SNVSB79B November 2018 – May 2020 LM25180
The LM25180 is a flyback dc/dc converter with integrated 65-V, 1.5-A N-channel power MOSFET. During the MOSFET on-time, the transformer primary current increases from zero with slope VIN / LMAG (where LMAG is the transformer primary-referred magnetizing inductance) while the output capacitor supplies the load current. When the high-side MOSFET is turned off by the control logic, the SW voltage VSW swings up to approximately VIN + (NPS × VOUT), where NPS = NP/NS is the primary-to-secondary turns ratio of the transformer. The magnetizing current flows in the secondary side through the flyback diode, charging the output capacitor and supplying current to the load. Duty cycle D is defined as tON / tSW, where tON is the MOSFET conduction time and tSW is the switching period.
Figure 19 shows a typical schematic of the LM25180 PSR flyback circuit. Components denoted in red are optional depending on the application requirements.