Section 4: Theory of Operation
4.2 Power Module Theory of Operation
0101-8242-0, Rev. C
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CV-6SLX User Manual
Two AC line phases from the Inverter board feed the primary of step-down transformer T2 (see
Figure 4-2). In 208 VAC units, T2 is wired with jumpers for a 1:1 ratio. In 400 VAC units, it is
wired for a 2:1 ratio. T2 powers the AC input of PS1, the +24 VDC auxiliary power supply (see
Figure 4-2). The +24 VDC output of PS1 connects back to the Inverter board and provides low-
voltage power to the other board assemblies in the power module.
4.2.2 Power Module Grounding
Grounding is provided through two threaded studs mounted on the unit’s rear panel (see Figure
4-1). The grounding stud labeled GND must be connected to an earth ground for safety. The
other threaded grounding stud, labeled RF GND, provides a ground return for the HV output and
must be properly connected to provide a low-impedance ground (for instructions, see section
2.6). Internally, ground wires are connected together by a ground block mounted to the bottom
panel.
4.2.3 Temperature Control
Temperature inputs come from two separate devices, thermostat S2 and IC sensor U1, which
are connected to the Inverter board. Thermostat S2 opens when the Inverter board’s heat sink
rises above a preset temperature, while U1 generates an analog voltage scaled to the
temperature of the heat sink near the Inverter board’s IGBTs. Both sensors feed the over-
temperature fault circuitry. Cooling of internal components is provided by +24 VDC fan B1
mounted on the rear panel. The fan draws air in through the front panel grille and exhausts it
through the rear of the unit. The fan features an integral jammed-rotor sensor, which is
designed to sense when the fan has stopped spinning and to trigger an over-temperature fault
in that event.
4.2.4 PCB Functionality
Inverter Board
From the load side of circuit breaker CB1, the three AC line phases are fed to the Inverter board,
which converts the 50/60Hz AC line power into high-frequency power. Part of that conversion
process involves rectifying the AC input voltage through a three-phase bridge rectifier and
employing a “DC link” choke (L1) to smooth the current. This inductor improves the power
factor of the power module as seen by the AC power grid. High-speed IGBTs on the Inverter
board switch the rectified bus voltage through HV transformer T1 at 25 kHz, thereby converting
the intermediate DC power once again into AC power. Other functions performed by the Inverter
board are rail capacitor charging, temperature sensing, and monitoring auxiliary power and rail
voltage.
HV Rectifier Board
The HV Rectifier board converts the high-frequency, high-voltage output of HV transformer T1
into DC high-voltage power. The Rectifier board also scales the output voltage and current for
feedback to the Regulator board’s control circuits.
