Push Button Power Supply

Discussion in 'The Projects Forum' started by spacejunk, Feb 13, 2009.

  1. spacejunk

    Thread Starter New Member

    Feb 13, 2009
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    First a quick bit of background. I am a highschool student who dabbles in the world of electronics. I am working on an amplifier design and I need a circuit to control the power. It will operate on one Lithium cell, so it needs undervoltage protection. This means I will need a MOSFET to control power, so I figured why not add a push button power switch, if I already have the power MOSFET. This is turning out to be much harder than I originally assumed.

    I need a circuit that will toggle the power to an amplifier I am designing. Web searches so far have turned up very little. It should toggle power to a FDS4465 MOSFET with the push of a single debounced button. The circuit should work on one Li-Poly cell (3-4V). I was able to make a working (simulated) circuit with a jk flip flop. The issue is lack of board space, and I could not find a single flip flop with the correct operating voltage. A simple discreet circuit would be preferred.

    Any help in this matter would be greatly appreciated.

    Thanks a lot.
     
  2. mik3

    Senior Member

    Feb 4, 2008
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    What do you exactly mean by toggling the power on an amplifier? For what purpose?

    You won't be able to use a MOSFET with a voltage of only 3V. Even logic level MOSFETs need at least 5V Vgs to fully turn on.
     
  3. spacejunk

    Thread Starter New Member

    Feb 13, 2009
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    Just a replacement for a regular toggle power switch. And the MOSFET I am using will operate down to that voltage, but with less current carrying capacity. This is not a problem as the amp only draws 100mA.
     
  4. mik3

    Senior Member

    Feb 4, 2008
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    No, this is can be quite a big problem because if the MOSFET does not fully conduct it will have high operating resistance, it will drop a significant amount of voltage across it and will may overheat. Also, the amplifier won't receive the proper voltage. Of course this depends on the MOS characteristics but it would be better to use a BJT or just a simple switch. I don't see a reason to replace the switch with a transistor.
     
  5. spacejunk

    Thread Starter New Member

    Feb 13, 2009
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  6. mik3

    Senior Member

    Feb 4, 2008
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    With this MOS it will work. Note that it is a p-channel MOS and you need to connect the source to the positive of the power supply and the load between the drain and ground. Then apply 0V to gate to turn it on.
     
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