[PIC] PWM with incandescent lamp (voltage checking)

[Mansoor Ahmed]

hello everybody, am facing a new problem with my project PWM using incandescent lamp. The problem is when i give the PWM duty cycle value (i.e apporx certain value) the voltage variations in that pin doesn't remain constant it keeps on moving from 0 V to 3.0 V and vice-versa, due to this the lamp keeps on flickering. how can i rectify this issue. why the voltage in pin keeps increasing and decreasing even though the value is directly given i am not aware of this kindly please help me to overcome this issue. waiting for your reply.

thank you u in advance.

 

[ard]

Hi,

You dont control an incandescent lamp using pwm. What you need to do is detect the zero-crossing of the sine wave, and then, after a delay, pulse the triac (say 1ms); the duration of the delay between the zzero-crossing and the pulse would control the intenisty.

That is, the sooner you pulse the triac gate after the zerocrossing, brighter the lamp would be, later you do it dimmer the lamp would be.

Regards,

Anand Dhuru

 

[Mansoor Ahmed]

thank you Anand for your reply. i am using MOC3031 optocoupler which has zero crossing inbuilt in it, even though am facing the problem. The zero crossing detector is in hardware, should i code zero crossing in software also, if so please give me suggestion for zero crossing code as i am not aware of the zero crossing code. Thank you.

 

[Allen6502]

Yes, you'll still need to code the zero crossing detection in your code even though you're using the MOC3031 with ZCC inside, if you want to control the brightness of your lamp. See the Q&A here:

https://electronics.stackexchange.com/questions/13390/how-to-use-a-phototriac-coupler-to-trigger-the-main-triac

PWM is only used when you want to control DC lamp brightness.

Allen

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Here is a simple dimmer circuit that uses zero crossing detection to fire a TRIAC though an opto-coupler from my harddisk. The mcu is a DIP8 pic.