Weida Yuan Technology explains the four modulation methods of switching power supply for you.
First type, pulse width modulation
Referred to as PWM, that is, pulse width modulation. The characteristic switching period is a constant value, and the duty ratio is changed by adjusting the pulse width to achieve the purpose of voltage regulation. Its core PWM controller. Pulse-width-modulated switching power supplies are most commonly used, with a wide duty cycle adjustment range, and the PWM can be synchronized with the clock of the main system.
Second, pulse frequency modulation
Referred to as PFM, that is, pulse frequency modulation. Its characteristic is that the pulse width is a constant value, and the duty ratio is changed by adjusting the switching frequency to achieve the purpose of voltage regulation. At its core is the PFM controller. The pulse-frequency modulation switching power supply is especially suitable for portable devices, which can reduce the quiescent current of the control chip under low duty cycle and low frequency conditions.
Third, pulse density modulation
Referred to as PDM, it is pulse-modulated. It is characterized by a constant pulse width and the purpose of voltage regulation by adjusting the number of pulses. It uses zero voltage technology to significantly reduce the loss of the power switch.
Fourth, mixed modulation
It is a combination of the first and second ways. The switching period and pulse width are not fixed and can be adjusted. It contains the PWM controller and the PFM controller.
The above four working modes are collectively referred to as "time ratio control" (TRC), in which the PWM controller is the most widely used. It should be noted that the PWM controller can be used as a stand-alone integrated circuit or integrated in a switching regulator or a single-chip switching power supply. Among them, the switching regulator belongs to the DC/DC converter, and the switching power supply is generally an AC/DC converter.
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