| Electronics > Beginners |
| FMMT597 transistor not working |
| (1/2) > >> |
| Chris Hasler:
I have a transistor circuit which is not working properly. There are six of them all failing the same way. There is a PNP transistor (FMMT597, datasheet https://www.diodes.com/assets/Datasheets/FMMT597.pdf) switching a 24V line to a LED and resistor. This is switched on/off from a 24V line via a potential divider. 24V - 1k5 - Base - 12k - NPN transistor - 0V The NPN transistor is triggering correctly, but the PNP transistor is continually passing 15V. Does anyone have any idea what I have managed to screw up on this? edit: I have swapped out the PNP transistor for a MPSA92G and achieved the same result, but with 15.6V passing the current. |
| Zero999:
Please post a schematic. It's impossible to know what the problem is, without one. |
| Chris Hasler:
Please see attached image with the schematic and measurement points highlighted. The rest of the circuit is not attached to the connector at the moment. |
| Zero999:
The PNP transistors are connected backwards, so are behaving like 7V zener diodes. If the collector emitter connections are corrected, it should work, but it's also possible the transistors have been damaged, due to the reverse voltage. I recommend replacing the PNP transistors with new ones, connected correctly. The schematic is also drawn in a confusing manner, which makes mistakes more likely. |
| CJay:
Sure that schematic is correct only it looks wrong to me, emitters of the transistors should be connected to +V and collectors to 0V surely? *edit* damnit, Hero999 posted while I was editing :) |
| Navigation |
| Message Index |
| Next page |