AN3471, Ceiling Fan Speed Control

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Freescale Semiconductor
Application Note
Document Number: AN3471
Rev. 0, 07/2008
Ceiling Fan Speed Control
Single-Phase Motor Speed Control Using MC9RS08KA2
by: Cuauhtemoc Medina
RTAC Americas
1
Introduction
This application note introduces a method for controlling
a single-phase AC induction motor. This motor is widely
used in ceiling fans due to various advantages over other
types of motors. It is low cost, low maintenance, and has
direct connection to the AC power source.
Using the MC9RS08KA2 MCU series combined with
the basic TRIAC topology is cost-performance solution.
The traditional mechanical speed control of the ceiling
fan can be replaced with this solution avoiding problems
such as non-linearity on speed.
© Freescale Semiconductor, Inc., 2008. All rights reserved.
Contents
1
2
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2.1 Single Phase Induction Motor Control Theory. . . . . 2
2.2 Typical Solutions . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.3 Proposed Solution and Phase Angle Control . . . . . 3
3
Design Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4
Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1 Board Configuration. . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2 Rectifier and Transformer . . . . . . . . . . . . . . . . . . . . 5
4.3 Connection from Rectifier to Board . . . . . . . . . . . . . 6
4.4 Pulse Width Modulation (PWM). . . . . . . . . . . . . . . . 6
4.5 Checking the PWM . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.6 Optocouplers (MOC) . . . . . . . . . . . . . . . . . . . . . . . . 9
4.7 TRIAC and SNUBBER . . . . . . . . . . . . . . . . . . . . . 10
5
Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.1 Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.2 Flow Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6
Testing and Validation . . . . . . . . . . . . . . . . . . . . . . . . . . 17
7
Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
9
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Appendix ABill Of Materials (BOM) . . . . . . . . . . . . . . . . . . . . 18
Appendix BSource Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Solution
2
Solution
2.1
Single Phase Induction Motor Control Theory
Single-phase induction motors are the most used. These motors have only one stator winding, operate with
a single-phase power supply, and are also squirrel cage. Because of the single phase, the motor is not
self-started when connected to a power supply. The necessary torque is not generated therefore causing the
motor to only vibrate and not rotate.
To provide the starting torque most single-phase motors have a main and auxiliary winding, both in
quadrature to help generate the phase-shifted magnetic field.
Figure 1. Capacitor Start AC Induction Motor
The auxiliary winding current from the main winding is phase-shifted. Connecting a capacitor in series
with the auxiliary winding causes the motor to start rotating. Using a centrifugal switch disconnects the
capacitor and the auxiliary winding at 75% of the motor nominal speed. This topology is used if high
torque is required. In most fan motors, the capacitor and the auxiliary winding remain connected. This
configuration is called permanent split capacitor (PSC) AC induction motor. No centrifugal switch is used
and are considered to be the most reliable single-phase motors. At rated load, they can be designed for
optimum efficiency and high power factor (PF).
Ceiling Fan Speed Control, Rev. 0
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Solution
Figure 2. PSC Starting Mechanism
2.2
Typical Solutions
Motors commonly used in ceiling fans are single-phase induction motors with a PSC starting mechanism.
Most of them have three different speeds that are mechanically selected by pulling a chain. Every time the
chain is pulled, the motor circuit changes to a predefined coil winding that causes the speed to vary. It is
recommended that the fan be set at maximum speed. Considering that the load of the motor is proportional
to the consumed current it is not the same range of speed variation with the load then without it. The range
of speed variation needs to be recalculated.
2.3
Proposed Solution and Phase Angle Control
When the TRIAC switch is connected between the AC power supply and the motor, the power flow can
be controlled by varying the RMS of the AC voltage. This is called an AC voltage controller. There are
two types of control normally used:
— On-off control — TRIAC switches connect the load to the AC source for a few cycles and then
disconnect it for another few cycles of the source voltage
— In phase control — TRIAC switches connect the load to the AC source for a moment in each
cycle Figure 3
A reliable speed control of a ceiling fan AC motor can be accomplished by combining the MC9RS08KA2
and the phase angle control using a TRIAC. A benefit of this approach is avoiding non-linearity that is
present if using only the TRIAC. Another benefit is, it can replace the mechanical speed variation
commonly used in ceiling fans.
