control the speed of the ac fan by pic with PWM

Thread Starter

Mohamad Knight

Joined Mar 21, 2016
23
Hello
I would like to know how to control the speed of the ac fan by pic with PWM
I used optoisolator to protect the pic
but the circuit does not work well
is the optoisolator doing his duty ?
is this circut working properly ?
please help me
 

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crutschow

Joined Mar 14, 2008
34,280
PWM does not work because once the TRIAC is turned on it will not turn off until the AC voltage returns to zero at the end of each half cycle.
That's why you need a phase-control circuit as bertus stated.
 

MaxHeadRoom

Joined Jul 18, 2013
28,617
The 2n7000 takes the detected zero crossings, and conditions it for the pic, this signal is required in order to pulse the Triac at the right point on each half cycle, the point in time after the zero crossing has occurred decides the motor energy, or trigger point of the triac.
Read up on Fairchild AN-3006 for another explanation.
Max.
 

Dodgydave

Joined Jun 22, 2012
11,284
thank you my friend , but I do not understand
What is the mosfet (2n700) function?
I want to control the speed of motor (Increase or decrease ) the speed
It's for a Zero crossing detection, this gives you a high pulse when the mains is at zero volts, so you can start your pwm signal.
 

DickCappels

Joined Aug 21, 2008
10,153
This might be a good time to mention that the circuit appears to float on the AC power lines, preferably on Neutral, so precautions need to be taken to assure that the nobody gets shocked while building and debugging the circuit currently under discussion. The best solution would be to use a 1:1 isolation transformer so you can be sure that the microcontroller part of the circuit is earthed. Otherwise, proceed with a clear head, insulated soles, and one hand in your back pocket (so the path to ground doesn't go through your heart)
 
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