Principle analysis of stepper motor constant voltage drive circuit
First, the use of external resistance drive:
When the winding of the stepping motor uses a thick wire, the value of the coil resistance Rw is small, as shown in the figure below. In each phase coil, an external resistor R is connected in series in order to limit the current flowing through the winding to be less than the rated current I. To limit the current flowing through the winding, two methods of reducing the power supply voltage and the external resistor R in series can be used.
Assume that the coil inductor of the stepper motor is L, the winding resistance is Rw, and the electrical time constant is τ. When the resistor R is applied, the electrical time constant is as follows:
The external resistor makes the time constant τ smaller and the current rises faster, so that the driving pulse frequency of the stepping motor becomes faster. The figure above shows the comparison of the current rising curve with no external resistor and the external resistor R. At time t1, there is no When the resistor R is used, the current only rises to I1. When the resistor R is used, the current rises to I2, so that the torque at high speed is greatly improved; the disadvantage is that the copper loss is increased. Constant current chopper driving has been used in recent years, and the constant voltage method is not commonly used.
Second, no external resistance drive
The stepping motor only needs to operate at low speed, and the coil is directly driven by the power supply voltage plus the power semiconductor for constant voltage. At this time, the radius of the winding wire of the stepping motor is finer, the number of turns is larger, and the resistance value is larger. . This method is mostly used for small current driving.
Third, voltage drive
When the stepping motor is driven, the applied voltage is used. For example, when the driving voltage is 24V, when the position is reached and the rotation is stopped, and the voltage is switched to 5v, the total loss power is decreased. This is the two voltage control method. It is also possible to add a certain current to maintain the accuracy of positioning according to the type of load. Another method is to drive at a low voltage with a low voltage, and at a high speed, that is, to switch to a high voltage drive at a certain speed or higher.