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.

  • Printer
  • Other Data Processing
  • Two-level OCP with 1700ms delay
  • Output short-circuited delay time: 100ms
  • Low startup current: 8µA
  • Low operating current: 3.7mA
  • Peak-current mode operation with cycle-by-cycle current limiting
  • Programmable PWM frequency with frequency hopping
  • PWM frequency continuously decreasing with burst mode at light loads
  • VDD over-voltage protection (OVP)
  • AC input brownout protection with hysteresis and constant output power limit
  • Constant output power limit (full AC input range)
  • Internal latch circuit for OVP, OTP, and OCP
  • Built-in soft-start
  • Open-loop protection with 1700ms delay time


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