I'm trying to combine two well known circuits, one is reverse polarity protection with MOSFET, another is crowbar circuit against overvoltage. Before trying to make the real circuit on the breadboard, I've decided to simulate it in TINA. However, I can't make it working. Separately both snippets work. Below is schematic and simulation result. It seems that SCR is always on for the reason I cannot explain. I've changed SCR to TRIAC (it was a wild guess), and now circuits works as expected. Zeners are rated 15V. In real application ammeter would be replaced by a 1.5A fuse. The power would be supplied by a off the shelf AC/DC 12V power supply, so protection is required in a situation when user accidentally plugs in wrong type of supply (24V, or reverse polarity). The load is actually a quite complicated electronic device with MCU, joystick, buttons, LCD screen, some BT transmitters and a couple of stepper motors.
Why first circuit isn't working as I expect in simulator? And will the second one work in a real application?
Why first circuit isn't working as I expect in simulator? And will the second one work in a real application?