Ceiling Fan Speed Control, Rev. 0
Freescale Semiconductor
3
Design Requirements
Figure 3. Line Voltage vs. Motor Voltage
3
Design Requirements
•
•
•
DEMO9RS08KA2 board and a computer running with CodeWarrior
A ceiling fan motor
Components Section Appendix A, “Bill Of Materials (BOM)”
4
Instructions
4.1
Board Configuration
Steps for configuring the board:
1. Pull out every jumper in j101 except for RESET and LED 0
2. Connect the j101 SW0 pin on the push button side of PTA5 on j102. The push button SW0 connects
to PTA5
3. Make sure the board is in host mode, j202 in the USB, and j203 VDD enabled
4. Set jumpers on j101 to RESET and LED
Ceiling Fan Speed Control, Rev. 0
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Freescale Semiconductor
Instructions
Figure 4. Board Configuration
In Figure 4, the upper left image shows the board. The following image to the right shows the board with
the proper connections and the last image shows a close-up of the jumper configuration and connections.
Ceiling Fan Speed Control, Rev. 0
Freescale Semiconductor
5
Instructions
4.2
Rectifier and Transformer
1. Identify the primary and secondary windings of the transformer (127 V – 60 Hz/ 6 V – 500 mA).
2. Connect common to GND. The GND must be common on the board
3. Connect the two cables of the secondary winding to the AC input on the bridge. Consult the
transformer data sheet to identify the cables.
4. Connect the positive side of the bridge to GND with a 10 K resistor.
5. Connect the negative side of the bridge to GND.
6. Check with an oscilloscope the voltage on the 10 K resistor. It must show the full wave rectified.
Figure 5. Rectifier and Transformer
Figure 6. AC Wave vs. Rectified Wave
4.3
Connection from Rectifier to Board
1. Connect the positive bridge output to j102 PTA1. This the negative input of the controller
comparator.
2. Make sure j102 GND is connected to the line GND.
3. Connect j102 PTA0 to the voltage on the output divider.
If j102 PTA0 is connected directly to 0 volts, the 0 voltage is not always reached. To ensure this detection
the voltage on j102 PTA0 is near 0 (0.1 volts must work).
Ceiling Fan Speed Control, Rev. 0
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Instructions
4.4
Pulse Width Modulation (PWM)
A pulse width modulation (PWM) signal is generated by using the timer and the comparator. The controller
performs the following tasks:
• The controller is constantly checking for zero crossings through the comparator
• If this condition is true the output pin is cleared and the timer is started
• The timer counts up to a certain value. If it reaches a predefined value (MODULO), it is stopped
and reset for the next cycle. The output pin is also set.
• The cycle is repeated by waiting for the next zero crossing.
The timer must not count more than the time it takes to detect a new zero cross. Calculate the correct value
for the MODULO. For example, the line is 120 V, 60 Hz (1 cycle: 1/60 =.016 s). The rectified wave is 120
Hz MODULO and has an 8-bit value. Each half-wave is .008 s (.008 s/ 255 bit = 31.3 s/bit). The
duty cycle = t/T. The calculated values are:
— MODULO = 128 (half). Timer counts 128*31.3 s = 4.006 ms. The output is 0 when it detects
the zero crossing. The timer counts up to 128 and the output value is 1 until the next zero
crossing occurs. The duty cycle is 50%.
— MODULO = 64 (quarter). Timer count 64*31.3 s = 2.003 ms. The output is 0 when it detects
the zero crossing. The timer counts to 64 and the output value is 1 until the next zero crossing.
The duty cycle of 75%.
