t_xen Posted June 19, 2008 Report Share Posted June 19, 2008 I have constructed a regulated bipolar PSU. Both positive and negative rails read as 11.7v.When I connect the power to J3 of the AOUT_NG the power on negative rail reads as 6.6v, the positive rail is still the same. Pin 4 and Pin 11 on IC3 and IC4 reflect this.Before I checked the power, I was also having a curious issue with the Bipolar and Unipolar configuration. the voltage output is not adjustable. no matter how many times I turn the gain trimmer, the voltage measured on the outputs do not change. is there something that I may have just missed? ??? ??? ???I went over it 3 times checking for bridges and bad solder joints and cannot find any reason for this problem. :-\ Quote Link to comment Share on other sites More sharing options...
seppoman Posted June 19, 2008 Report Share Posted June 19, 2008 I have constructed a regulated bipolar PSU. Both positive and negative rails read as 11.7v.When I connect the power to J3 of the AOUT_NG the power on negative rail reads as 6.6v, the positive rail is still the same. Pin 4 and Pin 11 on IC3 and IC4 reflect this.I hope the negative rail reads -11.7V? ;)Before I checked the power, I was also having a curious issue with the Bipolar and Unipolar configuration. the voltage output is not adjustable. no matter how many times I turn the gain trimmer, the voltage measured on the outputs do not change. is there something that I may have just missed? ??? ??? ???As long as there's troubles with the supply voltages, you can't expect any reasonable behaviour. If you want to check if the DAC alone works correctly, you could remove all jumpers and measure the JP1/JP2 pins coming from the DAC (against GND). This should give values between 0V and 4V when you change the values in your app (is the module already connected to the core and is some app running?).Make sure the bipolar PSU really works fine, recheck all soldering, parts orientation, parts values etc. I would definitely sort out the problems on the analog part before reconnecting the jumpers. The DAC probably wouldn't like it very much if e.g. it gets 12V or -12V fed into its outputs.S Quote Link to comment Share on other sites More sharing options...
t_xen Posted June 19, 2008 Author Report Share Posted June 19, 2008 I hope the negative rail reads -11.7V? That is correct, before I connect the PSU to the Aout_NG, then the power drops.recheck all soldering, parts orientation, parts valuesall joints look good, the orientation on the DAC, Resistors, and ICs look good. tested the value of all the resistors and they are correct and in the proper places. Quote Link to comment Share on other sites More sharing options...
seppoman Posted June 19, 2008 Report Share Posted June 19, 2008 That is correct, before I connect the PSU to the Aout_NG, then the power drops.I was asking because you said both pos and neg rail read 11.7V. So the neg is minus 11.7V measured towards GND, i.e. between the two voltages you measure 23.4V, right?all joints look good, the orientation on the DAC, Resistors, and ICs look good. tested the value of all the resistors and they are correct and in the proper places.Ok. You need to narrow down the problem a bit. As said before, please leave all jumpers open until the problem is found. that way, the DAC or other mistakes on the digital part can be left out of the search. Also remove the TL074s from the sockets. Is the voltage drop still present without tl074s? Does the 7912 get hot when the PSU is connected? Can you measure if the board takes excessive power from the negative rail?S Quote Link to comment Share on other sites More sharing options...
t_xen Posted June 20, 2008 Author Report Share Posted June 20, 2008 you said both pos and neg rail read 11.7VUmm, yea, it does read -11.7v. (oops! left that minus sign out). ;pIs the voltage drop still present without tl074sIt is, but that was before I had tested with the jumpers removed. I'll check again without the jumpers.Does the 7912 get hot when the PSU is connected?Didn't think about that. I'll let you know when I retest without the jumpers.Can you measure if the board takes excessive power from the negative rail?I cannot since my meter is really basic and does not have a setting to measure amperage. (I should invest in a really good one.) Quote Link to comment Share on other sites More sharing options...
t_xen Posted June 20, 2008 Author Report Share Posted June 20, 2008 update:7912 in the PSU does not get hot.power drops out on the negative rail and flips to positive voltage.Negative rail ends up reading as +7.4v on pin 11 of IC3 and IC4.(jumpers are currently off the module)When I check the current on the PSU I built, the positive and negative voltages are fine.Today I'm going to try a solder reflow in case there is a bad joint that I cannot visually detect. Quote Link to comment Share on other sites More sharing options...
t_xen Posted June 20, 2008 Author Report Share Posted June 20, 2008 ok. by looking at the board file in eaglePCB, I reflowed all the points that both the positive and negative rail contacts. I retested the voltage and am still getting the reverse polarity on Pin11 of the ICs.While I was looking, R14 - R40 are basically setting between the power rails. when I check the voltage on the positive rail It's still giving +11.7v, but when I check the other side of the resistors on the negative rail, I still get a reading of +7.5v.now, I don't know the formula for how much reduction in voltage an ohm rating will reduce the voltage, but what is interesting is the resistors on the positive rail will low the voltage from +11.7v to +9.3v. what's weird is the voltage on the negative rail reading a +7.47v to +9.1v???????Ok, I figure if it's supposed to reduce the voltage I should be getting a lower reading, but rather a higher reading.now I'm really confused. ??? Quote Link to comment Share on other sites More sharing options...
