hi Atif,
It is not good practice to apply a single voltage supply to devices that are normally powered by more than one supply voltage levels.

The single currents you are measuring could be misleading, only test each current when all the voltages are applied to the project.

E

 

I have checked impedence between common ground and board ground
Without turning on 5V supply, impedance is 0ohms which is correct but when i switch on 5v supply impedance changes to 89ohm which is a problem

Seems that those grounds are'nt connected to common point.

 

I have 4 DC supplies of 6V, 3.3V, -5V and 5V. But in my circuit voltages drops like
6V to 5.4V
3.3V to 2.7V
-5V to -5.6V
5V to 4.3V.
Is this problem due to common grounding issues?
I cannot debug this problem.

That your negative supply is going more negative is very telling. This would indicate a ground reference problem.

All of the supplies drop 0.6 V (the last drops 0.7 V, but that's close enough). That also argues for a shift in reference. That the shift is essentially one diode drop might or might not be significant.

Assuming you should be using a common reference for all supplies, verify that they are solidly connected together, preferably at a single point on your circuit board, and then back to each of the supplies.

Make sure that all of the currents being drawn from each supply is well within that supply's capabilities.

 

By giver proper common ground reference now i have drop has been reduced
Now 6v drops to 5.75V
3.3V to 3.14V
-5V to -5.1V
5v to 4.45V
6V load draws 0.24A current
5V draws 1.2A current
But there is another problem without switching 5V supply, load of 6V draws 0.24A current from its supply which is correct but as soon as i switch on 5V supply, current of 6V supply drops to 0.16A from 0.24A.
I have checked impedence between common ground and board ground
Without turning on 5V supply, impedance is 0ohms which is correct but when i switch on 5v supply impedance changes to 89ohm which is a problem

How are you measuring the impedance of your ground with a supply turned on?

 

How are you measuring the impedance of your ground with a supply turned on?

Yes

 

hi Atif,
It is not good practice to apply a single voltage supply to devices that are normally powered by more than one supply voltage levels.

The single currents you are measuring could be misleading, only test each current when all the voltages are applied to the project.

E

When i turn on all supply voltages, the current of 6V is still low. My amplifier in 6v path has low current and not giving desired gain

 

Yes

I ask you HOW are you making this measurement. Measuring impedances in a powered circuit is very difficult -- unless you don't care about the measurement meaning anything.

 

I ask you HOW are you making this measurement. Measuring impedances in a powered circuit is very difficult -- unless you don't care about the measurement meaning anything.

I was measuring by wrong method. I had placed dmm between two points and checked impedance on dmm but its wrong to do it

 

Measuring VOLTAGES between two points on an energized circuit, though, can be a very effective way of locating voltage drops. On low voltage circuits like this it is quite safe, as well.
For this problem it is probably the very best approach, other than rewiring the power supply connections. It should be able to reveal exactly which connection is causing the voltage drop.

 

I think we all agree, as you originally posted, there is a voltage drop on the reference ground wiring.

Can you take a picture of the system and post please, so we have idea what sort of system were dealing with.

The magic words for grounds are "star point" and " big and short"

 

Given the voltage drops as listed in post #24,it seems that the several power supply common connections are tied to each other, and that a lead from the negative 5 volt supply negative terminal then connects to the circuit common. So the problem is in that single negative connection wire.
Measuring the voltage from the powered circuit assembly common terminal to the commoned terminal of each supply will show the location of the voltage drop, which should be much less, not over 0.01 volt.

 

Given the voltage drops as listed in post #24,it seems that the several power supply common connections are tied to each other, and that a lead from the negative 5 volt supply negative terminal then connects to the circuit common. So the problem is in that single negative connection wire.
Measuring the voltage from the powered circuit assembly common terminal to the commoned terminal of each supply will show the location of the voltage drop, which should be much less, not over 0.01 volt.

I have connected multiples wires from my ground on circuit to common ground of supplies and my current issue is almost solved but i didnot understand the reason behind it. Can anyone suggest some article on problems of Dc grounding in pcb?

 

All wires and connections have resistance.
If a wire with 0.1Ω resistance has 1A flowing then there will be a drop of 0.1V across the wire.
If that wire is shared as the return path with other supplies then the other supplies will see that 0.1V drop.
This is why we prefer to use star connection to power supplies.

 

All wires and connections have resistance.
If a wire with 0.1Ω resistance has 1A flowing then there will be a drop of 0.1V across the wire.
If that wire is shared as the return path with other supplies then the other supplies will see that 0.1V drop.
This is why we prefer to use star connection to power supplies.

MrChips description is exactly correct.
The explanation of a "star" connection is that separate ground wires from both power sources and power loads each connect to one point. That way only current used or supplied by one section flows in each wire. Using a star-point is an excellent way to avoid creating "ground loops", which are another nemesis in many instances..