Voltage regulator - Heat sink?

[zpyder]

I've always assumed that the piece of metal coming out of many voltage regulators (has a round hole in it) was a heat sink.  Am I wrong?  Some voltage regulators don't have one...

thanks,
zpyder

[R.G.]

It's a thermally conductive tab. It either acts as a heat sink on its own, sufficient for low powers, about 1-2W maybe, or connects to a bigger heat sink for bigger powers.

The power dissipated in a voltage regulator is equal to the difference in the input and output voltages times the current being pulled. For instance, if the unregulated DC is 14Vdc, the output is 9Vdc, and you're pulling 200ma, the power is (14-9)*0.2 = 1W. At 1A, it's 5W.

Most three terminal regulators shut down internally if they get too hot.

[Sir H C]

That tab is often connected to either ground or the input voltage (I forget which).  So be careful when putting it to a heat sink as you could either short out the regulator or charge up something else.

[The Tone God]

That tab is often connected to either ground or the input voltage (I forget which).  So be careful when putting it to a heat sink as you could either short out the regulator or charge up something else.

I believe that in most TO-220 case parts the tab is connected to the center pin of the part regardless of the part function or pinout. One should take that in account when connecting the part to a conductive surface.

Andrew

[Sir H C]

That tab is often connected to either ground or the input voltage (I forget which).  So be careful when putting it to a heat sink as you could either short out the regulator or charge up something else.

I believe that in most TO-220 case parts the tab is connected to the center pin of the part regardless of the part function or pinout. One should take that in account when connecting the part to a conductive surface.

Andrew

Okay it is negative regulators that often have the tab be -V in since the substrate usually wants to be biased to the lowest potential (assuming an P doped substrate).

[The Tone God]

Okay it is negative regulators that often have the tab be -V in since the substrate usually wants to be biased to the lowest potential (assuming an P doped substrate).

Yeah the center pin is V- so if you connect the tab to something other then V- you would get a short. I usually order my negative regulators with isolated tabs to solve that problem. I also have insulator strips and insulated shoulder washers/bushings for parts that I can't get in isolated versions.

The tab/center pin rule applies to other part types too like FETs and diodes. I forget where I read that tidbit but I think it may be part of the TO-220 spec standard.

Andrew

[Sir H C]

Its more to do with the fab processes used.  There are exceptions, usually when company B copies company A's part but with a different process.  Some guys have P-well processes, most have N-well, and these lead to reversed substrates.

[Paul Perry (Frostwave)]

The common LM78xx series + regs have the tab connected to the ground pin, which is very handy when you are taking measurements on a board nice to have somewhere for the scope ground to clip securely.