Cooling a TO-220 7812 regulator

[Pimpom]

I'm going to use a standard 7812 TO-220 regulator on a single-sided 1 oz
board with the dissipation varying as below:

- Idle at 120-150mW
- 0.5W for 1-5 minutes at irregular intervals
- Up to 4W for 1 second at the start of each 0.5W phase

The interval between the 1-5-minute periods is variable and may be 1 to
10 minutes.

The ground pin is soldered to ~2 sq.in. of copper on the PCB.

Options:
1) As described. No extra heatsinking.
2) Mount it on a small Al heatsink.
3) Place the regulator horizontally on the underside and bolt it to the
copper.

Tamb = ~35ºC max

Do you think option 1) is enough? Or should I go for 2) or 3)?

[Martin Brown]

Post by Pimpom
I'm going to use a standard 7812 TO-220 regulator on a single-sided 1 oz
- Idle at 120-150mW
- 0.5W for 1-5 minutes at irregular intervals
- Up to 4W for 1 second at the start of each 0.5W phase
The interval between the 1-5-minute periods is variable and may be 1 to
10 minutes.
The ground pin is soldered to ~2 sq.in. of copper on the PCB.
1) As described. No extra heatsinking.
2) Mount it on a small Al heatsink.
3) Place the regulator horizontally on the underside and bolt it to the
copper.
Tamb = ~35ºC max
Do you think option 1) is enough? Or should I go for 2) or 3)?

I suspect that under those load conditions you will get away with it #1.
I'm pretty sure the package is well able to handle that dissipation and
if it can't it will fold back to thermally protect itself (in which case
you will have to add a bit more heatsinking).

I once built a 78xx based PSU that was in a bright bare metal aluminium
extruded box expecting it to be more than adequate heatsinking. It
wasn't! The bright metal was a terrible radiator and it got hot enough
to go into thermal foldback. A bit of matt black paint fixed that.

[Pimpom]

Post by Martin Brown

Post by Pimpom
I'm going to use a standard 7812 TO-220 regulator on a single-sided 1
- Idle at 120-150mW
- 0.5W for 1-5 minutes at irregular intervals
- Up to 4W for 1 second at the start of each 0.5W phase
The interval between the 1-5-minute periods is variable and may be 1
to 10 minutes.
The ground pin is soldered to ~2 sq.in. of copper on the PCB.
1) As described. No extra heatsinking.
2) Mount it on a small Al heatsink.
3) Place the regulator horizontally on the underside and bolt it to
the copper.
Tamb = ~35ºC max
Do you think option 1) is enough? Or should I go for 2) or 3)?

I suspect that under those load conditions you will get away with it #1.
I'm pretty sure the package is well able to handle that dissipation and
if it can't it will fold back to thermally protect itself (in which case
you will have to add a bit more heatsinking).
I once built a 78xx based PSU that was in a bright bare metal aluminium
extruded box expecting it to be more than adequate heatsinking. It
wasn't! The bright metal was a terrible radiator and it got hot enough
to go into thermal foldback. A bit of matt black paint fixed that.

Thanks. I'm inclined to think that way too. Calculating temerature rise
and heatsink requirement for steady-state dissipation is simple enough
and it's easy to make a good guesstimate from experience. But transient
cases like this are different.

[Bill Sloman]

Post by Pimpom

Post by Martin Brown

Post by Pimpom
I'm going to use a standard 7812 TO-220 regulator on a single-sided 1
- Idle at 120-150mW
- 0.5W for 1-5 minutes at irregular intervals
- Up to 4W for 1 second at the start of each 0.5W phase
The interval between the 1-5-minute periods is variable and may be 1
to 10 minutes.
The ground pin is soldered to ~2 sq.in. of copper on the PCB.
1) As described. No extra heatsinking.
2) Mount it on a small Al heatsink.
3) Place the regulator horizontally on the underside and bolt it to
the copper.
Tamb = ~35ºC max
Do you think option 1) is enough? Or should I go for 2) or 3)?

I suspect that under those load conditions you will get away with it
#1. I'm pretty sure the package is well able to handle that
dissipation and if it can't it will fold back to thermally protect
itself (in which case you will have to add a bit more heatsinking).
I once built a 78xx based PSU that was in a bright bare metal
aluminium extruded box expecting it to be more than adequate
heatsinking. It wasn't! The bright metal was a terrible radiator and
it got hot enough to go into thermal foldback. A bit of matt black
paint fixed that.

