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Kai Klaas
02/09/06 06:16
Read: 1495 times

#109595 - CMIVR
Responding to: Prahlad J. Purohit's previous message
Prahlad said:
In the LM311 case my supply voltage is single supply +5V, 0V. The input signal to LM311 circuit is 6V and not 2.5V. With LPC922 internal comparator it was 2.5V.

Common-mode input voltage range (CMIVR) is the range of input voltages, which can be applied without that the chip produces an error. An error here means for instance that an output phase reversal occurs, or that internal circuitry hangs in a long lasting metastate, or what so ever. The manufacturer does not state in datasheet, what exactly happens when the CMIVR is exceeded. Nevertheless we should never violate CMIVR.

This functional input voltage range has nothing to do with maximum ratings, where the chip becomes damaged, by the way.

CMIVR of LM311 is about 0.2V...3.8V (typically) at Vcc=5V. So, without the zener (here a red Led) potential at inverting input can easily exceed CMIVR, if you have a look at the circuit:

With the 1N6263 at inverting input and Vcc=5V, input voltage can rise up to 5.5V.
Now you might tell, that transformer does not produce such a big voltage at output. But, as mains is extremely contaminated by noise, glitches, spikes, bursts and surges, you can not at all expect an anyhow limited secondary output voltage. For this you need the zener at input of circuit.


List of 13 messages in thread
Zero cross detector led. [ Kai ]      Prahlad J. Purohit      02/08/06 08:08      
   Yes, still required      Kai Klaas      02/08/06 19:50      
      Please Elaborate      Abhishek Singh      02/08/06 21:21      
      Input signal.      Prahlad J. Purohit      02/08/06 21:59      
         CMIVR      Kai Klaas      02/09/06 06:16      
            Input smaller than reference.      Prahlad J. Purohit      02/09/06 06:36      
               yes works      Abhishek Singh      02/09/06 08:07      
               Will work!      Kai Klaas      02/09/06 18:36      
                  Re: Will Work.      Prahlad J. Purohit      02/10/06 07:29      
         are you aware      Erik Malund      02/09/06 06:48      
            Searched entire page.      Prahlad J. Purohit      02/09/06 07:08      
               sorry, it seems to be gone      Erik Malund      02/09/06 07:46      
                  Re: LPCxxx App note.      Prahlad J. Purohit      02/10/06 07:37      

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