LEDs have become increasingly popular in industrial applications, electronic signage and signal lights, home and mobile devices, automotive and consumer electronics because of their high efficiency, durability, long working life, environmental friendliness and superior visual effects. Therefore, the driver design of these LEDs has also received attention. In theory, the average working life of LEDs exceeds 100,000 hours. But the premise is that you need to choose the appropriate driver and circuit design, which will not only affect the life of the LED, but also their performance.
The use of a current limiting resistor to drive a standard 20 mA LED is a generally accepted and common way to be widely used in LED indicator functions.
A simple LED driver circuit is generally safe if it only contains conventional LEDs and the supply voltage does not fluctuate significantly. However, with the advent of high-power (HP) LEDs or high-brightness (HB) LED technology , these simple drivers are no longer suitable. HB or HP LEDs operate at higher current levels and require greater heat dissipation, while standard resistors do not meet such high requirements. The electrical characteristics of LEDs may also vary from type to type. In general, when the forward voltage (Vf) of the LED exceeds the forward voltage drop value, even if the Vf has a slight rise, the forward current (If) is greatly increased. A fast-increased If will cause the LED to be brighter and hotter, thereby accelerating LED losses and shortening the life of the LED.
Voltage-Current-Based Rate-of-Change Characteristics, LED Driver Characteristics e-Link Global Technical Support Center Feed LED drivers require a compliant design, so understanding their characteristics and selecting the appropriate driver circuit for a particular application is critical. Such a dedicated drive circuit can provide the rated voltage and current for these LEDs, creating a good condition for their normal operation.
To achieve the purpose of illumination, the LED needs a forward voltage to allow current to flow. The LED driver therefore has to provide a forward bias to the LED to illuminate it. The level of illumination or brightness of an LED is usually proportional to the magnitude of the forward current. In addition, the current through the LED should not exceed the rated current specified by the device, otherwise it may cause permanent damage.
Thus a constant current drive circuit is the ideal solution to control the current at the correct level of driving the LED.
In other words, the LED drive circuit is a power conversion circuit that provides a constant current instead of a constant voltage.
The LED driver circuit should contain at least one voltage detection circuit and one current switch circuit.
When the voltage detecting circuit detects different voltage levels of the power supply, it sends a signal to the current opening circuit, and then the current switching circuit is automatically activated, and the electrical setting of the LED is re-adjusted using a predetermined current value, thereby effectively lighting As many LEDs as possible.
Linear driver
Linear regulators provide a simple way to generate a constant current by connecting a current-sense resistor between the regulator output and the ground node. The constant output voltage of the regulator is passed through a feedback resistor to produce a constant current. The power reference voltage and current sampling resistor determine the LED current. Linear regulators are commonly used to drive low-power LEDs, such as backlights for portable devices such as PDAs. Typical values ​​for these LEDs range from 15 mA to 25 mA and Vf is between 3.0 V and 3.4V. If a linear driver is used to power multiple LEDs, these LEDs should be connected in series to ensure that the current through all of the LEDs is the same, resulting in approximately equal amounts of illumination.
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