Power Quality

Evaluation Kit High-Performance Digital PFC + LLC Combo Controller

The EVKT-1200 from Monolithic Power Systems, Inc. is an evaluation kit for the HR1200. A 240W evaluation board is designed with high power factor (PF) at light load (>0.95 at 20% load). The particular benefits for the board are the very low no-load power consumption (<150mW) and very high light-load efficiency (>90% at 10% load), which meets Energy using Product Directive (EuP) Lot 6 and Code of Conduct Version 5 Tier 2.

These features are suitable for applications such as PC, ATX power, notebook adapter, gaming and TV power supplies. With the programming dongle and GUI software, circuit configurations of the digital PFC part can be easily customized which greatly increases design flexibility.

The HR1200 is a high-performance controller that integrates an advanced digital PFC controller and a half-bridge LLC resonant controller. It requires quite low input power at no load or ultra-light load, making it compliant with Energy using Product Directive (EuP) Lot 6 and Code of Conduct Version 5 Tier 2 specifications.

The PFC of the HR1200 employs a patented average current control scheme, which can operate both in continuous conduction mode (CCM) and discontinuous conduction mode (DCM) according to the instantaneous condition of the input voltage and output load. The IC exhibits excellent efficiency and high power factor (PF) at light load.

In CCM, the HR1200 can be used in applications up to 500W with minimal board size limitations. The performance of the PFC can be optimized by programming multiple parameters through an I2C GUI. Programming can be completed either by the factory or by the customer referring to a detailed user guide.

(click on schematic to enlarge)

The half-bridge LLC resonant converter achieves high efficiency with zero-voltage switching (ZVS). The HR1200 implements an adaptive dead-time adjustment (ADTA) function to guarantee ZVS in different load conditions. Additionally, the HR1200 can prevent the LLC converter from operating in capacitive mode, making it more robust and easier to design.

The HR1200 integrates a high-voltage (HV) current source internally for start-up. When the AC input is removed, the HV current source also functions as an X-cap discharger. Such features are helpful to reduce related devices, thus reduce power consumption at no load.

The HR1200 has multiple protection features including thermal shutdown (TSD), open-loop protection (OLP), over-current protection (OCP), over-voltage protection (OVP), and brown-in/brown-out protection.

Gate Driver

This evaluation kit also uses the MP6922, a dual fast turn-off intelligent controller to drive two N-channel power MOSFETs in LLC resonant converters for synchronous rectification. The IC regulates the forward voltage drop of the power switch to about 70mV and turns it off before the voltage goes negative.

MP6922 has a light-load function to latch-off the gate driver at light load condition, during which only about 600µA quiescent current is consumed. The fast turn-off speed of MP6922 makes both CCM and DCM driving available.

An internal Reverse Current Protection (RCP) function ensures safe operation of the MOSFETs in high frequency CCM condition. MP6922 requires a minimum number of readily available standard external components and is available in SOIC8E, SOIC8 or SOIC14 package.

Monolithic Power Systems Inc.
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