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5 volts 1000 mA from 12 volts

Discussion in 'Electronics Homework Help' started by Schidtztorm, Oct 1, 2019.

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  1. Schidtztorm

    Schidtztorm

    1
    0
    Oct 1, 2019
    I'm trying to figure out a way to design a simple 5 volt 1000 mA regulator, or at least a way to drop the 12 volt supply down to 5 volts with 1 Amp. I don't have access to IC's or zeners, so I'll have to use voltage dividers to set voltage. And here's the real kicker! I have to make this with a FET. Enhancement/switcher type. But it's good for many amps, and up to 60 volts.
    This is a type of contest between a couple of colleagues of mine and I'm setting them up for it. Lol. I just want to make sure I have a realistic design before I dish it out. They don't think it can be done without risks of frying the gadgets plugged into it.
    Can anyone help me with this? I'm hoping for a general design that will work on most FETs of this caliber.

    The FETs are #1

    Power mosfet N channel
    6F433439
    D30NF
    SQM110. 06L

    #2

    High speed switching mosfet
    H7P0601
    4. K3
    PO 24
    P channel
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    10,614
    2,372
    Nov 17, 2011
    If you want to have a relaistic design, start by showing us your approach. Wouldn'T it be unfair to present another persons's solution as your own to your colleagues?
    This is also why I will move this thread to the homework section.

    A switcher FET is usually not a good choice for a linear application. You'll have to take great care to operate it within the SOA range.

    Any diode or bipolar transistors's Base-Emitter junction can work as a reference of sorts.
     
  3. Audioguru

    Audioguru

    3,002
    673
    Sep 24, 2016
    You will probably end up with the output voltage changing when the ambient temperature changes (even as it warms up) and if the load current changes. You mentioned "simple" then its performance will be horrible. That is why we use an IC or zener.
    An inexpensive 7805 IC works well and has 16 transistors and 2 zener diodes in it plus a lot of resistors and one capacitor.
     
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    10,614
    2,372
    Nov 17, 2011
    Google "discrete MOSFET voltage regulator" for circuit examples. Most if not all will, however, use a zender diode or voltage reference ic. YOu may replace the voltage reference by a bunch of diodes of base-emitter junctions, but you'll have to accept quite some inaccuracy.
    For better accuracy you can build a bandgap reference from discrete transistors (Google "discrete bandgap reference"). This will be better than simple diodes but still less accurate than an integrated and trimmed chip.
    I won't say it can't be done, on the contrary, but the challenge is a big one.
    And don't forget the SOA.
     
  5. WHONOES

    WHONOES

    953
    249
    May 20, 2017
    It is possible to do. I had a quick go on my simulator using as suggested by Harald, a DIY band gap reference. The regulator bit was done with a long tailed pair and other bits with an Nmos device as the pass element. I will say no more.
     
    Harald Kapp likes this.
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