Dimmer

[BMIelektonik]

What about the timing of the trigger pulse when they meet in the center "50%dutycyle". At one point the pic will be busy with 100us pulse for SCR1 and at the same time SCR2 should be triggerd. this might give some flicker. maybe the solution would be to make the dimfunction in lets say 10 or 20 steps and then take care of the overlap instead of a linear dimfuntion


Thanks

[ardhuru]

I've found that the trigger pulse can be as narrow as 5uS; therefore the flicker you refer to is imperceptible.

Also, you could put in a line that caters specifically to this situation; e.g., if X = (1000-X) then High Out1 - Pauseus 5 - Low OUt1 - High Out2 - Pauseus 5 - Low Out2.

BTW, I am using traics, not SCRs. Any particular reason you are using SCRs?

Regards,

Anand

[BMIelektonik]

I am using a opto triac Sharp S216S01 so its not a SCR. have to check what the shortest triggpulse can be

Thanks for you input

[sougata]

Hi there,

Which PIC are you using ayway and how are you detecting the zero cross.

It is also important if you are detecting every or alternate zero crosses.

If you are using an interrupt based routine then do the following

1. Play with Timer0 and reset it every zero cross. All turn off the outputs. Its best to do it in assembly.
2. Thus your timer functions as a digital ramp generator now use to loop to detect if the timer has reached the desired value. In this way you do not have to care about the glitches.
3. A 5us time might be not enough. It is best to keep the outputs latched till the next zero cross. This will also let you use low loads under the latching current of the SCR.

Regards

Sougata

[BMIelektonik]

I use a 16F84 8Mhz.Zero detection with an opto coupler after rectifyer 100Hz and then a schmittrigger to get the levels right. Have a <1ms puls around zero.
It might be a good idea to make the pulse as long as it can be ,and bring it low just before zero. Sharp "s216s01" recomends 1mS min ,
Assembly might be the best way of solving this ,since my goal is to control 5 outputs , I start with one then work my way up

thanks

[George]

I use a resistor as zero detect, 1 meg from phase straight into the port, I then have a 470K resistor on the pin next door to it and swing the bias in an opposite direction to the mains ie:

GPIO.5 is the output pin with the 470K on it - trigger is GPIO.4 which is connected upto the 1M which goes straight to phase. The triac is triggered by a BC327 and i trigger by turning pic from high impedance to low by changing from input to output.

LowSide: 'look for trigger points and trigger triac

IF trigger = 1 Then lowside 'wait for phase to go low
GPIO.5 = 0 'weight input to sense zero crossing
PauseUs dim 'wait for dim period
Output triac 'fire triac
triac = 0
PauseUs 400
Input triac


HighSide:

IF trigger = 0 Then HighSide
GPIO.5 = 1
PauseUs dim
Output triac
triac = 0
PauseUs 400
Input triac

GoTo start

[sougata]

Hi there,

Having the opto-triac driven till the zero cross would take care of inductive loads also.
Provide me with the following :

1. How the outputs would be controlled? (Internal timer /push button etc)
2. Your line frequency

I would try to play with the interrupt part simulate it.

Regards

Sougata