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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).

PWM Control

The oscillator frequency is constant and the pulse width (ON time) changes according to the amount of output load.

PWM Control

VFM Control

The pulse width (ON time) is constant and the oscillator frequency changes according to the amount of output load.

VFM Control

The features of VFM control and PWM control are as described below.

  Oscillator Frequency Pulse Width
(Duty)
Light Load Condition Noise
Suppression*1
Efficiency Ripple Voltage
VFM Control Change Constant Good High Difficult
PWM Control Constant Change Not Good Low Easy
  • *1Noise 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.

Tap to see the table

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.

RP506K Efficiency vs. Output Current

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