Post Date : Mar 09, 2023 / Last updated : Nov 14, 2023

Continuous Current Mode (CCM) and Discontinuous Current Mode (DCM) are the names of operation modes of switching power supplies, such as DC/DC and AC/DC.

The CCM and DCM are divided by the flow direction of the coil current. The difference in these operation modes causes a difference in the output voltage stability (transfer function model), so it is important to understand switching power supply control and stability.

The definitions for CCM and DCM are as follows.

Continuous Current Mode (CCM)The coil current is always flowing.
(There is no High Side/Low Side driver FET’s OFF/OFF period.)
Discontinuous Current Mode (DCM)There are times when the coil current is not flowing.
(There are High Side/Low Side driver FET’s OFF/OFF period.)

Step-down DC/DC CCM

Step-down DC/DC DCM

Generally, DCM is used under light load conditions and then changed to CCM when the output current becomes large. The output current at which the change from CCM to DCM occurs differs for each product and depends on the power supply specifications, inductance, IC control method, etc.

In addition, products that employ forced PWM control even during PWM control operate in CCM without changing to DCM even during light loads.

Condition: Vin=5V, Vout=3.3V/0mA