TRIAC based on/off circuit showing flash problem with LED lamp - Page 1
Forum section: electronics / projects

author: getfast_kiran
author_rank: Regular Contributor
timestamp: February 28, 2017, 06:35:06 am
content: I had made a circuit to turn load on and off using a TRIAC.It all worked fine until the load was resistive or inductive.As soon as I connected a LED lamp to the circuit all problems started coming in to the circuit. When the TRIAC was off. The LED lamp started to flash every few seconds with each flash becomingbrighter than the one before it.So when I read about it in eevblog forum. I found a post where Mr. SeanB had said" LED lamp with a TRIAC can cause issues of flashing when off, as the slight leakage current through the snubber capacitors can be enough to charge the power supply in the lamp up to startup, which will make the lamp either flicker when off, or flash every few seconds."But I could not find a solution to it being supplied in the post or across the forum that I could find.So if you guys could help me with the same. I really appreciate it and thankful for your time.Here is the modification I did from the schematic. I used the earth as the return for voltage resistor circuit for voltage sensing even though I knew the earth is such a bouncy return path.Also I removed one of those 100nf capacitors in the 5V stability correction.Also instead of the 360 ohm resistor and 470 setup changed it to the MOC 3021 datasheet recommended 180 ohm and 2.4k combo resistance along with the 0.1uf X rated capacitor.Looking forward for you instructions to recitify the issue.

author: getfast_kiran
author_rank: Regular Contributor
timestamp: February 28, 2017, 06:37:10 am
content: Following is the circuit used for the opto coupler 3021

author: Seekonk
author_rank: Super Contributor
timestamp: February 28, 2017, 07:15:51 am
content: re you talking about a you build it LED or a commercial LED LAMP. I use <19W E27 lamps as night lights sometimes by putting a .1uf or smaller in series with the lamp. Depending on the electronics inside, I get a nice low power lamp, it flashes, or doesn't turn on at all. All in series triac circuits have leakage issues. A good size RC (100ohm .47uF) across the lamp may solve some issues.

author: BrianHG
author_rank: Super Contributor
timestamp: February 28, 2017, 07:31:06 am
content: 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...

author: getfast_kiran
author_rank: Regular Contributor
timestamp: February 28, 2017, 08:41:54 am
content: Quote from: BrianHG on February 28, 2017, 07:31:06 amAs 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.

author: getfast_kiran
author_rank: Regular Contributor
timestamp: February 28, 2017, 08:43:55 am
content: When I removed the snubber capacitance of the optocoupler. I also shorted the 2.4k resistor part. Hence only that resistance R is present in the optocoupler triac pathto the gate of the Driven Triac.

author: getfast_kiran
author_rank: Regular Contributor
timestamp: February 28, 2017, 08:46:13 am
content: Quote from: getfast_kiran on February 28, 2017, 08:41:54 amAlso 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.

author: getfast_kiran
author_rank: Regular Contributor
timestamp: February 28, 2017, 10:21:37 am
content: https://www.mathiselectronics.com/amp-clampHow is the Amp-Clamp better? The Amp-Clamp shunts all leakage current away from the load, thus completely resolving all the above listed problems. It is also multi-volt. It can be used with controllers of any voltage from 24 to 120v. Simply insert the Amp-inator into your output circuit and the leakage current no longer appears at the load. Also, the Amp-Clamp only increases the “on” mode energy consumption by 0.14W, and it doesn’t get hot. Seriously! It operates at only a few degrees above ambient temperature.found this as a solution of 120V AC only.

author: getfast_kiran
author_rank: Regular Contributor
timestamp: February 28, 2017, 12:19:57 pm
content: Quote from: Seekonk on February 28, 2017, 07:15:51 amI 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.

author: capt bullshot
author_rank: Super Contributor
timestamp: February 28, 2017, 12:33:20 pm
content: Is there a reason why you need to use the triac? A simple relay would do the job fine, I believe.

author: madires
author_rank: Super Contributor
timestamp: February 28, 2017, 12:56:58 pm
content: 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

author: Seekonk
author_rank: Super Contributor
timestamp: February 28, 2017, 01:05:00 pm
content: Quote from: getfast_kiran on February 28, 2017, 12:19:57 pmThe snubber should be across the LOAD. That absorbs the leakage from the triac circuit.

author: BrianHG
author_rank: Super Contributor
timestamp: February 28, 2017, 01:20:54 pm
content: Quote from: madires on February 28, 2017, 12:56:58 pmThese 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.

author: Zero999
author_rank: Super Contributor
timestamp: February 28, 2017, 01:35:41 pm
content: Quote from: getfast_kiran on February 28, 2017, 08:46:13 amIf 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.

author: madires
author_rank: Super Contributor
timestamp: February 28, 2017, 03:56:19 pm
content: Quote from: BrianHG on February 28, 2017, 01:20:54 pmSTMicroelectronics Application Note 437:http://www.victronics.cl/index.php?option=com_docman&task=doc_view&gid=110&Itemid=4

author: getfast_kiran
author_rank: Regular Contributor
timestamp: March 01, 2017, 06:30:21 am
content: Yes I wanted to use Triac expecting it to deliver more life than the HIGH current mechanical relays. Do you think it justifies the cause.

