What is pulse width modulation generator?

Answer 1

A pulse width modulation generator regulates the on and off times of a square wave-form.

It is commonly used in dimmer-switches and utilizes high frequency.

Example of waveform:

555555555555555554444444422222222111111110000000000000000

This waveform is 50% on and 50% off. In a light-bulb this would mean that you only get approximately 50% of the light it can give you. It is dimmed down 50%.

By modulating this waveform, we can get more or less light whilst keeping frequency the same.

Example:

555555555555555555555444444444222222222111111111000000000000

As you can see, the frequency is the same, but it is more on than off.

In this example, it is 75% on and 25% off, giving you 75% of maximum light.

Another example:

555555555555544444444222222221111111100000000000000000000

Here we have only 25% on and 75% off, yet still keeping the frequency the same.

Dimmer-switches can be made in a few different ways.

We can chop off parts of the sinusoidal waveform we get from the AC outlet.

This would be the same as regulating the pulse width of the sinus curve of AC Voltage.

We can regulate the voltage. This could be an approach of a battery-operated lamp.

The problem is that voltage regulation mean a lot of heat. (depending on method used.)

If regulating a 12 volt source down to 6 volt in order to dim a light bulb, 6 volt will go to the bulb and 6 volt will "burn up" in the regulator circuitry. If the bulb is 50 watt, then 25 watt will burn in the bulb, and the rest will create heat in the circuitry.

Now for the art of Pulse Width Modulation.

We make a generator that vary the pulse width instead of the voltage.

At 50 Hertz, we will hear the bulb hiss and we might notice some flicker.

At 5 Kilo Hertz, we will hear the bulb sing at a high pitch but the flicker is all gone.

At 25 Kilo Hertz, we might hear a very high frequency sound, but for most this is not noticeable.

(It is actually possible to make a light regulator that utilizes the bulb as a speaker to play music.)

At 35 Kilo Hertz, all audible noise is gone (although your dog might notice it)

By regulating the pulse width at 35 Khz we can dim the light up and down very accurately using Power MosFets'

A Power Mosfet has got the ability to switch electricity on and off in a fraction of a second. It has got very low internal resistance and very little power is consumed as heat. (Frequencies of 100Khz is easily obtainable and is often utilized.)

Advantages of PulseWidth Modulation:

Low power-consumption (little heat)

Small circuitry needed.

Extended battery life. Dim down 50% and your battery last almost 50% longer.

Disadvantages:

As the voltage rise and fall extremely rapidly, this creates an electromagnetic pulse. These pulses might interfere with electrical equipment like radio and TV (Not limited by these)

(By introducing a coil, we can eliminate much of this radio-noise.)

It is "difficult" to make a proper working circuitry able to dim fluorescent light.

A pulse width modulator for DC as in a battery can be made using very few components.

2 OpAmp

a couple of resistors.

a couple of capacitors.

1 PowerMosFet

1 Variable resistor (for adjusting the pulse width)

1 zener diode (3,3-5,6 Volt)

Cheap to make and long lasting.