Electronics > Projects, Designs, and Technical Stuff
TRIAC based on/off circuit showing flash problem with LED lamp
madires:
--- Quote from: getfast_kiran on March 02, 2017, 08:36:51 am ---Why did you give reference to the particular application note.... I did not understand the reason behind it. Could you please explain.
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To give BrianHG a hint that a snubber is not always required when using snubberless TRIACs.
Zero999:
--- Quote from: getfast_kiran on March 02, 2017, 08:34:48 am ---
--- 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...
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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.
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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.
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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.
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Could you please send me the specs of the Transient Over voltage protection diode. ... to be added in parallel to TRIAC.
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http://www.littelfuse.com/~/media/electronics/datasheets/tvs_diodes/littelfuse_tvs_diode_1_5ke_datasheet.pdf.pdf
BrianHG:
Someone else has just posted my mosfet 240v AC switch on this thread:
https://www.eevblog.com/forum/projects/ac-rectified-dc-mosfet-dimmer/msg1149910/#msg1149910
getfast_kiran:
--- Quote from: capt bullshot on March 02, 2017, 08:59:03 am ---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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I tried the second option you suggested. I removed the 100n caps and replaced it with a 22n(Triac) and 47n cap(for optocoupler) caps instead of 10n since I only had those with me.
Now the problem of flashing of LED is gone. I am wondering how much it will affect my snubber circuit performance and what could be the possible tradeoff.
capt bullshot:
--- Quote from: getfast_kiran on March 07, 2017, 09:04:34 am ---I tried the second option you suggested. I removed the 100n caps and replaced it with a 22n(Triac) and 47n cap(for optocoupler) caps instead of 10n since I only had those with me.
Now the problem of flashing of LED is gone. I am wondering how much it will affect my snubber circuit performance and what could be the possible tradeoff.
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As always: it depends ...
The primary reason for having a snubber across the triac is to limit the dV/dt to keep it from turning on unwanted. As long as it doesn't turn on when it's supposed to stay off, the snubber is sufficient. A well behaved load may not require a snubber at all, but there's still the power line as a source of transients which could turn on the triac randomly. There are some standards for lab EMI testing, you'd optimize the snubber under these conditions in an EMC lab, supposed you want to sell your product. If you don't intend to sell your circuit, use whatever components you like as long as it works for you.
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