1. Dimming Function – Pulse-width Modulation (PWM)
Presented by: Illuminating Asia SG

2. What is Pulse-width Modulation(PWM)?
Lesser used method of low voltage dimmers out of all (Eg: 0- 10V, DALI, DSI, DMX and PWM)
Relationship between forward current and lumen output is effectively linear at lower forward current levels and becomes nonlinear as forward current increases
Source efficacy (lumens per watt) begins to decrease in the nonlinear segment of the range because an increasing percentage of output power is converted to heat
Commonly used for both static and dynamic dimming
Dimming of the LED is approximately proportional to the amount of on time to the amount of off time
Length of duty cycle determines the ultimate voltage of low-voltage signal delivered to ballast
Control signal is inverse to the dimming (The more the voltage is on, the dimmer the lamp appears)

3. Demonstration of 8RGB LED Diodes with PWM dimming

4. Duty Cycle of PWM
LED are turned on and off very quickly. At full light output, LED is turned on and never turns off
At 50% of light output, LED is on half the time and off half the time
To dim the light at any given level, simply change the ratio of time on and time off
If the speed of switching on and off (frequency) is high enough, human eye won’t see the switching

5. Pros and Cons of PWM Dimming
Smooth dimming capability
More precise output levels
Better consistency in color over various levels
Relatively more expensive
Flicker perceived in peripheral vision if the driver is run below 100Hz frequency
Stroboscopic effect evident in fast moving environments when driver frequency is low
Electromagnetic Interference (EMI) issues due to rise and fall of the current in PWM dimming
Performance issues arise when the driver is mounted remotely from the light source

6. Differences between 0-10V, PWM, Triac Dimmable
0-10V Dimming
PWM Dimming
Triac Dimming
How the dimming works
Control signal is a DC voltage that varies between 0 to 10V
Average value of voltage (and current) fed to the load is controlled by turning the switch between supply and load on and off at a fast pace
Conduct current in either direction when it is triggered (turned on)
Voltage Patterns