AN1965 Freescale Semiconductor / Motorola, AN1965 Datasheet - Page 7

• Manufacturer Part Number: AN1965
• Description: Design of Indirect Power Using the 56F800/E
• Manufacturer: Freescale Semiconductor / Motorola

Initialization - Initializes the on-chip peripherals, power line voltage and frequency detection
Input capture event handler - After initialization, the PFC software waits for the power lines’
zero-crossing signal, used for synchronization of the PFC algorithm with the line voltage, and sets the
time_base for the milestone table.
Output compare event handler - The main task of the function is to define the input current
waveform milestones, or time intervals, forming the input current waveform. During each step, the
next output comparison is programmed and the proper input current level is set by programming the
PWM duty cycle. Upon reaching a milestone of one of the input current waveform, the output DC bus
voltage (V
voltage is set to 385V DC. The output of the voltage regulator represents the amplitude of the input
current. The calculated input current is limited to the maximum input value and zeroed if negative.
New values representing the higher and lower level of the input current waveform are calculated, and
illustrated in
synchronization signal.
Analog-to-Digital Conversion routine - The routine reads the output DCBus voltage, required by the
PFC algorithm to sense the output voltage on a regular basis with a minimum period of 10ms. The
ADC channel can be shared with other applications running on the hybrid controller.
The PWM Signal is generated using Quad Timer D, Channel 1, in cascade with Channel 0. The output
of Channel 1 is connected to output pin TD1. Placing the timers in cascade mode is necessary to
generate a sufficient PWM frequency, and recommended to be higher than 100kHz. After filtering the
out
) is sensed and the sensed voltage is fed into the PID regulator. The nominal output
Figure
Activate inhibit
Program PWM
Read V
PID regulator
Milestone 1
3-3. When Milestone 4 is reached, the algorithm waits for the next
Figure 4-1. Indirect PFC Control Flowchart
out
Freescale Semiconductor, Inc.
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Indirect Power Factor Correction
Deactivate inhibit
Milestone 2
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Increment pointer
Select milestone
Wait for output
Wait for mains
Program PWM
zero crossing
Milestone 3
Set timer
by pointer
Initialize
compare
Start
Program PWM
Reset pointer
Milestone 4
System Design Concept
7