Power plane with two voltage sources

Thread Starter

engr_david_ee

Joined Mar 10, 2023
166
Hi, I have a general question. If a power source that can be a linear voltage regulator or a DC-DC converter is rated for a maximum current which is little more than half of the actual current needed by the components on the PCB to be designed. Can we use two identical voltage sources in the schematic and connect both voltage sources to power and ground plane ? What are the drawbacks with this solution to get the required higher current when one voltage source is not enough ?
 

crutschow

Joined Mar 14, 2008
34,455
What are the drawbacks with this solution to get the required higher current when one voltage source is not enough ?
Two voltage sources in parallel will cause the one with the slightly higher output voltage (and it's not possible to keep them identical) will hog the current and constantly run at its current-limit, which can damage the supply.
You need to get just one supply that can supply the total current, or use two separate split-planes for the supply.
 

MisterBill2

Joined Jan 23, 2018
18,538
That solution would work IFF the voltages are identical. (Not likely) An alternative that can work well is to add a diode in series with each supply so that the supplies will not interact. But then the supply voltages need to be adjusted
Of course, if the supplies are not regulated then simply connect them directly, no problem.
 

Thread Starter

engr_david_ee

Joined Mar 10, 2023
166
I guess one approach here could be to use one voltage source to power up half of the board components and the other voltage source to power up the other half of the board components. In such a way the current distribution remain almost even. This way they there will be two power planes and even if the voltage levels are bit different, they will not interact each other. Please comment.

How about the ground plane. Can it be one ground plane, same for both voltage sources as a return path ?
 

MisterBill2

Joined Jan 23, 2018
18,538
I guess one approach here could be to use one voltage source to power up half of the board components and the other voltage source to power up the other half of the board components. In such a way the current distribution remain almost even. This way they there will be two power planes and even if the voltage levels are bit different, they will not interact each other. Please comment.

How about the ground plane. Can it be one ground plane, same for both voltage sources as a return path ?
Good Question indeed. USUALLY power supply return connections can be common and tied to the system common. The simple check will be to examine the external circuit to see if both of the supply return sides are connected.
And now a disturbing thought hit me: Is it possible that the two supplies are separated so that one was for the digital segment and the other for the analog portions of the system?? I have done that in the distant past, and it is often shown that way for mixed signal IC devices. Certainly it is worth checking.
 

MrSoftware

Joined Oct 29, 2013
2,202
You could try making each source a self contained module with only an output, then put series load resistors on the outputs. Similar to how BJTs are used in parallel. The load resistors, very low value, are just enough to not let one supply run away with all the load. I've not done this before so I might be missing something, maybe someone can double check me here. I don't know if a current limiting stage would be needed.

But I think you're better off finding a single supply that can handle the load. You can build your own, Coilcraft sells piles of inductors and should have help available, Texas Instruments has the SwitcherPro Desktop software to help you design what you need using TI controller chips, so you can design a supply large enough for what you need.

1709122323439.png
 

MisterBill2

Joined Jan 23, 2018
18,538
If the board is an existing board and the system it is part of is an existing system, but something has changed, then there ae more questions and more answers. If the linear regulators are like most IC regulators, unable to sink current, and without an over-voltage protection scheme, then just connecting both supplies can probably work OK, although the load may not be shared equally. So it will make sense to check that both supplies are about the same temperature in operation.
 

Thread Starter

engr_david_ee

Joined Mar 10, 2023
166
This is a new design consideration. The dc-dc converter we have already chosen for some other reasons is just able to deliver more then half the current needed by the ICs on the board. So, we are considering to use two of them. Each will be powering up one half of the ICs on the board.
 

MisterBill2

Joined Jan 23, 2018
18,538
OK, then it might even be possible to split the load, or maybe not. One option might be if the DC-Dc converters have the option of linking together, which some systems do. That would be the best case situation. I understand about there being "other constraints", been there in the past.
 

Thread Starter

engr_david_ee

Joined Mar 10, 2023
166
Yes this is possible to use two power planes. One for each DC-DC converter. Half the load will be on one power plane and the other half load will be on the other power plane. This way each DC-DC converter need to supply almost equal amount of current. The return plane can be the same for both.
 
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