t_xen Posted June 20, 2008 Author Report Share Posted June 20, 2008 off a whim, I did a continuity check. pin4 has continuity to the positive rail. when I checked pin 11, I get continuity to both positive and negative rails. now I have to figure out where it's happening. Quote Link to comment Share on other sites More sharing options...
t_xen Posted June 20, 2008 Author Report Share Posted June 20, 2008 I was testing for continuity and started checking the pins under the trimmers. I found a bridge underneath p12. time to desolder the part and check. Quote Link to comment Share on other sites More sharing options...
t_xen Posted June 20, 2008 Author Report Share Posted June 20, 2008 I removed the trimmer and now the positive and negative rails aren't bleeding together, but unfortunately I'm still getting a + reading off the negative rail. Quote Link to comment Share on other sites More sharing options...
t_xen Posted June 20, 2008 Author Report Share Posted June 20, 2008 ok. no continuity when checking the pins on the board for P12. when checking the trimmer by itself, no continuity. but when I put the trimmer back into the board, I get continuity off 2 pins. Quote Link to comment Share on other sites More sharing options...
t_xen Posted June 20, 2008 Author Report Share Posted June 20, 2008 I put a probe on the jumper that runs from P12 after passing through the resistors, and the other on - rail. I can get a reading and adjust the resistance, but when I place the probe on the + rail, I get a reading, and cannot adjust it.At this point, I'm giving up on this. into th estatic bag it goes and into a box in the closet. :'( :'( :'( :'( :'( Quote Link to comment Share on other sites More sharing options...
seppoman Posted June 20, 2008 Report Share Posted June 20, 2008 would you mind describing your bipolar supply in detail? which kind of cirquit are you using (schematic)? single transformer, bipolar transformer, two transformers? Full or half bridge rectification? I still got the feeling your problem might be located at the PSU - like e.g. the PSU delivers its voltages only when no load is applied.Some hires pics of both PSU and AOUT_NG from both sides also could help getting an idea what's wrong - at the moment, I can't make much sense out of the effects you're describing...S Quote Link to comment Share on other sites More sharing options...
t_xen Posted June 21, 2008 Author Report Share Posted June 21, 2008 I think there is a possibility you might be right. It reads fine but the second I put a load on it, I get weird voltage readings from the module I connect to it. Pics and schematic will be posted in a bit. I need to take a break from it for a bit. :P Quote Link to comment Share on other sites More sharing options...
t_xen Posted July 8, 2008 Author Report Share Posted July 8, 2008 There could be a problem with the PSU being flakey cuz I tried puting a load on it from another project that works and it doesn't work on that. So....I got another design for a Bipolar PSU. Is this adequate?So for the caps after the regulators, I have some tantalum caps, but no electrolytic. Should those be fine? Quote Link to comment Share on other sites More sharing options...
seppoman Posted July 8, 2008 Report Share Posted July 8, 2008 good that you've narrowed down the problem :)the schematic you've posted is the same basic principle as the first one on this page: http://www.midibox.org/dokuwiki/bipolar_12v_psuBut I'd prefer the version from the Wiki - the differences in your schematic all don't make much sense. Two 4700uF caps is overkill for the normal applications with only a few hundred mA. 1uF caps are not typical (these are for preventing the 78xx from oscillating, 100nF..330nF ceramic caps are normal there). I also don't see a reason for using a Tantal cap.So to make it short, just build the PSU from the Wiki page (first version is best), using e.g. 1000uF electrolytic caps for "C". This is a proven and reliable cirquit, and as long as you make sure there are no wiring errors, there's hardly any chance it wouldn't work. (BTW I find it quite strange that so many people are discussing bipolar PSU designs on the forum, searching for schematics and alternatives, as this cirquit is present on uCApps for some years, is as simple as it can get and works perfectly well. So no need to reinvent the wheel, guys ;))S Quote Link to comment Share on other sites More sharing options...
doc Posted July 9, 2008 Report Share Posted July 9, 2008 (BTW I find it quite strange that so many people are discussing bipolar PSU designs on the forum, searching for schematics and alternatives, as this cirquit is present on uCApps for some years, is as simple as it can get and works perfectly well. So no need to reinvent the wheel, guys Wink)Thats what I also think.It's a proofen standard design used all over the world.I also don't see a reason for using a Tantal cap.I also don't see a need for tantal cap. And be warned: Tantal caps are causing the most problems after a couple of time. If a cap fails in a circuit it is mostly a tantal! So to say: A troubleshooting "standard".greetsDoc Quote Link to comment Share on other sites More sharing options...
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