AN1965 Freescale Semiconductor / Motorola, AN1965 Datasheet - Page 8

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

Hardware Implementation
5.
5.1 System Outline
8
PWM signal, the analog voltage is obtained. It corresponds with the required input current, fed to the
analog comparator (the external Pulse Width Modulator) switching the MOSFET.
The control technique is based on the hysteresis current control. The system operates in continuous
conduction mode with avariable switching frequency (30--80kHz). The desired shape of the input
current is a staircase waveform. The number and size of the stairs are optimized in order to fulfill these
requirements:
•
•
To provide current waveform generation, the PFC hardware has a subsystem which detects input
voltage at the zero crossing. This subsystem is the level comparator, generating pulses when the input
voltage crosses a particular level, illustrated in
real zero-crossing position because of the comparator’s hysteresis characteristic. This shift can be
recovered by the software, so a real input voltage zero-crossing position can be resolved as the center
of the zero-crossing pulse minus the offset value.
The hardware system is designed to drive the 3-phase AC/BLDC motor. The application note
described here is a PFC application example only and does not consider motor control. PFC can be
easily integrated with any motor control application.
Software is targeted for the following devices and Evaluation Module (EVMs):
How hardware is set up depends on the EVM used.
The designed software can run only with the high voltage hardware set described in
(after rectifier)
Zero-crossing
Hardware Implementation
Input Voltage
Least complex to create a low load on the hybrid controller
Harmonic currents’ content which complies with the standard EN 61000-3-2
•
•
Signal
56F805 and 56F805EVM
56F8346 and 56F8346EVM
Figure 4-2. Zero Crossing Signal Generation
Freescale Semiconductor, Inc.
For More Information On This Product,
Indirect Power Factor Correction
Go to: www.freescale.com
Figure
4-2. The center of the pulse is shifted from a
Zero-crossing
Signal Offset
T
T
Section
5.2.