Switching Power Supply Topology, Voltage Mode vs. Current Mode

Focus:

This three-page design note describes how innovations such voltage feed forward and high frequency capability, which were implemented in Unitrode’s UCC3570 controller IC, overcome certain limitations of voltage-mode control, making it preferable to current-mode control in certain switching regulator applications. The note begins by discussing the advantages and disadvantages of voltage-mode control as it was originally conceived in switching regulator designs. It then describes how current-mode control overcame those disadvantages, but at the same time, introduced a new set of difficulties, which then needed to be addressed in switching regulator design. Next, the design note explains how voltage feed forward and high frequency switching are accomplished in the UCC3570 and how they 1) improve line regulation and 2) alleviate the effects of the two poles associated with the output filter. Finally, the note offers guidance on where the use of current-mode control is preferable and where voltage-mode control is preferable.

What you’ll learn:

• How to understand the differences between voltage mode and current mode control
• How to understand pros and cons of voltage-mode control versus current-mode control in switching regulator design in light of enhancements to voltage-mode control such as voltage feed forward and higher frequency switching

Notes:

This Design Note, DN-62, was originally published as an article in Electronic Design Magazine, June 27, 1994.

View the Source

Author & Publication:

Robert Mammano, Vendor website, Oct 01 1994

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