The highly integrated SG6742HL/HR PWM controller 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 frequence is set above 22KHz. This green-mode function enables the power supply to meet international power conservation requirements. With the internal high-voltage startup circuitry, the power loss due to bleeding resistors is eliminated. To further reduce power consumption, SG6742HL/HR is manufactured using the BiCMOS process, which allows an operating current of 2.7mA. SG6742HL/HR integrates a frequency-hopping function internally that helps reduce EMI emission of a power supply with minimum line filters. 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 voltage range, from 90VAC to 264VAC. SG6742HL/HR 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 ~25V, the internal OVP circuit is triggered.
