PIC18F2331/2431/4331/4431
18.6.5
COMPLEMENTARY PWM
OPERATION
FIGURE 18-16:
TYPICAL LOAD FOR
COMPLEMENTARY PWM
OUTPUTS
The Complementary mode of PWM operation is useful
to drive one or more power switches in half-bridge
configuration as shown in Figure 18-16. This inverter
topology is typical for a 3-phase induction motor,
brushless DC motor or a 3-phase Uninterruptible
Power Supply (UPS) control applications.
+V
3-Phase
Load
Each upper/lower power switch pair is fed by a
complementary PWM signal. Dead time may be
optionally inserted during device switching, where both
outputs are inactive for
a
short period (see
Section 18.7 “Dead-Time Generators”).
In Complementary mode, the duty cycle comparison
units are assigned to the PWM outputs as follows:
• PDC0 register controls PWM1/PWM0 outputs
• PDC1 register controls PWM3/PWM2 outputs
• PDC2 register controls PWM5/PWM4 outputs
• PDC3 register controls PWM7/PWM6 outputs
The Complementary mode is selected for each PWM
I/O pin pair by clearing the appropriate PMODx bit in
the PWMCON0 register. The PWM I/O pins are set to
Complementary mode by default upon all kinds of
device Resets.
PWM1/3/5/7 are the main PWMs that are controlled by
the PDCx registers and PWM0/2/4/6 are the
complemented outputs. When using the PWMs to
control the half bridge, the odd numbered PWMs can
be used to control the upper power switch and the even
numbered PWMs used for the lower switches.
DS39616D-page 190
2010 Microchip Technology Inc.
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