My first PCB / My Dummy Load Project - Feedback? - Page 1
Forum section: electronics / projects

author: tomtomtomtom
author_rank: Newbie
timestamp: June 15, 2012, 10:44:49 am
content: Hi there (new here)Was just wondering if some people could give me some feedback on my design, in particular the PCB layout, but comments about the design over all are welcome, because I've never really designed a PCB beforeThanksTom

author: LEECH666
author_rank: Frequent Contributor
timestamp: June 15, 2012, 10:58:36 am
content: How about including a circuit diagram? And please be a good person and clean it before you post it (no overlapping texts, lines through symbols, et.). There are way too many crappy shematics (especially drawn by Eagle users) out in the wild.HINT: Use the smash function in Eagle to detach text form the smybols, to avoid overlapping.Also be aware that not everyone has Eagle installed, so please use a more versatile file format like PDF.Florian

author: Christopher
author_rank: Frequent Contributor
timestamp: June 15, 2012, 12:20:07 pm
content: Very nice! If it were me, I'd move the mounting holes over a little, can't have enough clearance!

author: Rerouter
author_rank: Super Contributor
timestamp: June 15, 2012, 01:10:15 pm
content: my first thought would be, why not double over your load resistors so you can lay the potentiometer flat on the board, also test point 4 is a little un ideal, its so close to the tab of your regulator that is grounded, you would risk shorting when you try and measure off it,

author: tomtomtomtom
author_rank: Newbie
timestamp: June 15, 2012, 05:13:17 pm
content: Ok I've attached my schematic to the original post.As for my PCB well spotted about TP4 I have now shuffled that over to reduce the risk of shorting it.The pot is going to be mounted off board as I am going to put this in an instrument case, so the board will be mounted at the back so that I can mount the heatsink on the rear panel and then the pot will be mounted on the front panel.But thanks for all the replies so far, were much quicker than I expected

author: MikeK
author_rank: Super Contributor
timestamp: June 15, 2012, 10:10:40 pm
content: And you're going to electrically isolate the heatsink from the MOSFET, right?

author: Harvs
author_rank: Super Contributor
timestamp: June 16, 2012, 06:36:48 am
content: Unless you've already got it, you may find cheaper op-amps than that one to do the same job. You don't really need a precision op-amp just to track the voltage of a hand turned pot.Instead of screwing the regulator down, you could consider pulling back the solder mask there and soldering it down. It'll just save you the extra screw, nut and washers, but you'll need a decent iron to heat it quickly.Do you have a reason why you need a 1A regulator? You may just be able to use the 78L09 or similar which is considerably smaller (TO92).What value POT were you going to use, just noting the 1M5 resistor will form a voltage divider with it, and clearly you're planning on having the 1.2V zener as a voltage limiter. You'll just need a reasonably high resistance pot, in which case you may need to consider the input current of the op-amp. (I haven't actually worked any of this out, they're just points to consider.)Obviously you're limiting the + input voltage of the op-amp to 1.2V with 1R sense resistors, yet you're silk screen states 1.5A max. Was this intentional? You're only going to get 1.2A...Anyway, just some quick thoughts.

author: tomtomtomtom
author_rank: Newbie
timestamp: June 16, 2012, 12:15:57 pm
content: Quote from: MikeK on June 15, 2012, 10:10:40 pmYepQuote from: Harvs on June 16, 2012, 06:36:48 amAbout the Op-amp I know I don't really need a precision one but I figured seeing as this is a one off hobby project and I'm not too worried about the cost I may as well go all out on the op amp.Regulator, urm actually now you mention it I have no Idea why I'm not using a 78L09 haha, I'm going to change that now and also I'm going to add a 78L05 for my panel meter.I'm using a 500K Pot which I think should be high enough.And finally the 1.2 1.5 limit again not sure why I put that yes the output is limited to 1.2 DUHH haha I will change the silkscreen now.