Transistor driven DC motor

1. Input and level conversion part:
The input signal line is introduced from DATA, pin 1 is the ground wire, and the rest are signal lines. Note that there is a 2K ohm resistor connected between pin 1 and ground. When the driver board and the microcontroller are powered separately, this resistor can provide a path for the signal current to return. When the driver board and the microcontroller share a power supply, this resistor can prevent large current from flowing into the ground wire of the microcontroller motherboard along the connection line and causing interference. In other words, it is equivalent to separating the ground wire of the driver board from the ground wire of the microcontroller to achieve "one point grounding".
The high-speed operational amplifier KF347 (TL084 can also be used) functions as a comparator, comparing the input logic signal with the 2.7V reference voltage from the indicator light and a diode, and converting it into a square wave signal with an amplitude close to the power supply voltage. The input voltage range of the KF347 cannot be close to the negative supply voltage, otherwise an error will occur. Therefore, a diode is added to the input terminal of the op amp to prevent the voltage range from overflowing. One of the two resistors at the input terminal is used to limit the current, and the other is used to pull the input terminal low when the input is left floating.
You cannot use LM339 or any other open-circuit output comparator to replace the op amp, because the high-level output impedance of the open-circuit output is above 1 kiloohm, the voltage drop is large, and the transistor of the subsequent stage will not be able to cut off.
2. Gate drive part:
The circuit composed of transistors, resistors and voltage regulator tubes at the back further amplifies the signal, drives the gate of the field effect tube and uses the gate capacitance of the field effect tube itself (about 1000pF) for delay to prevent the upper and lower parts of the H-bridge. The field effect transistors of the arms are turned on at the same time ("common mode conduction"), causing a short circuit in the power supply.
When the output terminal of the op amp is at a low level (about 1V to 2V, which cannot completely reach zero), the lower transistor is cut off and the field effect transistor is turned on. The above transistor is turned on, the field effect tube is turned off, and the output is high level. When the op amp output is at a high level (approximately VCC-(1V to 2V), not fully reaching VCC), the lower transistor is turned on and the field effect transistor is turned off. The above transistor is cut off, the field effect transistor is turned on, and the output is low level.
The above analysis is static, and the dynamic process of switching conversion is discussed below: the on-resistance of the triode is much less than 2 kiloohms, so the charge on the gate capacitance of the field effect transistor can be quickly released when the triode switches from off to on, and the field effect transistor Quick deadline. However, when the transistor switches from on to off, it takes a certain amount of time for the field effect transistor gate to charge through the 2 kiloohm resistor. Correspondingly, the speed of the field effect transistor switching from conduction to cutoff is faster than the speed of switching from cutoff to conduction. If the switching actions of the two transistors occur at the same time, this circuit can make the field effect transistors of the upper and lower arms turn off first and then turn on, eliminating the common-state conduction phenomenon.
In fact, it takes a certain amount of time for the op amp output voltage to change. During this time, the op amp output voltage is at an intermediate value between the positive and negative power supply voltages. At this time, the two transistors are turned on at the same time, and the field effect transistor is turned off at the same time. So the actual circuit is safer than this ideal situation.
The 12V Zener diode at the gate of the field effect transistor is used to prevent overvoltage breakdown of the gate of the field effect transistor. The withstand voltage of the general field effect transistor gate is 18V or 20V. If a voltage of 24V is applied directly, it will break down. Therefore, this zener diode cannot be replaced by an ordinary diode, but it can be replaced by a 2 kiloohm resistor, and the same result can be obtained. 12V divided voltage.
3. Field effect transistor output part:
There are diodes connected in reverse parallel between the source and drain inside the high-power field effect transistor. When connected as an H-bridge, it is equivalent to four diodes being connected in parallel at the output end to eliminate voltage spikes. Therefore, There are no external diodes here. Connecting a small capacitor in parallel with the output end (between out1 and out2) has certain benefits in reducing the peak voltage generated by the motor, but it has the side effect of generating peak current when using PWM, so the capacity should not be too large. This capacitor can be omitted when using a low-power motor. If you add this capacitor, it must be one with high withstand voltage. Ordinary ceramic capacitors may suffer from breakdown and short circuit failure.
A circuit composed of a resistor, a light-emitting diode, and a capacitor connected in parallel at the output terminal indicates the rotation direction of the motor.