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UCC28742: Voltage mode control vs current mode control

Naizeng Wang
Expert 5380 points
Part Number: UCC28742

Hi team,

In document "Switching Power Supply Topology Voltage Mode vs. Current Mode", it says that "A low-impedance power output provides better cross-regulation for multiple output supplies" is the advantage of voltage mode control. Why?

Thanks.

Nison Wang

  • 0
    TI__Mastermind 27095 points

    Hi Naizeng,

    In a current mode control scheme, the inductor looks like a voltage controlled current source. Due to this nature, the output impedance of a current mode controlled converter is determined by your output capacitance.In voltage mode control, you have both the inductor and capacitor determining the output impedance of the converter. Voltage mode control gives a lower output impedance compared to current mode control. 

    That being said, I should mention that voltage mode flybacks are quite uncommon these days. Type III compensation is required and you have to deal with a right half plane zero as well. The RHPZ is there in current mode flyback as well but its often much easier to stabilize over a wide operating range. For cross regulation, you are also dependent on how tightly coupled your output windings are so the cross regulation is not only dependent on the control scheme. 

    Best Regards,

    Ben Lough