Controlling Power to LED Lighting for High Efficiency
All the for mentioned lights can use a technique called PWM control. PWM stands for Pulse Width Modulation and is a method that switches power on and off quickly. By changing the ON time versus the OFF time you can control how much power is delivered to a device. This control approach typically uses a microcontroller to monitor and control the power output to an LED. A microcontoller is a single chip computer that can be programmed by an engineer to perform various functions. A typical PWM controller would use one micro controller, a power switching device called a P-channel mosfet, a resistor and a LED to create light. One other item needed is a power supply. Most LEDs need to powered by a DC power source like batteries or an AC-DC converter. One common AC-DC converter is the power adapter used to charge cell phones, MP3 players and gaming devices. These converters usually provide a USB port that delivers a 5 volt DC output with up to 2 amps of current.
Using a plug in USB wall converter as the power device to provide power to the microcontroller and also the LED can create a high efficiency light. The micro connects to the control gate of the mosfet switch and the LED is connected between the power source, the mosfets current path and a resistor. Each component in the system has a function. The micro will switch the mosfet very quickly controlling the delivery of power to the LED. The resistor limits current to the LED so it does not overheat. When a micro using PWM has been programmed to drive the LED on and off it is desirable to have a way to monitor an input that will allow the user to adjust the Pulse Width the micro outputs to the mosfet switch. This input can be as simple as a push button switch, a thumb wheel switch or other device that the micro can read. Then by press said switch 1,2, 3 or more times you can increase the ON time the micro switches thus controller the light level output by the LED.
The above is but just one example of a control technique that can be used produce a low power high efficiency light source. The true value of such a concept could be realized if all lighting devices would use this method, then a major reduction in power consumption worldwide could be achieved. How? by only using the power we need to produce the light we want.