AN892 Datasheet, PDF (4/16 Pages) Silicon Laboratories – DESIGN GUIDE FOR ISOLATED DC/DC USING THE

AN892
Now t_S1 and t_S2 can be expressed in terms of D and switching period as:
t_S1 = DT_SW
Equation 7.
t_S2 = 1 – DT_SW
Equation 8.
and assume diode D1 has no voltage drop when conducting, the volt-second balance equation for L_lkg can be
written as:
L^----_l^-_k^--L-_g^{---l-+k---g--}L^----_m^{-- VIN}
–
V_C1DT_SW
+


-^V----^O-_N---^U---^T--
–
V_{C 1}
1
–
DT_SW=
0
Equation 9.
With the condition that L_lkg << L_m, Equation 9 simplifies to:
The volt-second balance equation for L_m is:
V_C1  ^V-----^O-_N---^U---^T--
Equation 10.
–^V-----^O-_N---^U---^T--1 – DT_SW + _L----_l-_k---_g-^L---+^m-----_L----_m--V_IN – V_C1DT_SW= 0
Equation 11.
With the condition that L_lkg<<L_m, Equation 11 simplifies to:
-^V----^O-_N---^U---^T--1 – D  V_IN – V_C1D
Equation 12.
Substituting Equation 10 into Equation 12 yields the following relationships:
V_{-----O-N---U---T--  VIND}
Equation 13.
V_C1  V_IND
Equation 14.
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