problem with DC POWER

Discussion in 'The Projects Forum' started by dspcan, Dec 16, 2007.

  1. dspcan

    Thread Starter New Member

    Dec 16, 2007
    6
    0
    Dear sir,
    I want to make such DC power:
    input volt range:18v-70v
    output volt:5V
    maximum current:5A
    I cant't find such power chip to meet the requirements, someone have any ideas? I have been told to build the circuit by 7805+transistors+zenr dioder,but I don't know how to build it.
    thank you for your consideration
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Based on your maximum output power requirements of 25 Watts and the large input voltage range, I would think the 7805 linear regulator would not be the most efficient way to go.

    A better approach would be to use a switched mode power supply. Perhaps one of the National Semiconductor Simple Switchers would be valid choice. You can go to www.national.com and do a little research.

    hgmjr
     
  3. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
    7805 linear + large transistor
    Check page 24, they use an 8 amp pass transistor to handle regulation, the 7805 is just a voltage reference. Farther down on 26 they have the 7805 as a switcher.

    http://beta.octopart.com/Fairchild__LM7805CT.pdf

    Note:National semi datasheets now officially bite, they stripped out all the goodies and just have the dull charts.
     
  4. dmc0162

    Active Member

    Dec 13, 2007
    51
    1
    I thought the 7805 was only capable of 35v input?

    So if you use a transistor you can input more voltage?
     
  5. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Upon a little more research into my suggestion to use a member of the National Semiconductor SimpleSwitcher series as the basis for a solution, I discovered that the maximum input voltage that was recommended for the specific devices I had in mind is limited to 45 volts. This means that a pre-regulation scheme would need to be arranged to prevent the input of the SimpleSwitcher from seeing any input voltages greater that 45 volts.

    hgmjr
     
  6. dspcan

    Thread Starter New Member

    Dec 16, 2007
    6
    0
    in the attatched file. if the parameters of parts are arranged carefully ,I think the circuit can work normally for liner regulator/switcher or power module.
     
  7. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
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