Designed DC motor drive circuit
In the design of the DC motor drive circuit, the main consideration the following points:
1. Function:? Unidirectional or bidirectional motor is rotated one way or need for motor drive speed, as long as a power transistor or a FET or a relay can be directly driven by the motor, when the motor required bidirectional rotation,? It may be used by the H-bridge circuit consisting of four power elements or use a double pole double throw relay. If no speed, can simply use the relay; speed if desired, can be used transistor, FET, the switching element implemented PWM (pulse width modulation) speed.
2. Performance: For the motor driving circuit PWM speed control, mainly in the following performance indicators.
1) the output current and voltage ranges, which determines how much power circuit can drive a motor.
2) the efficiency, efficient means not only save power, heat generation driving circuit will be reduced. To improve the efficiency of the circuit, the switching state can ensure that the power device is turned on and preventing common mode (H-bridge or a push-pull circuit problem may arise, i.e. two power devices is turned on while the power supply short circuit) from the start.
Effect 3) on the control input. The power circuit input terminal thereof should be good signal isolation, prevent high voltage and high current into the control circuit, which may be a high input impedance or the photocoupler achieve isolation.
4) the impact power. Common conduction may cause a momentary voltage drop caused by a high frequency power supply pollution; large current may cause the floating ground potential.
5) reliability. The motor drive circuit should do as much as possible, regardless of the control signal plus, what kind of passive load, the circuit is safe.
Second, the transistor - the resistance for the gate driver
1. Enter the level conversion section:
Introduced by the input signal line DATA, 1 pin is ground, the rest is a signal line. Note that pin 1 is connected to a 2K ohm resistor. When the driver board and the microcontroller are powered, the resistor may provide a signal current return path. When the driver board and the power share a single chip, this resistor can be prevented from flowing into the large current board microcontroller interfere along the ground connection. Or, corresponding to the ground and the ground plate spaced apart from the drive microcontroller, enabling "ground."
KF347 high-speed operational amplifier (TL084 can also be used) the role of a comparator, the input logic signal with a reference voltage of 2.7V from the LED and a diode comparison, converted into a square wave signal access to the power supply voltage amplitude. Input voltage range KF347 is not close to the negative power supply voltage, or an error occurs. Thus the op amp input voltage range increases the diodes prevent overflow. Two input terminals of a resistor for current limiting, for a floating input on the input terminal is pulled low.
Can not replace a LM339 operational amplifier or any other comparator output is open, because the high level state of the output open output impedance than 1 kilohm, the larger the pressure drop, the transistor can not be turned off later stage.
2. The gate driving part:
Back transistor and a resistor, a circuit consisting of a further regulator amplified signal, drives the gate of the FET and the FET itself using the delay gate capacitance (approximately 1000pF), preventing the arms of the H bridge FET simultaneously turned on ( "total on-state") short the power supply.
When the op amp output is low (about 1V to 2V, not fully reach zero), following the transistor is turned off, the FET is turned on. The above transistor is turned on, the FET is turned off, the output is high. When the amplifier output is high (about VCC- (1V to 2V), does not fully meet the VCC), the following transistor turns on, the FET is turned off. The above transistor is turned off, the FET is turned on, the output is low.
The above analysis is static, dynamic process of switching are discussed below: The transistor resistance is much less than 2 kohms, so the transistor is turned off when the conversion to quickly release the charge FET on the gate capacitance FET rapidly closing. However, the transistor is turned on by the conversion to the gate of the FET 2 via the charging kilohm resistor it will take some time off. Accordingly, the conversion by the FET is turned off to speed faster than the turned off switching to speed. If the two transistors of the switching operation occurs simultaneously, this circuit allows the upper and lower arms of the field effect tube break before make, to eliminate the phenomenon of total on-state.
In practice, the op amp output voltage change takes time, during which time the operational amplifier output voltage is an intermediate value between the positive and negative supply voltage. While two transistors are simultaneously turned OFF while the FET on. So the actual circuit even safer than some of this ideal.
The gate of FET 12V Zener diode for preventing the gate of the FET overvoltage breakdown. Usually FET gate voltage is 18V or 20V, 24V voltage will be coupled directly to the breakdown, so that the Zener diode can not be used in place of conventional diodes, but instead of 2,000 ohms with the resistor, the same can be obtained partial pressure of 12V.
3. The FET output section:
Power FET inner tube in reverse parallel between the source and drain diode, when connected to the use of the H-bridge, corresponding to the output terminal has four diodes connected in parallel with the elimination of voltage spikes, and therefore there is no external diode. A small capacitance in parallel with an output terminal (OUT2 of the and between out1) generated by the motor has to reduce voltage spikes certain advantages, but cause side effects in the peak current using the PWM, so that the capacity should not be too large. When using low-power motors of this capacitor can be omitted. If you add this capacitor, it must use a high breakdown voltage, ordinary ceramic capacitor failure could short-circuit breakdown may occur.
Parallel output of the light emitting diode and a resistor, capacitor circuit consisting of indicating motor rotation direction.
4. Specifications:
Supply voltage 15 ~ 30 V, the maximum output current continuous 5A / each motor, a short time (10 seconds) can be achieved 10A, PWM frequencies up to 30KHz can be used (generally of 1 to 10KHz). The circuit board comprises four separate logic, an output terminal connected to twenty-two H-bridge power amplifying unit can be directly controlled by the microcontroller. And bidirectional rotation speed of the motor.
5. wiring:
Large current lines to try to short and thick, and try to avoid through vias must pass through the hole, then put through a number of holes bigger (> 1mm) and vias made small circle on the pad, for use in welding solder fill, or it may be blown. In addition, if a regulator, FET source should be kept as short and thick wires for power and ground, otherwise at high currents, the voltage drop across this might lead through forward-biased and the regulator conducting transistor to burn. In the beginning of the design, the source of the NMOS transistor is to have access between a 0.15 ohm resistor used to detect current, the resistance has become continuously burned culprit board. Of course, if the resistance regulator into the problem does not exist.
Third, a simple low-voltage drive circuit driving a gate
Usually the maximum gate-source voltage of the power MOSFET is approximately 20V, 24V so to ensure that the application can not exceed the gate-source voltage of 20V, the increased complexity of the circuit. However, the application of voltage 12V or less, the circuit can be greatly simplified.
上图就是一个12V驱动桥的一边，上面电路的三极管部分被两个二极管和两个电阻代替。(注意，跟上图逻辑是反的)由于场效应管栅极电容的存在，通过R3，R4向栅极电容充电使场效应管延缓导通;而通过二极管直接将栅极电容放电使场效应管立即截止，从而避免了共态导通。
这个电路要求在IN端输入的是边缘陡峭的方波脉冲，因此控制信号从单片机或者其他开路输出的设备接入后，要经过施密特触发器(比如555)或者推挽输出的高速比较器才能接到IN端。如果输入边缘过缓，二极管延时电路也就失去了作用。
R3，R4的选取与IN信号边沿升降速度有关，信号边缘越陡峭，R3，R4可以选的越小，开关速度也就可以做的越快。Robocon比赛使用的升压电路(原理相似)中，IN前用的是555
最后给大家分享一个关于电机驱动的资料可以参考使用