Hello
I'm new here and have come across a very strange problem that I can't get to the bottom of that maybe someone out there can suggest a resolution to. I've designed a light level detector with photo-transistor, MCP601 op-amp, MCP42100 dual digital pot and LM311 comparator (circuit attached). I also have a handful of PCBs manufactured by EuroCircuits to test out the design. The problem I'm having is that about 75% of the op-amps in the circuit don't seem to work, almost as though they are faulty, which I'm sure they're not. The problem with the non-working op-amps is that the negative input and output are set at almost supply voltage and altering the light level on the photo-transistor doesn't affect the input voltage at all.
I can remove the op-amp from the circuit and replace with another which will then work just fine (or maybe after replacing a few times!). So I'm presuming my design is OK and that there's something amiss that causes the circuit not to work. It can't be the PCB as that works, once I find a working MCP601. It's almost as though there are some slight manufacturing differences in the MCP601 that cause my circuit to work or not as I'm pretty sure they're not faulty.
Can anyone shed any light on why I might be experiencing the above please? I'm at my tethers end :-(
I'm sure it's not a faulty op-amp as I use them elsewhere and I'm very carefully avoiding static. I've even bought different batches from different suppliers to rule out faulty supplies. These are all SMD components BTW
Thank you
I'm new here and have come across a very strange problem that I can't get to the bottom of that maybe someone out there can suggest a resolution to. I've designed a light level detector with photo-transistor, MCP601 op-amp, MCP42100 dual digital pot and LM311 comparator (circuit attached). I also have a handful of PCBs manufactured by EuroCircuits to test out the design. The problem I'm having is that about 75% of the op-amps in the circuit don't seem to work, almost as though they are faulty, which I'm sure they're not. The problem with the non-working op-amps is that the negative input and output are set at almost supply voltage and altering the light level on the photo-transistor doesn't affect the input voltage at all.
I can remove the op-amp from the circuit and replace with another which will then work just fine (or maybe after replacing a few times!). So I'm presuming my design is OK and that there's something amiss that causes the circuit not to work. It can't be the PCB as that works, once I find a working MCP601. It's almost as though there are some slight manufacturing differences in the MCP601 that cause my circuit to work or not as I'm pretty sure they're not faulty.
Can anyone shed any light on why I might be experiencing the above please? I'm at my tethers end :-(
I'm sure it's not a faulty op-amp as I use them elsewhere and I'm very carefully avoiding static. I've even bought different batches from different suppliers to rule out faulty supplies. These are all SMD components BTW
Thank you
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