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Digital PWM controller eliminates no-load power waste

Posted: 03 May 2011     Print Version  Bookmark and Share

Keywords:Power controller  no-load  charger  adapter 

iWatt Inc. debuts the iW1700 Zero Power AC/DC Digital PWM Controller offering zero no-load power aimed at low-cost, energy-efficient 120V/230VAC offline adapters and chargers (up to 5W) such as in 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 5mW 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 72kHz) switching frequency to achieve no-load charger performance, meet manufacturers' power-supply requirements, and still enable a low bill-of-material (BOM) cost.

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 per cent output voltage and current regulation over the entire operating line, load, and temperature range, regardless of manufacturing variability or component tolerances.

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 72kHz, 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 per cent, well above the 68.2 per cent 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 Rs.11.42 ($0.25) in 10,000-piece quantities.

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