Argantix KDC 100-100, User Manual

Page: 80 / 137

User Manual
70 KDC Series II DC Power Supplies
6 Principle of Operation
6.1 General
An explanation of the circuits in the DC supply is given in this section. Refer to block diagram in
Figure 6-2.
6.2 Overall Description
Referring to block diagram in Figure 6-1, the KDC DC power source consists of one to three high
power DC modules, a controller, and a power supply board. The controller uses three boards:
CPU/Analog board, display board, and interface board. An EMI filter is mounted to the rear panel
and also serves as the input connection to the three phase AC mains.
The three phase mains is connected at the rear panel and passes through the EMI filter to provide
AC power to each DC module and to the power supply board. Overcurrent protection for the AC
input is provided by appropriately sized fuses on each module. There is no master switch or
circuit breaker, so, as long as mains power is applied to the input, the DC modules and power
supply board are powered. A front panel switch enables the DC supply board to put the whole unit
in the active state.
The controller, power supply, and each DC module are interconnected with a ribbon cable. This
ribbon cable serves as the Supply/Control bus. The low voltage power supplies are directed from
the power supply board to the controller and DC modules on this bus. Control signals also pass
between all assemblies on this bus. Among other uses, these signals program the output, sense
the output voltage, and detect fault conditions.
The standard interface assembly takes signals from the controller CPU board and drives the
RS232 connection on the rear panel.
The optional interface assembly drives the GPIB rear panel interface as well as the RS232. A
rear panel analog I/O connection allows remote isolated voltage and current programming of the
DC output. Multi chassis systems use the analog I/O connection and an auxiliary I/O connection
to coordinate operation of master and auxiliary units with a common output.
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 fly-back 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
c15 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.