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[SOLVED] square wave detector

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ats2

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Hello,

I want to create an enable signal for LT4356 hot swap controller using 12V-500Hz square wave. I designed the circuit below, the input is 12V 500Hz square wave and output is SC. However, I am looking for an alternative safer and/or simpler circuit.
Alternatively, using an frequency to voltage converter like LM2907 a good choice?
Can you help me?

Thanks in advance.

square_to_dc.PNG
 

LM2907 is a very old device and may be hard to find. Do you really need to measure the frequency? If you do, consider using a small MCU which could easily measure frequency and amplitude in one device.

You can simplify the circuit by removing D1 and shorting across C1, the voltage may be a little lower but it will still measure it and the voltage will still be proportional to the input amplitude.

Brian.
 

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Hi,

"Square wave detector"

What detail of the square wave are you interested in?
* frequency
* amplitude
are the most obvious ones.

Are you expecting a YES/NO output of your detector?
Then you should specify at which condition it should safely show a "YES" and at which condition it should show a "NO".

Klaus
 

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Hi,
Interested in frequency.
Yes, I need a high low output.
I want to keep the enable pin away from voltage noises. Any noise at square wave net must not effect the enable pin of lt4356 pin.
 

Hi,

Maybe like this:

Input signal --> narrow 500Hz bandpass filter --> rectifier --> low pass filter --> schmitt trigger --> enable signal

It reacts on 500Hz sinewave.
But a square wave includes sinewaves, thus it should work.

Mind: "zero noise" is impossible.

Klaus
 

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Thank you very much Klaus. What kind of low pass filter do you recommend?
Thanks in advance.
 

Hi,

depends on reaction time.

You may use a second order, but is has lower suppression of unwanted signals and is slow.

A second order (or higher order) may be faster and does more effectively suppress unwanted signals.

Klaus
 

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