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ALL ABOUT ELECTRONICS.
In this video, we will learn about pulse width
modulation technique.
The pulse width modulation technique is used
to control the analog devices.
And mainly the power which is delivered to
the analog device is controlled using this
technique.
Now, because of it's high efficiency, low
power loss and it's ability to precisely control
the power, this technique is used in many
applications.
For example, today for dimming the LED lights,
or for controlling the fan speed of the CPU,
this PWM technique is preferred over the conventional
methods.
And in some laptops, even the brightness of
the screen is also controlled using this pulse
width modulation technique.
So, apart from this applications, this PWM
is extensively used in the power electronics
applications.
so, in this video, let's understand what is
PWM, and how it can be used to control the
different analog devices.
So, in this pulse width modulation technique,
by changing the pulse width of the control
signal, the power which is delivered to the
load is controlled.
And let's understand what do we mean by it
by taking one example.
So, let's say, we want to control the brightness
of the LED using this pulse width modulation
technique.
So, here the electronic switch is connected
between the voltage source and the LED circuit.
And here, this electronic switch is controlled
using the external control signal.
So, whenever the switch is in the closed condition,
then the entire voltage will appear across
the LED circuit.
And here, let's assume that we are using the
9V of the battery.
And whenever the switch is in the open condition,
then the circuit will get isolated from the
voltage supply.
So, now if we apply the control voltage over
here like this, then the switch will get turned
ON and OFF very rapidly.
And if we see the waveform just after the
switch, then the waveform will look like this.
So, if you observe this waveform, here this
9V of voltage is appearing across the circuit
only for the half of the time.
So, we can say that effectively only 4.5 V
of voltage is applied to the LED circuit.
Or in other words, we can say that the average
value of the voltage is equal to 4.5 volts.
Now, instead of this 50 percent, if the switch
remains ON only for the 25 percent of the
time, then the waveform will look like this.
So, in this case, if you see the average value,
then the average value is reduced to the 2.25
volt.
So, now effectively only this 2.25 voltage
is applied to the LED circuit.
So, here what we are doing, by controlling
the pulse width of this output waveform, we
are actually controlling the voltage which
is applied to the LED circuit.
And in this way, we are controlling the brightness
of the LED circuit.
So, this same technique is also used for controlling
the speed of the DC motors.
So, whenever we talk about this pulse width
modulation, then the two factors are always
associated with it.
One is the switching frequency and the second
is the duty cycle.
So, if this switching frequency is 1Hz, in
that case, you can see the flickering in the
LED.
But instead of 1 Hz, if the switching frequency
is let's say 500 Hz, in that case, the switch
will get turned ON and OFF very rapidly.
And in that case, you feel like the LED is
continuously in the ON condition.
So, for the particular application, this switching
frequency should be optimum.
So, depending on the application, usually,
the switching frequency varies from 100s of
Hz to even kHz.
Then the next parameter for this pulse width
modulation is the duty cycle.
So, the duty cycle defines for the what fraction
of the time period, the pulse remains in the
ON condition.
Or we can say that it is the ratio of the
ON time to the total time period.
So, for some waveform, if the duty cycle is
50 percent, it means that the pulse remains
ON for the 50 percent of the time.
Likewise, for some other waveform, if the
duty cycle is 25 percent it means that the
pulse will remain On only for the 25 percent
of the time.
So, here the different waveforms with different
duty cycles are shown.
So, here by changing the duty cycle of the
waveform, we are actually changing the average
value of the output waveform.
And by doing so, we are actually changing
the average voltage which is applied to the
load.
So, by changing this duty cycle, we can control
the different devices.
Now, in pulse width modulation, usually, MOSFET
is used as an electronic switch.
And the advantage of this MOSFET switch is
that during the switching, the power which
is dissipated across this switch is negligible.
So, we can say that this pulse width modulation
technique is a very efficient technique.
And that is why nowadays it is preferred over
the conventional techniques.
So, if we see the conventional technique for
controlling the brightness of the LED, then
by changing the value of this resistance R,
we can change the current that is flowing
through the LED.
And in a way, we can control the brightness
of the LED.
But in this case, as the current that is flowing
through the LED increase, the power which
is getting dissipated across the resistor
will also increase.
Apart from that, the relationship between
the brightness of the LED and the current
is non-linear.
So, in this technique, it is not possible
to control the brightness linearly.
On the other end if we talk about the pulse
width modulation technique, then in this technique
whenever the switch is in the closed condition
then the entire voltage is appearing across
the circuit.
It means that whenever the switch is in the
closed condition, then the current that is
flowing through the LED will remain constant.
So, here just by controlling the width of
this pulse, we can change the duration for
which the current is flowing through the LED.
So, in this technique, it is possible to control
the brightness linearly.
So, these are the few advantages of this PWM
technique over the conventional methods.
And that is the reason, nowadays it is preferred
in the many applications.
So, that is being said, now let's see how
we can generate this PWM output signal.
So, the simple way of generating this PWM
output signal is using the comparator circuit.
So, here the triangular wave is applied at
the non-inverting node.
While the control voltage is applied at the
inverting node.
So, whenever this triangular wave voltage
is less than the control voltage, then the
output of the comparator will be low.
And whenever the voltage of this triangular
wave just go above this control voltage, then
the output of the comparator will become high.
So, depending on the value of this control
voltage, the width of the pulse can be changed.
So, suppose if we reduce this control voltage,
in that case, the width of the output pulse
will increase.
So, in this way, by controlling this voltage
it is possible to change the pulse width of
the output waveform.
So, this is a very simple way by which we
can generate this PWM output signal.
Apart from that this signal can also be generated
using the 555 timer IC.
And we have already discussed this circuit
whenever we have talked about the astable
mode of operation of the 555 timer IC.
So here, by changing the value of this resistance
R1, it is possible to change the duty cycle
of the output waveform.
And this circuit can be used for generating
the PWM output signal.
Apart from this methods, it is also possible
to generate this PWM output signal using the
microcontrollers.
So, suppose if someone uses the microcontroller
board like Arduino, then it has dedicated
output pins for the PWM output signals.
So, using these pins, it is possible to generate
the PWM output signal.
And using this PWM output waveform, we can
control the different devices.
so, I hope in this video, you understood,
what is pulse width modulation and using this
pulse width modulation, how we can control
the different devices.
So, if you have any question or suggestion,
do let me know here in the comment section
below.
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