Editing Commodore 64 Power-Supply Protector (C64 Saver) (section)

== Operating Principle ==
{| class="wikitable styled-table" style="width:70%; text-align:center;"
! Function block !! Component&nbsp;example !! Description
|-
| Over-voltage sense || TL431 programmable shunt (earlier boards use 5 V zener) || Monitors the 5 V rail; trips at 5.3–5.5 V (adjustable ± 50 mV).
|-
| Crowbar / latch || SCR (e.g. C106D) or P-channel MOSFET + relay || When tripped, shorts the rail through the SCR or mechanically opens the circuit; resets only when input power is removed.
|-
| Fuse element || Resettable polyfuse 1.1 A or fast-blow 1 A || Limits fault current so the PSU shuts down instead of the computer.
|-
| Visual alert || Bi-colour LED || Green = normal; Red = tripped/over-voltage.
|-
| Passthrough lines || 9 VAC pair, Sense line || These are '''not''' switched—protector covers only +5 V DC.
|}
*OpenC64Saver* introduces reverse-polarity protection, replaces the SCR with a low-R<sub>DS(on)</sub> MOSFET for cooler running, and adds a precision trim-pot for exact trip voltage set-up.