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| LM311P issue |
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| HendriXML:
Hi! For this little project, I'm using a LM311P bought from AliExpress (with the Texas Instruments logo on it, so it seems legit) https://www.eevblog.com/forum/projects/nerfo-meter-measuring-the-speed-of-nerf-darts/msg2640588/#msg2640588 It is has a collector/emitter output. Because my circuit didn't function the way it should, I started debugging. With the collector unconnected the emitter (pin 1) still sinks (11 mA) and sources (20 mA) current, when applying a square wave input. I measured mean dc amperage to either rail, so the max is higher. I cannot explain this behavior and starting to think that it isn't a LM311P at all. (I tried several from the same ali order) Doing the current measurement on the collector (pin 7) with an unconnected emitter I get 14 mA when sinking, and none when sourcing. But not following the input signal. Any suggestions what could cause this? |
| magic:
--- Quote from: HendriXML on August 28, 2019, 12:35:44 pm ---(with the Texas Instruments logo on it, so it seems legit) --- End quote --- :-DD TI is the favorite brand of counterfeiters to stamp onto jellybean parts. Post pics, oftentimes the shape of the package gives them away. |
| David Hess:
--- Quote from: HendriXML on August 28, 2019, 12:35:44 pm ---With the collector unconnected the emitter (pin 1) still sinks (11 mA) and sources (20 mA) current, when applying a square wave input. I measured mean dc amperage to either rail, so the max is higher. I cannot explain this behavior and starting to think that it isn't a LM311P at all. (I tried several from the same ali order) --- End quote --- The emitter output cannot sink current with the collector unconnected so the part is either damaged or not an LM311. --- Quote ---Any suggestions what could cause this? --- End quote --- Check the internal schematic of the LM311. The LM311 is not designed to work with only one of the collector or emitter outputs connected. If the collector is connected to a positive supply, then the emitter output can pull up. If the emitter is connected to a negative supply, then the collector output can pull down. |
| HendriXML:
Sometimes Chinees stuff makes me laugh. I one saw a toy figure of a Gorilla, it had quite a long tail. It was a good resemblance of the real thing. Except gorilla's don't have tails. So some guy in China made a pretty nice Gorilla from probably a photo which "hid" the non existing tail. But how did he determine the tail size, I wonder? And what kind of creature is my LM311 in reality, I really wonder. I'm now certain I got something else. (An op amp or push pull comparator) Because my circuit (no rocket science) works with a LM211 just fine. However even in my batch of LM211 I got a lot of fake ones! (They look the most pretty though) I think I learned my lesson. |
| ozcar:
I bought some LM311s about 9 months ago on Ebay. When the package arrived from China, it was marked “Gift. Plastic patch, Total Value 0.02”. The contents looked OK, TI marking, but as LM311s they worked about as well as plastic patches. I'm pretty sure that I then turned up an old thread here, from years ago(?) where somebody reported fake LM311s, which iirc they thought were likely some opamp. I can't find that thread now. So what is it about LM311s? Somebody mislabelled millions of them and continues to flog them? |
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