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???
12/07/05 18:17
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 		 #104835 - Every red LED should work
Responding to: ???'s previous message
Prahlad said:
Can I use any Red LED or there is some specific one.

The idea of this LED is to prevent, that input voltage leaves the allowed common mode input voltage range of comparator of LP922, which is Vcc-0.3V = 2.7V in your case. On the other hand, signal at input should rise well beyond 1V, which is the threshold level of comparator.
Every red LED shoud work in this application, because turn-on voltage should be between 1.6...1.8V. But if you want, then select a red LED, which shows a rather high turn-on voltage.
Turn-on voltage has to do with chemistry of pn-junction, which is made of GaAs. Certain nuances of red color show higher turn-on voltages, others lower. Check by yourself.

By the way, D8 can really be omitted, I had look into datasheet.

Kai

List of 35 messages in thread
TopicAuthorDate
LPC922 Comparator Interrupt Problems.            01/01/70 00:00      
   Vcc?            01/01/70 00:00      
      Vcc=3.0 to 3.3 Volts.            01/01/70 00:00      
         Possible causes            01/01/70 00:00      
            Noise could come from comparator itself            01/01/70 00:00      
               Re: Noise from Ground.            01/01/70 00:00      
                  Filter            01/01/70 00:00      
                     Exactly!            01/01/70 00:00      
                  R21 is contaminated            01/01/70 00:00      
                     Hystresis is 1.7 mV            01/01/70 00:00      
                        It's 20mV!            01/01/70 00:00      
                           oops calculation error            01/01/70 00:00      
                              waaaay too small a hysteresis..            01/01/70 00:00      
                                 Not at all !            01/01/70 00:00      
                                    there are (at least) 2 ways to skin this            01/01/70 00:00      
                                       Extreme care??            01/01/70 00:00      
                                          correct, but there has been umpteen post            01/01/70 00:00      
                     Please Suggest some filtering.            01/01/70 00:00      
                        100R plus 47µF            01/01/70 00:00      
                           Re: 100E + 47uF            01/01/70 00:00      
                              Like that...            01/01/70 00:00      
                                 Red LED.            01/01/70 00:00      
                                    Every red LED should work            01/01/70 00:00      
                                       also be aware            01/01/70 00:00      
                                          At 500µA...            01/01/70 00:00      
            Noisy ground?            01/01/70 00:00      
            Re: Possible Causes.            01/01/70 00:00      
               Mains Signalling?            01/01/70 00:00      
                  Mains filtering            01/01/70 00:00      
                     mains filtering            01/01/70 00:00      
                        Very informative!            01/01/70 00:00      
   Problem Frequency.            01/01/70 00:00      
      Filtering will help!            01/01/70 00:00      
         Problem Solved.            01/01/70 00:00      
            Nice to hear!            01/01/70 00:00      

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