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Diode choice

Discussion in 'General Electronics Discussion' started by NMNeil, Jun 24, 2018.

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  1. NMNeil

    NMNeil

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    Oct 3, 2014
    This is to total newbie question that I can't find an answer to.
    I'm using the 1980 National Semiconductors Voltage Regulator Handbook to design a simple regulated 5 volt output power supply for my old tractor. One of the first items in the input part of the circuit, as in most similar circuits, is a diode to help with negative spikes and as a safety feature to guard against reverse battery connection. The specified diode is the 1N4004, but my question is why. The diodes range from 1N4001 to 1N4007 and other than the peak voltage, all the other specs are exactly the same, so why specify one with a 400 volt peak capability rather than just using something like the 1000 volt 1N4007 on everything?
     
  2. AnalogKid

    AnalogKid

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    Jun 10, 2015
    Back when the line was invented, the process difference between 50 V and 1000 V diodes was enough to affect the price. Also, the higher voltage diode has a slightly higher forward conduction voltage Vf, higher junction capacitance, and a slower switching speed, so it is less efficient in low voltage applications

    ak
     
    abuhafss likes this.
  3. NMNeil

    NMNeil

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    Oct 3, 2014
  4. duke37

    duke37

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    Jan 9, 2011
    There used to be quite a difference in price. The low voltage ones became 1N4004 and the high voltage 1N4007. There seems to be little price difference now and you may as well use 1N4007 for everything.

    UF4007 may be preferred for faster swtching and lower noise generation.
     
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  5. AnalogKid

    AnalogKid

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    Jun 10, 2015
    The answer is that the parts and the datasheets were different 50 years ago. That one manufacturer chooses to specify the parts differently today does not mean all manufacturers do. Also, for things like Vf, the datasheet lists max values. But there is nothing that says the various voltage parts all measure exactly the same, only that they all will measure less than the max.

    ak
     
  6. NMNeil

    NMNeil

    109
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    Oct 3, 2014
    Ouch, 50 years ago!
    Where did all those years go?
     
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