Powermax30 AIR Service Manual 808850 55
Section 5
Troubleshooting and System Tests
Theory of operation
Functional description
AC power enters the system through the power switch (S1) to the input diode bridges (D24, D30). The voltage from the
diode bridges supplies the power factor correction (PFC) boost converter, which provides a nominal 375 VDC bus
voltage. The bus voltage then supplies voltage and current to the inverter, the flyback circuit power supply (DC to DC
converter) on the power board (PCB2), and the compressor-driver board (DC to DC converter). The power board
provides noise suppression and spike protection. A “soft start” is implemented via the power board resistor and relay
(K1).
The compressor-driver board (PCB3) converts 375 VDC bus voltage from the power board to nominal 15 VDC through
a DC to DC converter. The compressor-driver board supplies 15 VDC to power the internal air compressor.
The PFC boost converter consists of an insulated gate bipolar transistor IGBT (Q1), choke, and control circuit. It
provides a 375 VDC bus voltage when the input AC voltage is between 120 and 240 VAC.
The inverter consists of an IGBT (Q2), the power transformer, a current-sense transformer, and sections of the power
board. The inverter operates as a pulse-width modulator-controlled bridge circuit that is rectified by the output
diode (D27).
The output circuitry consists of two current sensors located on the power board, the pilot arc IGBT (inside the
D27 module), and the output choke.
The control board’s microprocessor monitors and regulates the system’s operation and safety circuits. The amperage
adjustment knob sets the output current to the desired value between 15 A and 30 A. The system compares the
set-point to the output current by monitoring the current sensor and adjusting the pulse-width output of the inverter
IGBT (Q2).
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