AN892 Datasheet, PDF (2/16 Pages) Silicon Laboratories – DESIGN GUIDE FOR ISOLATED DC/DC USING THE

AN892
2. Simplified DC Steady State Analysis
Analyzing the asymmetric half bridge 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, 100% efficiency
(P_IN=P_OUT), and the circuit has reached equilibrium.
Figure 2 shows the critical components of the asymmetric half bridge flyback. 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. Asymmetric Half Bridge Flyback Converter
To analyze this architecture, a cycle can be divided into eight distinct operating modes. However, 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 S2 is open, and when S1 is open and S2 is closed. Figure 3 depicts the simplified magnetizing and
leakage inductance current waveforms.
Figure 3. Inductor Currents
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