AC-to-DC Switching Power Supplies

“Engineers designing power supply adaptors must adhere to a number of energy-efficiency standards such as Energy2000, Blue Angel, and the EU Code of Conduct,” says CJ Kim, Fairchild Semiconductor’s Power Supply product line manager. In addition, new requirements for efficiency are being defined all the time. For example, the 80 PLUS performance specification requires power supplies in computers and servers to be 80 percent or greater energy efficient at 20, 50 and 100 percent of rated load with a true power factor of 0.9 or greater. As a result, an 80 PLUS certified power supply is substantially more efficient than current power supplies. This creates a market differentiation for power supply and computer manufacturers that meet the certification. Meeting this or other certifications could a garner power supply manufacturer a greater share of the ac-to-dc-power supply market forecast by Mohan Mankikar, president, Micro-Tech Consultants:

Today’s highly efficient switch-mode power supply (SMPS) designs require advanced semiconductor technology including integrated circuits (ICs) performing functions such as high-voltage resonant controller and power factor correction (PFC) control and FETs operating in the synchronous rectification mode.

POWER FACTOR CORRECTION

For SMPS designs under 250W that must meet the most stringent efficiency standards, Fairchild Semiconductor’s FAN7528 is an active PFC controller for boost PFC applications that operate in the critical conduction mode (CRM). The design uses the voltage mode PWM that compares an internal ramp signal with the error amplifier output to generate the MOSFET turn-off signal. The IC integrates a dual-output control function to increase efficiency and reduce standby power as much as 320 mW. By automatically sensing ac line voltage through the dual-output control function, the FAN7528 eliminates an input voltage-sensing network and requires only 80 mW. The IC has a low start-up current (typical 40 µA), low operating current (typical 2.5 mA), and provides 400 mA peak gate drive current. Additional features of the IC include an open-feedback disable function (65 µA) that provides system protection against power surges and a variable on-time control method that reduces total harmonic distortion (THD) and also increases power efficiency. Get more information on Fairchild Semiconductor FAN7528 PFC controller.

HIGH-VOLTAGE, RESONANT CONTROLLER

STMicroelectronics (STM) designed the L6599 high-voltage resonant controller for the series-resonant half-bridge SMPS topology. Capable of operating up to 500 kHz, the L6599 provides the 0.6A source and 1.2A sink (typical peak current) capability for both gate drivers in the half-bridge topology. Additional features in the IC that simplify and provide additional features for a SMPS design include a dedicated output for direct power factor corrector (PFC) connection, two-level over-current protection (OCP), latched disable input, burst-mode operation at light-load, and an input for power-on/off sequencing or brownout protection. The controller allows power-factor-corrected systems to meet energy-saving requirements. The IC has a dedicated output that switches off the PFC’s pre-regulator during burst-mode operation, eliminating the no-load consumption of this stage. The IC targets applications such as Liquid Crystal Display (LCD) and Plasma Display Panel (PDP) TVs, high-end ac-to-dc adapters for laptops and game consoles, 80 Plus initiative-compliant ATX silver boxes, servers, and telecom SMPS. Get more information on STMicroelectronics L6599 high-voltage resonant controller.

SYNCHRONOUS RECTIFICATION MOSFETS

In computers, increased data processing capability also means increased power supply challenges. International Rectifier designed a new and expanded range of 60V and 75V MOSFETs for ac-to-dc synchronous rectification applications in these supplies. The IRFB/S/SL3206, 3306, 3207Z and 3307Z families of MOSFETs improve power density by lowering R_DS(on) up to 10 percent compared to the previous industry standards. For the 75V devices, maximum R_DS(on) ranges from 4.1 mÙ to 5.8 mÙ, and for the 60V devices, from 3.0 mÙ to 4.2 mÙ. Available in TO-220, D2Pak, and TO-262 packages all units are qualified to industrial grade and moisture sensitivity level 1 (MSL1).

The MOSFETs target ac-to-dc synchronous rectification in servers, laptop adaptors and desktop power supplies, as well as usage in dc-to-dc converters and low-voltage motor drives. For more information on the International Rectifier IRFB/S/SL3207ZPbF.