Powerint 公司的3.67W LED驱动器反激设计方案采用LinkSwitch-II 系列LNK605DG,用于LED驱动器.设计的主要亮点是采用绿色封装和高效率:满负载时整个工作范围效率大于75%,无负载是在265VAC时消耗不到200mW的功率.该设计方案能驱动3个LED串,包括有功率开关器件,振荡器,CV/CC控制引擎,起动和保护功能.本文介绍了3.67W LED驱动器反激设计方案的电路图和所用变压器的基本特性.
New Design for 3.67W LED Driver Using Flyback Topology
Design Highlights:
Green package: halogen free and RoHS compliant
Highly energy efficient
Full load efficiency >74% throughout operating range
No-load consumption <200 mW at 265 VAC
Figure 1 provides the schematic for a universal input, 10.5 V, 350 mA CV/CC power supply using the LinkSwitch-II LNK605DG (U1) in a flyback configuration, useful for LED driver applications.
The design is intended to drive a 3 LED series string, delivering the rated output current over the range of LED VF. Integrated circuit U1 consists of a power switching device, an oscillator, a CV/CC control engine, startup and protection functions. The primary side CV/CC control functionality of U1 eliminates the need for sense resistors and optocouplers, which results in an ultra-compact footprint for this design which can mechanically fit inside a GU-10 LED enclosure.
Bridge BR1 rectifies the AC input voltage. The rectified DC is filtered by the bulk storage capacitors C1 and C3. Inductor L1, along with capacitors C1 and C3, form a pi (π) filter which attenuates conducted differential-mode EMI noise. This configuration, along with Power Integrations’ transformer E-Shield technology, allows this design to meet EMI standard EN55015 class B with 6 dB of margin, without using a Y capacitor. Fusible,flameproof resistor RF1 limits inrush current when AC is applied and during differential mode line surge.
One side of T1’s primary winding receives the rectified, filtered DC voltage. The MOSFET drives the other side of the primary.
The RCD-R clamp formed by D2, R4, R5, and C4 limits any drainvoltage spikes caused by leakage inductance. Device U1 is completely self-powered from the BYPASS (BP) pin and decoupling capacitor C2. It regulates the output using ON/OFF control for constant voltage (CV) regulation, and frequency control for constant current (CC) regulation. Feedback resistors R1 and R2 have 1% tolerance values to accurately center both the nominal output voltage and the current in CC operation. The CV feature also provides output over-voltage protection (OVP) in case any LEDs fail open-circuit.
设计亮点:
Fits inside an extended GU-10 lamp base
Accurate primary-side constant voltage/constant current (CV/CC) controller eliminates secondary-side control and optocoupler
No current-sense resistors, for maximized efficiency
Low part-count solution for lower cost
Over-temperature protection – tight tolerance (±5%) with hysteretic recovery for safe PCB temperatures under all conditions
Auto-restart output short circuit and open-loop protection
Highly energy efficient
Full load efficiency >74% throughout operating range
No-load consumption <200 mW at 265 VAC
Ultra-low leakage current: <5uA at 265 VAC input (no Y capacitor required)
Green package: halogen free and RoHS compliant
图1.1采用控制IC LNK605DG的 10.5 V, 350mA LED驱动器电路图
设计要点:
The IC package provides extended creepage distance between high and low voltage pins (at both the package and the PCB), required in very humid or polluted environments to prevent arcing and to further improve reliability.
Place C2 as close to the BYPASS pin as possible.
Feedback resistors R1 and R2 have 1% tolerance values to assist in centering both the nominal output voltage and the CC regulation threshold tightly.
An optional bias winding can be added to lower no-load power consumption.
下表为变压器主要参数:
