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LNK404 Datasheet(PDF) 5 Page - Power Integrations, Inc. |
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LNK404 Datasheet(HTML) 5 Page - Power Integrations, Inc. |
5 / 20 page Rev. D 08/11 5 LNK403-409/413-419 www.powerint.com Application Example 14 W TRIAC Dimmable High Power Factor LED Driver Design Example The circuit schematic in Figure 7 shows a TRIAC dimmable high power-factor LED driver based on LNK406EG from the LinkSwitch-PH family of devices. It was optimized to drive an LED string at a voltage of 28 V with a constant current of 0.5 A (±5%) ideal for PAR lamp retro-fit applications. The design operates over a universal input voltage range of 90 VAC to 265 VAC but provides the specified output current tolerance over a line voltage range of 90 VAC to 132 VAC (this is configurable for high-line only applications by simple component value changes). The key goals of this design were compatibility with standard leading edge TRIAC AC dimmers, very wide dimming range (1000:1, 500 mA:0.5 mA), high efficiency (>85%) and high power factor (>0.9). The design is fully protected from faults such as no-load, overload and output short-circuit conditions and over temperature. Circuit Description The LinkSwitch-PH device (U1) integrates the power FET, controller and start-up functions into a single package reducing the component count versus typical implementations. Configured as part of an isolated continuous conduction mode flyback converter, U1 provides high power factor via its internal control algorithm together with the small input capacitance of the design. Continuous conduction mode operation results in reduced primary peak and RMS current. This both reduces EMI noise, allowing simpler, smaller EMI filtering components and improves efficiency. Output current regulation is maintained without the need for secondary side sensing which eliminates current sense resistors and improves efficiency. Input Stage Fuse F1 provides protection from component failures while RV1 provides a clamp during differential line surges, keeping the peak drain voltage of U1 below the 725 V rating of the internal power FET. Bridge rectifier BR1 rectifies the AC line voltage. EMI filtering is provided by L1-L3, C1, R16 and R17 together with the safety rated Y class capacitor (C7) that bridges the safety isolation barrier between primary and secondary. Resistor R16 and R17 act to damp any resonances formed between L1, L2, C1 and the AC line impedance. A small bulk capacitor (C2) is required to provide a low impedance source for the primary switching current. The maximum value of C1 and C2 is limited in order to maintain a power factor of greater than 0.9. LinkSwitch-PH Primary To provide peak line voltage information to U1 the incoming rectified AC peak charges C3 via D2. This is then fed into the VOLTAGE MONITOR pin of U1 as a current via R2 and R3. This sensed current is also used by the device to set the line input overvoltage and undervoltage protection thresholds. Resistor R1 provides a discharge path for C3 with a time constant much longer than that of the rectified AC to prevent generation of line frequency ripple. The VOLTAGE MONITOR pin current and the FEEDBACK pin current are used internally to control the average output LED current. For TRIAC phase-dimming applications a 49.9 kW resistor (R4) is used on the REFERENCE pin and 4 MW (R2+R3) on the VOLTAGE MONITOR pin to provide a linear relationship between input voltage and the output current and maximizing the dimming range. Resistor R4 also sets the internal line input undervoltage and overvoltage protection thresholds. R11 2.4 M Ω R9 750 k Ω 1% R10 750 k Ω 1% PI-5997-061510 D S BP V R FB CONTROL FL1 T1 RM8 11 1 FL2 3 2 R2 2 M Ω 1% R1 240 k Ω 1/2 W R16 1 k Ω L1 1000 µH L3 1000 µH L2 1000 µH R17 1 k Ω R3 2 M Ω 1% R4 49.9 k Ω 1% R6 162 k Ω 1% R15 20 k Ω 28 V, 500 mA 90 - 265 VAC RTN L N R7 10 k Ω R8 150 Ω R5 3 k Ω R19 1 k Ω D2 DL4007 D3 UF4007 D5 1N4148 VR3 ZMM5259B-7 39 V Q3 MMBT3904 D7 BAV21WS-7-F D6 DL4936 D8 MBRS4201T3G D4 UF4002 VR1 P6KE200A R20 10 k Ω BR1 2KBP06M 600 V F1 3.15 A RV1 275 VAC C8 330 µF 50 V C7 2.2 nF 250 VAC C10 330 µF 50 V C4 10 µF 16 V C12 1 µF 50 V C13 100 nF 50 V C5 22 µF 50 V LinkSwitch-PH U1 LNK406EG C3 1 µF 400 V C1 47 nF 275 VAC C2 100 nF 630 V R18 510 Ω 1 W C11 220 nF 630 V R12 15 Ω 1% R13 130 Ω 1/2 W D1 DL4002 Q2 IRFR310 VR2 ZMM5245B-7 15 V Q1 FMMT558 C6 15 nF 50 V Figure 7. Schematic of an Isolated, TRIAC Dimmable, High Power Factor, Universal Input, 14 W LED Driver. |
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