The highly integrated SG6742 series of PWM controllers provides several
features to enhance the performance of flyback converters.
To minimize standby power consumption, a proprietary green-mode function
provides off-time modulation to linearly decrease the switching frequency at
light-load conditions. To avoid acoustic noise problems, the minimum PWM
frequency is set above 22KHz. This green-mode function enables the power supply
to meet international power conservation requirements. With the internal
high-voltage start-up circuitry, the power loss due to bleeding resistors is
eliminated. To further reduce power consumption, SG6742 is manufactured using
the BiCMOS process, which allows an operating current of 4mA.
SG6742 integrates a frequency a hopping function that helps reduce EMI
emission of a power supply with minimum line filters. Also, its built-in
synchronized slope compensation achieves stable peak-current-mode control. The
proprietary internal line compensation ensures constant output power limit over
a wide AC input voltages, from 90VAC to 264VAC.
SG6742 provides many protection functions. In addition to cycle-by-cycle
current limiting, the internal open-loop protection circuit ensures safety
should an open-loop or output short-circuit failure occur. PWM output is
disabled until VDD drops below the UVLO lower limit when the
controller starts up again. As long as VDD exceeds about 26V, the
internal OVP circuit is triggered.
SG6742 is available in an 8-pin DIP or SOP package.
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