Two LM7805’s

[Martaine2005]

This is probably the stupidest question ever!.
Can the two regulators share a heat sink without insulating them?.
My heart says no and my brain says yes as -neg and tabs are electrically connected.
Both regulators are on the same 9V rail too. So are in effect already connected together via the -neg rail. The outputs go to separate boards which also share the common -neg rail.
Can someone please clarify this either way?.
Thanks. Martin

 

[Harald Kapp]

Can the two regulators share a heat sink without insulating them?.

Of course they can. If they share a common GND, that is. The tabs on the TO220 case aer connected to Common aka GND:



Instead of using two 7805 you can use a single 7805 plus an external transistor to increase the max. output current like e.g. so.

 

[Martaine2005]

Thanks for the clarification #Harald Kapp. I really should trust my brain
I knew deep down but wasn’t sure.
Regarding using only one regulator, I have loads and they cost nothing. Plus, it keeps it simpler for me.
Thanks for the link, it’s a hard read (terrible English) but I’ll bookmark it and read it again.

 

[danadak]

Using two regs gives you the full protection each reg has, eg Thermal,
short circuit. A simple boosted reg does not have full protection.

 

[Martaine2005]

Using two regs gives you the full protection each reg has, eg Thermal,
short circuit. A simple boosted reg does not have full protection.

That’s a really good point that I never considered. It’s simply that I have loads of them.
Thanks @danadak

 

[AnalogKid]

ALWAYS check the datasheets for exceptions, but --

The tab of a TO-220 package *usually* is connected to the center pin. This is true for both power transistors such as the TIP series, and 3-pin ICs such as regulators. I've seen some parts where the tab is GND but none of the 3 pins are.

ak

 

[Martaine2005]

Thanks @AnalogKid .
Both negative terminals are electrically connected to tabs. It was a school boy question.
If you don’t know, ask an expert!.
Cheers AK

 

[bertus]

Hello,

Do you also intend to connect the outputs?
There will always be a slight difference in output voltage.
This will lead to imbalance.

Bertus

 

[Martaine2005]

Hello,

Do you also intend to connect the outputs?
There will always be a slight difference in output voltage.
This will lead to imbalance.

Bertus

No. The outputs are powering different devices.

 

[danadak]

Your only concern is power up sequencing of parts, to avoid CMOS latchup of parts.
So that I/O pins on parts spread across the 2 regulators meet their respective power
up constraints.

https://www.ti.com/lit/wp/scaa124/scaa124.pdf

https://www.analog.com/en/resources/app-notes/an-1311.html

Regards, Dana.