Apologies if I butcher the terminology. I'm a new hobbyist trying to learn the rope.

I have 1 power supply that I'd like to use to power 3 devices:

  • Commodore 64 motherboard: 9V 1.5 Amps
  • Commodore 64 peripherals: 5V 1 Amp
  • LCD Module: 12V 2.5 Amps

From doing some research, it looks like I will need at least a 12V, 6 Amp power supply.

From there, I know I need a switching regulator to down step the voltage.

My questions are:

  • How do I split the power supply into 3 outputs?
  • Once I have it split, do I need 1 switching regulator for each output that needs to be down stepped?


EDIT: The C64 needs 9V AC, not DC as @RJR pointed out.

  • 2
    \$\begingroup\$ It can be fun building your own multi-rail power supply, although it isn't a trivial project with the currents that you need. A much easier option is to use a power supply from a PC... \$\endgroup\$
    – bitsmack
    Aug 4, 2017 at 21:49
  • 1
    \$\begingroup\$ @bitsmack, but then there will be still a "problem" of getting 9V, although the "split problem" will be already solved by nature of PC PSU :-) \$\endgroup\$ Aug 4, 2017 at 22:59
  • \$\begingroup\$ @AliChen: Right, my bad, for some reason I thought I remembered 9V being in there... Thanks :) \$\endgroup\$
    – bitsmack
    Aug 4, 2017 at 23:09
  • \$\begingroup\$ @bitsmack: If I go with a PC power supply, could I use a switching regulator on own of the outputs to generate the 9V I need? \$\endgroup\$
    – Sancho9000
    Aug 5, 2017 at 0:07
  • 1
    \$\begingroup\$ Isn't the 9v power for a C64 9v AC, not DC? Careful! \$\endgroup\$
    – RJR
    Aug 5, 2017 at 2:59

2 Answers 2


As long as your 12V source supply can support the total current requirements this is a project that requires two switching regulators.

  1. Feed the input 12V directly to the output 12V loads.
  2. Feed the 12V input to the input of a switching regulator module to convert the 12V to 9V output. Make sure the module is capable of supplying all the 9V load current required.
  3. Feed the 12V input to the input of the second switching regulator. This module will be used to convert the 12V to 5V output. Make sure that this module can supply at least the 1A that you require.
  • \$\begingroup\$ Thank you so much for the simple explanation. @RJR pointed out that I got 1 thing wrong in my initial post. The C64 requires 9V AC not DC. How does that change step 2? Thanks! \$\endgroup\$
    – Sancho9000
    Aug 5, 2017 at 3:04

Edit due to 9V is now AC. Step 1 to 3 is the easiest and fastest way to power up your system.

  1. Get a step down transformer that is rated 9V 1.5A AC.
  2. Get a SMPS that can output 12V 3A DC.
  3. Use a DC-DC step down module; tap 12V supply to get the 5V.

Does not recommend to step down 9V AC to 12V DC due to:

  • More power loss in the step down transformer.
  • Higher AC voltage due to LCD is off and not drawing current.
  • 1
    \$\begingroup\$ "The 5V must step down from 9V because the efficiency is better." Why? \$\endgroup\$
    – Phil Frost
    Aug 5, 2017 at 2:02
  • \$\begingroup\$ ^This. That's only true for linear regulators. And even then it's only shifting the power loss around. \$\endgroup\$
    – Passerby
    Aug 5, 2017 at 3:02

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