Controlling Power to LED Lighting for High Efficiency
In the world of LED lighting there are various techniques and configurations that can be used to provide and control the delivery of light. LED lights are ideal for applications requiring high efficiency. Some lighting products that use LEDs are portable battery powered device like flashlights, camping lights, bike lights and others. LED lights do not have to be battery powered some other good applications include LED light bulbs, USB lights, Night Lights, Accent Lights and power fail safety lights.
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.