author: capt bullshot
author_rank: Super Contributor
timestamp: March 01, 2017, 07:46:34 am
content: Quote from: getfast_kiran on March 01, 2017, 06:30:21 amCan't tell that without knowing your constraints. In general - it depends.Mechanical relays are quite often used for such purposes, if chosen correctly I'd expect a life of >= 20 years and >= 100000 switching cycles for a standard power relay.For example - the relays controlling the gas furnace and water pumps in my home heating system are switching on and off 10 ... 100 times per day and is expected to do this for more than 20 years.If handled incorrectly, the relay may fail at first turn-on. A too large inrush current can weld the relay contacts together, exceeding the max. specified load may burn the contact at turn-off.

author: Zero999
author_rank: Super Contributor
timestamp: March 01, 2017, 08:42:02 am
content: Quote from: getfast_kiran on March 01, 2017, 06:30:21 amAs stated above, a TRIAC isn't guaranteed to last longer than a mechanical relay.Mechanical relays are expected to last a certain number of cycles before the contacts wear out. Semiconductor switches, such as TRIACs don't have that limitation, which makes them attractive in applications with more frequent switching than relays. Semiconductors are also more resistant to mechanical shock and vibration than mechanical switches.On the other hand, mechanical switches, such as relays, can be electrically more robust than semiconductors. They wont be destroyed by ESD and can withstand over voltage and over current for longer than semiconductors. It's also possible to build relays which work at higher temperatures and are more resistant to ionising radiation than semiconductors.

author: getfast_kiran
author_rank: Regular Contributor
timestamp: March 02, 2017, 08:21:45 am
content: Thank you both for that huge helpful info on mechanical relays. I forgot to mention the requirement of low height clearance of the circuit and space requirements.So could you guys please help with the same without the need to replace the Triac ??

author: getfast_kiran
author_rank: Regular Contributor
timestamp: March 02, 2017, 08:26:36 am
content: Quote from: madires on February 28, 2017, 12:56:58 pmI am using a snubberless TRIAC but the optocoupler is not snubberless will try it with a snubberless optocoupler in the future. For the time beingplease do help me with solution confined to snubberless TRIAC BTA16 and non snubberless optocoupler 3021.

author: getfast_kiran
author_rank: Regular Contributor
timestamp: March 02, 2017, 08:30:24 am
content: Quote from: Seekonk on February 28, 2017, 01:05:00 pmCould you give or point me towards a schematic that contains a snubber across the LOAD. Is the value of the snubber circuit the same.

author: getfast_kiran
author_rank: Regular Contributor
timestamp: March 02, 2017, 08:32:43 am
content: Quote from: BrianHG on February 28, 2017, 01:20:54 pmDo 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.

author: getfast_kiran
author_rank: Regular Contributor
timestamp: March 02, 2017, 08:34:48 am
content: Quote from: Hero999 on February 28, 2017, 01:35:41 pmCould you please send me the specs of the Transient Over voltage protection diode. ... to be added in parallel to TRIAC.

author: getfast_kiran
author_rank: Regular Contributor
timestamp: March 02, 2017, 08:36:51 am
content: Quote from: madires on February 28, 2017, 03:56:19 pmWhy did you give reference to the particular application note.... I did not understand the reason behind it. Could you please explain.

author: capt bullshot
author_rank: Super Contributor
timestamp: March 02, 2017, 08:59:03 am
content: 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.

author: madires
author_rank: Super Contributor
timestamp: March 02, 2017, 10:40:36 am
content: Quote from: getfast_kiran on March 02, 2017, 08:36:51 amTo give BrianHG a hint that a snubber is not always required when using snubberless TRIACs.

author: Zero999
author_rank: Super Contributor
timestamp: March 02, 2017, 11:44:47 pm
content: Quote from: getfast_kiran on March 02, 2017, 08:34:48 amhttp://www.littelfuse.com/~/media/electronics/datasheets/tvs_diodes/littelfuse_tvs_diode_1_5ke_datasheet.pdf.pdf

author: BrianHG
author_rank: Super Contributor
timestamp: March 03, 2017, 06:10:40 am
content: 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

author: getfast_kiran
author_rank: Regular Contributor
timestamp: March 07, 2017, 09:04:34 am
content: Quote from: capt bullshot on March 02, 2017, 08:59:03 amI 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.

author: capt bullshot
author_rank: Super Contributor
timestamp: March 07, 2017, 09:55:59 am
content: Quote from: getfast_kiran on March 07, 2017, 09:04:34 amAs 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.

author: getfast_kiran
author_rank: Regular Contributor
timestamp: March 09, 2017, 06:09:22 am
content: Quote from: capt bullshot on March 07, 2017, 09:55:59 amOKay understood what you said. Thanks so much for providing the viewpoint in terms of a product to sell or self use. Information was so useful to think about and move forward.Thanks again to you and all those who helped.

author: venkaty
author_rank: Newbie
timestamp: February 07, 2019, 03:00:40 pm
content: Hi getfast_kiran, Could you please share us your working circuit(which is fixed of TRIAC based on/off circuit showing flash problem with LED lamp)