Recently, I have been working on a battery charger design based on a flyback DC-DC converter and I am curious about one thing: the flyback converter can work in CCM (continuous conduction mode) and DCM (discontinous conduction mode), but most battery charger systems use a flyback set up for DCM and I know the DCM flyback converter can use the valley ZVS.
Is this the reason for ensuring that the flyback converter works in DCM (the valley ZVS)? Is there anything else that could motivate this?
Battery charging is usually low power and suits DCM better for size and efficiency. Whereas high current 100W converters reducing the current swing is advantageous with CCM to avoid saturation.
DCM advantages DCM disadvantages
Lower primary L needed Higher peak primary current
L sets the max %d.c. Higher peak rectifier current
Smaller Xfmr possible Increased input capacitance
No diode reverse losses Increased output capacitance
min FET turn-on losses Potentially increased EMI
No right half-plane zero Wider duty-cycle needed than CCM
Optimal for low Pout Increased bandwidth variation
DCM flyback designs have both advantages and drawbacks relative to CCM designs.
