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Per Westermark
03/24/12 15:00
Read: 616 times

#186867 - Freewheeel diodes
Responding to: ???'s previous message
If you take a closer look at how to connect relays, solenoids and other inductive loads, you will notice that they contain an extra diode.

This freewheel diode is there to make sure that the magnetic energy stored in the coil will not be converted into a huge voltage when the coil current is cut.

You do need it - you even face the risk of broken electronics if you don't. The coil want to maintain the same current. But since the resistance in the coil circuit changes from very low to very high, the voltage has to be stepped up tremendously. So you get a huge voltage spike - unless there is a reversed diode over the coil, that maintains a low-impedance loop for the coil current to take.

List of 12 messages in thread
Interrupts, the 8052 & Solenoids      Cian Young      03/24/12 13:33      
   Freewheeel diodes      Per Westermark      03/24/12 15:00      
      ULN2003a      Cian Young      03/24/12 18:34      
         more than one inductive load here      Jim Granville      03/24/12 19:11      
            Solenoids      Cian Young      03/24/12 19:26      
               diode choices      Jim Granville      03/24/12 19:42      
         Diodes in ULN2003a      Michael Karas      03/25/12 08:21      
         Within this chip      Erik Malund      03/26/12 07:03      
            Do I hear...      Michael Karas      03/26/12 07:07      
   Irish keypad layout!!      Andy Neil      03/25/12 06:27      
   Lack of resistors.      Michael Karas      03/26/12 08:00      
      Success      Cian Young      03/28/12 11:00      

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