Stand-By Operation - Daewoo DTF-2950-100D Service Manual

CP-850FX Service Manual
rating, and the standard voltage is automatically changed to VOCPBD(BS2).
Besides, the VOCP is OCP/BD terminal voltage at that time when the MOSFET gate voltage
starts down.
As described above, the standard voltage (VOCPBD(BS1), VOCPBD(BS2)) realizing the Bottom-
Skip operation provides the hysteresis operation automatically and makes it possible to have the
stabilized operation. Fig.17 shows the above operation switching changing mode.

5.10.6 Stand-By Operation

The STR-W6700 series contains the burst-mode switching function to reduce the power
dissipation at stand-by mode. At the stand-by with a remote controller, the switching mode is set
in the secondary side, which makes the HIC switch to the burst-mode automatically by reducing
the output voltage.
The transformer winding voltage falls reducing the output voltage by switching in the secondary
side, and it reduces the primary side auxiliary winding voltage, which cuts off the power supply
from the auxiliary winding to VCC terminal (Pin No. 4), and the VCC terminal voltage is reduced
by the HIC's dissipation current itself. Where the VCC terminal (Pin No.4) voltage reaches the
operation stop power supply voltage (9.6V TYP), the HIC stops its operation, and the dissipation
current of the HIC turns circuit current (ICC(S)) at stand-by non-operation, and with the charging
to the back-up condenser through a start-up resistor, the VCC terminal voltage (Pin No.4) rises
again, and the HIC starts its operation immediately after the VCC terminal voltage reaches the
operation start-up power supply voltage. Repeating the above cycles, the HIC has the power
supply continue the burst-mode.
In order to reduce the transformer's magnetostriction noises at the burst-mode, by lowering the
voltage gap between the operation start-up power supply voltage at the stand-by and the
operation stop voltage, the operation frequency is increased and switched to the mode
controlling the switching current as low as possible without increasing the loss at the start-up
resistor.
This switching is made by detecting that the FB terminal voltage exceeds the FB stand-by
operation threshold voltage VFB(S), and the operation voltage width of the VCC terminal is
determined as "the power supply voltage interval 1.5V(TYP) at stand-by" and the width is
approximately one fifth compared to the normal operation.
In the transition period from the normal to stand-by operation, the output voltage continues falling
because the HIC's oscillation is suspended by the feedback current. Thus, it is inevitable to
secure the voltage exceeding the required output voltage of secondary side in the period until the
HIC starts the stand-by operation.
Meanwhile, in the transition period from the stand-by to normal operation, the output voltage
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