Gnd AutoRouting

Hi everyone,

I just finalized my schematic and would like your feedback on the autorouting tool for this project. Can I rely on it, especially for creating ground connections? Additionally, I have a few inquiries about component placement rules. Should I place capacitors and resistors close to each other, or are there specific guidelines I should follow? Thanks for your replies!


What do you mean by rely on it? An autorouter isn’t aware of anything special about a net labelled GND, it just connects all the nets that need to be connected, otherwise it signals failure.

As for your layout, it leaves quite a bit to be desired, there’s no need to group resistors, capacitors and transistors as you have done. You should choose their positions for best routing, whether manual or autorouting. E.g. to suit the constraints of connectors, minimise trace length and crossings. That’s the most time consuming part of routing, good placement. You might want to set the GND and supply nets to a power netclass that has wider traces, and to add a GND fill.

Also this looks like some kind of power converter from the inductor. Those members with experience (not me) will have something to say about the nets that must be kept physically small and handle high pulsed current in such converters.

If this is a continuation of your buck converter posting, you know you buy converters off the shelf for very little money as they are mass produced? Such a circuit isn’t a good first project for learning.

Just keep practicing placement until the results are satisfactory. I often leave a layout for a day or two before coming back to it with better ideas. Fortunately I don’t have to work to deadlines.

The LED should be across the input, not in series.
You need a much more thought out layout, considering where the big and noisy switching currents flow.
I doubt L1 is in that style.

I design power supplies for a living, and I generally agree that this design looks pretty bad, from start to finish.

An autorouter is the last thing you ought to be concerned with. In 40+ years of designing power supplies, I have never worked with an autorouter and I sure as heck do not want to start now. The autorouter does not understand power supply design. (if there is an AI autorouter, I do not know about it. :frowning: )

  1. I do believe it is intended to be some sort of boost converter, but I seriously doubt even the schematic design. Did you design it or did you get it from somewhere else?

  2. PCB layout is the essential “secret sauce.” I have tried to fix a really bad layout of my schematic diagram and it did not run at all. Could not make it work.

  3. The first thing is a good schematic design. Placing the components is the second thing. And as mentioned above, grouping similar components together (for neatness?) is completely wrong.

  4. As for ground, best to use a ground plane. This circuit does not appear to be high power or high frequency, and you can probably do OK with a 2 layer board. Make the bottom layer as solid a ground plane as you can.

Regarding the schematic design: At first I was thinking that it would not start to run but now I think that it might run. But I say “briefy” because I spotted a likely problem:

If I am correct, I think that Q1 will get too much reverse base-emitter voltage which will make it fail. I have found the need to be very conservative with reverse base-emitter voltage on signal transistors. Typically reverse Vbe is rated for 5V to 7V maximum, but had a couple fail apparently due to only a couple of volts. So I would add a 1N4148 diode across Q1 Vbe to limit the reverse base-emitter voltage to about 700 mV.

What is autorouting tool?
If you add GND zone covering whole bottom (or top) PCB layer you certainly can relay on zone auto-filling :slight_smile: .

At your schematic there are two main circuits current flows. In one phase it is red circuit, in second it is blue:
You should certainly position elements laying along these circuits first to make these circuits areas as small as possible. Then you should position the rest (each element to make its connections as simple and as short as possible.
Arranging elements to create some order on the board is absolutely not justified in the case of a DCDC converter.

And powering your converter through 470 resistor and LED will not work.

There is a whole lot of sophistication into PCB design. It’s much more then just putting some footprints in a row and letting an autorouter draw some connections.

You can google for “pcb design basics” and “pcb layout best practices” and “top mistakes in pcb layout design” and “best tips for pcb layout design” etc.

This forum is mainly for tips and help for using KiCad, not general electronics or basics of design which doesn’t depend on the used software.

I’ll close this thread. Please come back when you know better what you need to achieve and can ask how it can be achieved with KiCad.