measuring power consumption of switching PSU.

[allegro]

Hello all.

I own the PSU - LNK306DN.
https://www.powerint.com/PDFFiles/lnk302_304-306.pdf

I wanted to ask please, how can I measure the power consumption of it?
I was told by someone that it takes taking graphs with scope and integrating them to receive the power consumption, and i'm not so sure what to do.

I though it would be just putting a shunt in the Drain entry and calculating 220Vac * I_shunt.

Thanks for any help.

 

[Nigel Goodwin]

You need at least a true RMS meter, if it's not true RMS you're getting no where near the correct reading.

 

[allegro]

You need at least a true RMS meter, if it's not true RMS you're getting no where near the correct reading.

Whats the problem with the scope?
I'd like to hear about it, because it measure well "regular signals", so i'd like to hear what is special in the input signal of the LNK.

Thanks.

 

[crutschow]

You can use a scope. But if it isn't a digital scope with a built-in RMS measurement function, then you will need to perform a graphical analysis of the waveform to generate it's root-mean-square value. That's not trivial to do for the very non-sinusoidal waveform that the input current is likely to be.

 

[Oblong]

First for safety the supply is not isolated so you should use an Isolation tranny.

At 100Hz you could use your scope and a shunt resistor to capture the input waveform then do the Integration. Rather then explain here is what I usually do see attached pdf. This is some of my test procedure for offline SMPS. I compared my readings and calculation to that cheap Kill A Watt meter and it’s pretty accurate. This neglects Rectifier and line filter and fuse losses but for the power level they are small.

For DC DC I use a opamp typically of suitable BW with a shunt.

 

[allegro]

Thank you everybody.
What is the shape of the graph, that i'll need to have accurate RMS measurement in scope?
Will it be periodical?

 

[Hero999]

First for safety the supply is not isolated so you should use an Isolation tranny.

Or a current transformer/hall effect transducer.

 

[Nigel Goodwin]

Thank you everybody.
What is the shape of the graph, that i'll need to have accurate RMS measurement in scope?
Will it be periodical?

It's basically a series of small pulses, just the top-up current for the reservoir capacitor. You would need to accurately measure the space under the curve.

 

[Mikebits]

Since the efficiency of the PSU is given in the spec sheet, could you not measure the PSU output current draw and infer the input power draw? May not be perfect but should give a good aproximation.

 

[allegro]

It's basically a series of small pulses, just the top-up current for the reservoir capacitor. You would need to accurately measure the space under the curve.

Thanks!
Will it be periodical?
So i know how many pulses i need to take.

Mikebits, I dont know the real efficiency of the PSU.

 

[Nigel Goodwin]

Thanks!
Will it be periodical?
So i know how many pulses i need to take.

It's just a pulse every half mains cycle, and will remain the same size as long as the load remains the same.