The selection of the LED driver scheme is a very important part of the LED design process. For the LED driver scheme selection, let's see what the experts say.
1. LED driver IC features and choices
User question: LED driver must use a dedicated LED driver IC? What are the advantages and disadvantages compared with ordinary IC?
Expert reply: The advantages of LED driver IC are wide Vin, large output current, high constant current accuracy, and frequency hopping can effectively reduce EMI.
The constant current source for LED driving is mainly to ensure that the brightness of the LED during the working period of the LED is uniform and does not flicker. Low-cost mobile phones use LDO to drive backlight LEDs are also commonly used, but the power utilization rate is not high, but in most mobile phone design lithium battery voltage drop to 3.3V shutdown. It is not a good idea to drive LED lighting with LDO. LDO can't keep constant current.
User question: So how do you choose domestic and foreign LED driver ICs?
Expert reply: LED driver ICs are many, the cost performance is different, the key is to see the target price of the design products, such as seeking competitiveness and more profits, local IC products are also good.
2. LED drive power selection and design issues
User question: What issues to consider when selecting and designing LED driver
Expert reply: LED drive power is a voltage converter that converts the power supply into a specific voltage and current to drive the LED to emit light. Normally, the input of the LED drive power includes mains, low voltage DC, high voltage DC, low voltage high frequency AC, and the like. The output of the LED driver is mostly a constant current source that changes the voltage as the LED's forward voltage drop changes.
According to the power consumption rules of the power grid and the characteristics of the LED drive power supply, the following issues should be considered when selecting and designing the LED drive power supply.
a. High reliability is especially like the driving power of LED street lamps. It is installed at high altitude, it is inconvenient to maintain, and the maintenance cost is also large.
b. The high efficiency power supply has high efficiency, its power consumption is small, and the heat generated in the lamp is small, which reduces the temperature rise of the lamp. It is beneficial to delay the light decay of LEDs.
c. There are two types of driving methods: one is a constant voltage source for multiple constant current sources, and each constant current source supplies power to each LED separately. The other is direct constant current supply, with LEDs running in series or in parallel. How to choose the startup method should be based on actual needs. Multi-channel constant current output power supply mode will be better in terms of cost and performance. Perhaps it is the mainstream direction in the future.
d. The ability of surge protection LEDs to resist surges is relatively poor, especially against reverse voltage capability. Due to the start of the grid load and the induction of lightning strikes, various surges will be invaded from the grid system, and some surges will cause LED damage. Therefore, the LED driver power supply must have the ability to suppress the intrusion of surges and protect the LEDs from damage.
e. Other factors, such as improving the power factor of the power supply; increasing the negative feedback function of the LED temperature; for external protection, it is waterproof and moisture-proof, and the outer casing is resistant to light; the life of the driving power supply should be compatible with the life of the LED; And electromagnetic compatibility requirements.
3. LED driver IC development direction
Experts explain: the development direction of LED driver IC for lighting
The LED light source is a long-life light source with a theoretical life of up to 50,000 hours. However, the application circuit design is unreasonable, the circuit components are not properly selected, and the LED light source is not well cooled, which will affect its service life. Especially in the application circuit, the electrolytic capacitor, which is the output filter of the AC/DC rectifier bridge, has a service life of less than 5,000 hours. This has become a roadblock for manufacturing long-life LED luminaire technology, which can be designed and produced in the application circuit. A new generation of LED driver ICs that eliminate electrolytic capacitors is a viable solution.
In addition, the design of the new generation of LED driver ICs must break the traditional DC/DC topology design concept, such as constant voltage, step-down type without hysteresis control, constant frequency constant current control, and use of halogen-type electronic transformers. The generated light source flashes and the multiple lamps are not lit in parallel, etc.; the LED driver IC must also be able to pass EMC, safety, CE, UL and other certifications in various application circuits; the application circuit is intended to be simple and use less components. It is also necessary for customers to reduce costs and compete with the market; isolated and non-isolated applications have always been the focus of business security and efficiency; increase the duty cycle of PWM controllers and so on.
0.5W-3W LED light source integrated with LED driver IC The new generation of chips in a CMC package has been produced in small batches. The display LED driver IC is developing in a highly integrated multi-chip CMC package; it can be directly driven by alternating current (AC). The new generation of light-emitting, special topology ACLED light source production technology is becoming more and more mature, and will create another new era of LED lighting technology.
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