Slide 1 Slide 2 Slide 3 Slide 4 Slide 5 Slide 6 Slide 7 Slide 8 Slide 9 Slide 10 Slide 11 Slide 12 Slide 13 Slide 14 Slide 15 Slide 16 Slide 17 Product List
Image of Diodes Inc. DC/DC Synchronous Buck Converter - Modes of Operation

The required output voltage for a Buck converter can be achieved by two main modes of operation: Pulse Width Modulation, known as PWM, and Pulse Frequency Modulation, known as PFM. Devices operating in PWM switch following a fixed frequency. This happens when the output has a high load so the Buck converter continually has to switch to supply current to the output. PWM operation allows for small output voltage ripple, making it easier to filter the noise downstream. For PFM, the device switches to provide power to the output load only as needed while still maintaining output voltage regulation and meeting load demand. Thus, the average switching frequency in PFM is reduced. In theory, a device in PFM can wait as long as it needs to before it determines it needs to switch again, so the average switching frequency can be very low. When there is a light load, the current consumed by the Buck converter itself is less since it is not switching as often. This helps the overall converter efficiency at light loads. There is actually a third mode of operation, called Ultrasonic mode, or USM. This mode is similar to PFM except for one key difference: where PFM operation can allow the average switching frequency to go as low as it needs to, USM will clamp the switching frequency above the audible frequency range at light load conditions.

PTM Published on: 2021-08-13