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Triac dimmer circuit firing parasitically

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anotherbrick

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help! - triac dimmer circuit firing parasiticaly

hello dear forum,

I try to build the following triac dimmer
which controls the power input to a 2 KW 28 KHz ultrasonic inverter

triac.jpg
triac2.jpg

the ISIS circuit detects the zero crossing of the mains
and I divide the 180 Degree of sinus voltage into 100
everything is fine until the firing angle is above %80

if the firing angle is above %80 the triac is parasiticaly fired at zero angle 2-3 times a second

the zero cross dedector of the dimmer is the rising edge of the ISIS circuit
and to be safe I also start a timer with the rising edge and enable the next zero crossing
as soon as the timer is 250 uS close to the next rising edge

( sorry this is my best english - I hope you understand what I mean)

here is the code

please help me to eliminate the parasitic firing of the triac

thank you

Code:
volatile uint8_t extintena=0;
void EXTI4_IRQHandler(void)
{
    /* Clear the Key Button EXTI line pending bit */
    EXTI_ClearFlag(EXTI_Line4);
    EXTI_ClearITPendingBit(EXTI_Line4);

    if(extintena){
    TIM7->CNT=0;TIM_Cmd(TIM7, ENABLE);GPIOC->BRR = GPIO_Pin_5;
    extintena=0;TIM2->CNT=0;}
}
void TIM2_IRQHandler(void){
 TIM_ClearFlag(TIM2, TIM_FLAG_Update);
 TIM_ClearITPendingBit(TIM2, TIM_IT_Update);

    extintena=1;
}
void TIM7_IRQHandler(void){
 TIM_ClearFlag(TIM7, TIM_FLAG_Update);
 TIM_ClearITPendingBit(TIM7, TIM_IT_Update);

GPIOC->BSRR = GPIO_Pin_5;TIM_Cmd(TIM7, DISABLE);
}
 

Re: help! - triac dimmer circuit firing parasiticaly

Without doing any math so I 'm probably wrong:
The first (top) schematic is for driving an inductive load, is that what your ultrasonic inverter appears as to the triac?
You might find the phase shift of 1.2K and 0.2uF is enough to skew the firing angle, see what happens if you remove the capacitor or drop it to a much lower value.

Brian.
 
Re: help! - triac dimmer circuit firing parasiticaly

ultrasonic transducer is a capacitive device but I insert inductor in series
to operate it in resonance approximately

secondly if I remove the 0.2 uF capacitor it gets worser - more parasitic firing of triac
 

Re: help! - triac dimmer circuit firing parasiticaly

Your posts don't tell much more than "there is parasitic firing". To understand why, you need to perform detailed measurements and specific tests to reveal how the unwanted triggering actually happens. It can be either failure of the zero crossing detector, a software problem or MOC/triac triggered by high dv/dt.


The RC snubber should prevent high dV/dt transients reaching the MOC, so it can be either transients exceeding the triac dV/dt rating or it's a problem with the trigger signal generation. An dedicated snubber across the triac with lower series resistance (e.g. 50 to 100 ohm) should be able to reduce possible transients.

But more likely, the problem is either in the zero crossing detector or in the software.
 
Re: help! - triac dimmer circuit firing parasiticaly

230Vac? also what is the voltage into BR1?
 

Re: help! - triac dimmer circuit firing parasiticaly

Easy Peasy raises a good point, the values in your original schematic suggest BR1 is fed from a low voltage (12V?) transformer. If that is the case, you may need to take into account the phase shift in the transformer. The waveform showing zero crossing detection may match the AC at BR1 but not the AC feeding the triac.

Brian.
 
Re: help! - triac dimmer circuit firing parasiticaly

some wave-forms of what is going on - when it starts to behave wrongly would be useful...
 

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