Power Supply Reference Design Trumpets Energy Efficiency

Power Supply Reference Design Trumpets Energy Efficiency
onsemi.com
Designed for 220W LCD-TV power supplies, the company's fourth GreenPoint reference design delivers standby power of less than 1W, addresses all functional blocks of the power supply, and meets international regulations for low standby power dissipation. To achieve this performance, the reference design utilizes several of the company's advanced power management devices and discrete components (see Key Components). A complete documentation package for the LCDTV power supply is available including description, schematic, bill-of-materials, Gerber images, and evaluation results on the company's web site, as are the product specifications and other supporting information.
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Architecture Overview
This supply uses active power factor correction in the front-end, which is implemented with the NCP1653, an 8-pin continuous conduction mode (CCM) PFC controller. This allows for system optimization, since the PFC output voltage is well regulated. And 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 385V.

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 controller and NCP5181 driver are used to implement the most effective control scheme for a half-bridge resonant LLC converter. For the standby output circuit, a higher integration level is made feasible by using the 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 the NCP1027 allows better regulation of the standby power supply.

During standby mode, both the PFC and the main PSU are shut off via the signal called SBE. Thus, only the 5V rail remains supplied and allows compliance with the international recommendations. In summary, the architecture selected for this reference design allows design optimization so that the desired performance is achieved without increasing component costs and circuit complexity.

More About GreenPoint
GreenPoint is ON Semiconductor's family of high-efficiency power supply reference designs that meet existing or emerging energy efficiency standards. GreenPoint reference designs are available for an ATX power supply, a CRT-TV power supply, an LCD-TV power supply and a notebook adapter. To acquire documentation packages for these designs, visit www.onsemi.com and run a keyword search on "GreenPoint."

Key Components

1. NCP1395 – A high performance resonant mode controller that offers everything needed to build a reliable and rugged power supply. Its architecture includes a 1.0 MHz voltage controlled oscillator and protections that feature various reaction times and contribute to a safer converter design, without additional circuit complexity. This device is offered in an SOIC-16 package priced at $1.38 each/2,500 and a PDIP-16 package, priced at $1.50 each/500.
2. NCP5181 – A high-voltage power MOSFET driver that provides two outputs to drive two N-channel MOSFETs. The device employs a bootstrap technique to ensure proper drive of the high-side power switch. This device is offered in an SOIC-8 package, priced at $1.60 each/2,500 and a PDIP-8 package, priced at $1.74 each/1,000.
3. NCP1653 – A compact power factor correction (PFC) controller that is well-suited for continuous conduction mode (CCM) PFC applications like those found in flat-screen televisions. This device reduces parts count and provides a robust, cost-effective front-end without range switches. It is offered in an SOIC-8 package, priced at $0.80 each/2,500 and a PDIP-8 package, priced at $0.88 each/1,000.
4. NCP1027 – A highly integrated switch mode power supply (SMPS) switcher. This device provides improved efficiency at light loads by entering a skip cycle when power demand is low. This device is offered in a PDIP-8 package, priced at $0.95 each/1,000.
5. TL431 – A programmable precision reference.
6. MBR10H100CT – 100V, 10A H-series SWITCHMODE power rectifier.
7. MBRS260 – 60V, 2A schottky power rectifier.
8. MMSZ7V5E – 225W, 7.5V energy rated zener.