Green-Mode PWM Controller for Flyback Converter, Programmable Frequency 47KHz ~ 109KHz

The highly integrated SG5842A/JA 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 continuously decrease the switching frequency at light-load conditions. To avoid acoustic-noise problems, the minimum PWM frequency set above 22KHz. This green-mode function enables the power supply to meet international power conservation requirements. To further reduce power consumption, SG5842A/JA is manufactured using the BiCMOS process. This allows a low startup current, around 14µA, and an operating current of only 4mA. As a result, a large startup resistance can be used. The SG5842A/JA built-in synchronized slope compensation achieves stable peak-current-mode control. SG5842JA integrates a frequency-hopping function that helps reduce EMI emission of a power supply with minimum line filters. SG5842A/JA 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, then the controller starts again. As long as VDD exceeds about 24V, the internal OVP circuit is triggered. An external NTC thermistor can be applied for over-temperature protection. SG5842A/JA is available in an 8-pin DIP or SOP package.