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greenPOWERZONE Products for the week of March 21, 2005
International Rectifier's µPF IC Adds
Power Factor Correction To High Density Designs from 75 W to 4 kW
New compact power factor correction IC cuts control board
size in half
International Rectifier has introduced its IR1150 family of µPFC for AC-DC power factor correction (PFC) circuits. The compact SO-8-packaged device cuts PFC control board space in half, and enables a simplified and flexible high density solution for computing, consumer electronics and home appliances from 75W to 4kW.
IR's new One Cycle Control (OCC) approach in the IR1150 delivers the performance of continuous conduction mode (CCM) PFC with the simplicity, reliability and low component count of a discontinuous current mode (DCM) circuit for PFC applications.
Power factor (PF) is the relationship between AC voltage and current waveforms and is a measure of "power quality" that affects the efficiency of electrical transmission networks. With unity PF as the ultimate goal, the IR1150 enables 0.999 PF with only 4% total harmonic distortion, enabling AC-DC applications to conform to international legislative requirements.
"High performance, high power density solutions in AC-DC SMPS circuits are needed for the 'Digital Future' in home, commerce and industry. The patented one-cycle control technique radically alters traditional thinking about PFC solutions. It's a form of CCM PFC using a new 'integrator with reset' control block. This simplifies and reduces the size and component count for the PFC control circuit, making it a smart solution for a global range of computing, home entertainment and many other products," said Stephen Oliver, Marketing Manager for AC-DC Products at International Rectifier.
Technical Highlights
The One Cycle Control method used in the IR1150 controller does not have
an analog multiplier, input voltage sensing, or fixed oscillator ramp, simplifying
circuitry and reducing component count. Instead, IR's OCC uses a proprietary
integrator with a reset circuit: The output of the error amplifier is integrated
over each clock cycle to generate a variable-slope ramp. This variable ramp
is compared with the error voltage and subtracted from the current sense
signal to generate the PWM gate drive.
Traditionally, Continuous Conduction Mode PFC offers high performance for high power applications above 250W. However, solutions using multiplier techniques are complex and require many design stages and a high component count, making CCM solutions very expensive and not appropriate for low power, price sensitive applications like laptop power adapters.
In low power applications from 75W to 250W, Discontinuous Current Mode systems are used for their simplicity and low system cost. However, as system power increases to 100W and above, DCM systems can be very large (low power density) due to high peak currents and EMI filter requirements.
For example, in a typical high power system such as a 1kW server SMPS, IR's µPFC solution has 40% fewer resistors and capacitors, halves the number of current transformers used and saves 50% of the PFC control PCB area compared to traditional multiplier-based CCM systems. In lower power applications where power density is critical, such as high power laptop and LCD TV adapters, an IR1150 controller in CCM mode means reduced peak currents and a 43% reduction in EMI filter needs. This translates into a 16% reduction in PCB space and an increase in power density of 10% for a 120W system.
In addition, a dedicated Over Voltage Protection pin offers greater protection for high power systems and the IC includes features such as enable- and micro-power start-up and "sleep mode" for compliance with energy efficiency standards such as 1W standby, Blue Angel and Energy Star.
The IR1150 is an elegant solution to PFC legislation such as IEC 1000-3-2
in Europe, JIC C 61000-3-2 in Japan and the China Compulsory Certificate
(CCC) for products using more than 75W. As manufacturers implement PFC in
response to these energy standards, the IR1150 control IC simplifies effective
PFC solutions, and enables a single design that can be used worldwide.
analogZONE Says...
It's great to see IRF producing devices that will green up both the environment, and their customer's bottom lines by making power factor correction (PFC) easy and inexpensive to implement in nearly any power supply of 75 W or more. PFC is becoming a hot business issue because there's a growing list of countries (around half of the world, including China, Japan, and Europe) who require PFC in supplies of 75 W or more. That's why IRF's recent introduction of simple, cost-effective PFC solutions for switching power supplies makes both environmental and economic sense.
For those not familiar with PFC issues, it's important to understand that while modern switching supplies are very efficient, they tend to draw their power across a small "spike" within the 50/60 Hz input waveform, creating the equivalent of a complex load on the power line. Unless somehow corrected this additional power factor wreaks havoc with generating plants making them burn more fuel to provide the same number of kW.
Until now, supplies under 250 W tend to use a simpler discontinuous current mode (DCM) solution because they require fewer components and are less expensive than their continuous conduction mode (CCM) counterparts. Unfortunately, DCM designs don't "smooth out" the supply's complex load as effectively as supplies using CCM. And DCM's troubles are compounded as their size increases because their filter components tend to grow rather large in supplies of 150 W or more. DCM's drawbacks are why continuous conduction mode (CCM) supplies are traditional solution for high-power supplies, where the circuit where the supply is forced to draw its energy across the entire cycle using a high-frequency switching rate.
IRF's new IR1150S series makes the design and manufacture of these more sophisticated supplies much less difficult and expensive, and offers several new twists to CCM design. Traditional CCM techniques employ ac line sensing and a multiplier to drive a PFC switch which does the actual conducting. These designs take several cycles to average and generate a correction signal. In contrast, the 1105S corrects PF in a single cycle, something that I believe accounts for its excellent power factor and THD specs (0.999 and 4%, respectively).
The device's innovative design also eliminates lossy ac line sensing, and allows it to use just one current sense transformer for peak power control. Designers will appreciate the device's high (1.5 A) gate drive, and auto re-start function that allows automatic power-up when a fault is cleared. The selectable frequency range (50 to 200 kHz) allows more flexibility in selecting your switch FET. The higher level of integration also simplifies your design process, requiring only 6 design steps (vs 11 for traditional designs), and cuts external components from 31 to 8.
The cost, space, and time-to-market savings offered by the IR1150S are hard to argue with, something that should help it find applications in both consumer and business products of all kinds. Thanks to their 4 kW upper power range and industrial temperature ratings, the "IS" series should also win many homes in higher-powered industrial designs, as well as some of the larger routers, switches, and other carrier-class equipment.
The IR1150S and IR1150IS (industrial range) are both in production inSO-8 and available in Pb-free packaging with the former priced at $1.05 and the latter at $1.38, both in 10-k piece lots.
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