Cheap H Bridge Driver
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H-Bridge Motor Driver 1A - SN754410 Faster, cheaper, smaller, better, right? The SN754410 Quad Half H-Bridge is just that. Capable of driving high voltage motors using TTL 5V logic levels, the SN754410 can drive 4.5V up to 36V at 1A continuous output current! For even higher current applications, it is possible to physically stack two devices on top of each other to get almost 2 A of drive current.
The SN754410 is a quad half H-bridge IC. This allows the chip to either control 4 motors in one direction using the 4 half H-bridges or to control 2 motors in both directions using a full H-bridge for each motor.
H Bridge Driver Circuit
The following shows the connections for controlling 2 motors in either direction using 2 full H-bridges. Pin Name H-Bridge Function Notes 1 1,2EN Motor 1 Enable Setting this pint o 0V (LOW) will turn off the motor, setting it to 5V (HIGH) will enable the motor. Connect this pin to the 5V supply, or use as an emergency shutoff. 2 1A Motor 1 Forward Set this pin to 5V (HIGH) to turn Motor1 in one direction. Motor Speed can be controlled by using PWM into this pin 3 1Y Motor 1 Power Connect to one pin of Motor1 4 Ground Ground Connect to ground - required for heat sinking 5 Ground Ground Connect to ground - required for heat sinking 6 2Y Motor 1 Power Connect to other pin of Motor1 7 2A Motor 1 Reverse Set this pin to 5V (HIGH) to turn Motor1 in the opposite direction. Motor Speed can be controlled by using PWM into this pin 8 VCC2 Motor Power Source Positive power source for your motors. Connect to battery - max 36V) 9 3,4EN Motor 2 Enable Setting this pint o 0V (LOW) will turn off the motor, setting it to 5V (HIGH) will enable the motor.
Connect this pin to the 5V supply, or use as an emergency shutoff. 10 3A Motor 2 Forward Set this pin to 5V (HIGH) to turn Motor2 in one direction. Motor Speed can be controlled by using PWM into this pin 11 3Y Motor 2 Power Connect to one pin of Motor2 12 Ground Ground Connect to ground - required for heat sinking 13 Ground Ground Connect to ground - required for heat sinking 14 4Y Motor 2 Power Connect to other pin of Motor2 15 4A Motor 2 Reverse Set this pin to 5V (HIGH) to turn Motor2 in the opposite direction. Motor Speed can be controlled by using PWM into this pin 16 VCC1 IC Logic Power Regulated +5V (VCC / VDD) Documents.
The H-Bridge is a circuit which can drive a DC motor in forward and reverse. The motor direction is changed by switching the polarity of the voltage in order to turn the motor one way or the other. This is easily demonstrated by applying a 9-volt battery to the leads of a small motor and then switching the terminals to change directions. The H-Bridge is given it's name based on the basic circuit which demonstrates it's operation. The circuit consists of four switches which complete the circuit when applied in pairs. When switches S1 and S4 are closed the motor gets power and spins.
H Bridge Driver
When S2 and S3 are closed the motor gets power and spins in the other direction. Note that S1 and S2 or S3 and S4 should never be closed together in order to avoid a short circuit. Obviously physical switches are impractical since no one is going sit there flipping switches in pairs to get their robot to move forward or in reverse. That's where the transistors comes in. A transistor acts as a solid state switch that closes when a small current is applied to it's base. Because only a small current is required to activate a transistor we are able to complete one half of the circuit with a single signal.
That's enough theory to get started so let's start building. The next step is to set up the transistors. Recall in the theory section that we need four switches to build an H-Bridge, so we'll be using all four transistors here. We're also limited to the layout of a breadboard so the actual circuit will not resemble the letter H. Let's take a quick look at a transistor to understand the current flow.
There are three legs on each transistor known as the collector, base, and emitter. Not all transistors share the same order so be sure to consult a datasheet if you're not using one of the part numbers mentioned in step one. When a small current is applied to the base, another larger current is allowed to flow from collector to emitter. That's important so I'll say it again.
A transistor allows a small current to control a larger current. In this case the emitter should always be connected to ground. Note that the current flow is represented by a small arrow in the figure below. Now we're going to line up the transistors on the bottom half of the breadboard, flipping the orientation for every other transistor. Each pair of adjacent transistors will serve as one half of the H-Bridge.
An adequate space needs to be left in the middle in order to fit some jumpers and eventually the motor leads. Next we'll connect the transistors' collector and emitter to the positive and negative power buses respectively. Lastly we'll add the jumpers which will connect to the motor leads.
The transistors are now ready to pass a current when the base is activated. We need to apply a small current to each of the transistors in pairs. First we need to hook up a resistor to each transistor's base. Next we'll connect each set of resistors to a common point in preparation to connect a switch. Then we'll add the two switches which also connect to the positive bus. These switches will activate one half of the H-Bridge at a time. And finally we hook up the motor.
Connect your battery and test your circuit. The motor should spin one direction when one button is pushed and the opposite direction when the other button is pushed.
The two buttons should not be activated at the same time. Okay, so you have a shiny new H-Bridge on a breadboard. The important thing is that you understand how a basic H-Bridge works and that the essentials are the same no matter how much power you're pushing. Here are a few tips to take it a step further in order to support larger motors and more power.
You can use Pulse Width Modulation (PWM) in place of the two switches to control the speed of the motor. This is easy when you have a microcontroller at your disposal and can also be accomplished with a 555 or 556 timer IC and a few passives without too much trouble.
The key to supporting higher power motors is higher power transistors. Medium power transistors and Power MOSFETs in TO-220 cases can handle significantly more power than the low power TO-92 transistors we're using here. Proper heatsinks will also increase the capacity. Most H-Bridges are built using both NPN and PNP transistors in order to prevent short circuits and optimize current flow. We used only NPN here to simplify the circuit. Flyback diodes are usually used in higher power H-Bridges to protect the rest of the circuit from dangerous voltages that are produced by the motor's coils when the power is disconected. These diodes are applied across the transistor in the direction of current flow and resist these harmful EMF back voltages.
The TIP 102 and TIP 107 are a pair of complementary power transistors that have built in flyback diodes. The TIP 122/127 and 142/147 are similar pairs of power transistors. That should be enough to put you in the right direction if you want to keep you going.