The STR-A6251/51M/52 Series from Allegro MicroSystems Europe is a family of low-output power offline switching regulator ICs featuring a novel 'jittering' function that minimises the need for external EMI noise-filtering circuitry.
The devices use a PWM (pulse-width modulation) topology to provide an output power of up to 20 W with a universal input or 24 W with a 230 V a.c. input. Each device incorporates a variety of functions to realise a 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 frequency jittering function enables cost reduction in the EMI noise-filtering circuitry by suppressing EMI noise. The centre frequency of the PWM operation is set to 50 kHz for the STR-A6251/52 and 67 kHz 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.
A number of other features reduce the overall costs of designs based on these ICs. The primary constant output eliminates the need for secondary-side control circuitry, which would normally include an operational amplifier, current-sensing resistor and passive components.
In addition to the overload protection, each device includes pulse-by-pulse overcurrent protection, overvoltage protection with latch, and thermal shutdown with latch. Auto-burst standby reduces standby input power to less than 100 mV at zero load and 264 V a.c., while the soft-start reduces MOSFET stress during start-up.
The proprietary 900 V BCD process connected to the internal MOSFET's drain to power the control circuit simplifies the peripheral circuit design and improves the system's efficiency. The STR-A6251/51M/52 Series is targeted at battery-changer, standby and low- output power-supply applications in the consumer, communication, industrial and home appliance markets, and is supplied in an 8-pin dual-inline package.
For more information contact Simon Churches, Arrow Altech Distribution, +27 (0)11 923 9600, [email protected]
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