Rainbow-electronics MAX5051 Manual do Utilizador descarregar pdf (Página 13)

If the charge stored on the boost capacitor is not ade-

quately replenished then the gate-driver lockout for the

high-side MOSFET is triggered, stopping the high side

from switching. The low side continues switching, even-

tually recharging the capacitor, at which point the high

side starts switching again. To prevent this behavior,

use the boost capacitor’s cycle-by-cycle charging cir-

cuit to prevent unwanted shutdowns of the high side

(Figure 2). Connect the gate of a small high-voltage

FET (with the same voltage rating or higher as the main

FETs) to the DRVB output of the MAX5051. Connect the

drain of this FET to XFRMRH, and connect the source

to the primary ground. DRVB will briefly (300ns) turn

this FET ON every cycle after the main PWM clock ter-

minates. This allows the boost capacitor to be replen-

ished under all conditions, even when switching stops

completely. A suitable FET for this is BSS123 or equiva-

lent (100V, 170mA rated). The boost-capacitor charge

MAX5051

Parallelable, Clamped Two-Switch

Power-Supply Controller IC

______________________________________________________________________________________ 13

MAX5051

CON

FLTINT

GND

RCFF

RCOSC

STARTUP

BST

REG9

SYNCIN

PVIN

AVIN

CSS

STT

DRVB

XFRMRH

DRVH

DRVDD

DRVL

PGND

COMP

UVLO

REG5

SYNCOUT

LXVDD

LXH

LXL

IN+

3.3V

10A

B2100

: 150µH

P: 14T

S: 4T

T: 6T

LOAD

MAX8515

USED FOR

BOOST

CAPACITOR

PRECHARGE

PS2913

IN-

fs = 250kHz

R12

1MΩ

C12

220nF

C13

100pF

C14

390pF

R13

100kΩ

R14

24.9kΩ

R15

1MΩ

R11

39.2kΩ

C10

4.7µF

1µF

R10

10Ω

2.2kΩ

360Ω

270nF

11.5kΩ

2.55kΩ

47nF

220nF

475Ω

150nF

3 x 270µF

2µH

B2100

SI4486

BSS123

28mΩ

1µF

4.7µF

10Ω

BAT46W

47Ω

4.7µF

MA111CT

15kΩ

C11

0.1µF

Figure 2. Typical Application Circuit

REG9

BST

DRVL

DRVH

XFMRH

BST

Figure 3. Boost Capacitor Charging Path During Transformer

Reset

1 2 ... 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Power-Supply Controller IC 1

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