Pulse width modulation (PWM) is a technique for creating modulated electronic pulses or electronic pulses of the desired width. LCD backlight control is one of the applications of PWM.
Topmicro's LCD displays use leds as backlight. By using a PWM scheme, several advantages can be achieved over a simple DC voltage approach. The main advantage is efficiency.
Delivers a pulsed high current to the LED for a short period of time instead of a constant DC current. For example, a normal LED drive current is 120mA. Now we apply 5 times the current 600mA, but only for 1/5 of the time. LCD displays do not consume more light. However, its perceived brightness is much brighter.
The human eye has a certain degree of permanence. It will remember the previous light for a short time. This allows us to think of movies as a steady stream of images. In fact, it flashes at a rate of 24-30 times per second. Similarly, our eyes remember the brightness of the LED backlight. The result is that the perceived brightness of the backlight is close to the high pulse brightness.
advantage
This effect brings several advantages to LCD display backlighting:
If an LCD display requires the brightest results, the display can be pulsed at a ratio of 1:4 with 5 times the typical current. The pulse frequency should be higher than 100Hz but lower than 1000Hz. So the human eye cannot detect the flicker.
This technology can also be applied to provide normal-looking brightness for LCD displays while reducing energy consumption by at least 50%. This is a big benefit for battery-powered products.
Another use is to facilitate brightness control of LCD displays. By adjusting the high/low current ratio, a wide range of brightness can be achieved while maintaining a very uniform backlight appearance.
