Datasheet

LT4430
14
4430fc
For more information www.linear.com/LT4430
applicaTions inForMaTion
Figures 4a to 4d demonstrate bias supply circuits for the
fully-synchronous push-pull topology. Biasing for full-
bridge schemes is identical to the push-pull circuits with
the obvious difference in the primary-side drive. In Figure
4a, the bias supply equals (V
IN
• N – V
F
). In Figure 4b and
4d, the bias supply equals (2 • V
IN
• N – V
F
). In Figure 4c
and 4e, the bias supply equals (V
Z1
– V
F
).
In general, one of the simple, low-cost biasing schemes
suffices for LT4430 applications. However, design con
-
straints such as a very wide input voltage range may force
employment of other biasing circuits. Other methods of
generating the bias supply may include an additional
transformer or output inductor winding, low-cost linear
regulators, discrete or monolithic charge pumps and buck/
boost regulators. However, if the bias supply gets this
complicated, a quick chat with your local LT C applications
engineer may result in a simpler solution.
•
•
•
•
V
IN
4430 F04a
T1
1:N
V
OUT
C
OUT
*OPTIONAL SEE TEXT
MF
L1
Q1
ME
Q2
LT4430
V
BIAS
C1
R1*
D1
•
•
•
•
V
IN
4430 F04b
T1
1:N
V
OUT
C
OUT
*OPTIONAL SEE TEXT
MF
L1
Q1
ME
Q2
LT4430
V
BIAS
C1
R1*
D1
Figure 4a. Typical Synchronous Push-Pull Converter
with Bias Generator
Figure 4b. Typical Synchronous Push-Pull Converter
with 2x Bias Generator