Table of Contents
Advertisement
VSUS High Voltage Source
Figure 19
The P-Board contains the drive-voltage oscillator circuit that develops the Vsus
voltage needed to operate the Scan and Sustain boards. Operation begins with
the 18Vdc supply derived at the main power supply. AC voltage from pin 4 of the
secondary of the transformer T502 is rectified filtered and applied to pin 1 of
IC550. The regulated 15 volts output of the IC enters pin 4 of IC551 to serve as
startup voltage and begin the oscillation of the IC. The regulated DC output of
IC550 is also applied to the voltage feedback circuit consisting of the optical
coupler D565 and Diode D553. The PWM output at pin 3 of IC551 is applied to
the transformer's primary. As current passes through the transformer, magnetic
field builds up in its core. The primary current passes through the transistor
located inside the IC and the four source resistors R550, R560, R568, and R574.
The voltage at the transistor's Source increases at a proportional rate to that of
32
Advertisement
Table of Contents
