Modular bench supply - Page 1
Forum section: electronics / beginners

author: just_fib_it
author_rank: Contributor
timestamp: June 21, 2014, 01:56:42 am
content: I'm planning to build an HP E3610A bench supply. I will basically use the schematic from the service manual, but want to do the PCB layout myself. Mostly as a learning experience I'm going to do a 4-layer board with the analog circuit (opamps, voltage reference), but to avoid wasting expensive 4-layer board space with big capacitors and power resistors I'll make a separate 2-layer board for the power circuit, and a third board with an LM317 and LM337 for the +/-12V supply, which will hopefully also come in handy for future projects.My question now is if this is a bad idea? Some sensitive signals will have to go from the power board to the analog board and back, most notably the voltage and current sense signals and the output of the pass transistor driver. Will things like wire inductance and contact resistance notably affect the accuracy and/or stability of the supply?I've attached an image of how I plan to split the circuits. Would it be better to put Q2 (the transistor that drivers the pass transistors) on the power board? Any other changes I should consider?

author: lapm
author_rank: Frequent Contributor
timestamp: June 21, 2014, 10:00:26 am
content: Learning my friend is newer bad idea. I fully expect you to find few tricks used you dint know.. Expecially if you have factory made model there to compare...I would say go for it. Trying to replicate functionality from schematics can be learning experience. PCB design is its own art form when we are talking about dealing with sensitive voltage levels of references, etc...

author: RazSlack
author_rank: Contributor
timestamp: June 21, 2014, 10:23:33 am
content: Going modular is always a good thing. Although I wouldn't go 4-layer for a power supply. Generally when I design a PCB, first I try to make it single-sided. Then as the amount of jumper links needed increase, I just make it double-sided, with the ground and the jumper links on the second layer.Although usually I etch my boards myself, I just don't want to hassle with fabs to make prototypes.

author: Dave
author_rank: Super Contributor
timestamp: June 21, 2014, 10:32:31 am
content: Just make the whole board on a 2-layer PCB and instead make the voltage/current monitor on a separate 4-layer board, if you really want to design one.Splitting things on several boards just adds more things that could go wrong (what would happen if for example the regulator board got disconnected and the series pass transistors suddenly got opened all the way - I bet your load wouldn't like that).

author: just_fib_it
author_rank: Contributor
timestamp: June 21, 2014, 12:20:20 pm
content: Quote from: RazSlack on June 21, 2014, 10:23:33 amI've just finished dividing up the schematic, and yes, you're right, the analog circuit is a lot less complex than I thought. So probably a 4-layer board is overkill here.Quote from: Dave on June 21, 2014, 10:32:31 amBuilding this E3610A is supposed to be just a stepping stone towards my next project: building a triple PSU consisting of an E3614A and two E3616As. The E3614A series is more complex than the E3610A, so probably I'll leave the 4-layer board for that project.I'll keep the separate LM317/337 board though, just because it seems like a handy little board to have at hand for other projects as well.