Here's a low-side switch for AC, and plus or minus DC sources, using two back-to-back N-MOSFETs and one PNP BJT to form a low-side AC/DC bipolar switch.
This has much lower On voltage drop and power loss than a TRIAC and it doesn't latch on with a DC source as a TRIAC does.
It can be used in place of an SSR when the AC/DC voltage source is already isolated from the Mains by a transformer and thus isolation of the control signal is not required
The circuit uses the fact that a MOSFET...