I have a power supply unit I extracted from a media player and there is a pin connector with the labels "-24V", "GND", "F+", "F-". I know what the first two mean but what do the last "F+" "F-" mean? Also bonus points if you can tell me why there is a negative 24V rail but not an opposite positive one (24V)?
Electronic – What do the “F+” and “F-” pins on a power supply unit stand for
markingspower supply
Best Answer
My guess is that the media player used a vacuum fluorescent display (VFD) and that the -24 V was required for that.
Figure 1. Vacuum fluorescent display. Source Wikipedia commons.
+5 V is clearly for the logic.
VFD filaments
Figure 2. VFD cross-section showing filaments. Source: Noritake Electric.
Thanks to @DaveTweed for suggesting "filament" for F+ and F-. This led me to the Noritake Itron page linked above. They state:
The rest of the article is quite interesting and detailed. I was not aware of the details of operation. I think the filaments are visible as seven light horizontal lines in the photo of Figure 1.