Electronics "silly" question thread

johnr66

Member
2009-03-05 1:55 pm
I have a couple that have crossed my mind and keep me wondering...

1) What is/was the 8 volt standard for? For example, the 78xx series of regulators had 5,8,9,12,15,18,24 volt versions. I can see the point in all the others but the 8 volt ones.

2) I have several diodes with glass casings. How the heck do they get the diode chip inside? I guess they mold the glass around it, but wouldn't this be at glowing hot destructive temperatures?
 
1) I'm not sure I would call any a standard. A variety of fixed reg voltages covers most any application. An 8V reg could be used with a 12V lead-acid battery to maintain regulation to full discharge, eg <11V.
2) I don't know for certain, but it is probably a glass tube, with end caps affixed. I assume you're referring to the 1N4148-type diodes. Not as common are those SMT parts stuffed into a leaded glass package.
 

johnr66

Member
2009-03-05 1:55 pm
1) I'm not sure I would call any a standard. A variety of fixed reg voltages covers most any application. An 8V reg could be used with a 12V lead-acid battery to maintain regulation to full discharge, eg <11V.
2) I don't know for certain, but it is probably a glass tube, with end caps affixed. I assume you're referring to the 1N4148-type diodes. Not as common are those SMT parts stuffed into a leaded glass package.

That could be possible. They make chips in huge batches planning on selling many to maximize profits, so there's a reason for the 8 volt version. I've never come across a regulated 8 volt circuit in the wild, however.

Yes, the axial lead devices like the 1N4148 or even many of the zener or germanium detector diodes. To seal in glass means the leads would be near the glass fusing temp to prevent stress cracks as it cools. Whatever is inside must be roasting hot during encapsulation.
 
2) I have several diodes with glass casings. How the heck do they get the diode chip inside? I guess they mold the glass around it, but wouldn't this be at glowing hot destructive temperatures?

There are two methods I'm familiar with.
1. After the nailheads are brazed to the silicon chip, a glass slurry is applied to the diode while is is slowly turning on axis. After it dries, it is put into a furnace and melted. I can't tell you what the actual temperature was for the process, but it has to be below the aluminum-silicon eutectic temperature of 577 C.

2. After the nailhead brazing, a low temp glass sleeve is slid over the diode, again melted in a furnace. I recall the sleeves bought by the guys I worked for were from Schott Glass, but that was in '81.

jn