ME 4447/6405
October 29th, 2009
By:
Val Tocitu
Jason Kulpe
Alexandre Mariuzza
Presenter: Val Tocitu
 Introduction and definitions
 Types of PWM
 Methods of generation
 Characteristics of PWM
 Applications and examples
 Implementation on the HCS12
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
2
What is it?
 Output signal alternates between on and off within
specified period
 Controls power received by a device
 The voltage seen by the load is directly proportional
to the source voltage
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
3
Definitions
 Duty Cycle: on-time / period
 Vlow is often zero
VAVG  DVHI  (1  D)VLOW
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
4
Types of Pulse Width
 Pulse center fixed, edges modulated
 Leading edge fixed, tailing edge modulated
 Tailing edge fixed, leading edge modulated
 Pulse Width constant, period modulated
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
5
Types of Pulse Width
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
6
Analog Generation of PWM
Analog PWM signals can be made by combining a
saw- tooth waveform and a sinusoid
PWM output is
formed by the
intersection of
the saw-tooth
wave and
sinusoid
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
7
Digital Methods of Generating PWM
 Digital: Counter used to handle transition
 Delta : used to find the PWM at a certain limit
 Delta Sigma: used to find the PWM but has advantage of
reducing optimization noise
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
8
Applications to DC Motors
• The voltage supplied to a DC motor is proportional
to the duty cycle
• Both brushed and brushless motors can be used
with PWM
• Both analog and digital control techniques and
components are available
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
11
Three Phase AC motors with PWM
 3 different AC currents at
different phases
 Phase: 120 degrees apart
 Creates constant power
transfer
 Rotating magnetic field
 Pulses substitute for AC
current
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
12
Space Vector Modulation
 Used for three-phase AC motors
 Convert DC current to AC current
 Gates turned on/off at different intervals
 3 PWM created
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
13
Motor Control Diagrams
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
14
Advantages of PWM
• average value proportional to duty cycle, D
• low power used in transistors used to switch
the signal
• fast switching possible due to MOSFETS
and power transistors at speeds in excess
of 100 kHz
• digital signal is resistant to noise
• less heat dissipated versus using resistors
for intermediate voltage values
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
15
Disadvantages of PWM
 Cost
 Complexity of circuit
 Radio Frequency Interference
 Voltage spikes
 Electromagnetic noise
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
16
Presenter: Jason Kulpe
 Introduction and definitions
 Types of PWM
 Methods of generation
 Characteristics of PWM
 Applications and examples
 Implementation on the HCS12
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
17
Applications of PWM
• In the past, motors were controlled at intermediate
speed by using resistors to lower delivered power
• Electric stove heater
• Lamp dimmers
• Voltage regulation – convert 12 volts to 5 volts by
having a 41.7% duty cycle
• Sound production: PWM controlled signals give
sound effects similar to a chorus
• Power transfer: PWM used to reduce the total
power given to a load without relying on resistive
losses
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
18
PWM used with D/A conversion
• commonly used in toys
• lowpass filter smooths out transients from harmonic effects
• frequency values of harmonics doesn’t change, but the
amplitude does, which adjusts the analog output signal
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
19
PWM used to transmit data
in telecommunications
• clock signal is found “inside” PWM signal
• more resistant to noise effects than binary data alone
• effective at data transmission over long distance transmission lines
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
20
Frequency of the PWM Signal
Upper Limits
Lower Limits
1. Must be at least 10 times higher
than the control system frequency
2. Higher than 20kHz – audible
frequency of sounds to avoid
annoying sound disturbances,
caused by magnetostriction
3. If too low the motor is pulsed, not
continuous, because the motor’s
inductance can not maintain the
current
4. Inverse of frequency should be
much less than the motor/load time
constant
5. Higher error from ripple voltages
10/29/2009
1. If too high the inductance of the
motor causes the current drawn to
be unstable
2. MOSFET transistor generates heat
during switching
3. Limited by resolution of controller
4. Eddy currents generated in
electromagnetic coils which lead to
adverse heating
5. Heat losses in electromagnetic
materials is proportional to
frequency squared
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
22
Example: PWM with 555 Timer
Potentiometer is
used to adjust
the duty cycle
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
23
Example: Specifying circuit elements
Requirements
1. Maxon EC-16 brushless motor,
Time constant = 8.75 ms
1
 8.5 ms 
f
f 117 Hz
2. Want to avoid audible frequencies
f ≥ 20 kHz
3. PID control loop running at 150 Hz
f ≥ 10 ∙ 150 Hz
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
24
Example: Specifying circuit elements
This circuit has a
PWM frequency
according to:
1.44
f 
R1C1
Check constraints
Set f to 25 kHz to add in a factor of safety
Choosing C1 to be 100 nF, R1 is 576 Ω ~ 500 Ω
Recalculating with these values f = 28.8 kHz
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
f
≥ 117 Hz
≥ 20 kHz
≥ 1.5 kHz
25
Matlab can do PWM!
The procedure works similar
to the generation of analog
PWM using a sinusoid and
saw-tooth wave
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
26
Where can I buy a PWM controller?
Texas Instruments
Digikey
Mouser Electronics
Critical Velocity Motor Control
SMALL
Texas Instruments
TAS5508B
8-Channel Digital Audio
PWM Processor
18 kHz frequency
64 pin chip, max 192 kHz
Continuous 28 amps
frequency
$55.95
$7.25
Pulse Width Modulation - Val Tocitu,
10/29/2009
Jason Kulpe, Alex Mariuzza
120 amps, used for
hybrid vehicles
$469.00
H
U
G
E
27
Presenter: Alex Mariuzza
 Introduction and definitions
 Types of PWM
 Methods of generation
 Characteristics of PWM
 Applications and examples
 Implementation on the HCS12
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
28
PWM Implementation
 The signal is outputted
through Port P
 Six Channels
 Dedicated Chip
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
29
PWM Module
 Each channel has a
dedicated counter
 Programmable duty
and period
 Independently
adjustable clock,
polarity, and
alignment
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
30
PWM Module- Other Features
 8-bit and 16-bit resolution supported
 Two PWM channels can be concatenated together
 Four source clocks (A, SA, B, SB)
 Emergency Shutdown
 Some changes take a complete cycle to be implemented
 Modes of Operation:
 Normal: everything is available
 Wait: Low-power consumption and clock disabled
 Freeze: Option to disable clock is available
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
31
PWM Configuration
 Configured through
specific registers
 Registers are located from
$00E0 to $00FE
 There are repeated
registers (ex. 0013-0017)
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
32
PWM Enable Register
 Located at $00E0
 Code Warrior variable: PWME
 Set PWMEx to 0 to disable the channel
 Set PWMEx to 1 to enable it
 Channel is activated when bit is set
 If 16-bit resolution used, then PWME4/2/0 are deactivated
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
33
PWM Polarity Register
 Located at $00E1
 Code Warrior variable : PWMPOL
 Set PPOLx to 0, signal goes from low to high
 Set PPOLx to 1, signal goes from high to low
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
34
PWM Clock Select Register
 Located at $00E2
 Code Warrior variable : PWMCLK
 Set PCLK5/4/1/0 to 0 to use clock A
 Set PCLK5/4/1/0 to 1 to use clock SA
 Set PCLK3/2 to 0 to use clock B
 Set PCLK3/2 to 1 to use clock SB
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
35
PWM Prescaler Register
 Located at $00E3
 Variable: PWMPRCLK
 Used to prescale clocks A and
B
Bus Clock Frequency
Resolution  PWM Frequency 
Bus Clock Frequency
 N
(2  1)  PWM Frequency 
Presclarer 
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
36
PWM Scale A Register
 Located at $00E8
 Code Warrior variable:
PWMSCLA
 Store a hexadecimal value
in order to change the clock
frequency of SA
 Note: if set to $00,
PWMSCLA is set to 256
10/29/2009
Clock SA Frequency 
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
Clock A Frequency
2  PWMSCLA
37
PWM Scale B Register
 Located at $00E9
 Code Warrior variable:
PWMSCLB
 Store a hexadecimal value
in order to change the clock
frequency of SA
 Note: if set to $00,
PWMSCLB is set to 256
10/29/2009
Clock SB Frequency 
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
Clock B Frequency
2  PWMSCLB
38
PWM Center Align Register
 Located at $00E4
 Code Warrior variable: PWMCAE
 Set CAEx to 0 for left align signal
 Set CAEx to 1 for center align signal
 Note: can only be set when channel is disabled
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
39
Signal Alignment
 Signal changes when counter
is equal to period register
 In the center aligned mode, the
PWM counter goes from a
down-count to a up-count to
down-count, etc.
 In the left aligned mode, the
PWM counter is a up-counter
and rests to zero when it
overflows
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
40
PWM Control Register
 Located at $00E5
 Code Warrior variable: PWMCTL
 Set CONxy to 0 to keep PWM channels separate (8-bit)
 Set CONxy to 1 to concatenate PWM channels x and y together (16



