Daewoo DTR-14D3VG, Руководство по обслуживанию

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(5) Stand-By Mode
When going into light load mode such as remote control standby mode, internal impedance at a signal terminal of a
microcomputer gets higher. Then the microcomputer have the current, I1, which has been bypassed from C9 through
R11 and D10 by the function of a microcomputer, flow into the base of Q4 to turn it on. As a current flows via R12 and
D11 into a photo coupler when Q4 to turn it on, each output voltage (including voltages of d1 and d2 windings) starts
descending and becomes stable when the voltage of the winding, S1 reaches Vs (Vs=V
R
11
+V
Z
(
DIO
)
+V
BE
(
Q
4)
). In this event,
a voltage across C10, which is a line voltage to the microcomputer, also descends and consequently the
microcomputer cannot be activated. A stable power source for the microcomputer can be established by supplying
the current, I2, from C9 through R9 and Q3 while Q4 is on.
Since the voltages of d1 and d2 winding in the primary also go down according to their ratios to S1’ at the same time,
power shall be supplied to the V
IN
terminal (Pin #9) from d2 winding when the load is light. In addition, because a
voltage at the INH terminal (Pin #8) gets lower than V
TH
1 in accordance with the decrease of D1 winding voltage,
OFF-time of the power transistor is fixed at set time (T
OFF
=50µsec at Ta=25˚C) of the built-in oscillator, and only ON-
time changes depending on input and output conditions of the power supply. Therefore, it enables to hold an
oscillation frequency in light load mode below 20KHz(typical).
• Refer to the Typical Application Circuit below
(6) Drive circuit
The STR-S6700 series applies the proportional drive system in
order to minimize turn-on and saturation loss, and storage time.
In the conventional RCC system, turn-on loss and switching
noise due to the surge current appearing when the power
transistor turns on are high as because the transistor is driven
by the drive current shown at the right . In addition, since I
B
decreases linearly when the transistor turns off and a peak
value of I
B
2 is not large, the storage time is long and the
V
CE
(
SAT
) voltage is high, which results in large turn-off loss.