SMPS input current measurement

[Nicholas]

wrong measurement smps

Hi, all
I try to measure the AC input current of a SMPS as illustrated. But I get different results when using different multimeter. Can't distinguish which result is right. What's the problem?

Thanks
Nicholas

 

[E-design]

The problem is that SMPS draw non-sinusoidal current from the mains unless it has PFC (Power factor Correction). Trying to make measurements without true RMS type meter will give wrong readings

 

[nicleo]

Old analog multimeter is designed to measure 'sinusoidal' waveform. You should try to get a digital multimeter and make sure that the digital multimeter measures the RMS value current or voltage. Usually you will find the "True RMS" label on top of the multimeter or in the datasheet of the multimeter if it's capable of measuring TRUE RMS.

BTW, how much different among those meters that you used to measure?

 

[rauol]

observe the waveform on the scope

 

[Nicholas]

Old analog multimeter is designed to measure 'sinusoidal' waveform. You should try to get a digital multimeter and make sure that the digital multimeter measures the RMS value current or voltage. Usually you will find the "True RMS" label on top of the multimeter or in the datasheet of the multimeter if it's capable of measuring TRUE RMS.

BTW, how much different among those meters that you used to measure?

one reads about 3.2VAC , while another reads about 5.6VAC

 

[nicleo]

one reads about 3.2VAC , while another reads about 5.6VAC

The readings are very much different.

Pls share with us the type (brand/model) of meters that you use so that we can know whether it's the meter problem. Make sure you do proper calibration before doing the measurement.