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?