Last time I dismantled a power supply using BUCK PFC, and its BUCK works in DCM mode. I do n’t understand why DCM BUCK is used instead of CCM BUCK. It depends on the materials used. Do you choose between efficiency, PF value, power density, temperature rise, EMC ...?
In my opinion:
Compared with CCM BUCK, DCM BUCK can reduce the number of inductance turns and reduce the current stress of the switch. The current stress is large, which will cause the temperature rise to increase, and the difficulty of EMC treatment will increase.
The impact on power density, PF value and efficiency is difficult to judge, and I look forward to discussing it.
Personal understanding:
This should be the same as BCM-BOOSTPFC. The efficiency in BCM (DCM) mode is higher than that in CCM mode. Assuming that the output power is not high, the current stress of each component is actually not large. Even BUCK-PFC, its output voltage still exceeds 100V, the selection of power semiconductor devices in CCM mode should be much more difficult than in BCM mode. Without specific analysis and calculation, it only represents a "temporary point of view". What can be determined is that BUCK-PFC's contribution to transformer design is unparalleled (especially flyback).
The output voltage of BUCK-PFC is generally as low as 100V, because the volume of the capacitor below 100V is relatively small, and the RON of the MOS tube will also be much smaller, which can be said to be a hurdle.
The current stress of the MOS tube and the diode is less than the difference, but the peak current of the inductor will be more than doubled.
Will DCM mode be more efficient than CCM? Must it be? Why?
According to the BUCK principle, the greater the step-down ratio, the lower the efficiency. So 220VAC input, + HVDC = 300V,
BUCK voltage should not be too low.
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