Low Noise Small signal Amplifier design question
Low Noise Small signal Amplifier design question
(OP)
I am looking for an application which can be used to compare the small input signal (0 to 10mV) and drive/trigger a 115VAC relay. The requirement is that the relay is off from 0 to 4mV. Between 5 and 10mV, it will trigger the relay. After the relay is closed, it will open again when the input is 4mV less than the signal previously set. Which OpAmp/Comparator or product line you have would be best for this application? What's your approach in designing such circuit? All response would greatly be appreciated. Thank you in advance.
P.S. Believe it this is used to replace the vacuum amplifier circuits in one of our application.
P.S. Believe it this is used to replace the vacuum amplifier circuits in one of our application.





RE: Low Noise Small signal Amplifier design question
The major manfacturers should have nice app notes.
I would guess if you wanted to build your own instead of buying a solution you could find a nice op-amp and a pecision voltage source. Then use precision resistor to divide down and use positive feedback to do the hysteresis. I am assuming there is no loading problem and no problem in providing a signal inptu back into your signal source.
If your circuit was designed with a set point of 4.5 mV then that would be the definition of your "signal previously set". You would then create a hysteresis value offset of 4 mV, making the reset value 0.5 mV. That could be a little touch, especially with a relay clicking.
If somehow you need to remember the highest value recorded during a "set" interval you will need some sort of memory device. Analog memory peak hold devices have pretty much disapeared from use so you might want to go straight to an A/D converter with some sort of control mechanism.
RE: Low Noise Small signal Amplifier design question
RE: Low Noise Small signal Amplifier design question
Once you have a reasonable signal any of the standard comparator ICs should be suitable.
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RE: Low Noise Small signal Amplifier design question
-Bill-
RE: Low Noise Small signal Amplifier design question
With the price and small size of microcontrollers these days, any low bandwidth, non-noise critical analog processing is formidably challenged by a sampled digital implementation.
A hi-gain amp with 8 pin uC cannot necessarily be ruled out for this app, apart from price.. I would think.