TND321/D NCP1395 NCP1653 NCP5181 NCP1027 IEC1000-3-2 EN61000-3-2 EN61000-3-3

TND321/D TND321/D Rev. 0, March-07 220 W LCD TV Power Supply Reference Design Featuring NCP1395 NCP1395 and NCP1653 NCP1653 Documentation 1 © 2006 ON Semiconductor. Disclaimer: ON Semiconductor is providing this reference design documentation package "AS IS" and the recipient assumes all risk associated with the use and/or commercialization of this design package. No licenses to ON Semiconductor's or any third party's Intellectual Property is conveyed by the transfer of this documentation. This reference design documentation package is provided only to assist the customers in evaluation and feasibility assessment of the reference design. It is expected that users may make further refinements to meet specific performance goals 2 1 Overview . 4 2 Introduction . 5 3 LCD TV Power Supply Requirements . 6 4 Limitations of existing solutions. 8 5 Overcoming limitations with NCP1653 NCP1653 / NCP1395 NCP1395 + NCP5181 NCP5181 / NCP1027 NCP1027. 8 5.1 Architecture Overview. 8 5.2 Main power supply: NCP1395 NCP1395 + NCP5181 NCP5181 . 9 5.2.1 Half Bridge Resonant LLC topology . 9 5.2.2 Protection . 11 5.2.3 Half bridge driver: NCP5181 NCP5181 . 11 5.3 Standby Power Supply: NCP1027 NCP1027 . 12 5.4 Power Factor Correction: NCP1653 NCP1653 . 12 6 Specifications . 13 7 Reference Design Performance Summary . 14 7.1 Efficiency . 14 7.2 Standby Power . 14 7.3 Standards and Regulations . 15 8 Board Picture. 16 9 Schematic . 17 10 Board Layout. 18 11 BOM. 19 12 Appendix . 23 12.1 NCP1395 NCP1395 . 23 12.2 NCP5181 NCP5181 . 23 12.3 NCP1653 NCP1653 . 23 12.4 NCP1027 NCP1027 . 23 12.5 References . 23 3 1 Overview This reference document describes a built-and-tested, GreenPointTM solution for an LCD TV power supply. The reference design circuit consists of one single-sided 130 mm x 200 mm printed circuit board designed to fit into an LCD TV. Height is 25 mm. An overview of the entire circuit is provided by Figure 1. As shown in that figure, ON Semiconductor devices are available for every block of the LCD TV power supply; and by judicious choice of design tradeoffs, optimum performance is achieved at minimum cost. Figure 1 4 2 Introduction From Tubes to Flat TVs Since 1936 when the BBC begins the world's first public-television broadcast in London, the TV world made huge progress. A few examples: · 1953: color broadcasting · 1956: first VCR · 1962: first television satellite (Telstar) · 1981: NHK (Japan) demonstrates an HDTV system But "the idea of sitting in front of a box in your living room is becoming obsolete. For the TV industry, technology is creating vast opportunities". Newsweek, June 2005. Obviously Flat Panel Display (FPD) is one of the technologies that will drive these opportunities: · High Definition TV (HDTV): Most of the flat TVs on the market are ready to cope with a higher resolution (more lines are needed and a classical CRT TV can not handle it). More and more events will use this new standard. As an example the 2006 Football World Cup will be broadcast in HDTV. · Digital TV: The analog TV signal will be shut down soon in Europe, as it is replaced by Digital Terrestrial signal. Satellite and Cable Digital decoders are already very common. To get the best out of these digital signals, a high definition TV is definitively a plus. Digital TV will also allow CD-quality audio and six channels of surround sound. · Bigger screen, smaller form factor: Now that we all have seen these fancy screens, who is willing to go back to the old big bulky box? FPD includes both LCD (Crystal Liquid Display) and Plasma technologies. Despite the fact that classical CRT TV will remain the main stream in TV worldwide shipment, FDP is expected to expand at a rapid growth. The CRT market is shrinking very rapidly in Europe, Japan and US. 5 RPJ: Rear ProJection PDP: Plasma Display Panel LCD: Liquid Crystal Display CRT: Cathode Ray Tube 3 LCD TV Power Supply Requirements In large FPD (> 27"), the power supply is generally internal as it requires from 100 W to 600 W. A few voltages are needed to supply the various blocks: backlighting, audio, video, demodulation, etc. Because the input power is above 75 W, the application has to be compliant with the IEC1000-3-2 IEC1000-3-2 class D standard. Power Factor Correction is therefore needed. Since the main power supply has to be optimized for higher efficiency and slimmer form factor, an active PFC must be implemented to limit the variation of the input voltage in front of the main PSU. Most of the LCD TV power supplies are designed to cope with universal mains: 90 Vac to 265 Vac, 47-63 Hz. CCFL lamps (Cold Cathode Fluorescent) are mainly used for the backlighting. A 24 V rail is used to supply inverters that drive the lamps. A 5 V auxiliary power supply is needed to supply the microcontroller that must remain alive in standby mode. Some flat TVs may also already integrate a Digital Tuner that needs 30 V. 6 Having a low consumption in standby mode is also a key requirement. Recent studies and in situ measurement campaigns have indicated that in the average EU household, between 5% and 10% of its total yearly electricity consumption is due to the standby mode of consumer electronics