Part # Application Notes Display Monitor Imaging datasheet

Part Manufacturer: ST Microelectronics

ST Microelectronics

Part Description: Using the STVM100 to fully auto adjust LCD flicker


Part Details:

AN2644 Application note An introduction to LLC resonant half-bridge converter Introduction Although in existence for many years, only recently has the LLC resonant converter, in particular in its half-bridge implementation, gained in the popularity it certainly deserves. In many applications, such as flat panel TVs, 85+ ATX PCs or small form factor PCs, where the requirements on efficiency and power density of their SMPS are getting tougher and tougher, the LLC resonant half-bridge with its many benefits and very few drawbacks is an excellent solution. One of the major difficulties that engineers are facing with this topology is the lack of information concerning the way it operates. The purpose of this application note is to provide insight into the topology and help familiarize the reader with it, therefore, the approach is essentially descriptive. Figure 1. LLC resonant topology schematics and waveforms May 2008 Rev 1 1/61 www.st.com Contents AN2644 Contents 1 Classification of resonant converters . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2 The LLC resonant half-bridge converter . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1 General overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.2 The switching mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 2.3 Fundamental operating modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 2.3.1 Operation at resonance (f = fR1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.3.2 Operation above resonance (f > fR1) . . . . . . . . . . . . . . . . . . . . . . . . . . . 24CCMA operation at heavy load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25 Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 DCMA at medium load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28 Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 DCMAB at light load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29 Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 2.3.3 Operation below resonance (fR2 < f < fR1, R>Rcrit) . . . . . . . . . . . . . . . . 30DCMAB at medium-light load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30 DCMB at heavy load. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30 Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 2.3.4 Capacitive-mode operation below resonance (fR2 < f < fR1, R<Rcrit) . . . 34Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 2.4 No-load operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2.5 Overload and short circuit operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2.6 Converter s startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 2.7 Analysis of power losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 2.8 Small-signal behavior . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 2.8.1 Operation above resonance (f > fR1) . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 2.8.2 Operation below resonance (fR2 < f < fR1, R>Rcrit) . . . . . . . . . . . . . . . . 44


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