What is pulse hashing – Troubleinthepeace


Pulse width modulation is modulation/changing the width of the pulse (Not the frequency). To best understand what PWM is, let’s first take a look at some basic terms.

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Microcontrollers are intelligent digital components that operate on binary signals. The representation of a binary signal is a band of square waves. The diagram below explains the basic terms related to square wave signals.

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As shown in the diagram above, it is important to note in PWM signals that the time and frequency are always fixed. Only the ON and OFF times of the pulse (duty cycle) change. By this technique we can adjust the given voltage. The difference between a square wave signal and a PWM signal is that a square wave signal has the same ON and OFF time (the duty cycle is both 50%), while a PWM signal has a variable period. Square waves can be seen as a special case of a 50% duty cycle PWM signal (ON = OFF).

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For example:

With a supply voltage of 50V, and if the load needs 40V, the best way to get 40v out of 50v is to do pulse hashing. The pulse generator needs a signal which is a PWM signal to turn the thyristor ON and OFF. This PWM signal can be easily generated by a microcontroller with a timer. The requirements for the PWM signal to generate a 40V using a thyristor from a 50v supply, Then ON = 400ms, OFF = 100ms (for a PWM signal period of 500ms). In general, this can be easily explained in the following way: Basically, the thyristor is operated like a switch. In the pulse generator, the load connects to the source through the thyristor. When the thyristor is in the OFF state, the load is not connected to the source, and when the thyristor is in the ON state, the load is connected to the source. The work of switching the thyristor ON and OFF is done by the PWM signal. The percentage of time that the PWM signal is high/ON is called the duty cycle of the signal. If duty cycle is 100% then the wave becomes a fixed DC current. So the duty cycle can be calculated using the following formula:

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Using the above formula, we can calculate tON for the voltage we want from the total voltage source. By multiplying the duty cycle by 100, we can get it to a percentage. So the ratio of duty cycle is proportional to the voltage taken from the source. In the example above, if we wanted 40V from a 50V source, this could be done by hashing the 80% duty cycle. Because 80% of 50 is 40.

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For example:

At a frequency of 50Hz design a PWM waveform with a duty cycle of 60%.

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The PWM pulses have the following form:

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One of the most common applications of pulse width modulation is motor speed control

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