So I got to wondering on a TO-220 is the metal tab the same for every transistor in that package?
This gets further convoluted because seems like I remember some voltage regulators in that package 📦 and the metal tab possibly being ground. Like when you guys fixed my audition chorus :tu:
Then seems like I remember on TO-3 packages like the metal output transistors (I'm not cheating and looking while typing this so hope I am right but the metal case is the collector?)
Hence why people have to use mica insulators and stuff.
So back to the TO-220 I'm off to see if the metal tab
-is always the same thing
-or no :grr
And oh yeah obviously the metal tab with a hole in it is for attaching to a heat sink but don't necessarily assume a heat sink is ground :loco
At the end of the day I guess the best thing to do is just make sure what stuff is before connecting or soldering or placing in service.
Since this post is already a rambling stream of consciousness I'll add that I guess the white paste is not an electric insulator it is there to conduct heat and aid in heat transfer xP
Which brings me to dielectric grease how many years did I put this on spark plugs and stuff not knowing why it's just what I am supposed to do.
Seems like I should know if it conducts or insulates electricity. xP
The tab on a TO-220 or the case on a TO-3 is connected to the Collector on a PNP or NPN power transistor. That's because the backside of the Silicon Die is mounted on the metal for best heat conduction. (The same applies to the Drain of a power MOSFET.) On a Positive Voltage Regulator chip, the backside of the Die is the Voltage Adjust Pin so that may be grounded depending on which Regulator you are using. On a Negative Voltage Regulator, the backside of the die is the Incoming Negative Voltage which is almost never grounded.
There are exceptions to these rules, you must consult the part's data sheet for the best information. On an Adjustable Positive Voltage Regulator, the Voltage Adjust pin goes to a couple of resistors connected in series between the Output pin and ground so the case must be insulated from the heatsink.
Connecting a big heatsink to anything except ground is considered bad design because people want to touch them to see if they are hot. They don't want to be shocked or killed. Little PCB mount heatsinks may not be grounded, don't touch unless you verify that there is no hazardous Voltage present.
Yes sir excellent thanks :dbtu: :tu:
I would like to add that some heat transfer paste is conductive and will cause shorts if used with heatsinks and mica washers.
The conductive heat transfer paste is often used in computers for the main processor heatsink, it makes no difference in there since there are no electrical terminals close by.
Make sure you only get non conductive heatsink paste if you get some, a small tube of really good expensive paste will last forever and ever so don't get anything cheap and nasty.
Excellent point sir thanks nice to hear from you. :dbtu:
Quote from: Tassieviking on May 06, 2025, 11:20:12 AMI would like to add that some heat transfer paste is conductive and will cause shorts if used with heatsinks and mica washers.
The conductive heat transfer paste is often used in computers for the main processor heatsink, it makes no difference in there since there are no electrical terminals close by.
Make sure you only get non conductive heatsink paste if you get some, a small tube of really good expensive paste will last forever and ever so don't get anything cheap and nasty.
Computer builders and modders swear by "Arctic Silver" paste, claimed to contain silver dust.
I much suspect Aluminum dust instead but in any case, any metal present will be conductive.
Quote from: Tassieviking on May 06, 2025, 11:20:12 AMI would like to add that some heat transfer paste is conductive and will cause shorts if used with heatsinks and mica washers.
The conductive heat transfer paste is often used in computers for the main processor heatsink, it makes no difference in there since there are no electrical terminals close by.
Make sure you only get non conductive heatsink paste if you get some, a small tube of really good expensive paste will last forever and ever so don't get anything cheap and nasty.
I have Radio Shack branded thermal paste I've been using for almost two decades lol. I don't need it often, but when I do it sure does come in handy. Still in good condition too. Cheap stuff "goes bad" and either gets dry or runny.