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TRIAC based on/off circuit showing flash problem with LED lamp

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getfast_kiran:

--- Quote from: Seekonk on February 28, 2017, 01:05:00 pm ---
--- Quote from: getfast_kiran on February 28, 2017, 12:19:57 pm ---
I will retry with the RC of 100 ohm and 0.47uf. But the thing is as fellow eevblog forum mate told me When I removed the snubber all together the problem got solved and there is not flickering or flashing.
But I need this circuit to operate with inductive load. So I will need a snubber circuit eventually.  So do you think this particular value of snubber will help me with the issue.

--- End quote ---

The snubber should be across the LOAD.  That absorbs the leakage from the triac circuit.

--- End quote ---
Could you give or point me towards a schematic that contains a snubber across the LOAD. Is the value of the snubber circuit the same.

getfast_kiran:

--- Quote from: BrianHG on February 28, 2017, 01:20:54 pm ---
--- Quote from: madires on February 28, 2017, 12:56:58 pm ---You can get snubberless TRIACs and snubberless TRIAC driver optocouplers:
- http://www.st.com/content/ccc/resource/technical/document/application_note/ca/ef/9d/1e/4a/9f/47/69/CD00003865.pdf/files/CD00003865.pdf/jcr:content/translations/en.CD00003865.pdf
- https://www.fairchildsemi.com/collateral/Snubberless-TRIAC-Drive-Optocouplers.pdf

--- End quote ---

These solutions wont work since they still have a resistor/cap snubber across the output triac, even if they don't have one across the opto-triac output driving the power triac's gate.  It is the current leaking across this cap and resistor which eventually builds up a charge in the LEDs power supply making it pulse on, then discharge it's internal cap.

There isn't much that can be done other than getting rid of the common snubber all together and finding an alternative route to switching the AC.  Now, I have a method using a power mosfet and AC-DC bridge rectifier, but, it's something like a 10 component solution and you need to switch the optocoupler on only during the 0 crossing phase of the AC & you also need both access to the hot and neutral.

--- End quote ---

Do you have a schematic of the 10 component solution. I would like to test it if there is no other solution since I will have to light a LED lamp eventually.

getfast_kiran:

--- Quote from: Hero999 on February 28, 2017, 01:35:41 pm ---
--- Quote from: getfast_kiran on February 28, 2017, 08:46:13 am ---
--- Quote from: getfast_kiran on February 28, 2017, 08:41:54 am ---
--- Quote from: BrianHG on February 28, 2017, 07:31:06 am ---As a test, can you try the circuit without the snubber cap?
Without the opto & add a resistive load on the gate to ensure it's off...

--- End quote ---


As you told I removed the Snubber capacitance from both the TRIAC and the optocoupler.  Now the LED is perfectly off for nearly 1 hour.

Should I do the second part with opto completely removed.

--- End quote ---

Also since I plan to switch inductive loads also with the same...I will need this snubber circuit to the optocoupler. So is there a solution that might fulfill both the inductive load problems and LED bulb problems.

--- End quote ---
If you can't put the snubber across the load, then you need to put a transient over voltage protection diode in parallel with the TRIAC. Hopefully it won't leak enough current to cause the LED to light.

--- End quote ---

Could you please send me the specs of the Transient Over voltage protection diode. ... to be added in parallel to TRIAC.

getfast_kiran:

--- Quote from: madires on February 28, 2017, 03:56:19 pm ---
--- Quote from: BrianHG on February 28, 2017, 01:20:54 pm ---These solutions wont work since they still have a resistor/cap snubber across the output triac, even if they don't have one across the opto-triac output driving the power triac's gate.  It is the current leaking across this cap and resistor which eventually builds up a charge in the LEDs power supply making it pulse on, then discharge it's internal cap.

--- End quote ---

STMicroelectronics Application Note 437: http://www.victronics.cl/index.php?option=com_docman&task=doc_view&gid=110&Itemid=4

--- End quote ---

Why did you give reference to the particular application note.... I did not understand the reason behind it. Could you please explain.

capt bullshot:
For a simple attempt:
leave your circuit as it is and place a resistor from its output to the neutral line. This should divert the snubbers leakage from the LED lamp.

In other words: Put that resistor (for example 22k, 3W, 250V rated) across the lamp. That should stop the flashing for the price of significant power dissipation in that resistor (you do not want that, but it is a quick fix).

For a better attempt:
change the values of the 100n caps (C9, C4) in your circuit to 10n. These cause the leakage that causes the LED lamp to flash. If the LED is still flashing, put a 100k Resistor across the lamp. This way you'll have less power dissipation and smaller components, but you need to check if the snubber is still effective enough.

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