equipment and other apparatus. TV sets are obviously one of the biggest contributors. In 1997, the European Commission concluded a negotiated agreement with individual consumer electronics manufacturers and the EU trade association EACEM, to reduce the stand-by losses of TVs and VCRs. In the year 2003 a new agreement for TVs and DVDs was concluded. Many initiatives have been taken around the word. Even if these requirements are not yet standards, most of the manufacturers have already applied these rules in their designs. Hereinafter the list of the most important initiatives: Region / Country China European Union European Union Europe Program name CECP Energy Saving EU EcoLabel EU Code of Conduct GEEA US Energy Star US 1 Watt Executive Order Korea Requirements for Televisions 3W Demoboard compliance Yes 3W Yes 1W 9 W with a STB Yes 3 W with a STB Yes 1W 1 W to 15 W New revision on going Yes 1W Yes 7 Yes 4 Limitations of existing solutions One of the key differentiating factors of a flat TV over a classical TV is the thickness of the cabinet - the thinner the better. But one must keep in mind: · The amount of power to be delivered is relatively large: the number of watts per cm3 is much larger compared to the one in a CRT TV. · Because the TV will be used in the living room, audible noise can be a problem, and the use of fans is limited. · Cost is key in the very competitive environment of the consumer electronics world. · The panel, the power supply and the audio card are close to each other; therefore EMI and pollution could severely alter the picture and sound quality. High efficiency and a low EMI signature at a reasonable cost are required, and classical topologies can hardly combine these needs: · Flyback: transformer usage is far from being optimal · Forward: the EMI signature is not reduced to its minimum 5 Overcoming limitations with NCP1653 NCP1653 / NCP1395 NCP1395 + NCP5181 NCP5181 / NCP1027 NCP1027 5.1 Architecture Overview First, the use of active power factor correction in the front-end allows system optimization because the PFC output voltage is well regulated. The implementation of the active PFC front end is made simpler by using the NCP1653 NCP1653, an 8-pin Continuous Conduction Mode (CCM) PFC controller. By choosing the CCM approach for PFC, the peak and rms currents are kept low and better efficiency is achieved in the PFC stage. The output of the PFC stage is set at 385 V. The SMPS stage uses a Half Bridge Resonant LLC topology. This topology offers a number of advantages as demonstrated in the schematics and the results. It improves efficiency, reduces EMI signature and provides better magnetic utilization. The NCP1395 NCP1395 controller and NCP5181 NCP5181 driver are used to implement the most effective control scheme of Half Bridge Resonant LLC converter. For the standby output circuit, a higher integration level is made feasible by using the NCP1027 NCP1027, a PWM regulator that also incorporates an appropriate switch to provide all functionality in one package. The use of the true current mode control technique in NCP1027 NCP1027 allows better regulation of the standby power supply. During the standby mode both the PFC and the main PSU are shut off via the signal so called "SBE". Thus, only the 5 V rail remains supplied and allows the compliance with the international recommendations. 8 In summary, the architecture selected for this reference design allows design optimization so that the desired performance is achieved without increasing the component costs and circuit complexity too much. The performance results section demonstrates the performance. 5.2 Main power supply: NCP1395 NCP1395 + NCP5181 NCP5181 5.2.1 Half Bridge Resonant LLC topology The Half Bridge Resonant LLC topology, that is a member of the Series Resonant Converters (SRC), begins to be widely used in consumer applications such as LCD TVs or plasma display panels. In these particular applications, the output power level ranges from 100 W up to 600 W. The Half Bridge Resonant LLC converter is an attractive alternative to the traditional Half Bridge (HB) topology for several reasons. Advantages include: · ZVS (Zero Voltage Switching) capability over the entire load range: Switching takes place under conditions of zero drain voltage. Turn-on losses are thus nearly zero and EMI signature is improved compared to the HB, which operates under hard-switching conditions. · Low turnoff current: Switches are turned off under low current conditions, and so the turn-off losses are also lowered compared to the HB topology. · Zero current turnoff of the secondary diodes: When the converter operates under full load, the output rectifiers are turned off under zerocurrent conditions, reducing the EMI signature. · No increased component count: The component count is virtually the same as the classical half bridge topology. Figure 2 is the structure of this resonant converter. A 50 % duty-cycle half-bridge delivers high-voltage square waves swinging from 0 to the input voltage VIN to a resonating circuit. By adjusting the frequency via a voltage-controlled oscillator (VCO), the feedback loop can adjust the output level depending on the power demand. 