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Combo-controller holds down standby power consumption in notebooks

Continuing to provide power supply manufacturers with innovative ways to reduce power consumption, ON Semiconductor introduces the NCP1603 – a combo PFC/PWM controller with integrated standby and high voltage startup capabilities.

The NCP1603 combines a power factor correction (PFC) controller chip and a pulse width modulation (PWM) control chip in a single, 16-pin SOIC package. This combination simplifies the task of designing an offline, ac-dc power supply that simultaneously meets governmental requirements for power factor correction and low standby power consumption. Target applications for this device include products such as notebook and LCD adapters, and other consumer electronics.

In these applications, PFC is typically required when a power supply is operating under normal load conditions. However, in light-load and no-load conditions, a PFC is not required and generates losses that make it almost impossible to meet the limits on standby power consumption established by the California Energy Commission, Energy Star, and other organizations.

Under light load conditions, the NCP1603 PWM controller disables the PFC function, saving in the range of 200 milliwatts (mW) of power. Currently, the most aggressive standards limit standby power consumption to 500 mW with plans to lower this limit to 300 mW in the future. Given those goals, the power saved by turning off the PFC is significant. Moreover, disabling the PFC ensures that the controller can meet even the 300 mW limit for standby power.

Typically, when separate PFC and PWM controllers are used in a power supply design, additional circuitry is required to disable the PFC. To address this, engineers often used a bipolar transistor to pull down the VCC of the PFC controller. The circuit would also require a comparator with hysteresis and components for sensing the load conditions — up to 10 additional components in all. Implementing the NCP1603, simplifies this task and reduces part count.

The NCP1603’s PFC-stage provides near-unity power factor and is designed to operate in fixed frequency, Discontinuous Conduction Mode (DCM) to lower EMI and reduce coil size. In the most stressful conditions, Critical Conduction Mode (CRM) can be achieved without power factor degradation and the circuit could be viewed as a CRM controller with a frequency clamp (given by the oscillator). The NCP1603 takes the benefit of both modes. It operates in voltage-mode, features programmable switching frequency for DCM operation and has the ability to synchronize PWM and PFC operation for improved noise immunity. In addition, the PFC offers a variety of protective features including inrush current detection, programmable overcurrent protection as well as overvoltage protection.

The PWM-stage is implemented in continuous conduction or discontinuous conduction mode, using current-mode control. The PFC bias voltage is disabled and the circuit enters in skip mode in standby condition, which yields no-load power consumption of less than 200 mW. This stage features an internal 2.5-ms soft start, and ±6.4% frequency jitter for improved electromagnetic interference (EMI) performance. The protection features provided for the PWM-stage are similar to those of the PWM controller. Fault protection is implemented by an internal timer, and independent of the auxiliary transformer winding’s coupling quality.

The NCP1603 is offered in an SOIC-16 package and priced at $0.96 per unit in quantities of 10,000. For more information, visit www.onsemi.com

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