DC/DC Converter Application Note
PWM Control and VFM Control
Ricoh’s DC/DC converters are pulse-width modulation (PWM) controlled or variable-frequency modulation (VFM) controlled. VFM is also called pulse-frequency modulation (PFM).
The oscillator frequency is constant and the pulse width (ON time) changes according to the amount of output load.
The pulse width (ON time) is constant and the oscillator frequency changes according to the amount of output load.
The features of VFM control and PWM control are as described below.
|Oscillator Frequency||Pulse Width (Duty)||Light Load Condition||Noise
|PWM Control||Constant||Change||Not Good||Low||Easy|
- *1 Noise suppression of VFM control can be difficult because oscillator frequency is inconsistent and it affects noise level.
Noise suppression of PWM control is relatively easier because oscillator frequency is constant and it does not affect noise level.
Ricoh’s DC/DC converters include the products that are only operated by PWM control and the products that can be automatically switched between PWM mode and VFM mode according to the load condition.