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

== What it actually does ==

'''It is not a crowbar.''' This is the single most common misdescription of the device, and Carlsen addresses it head on:

: "The Saver protector is essentially a fast-acting electronic circuit breaker. It functions to quickly cut off the 5 volt supply line to the computer if the voltage exceeds about 5.4 volts. '''It is not a "crowbar" device''' but opens the line from the supply to the computer before the voltage gets high enough to do damage. That's the safest way to do it."<ref name="carlsen" />

A crowbar shorts the faulty rail to ground and relies on a fuse to clear; a Saver opens the line instead, so the fault energy never reaches the machine and nothing has to blow to stop it.

{| class="wikitable styled-table" style="width:90%; text-align:left;"
|+'''Behaviour'''
! Property !! What Carlsen and OpenC64Saver document
|-
| Trip point || '''About 5.4 V''', set by trimming
|-
| Action on trip || The +5 V line is '''opened''', not shorted
|-
| Output element || A '''relay''' in the OpenC64Saver implementation<ref name="opensaver" />
|-
| Reset || The device stays in failsafe until the supply is unplugged
|-
| 9 V AC || '''Passed straight through, unprotected'''
|}

=== Why the trip point is as high as 5.4 V ===

Carlsen explains this, and it matters because a reader who sets it lower will get nuisance trips:

: "Feedback from a few users indicated the Saver would trip when they turned their computer off, and it remained in failsafe mode until unplugged from the PS. Apparently some power supplies output can jump up past the failsafe point when the load on them is suddenly removed (computer off). That's why the trip point is set as high as it is. '''5.4 volts is still under the "absolute maximum rating" specification for the RAM chips.'''"<ref name="carlsen" />

=== Temperature sensitivity ===

The Zener reference drifts with temperature: '''cold reads high, hot reads low'''. Carlsen's consequence is practical — if the Saver is fitted inside a machine, keep it away from anything that produces heat, and do not judge the trip point on a board that has just been soldered.<ref name="carlsen" />