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I am unable to find any IC that would allow me to have 2 DC inputs (5v/12v coming from the PC psu) and have one of them as output (being either 5v out or 12v out). This is for power to a PC Fan that should, at the far end when using a 140mm case fan, would pull 4.2 to 6W. So around ~400mA...

I figured that a DPST switch would work but I'm not quite sure that is what I need for this?

An illustration of what I am looking for the IC to do: enter image description here

Being hooked to a microcontroller (PIC), I would be able to switch from the default voltage (that being 5vdc) to the 12vdc and, if needed, back to 5vdc.

Anyone know of an IC that would work like this for my needed purpose? It would also be nice if the IC had 4 outputs (2 inputs) so that I wouldn't have to have so many of them on my PCB. I will have 8 4pin connectors so that would be a total of 8 outputs that I would need.

So something like this? enter image description here

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  • \$\begingroup\$ How about an SPDT relay? \$\endgroup\$
    – m.Alin
    Commented Feb 13, 2017 at 15:26
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    \$\begingroup\$ What current do you need? If it's low (mA or less) "analog switch". Otherwise "solid state relay". But you need a third DC voltage (usually a logic level) to control the switch. \$\endgroup\$
    – user16324
    Commented Feb 13, 2017 at 15:28
  • \$\begingroup\$ Also, you don't need 4 outputs. You only need two outputs to switch the 5 / 12 V lines. The GNDs of the power supplies can be tied together.. \$\endgroup\$
    – m.Alin
    Commented Feb 13, 2017 at 15:28
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    \$\begingroup\$ "I figured that a DPST switch would work" - think again. \$\endgroup\$
    – Andy aka
    Commented Feb 13, 2017 at 15:30
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    \$\begingroup\$ This question is unanswerable as you do not specify how much current you want to switch. Until you specify that current the safe option is to recommend relays. \$\endgroup\$
    – Bimpelrekkie
    Commented Feb 13, 2017 at 16:07

2 Answers 2

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A relay may be the simple answer to your need. You wire your output to the "common" terminal and then make it switch between 5V and 12V. Wire each DC input either to NC or NO taking into account which one will be used most of the time.

EDIT: if relays are not convenient for you, consider using analog switches like these from TI.

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  • \$\begingroup\$ Would like a ic way of doing it instead of having 8 big relays on the board. \$\endgroup\$
    – StealthRT
    Commented Feb 13, 2017 at 15:51
  • \$\begingroup\$ Then maybe analog switches will do (take a look at the edit in my answer) . \$\endgroup\$
    – Enric Blanco
    Commented Feb 13, 2017 at 15:58
  • \$\begingroup\$ Analog switches can only be used in certain circumstances. It is unclear from the question if these can be used in this case. \$\endgroup\$
    – Bimpelrekkie
    Commented Feb 13, 2017 at 16:09
  • \$\begingroup\$ I agree with you, @FakeMoustake. Maybe the OP could provide more info so we can advise him better? \$\endgroup\$
    – Enric Blanco
    Commented Feb 13, 2017 at 16:19
  • \$\begingroup\$ Ive updated my OP @EnricBlanco \$\endgroup\$
    – StealthRT
    Commented Feb 13, 2017 at 16:55
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Since you are using a PIC, I would suggest something as simple as 1 FET or BJT darlington driving the fan at 12V, and a PWM for the PIC output.

This way you can make the PIC output any voltage from 0 to 12V with only 1 pin.

Maybe your PIC already has embedded PWM. If not, PWM is simple to implement, just set the output pin high for, say, 500us, then low for 700us, and keep doing this forever. This way you will have a pulse of 1200us width with 41,7% duty cycle, which is equal to 5Vrms at 833,33Hz.

More examples:
1200us high, 0us low = 12V
700us high, 500us low = 7V
300us high, 800us low = 3V

Circuit should be something like this:

schematic

simulate this circuit – Schematic created using CircuitLab

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