REV.-A
PRINCIPLES OF OPERATION
2.2.3 RECTIFIER AND SMOOTHING CIRCUIT
The AC IN voltage from the filter circuit is full-wave rectified by diode bridge DB1, and converted to approx-
imately 2 x AC IN voltage by smoothing capacitor C7. The + 24 VDC, + 5 VDC, and ± 12 VDC voltages
are converted from this DC voltage.
DB1
NOTE:
The item in parentheses pertains to the 220/240 V version
Figure 2-19. Rectifier and Smoothing Circuit
2.2.4 STARTING CIRCUIT (MAIN SWITCHING CIRCUIT)
Figure 2-20 shows the starting circuit. The operation sequence is as follows.
(1) When the main power source is connected, the AC input passes through the input filter and is then rec-
tified and smoothed. The resulting DC voltage V
IN
is input into the circuit.
(2) VIN is applied to starting resistance R7 and passes through point A. Base current lB flows through tran-
sistor Q1, causing the transistor to conduct.
(3) At the same time,
VI
N
is applied to coil 4-3 of pulse transformer T1, causing a voltage of (7/60T)
(VI
N
)
at 8-2, so that the positive feedback current of switching circuit
I
B
flows in the direction of B. This causes
a sharp rise, and Q1 quickly switches on.
(4) Current
I
L
through coil 4-3 increases linearly over time. During this time, a voltage of (10/60T)
V
IN
is
induced through coils 7-8 and 8-11, and a voltage of (19/60T)
V
IN
through coil 9-10. For all these coils,
then, current attempts to flow in the direction of D; however, this direction opposes the direction of diodes
D22, D23, and D20, so that no current flows through the secondary side of the circuit.
LQ-510
2-15
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