Able to achieve a power factor of greater than 0.99 by actively modulating the input current, the LT8312 boost controller allows compliance with most harmonic current emission requirements, says Linear Technology. It operates with current mode control and critical conduction mode, a variable frequency switching scheme that returns the current to zero in the inductor with every cycle. This switching behavior is similar to zero voltage switching, which minimises EMI and energy lost in the power switch, and is claimed to improve efficiency by as much as 5%. The controller is suitable for universal AC (90 to 265V AC) input and higher ranges, depending on the choice of external components. An hysteretic start-up eliminates the need for a bias power supply. After start-up, the device is powered by a bootstrap winding off of the inductor. A strong 1.9A gate driver enables it to drive most high voltage MOSFETs. The low 102mV current sense threshold enables the use of small value shunt resistors, which increase efficiency. A 16-lead MSOP is offered with four temperature grades: -40 to 125°C for the extended and industrial grades, a high temp automotive grade of -40 to 150°C and a military grade of -55 to 150°C.

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