Abstract: The DC motor control system with TL494 as the core is introduced, and PWM technology is used. The H-bridge DC motor control system based on TL494 can simplify the circuit structure, strong driving capacity, low power consumption and convenient control, and stable performance.
Since the DC motor has good starting, braking and speed control, it has been widely used in various aspects such as industrial and aerospace. With the development of power electronics, pulse width modulation (PWM) speed control technology has become a common speed regulation method for DC motors, with high speed regulation accuracy, fast response speed, low speed range and low power consumption. The H-bridge circuit is used as the power drive circuit of the drive, and the four quadrant operation of the DC motor can be easily achieved, including forward rotation, forward braking, reverse, reverse braking, has been widely used in the modern DC motor servo system. .
1, DC motor PWM speed control principle
It is well known that the DC motor speed formula is:
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DC motor speed control can be divided into excitation control method and armature voltage control method. Excitation control methods are very useful, and most applications use the armature voltage control method. With the advancement of power electronic technology, the armature voltage can be achieved by a variety of ways, wherein the pulse width modulation (PWM) is commonly used to change the speed control method of the armature voltage. The method is to adjust the armature voltage U of the electric motor to adjust the DC motor by changing the ratio of the electrical electrical electrical travel and the power generation period (ie, the duty ratio), thereby controlling the motor speed.
The core component of the PWM is a voltage-pulse width converter that modulates the pulse width according to the control command signal to control the on-time communication time of the high power transistor with the width of the command change, and realizes two Control of end voltage.
The voltage-pulse width converter structure is composed of a triangular wave generator, an adder, and a comparator. Triangular wave generator is used to generate a triangular wave UT of a certain frequency, which adds a signal UI + UT with the input command signal UT, and then feeds to the comparator. The comparator is an operational amplifier working in an open-loop state with extremely high open loop gain and limiting switching characteristics. The weak changes in the signal difference between the two inputs will cause the comparator to output the corresponding switch signal. In general, the comparator is negative input, and the signal UI + UT is input from the positive terminal. When UI + UT "0, the comparator outputs a full level of positive level; when UI + UT" 0, the comparator outputs a full-amplified negative level.
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Figure 1 Voltage-pulse width comparator
The modulation process for the voltage-pulse width converter to the signal waveform is shown in Figure 2. Due to the limit characteristics of the comparator, the output signal US is unchanged, but the pulse width varies with the change of the UI, the frequency of the US is determined by the frequency of the triangular wave.
When the command signal UI = 0, the output signal US is a rectangular pulse equal to the positive and negative pulse width. When UI "0, the positive pulse width of the US is greater than the negative pulse width. When UI "0, the positive pulse width of the US is smaller than the negative pulse width. When UI "UTPP / 2 (UTPP is the peak of triangular waves), US is a positive DC signal; when UI" UTPP / 2, US is a negative DC signal.
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Figure 2PWM pulse width modulation waveform, reading full text, technology area
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