H-bridge constant current drive for brush DC motor PWM drive method

There are several PWM driving methods with brush DC motor. This article will introduce H-bridge constant current drives with brush DC motor PWM drive. Use the PWM output mode to drive the brush DC motor: H bridge constant current drive This is an example of constant current drive circuit with brush DC motor PWM. This is an ordinary driver circuit that can use the built-in comparator on / OFF control, ie PWM control. The resistance RS of the GND side (RNF pin) connected to the power transistor (MOSFET) is used to detect the resistance of the current. The built-in comparator compares the voltage generated by the RS to the voltage of the reference voltage set pin (VREF). When the RNF pin voltage exceeds the VREF voltage, the output of the comparator becomes L and the power transistor of the power supply side of the supply current is turned off. When supplying or stopping current, the ON / OFF state of the transistor is different due to working mode (eg, forward or reversing), but in any case, it will be responsible for switching current through the motor by VREF, RS, and comparators. . The shutdown time (TOFF) is set by counting the oscillator (OSC) frequency, and the current is regenerated during the shutdown period. When the setup is turned off, the turned power transistor will be turned on and supplied again. By repeating the process, the motor can be rotated by constant current control of the VREF voltage ÷ RS value peak current (IPEAK). The image is a waveform indicating the motor current, the RS current, and the RNF voltage. It should be noted that since there is no current flowing during the RS during the regenerative current flow, a large current change is generated in the RS when the current is re-supply, and a larger voltage noise may occur due to parasitic inductance, or The charging current of the parasitic capacitance of the power transistor flows and exceeds the VREF voltage. A very short blanking time (TBLNK) is required to avoid the power transistor without OFF because the voltage noise is performed. The setting of blanking time requires note not only the voltage noise caused by the current ON / OFF, but also avoids voltage noise when switching the motor rotation. The blanking time can be optimized or adjusted by the driver IC. Key points: · One method of the brush DC motor H-bridge PWM constant current drive is to use current detection resistance to detect motor currents, and compare it with the reference voltage with the reference voltage. • When driving a brush DC motor using the above method, due to a large current change in the current detecting resistor, noise voltage and malfunction may occur. • When using the above method to drive a brush DC motor, there is a method of suppressing malfunction by setting blanking time. Editor in charge: Tzh, Read more

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