9 Vin Qb Vout 1 Cs N:1 Ls 6 5 7 Lm C Q RL 9 Figure 2 The resonating circuit is made of a capacitor, Cs, in series with two inductors, Ls and Lm. One of these inductors, Lm, represents the magnetizing inductor of the transformer and creates one resonating point together with Ls and Cs. The reflection of the load over this inductor will either make it disappear from the circuit (Lm is fully short-circuited by a reflected RL of low value at heavy load currents) or will make it stay in series with the series inductor Ls in light load conditions. As a result, depending on the loading conditions, the resonant frequency will move between a minimum and a maximum: The frequency of operation depends on the power demand. For a low power demand, the operating frequency is rather high, away from the resonating point. To the contrary, at high power, the control loop reduces the switching frequency and approaches one of the resonant frequencies to deliver the necessary amount of current to the load. This topology behaves like a frequency dependent divider. Figure 3: Substitutive schematic of the LLC resonant converter 10 Rac = 8 RL n 2 2 Where: RL is the real loading resistance n is the transformer turns ratio is the expected efficiency 5.2.2 Protection The NCP1395 NCP1395 differs from other resonant controllers thanks to its protection features. The device can react to various inputs like: · Fast events input: Like an over-current condition, a need to shutdown (sleep mode) or a way to force a controlled burst mode (skip cycle at low output power). · Slow events input: This input serves as a delayed shutdown, where an event like a transient overload does not immediately stop pulses but starts a timer. If the event duration lasts longer than what the timer imposes, then all pulses are disabled. 5.2.3 Half bridge driver: NCP5181 NCP5181 In a Half Bridge Resonant LLC the upper MOSFET is connected to the high voltage rail, therefore it can not be directly driven by the controller (NCP1395 NCP1395) that is referenced to the ground: a "level shifter" is needed. The NCP5181 NCP5181 performs this function as it is a High Voltage Power MOSFET Driver that provides two outputs to drive two N-channel power MOSFETs. The NCP5181 NCP5181 uses the bootstrap technique to ensure a proper drive of the high-side power switch. The driver works with two independent inputs to accommodate any topology (including half-bridge, asymmetrical half-bridge). Figure 4: NCP5181 NCP5181 11 5.3 Standby Power Supply: NCP1027 NCP1027 A NCP1027 NCP1027 is used for the auxiliary flyback power supply. This power supply provides a stable Vcc to supply the NCP1653 NCP1653, the NCP1395 NCP1395 and the NCP5181 NCP5181 under all operating conditions, but it also supplies 5 V to the devices that must remain alive in standby mode. NCP1027 NCP1027 characteristics: · Brown-out detection: The controller will not allow operation in low mains conditions. You can adjust the level at which the circuit starts or stops operation. · Ramp compensation: Designing in Continuous Conduction Mode helps to reduce conduction losses. However, at low input voltage (85 Vac), the duty-cycle might exceed 50% and the risk exists to enter a subharmonic mode. A simple resistor to ground injects the right compensation level. · Over power protection: A resistive network to the bulk reduces the peak current capability and accordingly harnesses the maximum power at high line. As this is done independently from the auxiliary Vcc, the design gains in simplicity and execution speed. · Latch-off input: Some PC manufacturers require a complete latch-off in the presence of an external event, e.g., over temperature. The controller offers this possibility via a dedicated input. · Frequency dithering: The switching frequency (here 65 kHz) is modulated during operation. This naturally spreads the harmonic content and reduces the peak value when analyzing the signature. 5.4 Power Factor Correction: NCP1653 NCP1653 The NCP1653 NCP1653 is a controller for Continuous Conduction Mode (CCM) Power Factor Correction step-up pre-converters. It controls the power switch conduction time (PWM) in a fixed frequency mode and in dependence on the instantaneous coil current. Housed in a DIP-8 or SO-8 package, the circuit minimizes the number of external components and drastically simplifies the PFC implementation. The NCP1653 NCP1653 is an ideal candidate in systems where cost-effectiveness, reliability and high power factor are the key parameters. It incorporates all the necessary features to build a compact and rugged PFC stage. More specifically, the following protections make the PFC stage extremely robust and reliable: · Maximum current limit: The circuit immediately turns off the MOSFET if the coil current exceeds the maximum permissible level. The NCP1653 NCP1653 also prevents any turn on of the power switch as long as the coil current is not below this limit. This feature protects the PFC stage during the startup phase when large in-rush currents charge the output capacitor. · Undervoltage protection/shutdown: The circuit stays in shutdown mode as long as the feedback current indicates that the output voltage is lower than 8% of its regulation level. In this case, the NCP1653 NCP1653 consumption is 12 · very low (