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DIY Modular Test Equipment Project

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Leo Bodnar:
If you are designing your own modular instrumentation project you might find this http://www.easy-phi.ch/ interesting.
Leo

void_error:
Prasimix has an idea like that. I did mention in a previous post that my version of modular is not going to have everything in the same enclosure and try to keep the costs down, although you could combine some of them. It's not going to be rackmount either.

void_error:

--- Quote from: void_error on August 04, 2017, 05:14:18 am ---A simple solution to this is to use a window comparator circuit (LM393) for each rail and some P-channel MOSFETs paired with a delay circuit (CMOS 555 or some monostable using logic gates) and a cheap voltage reference (TL431 or LMV431).

--- End quote ---
Turns out that it's not going to be so simple so I'll just use an undervoltage lockout comparator for each rail, OR them together, some TVS diodes for overvoltage protection and rely on the polyfuses at the linear regulators' inputs to limit the current. The reference for the UVLO comparator is  going to be a TL431. Output disconnect will still be done using MOSFETs.

void_error:
After more than enough stupid ideas I managed to come up with a circuit that seems to work. You can find a crude mock-up of it below (http://falstad.com/circuit/circuitjs.html - File > Import From Local File). It's neither built up to scale (component values are subject to change) nor painted (no part numbers). Used a simple zener based series regulator instead of an LM317 just because it'll do for the simulation.

Time to see how I can add most the same to a negative rail. After that I'll draw it in LTspice and 'virtually' abuse it some more then breadboard it at some point.

Yes, I know, it's overkill.

void_error:
It's now time for a design goal (or feature?) update for each of the pieces of test equipment, it's the stuff on the first page.

Someone mentioned a useful feature would be to turn two channels of a bench power supply on at the same time here so I went ahead and opened my KiCad project for my bench supply to see if it was possible and it apparently is but more on that after I polish the schematic a little bit, I think it's lacking a few details at this point, like component values and associated footprints, maybe I should make a new component library for passive components with footprints associated instead of the standard generic resistor/capacitor ones which need to be linked to footprints manually since I have quite a few different size passives... anyway, since I'm using 595 shift registers for SPI addressing and the DACs used to set the voltage and current only have the clock input (SCLK) and the data input (MOSI) pins tied to the SPI bus they can be updated at exactly the same time given the output voltages are the same which is not that useful so I'll either have to find a DAC with a Latch DAC pin or find another way to make the DAC outputs rise at roughly the same time with the latter being an easier task as I already settled on some specific parts (see first page).

Another idea I've been messing around with is completely ditching the on-board fan control circuit on each of the PSU channel. The new location will be the aux digital supply board since that will be used by the DC load modules anyway, which are now going to be 200W or lower, depending on the power MOSFETs' type and number of devices used. An extra connector will be required. In the case of the bench power supply the aux digital board's fan control circuitry will drive one fan for both channels.

Also, sorry for not posting in a while, I thought I'd get enough stuff done first.

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