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???
08/09/05 11:21
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#99031 - 1N914 not Zener.
Responding to: ???'s previous message
Dear Kai,

Thanks a lot for your detailed reply.


the original circuit contains a zener diode, which in our case unfortunately allows a current to flow far below its turn-on voltage.


Sorry for that symbol looking like zener symbol my schematic editor shows 1N914 [ Fast Switching Diode Simillar to 1N4148 ] with that zener like symbol. 1N914 has characteristic exactly simillar to 1N4148 with only Reverse breakdown Voltage being diffrent. I will change it to your suggested Red Led and 1N6263 it appears much better than my 1N914.



The 1N6263 wasn't chosen because of its small leakage current or small reverse current, but because of its small forward voltage drop (it's a small signal Schottky diode)!


Thanks I leant a new thing.


A standard 1N4148 would violate the maximum specifications of micro, because then the potentials at inputs can exceed the 0.5V limits!


Sorry for not mentioning the micro specifications in first post. Though it is 3V microcontroller but it has 5V tolerant pins with Absolute Maximum ratings of 5.5V.


No spoecial care. 5k1 is ok. Are you sure that it's needed?


I have read the User Manual and datasheet very carefully. It says The Digital I/O pins can be configured as
1. Open Drain.
2. Quasi Bidirectional.
3. Inputs Only.
4. Push Pull.
For using comparators the Digital Input and Output on Comparator related pins is turned off using PT0AD P0M2 and P0M1 registers. In this mode I dont know if I need a resistor or not.[ Datasheet and User Manual is silent ]. I think a seasoned LPC9xx comparator user can help if I need a pull up on comparator output pin? Does it remain a regular digital I/O pin or becomes a special analog comparator pin when using comparators?

Do I need this 5k1 pull up if this Comparator output pin is 8051 like quasi bidirectional. [ With Open drain I know i need it. :) ]

Thanks & Regards,
Prahlad Purohit

List of 18 messages in thread
TopicAuthorDate
LPC9xx Comparators and Hysterisis            01/01/70 00:00      
   Feedback resistor is not enough            01/01/70 00:00      
      Is this allright            01/01/70 00:00      
         Tested it.            01/01/70 00:00      
         calculations            01/01/70 00:00      
            Re: Calculations.            01/01/70 00:00      
               step down rartio            01/01/70 00:00      
         Values need a change            01/01/70 00:00      
            Please show the analyses            01/01/70 00:00      
            Re: Value Changes.            01/01/70 00:00      
               my doubt is            01/01/70 00:00      
               Answers            01/01/70 00:00      
                  1N914 not Zener.            01/01/70 00:00      
                     Silent at many places            01/01/70 00:00      
            Low pass filter            01/01/70 00:00      
               Answer            01/01/70 00:00      
   Zero crossing detection            01/01/70 00:00      
   Thanks            01/01/70 00:00      

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