The advantages of PWM dimmable method:

(1) The PWM modulation method has high efficiency under heavy load, and has a good dynamic response to the change of load.

(2) The output ripple voltage is small and the linearity is high.

(3) The frequency is stable, the duty cycle adjustment is not limited, the control is simple, and both the current control mode and the voltage control mode are applicable.

Disadvantages of PWM dimming led driver:

(1) The efficiency of the PWM modulation method is reduced at light loads.

(2) The transient response is slow during constant voltage driver, and a more complex compensation circuit is required.

(3) An accurate current detection circuit is required for constant current drive.

PFM modulation method

Pulse frequency modulation Under the condition that the on-time of the switching power tube is constant, the output voltage can be controlled by adjusting the off-time of the switching power tube. When the output voltage changes, the error amplifier samples the feedback signal, and sends the output signal after comparing with the reference signal to the control circuit. The control circuit analyzes the error signal and generates a square wave signal with constant pulse width and changing frequency to control the switch. power tube to maintain the stability of the output voltage.