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???
09/21/05 15:33
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 		 #101311 - then use a Schottkey
Responding to: ???'s previous message
Datasheet lists Vil like this
VIL Input Low-voltage -0.5(Min) (0.2*VCC - 0.1)(Max) V
for Vcc = 5V max Vin = 5*0.2 - 0.1 = .9V
1N4148 lists the forward voltage drap as VF = 1V
then use a Schottkey

when o/p trasistor of LM339 conducts voltage that apears at the input pin is 1V.
or i'm wrong.
you are, but not for that reason, it is worse than you state. When the output of the comparator is low it is NOT zero, the datasheet specify it as 0.4V max. Thus in the above example the worst case "low" would be 1.4V, not very good.

Has anyone suggested using a dual comparator and letting one output go to 12V (for whatever reason) and the other to +5?

Erik


List of 46 messages in thread
TopicAuthorDate
AT89c2051 port pin remains latched            01/01/70 00:00      
   1-to-0 transition current            01/01/70 00:00      
   OC comparator            01/01/70 00:00      
      a diode in series will do...            01/01/70 00:00      
      LM336-5            01/01/70 00:00      
         Price!! and speed?            01/01/70 00:00      
            Hmmmmmm...............            01/01/70 00:00      
               write PID sotfware for mcs51 micro.            01/01/70 00:00      
                  Start it as a new thread            01/01/70 00:00      
      Using LM339 only            01/01/70 00:00      
         LM339!            01/01/70 00:00      
            Pull up to 339            01/01/70 00:00      
               Why?            01/01/70 00:00      
               here are the two schemes            01/01/70 00:00      
                  not 12V, but 5.7            01/01/70 00:00      
                     and            01/01/70 00:00      
                        ???            01/01/70 00:00      
                           Question            01/01/70 00:00      
                              LM339            01/01/70 00:00      
                              open Collector            01/01/70 00:00      
                                 OOPS.            01/01/70 00:00      
                  12V swing            01/01/70 00:00      
                     there were three pictures...........            01/01/70 00:00      
                        yep...            01/01/70 00:00      
   Use P1.0 or P1.1            01/01/70 00:00      
      P1.0 and p1.1 are used            01/01/70 00:00      
   yep!! that is solved            01/01/70 00:00      
      Nothing is solved...            01/01/70 00:00      
         why so complicated?            01/01/70 00:00      
            Vil for 89c2051            01/01/70 00:00      
               then use a Schottkey            01/01/70 00:00      
                  LM339            01/01/70 00:00      
                     It probably will in the lab, the            01/01/70 00:00      
                        noise immunity?            01/01/70 00:00      
                           it most certainly does            01/01/70 00:00      
            Low-voltage noise margin            01/01/70 00:00      
               Real Programmers don't use Pascal            01/01/70 00:00      
                  It's so easy to state your opinion and t            01/01/70 00:00      
                     no more words            01/01/70 00:00      
                  It's amateurish to reduce noise margins            01/01/70 00:00      
                     hair-picking            01/01/70 00:00      
                        Fan-out specification            01/01/70 00:00      
                           Circuits that work on.....            01/01/70 00:00      
                     Rise times at 3MHz            01/01/70 00:00      
                        a small correction            01/01/70 00:00      
   I second the motion            01/01/70 00:00      

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