With the light-emitting diode (LED) reduced production costs, the use of more and more common range of applications from handheld devices to the automotive, architectural lighting, and other fields. LED reliability (service life of more than 50,000 hours), efficiency (more than 120 lumens per watt), and near real-time response characteristics has become an attractive light source. LED can produce light in the time of 5 nanoseconds, while the reaction time of the incandescent light bulb is 200 milliseconds, so the auto industry has LED used in the brake lights. This article will focus on the LED characteristics and the drive LED of dispute, the case, the depth suitable for the led driver 120w and dimming, switching power supply topologies, and details related advantages.
The stability of LED drive current to maintain a fixed brightness
The LED driver is still facing many challenges, to maintain a fixed brightness, to stabilize the current drive LED, and not by the input voltage, compared to incandescent bulbs simply connected to the battery as a power challenge.
The LED Floodlight 80W has a forward VI characteristics, similar diode circumstances. White LED turn-on threshold of about 3.5 volts, under this threshold, the amount of current through the LED is very small. Exceed this threshold, the current will be enhanced exponentially, resulting in the increment of forward voltage, the LED and thus become the series resistance of the voltage source model. Should be noted, however, this model is valid only in the case of a single operation of the DC current DC current in the LED change, the resistance in the model should be changed to show the new operating current. Forward current, the electricity consumption in the LED will increase the device temperature, changing the forward voltage drop and dynamic impedance, determine the LED impedance, be sure to consider the heat of the environment.
If the LED Flood light 10W is a buck regulator drive, in addition to DC current, the LED will often conduction inductor AC ripple current situation according to the selected output filter arrangement. This will increase the RMS intensity of the LED current will increase its power consumption and junction temperature have a significant impact on the life of the LED. If the 70% limit established in the light output as the useful life of the LED can increase LED life of 15,000 hours from 74 ° C, 63 ° C was extended to 40,000 hours. LED Power Supply loss to determine the method, the square of the RMS current in the resistance multiplied by the LED, plus along the forward voltage drop multiplied by the average current value. As the junction temperature is determined by the average power, even if there is a lot of ripple current, power consumption is also very small. For example, in which the buck regulator is equal to the DC output current peak ripple current (Ipk-pk = Iout), the total power loss will increase by less than 10%. If the extent is larger than this, quite a few cases, you must reduce the exchange of supply chain wave current to maintain the junction temperature and operating life. A practical basic principles, this is reduced by 10 ° C junction temperature, the life of the semiconductor will increase twice. In fact most of the design, because the relationship between the inductance limit, tend to use many of the low on the chain-wave current. In addition, the peak current in the LED should not exceed the maximum safe operating rated value specified by the manufacturer.
The LED Spotlight 30W used in a variety of areas need a variety of power supply topologies to support
Information is available in Table 1 to choose the best switching topology LED driver reference. In addition to these topologies, using a simple current limiting resistor or linear regulator, but these methods usually consume too much power. The input voltage range, the number of driven LEDs, LED current, isolation, electromagnetic interference (EMI) constraints and performance are related to the design parameters. Most of the LED driver circuit can be divided into the following topological category: buck, boost, buck-boost, SEPIC, and flyback.
