DAEWOO CP-850FX CHASSIS
Service Manual

CP-850FX Service Manual 5.10 POWER SUPPLY (STR-W6754) - Functions of Each Terminal 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

R2

P

the latch circuit (150µA Max), which is described later, to be flown at the minimum AC input. 1 However, where the R2 value is too high, the current charging D2 D 4 to C3 shall be reduced after AC input. Consequently, it takes VC C much time to reach the operation start-up voltage, so it is C3 D S/ N 3 GD 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 STRW6700 drop is reduced by the increase of the C3 capacity. Therefore, Fig.1. Start-up Circuit even if the auxiliary drive winding voltage is delayed in rising, �1 起��路 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.
C ＩC

100 μ A M ( AX ) 9 .6 V (TYP ) 1V 5 1 .V 82 ( TYP )

ＶC C

Fig.2. VCC Terminal� � 路 � CC � � VCC端 Vol. � Circuit Cur. Ｉ ���� ICC

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