AN901 Datasheet, PDF (2/25 Pages) STMicroelectronics – Electromagnetic compatibility

AN901
2. Simplified DC Steady State Analysis
Analyzing the flyback behavior in DC steady state provides formulas to assist with selecting values for the
components used in Figure 1. For this analysis, it is assumed that components are ideal, at 100% efficiency
(P_IN = P_OUT), and the circuit has reached equilibrium.
Figure 2 shows the critical components of the flyback converter. The transformer model includes magnetizing
inductance L_m and inductance leakage L_lkg. R_LOAD does not necessarily represent a physical resistor, rather it is
an expression of V_OUT/I_OUT.
Figure 2. Flyback Converter
For DC steady state analysis, the two modes where the system operates the majority of the cycle are only required
when S1 is closed and when S1 is open. Figure 3 depicts the simplified magnetizing and secondary current
waveforms.
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