Im a beginner. In a project im assigned to use 9V battery, I have a variable power supply. Can I use it with 9V selection instead of battery? Pls help me out

 

Yes. In general you can use a regulated DC power supply of comparable current capacity to replace a battery.

 

Thanks, so small difference in current will not matter??

 

Because we don't know the details of your project, and the 9V battery just can offer a small current, so when you using the variable power supply to replacing the battery, the circuit could be working fine, but it doesn't means that it will also working ok with 9V battery.

Using the variable power supply to do the experiment is very common, I also do that, but if the circuit will working with a 9V battery then I will calculate how much current that I should provide for it, I will also measure the current.

 

Thanks, so small difference in current will not matter??

A circuit normally takes only the current it needs at a given voltage. So you just need a power supply that will supply more current then that. Any power supply excess current capability is just ignored by the circuit.

 

The only concern - and it's a bit of a reach - is that you're working with a poorly designed circuit that relies on the low current capacity of the 9V battery. This hypothetical circuit might be operating at 6V once it pulls down the battery voltage when under load. When you come along with a genuine "unlimited" 9V supply, the circuit may not last as long.

 

To elaborate on wayneh's comments...this is due to the "internal resistance" of the battery. It acts like a series resistor inside the battery. Bench power supplies have an almost zero effective internal resistance.
http://www.learningaboutelectronics.com/Articles/Battery-internal-resistance

Then again we may have told you more than you wanted to know!

Ken