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dre007
Joined: 04 Nov 2004
Posts: 1
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 04 Nov 2004 8:33 build an alarm circuit using a comparator with hysteresis |
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so far i know that a comparator with hysteresis is also known as a schmitt trigger.. how do i hook up an alarm circuit with a schmitt trigger??
tjamls/
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nicleo
Joined: 06 Sep 2004
Posts: 717
Helped: 60
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| 04 Nov 2004 14:08 build an alarm circuit using a comparator with hysteresis |
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Your circuit will alarm when it's triggered.
For example, you want to monitor whether the battery of a portable device is still OK or not. Say the battery is 12V, and if the voltage below than 11V, the battery is considered NOT OK already. So, you monitor the voltage battery (Vbat) and connect the Vbat to the positive input terminal of the comparator. You need a Vref (threshold) and in this case it's 11V. The Vref is connected to the negative input terminal of the comparator. Pls refer to the datasheet of LM311 for more detailed explanation.
Last edited by nicleo on 04 Nov 2004 18:42; edited 2 times in total |
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samcheetah
Joined: 25 May 2004
Posts: 672
Helped: 31
Location: Pakistan
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| 04 Nov 2004 17:31 Re: build an alarm circuit using a comparator with hysteresi |
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| nicleo wrote: |
"comparator with hysteresis" is NOT schmitt trigger.
"comparator with hysteresis" is STILL a comparator but with 'schmitt trigger' input |
could you explain this a little bit more. do you mean that the feedback loop is called the schmitt trigger?
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nicleo
Joined: 06 Sep 2004
Posts: 717
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| 04 Nov 2004 18:29 Re: build an alarm circuit using a comparator with hysteresi |
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| samcheetah wrote: |
| could you explain this a little bit more. do you mean that the feedback loop is called the schmitt trigger? |
Thanks for reminding me that some of my comments were not correct. I have messed up with other circuit. 
Anyone who is insterested in "comparator + hysteresis" probably would like to read this article: "Curing Comparator Instability with Hysteresis" ( http://www.analog.com/library/analogDialogue/archives/34-07/comparators/comparators.pdf )
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