PWM with adjustable Freq and Duty Cycle

Thread Starter

mazur50

Joined Feb 5, 2007
28
I am looking for a PWM Circuit that i can adjust the Freq and the Duty Cycle independent of each other. and looking for Duty cycle of 0-100%

thanks
Mike
 

beenthere

Joined Apr 20, 2004
15,819
How are your programming skills? You will probably need to do one from the ground up with a microcontroller running the circuit.
 

Thread Starter

mazur50

Joined Feb 5, 2007
28
What i am looking to do is make a pwm circuit to control a mosfet to bake a dc motor. and i would like to make it pluse like abs and also have a variable brake.
 

Papabravo

Joined Feb 24, 2006
15,127
The reason we ask is that frequency control in a PWM application may be a bit coarse. Think discrete frequency choices rather than a continuously variable frequency. The microcontroller route may still be the right solution but maybe a dual 555 circuit could also do the job.
 

beenthere

Joined Apr 20, 2004
15,819
If by "notice the pulse" you mean to be able to have a visual indication, then you will need an oscilloscope. A LED will flash too rapidly to let you see the pulse rate - PWM likes to get done at thousands of Hz to hold down the motor noise.
 

Thread Starter

mazur50

Joined Feb 5, 2007
28
right but i am not using this to control the motor speed I am using it to control the braking of the motor. So would changing the frequency make it work like if i want to make a led blink faster to slower.
 

beenthere

Joined Apr 20, 2004
15,819
For braking, the PWM would be applied to drive the motor in reverse (needing a full bridge setup). You would need some device on the shaft to indicate that the shaft had stopped.

There is another way out. I once worked with a tape drive that used brakes on the reel motors. The braking device was a chamber filled with a magnetic material. The shaft turned a perforated plate inside the chamber. Applying a magnetic field caused the ferrous powder to string along the lines of force. The disk got braked because the strings ran through the perforations and created drag.

Here's a link to a manufacturer - http://www.ogura-clutch.com/product...ml?PHPSESSID=578be01984d770dc7f369e62b32b331d
 

h.d

Joined Oct 22, 2007
150
braking or forward drive its the same concept, the diffrence is the value of the duty cycle and its variation direction increasing or decreasing.
for braking you will start with 100% d.c to trigger the mosfet the for braking start decrease it.
for abs i theink you should do the decreasing frequently you can do that by microcontroller.
 
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