Switching ground, but need to switch positive side

[mickc]

Hi

I have some real aircraft cockpit warning lights that are in a flight simulator.  These run on 28v DC, and are controlled by some USB cards that sink to ground to activate the light, ant the other side is powered with 28v.

This is fine, and all works as it should, but there are some that use a different power setup, where they are grounded all the time, and use the 28v positive to activate the lamp.

My USB boards can only sink to ground, not to the source.   Also the warning lights have internal diodes for protection and the push to test function so I can change them.

Bottom line is, what is the easiest way to change a low side switched circuit to a high side switched circuit?  I have used small 28v relays for this in the past but thats quite tedious to wire into the panel.

Im thinking some sort of transistor array etc?    Each warning lamp draws 80mA at 28v DC

Open to any ideas, Cheers.

[Ian.M]

P-MOSFET, source to +28V, drain to load, and gate driven by the tap of a potential divider (2x 4K7) between +28V and your card output.
 

[mickc]

P-MOSFET, source to +28V, drain to load, and gate driven by the tap of a potential divider (2x 4K7) between +28V and your card output.

Thanks Ian,

Are there any P-Mosfet array chips available that you know of?

[Ian.M]

Nothing I've actually used.  You could hit a major component distributor's parametric search and look for dual or quad P-MOSFETS with suitable voltage and current ratings, but I'd bet on the result being more expensive and far more difficult to lay out a board for than using individual 'jellybean' SMD P-MOSFETs and individual resistors, as you wont be able to simply layout one channel and clone it N times.