The type of LED drive power supply is divided into two types: constant voltage drive and constant current drive, constant current LED drive and constant voltage LED drive; constant current LED drive circuit samples the current flowing through the LED lamp through the control circuit, and outputs a control signal to control the switching power The turn-on and turn-off of the tube is to adjust the output current as the set value. The dimming control circuit mainly includes SCR dimming circuit, pulse width modulation (PWM), pulse frequency modulation (PFM), PWM_PFM modulation, PSM modulation and so on.

PWM dimming led drive modulation method

Pulse width modulation refers to the stability of the output voltage by changing the on-time of the switching power tube in each cycle at a specific frequency, that is, by adjusting the duty cycle. When the output voltage changes due to factors such as working environment and noise, the error amplifier samples the voltage change and sends the signal to the control circuit. The control circuit adjusts and controls the duty cycle of the switching power tube signal to maintain the stability of the output voltage.

Advantages of PWM modulation method:

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

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

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

Disadvantages of PWM modulation method:

(1) The efficiency of PWM modulation method decreases at light load.

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

(3) Accurate current detection circuit is required for constant current driving.