4.5
Checking the PWM
1. Open the project DEMO.mcp in the demo folder. If CodeWarrior is not installed refer to the starter
kit user´s manual.
2. Connect the board to the computer. Use the USB cable.
3. Click on the green arrow with the bug, it enters debug mode. This downloads the program. See
Figure 7.
4. The true time simulator real time debugger is opened and requests the MCU configuration. Choose
DEMO9RS08KA2. See Figure 8.
5. Click on the green arrow to run the program. See Figure 9.
6. Connect the oscilloscope to see the signal in j102 PTA4. This is the PWM output.
7. On the windows for data variables find the duty cycle. See Figure 10.
8. Double-click on the number to select it and change it. This is an 8-bit number and only varies from
0 to 255.
9. Watch the signals on the oscilloscope by varying the duty_cycle variable.
Ceiling Fan Speed Control, Rev. 0
Freescale Semiconductor
7
Instructions
Figure 7. CodeWarrior Menu
Figure 8. True Time Simulator – Real Time Debugger Configuration Window
Figure 9. True Time Simulator Menu
Figure 10. True Time Simulator Data Window
Ceiling Fan Speed Control, Rev. 0
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Instructions
Figure 11. Rectified Wave and PWM at 87%, 50%, and 25%
4.6
Optocouplers (MOC)
Optocouplers (MOCs) are used to transmit signals between circuits that do not share a power source.
MOCs have a LED and a sensor inside. If the led is turned on, it activates the sensor and lets the current
flow.
This circuit is used to isolate signal circuitry from transients generated or transmitted by power supply and
high-current control circuits.
1. Connect j102 PTA4 (PWM output) to pin1 of the MOC
2. Connect pin 2 to GND
3. Connect pin 4 to the TRIAC gate
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Instructions
Figure 12. Schematic of the Power Circuit
4.7
TRIAC and SNUBBER
The TRIAC is an electronic bi-directional switch. If there is voltage on the gate, it transmits over its
terminals until the current through it drops below a certain threshold value. A snubber network is used to
assist the turn off and prevent premature triggering. In this circuit the combination of resistors and
capacitors are used to suppress the rapid rise and fall of the voltage.
1. Connect to pin 6 of the MOC a resistance of 180  in series with 2 K
2. Between the two resistances connect a capacitor of .2 uF to the reference.
3. Connect any of the terminals of the TRIAC in series with the 2 K
4. Connect the other TRIAC terminal to the reference.
5. Connect pin 4 of the MOC to the gate of the TRIAC.
6. Connect the motor one cable where the 2 K and the TRIAC are connected and the other to the
reference Figure 13.
7. Check the output of the TRIAC and compare it with the AC voltage. See Figure 14.
Ceiling Fan Speed Control, Rev. 0
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Instructions
Figure 13. Complete Circuit
The PWM output signal starts with 0, after a certain time it triggers the TRIAC and conducts until AC
reaches 0 again. Starting with one on the cross detection, the motor always runs at a certain speed. To see
what the gate and terminals are consult the motor documentation.
Ceiling Fan Speed Control, Rev. 0
Freescale Semiconductor
11
Code
Figure 14. AC Voltage vs. TRIAC Output at Different PWM Values
5
Code
5.1
Description
The code can be divided into three modules:
• Init — This section of code is in charge of configuring the controller for this task. It disables the
COP, configures FLL as clock source, configures the timer (8 Mhz input, and prescaler 256),
configures the comparator (external reference, falling edge), and the GPIO’s (PTA4 as output,
PTA5 as input).
The timer is configured to fit the frequency of 120 Hz of the rectified wave. Equation 1 and
Equation 2.
 8Mhz    prescaler  256   = 31.250Khz
Eqn. 1
 31.250Khz    256counts  = 122Hz
Eqn. 2
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Code
•
•
Main Flow — This the infinite loop of the program. It waits for the zero crossing detected with the
comparator. The timer then starts. When the timer overflows it activates the output PTA4 and the
TRIAC gate. On the next zero crossing detection, it turns off the TRIAC gate and the cycle is
repeated. It is also calls the check button function.
