78H05 - Page 1
Forum section: electronics / projects

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: January 31, 2015, 07:00:42 am
content: Recently dug up an old power supply I made, it uses a 78H05 regulator. All I could find is that's it's a "hybrid" part.I'm curious what that means. I'm guessing there's two dies in the TO-3, one is a pass transistor to allow the 5 amp output current?Not a lot of info on this part.

author: justanothercanuck
author_rank: Frequent Contributor
timestamp: January 31, 2015, 07:37:16 am
content: They look fairly similar in design to a TO-220 LM7805. I can only guess that they're rated for higher amperage due to the internal bond wiring and enormous case partially acting as a heatsink, unless there's something in the datasheet schematic they're not telling us.edit: how many pins does it have? If there's only 2 or 3, then it's a single output.

author: SeanB
author_rank: Super Contributor
timestamp: January 31, 2015, 08:52:09 am
content: The original likely had a hybrid construction, using 2 dies on a ceramic substrate. One was the pass transistor, and the other is the rest of the regulator, with the ceramic substrate providing connection pads and isolation for the pass transistor, and probably with some deposited cermet resistors to use for the current sense and the voltage trim operation. Later versions with better processing got the lot onto a single die.Originally these were a very expensive part, as they had a ceramic inner, and had to be soldered to the die spreader with a low melting point solder after ceramic assembly.Pic of the inside from the NS datasheet is herehttp://www.datasheetspdf.com/PDF/78H05/623542/1

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: January 31, 2015, 07:16:02 pm
content: I figured it was just what it said, but that picture wasn't too clear to me.I guess you don't see too many hybrid 5 amp linear regulators these days.

author: Fraser
author_rank: Super Contributor
timestamp: January 31, 2015, 07:45:16 pm
content: I have a few of these in the spares drawer. I recall that when I was a student they seemed very expensive parts. As a result I only used one or two in DIY projects. Big chunky TO3 format, perfect for good heat transfer to the heatsink.Aurora

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: February 02, 2015, 04:27:34 am
content: Yeah I have lots of standard 3 amp TO-3 parts like the LM323K, seems 5 amps was unusual back then.

author: dannyf
author_rank: Super Contributor
timestamp: February 02, 2015, 12:12:50 pm
content: Quote

author: SeanB
author_rank: Super Contributor
timestamp: February 02, 2015, 05:24:44 pm
content: I still have **somewhere** a few 78ASC regulators in a 4 lead TO3 package. Next time I see them I must undo one from the heatsink they are on and introduce it to the grinding wheel and some coolant. Then pop it under the microscope and get some images of what is inside. They came from a coin counter I bough a decade or so ago as part of an auction lot. Came with an IBM minicomputer I used as parts. Still have the SMPS panel from that somewhere, massive casting with assorted converters on it.

author: Andrew Morton
author_rank: Newbie
timestamp: April 08, 2019, 11:08:34 am
content: Make sure to check the data sheet before opening a 78-series voltage regulator in a TO-3 package. Some of them used beryllium oxide inside, which you want to avoid. (The 78HGKC definitely did.)

author: Yansi
author_rank: Super Contributor
timestamp: April 08, 2019, 11:11:06 am
content: So what? You are not going to grind that beryllium ceramics, are you?