PWM Output voltage

[electronicsman]

It is just a concept which i want to understand, let us assume V1 supply and i can control it either using controller and apply pwm signal of the required duty, and L1 is a motor. My question is if i apply a pwm of duty 50% will i see a voltage of v1/2 on the motor and similarly based on the duty the corresponding voltages are applied? Am i correct? The second question what is the minimum frequency of the pwm, i assume that if the frequency is below some level the formula of v1/2 may not apply. Am i correct?

 

[KlausST]

Hi,

Insufficient information.
Incomplete simulation.

How does your PWM work?
A simple switch ON/OFF, without voltage clamp? With voltage clamp - what clamp voltage?
Or a true half bridge with output voltage levels: V1, 0V?
Which mode? DCM? CCM?

A motor is no simple inductance.
A stalled motor comes close to it, but i motor that does not move makes nit much sense.
A running motor ... when you switch OFF (switch = high impedance) will cause a short negative pulse (like a pure inductance) followed by a positive EMF voltage proportional to RPM.

Then what measurement method do you use?
Average or RMS?
A square wave with clean switching to two levels: V1 and 0V....will result in:
* V_avg= V1 x duty_cycle (average method)
* V_ rms = V1 x sqrt(duty_cycle)

You see it depends a lot on the details ... and thus can't be answered generally.

Klaus

 

[danadakk]

If sensorless BLDC application this ap note might help -

https://www.cypress.com/file/157806/download

Ap Note

StackPath

Atmel one attached.....

Regards, Dana.


This is a low end part solution, sensorless design for speed control.

 

[Carry for cents bazar]

If I understand correctly, you are asking about the rising time and falling time of the voltage over the motor. The motor must be built for PWM control. When you supply a different frequency of the PWM for 1 second, this will result in a different strength of the electromagnetic field, which in turn rotates the motor. The voltage will either drop a little or a lot from the PWM maximum. This depends on the frequency, duty cycle and circuit. Without knowing the exact values of the motor, PWM and driver, we can not tell you.

1. Here is a simple tutorial.
2. Here are the time diagrams.