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3.3 CURRENT MODE CONTROLLER
START UP CIRCUIT
.
(Refettotircuit diagram Fig-3)
Current Mode PWM controller module 1801 (UC3842)
is used to drive the SMPS switching MOSFETs 0803.
The drive signal is inhibited if the current sense line
(pin 3) rises above 1V.
The start up voltage to the module (pin 7) is provided
from C808 which charges through Ra09-R810
(connected to the HOT LINE) on turn on. The start
up line is about 20V during normal operation.
R812 reduces the supply voltage to the module in
order to decrease the gate drive to within the
manufacturers specification
SMPS DRIVE
RBII
47K
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T801
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7
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R810
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TEST
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GATE VOLTAGE
SOURCE VOLTAGE
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Fig-3
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TN
T'7
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