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Hello,
I have been doing a university assignment which is to design an (automatically changing) two-tone alarm circuit based around the 74HC14 inverting schmitt trigger. I have a design that seems to work well in real life, but I have a question as to the LTSpice simulation output.
If you take a look at the simulation screenshot, you can see negative-going peaks that are below the supply voltage of 3VDC. I don't understand why these peaks are below the supply voltage and why they occur.
My initial thought was that because the peaks are around about the diode forward voltage, that this had something to do with it, so I changed the diodes to LEDs with a much greater Vf, and the peaks reduced (of course, this doesn't say why they're there in the first place).
It should also be noted that the peaks exist in real life as well, even when using many different sizes of bypass capacitor. Also, when the schematic is changed so that there is no "combined output" (the node furthest to the right on the schematic), there are no peaks and the circuit simulates as expected (maybe the diode reverse leakage current plays a part??)
I have attached my LTSpice circuit simulation file, as well as a screenshot of the simulation for those without LTSpice, and also a scope trace from the real-life circuit. I would greatly appreciate any insight, as my tutor was unsure as the the origins of the voltage spikes.
Thanks!
I have been doing a university assignment which is to design an (automatically changing) two-tone alarm circuit based around the 74HC14 inverting schmitt trigger. I have a design that seems to work well in real life, but I have a question as to the LTSpice simulation output.
If you take a look at the simulation screenshot, you can see negative-going peaks that are below the supply voltage of 3VDC. I don't understand why these peaks are below the supply voltage and why they occur.
My initial thought was that because the peaks are around about the diode forward voltage, that this had something to do with it, so I changed the diodes to LEDs with a much greater Vf, and the peaks reduced (of course, this doesn't say why they're there in the first place).
It should also be noted that the peaks exist in real life as well, even when using many different sizes of bypass capacitor. Also, when the schematic is changed so that there is no "combined output" (the node furthest to the right on the schematic), there are no peaks and the circuit simulates as expected (maybe the diode reverse leakage current plays a part??)
I have attached my LTSpice circuit simulation file, as well as a screenshot of the simulation for those without LTSpice, and also a scope trace from the real-life circuit. I would greatly appreciate any insight, as my tutor was unsure as the the origins of the voltage spikes.
Thanks!
