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Raspberry Power DC Power Supply

gadget.iom

A recent discussion by Robin Gunning (Raspberry pi powersupply change from micro usb to dc power plug) led me to investigate the feasibility of creating a board allowing a DC power jack to be connected to the Raspberry Pi.

 

 

I have created my first ever Eagle Schematic but would appreciate some feedback on the suitability of the design and any comments/suggestions you may have for improvements or potential pitfalls.

 

image

The aim is to have a 26-way extension header so that shields can be added on top of this board. The 26-way header should also be compatible with the 40-way header on the newer plus editions of the Raspberry Pi.

 

Thanks

Paul

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  • It is -3 degrees (why no super/sub on text editor?) Fahrenheit outside here in Chicago.  Fretting about 5 to 15 W of static dissipation (presuming this heat is properly spread) at the corner of my bench seems neurasthenic today.  People make the gadget you describe all of the time.  The problems a prior poster mentioned about the ubiquity of the connector do obtain.  Here are some solutions:

     

    The plug could be polarized the wrong way:  If you want to have non-functionality in this context, use an input diode.  If loss in this diode upsets you, use a shottky.  If you want to have functionality in this context, use a bridge rectifier (absolute value circuit) on the input instead.  Throw in a cap and a protection diode to guard the regulator during discharge and you are even proof of AC adapters.

     

    The supply features too great a potential:  Add an input fuse, really you should anyway.  Shunt the supply with a backwards power (clamp) Zener.  This can be fashioned out of a regular-old Zener and a bipolar power transistor.  Use NPN, in Si electrons are lighter than holes.  With this scheme you can get reversal protection by shunting the power Zener with a backwards (to normal operation) power shottky.diode.  No static dissipation, but tape a couple spare fuses under the lid of the chassis.  In a non-conductive box, of course.

  • in reply to D_Hersey

    The plug could be polarized the wrong way:

    We had some field equipment that sought to eliminate 'oops wrong way round' on the battery.

    They cleverly used a relay, that had a diode in series with the coil.

    If the input volts was correct it would close the relay contact and apply the voltage to the rest of the circuitry.

     

    You could also use this to ensure the voltage was 5v was within whatever tolerance you want, and prevent the relay from closing.

     

    Mark

Reply
  • in reply to D_Hersey

    The plug could be polarized the wrong way:

    We had some field equipment that sought to eliminate 'oops wrong way round' on the battery.

    They cleverly used a relay, that had a diode in series with the coil.

    If the input volts was correct it would close the relay contact and apply the voltage to the rest of the circuitry.

     

    You could also use this to ensure the voltage was 5v was within whatever tolerance you want, and prevent the relay from closing.

     

    Mark

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