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Power controller device cuts wasted power

Posted: 05 May 2011 ?? ?Print Version ?Bookmark and Share

Keywords:Power controller? zero wasted power? chargers? adapters?

iWatt Inc., a developer of energy-efficient digital power supply control integrated circuits (ICs), launched the iW1700 Zero Power AC/DC Digital PWM Controller. The controller is designed to enable low-cost, energy-efficient 120V/230VAC offline adapters and chargers (up to 5W), which consume zero no-load power for cell phones, audio players, digital cameras, and other low-power portable devices.

iWatt's patented adaptive digital PWM/PFM technology sends the controller into sleep mode when the load is disconnected, cutting no-load power consumption to less than 4mW, or effectively zero. The IEC 62301 standard for measuring standby power in household electrical appliances has power usage of 5 mW or less to zero.

Enabled by digital techniques, the iW1700 features primary-side control to eliminate an opto-coupler, quasi-resonant switching for low EMI, cycle-by-cycle waveform analysis, and a high (up to 72 kHz) switching frequency to achieve no-load charger performance, meet manufacturers' power-supply requirements, and still enable a low bill-of-material (BOM) cost.

No-load (or standby) power is the energy used by "vampire" chargers left plugged into outlets after their end devices are disconnected or "vampire" electrical appliances that are supposedly turned off. Standby power from such "energy vampire" devices consumes more than 100 billion kilowatt hours of annual U.S. electricity amounting to more than $10 billion in annual energy costs according to Energy Star.

This wasted energy is said to be enough to power 9.4 million U.S. households which consume, on average, 10,656 kilowatt hours per household per year. To keep vampire chargers from wasting energy, users must either unplug their chargers, or press a relay switch that comes on very few mobile chargers. Neither measure has caught on.

The iW1700 seamlessly eliminates no-load power waste without a relay switch or microcontroller using iWatt's proprietary digital algorithms to switch between PWM and PFM modes multiple times as the end device charges. This approach eliminates audible noise, improves efficiency, and reduces switching losses by operating at a pre-determined minimum frequency at no-load. When the load is disconnected, the controller enters sleep mode and turns off non-essential circuits.

The device also includes an active start-up function which disconnects the start-up resistor after the IC powers up. This eliminates the standby power the resistor normally wastes, and allows fast, one-second or less start-up time.

Portable device manufacturers often require that power supplies meet a minimum output undershoot voltage to prevent their devices from resetting when the output changes from no-load to full load. iWatt meets these specifications using digital techniques in its adaptive, cycle-by-cycle waveform analysis which delivers tight regulation of the output voltage and output current, as well as fast response to step load changes. The iW1700 maintains better than 3 percent output voltage and current regulation over the entire operating line, load, and temperature range, regardless of manufacturing variability or component tolerances.

Suitable for touch screen smart phones and other portables which can be sensitive to common-mode noise, the iW17100 drives an external low-cost bipolar junction transistor (BJT) power switch which has intrinsically lower common-mode noise than a MOSFET power switch. Built-in frequency jitter and quasi-resonant (or valley mode) switching enable iW1700-based power supplies to meet EN55022 class-B-conducted EMI with 10dB margin.

With a high switching frequency, up to 72 kHz, to reduce the size of the transformer and capacitors, designers can fit a 5V/1A universal AC input zero power charger into a compact 25mm x 25mm x 25mm form factor using only 28 low-cost components. An active average efficiency of 80 percent, well above the 68.2 percent specified by Energy Star EPA version 2.0, keeps components in such compact chargers from overheating.

"Portable wall chargers with zero no-load power that hit the power supply sweet spot required design trade-offs, or a micro-controller and other components, until now," said Zahid Rahim, vice president and general manager of iWatt's AC/DC business unit. "The iW1700 cuts wasted power to almost zero without costing an arm and a leg in special components."

Rahim continued, "Accurately measuring ultra low power is complicated because measurement instruments have a minimum resolution, and the standby load may be pulsed and/or draw asymmetric current." The IEC 62301 standard specifies a measurement uncertainty of less than 10mW (i.e. 5mW) at 95 percent confidence level. "As such, devices that consume 5mW or less can be rounded to zero power."

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