Electronics- H-Bridges and DC Motorsdenethor.wlu.ca/pc320/lectures/hbridgebeam.pdf · Electronics H-Bridges and DC Motors Terry Sturtevant Wilfrid Laurier University April 22, 2019

DC motor operationH-Bridge

Other considerations

ElectronicsH-Bridges and DC Motors

Terry Sturtevant

Wilfrid Laurier University

April 22, 2019

Terry Sturtevant Electronics H-Bridges and DC Motors


Other considerationsPermanent Magnet DC Motor (PMDC)

DC motor

PMDC (Permanent Magnet DC)uses permanent fixed magnetsarmature on shaft has electromagnetcommutator on shaft reverses current direction every halfrotationspeed controlled by currentdirection controlled by polaritycontinuous motion




DC motor

PMDC (Permanent Magnet DC)

uses permanent fixed magnetsarmature on shaft has electromagnetcommutator on shaft reverses current direction every halfrotationspeed controlled by currentdirection controlled by polaritycontinuous motion




DC motor

PMDC (Permanent Magnet DC)uses permanent fixed magnets

armature on shaft has electromagnetcommutator on shaft reverses current direction every halfrotationspeed controlled by currentdirection controlled by polaritycontinuous motion




DC motor

PMDC (Permanent Magnet DC)uses permanent fixed magnetsarmature on shaft has electromagnet

commutator on shaft reverses current direction every halfrotationspeed controlled by currentdirection controlled by polaritycontinuous motion




DC motor

PMDC (Permanent Magnet DC)uses permanent fixed magnetsarmature on shaft has electromagnetcommutator on shaft reverses current direction every halfrotation

speed controlled by currentdirection controlled by polaritycontinuous motion




DC motor

PMDC (Permanent Magnet DC)uses permanent fixed magnetsarmature on shaft has electromagnetcommutator on shaft reverses current direction every halfrotationspeed controlled by current

direction controlled by polaritycontinuous motion




DC motor

PMDC (Permanent Magnet DC)uses permanent fixed magnetsarmature on shaft has electromagnetcommutator on shaft reverses current direction every halfrotationspeed controlled by currentdirection controlled by polarity

continuous motion




DC motor

PMDC (Permanent Magnet DC)uses permanent fixed magnetsarmature on shaft has electromagnetcommutator on shaft reverses current direction every halfrotationspeed controlled by currentdirection controlled by polaritycontinuous motion




Permanent magnet DC motor
























TransistorsMOSFETBJT

H-Bridge

Allows a DC motor to run in either direction with a singlesupplyuses four transistorseither BJTs or FETs can be usedonly two transistors are “on” at a time





H-Bridge

Allows a DC motor to run in either direction with a singlesupply

uses four transistorseither BJTs or FETs can be usedonly two transistors are “on” at a time





H-Bridge

Allows a DC motor to run in either direction with a singlesupplyuses four transistors

either BJTs or FETs can be usedonly two transistors are “on” at a time





H-Bridge

Allows a DC motor to run in either direction with a singlesupplyuses four transistorseither BJTs or FETs can be used

only two transistors are “on” at a time





H-Bridge

Allows a DC motor to run in either direction with a singlesupplyuses four transistorseither BJTs or FETs can be usedonly two transistors are “on” at a time





Transistors

There are several types of transistor; each is a three terminaldevice.The most common types of transistors are BJTs and FETs.Transistors are often used in voltage dividers to act as variableresistors.





Transistors

There are several types of transistor; each is a three terminaldevice.

The most common types of transistors are BJTs and FETs.Transistors are often used in voltage dividers to act as variableresistors.





Transistors

There are several types of transistor; each is a three terminaldevice.The most common types of transistors are BJTs and FETs.

Transistors are often used in voltage dividers to act as variableresistors.





Transistors

There are several types of transistor; each is a three terminaldevice.The most common types of transistors are BJTs and FETs.Transistors are often used in voltage dividers to act as variableresistors.





Metal Oxide Semiconductor Field Effect Transistors

A MOSFET (or Metal Oxide Semiconductor Field EffectTransistor) is a three terminal device.

drainsourcegate







drainsourcegate







drain

sourcegate







drainsource

gate







drainsourcegate





FET symbol





FET symbol

drain





FET symbol

drain

source





FET symbol

drain

sourcegate





FET operation

FETS are voltage amplifiers; a small gate voltage controls amuch larger drain/source current.

