2020. 2. 16. 03:52ㆍ카테고리 없음
Motor DrivingThe most common type of motor you might come across in hobbyist circles for low power applications is the 3V DC motor shown below. This kind of motor is optimized for low voltage operation from two 1.5V cells.And running it is as simple as connecting it to two cells – the motor fires up instantly and runs as long as the batteries are connected. While this kind of setup is good for ‘static’ applications like a miniature windmill or fan, when it comes to a ‘dynamic’ application like, more precision is needed – in the form of and torque control.It’s obvious that decreasing the voltage across the motor decreases the speed and a dead battery results in a slow motor but if the motor is powered from a rail common to more than one device, a proper driving circuit is needed.This can even be in the form of a – the voltage across the motor can be varied to increase or decrease speed. If more current is needed, this circuit can be built discreetly with a few bipolar. The biggest drawback with this kind of setup is the efficiency – just like with any other load, the transistor dissipates all the unwanted power.The solution to this problem is a method called.
Here, the motor is driven by a square wave with an adjustable duty cycle (the ratio of on time to the period of the signal). The total power delivered is proportional to the duty cycle. In other words, the motor is powered for a small fraction of the time period – so over time the average power to the motor is low. With a 0% duty cycle, the motor is off (no current flowing); with a duty cycle of 50% the motor runs at half power (half the current draw) and 100% represents full power at maximum current draw.This is implemented by connecting the motor high side and driving it with an N-channel MOSFET, which is driven again by a PWM signal.This has some interesting implications – a 3V motor can be driven using a 12V supply using a low duty cycle since the motor sees only the average voltage.
With careful design, this eliminates the need for a separate motor power supply.What if we need to reverse the direction of the motor? This is usually done by switching the motor terminals, but this can be done electrically.One option could be to use another and a negative supply to switch directions. This requires one terminal of the motor to be permanently grounded and the other connected to either the positive or negative supply. Here, the MOSFETs act like an SPDT switch.However, a more elegant solution exists.The H-Bridge Motor Driver CircuitThis circuit is called H-bridge because the MOSFETs form the two vertical strokes and the motor forms the horizontal stroke of the alphabet ‘H’. It is the simple and elegant solution to all motor driving problems.
The direction can be changed easily and the speed can be controlled.In an H-bridge configuration, only the diagonally opposite pairs of MOSFETs are activated to control the direction, like shown in the below figure:When activating one pair of (diagonally opposite) MOSFETs, the motor sees current flow in one direction and when the other pair is activated, the current through the motor reverses direction.The MOSFETs can be left on for full power or PWM-ed for power regulation or turned off to let the motor stop. Activating both bottom and top MOSFETs (but never together) brakes the motor.Another way to implement, which we discussed in previous tutorial.Components Required. Nice idea for learning H-bridge circuits, your logic is right on; some major things you may have missed.Shoot thru occurs when both the upper and lower MOSFETs turn on at the same time. With your circuit as shown this will happen at the transition where one is turning on the is turning off. Note: the higher the VCC the worse it will get, causing excess heating of the MOSFETs and eventually failure to occur.Examine the Vgs of both upper and lower devices over the full gate voltage swing. You will fine you have them both in the partially enhancement mode where both are trying to conduct.
The slower the rise and fall time of the gate the worse this will be. This will create some huge current spikes.What is shown on the breadboard will work because of the limiting impedance of the interconnections. If this is built for say 20A 40V you will be blowing MOSFETs. The primary failure will be either shoot through or VGS over voltage.The Vgs of both devices is +- 20V which is way short of the max 40V suggested. At approximately 3V Vgs both devices are turning on.
Gate Driver Circuit For Mosfet Pdf Download
There is also the Miller Capacitor effect which will also slow down the switching time however the TC4427 (4.5 - 18V) is a good choice to solve this problem.Do continue with this, you have made a great start.Gil.