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I picked up an old Toshiba MSX computer with a duff power supply.

I need: Ground, +12v, +5v and -5v.

I've picked up a 12v power supply and I thought I could use a buck converter for the +5v, but I'm at a loss how I can get the -5v and how I can complete the circuit (can I use the negative terminal of the 5v for the -5v?).

Many thanks for any answers.

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    \$\begingroup\$ The current requirements are just as important as the voltage requirements. \$\endgroup\$
    – HandyHowie
    Commented Mar 9, 2019 at 16:13
  • \$\begingroup\$ What does "duff" mean? \$\endgroup\$
    – Elliot Alderson
    Commented Mar 9, 2019 at 16:13
  • \$\begingroup\$ @ElliotAlderson: Nonfunctioning. \$\endgroup\$
    – Dave Tweed
    Commented Mar 9, 2019 at 16:28
  • \$\begingroup\$ Might be worth trying to figure out what the -5v supply is used for. Likely it is low current, which could make using a PC supply with a -12v rail and a 7905 linear regulator to provide -5v from that a possibility. \$\endgroup\$
    – Chris Stratton
    Commented Mar 9, 2019 at 18:27
  • \$\begingroup\$ @HandyHowie - I've discussed this with another MSX enthusiast who has replaced power supplies and he indicated that the minimum required for the 5v would be 1.2A \$\endgroup\$
    – Martin Cole
    Commented Mar 9, 2019 at 19:21

1 Answer 1

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You have a number of options. Given your evident level of expertise, the simplest thing to do is to get three separate AC-input power supplies:

  • 12VDC - connect the negative terminal to ground - this provides +12V
  • 5VDC - connect the negative terminal to ground - this provides +5V
  • 5VDC - connect the positive terminal to ground - this provides -5V
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  • \$\begingroup\$ I would add that the 5V supply that provides -5V must have an isolated output. Most do, but I would keep it in mind while shopping. \$\endgroup\$
    – Elliot Alderson
    Commented Mar 9, 2019 at 17:19
  • \$\begingroup\$ @Elliot since Dave was talking about AC input supplies, they better all have isolated outputs anyway. Unless you want a new haircut... \$\endgroup\$
    – dim
    Commented Mar 9, 2019 at 22:00
  • \$\begingroup\$ Using multiple AC supplies may lead to sequencing issues.Even more - absence of some source (-5V for example) may lead to permanent damage. \$\endgroup\$
    – Eugene K
    Commented Mar 10, 2019 at 8:11

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