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| TRIAC based on/off circuit showing flash problem with LED lamp |
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| madires:
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 |
| Seekonk:
--- 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. |
| BrianHG:
--- 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. |
| Zero999:
--- 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. |
| madires:
--- 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 |
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