Choose an H-Bridge to Drive Your DC Motor
Pulse
Octopart Staff
May 5, 2018

Choose an H-Bridge to Drive Your DC MotorRotate electromechanical parts with an H-Bridge

I’m sure you already know how DC Motors are used to drive rotational devices such as motors, gears, or fans like those found in disc drives or robot wheels. But, before you choose your motor, consider the device you’ll operate and its requirements for your application. Take some time to resolve packaging, pin counts, connectors, and maximum power to define your design intent. Once you’ve defined your design specifications, take a look at H-Bridge circuit topology to meet your motor’s drive requirements.

The drive circuit has its share of topology solutions and here’s how to know if an H-Bridge topology is your best choice. The H-Bridge uses electromotive force to control current through the motor, allowing speed control via pulse width modulation (PWM). By knowing the parameters affecting your choice in H-Bridge topologies, you will be able to drive DC motors without encountering problems such as motor stall, excessive noise, or shoot-through currents. This article looks at what to consider when choosing an H-Bridge to drive your DC Motor and compares some of the most popular ones on the market.

DC Motor Specifications for Finding Required Drive Strength

Whether you're building a motor, gear, or a fan, you need to consider your required DC motor specifications. Begin with assessing the required drive strength. Knowing the requisite drive strength will inform your choice of motor characteristics, such as the rotational speed used for providing the force to move your device. DC motors may be rotated in one of two directions using electromotive force. You can vary its rotation by controlling current through the motor using H-Bridge circuit topology.

Good applications for a DC brushless motor driven by an H-Bridge are devices where you have need to rotate something like wheels, gears, or fans. Furthermore, the rotation might not need precision, but it does need to go forward and back. The rotational speeds required for an application with a DC brushless motor driven by an H-Bridge are somewhere in the neighborhood of 3000 to 8000 rpms.

To establish how much rotational speed is needed to drive the motor, take a look at its stall current and stall torque. Below is how to define these key parameters:

Rotational Speed: Speed, or revolution, of an object rotating around an axis is the number of turns of the object divided by time, specified as revolutions per minute (rpm), revolutions per second (rev/s), or radians per second (rad/s).

Stall Torque: The maximum torque required to prevent rotation (motor stops turning).

Stall Current: The maximum current required to prevent rotation (motor stops turning).

Exceeding the motor’s maximum ratings will cause the motor to heat up, causing irreparable damage, so you want to be sure to select a motor that is suitable for your application. Stall current is the amount of current that will cause the motor to stop working; this relates to torque. Your motor is unable to rotate past its maximum torque. Because of this, you’ll design to just under stall.

To find a selection of motors to choose from for your application, conduct a search from our main page for “dc motors.” From the results page, select “AC, DC and Servo Motors” and refine the search by clicking on “electromechanical.” There you’ll find a selection of motors to choose for your application.

Using an H-Bridge to Drive a DC Motor

An H-Bridge is a common topology used to drive rotational devices such as motors, gears, or fans. An H-Bridge circuit topology is able to drive your rotational device in two directions. You can build the H-Bridge yourself, using individual transistors and bias components or you can purchase ICs containing H-Bridge topologies. Most small DC motors require half an ampere or more of current and operate at voltages between 1.5V to 24V.

H-Bridge operates by arranging four transistors in a configuration shape similar to the letter “H,” with the device, in this case, a motor placed in the middle, similar to the figure below.

Schematic of H-Bridge topology in Altium DesignerH-Bridge topology

To drive the motor in one direction (forward), alternate transistors in the bridge are activated. To go the other direction (reverse), the opposite pair of transistors are activated. To control the speed, you need to use a pulse-width modulator and use differing pulse widths in a defined cycle. Changing percentages of the pulse widths defines the duty cycle. Varying the width, and thereby the duty cycle, of the drive signal changes the amount of current, or drive strength, through the motor. In this way, you control the speed of the motor with the H-Bridge.

