Adding a heatsink to an IC (Electronics Project)

[Scarletpimpofnel]

I'm making a project with a 7805 voltage regulator which I'll add a heatsink to, see image below to show the parts I'm using (+ some heat sink grease stuff to exclude air from the thermal surfaces).

A few questions:
1 - Is the metal back plate of the 7805 regulator actually at ground potential? I believe it is.
2 - If it is at earth potential do I actually need the polythene "patch" to put between the 7805 and the heatsink if the heatsink won't come into contact with anything live?

Thanks

[JoshSm]

Backplate is ground.

You can add the full set of bits if you want, if you skip the screw spacer it might affect the fit. The rectangular thing is usually TIM not an insulator.

[Scarletpimpofnel]

JoshSm said:

Backplate is ground.

You can add the full set of bits if you want, if you skip the screw spacer it might affect the fit. The rectangular thing is usually TIM not an insulator.

Right thanks for that. So if that rectangular patch is TIM then do I need to add additional paste?

[biggiles]

If you're putting heatsinks on 7805s, is there a better solution? While 7805s are gloriously simple bits of kit, there are better options e.g. if you're trying to get a goodly quantity of power at 5v from a 12v source, you're wasting around 60% as heat (IIRC).

[Scarletpimpofnel]

biggiles said:

If you're putting heatsinks on 7805s, is there a better solution? While 7805s are gloriously simple bits of kit, there are better options e.g. if you're trying to get a goodly quantity of power at 5v from a 12v source, you're wasting around 60% as heat (IIRC).

Yes I started off with a 5V supply (plug in the wall mains to 5VDC out) but I need to drive a motor and 5V wasn't cutting it so got 12VDC plug in the wall thing to drive the motor but still need 5VDC for all the other stuff I've already designed.

[biggiles]

Scarletpimpofnel said:

biggiles said:

If you're putting heatsinks on 7805s, is there a better solution? While 7805s are gloriously simple bits of kit, there are better options e.g. if you're trying to get a goodly quantity of power at 5v from a 12v source, you're wasting around 60% as heat (IIRC).

Yes I started off with a 5V supply (plug in the wall mains to 5VDC out) but I need to drive a motor and 5V wasn't cutting it so got 12VDC plug in the wall thing to drive the motor but still need 5VDC for all the other stuff I've already designed.

OK. Perhaps a small computer power supply would be helpful if you need lots of power: those give you 12v and 5v. There's also an old IT trick to get 7v out of that for running motors (e.g. fans) more slowly if that's useful, by wiring across the +ve connections.

There are also plenty of "alarm-type" power supplies out there which will give you 12v and 5v in an easy package if that's appealing e.g. "12v 5v power supply" on Amazon gives masses. It's amazing what is available these days - I generally use usb-c-to-5v adapters these days if I need 5v.

[JoshSm]

Lots of 12V->5V DC-DC converter modules out there, obviously quality will vary.

[ATG]

780n are fine for low current applications where you don't really care about efficiency of the power supply. They're also really compact, though you need to consider heat dissipation. They're dirt cheap. They also produce a pretty clean output.

They aren't a silver bullet, of course. Sometimes all you need is a zener diode, sometimes you want something efficient, sometimes you want something that can output far more power.

How much current are you going to draw from the 7805?

[Scarletpimpofnel]

Basically the 5VDC current draw is low, just a RPi Pico and some LEDs and some switches feeding the Pico's GPIO. So all in maybe 100mA, that is what I am using the 7805 for.

My original 5V plug in the wall type supply was fine for the demand but I added a 5V motor (still ok for the plug in the wall) BUT there was a lack of torque so changed the plug in t he wall to 12VDC, the motor to 12VDC and added a 7805 (12VDC to 5VDC) for the Pico etc.

Basically space is at a premium in my enclosure hence not adding a boost converter or salvage a supply from a laptop etc.

I accept it's not energy efficient but don't really care as it'll be seldom on and next to bugga all wastage anyway.