Rookie LTspice simulation and build of TAE linear PSU using LT1028C help - Page 1
Forum section: electronics / projects

author: denimdragon
author_rank: Regular Contributor
timestamp: August 27, 2019, 10:33:02 am
content: I'm attempting to build a dual rail linear power supply based on the one in TAE pg. 608 Fig. 9.15, but I'm using 2 LT1028CN instead of the OP27, and I'm omitting the TLV431 (down to zero) and also instead of the +5 VCC on A2 I'm running the rail directly off the 30V rail just as A1. The reason I'm using this is because I don't have a dual pot right now and I need this psu for other projects using op-amps.It simulates fine but that could be a gotcha. My LTspice skills are minimal at best, but they are decent enough for me to use it as a tool to see if I am thinking in the right direction. Other than the LT1028s I have on hand, I also have a couple of LT1002s which I thought about using as the LT1028s or considerable more expensive, but I want the PSU to be the best I can do currently.Any help/advice would be appreciated before I finish it up and make a "whoops".

author: Kleinstein
author_rank: Super Contributor
timestamp: August 27, 2019, 11:31:30 am
content: The right OP for this circuit with low voltages would be something like the LM358 (or cheaper).At high voltage one may need to use 2 single OPs and separate lower supplies (e.g. -5 V for the 1 st OP and +5 V for the negative side OP) to avoid special high voltage OPs. The LT1028 would be a poor choice - in the given circuit it is not even low noise.

author: denimdragon
author_rank: Regular Contributor
timestamp: August 27, 2019, 01:15:02 pm
content: Quote from: Kleinstein on August 27, 2019, 11:31:30 amI think I can salvage a LM358 and maybe some UA741s from some old projects that I no longer use. I'll see what I can come up with. Thanks again.I'm also attaching a screen shot of the circuit in case others want to ad there expertise with open up LTspice.

author: SiliconWizard
author_rank: Super Contributor
timestamp: August 27, 2019, 06:25:12 pm
content: Is your input supply +/-15V or +/-30V?

author: denimdragon
author_rank: Regular Contributor
timestamp: August 28, 2019, 08:45:35 am
content: Quote from: SiliconWizard on August 27, 2019, 06:25:12 pmAh, yeah. That voltage source model is one I grabbed from Yahoo usergroup. Very handy but ambiguous. It's +/- 30V. That's a rough calculation based on my transformer measurements from a little one I grab from an old BKPrecision pulse generator. Now I'm contemplating on using a bigger transformer that I salvaged from an Onkyo TX-21. It's a tank with one primary and two secondary windings. The configuration is a bit confusing as I've not seen a transformer with this particular layout, but my measurements show that the largest secondary has 25V-0-25V which comes out to around 35ish volts. I think I really want to use it versus the little one from the BKPrecision.I'm thinking I could use the main secondary for my adjustable source for the LM317/337 pair and the lesser voltages to run a fixed +/-12V, +/-9V, +/-5V for quick school projects with no fiddling. This started off as a somewhat quick build for school, but now I've kind of committed myself to make a decent PSU that I can be proud of and use with all my projects. I have a Tektronix PS282 (linear) 0-18V 0-5A and a BKPecision 0-18V 0-5A (Switcher that I use for LabVIEW projects) but I don't have anything dual pole.I'm planing on housing it in an old EVGA PSU housing that has the right amount of space and a huge fan on top to keep things cool as there will be intense thermals with 8 regulators. The other regulators for the fixed voltages are TO-220F packages so I figure I can mount them on the chassis for heat evacuation.All this is speculative as I am a rookie to designing electronics systems so if I said something stupid or incorrect, please correct me. I wanna be great at this so my pride and ego are in my pocket.See transformer pics below.P.S. Tomorrow I will have access to ICs and other components (standard stuff but mostly new old stock, some REALLY old stock) so if anyone has some suggestions for other parts other than the LM358, please let me know as I can grab them while I'm there. Thanks again.

author: SiliconWizard
author_rank: Super Contributor
timestamp: August 28, 2019, 02:42:22 pm
content: Quote from: denimdragon on August 28, 2019, 08:45:35 amI suspected so.There's no way you can power LT1028 opamps at +/-30V. You will just blow them up.

author: denimdragon
author_rank: Regular Contributor
timestamp: August 29, 2019, 03:35:14 am
content: Quote from: SiliconWizard on August 28, 2019, 02:42:22 pmYes I'm aware lol. I just did that for simulation purpose. I'm super green at LTspice so I was just trying to get the thing to work so I could see a few of the V/I numbers and see how close my manual calculations were. Good looking out though and if you ever see me on a "crash dummy" run, by all means pull my coattail as such.I planned to run them off separate supplies as suggested in the book and Kleinstein, but now I'm thinking I'm going to use 741s in there place. I picked up a few today and I would prefer to use my LT1028s for my LM399 builds in the future. Any input on the transformer I should use and my idea with the multi-voltage set up? I don't wanna over do it. The idea seems plausible but I'm not incredibly familiar with all the ramifications.Thanks again for taking out the time guys.