LM34927SD Datasheet, PDF (12/26 Pages) Texas Instruments – LM34927 Integrated Secondary Side Bias Regulator for Isolated DC-DC Converters

LM34927
SNVS799F – APRIL 2012 – REVISED DECEMBER 2013
APPLICATION INFORMATION
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Typical Isolated Bias Application Schematic
A typical isolated bias supply application is shown in Figure 16. Inductor (L) in a typical buck circuit is replaced
with a coupled inductor (X1). A diode (D1) is used to rectify the voltage on the secondary output. The nominal
voltage at the secondary output (V_OUT2) is given by:
V_OUT2 = V_OUT1 x
N_S
N_P
-
V_F
(6)
where VF is the forward voltage drop of D1, and NP, NS are the number of turns on the primary and secondary
of coupled inductor X1. For output voltage (V_OUT1) above the maximum V_CC (8.3V), the V_CC pin can be diode
connected to V_OUT1 for higher efficiency and low dissipation in the IC.
D1
VOUT2
VIN
9V-100V
+
C_IN
R_UV2
R_UV1
R_ON
LM34927
7
2
BST
V_IN
4 _RON
SW ⁸
3 _UVLO
VCC ⁶
FB ⁵
RTN
1
+
C_OUT2
N_S
+
C_BST
X1
N_P
VOUT1
D2
+
C_VCC
R_FB2
R_FB1
R_r
+
C_OUT1
Figure 16. Typical Isolated Application Schematic
3W Isolated Bias Application Schematic
A complete 3 W bias supply for isolated bias supply application is shown in Figure 17.
D1
+ C4
1 F
20V-100V
VIN
C1 ⁺
0.47F
GND
T1
R1
127 NŸ
R2
8.25 NŸ
7
BST
2 _VIN
SW ⁸
4 _RON
R3
130 NŸ
LM34927
+ _{0.01 F}
C2
33 H
(1:1)
R8
C7
46.4 NŸ ^{3300 pF}
C8
0.1 F
3 _UVLO
EXP
VCC ⁶
FB ⁵
RTN
1 _U1
D2
+
C6
1 F
R4
6.98 NŸ
R5
1 NŸ
VOUT2
9.5V
IGND
VOUT1
10V
(TP3)
0Ÿ
R6
+
C3
1 F
GND
Figure 17. A 3 W Isolated Application Schematic
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