![4 modulation methods of switching power supply(图1) 4 modulation methods of switching power supply(图1)](/uploads/ueditor/20220512/b06653e0c85942e9678e51f8b00af11b.png)
The first, pulse width modulation
PWM is abbreviated as Pulse Width Modulation. Its characteristic switching
cycle is a constant value, and the duty cycle is changed by adjusting the pulse
width to achieve the purpose of voltage regulation. Its core PWM controller. The
application of pulse width modulation switching power supply is the most common,
and its duty cycle adjustment range is large, and PWM can also be synchronized
with the clock of the main system.
The second type, 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 cycle is changed by
adjusting the switching frequency to achieve the purpose of voltage regulation.
At its core is the PFM controller. The pulse frequency modulated switching power
supply is especially suitable for portable equipment, which can reduce the
quiescent current of the control chip under the condition of low duty cycle and
low frequency.
The third type, pulse density modulation
Abbreviated as PDM, which means pulse density modulation. Its
characteristic is that the pulse width is a constant value, and the purpose of
voltage regulation is achieved by adjusting the number of pulses. It adopts
zero-voltage technology, which can significantly reduce the loss of the power
switch tube.
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 PWM controller and
PFM controller.
The above four working modes are collectively referred to as "time ratio
control" (TRC for short) mode, among which PWM controller is the most widely
used. It should be pointed out that the PWM controller can be used as an
independent integrated circuit, and can also be integrated in a switching
regulator or a single-chip switching power supply. Among them, the switching
regulator is a DC/DC converter, and the switching power supply is generally an
AC/DC converter.
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