Zero crossing detection, traic triggering helpppplss!!!!!!!!

you are sensing voltage at ZERO point. This is indication that at this moment you have 0 V at L.
In this moment you should change state of T1 and T2 by setting level at PIC_T1, T2

Re: Zero crossing detection, traic triggering helpppplss!!!!

cancel said:

you are sensing voltage at ZERO point. This is indication that at this moment you have 0 V at L.
In this moment you should change state of T1 and T2 by setting level at PIC_T1, T2

Click to expand...

Thanks for answering, but i don't understand anything about these 2 circuit. I need detail explaination of these circuits. One of them is zero crossing and another one is traic triggerings. Can you explain me each elements work? I'm really lost in these circuits.

Why we use R30, R47, D30, D33, FUSE, R49, R48, C17, C18? If u can help me in these questions, i'Ll be so happy.



8)

Hi

I am going to do it the first circuit

FUSE S2, is emplyed to protect the circuit against overcurrents. what amazes me is the 1A value of that fuse, usually LED diodes such as D30 and the one in U20 uses around 200mA, I am not sure if they will blow at around 1A.

D33 is a rectifier, it lets you sense certain positive volatge at which the circuit is triggered. It doesnt activate at zero volts, assuming 2V in both leds and 0.7V in in D33, it activates at around 4.7V. you didnt mention it clearly so I am assuming and alternate voltage at L

R47 is a current limiter, it is necessary to set the current in the circuit.

D30 is just an indicator of the circuit activation.

D32 is a protection diode against high inverse voltages, it protects the diode in U20.

U20 isolates 2 circuits, the one which has the alternating current and the other which seems digital, this kind of circuits are used to avoid noise transference.

R30 has the purpose of setting the terminal ZERO to +5V when the circuit is not triggered, plus gives polarization to the transistor in U20.

if you think this info is useful click on "helped me" fo statistics

Sal

Re: Zero crossing detection, traic triggering helpppplss!!!!

Top circuit:

(L) & (N) = Line (A.C. current) and Neutral. Current is applied to line. D33 only passes the positive element of the signal and blocks the negative. R47 limits the current through the LED (D30). The LED looks like it is only there for indicator purposes. U20 is an opto-isolator. The current lights the internal LED which biases the base of the internal photo-transistor. When the photo-transistor "turns on", ZERO is pulled to ground potential (versus the +5V potential it is at in the off state). D32 is simply there for protection. (R30 "pulls" ZERO to +5V).

Middle circuit and bottom circuit (identical):

Signal is applied to PIC_T1 which "turns on" the photo-triac gate. Photo-triac gate conducts and "turns on" the gate of T1 (or T2).

R48 and C17 "pass some of the current from L1 which is fed to the photo-triac and they also set a time constant for the "turn on" time of T1. T1 senses the zero crossing of the AC signal and conducts for the length of time determined by the time constant of R48 and C17.

Someone else correct me if I'm wrong. I am sometimes

Regards,

Pld4me

Re: Zero crossing detection, traic triggering helpppplss!!!!

Sal said:

FUSE S2, is emplyed to protect the circuit against overcurrents. what amazes me is the 1A value of that fuse, usually LED diodes such as D30 and the one in U20 uses around 200mA, I am not sure if they will blow at around 1A.

Click to expand...

so i should use 200mA fuse to make circuit ok?


thanks for helps friends. They will help me so much. Thanks so much again


8)

Re: Zero crossing detection, traic triggering helpppplss!!!!

Sal is right.

The 1A fuse is very high for this circuit.

If this were a pure DC circuit, I wouldn't even use a fuse, but since you're dealing with AC, you should have it in case the AC shorts to ground.

Regards,

Pld4me

Re: Zero crossing detection, traic triggering helpppplss!!!!

Pld4me said:

Top circuit:

(

Signal is applied to PIC_T1 which "turns on" the photo-triac gate. Photo-triac gate conducts and "turns on" the gate of T1 (or T2).

R48 and C17 "pass some of the current from L1 which is fed to the photo-triac and they also set a time constant for the "turn on" time of T1. T1 senses the zero crossing of the AC signal and conducts for the length of time determined by the time constant of R48 and C17.

Someone else correct me if I'm wrong. I am sometimes

Regards,

Pld4me

Click to expand...

But if time is constant by R48 and C17, we're always triggering triacs in same phase degree?
and my main question is " which parts in circuit decide to work triac in different phase degrees?"

thanks for helps.


8)

Re: Zero crossing detection, traic triggering helpppplss!!!!

R48 and C17 have nothing to do with "timing" ..
It is simple snubber circuit .. see picture below ..

Component that decides when to fire triacs is PIC microcontroller - not on the picture ..
It uses signal from zero-crossing detector as reference and, depending on how do you program it, sends pulses to PIC_T1 and PIC_T2 to control both triacs ..

Regards,
IanP

Re: Zero crossing detection, traic triggering helpppplss!!!!

Ian is correct.

At a glance, I was thinking of a Triac light dimming circuit when I saw R and C.

Regards,

Pld4me

Re: Zero crossing detection, traic triggering helpppplss!!!!

good post.and can anyone suggest how to fire thyristor with the same structure also some piece of pic code how to change phase angle?