Thanks. I'm inclined to think that way too. Calculating temerature rise
and heatsink requirement for steady-state dissipation is simple enough
and it's easy to make a good guesstimate from experience. But transient
cases like this are different.

It's not that difficult to weigh a chunk of material and calculate it's
heat capacity. We did it back in 1993.

Sloman A.W., Buggs P., Molloy J., and Stewart D. “A
microcontroller-based driver to stabilise the temperature of an optical
stage to 1mK in the range 4C to 38C, using a Peltier heat pump and a
thermistor sensor” Measurement Science and Technology, 7 1653-64 (1996)

and measured the step response of the system as well, with three
different Peltier junctions between the point we were stabilising and
the heat sink.

It's discussed in the third page of the paper. It does get a bit messy,
but it is do-able.

[Jan Panteltje]

On a sunny day (Sun, 15 Sep 2024 16:58:01 +0530) it happened Pimpom

Post by Pimpom
I'm going to use a standard 7812 TO-220 regulator on a single-sided 1 oz
- Idle at 120-150mW
- 0.5W for 1-5 minutes at irregular intervals
- Up to 4W for 1 second at the start of each 0.5W phase
The interval between the 1-5-minute periods is variable and may be 1 to
10 minutes.
The ground pin is soldered to ~2 sq.in. of copper on the PCB.
1) As described. No extra heatsinking.
2) Mount it on a small Al heatsink.
3) Place the regulator horizontally on the underside and bolt it to the
copper.
Tamb = ~35ºC max
Do you think option 1) is enough? Or should I go for 2) or 3)?

Rth to ambient is about 50 IIRC
so 4 W long enough makes a 200 degrees rise..
.5W makes a 32 degrees rise.
But the thing will thermal limit
That limit may affect whatever it is you power from it.
I always used cheap small heatsinks with the thing standing up,
no need to warm the PCB whith maybe sensitive stuff on it
If you have an alu housing an need more power screw it against that, pehaps with a Mica insulator
Loading Image...

If all else fails, biiger heatsink, this is the biggest one I have :
Loading Image...
:-)

[Pimpom]

Post by Jan Panteltje
On a sunny day (Sun, 15 Sep 2024 16:58:01 +0530) it happened Pimpom

Post by Pimpom
I'm going to use a standard 7812 TO-220 regulator on a single-sided 1 oz
- Idle at 120-150mW
- 0.5W for 1-5 minutes at irregular intervals
- Up to 4W for 1 second at the start of each 0.5W phase
The interval between the 1-5-minute periods is variable and may be 1 to
10 minutes.
The ground pin is soldered to ~2 sq.in. of copper on the PCB.
1) As described. No extra heatsinking.
2) Mount it on a small Al heatsink.
3) Place the regulator horizontally on the underside and bolt it to the
copper.
Tamb = ~35ºC max
Do you think option 1) is enough? Or should I go for 2) or 3)?

Rth to ambient is about 50 IIRC
so 4 W long enough makes a 200 degrees rise..
.5W makes a 32 degrees rise.
But the thing will thermal limit
That limit may affect whatever it is you power from it.

The 'up to 4W' burst is timed to 1 sec. I think there's enough thermal
mass to keep Tj from reaching a critical temp in that time. But then
that's where I'm asking for the group's collective wisdom.

Post by Jan Panteltje
I always used cheap small heatsinks with the thing standing up,

I do that when there's a significant amount of continuous dissipation.

Post by Jan Panteltje
no need to warm the PCB whith maybe sensitive stuff on it

No sensitive parts anywhere close by.

Post by Jan Panteltje
If you have an alu housing an need more power screw it against that, pehaps with a Mica insulator

I've done that many times. In this particular case though, the PCB has
to be more than an inch away from the wall.

Post by Jan Panteltje
https://panteltje.nl/pub/8052AH_BASIC_computer/8052AH_BASIC_computer_inside_img_1727.jpg
https://panteltje.nl/pub/big_heatsink_IMG_6292.JPG
:-)

Oh yeah, I've used some huge heatsinks too, when I was into audio and
output transistors could easily dissipate several tens of watts each -
and cooling fans were not easily available here. And then there was the
time I made a limited production using 40A SSRs some 30 years ago.

