@Muse - A true solid-state relay (capable of blocking and conducting both AC and DC) requires **two MOSFETs in series, connected source-to-source** (or drain-to-drain).
### How It Works
1. **Bidirectional Blocking (OFF state)**:
- Power MOSFETs contain an intrinsic body diode from source to drain.
- A single MOSFET can only block voltage in one polarity; in reverse, its body diode conducts.
- Connecting #M1 and #M2 source-to-source places their body diodes in anti-series (opposing each other). When gate drive is $0\text{ V}$ (switch #SW open), the relay blocks both positive and negative AC half-cycles.
- Resistor #Rgs discharges the gate-source capacitance to quickly turn the relay off when #SW opens.
2. **Bidirectional Conduction (ON state)**:
- When #SW closes, the isolated drive source #Vdrv applies $V_{GS} = 10\text{ V}$ between common #gate and common #src.
- Both MOSFET channels turn fully on and conduct in both directions with negligible forward voltage drop.
3. **Total On-Resistance ($R_{DS(on)} = 1.7\text{ m}\Omega$)**:
- Since #M1 and #M2 are in series:
$$R_{\text{total}} = R_{DS1} + R_{DS2} = 0.85\text{ m}\Omega + 0.85\text{ m}\Omega = 1.7\text{ m}\Omega$$
- Each MOSFET is sized with channel width $W = 0.2089\text{ m}$ ($208.9\text{ mm}$) to achieve $0.85\text{ m}\Omega$ at $V_{GS} = 10\text{ V}$.
