Is there some one who can explain me the PWM in his way

[FERMED]

PWM

Hi,

Is there some one who can explain me the PWM in his way, as I read so many explanations in the web and other books, but unfortunately I found some difficulties to understand it.

Many thanks

 

[srizbf]

Re: PWM

please check


whether it is sufficient or you require more.

srizbf
16thmay2010

 

[amriths04]

I would interpret it as information being communicated through time instead of the conventional amplitude.

I understand it like this. Assume you are forced to communicate with your friend using only a torch light. Now you have 2 options:

1) you could convey the information by changing the brightness of the light (a modern torch light) (amplitude modulation)

2) you could convey the information by changing the time for which you switch on the torch light. (An old torch light is enough). (Time modulation = PWM)

Of course you must have a mutually agreed set of protocols for effective communication. (demodulation/decoding)

 

[fcfusion]

LOL, amriths04 complicates it quite a lot.

A PWM modulator converts an anlog signal (ex: sinuoise) into a series of very fast pulse. Theoretically, the faster the pulses frequency, the better.

These pulse's duty cycle is proportional to the input signal's amplitude, at each instant.
So, for each instant of time, the average value of the pulses is equal to input signals amplitude.

So, in theory, for a small instant of time (compared to the input signals frequency) we'll have:

Average (Pulses) = Amplitude (Input_Signal)

Averaging pulses is done through a simple low pass filter.

Like I said pulse frequency must be must greater than the input signal's frequency, at least 64 times.


Hope it helped.

 

[himrwt]

it seems to me that FERMED is asking about PWM in power electronics not communication.
correct me if i am wrong.
PWM is used in power electronics to vary rms voltage input to a device.
consider a 100V voltage pulse train going high and low within a time period T and duty cycle dty. dty is the percentage of T for which voltage is high.
if dty is 50% then rms voltage would be 50V.
same voltage will appear to a motor.

a motor due to its inertia may not show any response to a very high frequency voltage. so we can use pwm for effectively varying speed of motor by varying duty cycle of voltage.

 

[manju_nath200]

I will teach you PWM to my best........

Let me try this........

1. PWM - Pulse Width Modulation

2. Its purely control phenomenon and helps you generating triggering signals

3. Triggering signals..? What is this....

Consider combination of 4 MOSFETS (Power Electronic Switches, which have switching frequecny of 100K Hz i.e. a MOSFET can turn off and on 100000 times in a sec., certainly un imaginable ) such that it forms an INVERTER configuration.

As we know, o/p of Inverter to be a Pure Sine wave (certain Voltage Vo = 230 V rms and Frequecny Fo = 50 Hz), But how to produce it.

Inverter is fed with DC input supply (mandatory) , and a control technique.

There are numorous control techniques available (PWM, Hys, SMC, PID, etc )

PWM is very basic and very popular technique , which can easily understood and fabricated on board unlike others.

In our case, 600 V rated MOSFET is required ....Even a MOSFET of 10KV and 3000A rating needs only 5 V or 10 V supply at its gate terminal to turn it on i.e. beauty of Power Electronics (Controlling bulk power with 10V)

4. In PWM , two signals will be compared of which one must be Triangular and other may be choice.

To choose second,

If output of Inverter is to be Sine wave, then choose Sine hence called Sine PWM

If output of Inverter is to be Square , then choose Square wave , called Square PWM

5. Both signals, triangle and sine signal (known as control signal), will be of amplitude of maximum 1V only

6. Frequency of output Sine signal will be same as control signal.


Reply me if any clarification needed