[john larkin]

Post by Pimpom
I'm going to use a standard 7812 TO-220 regulator on a single-sided 1 oz
- Idle at 120-150mW
- 0.5W for 1-5 minutes at irregular intervals
- Up to 4W for 1 second at the start of each 0.5W phase
The interval between the 1-5-minute periods is variable and may be 1 to
10 minutes.
The ground pin is soldered to ~2 sq.in. of copper on the PCB.
1) As described. No extra heatsinking.
2) Mount it on a small Al heatsink.
3) Place the regulator horizontally on the underside and bolt it to the
copper.
Tamb = ~35ºC max
Do you think option 1) is enough? Or should I go for 2) or 3)?

Option 1 sounds fine to me. It will barely get warm.

You don't need it, but internal plane layers help spread out heat too.

https://www.dropbox.com/scl/fo/l0pfn2qtj9pylri0kxnbs/ADjThVe5WV989K8DgotdKVI?rlkey=z4gtiaxmnybem099s6l9yz20m&dl=0

https://www.dropbox.com/scl/fo/dcua00tr8fgxtudnqzhzr/APMIydE2mZFz5e2aFRd-2TY?rlkey=2y16ic2watsnfnthzcf7zbt0i&dl=0

[Pimpom]

Post by john larkin

Post by Pimpom
I'm going to use a standard 7812 TO-220 regulator on a single-sided 1 oz
- Idle at 120-150mW
- 0.5W for 1-5 minutes at irregular intervals
- Up to 4W for 1 second at the start of each 0.5W phase
The interval between the 1-5-minute periods is variable and may be 1 to
10 minutes.
The ground pin is soldered to ~2 sq.in. of copper on the PCB.
1) As described. No extra heatsinking.
2) Mount it on a small Al heatsink.
3) Place the regulator horizontally on the underside and bolt it to the
copper.
Tamb = ~35ºC max
Do you think option 1) is enough? Or should I go for 2) or 3)?

Option 1 sounds fine to me. It will barely get warm.
You don't need it, but internal plane layers help spread out heat too.
https://www.dropbox.com/scl/fo/l0pfn2qtj9pylri0kxnbs/ADjThVe5WV989K8DgotdKVI?rlkey=z4gtiaxmnybem099s6l9yz20m&dl=0
https://www.dropbox.com/scl/fo/dcua00tr8fgxtudnqzhzr/APMIydE2mZFz5e2aFRd-2TY?rlkey=2y16ic2watsnfnthzcf7zbt0i&dl=0

Thanks for the input. Calculating heatsink requirement for continuous
dissipation is one thing. Short bursts are another.

[john larkin]

Post by Pimpom

Post by john larkin

Post by Pimpom
I'm going to use a standard 7812 TO-220 regulator on a single-sided 1 oz
- Idle at 120-150mW
- 0.5W for 1-5 minutes at irregular intervals
- Up to 4W for 1 second at the start of each 0.5W phase
The interval between the 1-5-minute periods is variable and may be 1 to
10 minutes.
The ground pin is soldered to ~2 sq.in. of copper on the PCB.
1) As described. No extra heatsinking.
2) Mount it on a small Al heatsink.
3) Place the regulator horizontally on the underside and bolt it to the
copper.
Tamb = ~35ºC max
Do you think option 1) is enough? Or should I go for 2) or 3)?

Option 1 sounds fine to me. It will barely get warm.
You don't need it, but internal plane layers help spread out heat too.
https://www.dropbox.com/scl/fo/l0pfn2qtj9pylri0kxnbs/ADjThVe5WV989K8DgotdKVI?rlkey=z4gtiaxmnybem099s6l9yz20m&dl=0
https://www.dropbox.com/scl/fo/dcua00tr8fgxtudnqzhzr/APMIydE2mZFz5e2aFRd-2TY?rlkey=2y16ic2watsnfnthzcf7zbt0i&dl=0

Thanks for the input. Calculating heatsink requirement for continuous
dissipation is one thing. Short bursts are another.

You can estimate the mass and specific heat of a fet and do the math.
It's even easier to test one. You could do that quickly.

Given a TO-220 gadget, it would be nice to know the temp rise per
joule dumped into it. Maybe I'll measure that.

First google hit:

https://www.avrfreaks.net/s/topic/a5C3l000000UNfNEAW/t104767

"A TO-220 package has a thermal capacitance of 0.54(J/C) and thermal
resistance of about 62(C/W) without a heatsink."

