[SOLVED] help with understanding pwm

[ian123]

please help with my understaidng of PWM for current control

in order to slow down a motor yuo would use pwm the more on time the faster it goes (within Limits)
but how does pwm work with current control.

lets say you want to limit the current of the motor to 3 amps so by switching it on for a determined period would that then limit the current in the motor or not.

 

[FvM]

PWM current control usually involves a current measurement and a control loop. The PWM ratio is set by the controller output.

 

[kak111]

Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a commonly used technique
for controlling power to inertial electrical devices, made practical by modern electronic power switches.

The average value of voltage (and current) fed to the load is controlled by turning the switch between
supply and load on and off at a fast pace. The longer the switch is on compared to the off periods,
the higher the power supplied to the load is.

The PWM switching frequency has to be much faster than what would affect the load, which is to say
the device that uses the power. Typically switchings have to be done several times a minute in an electric stove,
120 Hz in a lamp dimmer, from few kilohertz (kHz) to tens of kHz for a motor drive and well into
the tens or hundreds of kHz in audio amplifiers and computer power supplies.

The term duty cycle describes the proportion of 'on' time to the regular interval or 'period' of time;
a low duty cycle corresponds to low power, because the power is off for most of the time.
Duty cycle is expressed in percent, 100% being fully on.

The main advantage of PWM is that power loss in the switching devices is very low.
When a switch is off there is practically no current, and when it is on, there is almost no voltage
drop across the switch. Power loss, being the product of voltage and current, is thus in both cases
close to zero. PWM also works well with digital controls, which, because of their on/off nature,
can easily set the needed duty cycle.

Pulse-width modulation - Wikipedia, the free encyclopedia

Delta modulation - Wikipedia, the free encyclopedia

Space vector modulation - Wikipedia, the free encyclopedia

About current regulation look p.3...9
**broken link removed**

Look : 10. Current limiting
**broken link removed**

 

[ian123]

PWM current control usually involves a current measurement and a control loop. The PWM ratio is set by the controller output.

Ok so then to control current you would turn off the pwm until the current drops then turn it back on

So in pactise the current controller would pulse on and off as then current rises and drops below the setpoint would it be fair to do this in a circuit

 

[FvM]

Ok so then to control current you would turn off the pwm until the current drops then turn it back on

This would be the simple case of a direct current control, just setting a current threshold. The PWM frequency can be defined indirectly by a hysteresis. I was thinking primarly of a PWM generator with fixed PWM frequency and current controlled loop setting the PWM duty cyle.

 

[ian123]

This would be the simple case of a direct current control, just setting a current threshold. The PWM frequency can be defined indirectly by a hysteresis. I was thinking primarly of a PWM generator with fixed PWM frequency and current controlled loop setting the PWM duty cyle.

OK in order for me to understand correctly please bear with me
Could you draw me a sketch of the pwm waveform so I can understamd what you mean