Check button — This in charge of validating the button pushes. When a push is validated it changes
the duty cycle of the PWM. This is the value to load in MODULO. Special care must be taken of
the button. The code checks if the pin is low every cycle. If it is, the button is then pressed. In the
next cycle the controller checks again if the pin remains low. The pin level is checked each cycle,
120 times each second.
There are two options for the button:
• When pressed, cpcb_count counts how many cycles the button remains pressed. If cpcb_count
equals cyc_per_check_b the speed is changed.
• When pressed, each change of speed checks the low pin, considers the button pressed, and waits
until the pin is high to check it again.
Ceiling Fan Speed Control, Rev. 0
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Code
5.2
Flow Diagram
Init controller
Start
Configures system control
•
Disables COP
•
Enables BKGD
•
Enables reset
Configures clock
•
Set trimming value
•
FLL as CLK source
•
ICSOUT = DCO
Configures timer
•
Enables interrupt
•
Resets counter
•
Stop timer
•
fBUS (8M) as
reference
•
Prescaler = 256
Configures comparator
•
Enables comparator
•
ACMP+ as external
reference
•
Enables interrupt
•
Output disabled
•
Falling edge event
Configures GPIO’s
•
PTA4 as output
•
PTA5 as input
•
PTA4 = 0
Return
Figure 15. Init Flow Chart
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Code
1
Main flow:
Activate comparator
No
Comparator
event?
Start
Yes
Deactivates comparator
Init controller
Clears comparator flag
Resets DC pointer
speed_count= 0
Timer MODULO = duty_cycle
PWM output PTA4 = 0
Resets DC value
duty_cycle= 0
Start timer
Check button
Resets buttons time counter
cpcb_count= 0
Timer overflow?
No
Yes
1
Stop timer
Clear timer flag
No
Is turned on?
speed_count != 0
Yes
PWM output PTA4 = 1
Figure 16. Main Program
Ceiling Fan Speed Control, Rev. 0
Freescale Semiconductor
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Code
Start
Button pressed
PTAS = 0
No
Button counter = 0
Yes
Clear button
pressed tag
Yes
Button already
pressed
No
Increments button
counter
No
The button counter =
Cycles per check?
(cyc_per_check_b)
Yes
Set button
already pressed
Button counter = 0
Increment index
speed_count
Last
element
No
Yes
Reset index
Set new duty cycle
value (duty_cycle)
Return
Figure 17. Push Button Flow Chart
Ceiling Fan Speed Control, Rev. 0
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Testing and Validation
6
Testing and Validation
The entire circuit can be divided in three modules and can be checked independently.
• The first module is the transformer and rectifier. At the end of this stage there is a rectified AC
wave at 120 Hz at half of the original voltage peak-peak.
• The next module is the zero cross detection circuit. To test this module the previous is needed and
the MCU with the program running. The designated output pin of the MCU is expected to have a
pulse at 120 Hz. If this signal and the previous stage signal outputs are viewed at the same time, it
generates a pulse each time the rectified sine wave reaches zero.
• The last module has the MOC and TRIAC. To test if this part of the circuit is working properly,
disconnect the side of the MOC connected to the MCU and replace it with 3.3 VDC. The motor
has to start working when on and if off the motor has to turn off. When the motor switches on/off
it makes a sound, to be sure wait a lapse of time while the motor is off. It must come to a complete
stop.
7
Conclusion
Using an MC9RS08KA2 microcontroller combined with the TRIAC topology, a reliable solution is
reached for varying the speed of a ceiling fan. This solution is viable for replacing the existing commonly
used mechanism.
8
References
See the Freescale web page www.freescale.com.