bit).
Channel y determines the configuration
x becomes the high byte and y becomes the low byte
Bits PSWAI and PFRZ set either wait or freeze mode
Changes only occur when channels are disabled
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
41
PWM Counter Register
 Located at $00EC through $00F1
 Code Warrior variable: PWMCNTx
 One per channel
 It tracks the cycle counts
 It can be read
 If written to, the count is reset to $00 and a up-count starts
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
42
PWM Period Register
 Located at $00F2 through $00F7
 Variable: PWMPERx
 Store a hexadecimal value to limit
maximum value of counter
 Changes occur when:
 Current period ends
 Counter is written to
 Channel is disabled
10/29/2009
Left-Aligned:
PWMPERx 
PWM Source Frequency
PWM Signal Frequency
Center-Aligned:
PWM Source Frequency
PWMPERx 
2  PWM Signal Frequency
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
43
PWM Duty Register
•
•
•
•
Located at $00F8 through $00FD
Code Warrior variable: PWMDTYx
Store a hexadecimal value to control when signal changes
Changes occur when:
• Current period ends
• Counter written to
• Channel is disabled
Duty Cycle  PWMPERx
100
Duty Cycle  PWMPERx
Polarity = 1: PWMDTYx 
100
Polarity = 0: PWMDTYx  PWMPERx 10/29/2009
44
PWM Shutdown Register
•
•
•
•
•
•
•
Located at $00FE
Code Warrior variable: PWMSDN
PWMENA: Enables and disables emergency shut down
PWMIF (Interrupt flag): Set when an input is detected in pin 5
PWMIE (Interrupt Enable): Enables and disables CPU interrupts
PWMRSTRT: Resets the counters
PWMLVL (Shutdown Output Level): Determines if output is high
or low when shutdown
• PWM5IN (Input Status): Reflects status of pin 5
45
• PWM5INL: Determines active level of pin 5
How it all works
Clock A, SA, B, or SB
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
46
Example
 Desired Signal:
 8 kHz PWM signal
 Duty Cycle of 30%
 Left Aligned
 Channel 1
 Low → High
 8-bit channel
8 106
Prescaler  8
 3.91  4  PWMPRCLK  $02
(2  1)  8 103


