Current consumption by circuit

[Rajashri.Shevale]

how do i come to know , how much current is consuming my circuit? I required this because I want to give exact power to my circuit. Shall I connect a simple 10K resistor at the input side and measure voltage across it ? will it works ? if anybody have an idea please suggest me......

 

[barry]

No! Remember Ohm's Law? If your circuit draws just 1 milliamp, it will drop 10 volts across your huge resistor. You have a volt meter, but you don't have an ammeter? Forgetting that for a moment the big question is, what do you mean you "want to give exact power"??? Will you adjust the voltage so that you supply some fixed power? Or adjust the current? This just doesn't make sense. Maybe tell us more about your circuit...

 

[Audioguru]

I want to give exact power to my circuit.

A circuit is supposed to be designed to take only as much power as it needs.

For example:
A car battery can supply 500 Amps at 12V (6000 Watts) to the starter motor to start a cold engine. But the car has its clock always connected to the same battery. Does the clock also draw 500W and consume 6000W? No, the clock is designed to draw only about 5mA (0.005A) and consume 0.06W which is almost nothing.

 

[FvM]

how do i come to know , how much current is consuming my circuit?

Connect a power supply of nominal voltage, measure the current with an ampere meter. Alternatively connect a low ohmic resistor in series (a shunt) and measure the voltage drop.

With a high ohmic resistor you'll probably have difficulties to set the right voltage for the device under test. 10k can be of course O.K. if the current is only a few µAs. In any case the shunt voltage drop should be small in relation to the supply voltage.

 

[treez]

also, you could use a current clamp if you wish, dc or ac as required, or also, use a hall sensor.

 

[Audioguru]

If you limit the current to a circuit then the circuit will probably stop working properly.