Renesas Unveils First Critical-Conduction-Mode PFC Control IC

Renesas Technology America, Inc. announced the R2A20112 critical-mode(1) power factor correction (PFC)(2) control IC for AC/DC power supplies, the first device of its type to implement interleaved operation(3). The new device enables the design of small, thin, low-noise, high-efficiency AC/DC power supplies that are essential for flat-panel TVs, game machines, PCs, copiers, and many other consumer and office automation products.

Better power supply solutions will make possible key end-product features In years past, AC/DC power supplies typically used simple choke input(4) rectification or similar voltage conversion techniques that suffer power losses due to waveform mismatches and timing variations between the voltage and current waveforms. More recently, regulations have come into effect mandating that various kinds of devices incorporate a PFC controller, such as Renesas’ previously released HA16174 and R2A20111 intelligent-type continuous-current-conduction-mode PFC control ICs. While these ICs suffice for many applications, today’s digital home appliances such as flat-panel TVs require smaller, slim and quiet power supplies with higher efficiency. Thus, there is a need for a better PFC control solution: a device that can shrink the size of the power supply and reduce the amount of heat dissipated to a level low enough to eliminate the requirement for a noisy cooling fan.

The R2A20112 critical-conduction-mode PFC control IC meets these power supply design needs in three ways. First, it uses two signals (master and slave) for control, allowing critical mode PFC control with interleaved operation that reduces variations in operating timing. The slave control circuit allows highly precise current distribution, making it possible to reduce the size of components such as the input filter, step-up coil, and input/output capacitors.

Second, the device uses various techniques that enable system simplification. For example, a ZCS (zero-current switching)(5) function causes the power MOSFET to switch at the exact instant at which no current is flowing. This reduces the device’s heat emission and allows a smaller, less complex heat sink. Also, the combination of ZCS and interleaved operation prevents the flow of redundant currents such as step-up-diode recovery current. It also controls the flow of appropriate currents and reduces the power supply line noise and ripple current. These benefits combine to decrease the peak level of radiation noise in the power supply, allowing simplifications of the noise shielding and AC input filter.

Third, the power conversion efficiency of the R2A20112 IC is better by 5% or more compared with Renesas’ previous products, due to reductions in switching loss, recovery loss, and conduction loss. As a result, heat sinks can be even smaller and the overall dissipation of the power supply can be reduced enough to make a cooling fan unnecessary.

Renesas Technology is developing additional standard product and application-specific PFC control ICs, aiming to provide a lineup that extends from 50W products for low-power requirements to kilowatt-class products for high-power applications.

Price and availability
R2A20112SP – SOP-16 – $1.0/Q1 2007
R2A20112DD – DILP-16 – $1.0/Q1 2007

About Renesas Technology Corp.
Renesas Technology Corp. is one of the world’s leading semiconductor system solutions providers for mobile, automotive and PC/AV (Audio Visual) markets and the world’s No.1 supplier of microcontrollers. It is also a leading provider of LCD Driver ICs, Smart Card microcontrollers, RF-ICs, High Power Amplifiers, Mixed Signal ICs, System-on-Chip (SoC), System-in-Package (SiP) and more. Established in 2003 as a joint venture between Hitachi, Ltd. (TOKYO:6501)(NYSE:HIT) and Mitsubishi Electric Corporation (TOKYO:6503), Renesas Technology achieved consolidated revenue of 906 billion JPY in FY2005 (end of March 2006). Renesas Technology is based in Tokyo, Japan and has a global network of manufacturing, design and sales operations in around 20 countries with about 26,200 employees worldwide.

A specification summary is included in this release, and a photo of the R2A20112 critical-mode PFC control IC is available.

1. Critical-conduction mode: A mode in which an external power MOSFET is switched after detection of a zero step-up coil current.
2. Power factor correction (PFC): In an alternating current, the voltage and current constantly switch back and forth between positive and negative, and there may be a time lag (phase lag) between the voltage waveform and current waveform. With a simple choke (inductor) input method, the current waveform is not a sine wave, but has a pulse form, and the occurrence of ineffective power at this time needs to be corrected. Power factor correction is a means of regulating a higher harmonic wave (a sine wave that is an integral multiple of the 50Hz or 60Hz of a commercial power supply) stipulated by the IEC and JIS standards.
3. Interleaved operation: A method whereby a number of switching elements (MOSFETs) are operated alternately. While single switching performed by one control signal is normally used, interleaved operation provides for the use of a separate complementary switching line between switching operations.
4. Choke input: A type of smoothing circuit that smoothes a waveform rectified by a rectification circuit. At a particular load-current, the voltage fluctuation rate is good. Choke-input circuits are quite heavy, though.
5. ZCS (zero current switching): A method whereby the line current value of a switching MOSFET is monitored, and switching is performed after the current value becomes zero.