Green-Mode PWM Controller for Flyback Converter, 65KHz, 2 level OCP

The highly integrated SG6846A series of PWM controllers provides 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 under light-load conditions. Under zero-load conditions, the power supply enters burst-mode. The SG6846A is especially designed for SMPS with surge-current output, incorporated with a two-level OCP function. Besides the cycle-by-cycle current limiting, if the switching current is higher than two thirds the peak-current threshold for 1700ms, over-current protection is activated and the SG6846A latches off. If the switching current is higher than two thirds the peak-current threshold for 100ms and the voltage on the VDD pin is higher than VDD-OFF + 1V, the PWM pulses are latched off immediately once VDD voltage is lower than VDD-OFF + 1V; useful if an output short-circuit occurs. SG6846A also integrates a frequency hopping function that reduces EMI emission of a power supply with minimum line filters. Its built-in synchronized slope compensation provides proprietary internal compensation for constant output power limit over a universal AC input range. Also, the gate output is clamped at 18V to protect the external MOSFET from over-voltage damage. Internal soft-start is built-in to reduce stress on the MOSFET and start-up current during power-on period. Other protection functions include: AC input brownout protection with hysteresis, VDD over-voltage protection, and over-temperature protection. For over-temperature protection, an external NTC thermistor can be applied to sense the ambient temperature. When OCP, VDD OVP, or OTP are activated, an internal latch circuit is used to latch-off the controller. The PWM pulses stay latched off until the power supply is unplugged from the main outlet. SG6846A is available in an 8-pin SOP package.