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Techno Linear Motion Catalog 36 Technical Information Power Supplies have the task of converting supply AC voltage into usable form.  The most common type of  power  supply  is  the  regulated  type  which  uses  transformers  or  switching  transistors  and  a  rectifying stage.  Accurate power requirements will use different filtering techniques to eliminate AC supply line ripple. Motor voltage supplies can usually be simple or even unregulated DC supplies.  Care should be taken with overvoltage  protection.    Since  a  motor  is  basically  a  generator  run  in  “reverse”,  it  generates  a  braking current when being stopped.  This current either has to be dissipated through resistors or regenerated back into  the  voltage  supply  capacitors.    Rapid  or  frequent  braking  could  overcharge  the  capacitors,  so  a mechanism for “dumping” excess current must be used to protect the power supply. Stepper Motor Drivers are supplied with the required step sequence from the stepper control card and, in turn, supplies stepper motors with current and voltage.  The function of a stepper motor driver is to drive current through the appropriate phase windings of the motor to produce a stepped motion. A unipolar driver is only able to supply current through a winding in one direction, and the voltage cannot reverse polarity.  This means that the windings are split and only half of the winding is used at a time.  A benefit  to  this  approach  is  that  the  electrical  time  constant  is  reduced  and  the  motor  will  have  a  faster response  time;    however,  there  are  significant  limitations.    To  change  rotational  direction  of  the  motor, current must be channeled to the other half of the winding in reverse polarity.  This creates mutual inductance in the unused portion of the winding, which reduces motor accuracy.  Also, there is a significant loss of torque at low speeds and the motor becomes very inefficient. A bipolar driver utilizes all of the windings simultaneously.  When reversing direction, the current can be driven out which reduces current decay and enhances motor performance.  In a bipolar drive, phase voltage switches  from  positive  to  negative  —  i.e.,  current  is  actively  forced  into  and  out  of  the  windings.    Best performance is usually attained with a four or eight lead motor wired for bipolar parallel drive due to the torque-speed curves associated with this type of arrangement. Servo Motor Amplifiers perform a very similar task to the stepper driver;  however, motion is not actuated in steps.  Servos have smooth continuous motion capabilities, and the amplifiers are designed to provide the required voltage and current to the motor winding.  Since servo motors have only two leads, the motor is reversed by reversing the polarity of the voltage across the leads.  Servo amplifiers are supplied with the current and voltage requirements, from the servo controller card, which is updated in real time via feedback. Typically, the controller supplies a 10V analog signal and the amplifier produces a current proportional to this signal.  Some of the newer amplifier/controller systems produce digital signals and skip the analog conversion.  This arangement simplifies the circuitry. 2-phase stepper driver in unipolar mode Note  that  only  half  of  each  phase  or  coil  is energized at any time.  The electronics are less expensive to manufacture but the performance is degraded. 2-phase stepper driver in bipolar mode Notethattheentirephaseisenergized,providing greater  power.    Also  note  that  the  drive electronics  have  twice  as  many  power components as in the unipolar mode. V+ 1B 1A 2A 2B 1 2 V+