Power Supply Board

Created Aug 1, 2001

    This is a very simple power supply board.  It features very heavy copper traces and ground planes to keep noise down.  In the picture below, the blue is the circuit side layer.  The orange that you see peaking through is the component side copper.

    The power supply requires a pair of transformers.  30 VCT -> 40VCT is needed for the +/- 15 volt supply, and 12.6 VCT -> 18 VCT is required for the +5 volt supply.  It should be noted that the higher the voltage, the more heat will be disipated by the regulators.  This heat will determine how much power you can get.

Please Note:DANGER HIGH VOLTAGE.  Do not attempt to build this project unless you are familiar with High Voltage Wiring.

    Bill of Materials

Additional parts you will need

    You will need some heatsinks for the card.  I recomend these:

    Mouser Part Number 532-568303b00    $4.17    This is the cadalac.  Die cast.  Very rugged
    Mouser Part Number 532-500403b00    $1.74    Stamped Metal, but, disapates more power than the cadalac.

    You will also need some transformers.  Here are the ones I recomend.  These are torriod transformers.  Very low magnetic radiation.

    Digikey Part Number TE62060    $13.32    2x7 VAC 25VA Transformer.  Use for +5 volt power supply
    Digikey Part Number TE62073    $14.85    2x15 VAC 35VA Transformer.  Use for +/-15 volt supplies
    Digikey Part Number TE62072    $14.85    2x12 VAC 35VA Transformer.  Use for +/- 12 volt supplies

    You do not need to insulate the regulator from the heat sink.  But, I do recomend you put heat sink grease between the regulator and heat sink, or, use a sil pad if you don't like grease.

    Purchasing Information


Building the Power Supply Module
    This board can be built in many ways.  While I intended it to be a +/- 15 and +5 volt power supply, it does not have to be built this way.  By changing the components, you can have any set of voltages that you can get a TO-3 78xx/79xx regulator for.  Here are some guidelines.

    It shoud be noted that you can calculate the filter capacitance as such:

    Capacitance (FARADS) = current (amps) / ( Frequency (Hz) * Ripple (volts) ).

    To get uF (microfarads), multiply FARADS * 1,000,000.
Dual Power Supply Components
Supply Voltage
Load Current Max
Filter Capacitors
+/- 15 volts 1 amp 30VCT @ 1 amp 4700uF 7815K/7915K (TO-3)
+/- 12 volts 1 amp 24VCT @ 1 amp 4700uF 7812K/7912K
+/- 8 volts 1 amp 20VCT @ 1 amp 4700uF 7808K/7908K
+/- 5 volts 1 amp 18VCT @ 1 amp 3300uF 7805K/7905K
+/- 5 volts 1 amp 12.6VCT @ 1 amp
  This will run cooler.
10,000uF 7805K/7905K
+/- 24 volts 1 amp 48VCT @ 1 amp 2200uF 7824K/7924K

    The single power supply is identical, except, it uses only the positive regulators (78xx) series.

Picture of assembled board.

Checking Out the Powersupply

    Before powering up, inspect the board for solder bridges.  The easiest place to have a solder bridge is on the output bypass capacitors, C2, C4, C6.  After connecting up the transformers, you can power it up.  If there is no smoke (most likely from capacitors that are in backwards), it is probably working ok.  Check the voltages at the outputs.  The +15 output should read very close to +15 (the regulators are rated at +/- 0.25 volts tolerance), so the voltage could vary from 14.75 to 15.25.  Now, the -15 volt output will probably not read -15, that is because the 79xx regulators require a minimum load.  Putting a 100 ohm load on the output should bring this close to -15 volts (again, +/- 0.25).  Finaly, check the +5 volt output (If you put it on), it should be 4.75 to 5.25 volts.