Timeline for TLP184 Optocoupler - Something is going wrong
Current License: CC BY-SA 4.0
20 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Aug 18, 2020 at 8:44 | answer | added | VirtApp | timeline score: 0 | |
| Aug 17, 2020 at 18:11 | answer | added | Spehro 'speff' Pefhany | timeline score: 1 | |
| Aug 17, 2020 at 9:24 | answer | added | D.A.S. | timeline score: 1 | |
| Aug 17, 2020 at 9:19 | comment | added | tlfong01 | You might like to know why I suggest to use If = 15mA to 20mA. Part C of my answer to the following question has a spec for EL354 bidirectional optocoupler which mentions If = +-20mA operation, it is then I noticed that 5mA in many example designs might be for Arduino 5V Vcc and might not be good for 3V3 Rpi, perhaps CTR spec is often exaggerated. (1) electronics.stackexchange.com/questions/505318/…. | |
| Aug 17, 2020 at 9:06 | comment | added | tlfong01 | Oh my goodness, I was a bit embarrassed to ask if you know how to use a multi-meter. But if you have a scope, of course you should be rich enough to buy spares to do swap testing/troubleshooting. Electronic toys are so dirt cheap these days, it is criminal not to buy more for just in case spares. Ah, jogging/supper time. See you later. Good luck, cheers. | |
| Aug 17, 2020 at 9:00 | comment | added | tlfong01 | If you change R7 to 330R, can you use a multimeter to measure the If for 1k and 330R? | |
| Aug 17, 2020 at 9:00 | comment | added | VirtApp | Yes, i have a multimeter and also an oscilloscope and i've measured the voltage between pin 4 and GND and i'm getting 2.5V. in any case, i'll try another TLP184 | |
| Aug 17, 2020 at 8:59 | comment | added | Bruce Abbott | "if the connector pins are opened, from pin 4 and GND i get 2.5V." - With no LED current the transistor should be off and you should get 0V across R12. So either there is a wiring error, or your optocoupler is faulty. | |
| Aug 17, 2020 at 8:58 | comment | added | tlfong01 | @VirtApp, but have you another TLP184 to swap? Do you have a multi-meter (I don't insist a scope) to check the voltages at the "test" points? I remember one more things, usually many Arduino designs assume 5V Vcc, but if you use 3V3 Rpi then often you need to adjust the biasing, or you might be in trouble. | |
| Aug 17, 2020 at 8:54 | comment | added | tlfong01 | I once played with another opticalcoupler. I remember that the schematic (for a relay) uses If = 5mA, I did find the Ic is too small to get big enough Ic to pull down the NPN BJT next. The device manufacturerer might screen bad low CTR guys before assembly and testing. So they have guarantee CTR, But you eBay stuff has not guarantee! | |
| Aug 17, 2020 at 8:50 | comment | added | VirtApp | @tlfong01, changed R7 and R9 to 330ohm, nothing changed | |
| Aug 17, 2020 at 8:48 | comment | added | tlfong01 | (3) It would be nice if you have another TLP to do swap testing, because if you get your TLP184 from eBay, there is a chance that they give you sub standard grade, with CTR < 50. | |
| Aug 17, 2020 at 8:48 | comment | added | tlfong01 | (1) The TLP184 datasheet I am reading says recommended condition If = 16mA. I checked that your datasheet does not seem to give recommend If, but says +-10mA somewhere. Anyway, I think it is OK to try 15mA. (2) Now let me check Ic. Spec says typ 1mA, Now your Ic = 3V3 / 4k7 ~= 1mA should be OK. but if Ic max is much bigger, there is no harm changing 4k7 to say 3k3. Anyway, you can use a multimeter/scope to verify. About the pull up/down thing. Usually pull up is preferred, for efficient reasons, but I think pull down is also OK. | |
| Aug 17, 2020 at 8:43 | comment | added | Andy aka | Why do you need an opto coupler? Vheck R12 is 4k7 and not something stupidly higher like 4M7. | |
| Aug 17, 2020 at 8:31 | comment | added | tlfong01 | Ah, let me see. Let us troubleshoot from the left side, and first check if your LED is correctly biased to give the typical If of 16mA (according to datasheet TLP184). Your series biasing seems to be 1k or 2k. So If = 5V / 1k = 5mA << 16mA required. So I suggest the first thing is to change the biasing resistor to 5V / 16mA = 5/15k = 330R. | |
| Aug 17, 2020 at 8:26 | comment | added | akwky | The transistor is NPN which means it "pulls down" when active. Therefore the GP135 should connect to pin 6 and the resistor should be a pull-up (between pin 6 and +3.3V). Tie pin 4 directly to ground. | |
| Aug 17, 2020 at 8:25 | comment | added | jonk | I don't know that much about what you are doing. Get that right. You haven't written enough. But I think, just perhaps, that you might use that resistor as a pull-up from the collector to the +_3.3 V supply and ground the emitter. Take the output from the collector. See if that fixes anything. | |
| Aug 17, 2020 at 8:23 | comment | added | VirtApp | I've tought that the resistor can be a pulldown resistor, so i've connected it from emitter to ground. | |
| Aug 17, 2020 at 8:21 | comment | added | jonk | Where did you get the idea to use a resistor from emitter to ground? | |
| Aug 17, 2020 at 8:12 | history | asked | VirtApp | CC BY-SA 4.0 |