Best device to use for this purpose

Discussion in 'General Electronics Chat' started by vijaybala85, Mar 17, 2010.

  1. vijaybala85

    Thread Starter Member

    Jan 7, 2010
    92
    0
    Hi,

    I was just wondering what device is the best one to use for the following purpose.

    It is basically an On/Off situation.
    5V input -> On = 24V output
    0V input -> Off = 0V output.

    The prime purpose is conversion of 5V to 24V when needed. Any suggestions?

    Thanks!

    V
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If the input is AC, use a transformer.
    If the input is DC, you will need a DC-DC converter.
    For a DC-DC converter, whatever your current requirements are at 24v, you will need roughly six times that much current at 5v, depending on the efficiency of the DC-DC converter.
    24v/5v=4.8
    Assuming 80% efficiency, 4.8/80% = 6.
    So, for each 1A of output current required, you will need 6A input at 5v.

    Transformers are quite efficient. For AC, if you need 1A out at 24v, you'll need around 4.9A at the input.
     
    Last edited: Mar 17, 2010
  3. Terp

    Active Member

    Jun 6, 2008
    32
    1
    Charge Pumps....... e.g. Dickson pumps.
     
  4. vijaybala85

    Thread Starter Member

    Jan 7, 2010
    92
    0
    Thanks guys!! I think I should have been clearer. I have a 24V power supply. I basically need the 5V input to act as a switch between the drive circuit and 24V supply. Kind of like a relay, only here, I need lower currents < 50mA. The power supply is a 24V, 12A industrial supply. Currently, I am using an opamp LM324 to do this, where 24V and GND are on the rails, but I thought I needed a better circuit.

    Thanks!

    V
     
  5. vijaybala85

    Thread Starter Member

    Jan 7, 2010
    92
    0
    duh!! I shldnt hv said conversion, but It is good to know that you can do that.! :)
     
  6. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
    69
    Use a P channel FET connected between 24V and the load.
    Add a resistor between it's gate and source (+24V).

    Use a second, logic level FET with source to 0V and gate from the logic input.
    The drain of that goes to the gate of the first FET via another resistor.

    The two resistors can be equal value, both 1K or both 10K.

    Add a 10K or 100K from the input gate to 0V to hold the circuit off if the input is likely to be disconnected.

    The rating of the first FET depends on the load current; if it's just a control signal rather than power switching, many general purpose FETs woudl be suitable.
     
  7. vijaybala85

    Thread Starter Member

    Jan 7, 2010
    92
    0
    @rjenkins

    Would you mind giving me a mock up diagram? I still dont get the setup by reading it. Thanks!

    V
     
  8. Markd77

    Senior Member

    Sep 7, 2009
    2,803
    594
  9. Bychon

    Member

    Mar 12, 2010
    469
    41
    Excuse me for being "old school" but you can do this with bipolar transistors. I don't mess with static sensitive parts if I can avoid it. An NPN arranged common emitter so the 5 volt signal turns it on and its collector pulls down the base of a PNP transistor that delivers the +24 to the load.
     
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