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DC-Voltage stepping up and down

Discussion in 'General Electronics Discussion' started by NS2012, Jan 24, 2013.

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  1. NS2012


    Dec 17, 2012
    Can you please confirm my design here or kindly provide me with your advice?

    I have a push down switch that I want to replace with a proximity card reader. So whenever the reader reads an authorized card, it will act as if the button was pushed. The power source I have is 25V DC and the reader takes in 12V DC and puts out 12V DC. The signal I want to send from the switch is supposed to be 25V DC too. So in a summary I have a 25V in and out from the circuit, but the circuit itself operates internally at 12V (all DC).
    The design I have in mind now is the following:
    1- take the 25 V, send it across two resistors (470 ohm each). take the voltage across one of them (result~12.5 which is acceptable i guess).
    2- send the output of #1 to the reader.
    3- at the output side, the reader has a relay which produces 12V.
    4- take output of #3, send it through LT1680 or LT1720 and the output should go to the other side of the switch which takes 25V DC.

    I'm assuming the power on the output is 100W.

    My questions:
    1- In general, any comments about the design mentioned above?
    2- Any comments about the choice of the ICs? Any suggestions? I never worked with LT1680 or LT1270 or any other DC voltage booster. How can I control the voltage value at the output to set it at 25V?

    Thanks in advance:)
  2. GreenGiant


    Feb 9, 2012
    You would be better off using either 2 separate supplies or splitting the one that you have, like you suggested, but rather than divide the voltage then amplify it again, just use a relay to switch on and off the 25V line.

    Does the card reader have a specific power requirement (you mentioned 12V but no current requirements)
  3. NS2012


    Dec 17, 2012
    you have a very good point regarding the relay. Thanks much

    Any other ideas, please let me know.
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