LT3758 datasheet(13/26 Pages) LINER

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LT4430

4430fb

APPLICATIONS INFORMATION

Generate a bias supply for a forward converter using similar

techniques to that of the ﬂyback converter. Figure 3a to 3c

detail the three common bias circuits for the synchronous

single-switch forward converter. In the ﬂyback converter

of Figure 1d, the bias supply is proportional to VIN and

•

VIN

4430 F03a

1:N

VOUT

COUT

*OPTIONAL SEE TEXT

LT4430

VBIAS

R1*

4430 F03b

•

1:N

N = N1 + N2

VOUT

COUT

*OPTIONAL SEE TEXT

LT4430

VBIAS

R1*

••

VIN

•

VIN

4430 F03c

1:N

VOUT

LT4430

VBIAS

COUT

R1*

*OPTIONAL SEE TEXT

R3*

QBS

Figure 3a. Typical Single-Switch Synchronous Forward

Converter with Bias Generator

Figure 3b. Single-Switch Synchronous Forward Converter

with Tapped Secondary Bias Generator

Figure 3c. Single-Switch Synchronous Forward Converter

with Preregulator Bias Generator

VOUT. However, in the forward converter, L1’s presence

decouples the bias supply from VOUT. In Figure 3a, the

bias supply equals (VIN • N – VF). In Figure 3b, the bias

supply equals (VIN • N1/N – VF). In Figure 3c, the bias

supply equals (VZ1 – VF).

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