting and learning lots more about power supplies. What I meant by it's been a long day at work (14hr shift) I love it when you get stuck into something that is really interesting. I just look forward to the finsh product and will be proud to show it off R5 at the moment is a 0.1R 10W instead of the 15MR like in the shcematic, I'm sure that I was getting 1.6A. But may be I was carrying out the test wrong. How I did it was for the load testing I just used my multimeter in the current mode in line of the +&- which is using the shunt in the meter which is not very good. I shall pick a low ohm resistor and work it oiut like you have. What I shall do is get armed with pen and paper start from the beging again measure and check all the Vref and the gain of of the differential amplifier, M1, I will make sure i look at every angle of it, Then recored all data jot it onto the schematic then upload for you to have a ponder over. Then we can take it from there. I've just remembered when I had a quick look at it last night and just looking at the schematic I did put in a 10K and not a 100k, So I will get that changed silly me :-[ ;D

Sorry it was a long day, It should have said is easy enough done. so it's a yes. OK it was just a thought that's all Yes I substituted a few resitors, Maplins did not have thevalues I wanted plus rather exspensive 16P each, Rip off or what. I searched through my bins for the correct value and out of the thousands I got I gave up. but has this is just a test PCB I thought it would not matter has long they are the right values. I shall look into using a PIC to measure the time it takes to drop. For the moment becasue I've got a .1R resistor for the shunt could I use a 10amp fuse in place of it means they have a lower resitance value ? I'm good at just for thoughts ;D Saturday may be the next time I get to spend more time on it, I will try to play with it in the week if possible

I will try that and let you know. I thought that but if I remmember in the sim it does not do it. I know the sim to real world might not be the same. The only reason I asked becuase, A velleman PSU I had has a 47K & 1K pot for the voltage adjust, The 1K pot gives you a fine tune over 1V has it went up in 0.01V steps which was good so you could set it to 13.84V easy. That's wasy enough done. The only scope I have at the moment is a velleam 10MHZ one, My other old analogue one packed up some time ago and I've never got around to replace. (well the wife put her foot down. may be I need to earn some more browning points ;D), Has for the pulse generator I can hook up a pic to create the pulses(I think).N-Fet and power already have set up for another job I did(load testing). My skill of understanding scopes are limited may be if the velleman scope would be up to it I could take pics of the screen if that would help. The rest I have copied and printed for bed time reading and to get it to sink in, attached is my schematic I created to make the PCB, I know some of the vaules in the schematic may not be correct but on the real PCB they are, Once we get closer in the final design I will correct all values and make the modifications then creat the BOM for it.mosffet_power_supply.pdf

Update, I have finally got it built and working, Well I have only tried the voltage through the full range from 0-30 volts, Partly tried the current draw test on it, at the moment I can't do a full current test due to the fact I have not got the 15mr resistor I only have a 0.1R which only draws 1.97amps, I think this can be altered by the resistor values but not tried it yet. The only thing that I did notice is that the current pot has to be turned up slightly to get any output voltage.The good thing is that the ouput voltage goes right down to ZERO ;D I shall carry out lots more investigstion on it, Has there is lots more to be tested, I think that it would be a good idea to to put an extra 1L pot for fine tune on the voltage ? Herro do the pots have to be 100K or could we get away with 47K pots also which are the best pots to use LOg or LIN ? Here are some Picutres of it so far. What other tests do I need to look at carrying out ?