Actually it’s the voltage between the gate and the source whichmatters.





FET operation

FETS are voltage amplifiers; a small gate voltage controls amuch larger drain/source current.

Actually it’s the voltage between the gate and the source whichmatters.





D and E MOSFETs

There are two kinds of MOSFETenhancement mode (E type)When Vgs is below Vth, ID = 0As Vgs increases above Vth,ID increases.depletion mode (D type)To get ID to zero, a negative Vgsoff must be applied.

In an H-bridge, you want E-MOSFETS so no current flows with noapplied gate-source voltage.





D and E MOSFETs

There are two kinds of MOSFET

enhancement mode (E type)When Vgs is below Vth, ID = 0As Vgs increases above Vth,ID increases.depletion mode (D type)To get ID to zero, a negative Vgsoff must be applied.






D and E MOSFETs

There are two kinds of MOSFETenhancement mode (E type)

When Vgs is below Vth, ID = 0As Vgs increases above Vth,ID increases.depletion mode (D type)To get ID to zero, a negative Vgsoff must be applied.






D and E MOSFETs

There are two kinds of MOSFETenhancement mode (E type)When Vgs is below Vth, ID = 0

As Vgs increases above Vth,ID increases.depletion mode (D type)To get ID to zero, a negative Vgsoff must be applied.






D and E MOSFETs

There are two kinds of MOSFETenhancement mode (E type)When Vgs is below Vth, ID = 0As Vgs increases above Vth,

ID increases.depletion mode (D type)To get ID to zero, a negative Vgsoff must be applied.






D and E MOSFETs

There are two kinds of MOSFETenhancement mode (E type)When Vgs is below Vth, ID = 0As Vgs increases above Vth,ID increases.

depletion mode (D type)To get ID to zero, a negative Vgsoff must be applied.






D and E MOSFETs

There are two kinds of MOSFETenhancement mode (E type)When Vgs is below Vth, ID = 0As Vgs increases above Vth,ID increases.depletion mode (D type)

To get ID to zero, a negative Vgsoff must be applied.In an H-bridge, you want E-MOSFETS so no current flows with noapplied gate-source voltage.





D and E MOSFETs







D and E MOSFETs







Bipolar Junction Transistors

A BJT (or Bipolar Junction Transistor) is a three terminal currentdevice.The terminals are

collectoremitterbase

The current from the collector to the emitter is controlled by thecurrent into the base.






A BJT (or Bipolar Junction Transistor) is a three terminal currentdevice.

The terminals arecollectoremitterbase
















collector

emitterbase








collectoremitter

baseThe current from the collector to the emitter is controlled by thecurrent into the base.

























collector





collector

emitter





collector

emitterbase





BJT operation

BJTS are current amplifiers; a small base current controls amuch larger collector/emitter current.You should always have a base resistor with a BJT!





BJT operation

BJTS are current amplifiers;

a small base current controls amuch larger collector/emitter current.You should always have a base resistor with a BJT!





BJT operation

BJTS are current amplifiers; a small base current controls amuch larger collector/emitter current.

You should always have a base resistor with a BJT!





BJT operation

BJTS are current amplifiers; a small base current controls amuch larger collector/emitter current.You should always have a base resistor with a BJT!





H bridge (shown with BJTs)

V +

V−

RL1

2

3

4






V +

V−

RL1

2

3

4-

Current flows from left to right.






V +

V−

RL1

2

3

4�

Current flows from right to left.



Other considerationsEMF considerationsControlling Speed

EMF considerations

inductive loads require a few special considerationsa motor is an inductive load




EMF considerations

inductive loads require a few special considerations

a motor is an inductive load




EMF considerations

inductive loads require a few special considerationsa motor is an inductive load




Induced EMF

Quickly changing voltage across inductor produces inducedEMFinduced voltage tries to counteract change in currentcan produce big voltage spikesA diode across a coil will limit voltages to ≈ 0.7V .A zener diode can limit voltages the other way to about thezener voltage.




Induced EMF

Quickly changing voltage across inductor produces inducedEMF

induced voltage tries to counteract change in currentcan produce big voltage spikesA diode across a coil will limit voltages to ≈ 0.7V .A zener diode can limit voltages the other way to about thezener voltage.




