CXAC85270 is a driver chip designed specifically for high voltage, low current LED light strings powered by mains electricity. It integrates 500V high-voltage MOS transistors internally, without the need for external varistors. The system structure is simple, with very few peripheral components, greatly reducing the cost and volume of the solution. The chip supports an output current accuracy of ± 5% and can flexibly set the LED current through external resistors. It has excellent linear adjustment and over temperature protection capabilities.
-
[ CXAC85270 ]"
CXAC85270: Analysis of High Performance Single Channel LED Constant Current Driver Chip
In today's LED lighting market, efficient, stable, and energy-saving driving solutions have become the key to product competitiveness. CXAC85270, as a high-precision single channel LED constant current drive control chip, has become an ideal choice for various LED lighting products due to its integrated high-voltage rectifier tube and JFET high-voltage power supply function. This article will provide an in-depth analysis of the features, application scenarios, and design points of CXAC85270, to assist engineers in creating higher quality LED lighting systems.
1、 Chip Overview and Core Advantages
CXAC85270 is a driver chip designed specifically for high voltage, low current LED light strings powered by mains electricity. It integrates 500V high-voltage MOS transistors internally, without the need for external varistors. The system structure is simple, with very few peripheral components, greatly reducing the cost and volume of the solution. Chip support± 5% output current accuracy, flexible setting of LED current through external resistors, with excellent linear regulation and over temperature protection capabilities.
1、 The main features include:
• high integrationBuilt in high-voltage JFET power supply and rectifier tube, no magnetic components required;
• Quick StartUltra fast LED startup response enhances user experience;
• Accurate constant currentHigh precision output current, supporting external resistance setting;
• Over temperature regulationIntelligent temperature control mechanism ensures system reliability;
• Dual package selectionT0252-3 and SOT89-3 are packaged to meet different layout requirements.
2、 Internal structure and pin function
The internal structure of CXAC85270 mainly includes a high-voltage power supply module, a reference voltage module, a constant current control unit, MOS transistors, and an over temperature regulation circuit. Its pin configuration is simple and clear:
• DRAIN (Pin 1)LED string interface, supporting high voltage input;
• GND (pin 2)System grounding, attention should be paid to heat dissipation and wiring;
• CS (Pin 3)Connect the current sampling terminal to the external sampling resistor and ground.
Reasonable PCB layout and heat dissipation design are crucial for chip performance. It is recommended to connect the GND pin and heat sink to a large copper sheet to reduce thermal resistance and improve system stability.
3、 Electrical characteristics and limit parameters
3.1. At a working environment of 25 ℃, the typical electrical parameters of CXAC85270 are as follows:
• Static working current: 90 μ m; A (typical value)
• Constant current reference voltage: 600mV
• Overheating regulation temperature: 150 ℃
• DRAIN port withstand voltage: 500V
• Output current range: 5mA~60mA
3.2. To ensure the long-term reliable operation of the chip, the following limit parameters should be noted:
• DRAIN voltage not exceeding 500V;
• Maximum saturation current 80mA;
• Package power consumption limit (T0252-3 is 1.8W, SOT89-3 is 1.25W);
• Working temperature range: -40 ℃ to+150 ℃.
4、 Function Description and Application Design
4.1. Power supply mechanism
After the system is powered on, the DRAIN terminal supplies power to the chip through an internal JFET. When the voltage exceeds 10V, the chip starts working to ensure stable startup.
4.2. Constant current control and current setting
The LED current is set by an external sampling resistor (R_cs), and the formula is as follows:
Among them, VREF is 600mV. It is recommended to set the current below 40mA for 220V input and below 80mA for 110V input to balance efficiency and heat dissipation.
4.3. Over temperature regulation function
When the system temperature rises to the set threshold, the chip automatically reduces the output current, controls the temperature rise, avoids overheating damage, and significantly improves the system life.
4.4. PCB design suggestions
• The sampling resistor ground wire should be as short as possible;
• The GND area needs to be expanded to enhance heat dissipation;
• The bottom heat sink of the chip should be connected to the PCB ground plane.
5、 Typical Application Circuits and Efficiency Optimization
The typical application circuit of CXAC85270 is shown in Figure 4, which is suitable for LED driving scenarios with AC mains input. The efficiency calculation formula is:
Among them, VN is the input voltage, VLEDFor the voltage drop of a single LED, n is the number of LEDs connected in series. The more LEDs are connected in series, the higher the system efficiency.
5.2. Calculation of LED series connection quantity:
It is necessary to ensure that the voltage at the DRAIN terminal is within a reasonable range to balance efficiency and chip operation status.
5.3. Selection of electrolytic capacitor C2:
among which, t≈ 5ms（50Hz），Δ V is the voltage ripple at the D terminal. It is generally recommended to take the value of C2 as 4.7µ F~22µ F/400V。
6、 Parallel application and flicker free scheme
CXAC85270 supports multi chip parallel connection, suitable for high current or multi-channel LED systems. When connected in parallel, the constant current turn-on voltage of the system is based on the highest one among each chip. Resistors Res1~ResN can be independently set, allowing for flexible adjustment of various currents.
For the requirement of no flicker, a 3W application solution is recommended. The LED light string voltage is recommended to be set between 250V~270V, and equipped with C3 anti-interference capacitor to effectively suppress flicker and improve visual comfort.
7、 Packaging and Size
CXAC85270 offers two packaging options:
• T0252-3Suitable for medium to high power scenarios, with excellent heat dissipation performance;
• SOT89-3Compact size, suitable for compact design.
Please refer to pages 6-7 of the data manual for detailed mechanical dimensions.
8、 Conclusion
CXAC85270 has become the preferred driver chip for lighting products such as LED bulbs, ceiling lights, spotlights, candle lights, etc. due to its high integration, high precision, and powerful protection functions. Its concise peripheral circuit and flexible design options can help developers quickly implement efficient, reliable, and low-cost LED driving solutions.
For more information about CXAC85270 and other IC products, please visitJTMIC official website.
9、 Download the relevant chip selection guide; ►More similar products ...
