Triac no getting fully on (design attached)

[skmdmasud]

Hi..
In my following circuit my Triac (BTA16 and BTA12 tried both) dont get fully on. When my Main is 232VAC i get 160VAC from my triac. I also removed the gate resistor but it did not make any difference. Other than that my circuit works fine. My uC PC0, PC1 and PC2 reads 4.8V when ON.

 

[MikeMl]

What is the relationship between Neutral and Gnd ?

 

[skmdmasud]

What is the relationship between Neutral and Gnd ?

Its a transformer less power supply so Neutral and Gnd is same.

 

[MikeMl]

Its a transformer less power supply so Neutral and Gnd is same.

Then why doesn't the schematic reflect that? It would not be in the USA or Canada; they are three different wires here.

 

[skmdmasud]

Then why doesn't the schematic reflect that? It would not be in the USA or Canada; they are three different wires here.

Hi.. Ok, i get you. Thats for safety we should put it there. Apart from that any idea why i am not getting 220 from my triac.

 

[MikeMl]

Assuming that the Gnd vs Neutral issue has nothing to do with it, the next question is when does the MCU drive the port pin high relative to the zero crossing of the AC wave? If your gate drive routine has any internal delay, that would deliver only a partial half-cycle. Also, the ability of the MCU to source enough current to trigger the triac comes into question.

 

[Nigel Goodwin]

Apart from that any idea why i am not getting 220 from my triac.

Because you don't have 220V connected to it - the 220V connects to the 'top end' of the load, and the triacs switch the 'bottom end' of the load to neutral.

 

[NorthGuy]

I'm not an expert in triacs. But the circuit looks very strange to me. I've seen triacs driven with AC, but you use DC. Perhaps you (or someone else) can explain how it is supposed to work?

 

[MikeMl]

Hi.. Ok, i get you. Thats for safety we should put it there. Apart from that any idea why i am not getting 220 from my triac.

In the US, our line cords have three conductors:
Black, called Line or L1, measures 120Vac with respect to earth, is a current carrying conductor that supplies power to the appliance.
White, called Neutral, measures oVac with respect to earth , is a current carrying conductor that provides the return path to power the appliance.
Green, called Ground or Gnd, measures oV with respect to earth, is not a current carrying conductor except if a fault occurs.

The use of Gnd in your schematic causes terrible confusion. Call it what it is: Neutral.

 

[skmdmasud]

Assuming that the Gnd vs Neutral issue has nothing to do with it, the next question is when does the MCU drive the port pin high relative to the zero crossing of the AC wave? If your gate drive routine has any internal delay, that would deliver only a partial half-cycle. Also, the ability of the MCU to source enough current to trigger the triac comes into question.

Hi.. The port pin is fully on, not doing zero crossing for this pins. the pin can easily supply over 20mA tested with led.

 

[skmdmasud]

Because you don't have 220V connected to it - the 220V connects to the 'top end' of the load, and the triacs switch the 'bottom end' of the load to neutral.

Hi.. My connectivity is like this

so i connected a small table fan which spins very slowly and also measured the VAC from the hot and neutral and got 160VAC and when the triac is off i get 0VAC.

 

[ChrisP58]

Hi.. My connectivity is like this
View attachment 82984

so i connected a small table fan which spins very slowly and also measured the VAC from the hot and neutral and got 160VAC and when the triac is off i get 0VAC.

What is the timing between the trigger pulse from the uC to the gate pin of the triac and the AC sinewave?
What does the waveform look like on a scope?

 

[skmdmasud]

What is the timing between the trigger pulse from the uC to the gate pin of the triac and the AC sinewave?
What does the waveform look like on a scope?

uC pin is either always on or always off, i am not doing zero detection and pwm.

 

[KeepItSimpleStupid]

You need at least 5 mA (5% of 100 mA) in quadrant 4, so let's make it 8 mA. R <= (5-1.3-x)/8e-3

I have no idea what your port looks like, so I don;t know what x is.

 

[skmdmasud]

You need at least 5 mA (5% of 100 mA) in quadrant 4, so let's make it 8 mA. R <= (5-1.3-x)/8e-3

I have no idea what your port looks like, so I don;t know what x is.

Hi..
i removed the R from the gate and got the same result.

 

[KeepItSimpleStupid]

Point to a datasheet of the ATMEL part. You should never remove the resistor.

Your second schematic shows a 15 V supply, not 5.

What happens when you use 5V directly with a series resistor R <= (5-1.3)/10e-3 ohms.

Make sure that MT1 and MT2 aren't mixed up.

Most designs of this type might use an Opto triac and a triac for the larger loads. This keeps your 5V supply isolated from the line. Depending on your load, you can use a zero cross or random opto-triac. Zero cross is generally used to reduce interference.

 

[ChrisP58]

I'm not an expert in triacs. But the circuit looks very strange to me. I've seen triacs driven with AC, but you use DC. Perhaps you (or someone else) can explain how it is supposed to work?

Most Triacs can be triggered by a DC voltage of either polarity. But the current required varies depending on which quadrant it is in at the moment. See this document for an explanation of the quadrants. https://www.littelfuse.com/~/media/...lding_of_SCRs_and_Triacs_Application_Note.pdf
See the individual data sheet for the triac you are using to get it's requirements.

This document has good info on connecting triacs and uControllers. https://www.littelfuse.com/~/media/...rol_Using_Thyristors_Application_Note.pdf.pdf

 

[NorthGuy]

Most Triacs can be triggered by a DC voltage of either polarity. But the current required varies depending on which quadrant it is in at the moment.

Thank you very much Chris. I used triacs in few projects and I always used optocouplers to trigger them. I didn't know there was another way. Your documents provide a good explanation. I'll need to study them, and then, hopefully, I'll understand triacs better.

 

[ronsimpson]

so i connected a small table fan which spins very slowly and also measured the VAC from the hot and neutral and got 160VAC and when the triac is off i get 0VAC.

If your output voltage is 1/2 of the input voltage, then I think your triac is on for 1/2 cycle and off for the other 1/2 cycle.

 

[KeepItSimpleStupid]

Triac datasheet: https://www.st.com/web/en/resource/technical/document/datasheet/CD00002265.pdf

What suffix part are you using?