Jittering minimises external EMI noise-filtering circuitry

The new STR-A6251/51M/52 Series from Allegro MicroSystems Europe is a family of low-output power offline switching regulator ICs. They share a ‘jittering’ function that suppresses EMI noise so that the need for external EMI noise-filtering circuitry is minimal.

The devices use pulse-width modulation (PWM) to provide output power of up to 20W with universal input or and 24W with 230V AC input. The centre frequency of the PWM operation is set to 50kHz for the STR-A6251/52 and 67kHz for the STR-A6251M. The frequency jittering provides a variation of ±2.5% of the centre frequency, and the fluctuation speed is adjusted by an external capacitor for optimum results.

Each device incorporates functions to realise simple and reliable design in a switched-mode power supply system, including primary controlled constant-voltage/constant-current operation, automatic standby, soft start, circuit protection and an avalanche-energy-guaranteed MOSFET. The primary constant output eliminates the need for secondary-side control circuitry. The overload protection circuit also incorporates an integral delay timer for automatic re-start, eliminating the need for external components.

The Series is designed for battery-changer, standby and low-output applications in the consumer, communication, industrial and home appliance markets, supplied in an 8-pin dual-inline package.

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