Counterfeit LM35 sensors that sort-of work

[cleo]

I've been trying to reuse a handful of LM35 temperature sensors that came with various lipo battery chargers. All of them malfunction when connected directly to things like Arduinos. They do work properly, however, with the battery chargers. After a lot of testing, I discovered the sensors are capable of drawing up to 8 mA of current (~100x of spec!) and heat up internally to give an output corresponding to about 54 ˚C. I further discovered the reason the sensors work in the battery chargers is that they limit the current to the sensor to about 0.5 mA.

I concluded these are not real LM35s, and that whatever they are, Chinese battery charger designers know about this behavior and design their sensor circuits to work with counterfeit sensors.

Here are pictures of the sensors. They're all labeled LM35DZ. One of them was really a blacktopped LM35CAZ. The only explanation I have is that they're some sort of defect sensors that were reclaimed and resold. The most unexpected aspect was that this seems to be common enough to design circuits to use these.

I'm curious if anyone else has seen behavior like this.

[oPossum]

They may be bipolar transistors. Check for the B-E and B-C diode characteristic of a bipolar transistor. An ordinary diode or bipolar transistor can be used as a temperature sensor. This is quite common.

[cleo]

I don't think it's a plain BJT, because the measured voltage between the output and ground wire when I power the sensors from the battery charger is always the expected voltage for a real LM35. Plus, any of the sensors give accurate readings with any of the chargers, which I wouldn't expect for something that has to be calibrated for each different component.

In any case, I checked each pair of leads in both polarities, with multimeter diode check and found 3 junctions, with drops of 0.686, 0.636, and 0.645 V, which isn't consistent with a BJT.

[AtlanticSurfer]

I received a pack of 5 LM35CAZ today that i bought from ebay seller kc_acepa.  After the 2nd one I tested also failed I popped it in my component tester and it came up as an npn transistor  - definitely counterfeit.