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Introduction of the basic operations of the L6561 power factor corrector and its applications

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- 1. <ul><li>Source: STMicroelectronics </li></ul>L6561 Power Factor Corrector
- 2. Introduction <ul><li>Purpose </li></ul><ul><ul><li>This training module introduces the basic operations of the L6561 power factor corrector and its applications. </li></ul></ul><ul><li>Outline </li></ul><ul><ul><li>Overview of the L6561 </li></ul></ul><ul><ul><li>Block Diagram </li></ul></ul><ul><ul><li>Basic operations </li></ul></ul><ul><ul><li>Typical application circuits </li></ul></ul><ul><li>Content </li></ul><ul><ul><li>16 pages </li></ul></ul>
- 3. Overview <ul><li>L6561 is the improved version of the L6560 standard Power Factor Corrector. </li></ul><ul><li>It has a superior performant multiplier making the device capable of working in wide input voltage range applications (from 85V to 265V) with an excellent THD. </li></ul><ul><li>Micro power start up current. </li></ul><ul><li>Soft Output Over Voltage Protection. </li></ul><ul><li>No need for external low pass filter on the current sense. </li></ul><ul><li>very low operating quiescent current minimises power dissipation. </li></ul><ul><li>The start up current has been reduced at few tens of mA and a disable function has been implemented on the ZCD pin, guaranteeing lower current consumption in stand by mode. </li></ul>
- 4. Key Features <ul><li>Very precise adjustable output overvoltage protection. </li></ul><ul><li>Micro power start-up current (50μa typ.). </li></ul><ul><li>Very low operating supply current(4ma typ.). </li></ul><ul><li>Internal start-up timer. </li></ul><ul><li>Current sense filter on chip. </li></ul><ul><li>Disable function. </li></ul><ul><li>1% precision (@ tj = 25°c) internal reference voltage. </li></ul><ul><li>Transition mode operation. </li></ul><ul><li>Totem pole output current: ±400ma. </li></ul><ul><li>Dip-8/so-8 packages. </li></ul>
- 5. Block Diagram <ul><li>The totem pole output stage is capable of driving </li></ul><ul><li>a Power MOS or IGBT with source and sink currents </li></ul><ul><li>of ±400mA. </li></ul><ul><li>The device is operating in transition mode and it is optimised for Electronic Lamp Ballast application, AC-DC adaptors and SMPS. </li></ul><ul><li>The DC output voltage to be higher than the maximum expected line peak voltage. </li></ul>
- 6. Error Amplifier & Overvoltage Detector Block
- 7. Zero Current Detection, Triggering & Disable Block <ul><li>The Zero Current Detection (ZCD) block switches on the external MOSFET as the voltage across the boost inductor reverses, just after the current through the boost inductor has gone to zero. </li></ul>
- 8. Multiplier Block <ul><li>The multiplier has two inputs: </li></ul><ul><ul><li>The first one takes a partition of the instantaneous rectified line voltage </li></ul></ul><ul><ul><li>The second one is the output of the E/A. </li></ul></ul><ul><li>If this voltage is constant (over a given line half-cycle) the output of the multiplier will be shaped as a rectified sinusoid. </li></ul><ul><li>It is used as the reference signal for the current comparator. </li></ul>
- 9. Current Comparator and PWM Latch <ul><li>The current comparator senses the voltage across the current sense resistor (Rs) and </li></ul><ul><li>It determines the exact time when the external MOSFET is to be switched off. </li></ul><ul><li>The PWM latch avoids spurious switching's of the MOSFET which might result from the noise generated. </li></ul>
- 10. Output Driver <ul><li>A totem pole buffer, with 400mA source and sink capability, allows driving an external MOSFET. </li></ul><ul><li>An internal pull-down circuit holds the output low when the device is in UVLO conditions, to ensure that the external MOSFET cannot be turned on accidentally. </li></ul>
- 11. Transition Mode PFC Operation (Boost Topology) <ul><li>The AC mains voltage is rectified by a diode bridge and the rectified voltage delivered to the boost converter. </li></ul><ul><li>Using a switching technique, boosts the rectified input voltage to a regulated DC output voltage (Vo). </li></ul><ul><li>The boost converter consists of a boost inductor (L), a controlled power switch (Q), a catch diode (D), an output capacitor (Co) and, a control circuitry. </li></ul><ul><li>The goal is to shape the input current in a sinusoidal fashion, in-phase with the input sinusoidal voltage. To do this the L6561 uses Transition Mode technique. </li></ul>
- 12. The Control Loop Of the L6561 <ul><li>The control loop will have quite a narrow bandwidth so as to maintain VCOMP fairly constant over a given line cycle. </li></ul><ul><li>It is not possible to achieve a very high PF (>0.99), thus it makes no sense to have a very narrow bandwidth (<20 Hz) like in boost PFC pre-regulators. </li></ul>
- 13. THD Corrector: Block Diagram The Total Harmonic Distortion (THD) of the line current is defined in percentage as:
- 14. Typical Application Circuit (80W, 110VAC)
- 15. Lighting Application with PFC
- 16. Additional Resource <ul><li>For ordering the L6561 PFC, please click the part list or </li></ul><ul><li>Call our sales hotline </li></ul><ul><li>For additional inquires contact our technical service hotline </li></ul><ul><li>For more product information go to </li></ul><ul><ul><li>http://www.st.com/stonline/products/support/smps/tools/tutorial/pfcintro.htm </li></ul></ul>Newark Farnell

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