Argantix XDS 100-100, User And Programming Manual

Page: 47 / 116

User and Programming Manual
XDS Series 47
6.3 Bias Power Supply (A7)
The power supply board (A7) uses the three phase AC mains to generate the various low voltage
supplies required by the internal control circuits.
Three phase AC mains from the chassis EMI filter feeds the power supply board through one amp
fuses. The AC is full wave rectified to feed bulk electrolytic capacitors through surge limiting
thermistors. The bulk DC voltage is used by a flyback PWM converter to generate five isolated
output windings and a sense winding. The PWM uses the sense winding to power it’s circuitry and
regulate all of the outputs. Two of the output windings generate the +/- 19V SELV supply, two of the
output windings generate the +/- 19V control supply, and the last output winding generates the +24
VDC supply to power the fans. Each of the five outputs goes through various stages of rectification
and filtering, and each is protected by a polymeric fuse.
The +19 V control supply is down regulated by a small converter to create the relatively high current
+15 V supply required by the DC module gate drive circuits.
The +24 V fan supply passes through a small variable output voltage converter. The output voltage
is controlled b12 V and +24 V depending on the master DC module output current. This
controls the fan speed to reduce audible noise when the module is lightly loaded.
An over voltage, under voltage or phase lost detect comparator monitors the rectified input AC
voltage and sends isolated logic signals to the controller if the mains voltage is not within the
operating range.
Each of the DC output modules is synchronized to a common frequency, 93.75 kHz. The reference
clock is generated from a crystal controlled oscillator on the power supply board. The oscillator
frequency is divided down to provide three separate 93.75 kHz references, each separated by 120
degrees of phase from the other two.
The three phase AC mains is always active on the DC output modules and the DC supply board;
there is no master switch or circuit breaker. The chassis is turned on or off by a small switch on the
front panel. This switch applies or removes power from the DC supply board PWM controller chip.
When the power to the PWM chip is removed, the flyback converter stops switching, all the bias
supplies discharge to zero, and the complete unit is put in an “off” state.
Both power and control signals are distributed to the power modules and the controller through a 40
pin ribbon cable system interface, P/N 5005-234-1.