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LNK454 Datasheet(PDF) 3 Page - Power Integrations, Inc. |
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LNK454 Datasheet(HTML) 3 Page - Power Integrations, Inc. |
3 / 20 page Rev. A 11/01/10 3 LNK454/456-458/460 www.powerint.com Functional Description The LinkSwitch-PL combines a high-voltage power MOSFET switch with a power supply controller in one device. The IC provides a single stage power factor correction plus LED current control. The LinkSwitch-PL controller consists of an oscillator, feedback (sense and logic) circuit, 5.85 V regulator, hysteretic over-temperature protection, frequency jittering, cycle-by-cycle current limit, loop compensation circuitry, auto- restart, switching on-time extension, power factor and constant current control. In a direct LED current sensing configuration, the average FEEDBACK pin voltage is a replica of the LED current, scaled by the sense resistor (R SENSE in Figure 4). A small low-pass filter (R F and CF in Figure 4) reduces high frequency noise at the FEEDBACK pin. Figure 5 illustrates the operating regions of the FEEDBACK pin voltage. The LinkSwitch-PL sets its operating point such that the average FEEDBACK pin voltage in steady-state operation is 290 mV. This threshold is set low to minimize the sensing resistor dissipation. The internal MOSFET switching frequency and on-time are updated once every input AC half-cycle to regulate the output current and maintain high power factor. If the FEEDBACK pin peak voltage exceeds 520 mV, cycle skipping mode is triggered and the power processed by the integrated power MOSFET is clamped on a cycle-by-cycle basis. Switching frequency may vary during an input voltage half-cycle to reduce thermal stress on the output LEDs. Figure 4. Typical Application Schematic. Figure 5. FEEDBACK Pin Operational Voltage Thresholds. Auto-restart protection is triggered by a FEEDBACK pin voltage in excess of 2 V. This feature can be used to provide output overvoltage protection (via DZ OV and ROV, in Figure 4), which triggers the IC to enter auto-restart. PI-5838-091010 Auto-Restart 2 V 520 mV Cycle Skipping Mode Normal Operation 290 mV D S BP CONTROL FB PI-5837-060710 LinkSwitch-PL AC IN CF RSENSE RF ROV DZOV RES DES |
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