• DRM039 — Single Phase AC Induction Motor Control Designer Reference Manual
• MC9RS08KA2 MC9RS08KA1 Data Sheet
• RS08 Core Reference Manual
Ceiling Fan Speed Control, Rev. 0
Freescale Semiconductor
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References
Appendix A Bill Of Materials (BOM)
•
•
•
•
•
•
•
•
•
•
Transformer, Input: 127 Vac, Output: 6 V 500 mA
Rectifier bridge 50 V, 2 A
10 K resistor
7 K resistor
220  resistor
MOC 3011
0.1 uF capacitor
180  resistor
2.2 K resistor
MAC223A TRIAC
Ceiling Fan Speed Control, Rev. 0
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References
Appendix B Source Code
;**********************************************************************************
;
MAIN.ASM
;**********************************************************************************;
; Single Phase Demo for the DEMO9RS08KA2
; --------------------------------------------------------------------------------; This example controls a single phase motor through a PWM.
; The PWM is generated with the comparator (to detect zero crossing) and the timer (to; generate
duty cycle
;
; ACMP - is fed with a value approximate to 0
; ACMP + rectified wave
; PTA4 PWM output to feed the MOC, also connected to a LED to show the speed
; through LED's;intensity
; PTA5 push button to vary the speed
; RESET/PTA2 turns off the motor
;
;
; ********* If you want the button to run free the comment values, button to comment
; ********* set cyc_per_check_b to the value wanted
; ********* notice that cyc_per_check_b also avoids bouncing.
; ********* understand RUN FREE as the button is checked every
; ********* cyc_per_check_b * 8.4 ms (120 ;hz) that is, if kept pressed it
; ********* changes duty or press and release the button in
; ********* order to change duty values
; ***************************************************************************
; export symbols
XDEF _Startup, main
; export both '_Startup' and 'main' as symbols. Either can
; be referenced in the linker .prm file or from C/C++ later on
; Include derivative-specific definitions
INCLUDE 'derivative.inc'
D_X
X_
CLKST
PTA4
PTA5
ACF
ACME
TOF
TSTP
BUTTON_PRESSED
equ
equ
EQU
EQU
EQU
EQU
EQU
EQU
EQU
EQU
$0000000E
$0000000F
2
4
5
5
7
7
4
0
MY_ZEROPAGE: SECTION
speed_count:
DS.B
SHORT
1
button_control
duty_cycle:
1
1
cpcb_count
DS.B
DS.B
DS.B 1
; line for button pressed
; Variable/Data Section
; this is a pointer to select
; which value is used in line_speed array
; flag for button
; this value is how long (timer) it
; stays up/down
; cycles to check button counter
; number of cycles it waits to check the
; button again
; Const Section
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References
ConstSection: SECTION
cyc_per_check_b DC.B $09
size_speed
line_speed
DC.B
DC.B
;line_speed
DC.B
; number of counts (wave cycles) it takes to
; read button
$07
; number of elements in line speed array
$01,$20,$40,$80,$C0,$E0,$F0
; if you change the size of the
; linespeed do not forget to modify Project.map
$F0,$E0,$C0,$80,$40,$20,$01
; if you change the size of the
;linespeed do not forget to modify Project.map
; Code Section
MyCode:
SECTION
;**********************************************************************************
; Peripheral Initialization
;**********************************************************************************
init:
;CONFIGURES SYSTEM CONTROL
MODE:
EQU 0
IFNE MODE
mov #HIGH_6_13(SOPT), PAGESEL
mov #$01, MAP_ADDR_6(SOPT)
ELSE
mov #HIGH_6_13(SOPT), PAGESEL
mov #$03, MAP_ADDR_6(SOPT)
; MODE=0 Background Mode, MODE=1 Run Mode
; Disables COP and enables RESET (PTA2) pin
; Disables COP and enables BKGD (PTA3) and
; RESET (PTA2) pins
ENDIF
