iWatt Inc., has introduced the iW1700 Zero Power AC/DC Digital
PWM controller, which is designed to enable low-cost, energy-efficient
120 V/230 VAC offline adapters and chargers (up to 5W) that 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 4 mW, or effectively zero. (The
IEC 62301 standard for measuring standby power in household electrical
appliances rounds 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)
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. The 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% output voltage and
current regulation over the entire operating line, load, and temperature
range, regardless of manufacturing variability or component tolerances.
Suitable for touchscreen 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 10 dB 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 25 mm x 25 mm x 25 mm form
factor using only 28 low-cost components. An active average efficiency
of 80%, well above the 68.2% specified by Energy Star EPA version 2.0,
keeps components in such compact chargers from overheating.
The iW1700 comes in a low-cost, standard six-pin SOT-23 package and is available now at $0.25 in 10,000-piece quantities.
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