The attached circuit is part of a home automation project which determines events and then counts them.
The input to the LM339 (configured as a dual supply zero crossing detector) is variable frequency(0 to 15Hz), variable amplitude(DC to +10/-10V), sinusodial-like.
The circuit as shown, does in fact work pretty well.
However, there is some variability in the results which I can't let go of.
Poking around circuit while no events are being generated (LM339 input is -1.3V), the voltage at point A is -15V, at point B is -12.6V, and at point C is -4.9V. According to LTSpice, these voltages should be -15V,-15V, and 0V.
I suspect, but do not know, that I am driving Q1 (2N3904) outside of its operating range and perhaps have damaged it.
My question then, is this a valid use of a 2N3904 with a dual supply LM339? If not, what design change(s) are called for? TIA
Best Regards
The input to the LM339 (configured as a dual supply zero crossing detector) is variable frequency(0 to 15Hz), variable amplitude(DC to +10/-10V), sinusodial-like.
The circuit as shown, does in fact work pretty well.
However, there is some variability in the results which I can't let go of.
Poking around circuit while no events are being generated (LM339 input is -1.3V), the voltage at point A is -15V, at point B is -12.6V, and at point C is -4.9V. According to LTSpice, these voltages should be -15V,-15V, and 0V.
I suspect, but do not know, that I am driving Q1 (2N3904) outside of its operating range and perhaps have damaged it.
My question then, is this a valid use of a 2N3904 with a dual supply LM339? If not, what design change(s) are called for? TIA
Best Regards
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