Induced EMF

Quickly changing voltage across inductor produces inducedEMFinduced voltage tries to counteract change in current

can produce big voltage spikesA diode across a coil will limit voltages to ≈ 0.7V .A zener diode can limit voltages the other way to about thezener voltage.




Induced EMF

Quickly changing voltage across inductor produces inducedEMFinduced voltage tries to counteract change in currentcan produce big voltage spikes

A diode across a coil will limit voltages to ≈ 0.7V .A zener diode can limit voltages the other way to about thezener voltage.




Induced EMF

Quickly changing voltage across inductor produces inducedEMFinduced voltage tries to counteract change in currentcan produce big voltage spikesA diode across a coil will limit voltages to ≈ 0.7V .

A zener diode can limit voltages the other way to about thezener voltage.




Induced EMF

Quickly changing voltage across inductor produces inducedEMFinduced voltage tries to counteract change in currentcan produce big voltage spikesA diode across a coil will limit voltages to ≈ 0.7V .A zener diode can limit voltages the other way to about thezener voltage.




No diode to reduce induced EMF

I ≡ 0

Initially I = 0.





I = 0

+

-

Induced voltage tries to maintain I = 0.





I?

Eventually current is established determined by resistance in circuit.





I?

-

+

Induced voltage tries to maintain I at the previous value.





I = 0

Eventually current is reduced to I = 0.




Diode to reduce induced EMF

I ≡ 0

Initially I = 0.





I = 0

+

-

Induced voltage tries to maintain I = 0, but cannot exceed VZ .





I?

Eventually current is established determined by resistance in circuit.





I?

-

+

Induced voltage tries to maintain I but cannot exceed ≈ 0.7V .





I = 0

Eventually current is reduced to I = 0.




H bridge with diodes included

V +

GND

motor1

2

3

4




Diodes across the transistors

Putting a diode across each transistor keeps the voltage fromspiking at the terminals.This includes the base or gate.This will prevent spike getting to whatever is controlling it.





Putting a diode across each transistor keeps the voltage fromspiking at the terminals.

This includes the base or gate.This will prevent spike getting to whatever is controlling it.





Putting a diode across each transistor keeps the voltage fromspiking at the terminals.This includes the base or gate.

This will prevent spike getting to whatever is controlling it.





Putting a diode across each transistor keeps the voltage fromspiking at the terminals.This includes the base or gate.This will prevent spike getting to whatever is controlling it.




L9110 H-bridge

There are several H-bridge chips available.The L9110 is one example.There are boards with two allowing independent control oftwo motors.




L9110 H-bridge

There are several H-bridge chips available.

The L9110 is one example.There are boards with two allowing independent control oftwo motors.




L9110 H-bridge

There are several H-bridge chips available.The L9110 is one example.

There are boards with two allowing independent control oftwo motors.




L9110 H-bridge

There are several H-bridge chips available.The L9110 is one example.There are boards with two allowing independent control oftwo motors.




All the two motors have in common are the supply voltages.




If the 1A input is HIGH and the 1B input is LOW, the motor willrun in one direction.




If the 1A input is LOW and the 1B input is HIGH, the motor willrun in the other direction.




Controlling Speed

Controlling the base current or gate voltage may be difficult.However, pulse-width-modulation allows you to control theaverage power.This is the easy way to control speed.

As long as the frequency is high enough, mechanical inertia willmake the motion smooth.




Controlling Speed

Controlling the base current or gate voltage may be difficult.

However, pulse-width-modulation allows you to control theaverage power.This is the easy way to control speed.





Controlling Speed

Controlling the base current or gate voltage may be difficult.However, pulse-width-modulation allows you to control theaverage power.

This is the easy way to control speed.





Controlling Speed






Controlling Speed






Pulse width modulation to limit current

PWM can be used on one input..





or the other.





Alternatively, you can use PWM on one input..





and control direction with the other.





In this case decreasing the duty cycle will increase power in onedirection.


Documents

Electronics- H-Bridges and DC Motorsdenethor.wlu.ca/pc320/lectures/hbridgebeam.pdf · Electronics H-Bridges and DC Motors Terry Sturtevant Wilfrid Laurier University April 22, 2019