CURRENT OR VOLTAGE MODE SELECTIONS
Jumpers E2, E4, E6, and E8 on the board determine whether amplifiers 1, 2, 3, and 4 respectively,
are in voltage mode or current mode. In voltage mode (2-3 connected), the output voltage to the
motor is directly proportional to the input voltage, regardless of the present current level through
the motor or actuator. In current (transconductance) mode (1-2 connected), the amplifier outputs
a current which is proportional to the input voltage, forcing whatever output voltage is required to
achieve that current.
In general, driving a motor in current mode provides a higher performance voltage mode,
particularly in high-bandwidth applications. This is because the current loop overcomes the lag
introduced by the inductance of the motor. However, this inductance can provide damping that
aids in stability (especially at low bandwidth), so the current mode requires higher derivative gain
(Ix31) within PMAC to achieve the same stability as voltage mode. Hydraulic valves are
normally driven in current mode.
If in current mode, jumpers E1, E3, E5, and E7 determine the ratio of output current to input
voltage (and so the maximum current) for amplifiers 1, 2, 3, and 4 respectively. A jumper
connecting pins 1 and 2 provides 200 mA/V (2A max); A jumper connecting pins 2 and 3
provides 20 mA/V (200mA max); no jumper provides 10 mA/V (100 mA max). If any amplifier
is put in voltage mode, the odd-numbered jumper for that amplifier must connect pins 1 and 2.
Note
If the amplifier is driving a DC motor at high speeds, the current supply to the
motor may be reduced if the back e.m.f. Voltage of the motor is sufficiently large
(refer to the motor manufacture's data sheet).