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LYT4313 Datasheet(PDF) 11 Page - Power Integrations, Inc. |
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LYT4313 Datasheet(HTML) 11 Page - Power Integrations, Inc. |
11 / 20 page Rev. B 02/13 11 LYT4211-4218/4311-4318 www.powerint.com Audible Noise Considerations for Use with Leading Edge Dimmers Noise created when dimming is typically created by the input capacitors, EMI filter inductors and the transformer. The input capacitors and inductors experience high di/dt and dv/dt every AC half-cycle as the TRIAC fires and an inrush current flows to charge the input capacitance. Noise can be minimized by selecting film vs. ceramic capacitors, minimizing the capacitor value and selecting inductors that are physically short and wide. The transformer may also create noise which can be minimized by avoiding cores with long narrow legs (high mechanical resonant frequency). For example, RM cores produce less audible noise than EE cores for the same flux density. Reducing the core flux density will also reduce the noise. Reducing the maximum flux density (BM) to 1500 Gauss usually eliminates any audible noise but must be balanced with the increased core size needed for a given output power. Thermal and Lifetime Considerations Lighting applications present thermal challenges to the driver. In many cases the LED load dissipation determines the working ambient temperature experienced by the drive so thermal evaluation should be performed with the driver inside the final enclosure. Temperature has a direct impact on driver and LED lifetime. For every 10 °C rise in temperature, component life is reduced by a factor of 2. Therefore it is important to properly heat sink and to verify the operating temperatures of all devices. Layout Considerations Primary-Side Connections Use a single point (Kelvin) connection at the negative terminal of the input filter capacitor for the SOURCE pin and bias returns. This improves surge capabilities by returning surge currents from the bias winding directly to the input filter capacitor. The BYPASS pin capacitor should be located as close to the BYPASS pin and connected as close to the SOURCE pin as possible. The SOURCE pin trace should not be shared with the main power FET switching currents. All FEEDBACK pin components that connect to the SOURCE pin should follow the same rules as the BYPASS pin capacitor. It is critical that the main power FET switching currents return to the bulk capacitor with the shortest path as possible. Long high current paths create excessive conducted and radiated noise. Secondary-Side Connections The output rectifier and output filter capacitor should be as close as possible. The transformer’s output return pin should have a short trace to the return side of the output filter capacitor. Figure 13. DER-350 25 W Layout Example, Top Silk / Bottom Layer. PI-6904-101612 Output Capacitors VOLTAGE MONITOR Pin Resistor FEEDBACK Pin Resistor REFERENCE Pin Resistor Input EMI Filter LYT4317EG Bullk Capacitor Clamp Transformer Output Diode Output Capacitor BYPASS Pin Capacitor |
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