LT4430HS6 LINER [Linear Technology], LT4430HS6 Datasheet - Page 12

• Manufacturer Part Number: LT4430HS6
• Description: Secondary-Side Opto-Coupler Driver Ground-Referenced Opto-Coupler Drive
• Manufacturer: LINER [Linear Technology]

LT4430
APPLICATIONS INFORMATION
The second solution is to make a preregulator as shown
in Figure 2b. In this example, the bias supply equals (V
– V
base current to QBS. Resistor R3 (on the order of a few
hundred ohms), in series with Q5’s base, suppresses
possible high frequency oscillations depending on QBS’s
selection. The preregulator circuit has additional value for
fully synchronous converters. Fully synchronous convert-
ers require gate drivers to control the secondary-side
12
BE
). Select R2 to bias Zener diode Z1 and to supply
Figure 2a. Flyback Converter with Tapped Secondary Bias
Figure 2b. Flyback Converter with Preregulator Bias
V
*OPTIONAL SEE TEXT
IN
•
V
1:N
IN
T1
*OPTIONAL SEE TEXT
N = N1 + N2
•
• •
1:N
T1
D2
D1
•
•
N1
N2
Z1
R1*
D2
D1
MOSFETs turn on and turnoff. The gate driver circuitry
requires supply current in the range of 10mA to 100mA
depending on the gate driver supply voltage, MOSFET size
and switching frequency. The preregulator bias supply is
ideal for powering both the LT4430 and the gate driver
circuitry, especially since the gate drivers typically use a
supply voltage between 5V to 12V. The preregulator circuit
fi nds wide use in fully synchronous forward converters,
push-pull converters and full-bridge converters.
C1
R1*
R2
Z1
R3*
C1
C
OUT
LT4430
V
V
BIAS
4430 F02a
OUT
QBS
C2
C
OUT
V
LT4430
V
4430 F02b
OUT
BIAS
4430fb