The possibility of shoot-through currents demands awareness in H-Bridge topologies. The shoot-through current condition happens when transistors on the same side of the bridge turn on at the same time. Avoid shoot-through currents as much as possible because they provide a direct short through your transistors and will catastrophically damage them. If you are unsure how to provide shoot-through protection, several vendors offer ICs with H-Bridge topology that include a shoot-through protection feature. Below are a few options for families of ICs.

Selecting Drive Transistors for Your H-Bridge

There are options when considering components to drive your device, whether it’s a gear or a motor. For a small hobby DC motor, a general purpose NPN transistor, 2N2222, works well. The 2N2222 provides up to 800mA of current, enough to drive a small brushless DC motor. In this way, you can use all the motor power available.

If you’re considering using a 2N2222, a search on our website yields up to 127 choices, with pricing and packaging information for each. Use the search columns to refine your parameters of interest.

Product description screenshot from Octopart2N2222 transistor selection, filtered on price from lease expensive

Another option is to use an H-Bridge drive IC. This option can be useful if you have more than one rotational device to operate. In addition, using an IC provides integrated features such as ESD protection, high-noise-immunity inputs, output clamp diodes for inductive transient suppression, and protections from shoot-through currents.

Some commonly-used ICs of this type, with varying drive current capabilities, include the following:

L293 series: The L293 and L293D devices are quadruple high-current half-H drivers. The L293 is designed to provide bidirectional drive currents of up to 1A at voltages from 4.5V to 36V. The L293D is designed to provide bidirectional drive currents of up to 600mA at voltages from 4.5V to 36V. Both devices are designed to drive inductive loads such as relays, solenoids, DC and bipolar stepping motors, as well as other high-current/high-voltage loads in positive-supply applications.

L298P013TR: The L298 is a 4A integrated monolithic circuit in a 15-lead multiwatt and PowerSO20 package. It is a high voltage, high current dual full-bridge driver designed to accept standard TTL logic levels and drive inductive loads such as relays, solenoids, DC and stepping motors. Two enable inputs are provided to enable or disable the device independently of the input signals. The emitters of the lower transistors of each bridge are connected together and the corresponding external terminal can be used for the connection of an external sensing resistor. An additional supply input is provided so that the logic works at a lower voltage.

LMD18200T/NOPB: The LMD 18200 is a 3A H-Bridge designed for motion control applications. The device is built using a multi-technology process which combines bipolar and CMOS control circuitry with DMOS power devices on the same monolithic structure. Ideal for driving DC and stepper motors, the LMD18200 accommodates peak output currents up to 6A. An innovative circuit which facilitates low-loss sensing of the output current has been implemented.

Each of the above ICs come in several package types. For solderless breadboarding, you can find DIP packages which are easily pressed into the connection holes of the breadboard. Or if you are fabricating boards for either prototyping or production, where real estate is scarce, you can find surface mount packaging styles. Take some time to use the search features within each column of Octopart to select for your needs.

hbridge3Search results for half and full bridge ICs in L293 family

It is helpful to have all available parts in one place when looking for specific options to make your H-Bridge. Before making any purchases, you'll want to decide whether you plan to select individual transistors or whether you'll choose a drive IC. Here are the benefits of each option:

  • Individual Transistors: Individual transistors are good for prototyping and experimentation. Arranging them onto a solderless breadboard offers opportunities to evaluate circuit performance, using bench tools such as an oscilloscope, to observe each part’s behavior.

  • Drive IC: If you are designing for production, where cost, PCB real estate, and sophisticated features are desirable, an IC is a better bet. IC vendors build extra protections and design features into their parts, saving development time and money.

Once you’ve identified the drive current you’ll need, along with the power available to you within your design, use Octopart’s search engine to narrow your search.

  • Power Availability: Be sure to have the power requirements of the part you are driving, whether it is a motor, fan, or some other moving part. You will also need to know its power requirements, in terms of current, for providing rotational torque.

With all the necessary information available and an immense selection of parts to choose from, Octopart is sure to be able to better equip you for your choice of H-Bridge topology, DC motor, or any part you need for your designs. If you have any comments or suggestions on part selection, drop us a note in our Slack chat room or in comments below. Check out other series of how to select a capacitor, resistor, inductor, connector, IC packages, and MCUs.

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