SIGMATEK ST 151, Manual

Page: 29 / 48

S-DIAS STEPPER MOTOR OUTPUT STAGE ST 151
02.12.2019 Page 27
7.2 Stepper Motor Current Regulator
The current regulation for the stepper motor is influenced by the current rise and/or fall time
in the motor windings. These times are critically dependent on the supply voltage level,
inductivity and the resistance of the motor windings.
The current rise time can be influenced by the supply voltage level. The higher the supply
voltage, the faster the motor winding current rises.
The current regulator functions so that the H-bridge actively energizes the motor windings
until the value setting of the current (I
TRIP
) is reached. Afterwards, the current reduction
process (decay) is started. The current fall time in the motor windings is affected by the
decay mode.
In slow decay mode, the motor windings are shorted over the H-bridge.
The energy stored in the windings is dissipated over the internal resistance of the motor
and the H-bridge of the output stage.
In fast decay mode, the current sinks significantly faster since the windings are shorted by
reversing the polarity. The energy stored in the windings is thereby fed back to the supply.
If both variants are used during reduction of the motor current, the motor is in mixed decay
mode. In this mode, the advantages of both processes are unified. The current is first re-
duced to a threshold with fast decay and then switched to slow decay to keep the current
ripple low.