I have a design concept for a device that uses light signals to operate a relay. I'm having some trouble and I'd appreciate some expert advice.
I've been making these circuits and they seem to work fine but once in a while I notice one of the transistors will get hot. Also, once in a while, one of the circuits will just fail. When analyzing the failure, I find that the same transistor is toast. Replacing the torched transistor restores the circuit to its normal function. The circuit runs off of 12VDC, either from a regulated wall adapter or a 12V automotive battery. The transistors are rated for much higher than that. I've tried putting the circuit into spice but I'm not an electronics engineer and I'm still trying to teach myself how to understand the simulations.
I'm wondering if the inductor is affecting the voltage or current to Q1. If so, how do I fix?
I've pasted a picture of the circuit below. I didn't find the actual semiconductors in Spice, so I substituted something I thought was close for the sake of the example. The real components are Q1=NTE159 PNP Transistor, Q2 and Q3 are NPN NTE0289A. Q1 is the one that seems to burn out. ALso, there is a phototransistor across C2. I didn't find that component in spice. It pretty much acts like a switch, I think. The inductor L1 is the coil from the relay. The 12V coil resistance is 400ohms and 360mW.
Thanks in advance for any help. I don't know anyone else who cares about electronics, so I don't know who else to ask!
I've been making these circuits and they seem to work fine but once in a while I notice one of the transistors will get hot. Also, once in a while, one of the circuits will just fail. When analyzing the failure, I find that the same transistor is toast. Replacing the torched transistor restores the circuit to its normal function. The circuit runs off of 12VDC, either from a regulated wall adapter or a 12V automotive battery. The transistors are rated for much higher than that. I've tried putting the circuit into spice but I'm not an electronics engineer and I'm still trying to teach myself how to understand the simulations.
I'm wondering if the inductor is affecting the voltage or current to Q1. If so, how do I fix?
I've pasted a picture of the circuit below. I didn't find the actual semiconductors in Spice, so I substituted something I thought was close for the sake of the example. The real components are Q1=NTE159 PNP Transistor, Q2 and Q3 are NPN NTE0289A. Q1 is the one that seems to burn out. ALso, there is a phototransistor across C2. I didn't find that component in spice. It pretty much acts like a switch, I think. The inductor L1 is the coil from the relay. The 12V coil resistance is 400ohms and 360mW.
Thanks in advance for any help. I don't know anyone else who cares about electronics, so I don't know who else to ask!