300 SERIES USER GUIDE
30
PWM Operation
PWM signals are of two distinct types that we refer to as 0-100% and 50%.
The 0-100% type uses two signals: one to control the amplitude and the other to control
direction. The 50% type uses only one signal that is at 50% duty cycle for a zero output
from the amplifier, and changes to 0, or 100% for full output in the positive, or negative
directions.
The table of jumper setting shows how to setup the MB4 card for the different modes.
Connections for the 0-100% type of inputs are shown below:
PWM PULSE
PWM DIR
POS
NEG
0-100%
P2-9
P2-12
MB4
+
AMP
JP-104 = 1-2
2C
2A
Eurocard
+
AMP
JP-104 = 1-2
Fig. 16
The PWM signals should be +5V CMOS compatible, and the 0-100% signal should be
normally LO, going HI for 0-100% duty cycle to enable the amplifier.
The DIR signal will cause an immediate change in the polarity of the voltage going to the
amplifier. Control systems will usually change the polarity of this signal when the 0-
100% signal is at 0% to eliminate jerkiness in the motor.
Here are the connections for a 50% type of PWM system:
P2-12
MB4
+
AMP
JP-104 = 2-3
PWM SIGNAL
ZERO
10%
90%
OUTPUT
FOR
of
2A
Eurocard
+
AMP
JP-104 = 2-3
Fig. 17
Note that a 50% duty cycle signal now produces zero current at the output of the
amplifier. Changing from 50-0% duty cycle will increase the current in the positive
direction, and going from 50-100% increases the current from 0-100% in the negative
direction.
PWM inputs can be used in either the current or voltage modes of operation.
In current-mode, the feedback trimpot may have to be adjusted to increase the gain of
the amplifier because of the lower (±2.5V) signals that now control the amplifier.
In voltage mode, adjust the voltage gain based on a reference voltage of 2.5V (see
previous section on voltage-mode and gain-setting).
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