I was having false triggering on my LM393 input when I switch on the lamp (tungsten or florescent) in my room. After experiment a bit, 2 ceramic capacitors(2200pF) at both LM393 input seems to solve the problem. Why is there such a "switch-on" voltage spike & what is the voltage frequency?
Thanks in advance ck
Without the bypasses, the LM393 will respond to sub-microsecond pulses.
With a 2200pF C on the inputs with circa 10k-ohm impedances, the time constant is now 20 microseconds.
If the R is a megohm instead of 10K, the time constant with the 2200pF bypasses is 2 milliseconds.
Does that answer your question about spikes? Or where the "false" in "false triggering" lies?
Tim.
I think the problem is down to your power supply. It is important to filter the incoming mains properly. The transformer will pass through much higher frequencies than just mains frequency. Any high frequency noise will pass right through unless you have sensible capacitors across the power supply.
High value electrolytics are useless as they are quite unductive and allow the HF through. You need 100nf or similar across the electrolytics.
Sorry if I understand it incorrectly.What I would like to know is the value of capacitance just enough to surppress such spike induce by switching ON/OFF the AC socket.
ck
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