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Kai Klaas
02/23/06 05:58
Read: 450 times
Germany


 
#110580 - Read again my calculation example
Responding to: Sun Din's previous message
Sun said:
I was thinking of using a 2K ohm connected to the +15V supply in series with the 1K ohm connected to ground. This should idealy give me a 5V drop across the 1K resistor and hence the the 4.7V zener in parallel with it.

With these resistor values it can not work! Please read again how I calculated the upper resistor value, then you will notice, that in your calculation neither a current through the TTL chip nor through the zener can flow!

Also, it's not useful to neglect the cap in parallel to the zener. Remember, you have to deal with high frequency noise resulting from the spiky supply currents of TTL chip. So, why not using this additional cap to improve supply decoupling??

Again, why not using a simple 7805?

Kai

List of 21 messages in thread
TopicAuthorDate
Zener Turn-on-time      Sun Din      02/20/06 01:16      
   Remedy        Kai Klaas      02/20/06 07:08      
      Thank You Kai      Sun Din      02/22/06 06:18      
         Divider      Kai Klaas      02/22/06 06:34      
            Resistor values      Sun Din      02/23/06 03:27      
               Read again my calculation example      Kai Klaas      02/23/06 05:58      
               drop that stupid resistor to ground      Erik Malund      02/23/06 07:04      
         can you draw the schematic?      Abhishek Singh      02/22/06 07:21      
            Assistance required to post Sch      Sun Din      02/23/06 03:38      
               If using "Windows"        Jon Ledbetter      02/23/06 07:57      
                  Typo Oops      Jon Ledbetter      02/24/06 08:19      
         Using a cap is enough      Kai Klaas      02/22/06 09:13      
            actually for the "typical" use it is not      Erik Malund      02/22/06 09:53      
               Less than 1nsec      Kai Klaas      02/22/06 10:12      
            Resistor instead of the cap      Sun Din      02/23/06 03:32      
   Sch      Sun Din      02/24/06 04:48      
      ALWAYS design to worst case.      Erik Malund      02/24/06 07:42      
      Homepage      Jon Ledbetter      02/24/06 08:13      
         why is that 1k still there      Erik Malund      02/24/06 08:52      
      Aha!      Kai Klaas      02/25/06 06:47      
         Thank you all for your help.      Sun Din      02/27/06 08:42      

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