This application note describes a detailed design strategy for a high-efficiency, compact flyback converter. Design considerations, mathematical equations, and guidelines for printed circuit board layout are presented.
The SG6846 is a highly integrated PWM controller IC designed for low standby power consumption and high-efficiency power conversion. It features a proprietary green-mode function that reduces switching frequency under light-load conditions and enters burst-mode at no-load. The IC incorporates multiple protection functions, including over-temperature protection, AC input brownout protection, and Vpp over-voltage protection, with an internal latch circuit for critical faults.
The document details the application of the SG6846 in flyback converters with surge-current output, such as those used in printers and motor drivers. It covers design considerations, mathematical equations for setting the PWM frequency and feedback loop, and guidelines for printed circuit board layout. Key features include built-in synchronized slope compensation for stable continuous conduction mode (CCM) operation and a two-level over-current protection function.
| Operating Current | 3.7mA |
|---|---|
| Gate Output Clamp Voltage | 18V |
| PWM Frequency (Nominal) | 65kHz |
| PWM Frequency (Green Mode) | 22.5kHz |
| FB Threshold Voltage for Frequency Reduction | 2.1V |
| FB Voltage for Termination | 1.6V |
It is designed for general-purpose switch-mode power supplies and flyback power converters, including power adapters and SMPS with surge-current output for printers and motor drivers.
An external NTC thermistor can be applied to sense the ambient temperature. When activated, an internal latch circuit shuts off the controller until the temperature cools sufficiently or AC supply is disconnected.
Yes, it enables design of a flyback power supply operating in CCM without adding external components due to its built-in synchronized slope compensation.