;CONFIGURES CLOCK (FEI Operation Mode)
mov #HIGH_6_13(NV_ICSTRM),PAGESEL
lda MAP_ADDR_6(NV_ICSTRM
sta ICSTRM
; Sets trimming value
clr ICSC1
; Selects FLL as clock source and disables it
; in stop mode
clr ICSC2
; ICSOUT = DCO output frequency
wait_clock:
brset CLKST,ICSSC,wait_clock
; Waits until FLL is engaged
;CONFIGURES TIMER
mov #$70, MTIMSC
mov #$08, MTIMCLK
;CONFIGURES ACMP
mov #$F0, ACMPSC
;CONFIGURES PORT
bset PTA4, PTADD
bclr PTA5,PTADD
bclr PTA4, PTAD
;
;
;
;
Enables interrupt, stops and resets timer counter
Selects fBUS as reference clock (8 MHz)
prescaler = 256 (increments timer counter every
32 us)
; Comparator enabled, ACMP+ as external reference
; clear flag and enable interrupt, output disabled
; Comparator falling edge
; set port A4 as output
; sets port A5 as input
; clears port PTAD4
rts
;**********************************************************************************
; Entry Point
;**********************************************************************************
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Freescale Semiconductor
References
_Startup:
main:
bsr init
mov #0, speed_count
mov #0, duty_cycle
;
;
;
;
;
this is a pointer for the main speed wanted, first
set it to 0
this is a parameter for the timer, indicating when
it stops counting
reset cycles count for button check
mov #0, cpcb_count
tag1:
bset ACME,ACMPSC
; activates analog comparator
loop1:
;wait
; sends controller to wait state
brclr ACF,ACMPSC,loop1 ; waits until there is a comparator event
bclr ACME,ACMPSC
; deactivates comparator
bset ACF,ACMPSC
; clears comparator flag
mov duty_cycle,MTIMMOD
; sets Modulo to maximum count, also resets
; counter and clears timer flag
bclr PTA4, PTAD
bclr TSTP,MTIMSC
; starts timer
bsr check_button
check_timer:
;wait
; sends controller to wait state
brclr 7,MTIMSC,check_timer
; waits until there is a timer overflow
bset TSTP,MTIMSC
; stops timer
bclr TOF,MTIMSC
; clears timer overflow flag
lda #$00
; turns off completely when it points to
; the minimum speed
cmp speed_count
beq end_main
bset PTA4, PTAD
end_main:
jmp tag1
check_button:
brclr PTA5,PTAD,chb_cont
; if the button is pressed, it goes to check_button
mov #$00,cpcb_count
; if button is released, it resets the counter to
bclr BUTTON_PRESSED,button_control ; bit 0 as flag for button already pressed
jmp button_return
;
chb_cont:
; check counter to wait to check button
brset BUTTON_PRESSED,button_control,button_return ; BUTTON TO COMMENT
;if the button has not been released, it returns
; from subroutine
inc cpcb_count
; increments counter for push button
lda cpcb_count
; compares cpcb_count value with defined
; constant value
mov #HIGH_6_13(cyc_per_check_b), PAGESEL
cmp MAP_ADDR_6(cyc_per_check_b)
bhs chb_cont2
; if the value is reached it jumps chb_count2, or
; returns and continues counting
jmp button_return
chb_cont2:
bset BUTTON_PRESSED,button_control ; sets it to mark the button as already pressed
mov #$00,cpcb_count
; resets counter because the button has been
; pressed long enough
inc speed_count
; increments pointer, (this value is used
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References
; with X)
lda speed_count
; compares pointer value with array size
mov #HIGH_6_13(size_speed), PAGESEL
cmp MAP_ADDR_6(size_speed)
blo set_duty
mov #0,speed_count
; if pointer > array size then resets 0
set_duty:
mov #HIGH_6_13(line_speed), PAGESEL;load duty value into duty_cycle variable
lda #MAP_ADDR_6(line_speed)
add speed_count
sta X_
mov D_X,duty_cycle
button_return:
rts
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Document Number: AN3471
Rev. 0
07/2008

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