Switching polarity of rectified AC power with a microcontroller

Question

I am trying to create a circuit that will allow me to control the polarity of the current flowing through a coil in order to attract or repel a magnet. I would like to use two MOSFETs in series since activating a single MOSFET will half wave rectify the current by flowing through the body diode of the other MOSFET.

I have attached a simplified version of what I have envisioned. A microcontroller (not shown) would control through the Opto-coupler. The circuit works fine until the bottom MOSFET is activated. When that happens, on the negative AC power cycle the power flows through the bottom MOSFET, takes a least path of resistance shortcut at the problem point to the bridge rectifier and back to it's home in 110VAC. Poof.

In theory, a battery could operate this circuit fine, but my I would like to design this circuit so it works completely on AC power. How can I control these MOSFETS without shorting the circuit?

^{simulate this circuit – Schematic created using CircuitLab}

Answer 1

If you're okay using four MOSFETs instead of two, you could use a pair of push-pull circuits. Adding a diode in the AC path will prevent reverse conduction through the body diodes. If you want to draw current during both half-cycles, use a bridge rectifier. Or you could add a capacitor if you want something closer to DC.

^{simulate this circuit – Schematic created using CircuitLab}

Answer 2

First, figure out the desired flow of the power. Draw the circuit in an H bridge configuration, where one side of the H bridge is D1 and D3, other side is M1 and M2. You'll see the L1 is not in the right place, the load should the load across the H bridge.

Next, find a few ways to control it. Usually this kind of solution needs an isolated power or isolated drivers, perhaps with optocouplers after your MOSFET driver, not just front of it.

Did you consider a TRIAC instead? You can have only the + or - half wave to drive your load, and you've only used one power component.

Answer 3

Here's an easy way to do it using solid-state relays, and here's an OPTO 22 selection guide, representative of what's generally available with DC control from all of the SSR guys.