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In a robotic system I am designing, the computer, motor controller and motor amplifier circuits all run on the same 24VDC power bus, which is provided by a switching power supply. Like below:

Bus Block Diagram

In the case of power supply failure, a capacitor/supercapacitor needs to provide backup power to the computer for 100 milliseconds, long enough for it to shut down properly. However, putting the capacitor in parallel with the computer also puts it in parallel with everything else on the bus, which means it would have to provide power to everything else for 100ms as well. This would require the cap/supercap to be prohibitively large.

What is the simplest change to the system such that the capacitor only provides power for the computer? I would really prefer to not need a separate power supply for the computer.

Edit after Josip's Suggestion

So something as simple as this will do? The computer does indeed have a DC-DC converter that can tolerate the diode voltage drop.

Bus with Diode

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Assuming computer has local DC-DC converter and can handle slight voltage drop on 24V line, probably the easiest approach would be putting diode in serial just in front of capacitor.

That way computer would be powered during normal operation while diode would prevent it from powering rest of the circuit when supply is out.

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  • \$\begingroup\$ The way it is in the edited post? \$\endgroup\$ – thechimp Mar 26 '18 at 20:01
  • \$\begingroup\$ Yes, that positioning of diode will prevent capacitor from powering motors and motor controller. \$\endgroup\$ – Josip Medved Mar 27 '18 at 20:55

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