| Critical-Conduction Mode PFC Controller IC |
Aimed at compact power supply units in digital consumer electronics products and elsewhere, the R2A20112 is the first device of its type to use interleave operation.
To save electrical power, power supplies increasingly are incorporating PFC (Power Factor Correction) circuits that control the AC input current waveform to have the same phase and sinusoidal shape as the AC input voltage. The Renesas R2A20112 PFC controller is ideal for this application. Intended for use in the power supply units in digital consumer electronics and other products where small size is a requirement, the new controller is the first in the industry to use interleave operation. It uses fewer external components and enables engineers to produce small, low-noise power supply units that have slim profiles and achieve high-efficiency.
|Helping to boost to the efficiency of AC-input power supplies by making it easier to incorporate PFC control|
The first stage of power supply units in line-powered electronic equipment consists of an AC/DC converter that converts the AC (alternating current) voltage to DC (direct current). Traditional designs use a simple choke-input rectification circuit to convert the voltage. The operation of that circuit causes a poor power factor because the AC input current waveform is non-sinusoidal and out of sync with the sinusoidal AC input voltage waveform. This results in the generation of waste power (voltage x current), causing heat.
Not only does equipment with a poor power factor waste energy, the distortion in the current waveform causes the AC power supply to vibrate, and that vibration can lead to faults or misoperation of other devices. The solution to these problems is a PFC (power-factor correction) circuit. It saves power by controlling the AC input current waveform so that it has the same phase and shape as the AC input voltage waveform.
Rules set by standards organizations such as the IEC (International Electrotechnical Commission) and JIS have been put into law, making it mandatory for equipment to include PFC control in their power supply circuits. However, implementing PFC control typically requires the use of external components such as coils and capacitors, as well as measures to deal with factors such as noise and heat. These factors cause problems in digital consumer electronics such as flat-panel TVs, where there is a very strong demand to make products smaller and, especially, thinner.
Renesas has previously introduced intelligent-type continuous current mode PFC control ICs: our HA16174 and R2A20111 devices. However, to meet the ever-growing market demand for features such as higher efficiency and smaller power supply circuit size, we have now released the R2A20112 PFC control IC, which enables good power factors, small size and improved efficiency. The main features of this device are shown below.
. Interleave operation that allows the use of smaller components — PFC controller ICs work by operating external switching MOSFETs connected across the AC inputs. The single-mode operation used in the past uses one signal to drive multiple external MOSFETs. This approach results in variations in the timing of MOSFET switching operations due to differences in wiring length, impedance, etc. By contrast the R2A20111 is the first critical-conduction mode PFC controller IC in the industry to use interleave operation. That is, it generates two control signals (master and slave) to reduce the timing variations. The slave control circuit we developed in-house for critical-conduction mode controls the variation in current with high accuracy. Also, a ZCS (Zero-Current Switching) function switches the external MOSFETs when there is no current is flowing in the step-up coil. These features allow the use of smaller components for the input filters, step-up coils, input and output capacitors, and similar circuit elements.
. Noise reduction measures for simpler system design — Because the ZCS function which performs switching when it detects that the current level is zero, less heat is generated in the switching MOSFETs. Two additional benefits of ZCS and interleave operation are minimizing unwanted current flows such as the recovery current in the step-up coil, and improving control of current flow, thereby reducing the ripple current and other noise on the power supply line. Thus, the power supply unit can use a simpler AC input line filter. Moreover, because a lower peak level of spurious radiation is produced, anti-noise measures such as shielding can be simplified, as well.
. Improved power supply conversion efficiency for less heat generation — The reductions in switching, recovery, conduction, and other losses achieved by the R2A20112 PFC control IC make its conversion efficiency 5 percent better than our previous HA16174 controller IC. The associated reduction in heat dissipation aids the design of power supply units that use of smaller, simpler heat sinks for the switching MOSFETs, or that don't require cooling fans. As with the previous HA16174 and R2A20111 devices, the R2A20112 IC is available in either a SOP-16 surface-mount package or a DILP-16 insertion-type package. Renesas plans to develop additional PFC controller ICs for different applications and output powers, including kW-class devices for use with high-power equipment and 50W-class devices for smaller equipment.