Pulse Width Modulation - Revision history

Lynch at 21:20, 6 January 2007

2007-01-06T21:20:56Z

Lynch at 21:17, 6 January 2007

2007-01-06T21:17:07Z

Lynch at 21:12, 6 January 2007

2007-01-06T21:12:30Z

Lynch at 21:12, 6 January 2007

2007-01-06T21:12:16Z

Lynch at 21:11, 6 January 2007

2007-01-06T21:11:28Z

Lynch at 21:04, 6 January 2007

2007-01-06T21:04:58Z

Lynch at 14:48, 4 January 2007

2007-01-04T14:48:42Z

Lynch at 23:50, 20 October 2006

2006-10-20T23:50:13Z

Stephens at 19:18, 9 June 2006

2006-06-09T19:18:18Z

Stephens at 19:16, 9 June 2006

2006-06-09T19:16:57Z

@@ Line 24: / Line 24: @@
 [[image:half_b.jpg|300px]]
-The diode is there because the inductance of the motor does not want the current through the motor to change instantaneously.  (Remember that the voltage across an inductor is equal to <math>v=L di/dt</math>, so an instantaneous change in <math>i</math> means an infinite <math>di/dt</math>, resulting in infinite voltage, at least theoretically.)  If the motor has current flowing through it, and then we open a switch, the diode provides a path for current to continue to flow through the motor as the energy of the motor is gracefully dissipated through the resistance of the motor (and the diode).  This prevents a large voltage transient (an "inductive kick") that could damage your electronics.  When a diode is used this way it is called a ''flyback diode''.  Such a diode should be capable of carrying large currents and switching on and off quickly.
+The diode is there because the inductance of the motor does not want the current through the motor to change instantaneously.  (Remember that the voltage across an inductor is equal to <math>v=L di/dt</math>, so an instantaneous change in <math>i</math> means an infinite <math>di/dt</math>, resulting in infinite voltage, at least theoretically.)  If the motor has current flowing through it, and then we open a switch, the diode provides a path for current to continue to flow through the motor as the energy of the motor is gracefully dissipated through the resistance of the motor (and the diode).  This prevents a large voltage transient (an "inductive kick") that could damage your electronics.  When a diode is used this way it is called a ''flyback diode''.  Such a diode should be capable of carrying large currents and switching on and off quickly.  See more at [[Diodes and Transistors]].
 There are different ways to control the speed of a DC motor:

@@ Line 24: / Line 24: @@
 [[image:half_b.jpg|300px]]
-The diode is there because the inductance of the motor does not want the current through the motor to change instantaneously.  (Remember that the voltage across an inductor is equal to <math>v=L di/dt</math>, so an instantaneous change in <math>i</math> means an infinite <math>di/dt</math>, resulting in infinite voltage, at least theoretically.)  If the motor has current flowing through it, and then we open a switch, the diode provides a path for current to continue to flow through the motor as the energy of the motor is gracefully dissipated through the resistance of the motor (and the diode).  This prevents a large voltage transient that could damage your electronics.  When a diode is used this way it is called a ''flyback diode''.  Such a diode should be capable of carrying large currents and switching on and off quickly.
+The diode is there because the inductance of the motor does not want the current through the motor to change instantaneously.  (Remember that the voltage across an inductor is equal to <math>v=L di/dt</math>, so an instantaneous change in <math>i</math> means an infinite <math>di/dt</math>, resulting in infinite voltage, at least theoretically.)  If the motor has current flowing through it, and then we open a switch, the diode provides a path for current to continue to flow through the motor as the energy of the motor is gracefully dissipated through the resistance of the motor (and the diode).  This prevents a large voltage transient (an "inductive kick") that could damage your electronics.  When a diode is used this way it is called a ''flyback diode''.  Such a diode should be capable of carrying large currents and switching on and off quickly.
 There are different ways to control the speed of a DC motor:

@@ Line 17: / Line 17: @@
 of the voltage applied across its terminals.
-The PWM signal can be used to drive an H-bridge to control the direction of the motor.  See [http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/index.html this page] for a nice tutorial, or this [[media:L293.pdf L293 H-bridge data sheet]] to learn more about H-bridges.
+The PWM signal can be used to drive an H-bridge to control the direction of the motor.  See [http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/index.html this page] for a nice tutorial, or this [[media:L293.pdf|L293 H-bridge data sheet]] to learn more about H-bridges.
 If the motor only has to turn in 1 direction, we can just use a

@@ Line 17: / Line 17: @@
 of the voltage applied across its terminals.
-The PWM signal can be used to drive an H-bridge to control the direction of the motor.  See [http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/index.html this page] for a nice tutorial, or this [[L293.pdf|L293 H-bridge data sheet]] to learn more about H-bridges.
+The PWM signal can be used to drive an H-bridge to control the direction of the motor.  See [http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/index.html this page] for a nice tutorial, or this [[media:L293.pdf L293 H-bridge data sheet]] to learn more about H-bridges.
 If the motor only has to turn in 1 direction, we can just use a
@@ Line 39: / Line 39: @@
 When using a integrated chip, one of the concerns is heat sinking. It is because there are lots of power dissipation and we need to take the heat away. Usually, these chips come with some way to attach to piece of metal or copper (a heatsink).
-You can find a nice tutorial on H-bridges [http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/index.html here].
 For a practical circuit that controls a DC motor using PWM, see the [[PIC PWM Motor Driver]].

