Pulse Width Modulation also called Pwm, is a great method of controlling the number of power delivered to a load without dissipating any wasted power because the midpoint power delivered to the load is proportional to the modulation duty cycle.
Many habitancy endeavor to control the speed of a D.C. motor using a large changeable resistor (called a rheostat) in series with the motor to control the number of current and therefore the speed of the motor. While this may work it generates a lot of heat and wasted power in the resistance. One uncomplicated way to control the speed of a motor is to regulate the number of voltage over its terminals. This is achieved using "Pulse Width Modulation" or Pwm by driving the motor with a series of "On-Off" pulses rather than a continuously varying (analog) voltage. By increasing or decreasing the pulse widths, the Pwm circuit regulates vigor flow to the motor while keeping the frequency constant.
DC Motor Controller
The power applied to the motor can be controlled by varying the width of these applied pulses and thereby varying the midpoint voltage applied to the motors terminals. By changing or modulating the timing of these pulses the speed of the motor can be controlled, i.e. The longer the pulse is "On", the faster the motor will rotate and likewise, the shorter the pulse is "On" the slower the motor will rotate. The distinction in the ratio between the "On" pulse and the "Off" pulse is called the duty cycle. Duty cycle is expressed as a percentage relating to the fraction of time that the output voltage is "On" and may be various from 0 to 100 percent. So for a duty cycle of 0 percent the motor is fully-off, 50 percent the motor is carrying out at half speed, and 100 percent the motor is fully-on.
The use of pulse width modulation to control a small motor or fan has the advantage in that the power loss in the switching gismo is small because it is whether fully "On" or fully "Off" therefore the switching gismo has a much reduced power dissipation giving a linear type of control resulting in better speed stability. Also the amplitude and frequency of the motor voltage remains constant so the motor is all the time at full strength.
One additional advantage of pulse width modulation is that the pulses reach the full provide voltage and will yield more torque in a motor by being able to overcome the internal motor resistances more easily. The result is that the motor can be run gradually without stalling. Also, in a pulse width modulation circuit, small ordinarily ready potentiometers can be used to control a wide variety of motor loads whereas large and expensive high power changeable resistors called Rheostats are needed for resistive controllers.
Pulse width modulation can also be used to control the brightness of light sources such as Dc lamps or Light Emitting Diodes. Light emitting diodes (Leds), turn "On" and "Off" extremely quickly and would appear to flicker if supplied with a low frequency voltage. The result of this flicker can be reduced by increasing the pulse width modulation frequency. If the "On/Off" switching frequency is sufficiently rapid, the human eye can not see this switch performance and only sees the brightness of the lamp without flicker.
Pulse Width Modulation is a great method for controlling the number of midpoint power delivered to a load without dissipating any wasted power. Pwm circuits can be used in many dissimilar applications to control the speed of motors and fans or to dim the brightness of Dc lamps or Led's. If you need to control it, use Pulse Width Modulation to do it.
Pulse Width Modulationdc motor controller