H-BridgesH-bridge Circuit containing 4 switching elements + 4 catch diodes Switching elements are usually bipolar transistors or MOSFETs Catch diodes are used to prevent short circuiting

H-BridgesEsther Yan, Marta Menéndez,

Sarah Chen

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Overview● What is an H-bridge?● How does it work?● How will we use them?

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Overview● What is an H-bridge?● How does it work?● How will we use them?

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DC motor● Velocity depends on Vo,avg● Torque varies with Ia

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DC motor control● Direction

○ Chopper (Unidirectional)○ H-bridge (Bidirectional)

● Velocity○ Varying voltage○ PWM

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https://www.sunfounder.com/learn/Super_Kit_V2_for_RaspberryPi/lesson-7-how-to-drive-a-dc-motor-super-kit-for-raspberrypi.html

Chopper

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Chopper

motor

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Chopper

- one directionmotor

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Chopper

- one directionmotor

transistor

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Chopper

- one directionmotor

transistor

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H-bridge● Circuit containing 4 switching elements +

4 catch diodes○ Switching elements are usually bipolar

transistors or MOSFETs○ Catch diodes are used to prevent

short circuiting● Path of current controlled by switches

http://www.modularcircuits.com/blog/articles/h-bridge-secrets/h-bridges-the-basics/

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Potential paths and switch combinations

http://www.modularcircuits.com/blog/articles/h-bridge-secrets/h-bridges-the-basics/ 12

Incorrect path

http://www.modularcircuits.com/blog/articles/h-bridge-secrets/h-bridges-the-basics/ 13

Building your own H-bridge● Make sure you never close both transistors on one side● Use catch diodes (or something similar) to prevent short circuiting

○ There may be delays in switching times● Also consider

○ Internal resistance of transistor○ Delay time of transistors (high → low and low → high)

* If you use pre-built H-bridges, you don’t have to worry about these things

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Why use an H-bridge?● Easiest way to control DC motor direction● Most motors require more power than a microcontroller can

supply○ H-bridge uses external power source

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Overview● What is an H-bridge?● How does it work?● How will we use them?

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Using the H-BridgeSimplify Circuit:

http://www.ti.com/lit/ds/symlink/sn754410.pdf17

VCC

Using the H-Bridge● Enable Signal● Direction● Sensing Pin● Transistors turn-on resistance

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VCC

Using the H-Bridge● Enable Signal (PWM) : controls velocity● Direction

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12V

Using the H-Bridge● Sensing Pin

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Using the H-Bridge● Transistors turn-on resistance

Vcc1=5V, Vcc2=24V

http://www.ti.com/lit/ds/symlink/sn754410.pdf 21

Using the H-Bridge● Transistors turn-on resistance

Vcc1=5V, Vcc2=24V

http://www.ti.com/lit/ds/symlink/sn754410.pdf 22

Using the H-Bridge● Transistors turn-on resistance

Vcc1=5V, Vcc2=24V

http://www.ti.com/lit/ds/symlink/sn754410.pdf 23

Using the H-BridgeEx: You want 18V and 0.5A (@ 25C). Duty cycle?

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Overview● What is an H-bridge?● How does it work?● How will we use them?

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Types● 2 types of H-bridges available in the 373 lab● Both have 2 H-bridges

○ SN754410 - Quadruple half-h bridge driver○ L298 - Dual full-bridge driver

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VCC VCC

SN754410 Pin Layout

http://www.ti.com/lit/ds/symlink/sn754410.pdf 27

L298 Pin Layout

https://www.sparkfun.com/datasheets/Robotics/L298_H_Bridge.pdf 28

L298 Pin Functions

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SN754410 Timing Diagram

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L298 Timing Delays

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Things to consider when choosing an H-bridge● Needed input voltage for motor - determines motor speed● Needed input current for motor - determines torque provided by

motor● May need heat sink for high power

http://www.coolingsource.com/heatsinks/

Characteristic L298 SN754410

Power Supply Up to 46V 4.6-36V

Logic Supply Voltage 5V (typical), 7V (max) (Vss) 5V (Vcc)

Peak Output Current 3A 2A

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Comparisons

Applications

AC Current

2-way motors

http://ieeexplore.ieee.org/document/6556324/

Regenerative Energy

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http://ieeexplore.ieee.org/document/6556324/http://ieeexplore.ieee.org/document/6556324/

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Questions?