 8 106 


4
2 106


PWMPER1 

 250  $FA
8 103
8 103
PWMDTY1  250 -
30  250
 175  $AF
100
PWMCLK  $00
PWMCAE  $00
PWMPOL  $00
PWMCTL  $00
PWME  $02
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
47
Assembly Code
PWME
PWMPOL
PWMCLK
PWMPRCLK
PWMCAE
PWMCTL
PWMPER1
PWMDTY1
10/29/2009
EQU
EQU
EQU
EQU
EQU
EQU
EQU
EQU
$00E0
$00E1
$00E2
$00E3
$00E4
$00E5
$00F3
$00F9
ORG
LDAA
STAA
STAA
STAA
STAA
LDAA
STAA
LDAA
STAA
LDAA
STAA
STAA
……
$1000
#$00
PWMCLK
PWMPOL
PWMCTL
PWMCAE
#$FA
PWMPER1
#$AF
PWMDTY1
#$02
PWMPRCLK
PMWE
; Sets source clocks to clock A
; The signal goes from low to high
; Makes all channels 8-bit
; Signals are left aligned
; Sets the period to 250 clock cycles
; Makes the duty cycle equal to 30%
; Sets the prescaler to 4
; Enables and starts channel 1
48
C Code
#include <hidef.h>
/* common defines and macros */
#include <mc9s12c32.h> /* derivative information */
#pragma LINK_INFO DERIVATIVE “mc9s12c32”
// Set up chip in expanded mode
MISC = 0x03;
PEAR = 0x0C;
MODE = 0xE2;
//Set up PWM Registrer
PWMCLK = 0;
// Sets source clocks to clock A
PWMPOL = 0;
// The signal goes from low to high
PWMCTL = 0;
// Makes all channels 8-bit
PWMCAE = 0;
// Signals are left aligned
PWMPER1 = 250; // Sets the period of the signal to 250 clock
PWMDTY1 = 175;
// Makes the duty cycle equal to 30%
PWMPRCLK = 2;
//Sets the prescaler to 4
PMWE = 2;
//Enables and starts channel 1
….
Pulse Width Modulation - Val Tocitu,
10/29/2009
Jason Kulpe, Alex Mariuzza
49
REFERENCES
http://en.wikipedia.org/wiki/Pulse-width_modulation
http://www.netrino.com/Embedded-Systems/How-To/PWM-Pulse-Width-Modulation
Cetinkunt, Sabri. Mechatronics. Hoboken, NJ: Wiley, 2006. Print.
http://www.jimfranklin.info/microchipdatasheets/00538c.pdf
http://www.allaboutcircuits.com/vol_6/chpt_6/9.html
http://www.dprg.org/tutorials/2005-11a/index.html
http://www.4qdtec.com/pwm-01.html
http://skywalker.cochise.edu/rgill/ch02elec.ppt
http://pcbheaven.com/wikipages/PWM_Modulation/
Matlab 2009 online documentation
http://www.epanorama.net/links/motorcontrol.html#ac
MC9S12C Family, MC9S12GC Family Reference Manual, (pp. 347-382)
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
50
Questions?
10/29/2009
Pulse Width Modulation - Val Tocitu,
Jason Kulpe, Alex Mariuzza
51