Grounding of multiple SMPS's
Grounding of multiple SMPS's
(OP)
Hello,
We have a PCB , 26mm x 45mm (double-sided).
(This area does not include the offline flyback at the front end, because this question does not concern that part)
The secondary side of the PCB contains two switch-mode , 7W, Buck LED Drivers and one 5V, 250mW SMPS, and two microcontrollers.
The microcontrollers also read the average LED current with their ADC's which read the LED Drivers' current sense resistor voltage via RC filters.
We are wondering about the best way to ground these converters?
Do you think that the gold line , in the picture below, is necessary to make the 5V ground the same as the other grounds?
Here is the diagram, which i wonder if it's right or not.?
http://i49.tinypic.com/2zhr60y.jpg
We have a PCB , 26mm x 45mm (double-sided).
(This area does not include the offline flyback at the front end, because this question does not concern that part)
The secondary side of the PCB contains two switch-mode , 7W, Buck LED Drivers and one 5V, 250mW SMPS, and two microcontrollers.
The microcontrollers also read the average LED current with their ADC's which read the LED Drivers' current sense resistor voltage via RC filters.
We are wondering about the best way to ground these converters?
Do you think that the gold line , in the picture below, is necessary to make the 5V ground the same as the other grounds?
Here is the diagram, which i wonder if it's right or not.?
http://i49.tinypic.com/2zhr60y.jpg





RE: Grounding of multiple SMPS's
Do inspect your layout and make sure signal traces don't hack up your resulting ground plane in a way that could cause isolations that would be bad.
Yes, essentially you need the gold line - but a plane would be much better.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Grounding of multiple SMPS's
-though i was worried that you have mostly agreed with the diagram, because in fact, due to severe PCB space limitations, it looks like we are going to have to go for this:-
http://i49.tinypic.com/2s9ypsw.jpg
....that is , unless any major problems can be seen with it?
There is no ground plane on this PCB as such , since the top & bottom of the double-sided PCB are too heavily populated with components and signal tracks.
-our first board came back after someone hurriedly , virtually auto-routed it, and the malfunction in the LED Drivers was totally unacceptable.
-We then manually re-wired this bad PCB and got it working, though the LED current was slightly jittery and uneven, -especially when both LED Drivers are running at the same time.
I wondered what can be recommended here for the best in terms of grounding a PCB with no room for large ground plane and multiple SMPS's?
RE: Grounding of multiple SMPS's
But you're already pressed for space, so you may not be able to route individual power and ground traces to the edge of your board.
Unless you move them off the board, into the space above or below the board, with busbars or actual wires, which is sort of the next least awful way...
Mike Halloran
Pembroke Pines, FL, USA
RE: Grounding of multiple SMPS's
Your second plan would work. Probably fine.
BTW: Why the 5V switcher? Why not use it as the 3.3 and gain a little board space by jettisoning the 3.3V?
Keith Cress
kcress - http://www.flaminsystems.com