@@ Line 1: / Line 1: @@
 To control the speed of the motor, the switches of an H-bridge are opened and closed at different rates in order to apply different
-average voltages across the motor. This technique is called <B>pulse width modulation</B>. Let's look at the following diagrams:
+average voltages across the motor. This technique is called <B>pulse width modulation</B> (PWM). Let's look at the following diagrams:
 {|
@@ Line 15: / Line 15: @@
 Pulse-Width Ratio = <math>\begin{matrix}\frac{t_{on}}{t_{period}}\end{matrix}</math>
-of the voltage applied across its terminals. If the motor only has to turn in 1 direction, we can just use a
+of the voltage applied across its terminals.
+The PWM signal can be used to drive an H-bridge to control the direction of the motor.  See [http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/index.html this page] for a nice tutorial, or this [[L293.pdf|L293 H-bridge data sheet]] to learn more about H-bridges.
+If the motor only has to turn in 1 direction, we can just use a
 half bridge:

@@ Line 19: / Line 19: @@
 [[image:half_b.jpg|300px]]
+The diode is there because the inductance of the motor does not want the current through the motor to change instantaneously.  (Remember that the voltage across an inductor is equal to <math>v=L di/dt</math>, so an instantaneous change in <math>i</math> means an infinite <math>di/dt</math>, resulting in infinite voltage, at least theoretically.)  If the motor has current flowing through it, and then we open a switch, the diode provides a path for current to continue to flow through the motor as the energy of the motor is gracefully dissipated through the resistance of the motor (and the diode).  This prevents a large voltage transient that could damage your electronics.  When a diode is used this way it is called a ''flyback diode''.  Such a diode should be capable of carrying large currents and switching on and off quickly.
 There are different ways to control the speed of a DC motor:
-# switching from full positive to full negative</P>
+# switching from full positive to full negative
-# full positive to open</P>
+# full positive to open
-# full negative to open</P>
+# full negative to open
-# braking by shorting</P>
+# braking by shorting
-# free wheeling by leaving the circuit open.</P>
+# free wheeling by leaving the circuit open.
 One of the possibilities is to use a full H-bridge chip, such as the L6201 shown below:

← Older revision		Revision as of 23:50, 20 October 2006
Line 34:		Line 34:
	When using a integrated chip, one of the concerns is heat sinking. It is because there are lots of power dissipation and we need to take the heat away. Usually, these chips come with some way to attach to piece of metal or copper (a heatsink).		When using a integrated chip, one of the concerns is heat sinking. It is because there are lots of power dissipation and we need to take the heat away. Usually, these chips come with some way to attach to piece of metal or copper (a heatsink).

	For a practical circuit that controls a DC motor using PWM, see ~~PWM~~ ~~Circuit~~ ~~Using~~ ~~PIC~~.		For a practical circuit that controls a DC motor using PWM, see the [[PIC PWM Motor Driver]].

← Older revision		Revision as of 19:18, 9 June 2006
Line 33:		Line 33:

	When using a integrated chip, one of the concerns is heat sinking. It is because there are lots of power dissipation and we need to take the heat away. Usually, these chips come with some way to attach to piece of metal or copper (a heatsink).		When using a integrated chip, one of the concerns is heat sinking. It is because there are lots of power dissipation and we need to take the heat away. Usually, these chips come with some way to attach to piece of metal or copper (a heatsink).

			For a practical circuit that controls a DC motor using PWM, see PWM Circuit Using PIC.

@@ Line 28: / Line 28: @@
 # free wheeling by leaving the circuit open.</P>
-One of the possibilities is to use a L293D chip shown below:
+One of the possibilities is to use a full-bridge chip, such as the L6201 shown below:
-[[image:L293.jpg|450px]]
+[[image:L6201.jpg|450px]]
-When using a L293D chip, one of the concerns is heat sinking. It is because there are lots of power dissipation and we need to take
+When using a integrated chip, one of the concerns is heat sinking. It is because there are lots of power dissipation and we need to take the heat away. Usually, these chips come with some way to attach to piece of metal or copper (a heatsink).
-the heat away. One of the ways to do this is to connect pins of the L293 to piece of metal or copper.