Kristel 1428-30k series, Руководство по обслуживанию

Страница: 16 / 43

1.1 LINE FILTER CIRCUIT
The line filter circuit is comprised of C501, C502 and L501. This line filter tends to reduce the noise of con-
ducted EMI from monitor into the power line.
1.2 INPUT RECTIFIER CIRCUIT
The input rectifier circuit is comprised of BD501 and C505. BD501 and C505 is a full - wave mode rectifier.
L501 is used to reduce the surge current while the power supply is turned on.
1.3 START UP CIRCUIT
The resistor R502 provides the start-up current of IC501. The turn-on and turn-off thresholds of under volt-
age lockout circuit in IC501 are set up internally at 16vDC respectively. To start up, C506 must be charged to
16vDC with a current of 0.3mA - 0.5mA which depends on the IC501 start-up current characteristics and
R502 resistor value.
1.4 CURRENT MODE CONTROL OPERATION
When Vcc of IC501 pin 7 is charged to more than 16V, there is a square wave on the output pin 6 which can
be adjusted to peak +/- Amp. for driving the gate of Q501. The current-mode sensing resistor R513 senses the
primary current wave in order to control the current-mode PWM and limit the total output power. Pin 2 and
pin 1 is an error AMP section. IC501 detects the output voltage while the line voltage and load current
change.
1.5 OVP CIRCUIT
ZD502 is the OVP circuit (over voltage protection). If an over voltage condition exists the ZD502 will shut
down IC501.
Per above related considerations a switching power supply is a relatively complex circuit (see functional
block diagram). It is apparent here that the heart of the supply is really the high frequency inverter. It is here
that the work of chopping the rectified line at the high frequency (20-200kHz) is done. Also the line voltage is
transformed down to the correct output level. The 60 Hz input line is rectified and filtered by one block and
after the inverter steps this voltage down, the output is again rectified and filtered by another.The task of regu-
lating the output voltage is left to the control circuit which closes the loop from the output to the inverter.
pg.11
1428-30k series