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LYT4317E Datasheet(PDF) 6 Page - Power Integrations, Inc. |
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LYT4317E Datasheet(HTML) 6 Page - Power Integrations, Inc. |
6 / 20 page Rev. B 02/13 6 LYT4211-4218/4311-4318 www.powerint.com Application Example 25 W TRIAC Dimmable High Power Factor LED Driver Design Example (DER-350) The circuit schematic in Figure 8 shows a TRIAC dimmable high power factor LED driver based on LYT4317E from the LYTSwitch family of devices. The design is configurable for non-dimmable only applications by simple component value changes. It was optimized to drive an LED string at a voltage of 36 V with a constant current of 0.7 A ideal for Lumens PAR lamp retro-fit applications. The design operates over an input voltage range of 90 VAC to 132 VAC. The key goals of this design were compatibility with standard leading edge TRIAC AC dimmers, very wide dimming range (1000:1, 700 mA:0.7 mA), high efficiency (>85%) and high power factor (>0.9). The design is fully protected from faults such as no-load (open load), overvoltage and output short-circuit or overload conditions and over temperature. Circuit Description The LYTSwitch device (U1- LYT4317E) 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, C4, R2, R24 and R25 together with the safety rated Y class capacitor (CY1) that bridges the safety isolation barrier between primary and secondary. Resistor R2, R24 and R25 act to damp any resonances formed between L1, L2, L3, C1 and the AC line impedance. A small bulk capacitor (C4) is required to provide a low impedance source for the primary switching current. The maximum value of C2 and C4 is limited in order to maintain a power factor of greater than 0.9. LYTSwitch Primary To provide peak line voltage information to U1 the incoming rectified AC peak charges C6 via D2. This is then fed into the VOLTAGE MONITOR pin of U1 as a current via R10. This sensed current is also used by the device to set the line input overvoltage protection threshold. Resistor R9 provides a discharge path for C6 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 k W resistor (R14) is used on the REFERENCE pin and 2 M W (R10) on the VOLTAGE MONITOR pin to provide a linear relationship between input voltage and the output current and maximizing the dimming range. Diode D3, R15 and C7 clamp the drain voltage to a safe level due to the effects of leakage inductance. Diode D4 is necessary to prevent reverse current from flowing through U1 for the period of the rectified AC input voltage that the voltage across C4 falls to below the reflected output voltage (V OR). R6 360 k Ω PI-6875-101812 D S BP V R FB CONTROL FL1 T1 RM8 12 1 FL2 10 11 R10 2 M Ω 1% R15 200 k Ω R9 510 k Ω 1/8 W R24 47 k Ω 1/8 W R1 510 1/2 W R25 47 k Ω 1/8 W R2 47 k Ω 1/8 W L1 1 mH L2 1 mH R14 49.9 k Ω 1% 1/16 W R18 165 k Ω 1% 1/16 W R23 20 k Ω 36 V, 700 mA 90 - 132 VAC RTN L N R19 20 k Ω 1/8 W C5 100 nF 50 V R26 30 Ω R20 39 Ω 1/8 W R17 3 k Ω 1/10 W R27 10 Ω 1/10 W D2 DFLU1400 C7 2.2 nF 630 V D3 US1J D5 BAV16 Q2 MMBT3904 D8 BAV21 Q1 X0202MA2BL2 D6 BAV21 D7 BYW29-200 D4 US1D R22 1 k Ω 1/10 W BR1 MB6S 600 V RV1 140 VAC F1 5 A C11 330 µF 63 V C13 100 pF 200 V CY1 470 pF 250 VAC C12 330 µF 63 V C8 47 µF 16 V C15 100 nF 50 V C14 10 nF 50 V C9 56 µF 50 V LYTSwitch U1 LYT4317E C6 2.2 µF 250 V C1 220 nF 250 V C4 100 nF 250 V L3 5 mH R8 100 Ω 1 W C3 470 nF 50 V C2 100 nF 250 V D9 DFLU1400-7 Figure 8. DER-350 Schematic of an Isolated, TRIAC Dimmable, High Power Factor, 90-132 VAC, 25 W / 36 V / 700 mA LED Driver. |
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