To maximize its efforts in improving power supply efficiency, ON Semiconductor today introduced a series of highly-integrated, off-line switching regulators, enabling ease of design for suppliers of on-board AC—DC converters. The company designed the NCP1000-02 series to minimize the number of parts on a circuit board, solving designer’s board space limitations for low-cost applications that utilize an AC input.

The internal high-voltage switch circuit and start—up circuit can function in continuous operation over a wide range of inputs, from 85 volts AC to 265 volts AC, and thus can be used in virtually any existing power system in the world. These devices include a number of features such as no minimum load requirements, under-voltage lockout, over—temperature protection, band-gap reference and leading edge blanking that make them an excellent value to designers of cellular-phone chargers, wall adapters and on-board AC-DC converters. The opto fail—safe shutdown circuit feature protects the critical loads from damage if the opto-coupler fails.

ON Semiconductor offers power management chips and design services that enable designers to deliver smaller and more efficient electronic devices. The introduction of these devices supports the company’s strategy of developing products and technologies to enhance power management applications

The NCP1000 through NCP1002 series of integrated switching regulators, combines a fixed frequency pulse width modulator (PWM) controller with an integrated high voltage power switch circuit. It is designed to power a discontinuous mode flyback, with secondary side sensing.

The internal high voltage switch circuit and start-up circuit can function in continuous operation over a wide range of inputs, from 85 VAC to 265 VAC, and thus can be used in any existing power system. The devices include features such as undervoltage lockout, over-temperature protection, bandgap reference and leading edge blanking.

The NCP1000 thru NCP1002 provide on a single monolithic chip, all of the active power, control, logic, and protection circuitry required to implement a high voltage flyback or forward converter. This device series is designed for direct operation from a rectified 240 VAC line source and requires minimal external components for a complete converter solution. Potential markets include office automation, industrial, residential, personal computer, cell phone chargers, wall adapters, and onboard AC-DC converters.

The oscillator block of the regulator consists of two comparators that alternately gate on and off a trimmed current source and current sink that are used to respectively charge and discharge an on-chip timing capacitor between two voltage levels. This configuration generates a precise linear sawtooth ramp signal that is used to pulse width modulate the MOSFET of the Power Switch circuit. The Oscillator frequency is internally programmed for 100 kHz operation with a controlled charge to discharge current ratio that yields a maximum Power Switch Circuit duty cycle of 72%.

The NCP1000 series uses cycle-by-cycle current limiting as a means of protecting the output switch transistor from overstress. Current limiting is implemented by monitoring the instantaneous output switch current during conduction, and upon sensing an overcurrent condition, turns off the switch for the duration of the oscillator ramp down period. The current limit comparator detects if the voltage across the sense resistor exceeds the reference level at the noninverting input. If exceeded, the comparator resets the PWM latch to protect the power switch circuit. The power switch circuit is capable of switching 700 V with an associated drain current that ranges from 0.5 A to 1.5 A.

The NCP1000 series of offline converters offers a high efficiency power source for low power, electronic equipment. It serves the same function as small, line frequency transformers, but with the added benefits of line and load regulation, and transient suppression across the universal input voltage range. This kit provides a 5.0 volt, 1.0 amp output, which is derived from an input source of 85 to 265 VAC, at 50 Hz to 60 Hz. The output is regulated and current limited, and EMI filters are included on both the input and output.

Undervoltage lockout (UVLO) is used to guarantee that the chip has sufficient voltage to be fully functional before the output stage is enabled. It inhibits operation of the major functions of the device by disabling the Internal Bias circuitry, and assures that the power switch circuit remains in its "off’’ state as the bias voltage is initially brought up from zero volts.

ON Semiconductor offers the NCP100xP and NCP100xT devices in DIP-8 and TO220-5 packages, respectively, with samples and production quantities currently available. For the NCP100xP, the suggested resale pricing ranges from $0.87 to $1.30 per 10,000 units. For the NCP100xT, the suggested resale pricing ranges from $0.92 to $1.34 per 10,000 units. The company provides additional technical information on the switching regulators at http://www.onsemi.com/ncp1000