An LED emits light by applying a voltage to its PN junction to form an energy level transition to produce a photon. The LED device cannot be directly connected to 220V AC. It should be powered by a low voltage of 2-3V, that is, a complex conversion circuit (drive circuit) should be designed according to different applications and supply voltages. The LED drive circuit should have the characteristics of high power conversion efficiency, high reliability, high power factor, low cost, and small size.
LED driver circuit power supply type
According to the difference of the supply voltage, the drive circuit can be divided into two types: DC-powered low-voltage (0.8-1.65V) batteries (such as button batteries), and the drive circuit should use DC/DC boost converter. For other DC power supplies greater than 5V, the drive circuit should use a DC/DC buck converter; the power directly supplied by the AC mains is generally required to be AC/DC/DC converted.
LED lighting drive circuit main technology
LED lighting circuits are also divided into two categories according to the driving method. The output current of the constant current drive is constant, and the output voltage varies with the load resistance value; the output voltage of the constant voltage drive is constant, and the output current changes with the load resistance value. Constant current drive is an ideal way. The actual drive circuit generally has a constant voltage and constant current function.
The LED lighting driver circuit is divided into two types: device step-down and PWM switching power supply. Among them, the device step-down has a way of resisting the voltage drop, the resistance stepping down, and the transformer stepping down. The PWM switching power supply refers to a driving method that adjusts the width of the on-pulse of the main circuit switching device to keep the output voltage or current stable. Changing the duty cycle changes the average drive current of the LED, which changes the illumination intensity of the LED.
LED lighting driver circuit typical chip
When the LED lighting circuit needs to adjust the brightness, its control mode mainly includes linearly adjusting the LED current (analog dimming) and using PWM to set the duty cycle and duty cycle (digital dimming). Faced with hundreds of LED driver chips from various electronic companies at home and abroad, it is recommended that: first, try to use products of big brands, and secondly, consider quality and cost according to needs. Listed below are several commonly used typical driver chip models.
(1) Foreign products
1 US Maxim-MAX168XX series. The MAX16818 operates from a 4.75-28V supply and has an output current of 30A. A wide range of brightness adjustments are available through the PWM signal. The MAX16819/MAX16820 have an input voltage range of 4.5-28V and a drive current of 3A. The MAX16832A/MAX16832C have an input voltage range of 6.5-65V and a maximum output current of 1A. The MAX16802A/B is suitable for low voltage (10.8-24V) illumination and display drivers.
2 US TI-LM340X series. The LM3401 has an input voltage range of 4.5-35V and an output current of 3A. The LM3402 is a dimming driver IC, and the output current of the LM3404 and LM3402 is 1A. The LM3405A can output 1A constant current and drive 3W or 5W LEDs. The LM3405A can drive general lighting systems with 12V AC and 12V DC.
3 British Jetko-ZXLD1350. The input voltage range is 7-30V, the maximum output current is 350mA, and the maximum output power is 8W.
4 Japan Toshiba-MP4021A. The MP4021A has a built-in PFC (power factor correction) with an input voltage range of 90-264V, an output voltage range of 36-42V, and an output current of 420mA.
(2) Domestic products. The core technology - MT7930. This is an isolated driver IC with AC input voltage range of 85-265V, high precision constant current output, 50W drive capability, adjustable output current and output power.
(3) Taiwan Guangpeng Technology-AMC7150. The AMC7150 can be used in automotive and general lighting LED drives with an input operating voltage range of 4-40V, a drive current of 1.5A, and an output power of 24W.
Quality and price are the main factors to consider when selecting a product IC when technical requirements are met. Toshiba, Texas Instruments, and the national half of the IC are more expensive, but the quality is reliable. In addition, NXP, Infineon, Dianjing Technology and other companies' products are also good. Domestic chips have obvious advantages in terms of cost and can be selected as needed. As the power of LED light sources continues to increase, chip vendors are racing to develop more integrated, smarter IC drive solutions and continue to reduce costs.
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