The Modular Bench Power Supply ++ - Power Output Stages

RE: The Modular Bench Power Supply ++ - Power Output Stages

jw0752 — Mon, 01 Dec 2014 05:44:38 GMT

I continued my experiment and got a rough approximation of your design to work with Darlingtons and MOSFETs in both the regulated voltage and regulated current modes. The problem at the low end is definitely related to the Op Amp. I think that while the little Op Amps work quite well, expecting them to operate 0 to 40 volts and still maintain linearity all the way to the rail is perhaps expecting too much. This design is a nice simple structure and as such has points in its favor but if you really want to go as precise as possible your idea to operate the control system in the 12 to 15 volt range and then use transistors and other architecture to leverage the output voltage to 40 volts probably has a lot of merit. You also mentioned that some of the expensive supplies use relays to maintain a closer delta V between Output voltage and Input voltage so the outputs don't overheat as much. Perhaps the relays could switch control structure as well to better maintain linearity too. Thanks for taking the time to look into my observations. I eagerly await your next presentation.

John

RE: The Modular Bench Power Supply ++ - Power Output Stages

jw0752 — Fri, 28 Nov 2014 20:33:38 GMT

I was using a linear 270 degree 10 K pot, so you are correct that my resolution at the ends were not good. My voltage readings were being supplied by the oscilloscope so here again accuracy was not being taken very seriously. My goal was to show proof of concept and while I logged data including multiple load settings for several data points I was less than consiencious over all. Tonight I am going to make the slight redesign of the circuit to accomodate a MOSFET and do a similiar experiment. I also want to see how it works in a constant current mode. I will let you know if I run into any anomolies.

John

RE: The Modular Bench Power Supply ++ - Power Output Stages

jw0752 — Fri, 28 Nov 2014 17:06:38 GMT

Hi Peter, Yes I was able to bring it below 4.6 volts output but my gain became non linear below the 0.7 volt reference voltage input to the
ISL 28218. It would be easy to set up the voltage divider off the emitter so that there was a different ratio and outputs could be brought to less than a volt linearly. The control voltage was being measured at the non inverting input of the ISL 28218.

Thanks John

RE: The Modular Bench Power Supply ++ - Power Output Stages

jw0752 — Fri, 28 Nov 2014 07:21:24 GMT

Hi Peter, The ISL28218 40 Volt R to R Op Amps came in and so I tested one out using your designs. Using a REF02 I varied the input to non-inverting input of the ISL28218. I found that with a 25 volt supply I was able to control the voltage on the Emitter of the TIP102 Darlington. The control voltage began at 0.7 volts and went (with effect) as high as 4 volts, while the voltage at the TIP102 Emitter went from 4.6 volts all the way to 23 volts. I varied the load on the TIP 102 from 25 mA to 300 mA without a noticeable drop in voltage. My ratio of output voltage to control voltage matched almost exactly to the ratio of the resistances in my feedback voltage divider. Fun stuff.

John

Here is a schematic of the circuit I tested:

[View:/resized-image/__size/620x468/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-b2750742-3d1e-43ff-a0b2-84087b441358/8081.contentimage_5F00_177674.bmp:620:468]

RE: The Modular Bench Power Supply ++ - Power Output Stages

jw0752 — Thu, 20 Nov 2014 14:45:58 GMT

Hi Peter, I did some digging last night and I came up with a candidate for an op amp to use to experiment with the ideas that you have been teaching. It is the Intersil ISL28218. Here is the data sheet: http://www.newark.com/intersil/isl28218fbz-t7a/ic-op-amp/dp/99R4767?ost=99R4767. If you don't see any problems with it covering the needs of this project let me know and I will get two or three for my experimentation. I did some work already using the 741 but since it isn't rail to rail it required a bias voltage and was difficult to integrate with a MOSFET and the REF02 that you talked about earlier.

Thanks John

RE: The Modular Bench Power Supply ++ - Power Output Stages

jw0752 — Wed, 19 Nov 2014 16:42:19 GMT

Hi Peter, Would you mind telling me what are your recommended OP AMPS going to be for use in this project.. I would like to get a few in so I can start experimenting with them.

Thanks John

RE: The Modular Bench Power Supply ++ - Power Output Stages

jw0752 — Mon, 17 Nov 2014 06:59:16 GMT

Hi Peter, I enjoyed it and the time went by with out me noticing it. I am not sure you could condense it more and still give all of your audience the information that is needed. The subject was very close to what we were talking about earlier with my question. Thanks again for your tutorials.

John

RE: The Modular Bench Power Supply ++ - Power Output Stages

DAB — Sun, 16 Nov 2014 20:05:09 GMT

Good job Peter.

It has been a long time since I went through transistor theory.

You bring back long buried memories.

DAB