Power Supply (Str-W6754) - Functions Of Each Terminal; Vcc Terminal (Pin 4); Start-Up Circuit - Daewoo DTF-2950-100D Service Manual

5.10 POWER SUPPLY (STR-W6754)

5.10.1 Vcc Terminal (Pin 4)

5.10.1.1

Start-up Circuit

The start-up circuit detects Vcc terminal (No.4 pin) voltage,
and makes a control IC start and stop. The power supply of the
control IC (Vcc terminal input) employs a circuit as shown in
Fig.1. At start-up, C3 is charged through a start-up resistor R2.
The R2 value needs to be set more than the holding current of
the latch circuit (150µA Max), which is described later, to be
flown at the minimum AC input.
However, where the R2 value is too high, the current charging
to C3 shall be reduced after AC input. Consequently, it takes
much time to reach the operation start-up voltage, so it is
required to monitor the capacity of C3 that is mentioned later
simultaneously. The Vcc terminal voltage falls immediately
after the control circuit starts its operation; however the voltage
drop is reduced by the increase of the C3 capacity. Therefore,
even if the auxiliary drive winding voltage is delayed in rising,
the Vcc terminal voltage does not fall up to the operation stop voltage to maintain the start-up
operation. However, with larger capacity of C3, it takes much time, after AC input, to reach the
operation start since the certain time is required to charge C3. In general, SMPS performs its
operation properly with the value, C3 is 10 to 47µF, R2 is 47k to 150k Ohm for 100V wide input,
and 82K to 330K Ohm for 200V narrow input for its start up.
As shown in Fig.2, the circuit current which makes
the control circuit start is regulated at 100µA MAX
(Vcc = 15V, Ta = 25C), and higher value resister R2
is applicable to the circuit. Once the Vcc terminal
voltage reaches 18.2V (TYP), the control circuit starts
its operation by the Start-up Circuit, and current
consumption shall be increased. Once the Vcc
terminal voltage falls and it becomes lower than the
operation stop voltage 9.6V (TYP) with the decrease
of the Vcc terminal voltage, Under Voltage Lock Out
(UVLO) circuits stops the controlling operation and
returns to the start-up mode.
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- Functions of Each Terminal
1
S/ G N D
STR- W6700
Ｉ
C C
100 μ A
( M AX )
図 ２ V 端 子 電 圧 － 回 路 電 流 Ｉ
Fig.2. V
CC
CP-850FX Service Manual
R2
D2
D
4
V
C C
C3
3
Fig.1. Start-up Circuit
図 1 起動回路
9 .6 V 1 5 V
(TYP )
C C
Terminal Vol. – Circuit Cur. I
P
D
Ｖ
C C
1 8 . 2 V
( TYP )
C C
CC
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