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I'm trying to see if it's possible to build a large grid (hundreds) of electromagnets, where very electromagnet should be able to get both directions of currents (to generate magnetic fields with both polarities). A simplifying condition is that only a single electromagnets has to be active at a given time.

Controlling multiple EM's can be done with bitshifters and Darlington arrays, while making a bi-polarity EM circuit can be done with an H-bridge. I'm having trouble combining the two. Darlington arrays seem to only come in NPN flavor, and not the PNP that one would need to complete the H-bridge type circuit (if my understanding here is correct.) I was hoping to avoid making an H-bridge for every EM, especially since only one EM needs to be activated at a time.

Is it possible to make a circuit with these requirements in a scalable way?

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  • \$\begingroup\$ I would use MOSFETs for this, not BJTs. And you can make your own darlington pair with two discrete BJTs anyway, of whichever polarity you want. Or mix polarities and get the advantages of a Sziklai pair instead. \$\endgroup\$ – Hearth Nov 29 '20 at 15:00
  • \$\begingroup\$ Useful search term : core memory. \$\endgroup\$ – user_1818839 Nov 29 '20 at 15:17
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If you have a lot of magnets (or anything else) arranged in a grid, and you want to power only one at once, in either direction, then what you need is half a bridge on every row and column.

That is, each row or column end needs to be able to be connected to either the positive rail or negative rail. It then forms a full "H" with one side being the end of the row, the other being the top of the column, and the magnet in the middle.

Darlington arrays seem to only come in NPN flavor

You could possibly counteract this by using "high side" switching, where the voltage driving the base of the darlington is higher than the top voltage rail it's powered from. More normally done with MOSFETs.

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