How to turn off an opto-triac

[long88]

Hi All,

I am very new about the opto triac driver circuit. My intention is to use a microcontroller I/O to switch the 240VAC signal to control a solenoid coil . The solenoid coil require a input of 240VAC, 50 - 60Hz and 80ma. After I done my research, I find that opto-triac and mechanical relay are very common to use in this kind of application. As I compare this two methods, I think that the opto triac methods is more suitable if compare to mechanical relayfor long term purpose.

Thus, i have brought a few pieces of K3012p opto triac (**broken link removed**). I manage to turn on the opto triac and output 240Vac signal to power up the solenoid coil . However, I fail to switch off 240Vac although I did set my control signal to low.

I read from some documents, it mention that the triac can turn off only if the current flow through triac is smaller than the holding current plus a low signal input to Vgate or a zero voltage across triac plus low signal input to Vgate. Please advice me whether my concept is correct.

I attached my schematic(fail to turn off AC output) and a schematic (from internet). Please advice me whether the schematic (from internet ) able to solve the switching off issue.

Question to schmetic (from internet):
1. How this circuit able to turn off the Triac?
2. I read few data sheet regard the specification of triac. The Vgate signal is always a DC signal. From the schematic (from internet), it use the opto-triac ouput a signal (Is this a AC signal?) to feed in to the gate control of a triac.
3. Can I use 240VAC signal to feed into to the gate as a control signal to drive a triac?

Sorry, I am really not very familiar with the opto-triac. I really appreciate if you guys lecture me on this part.
Thank you very much

 

[chuckey]

With your arrangement, are you sure that you have not got a short circuit Triac?, it should have a voltage snubbing C and R across it like the fig2. (.01 MF+39 ohms). then there is a question of the Triacs voltage and current ratings - was it man enough for the job? Else I see no reason why it should not work providing the drive to the opto is really hi or lo.
Frank

 

[long88]

Hi chuckey,
Thank you for your suggestion. The internal resistance of the solenoid coil is 120 ohms. When i feed a high signal into the pin 1 of opto-triac, the triac turn on and current flow through my solenoid coils.
When i try to cut off the 240 VAC by feed in a low signal to the pin 1, the triac is not turned off and current is still flowing through to my solenoid coils. I try to connect the pin 1 signal to ground, but the triac is still turn on.

I am using k3012P Vishay opto-triac, the triac able to work for 250V and I on state rms is 100mA. It shall be able to meet my requirement.

You mean both fig1 and fig2 shall work fine without switching off issue?
In Fig 2, it use the opto-triac output signal to control an external triac. The output of the opto triac signal is a 240V AC signal, am i right? If i connect this signal to gate of triac signal, it show blow the triac right ? As i saw in data sheet, the gate voltage shall be a dc signal and normally lower than 5v

 

[picgak]

You try removing the signal from the opto , if it switches off . then the problem is with the logic circuit

 

[schmitt trigger]

Most likely you are exceeding the optocoupler's dv/dt rating. That could be cured with a snubber circuit.

Having said that, I remember reading many times advice from optocoupler's manufacturers that the optocouplers are only designed to trigger triacs..... and not to drive a load directly, therefore you should use a triac as in your second image.

For instance, read the note on the middle of page 6 in the following datasheet:

https://www.fairchildsemi.com/ds/MO/MOC3023M.pdf

 

[long88]

Hi schmitt trigger and picgak ,

After i add in a snubber circuit in parallel with opto triac,the circuit work fine. Thank you very much for precious suggestion to me. I will combined the external triac with my current circuit.

 

[picgak]

Most likely you are exceeding the optocoupler's dv/dt rating. That could be cured with a snubber circuit.

Having said that, I remember reading many times advice from optocoupler's manufacturers that the optocouplers are only designed to trigger triacs..... and not to drive a load directly, therefore you should use a triac as in your second image.

For instance, read the note on the middle of page 6 in the following datasheet:

https://www.fairchildsemi.com/ds/MO/MOC3023M.pdf

Hi,
For your kind info k3012P is a opto with triac