18.104.22.168 PWM Phase-Shifting
A PWM phase-shifting scheme allows delaying the time when each LED driver is active. When the LED drivers are not activated simultaneously, the peak load current from the pre-stage power supply is significantly decreased. The scheme also reduces input-current ripple and ceramic-capacitor audible ringing. LED drivers are grouped into three different phases.
- Phase 1—the rising edge of the PWM pulse is fixed. The falling edge of the pulse is changed when the duty cycle changes. Phase 1 is applied to LED0, LED3, …, LED21.
- Phase 2—the middle point of the PWM pulse is fixed. The pulse spreads in both directions when the PWM duty cycle is increased. Phase 2 is applied to LED1, LED4, …, LED22.
- Phase 3—the falling edge of the PWM pulse is fixed. The rising edge of the pulse is changed when the duty cycle changes. Phase 3 is applied to LED2, LED5, …, LED23.
Figure 12. PWM Phase-Shifting