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Troubleshooting
20
Keysight RP7900 Series Advanced Service Guide
PFC bias control board operation
– The PFC bias control board consists of AC/DC current sensing, instantaneous
current protection, IGBT DESAT and PEAK current latch circuitry, AC/ DC
voltage sensing circuitry, current control loop, DC voltage error amplifier, and
dead circuitry.
– The main purpose of the PFC control board is to provide the protection when
abnormalities are detected on the peak current and to control and adjust the
DC output voltage.
– The DC bus voltage monitors the output capacitor voltage. The center tap
monitors voltage across one capacitor whereas the DC bus monitors voltage
across the output cap. The main function of the center tap sensing is to ensure
that the voltage across is balanced.
– The function of the dead time circuit is to make sure that the gates will not be
turned on at the same time. It allows certain delays to prevent a short circuit.
– The triangle wave generator function acts as a reference signal, which
compares the IMON signal, which eventually determines the PWM gate duty
cycle. This is a triangle waveform with a frequency of 33 kHz.
– The IPEAK_fault signal (peak current latch signal) will go into the inhibit logic
circuitry. In normal mode, IPEAK_latched and OC_latched must always stay
high whereas the Inhibit_R,Y,B depends on the Inverter_ON_R,Y,B to decide
whether it needs to turn the gate drive on or off. If the Inhibit_R,Y,B signal goes
low, the microprocessor will shut down the gate immediately.
