Is ground can be common for different current rated loads....Example i am using 12v car battery in that load side i have 5W and 21W lamps can i connect ground of these 2 commonly....because i am using ground switching for output....supply is directly given to all lamps.

 

Yes you can connect two ground supplies together from two separate DC voltages, it makes a Common ground.

 

I am using ULN2003A for ground switching can i use it for different load currents....Example i am giving ground supply for 5W and 21W is that affect the circuit all are operated in 12V but different current ratings

 

The Uln2003 only takes 500mA, post a diagram of what you want to do.

 

Although 5 watts at 12 volts would be 420 mA as the load is a lamp it's initial current will bw quite a lot higher so it would then exceed the 500 mA maximum current rating for the ULN2003. Any 12 volt 21 watt load (1.75 amps.) would exceed the ULN2003 current rating.

Les.

 

Is ground can be common for different current rated loads....Example i am using 12v car battery in that load side i have 5W and 21W lamps can i connect ground of these 2 commonly....because i am using ground switching for output....supply is directly given to all lamps.

Yes, you can switch the grounds. This is done on a lot of systems, including the F-15 fighter aircraft (and probably many others, that's the just the one I know about most). To some degree you are simply making the system a "positive ground" system, which some cars used to be. You can also switch power to some circuits and ground to other circuits. You do need to be on the lookout for sneak paths between circuits.

A schematic of what you are doing/thinking is always helpful.