Output Line Ripple on Power Factor Corrected AC-DC Power Supply Outputs (Part 4)

This is the fourth in a series of blog posts by Harry Vig, Principal Applications Engineer at Vicor. To go to Output Line Ripple on Power Factor Corrected AC-DC Power Supply Outputs (Part 1) click here.

How much does the load affect the output ripple?

The output ripple model was presented with a constant resistance load so that no feedback loop is needed to set the output voltage. Rather than create two more models, I took the easier route of retesting on the lab bench with all three types of loads.

The results are summarized in the table below:

output-voltage-ripple-figure-9

Figure 9 – Output Ripple for Different Loads

The net result is that the ripple voltage, at just over 10% of the average bus voltage, creates a ripple current about 10% of average current to the load. As you can see in the oscilloscope graphs, they are opposite in direction, but their magnitude is not large enough to cause a large error. The constant resistance model, which is far less computationally intensive, is a reasonable simplification.

The other unexpected result is that the constant power load has lower voltage ripple than the constant current load. While it is true that the load current ripple was higher, the higher input impedance of the constant current mode operation made the voltage ripple higher.

 

Read part five of this series: A Simple Average Model for Output Current Ripple.

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