L6564TD is a power factor correction controller from STMicroelectronics designed for boost-type PFC stages in offline AC-DC power supplies. It operates the power stage in transition mode, also known as critical conduction mode, to improve input current shaping and power factor.
The device is intended for applications where the AC input current needs to follow the input voltage waveform more closely. It can be used as the PFC control stage ahead of a downstream DC-DC converter or isolated power converter.
L6564TD is designed for transition-mode PFC operation and uses a current-sensing feedback architecture to control the external boost power stage.
The controller incorporates functions required for a practical PFC circuit, including multiplier circuitry, current sensing, output-voltage feedback and protections.
It operates with an external power MOSFET and boost inductor rather than integrating the high-power switching components directly into the IC.
The device is supplied in a compact surface-mount package and is suitable for applications where board space and power-conversion efficiency are important.
Transition-mode PFC operates differently from conventional fixed-frequency continuous-conduction PFC.
The boost converter is controlled so that the MOSFET turns on at the appropriate point after the inductor current has fallen back toward zero.
This allows the controller to operate the boost stage near the boundary between continuous and discontinuous conduction.
The approach can provide good power-factor performance while reducing some of the switching losses associated with hard-switching operation.
It is particularly suitable for low-to-medium power AC-DC applications.
The purpose of the PFC stage is to improve the relationship between the current drawn from the AC mains and the input voltage.
Without appropriate power-factor correction, many switching power supplies draw current in narrow pulses. This can increase harmonic distortion and reduce the effective utilization of the AC input.
L6564TD controls an external boost converter so that the input current more closely follows the instantaneous input voltage.
This produces a more sinusoidal input current and can significantly improve the power factor of the overall power supply.
A typical L6564TD circuit uses a boost inductor, diode, MOSFET and output capacitor together with the controller.
The AC input is first rectified to create a high-voltage DC waveform. The boost stage then raises and regulates this voltage to the required PFC bus level.
L6564TD controls the external MOSFET according to the feedback signals from the PFC stage.
The resulting DC bus can then supply a second converter stage responsible for generating the isolated or regulated output voltage.
L6564TD can be used in AC-DC power supplies and other offline power-conversion equipment.
Typical applications include power adapters, industrial power supplies, lighting power supplies, consumer electronics and other equipment requiring active power-factor correction.
The controller is particularly relevant to designs where transition-mode operation provides an appropriate balance between circuit complexity, efficiency and power level.
The actual suitability depends on the required input power, switching frequency, thermal design and regulatory requirements of the final product.
Current sensing is an important part of the L6564TD control system.
The controller monitors the current flowing through the boost power stage and uses this information to control the MOSFET switching cycle.
Accurate current sensing helps establish the correct input-current waveform and provides protection against excessive current.
The current-sense resistor and associated PCB traces therefore need to be designed carefully. Excessive parasitic resistance or inductance can influence the sensed signal and affect overall PFC performance.
L6564TD also monitors the PFC output voltage through a feedback network.
The feedback circuit allows the controller to regulate the high-voltage DC bus produced by the boost converter.
The resistor divider connected to the feedback input must be selected according to the required output voltage and the controller's feedback characteristics.
Because the PFC bus can operate at several hundred volts in typical offline applications, appropriate resistor voltage ratings, creepage distances and PCB clearances are important.
A PFC controller needs to respond safely to abnormal operating conditions.
L6564TD incorporates protection functions intended to help manage conditions such as excessive current and abnormal feedback conditions.
Protection functions should not be treated as a replacement for proper power-stage design. The external MOSFET, boost diode, inductor and sensing components must all be selected according to the expected voltage, current and transient conditions.
Proper startup and shutdown behavior should also be evaluated when the controller is used in an offline power supply.
L6564TD is available in a surface-mount package suitable for compact power-supply PCB layouts.
The package allows the controller to be positioned close to the current-sense and gate-drive circuitry while remaining physically separated from high-voltage power components.
When laying out the PCB, designers should maintain appropriate separation between the controller's low-voltage control circuitry and the high-voltage switching node.
Short gate-drive and current-sense connections can also help reduce noise and improve switching behavior.
When replacing L6564TD, engineers should first verify that the replacement supports transition-mode PFC.
A PFC controller designed for continuous-conduction operation is not automatically a suitable replacement even if it provides similar input-voltage and output-voltage functions.
Other important parameters include supply voltage range, current-sense characteristics, gate-drive capability, feedback architecture, protection functions and package.
The external boost stage should also be checked because changing the controller can affect switching frequency, inductor selection and overall PFC behavior.
L6564TD is particularly useful as the front-end controller in two-stage AC-DC power supplies.
In a typical architecture, the first stage performs rectification and active power-factor correction. The resulting high-voltage DC bus then feeds an isolated DC-DC converter.
This architecture allows the PFC stage and output-regulation stage to be optimized independently.
The PFC controller therefore plays an important role in improving input-side performance while the downstream converter handles output isolation and voltage regulation.
Designing a power supply around L6564TD requires careful attention to the boost inductor, MOSFET, diode, current-sense resistor and output capacitor.
The switching node should be kept compact to minimize parasitic inductance and electromagnetic interference.
The high-voltage feedback network also requires appropriate resistor voltage ratings and PCB creepage distances.
Thermal performance should be evaluated under the highest expected input power and worst-case ambient temperature.
L6564TD provides a dedicated transition-mode PFC control solution for AC-DC power supplies.
Its external boost architecture allows designers to select the power MOSFET, diode, inductor and other components according to the required power level and operating conditions.
For replacement applications, the exact controller topology and pin configuration should be matched carefully. For new designs, engineers should evaluate power level, efficiency, input-current requirements, protection functions and thermal performance together before selecting the PFC controller.
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