30V 5A regulator

Discussion in 'General Electronics Chat' started by brodonh1, Sep 15, 2008.

  1. brodonh1

    Thread Starter Member

    Sep 15, 2008
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    I'm learning and must have said regulator for a project.
    It will be powered by a PM alternator that outputs DC.
    31-40v input. 30v up to 5A output.
    Application runs well at 28v, 4.4A. from a Mastech power supply

    Guidance would greatly be appreciated.
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,343
    Hello,

    If you are using a linear regulator you will have to dissipate upto 50 Watts.
    This becomes heat wich is lost.
    For more efficiency you can use a switching regulator.
    One example is the LM5116 of National Semiconductors.
    See the datasheet for more details.

    Greetings,
    Bertus
     
  3. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Looking at the third to last graph on page 10 of Bertus' reference I think there would be trouble using this chip with an input/ouput differential of less than 10 volts ( it appears to stabilise at 7).

    The minimum available input voltage is 31 volts. This will be very difficult to stabilise 30 volts at 5 amps from.

    You also state you circuit runs at 28 volts. Perhaps you should reconsider your requirements before embarking upon design.
     
  4. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Another switching regulator to consider is the MC33167. It requires fewer components and should be able to get within 2V of the supply. John
     
  5. brodonh1

    Thread Starter Member

    Sep 15, 2008
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    I greatly appreciate the input form the experienced.

    Could I be directed to a schematic that is a basic design using one of the recommended regulators?

    Thanks,

    Donald
     
  6. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Hi Donald,

    A schematic, parts list, PCB, and parts layout for the step-down regulator that I mentioned is given beginning on page 8 (Figure 19) of the datasheet in link I gave. Did you look at the link or have trouble opening it?

    SMPS's don't get a lot simpler than that at the power ratings and voltage drop at which you need to operate. If you could be more flexible in your design specifications, other regulators might work and be simpler.

    Here is another link to a TI supply (PTN78020HAH). It's a bit more expensive and only goes to 22V, but also only requires 3 external components.

    John
     
  7. brodonh1

    Thread Starter Member

    Sep 15, 2008
    12
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    Hi JOhn,
    I went over the data sheet for LM2678adj today and plugged in my values for their math and worked the whole thing out. On the Natiional website there circiut building software said my values would only go to 25v.

    I will use my free time tomorrow to learn the MC33167 sheet

    I will keep in touch.

    Thanks,
    donald
     
  8. Tahmid

    Active Member

    Jul 2, 2008
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    25
    Hi,
    Why don't you use the L4977?
    Thanks.
    Tahmid.
     
  9. brodonh1

    Thread Starter Member

    Sep 15, 2008
    12
    0
    Hi John,

    I went over the data sheet for this device and my question is do the component values need to be adjusted for my in and out values? (fig 19)

    I see that R1 has to be added with higher outputs.

    The perfect ohm value for 28Vout is 1496.

    Always grateful,

    Donald
     
  10. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    Yes, R1 will need to be added. R1 and R2 form a voltage divider to adjust the input to the voltage feedback pin (see description in datasheet). What is important is the ratio of R2 to R1. The current into the FB pin is very low, and the absolute values of R2 and R1 are not critical. According to a communication with tech service, you can change the total to at least double its value without a problem. That will allow you to get reasonable values for both resistors according to the formula Vout=5.05((R2/R1) +1)).

    John
     
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