Victory1981
Newbie level 6
I met with a strange problem these days.
I used a LM311 to make a zero-cross detector,I found that when the frequency is high(say,40KHz), the rising edge of the TTL output is very neat(I adjusted the oscilloscope to 100ns/Div to look close to the rising edge), but when it comes to low frequency(say, 400Hz), the rising edge twittered badly, and 40Hz even worse.(although it looked nice when I adjusted the oscilloscope to 1ms/DIV or 250ms/DIV).
Why? I didn't connected digital circuit to the analogy part, just a simple zero-cross detector. I don't think it's noise...But I have no idea why it happened and how to slove the problem. I'm making a frequency measurer, so I need a nice rising edge.
Please help me. Thanks in advance.
I used a LM311 to make a zero-cross detector,I found that when the frequency is high(say,40KHz), the rising edge of the TTL output is very neat(I adjusted the oscilloscope to 100ns/Div to look close to the rising edge), but when it comes to low frequency(say, 400Hz), the rising edge twittered badly, and 40Hz even worse.(although it looked nice when I adjusted the oscilloscope to 1ms/DIV or 250ms/DIV).
Why? I didn't connected digital circuit to the analogy part, just a simple zero-cross detector. I don't think it's noise...But I have no idea why it happened and how to slove the problem. I'm making a frequency measurer, so I need a nice rising edge.
Please help me. Thanks in advance.