Based on that, 4 watts for 1 second works out to about 8C rise. The
PCB will help a little.

[Pimpom]

Post by john larkin

Post by Pimpom
Thanks for the input. Calculating heatsink requirement for continuous
dissipation is one thing. Short bursts are another.

You can estimate the mass and specific heat of a fet and do the math.
It's even easier to test one. You could do that quickly.
Given a TO-220 gadget, it would be nice to know the temp rise per
joule dumped into it. Maybe I'll measure that.
https://www.avrfreaks.net/s/topic/a5C3l000000UNfNEAW/t104767
"A TO-220 package has a thermal capacitance of 0.54(J/C) and thermal
resistance of about 62(C/W) without a heatsink."
Based on that, 4 watts for 1 second works out to about 8C rise. The
PCB will help a little.

That's good to know. Even if those data are a bit off, it still leaves
plenty of headroom for a safe operation including hotspots on the chip.

BTW I think it was you who mentioned Saturn PCB Toolkit in a thread
several years ago. I've been using it since then. It's a useful tool.

There was a time when they seemed to have blocked downloads from outside
the US. They didn't actually say so and it took me some time to figure
it out. I managed to get around that with a VPN. I'm using v8.39 now.

[john larkin]

Post by Pimpom

Post by john larkin

Post by Pimpom
Thanks for the input. Calculating heatsink requirement for continuous
dissipation is one thing. Short bursts are another.

You can estimate the mass and specific heat of a fet and do the math.
It's even easier to test one. You could do that quickly.
Given a TO-220 gadget, it would be nice to know the temp rise per
joule dumped into it. Maybe I'll measure that.
https://www.avrfreaks.net/s/topic/a5C3l000000UNfNEAW/t104767
"A TO-220 package has a thermal capacitance of 0.54(J/C) and thermal
resistance of about 62(C/W) without a heatsink."
Based on that, 4 watts for 1 second works out to about 8C rise. The
PCB will help a little.

That's good to know. Even if those data are a bit off, it still leaves
plenty of headroom for a safe operation including hotspots on the chip.
BTW I think it was you who mentioned Saturn PCB Toolkit in a thread
several years ago. I've been using it since then. It's a useful tool.
There was a time when they seemed to have blocked downloads from outside
the US. They didn't actually say so and it took me some time to figure
it out. I managed to get around that with a VPN. I'm using v8.39 now.

Saturn is great, but the current version defaults to a hideous color
scheme, which fortunately can be fixed.

[piglet]

Post by Pimpom
I'm going to use a standard 7812 TO-220 regulator on a single-sided 1 oz
- Idle at 120-150mW
- 0.5W for 1-5 minutes at irregular intervals
- Up to 4W for 1 second at the start of each 0.5W phase
The interval between the 1-5-minute periods is variable and may be 1 to
10 minutes.
The ground pin is soldered to ~2 sq.in. of copper on the PCB.
1) As described. No extra heatsinking.
2) Mount it on a small Al heatsink.
3) Place the regulator horizontally on the underside and bolt it to the
copper.
Tamb = ~35ºC max
Do you think option 1) is enough? Or should I go for 2) or 3)?

You mentioned single sided board so I would be wary of just having the
regulator standing straight up anchored only by the legs. Without plated
through holes a s/s board joint cannot reliably support the weight of a
TO220 package if the unit is dropped or shaken. My preference would be to
screw it down to board if only for mechanical reasons-then the bolt
hardware and area of copper underneath provide a little bit of extra
heat-sinking it also gives more allowance against someone installing the
unit next to a furnace or somewhere hotter than 35degC

[john larkin]

On Mon, 16 Sep 2024 17:46:29 -0000 (UTC), piglet

Post by piglet

Post by Pimpom
I'm going to use a standard 7812 TO-220 regulator on a single-sided 1 oz
- Idle at 120-150mW
- 0.5W for 1-5 minutes at irregular intervals
- Up to 4W for 1 second at the start of each 0.5W phase
The interval between the 1-5-minute periods is variable and may be 1 to
10 minutes.
The ground pin is soldered to ~2 sq.in. of copper on the PCB.
1) As described. No extra heatsinking.
2) Mount it on a small Al heatsink.
3) Place the regulator horizontally on the underside and bolt it to the
copper.
Tamb = ~35ºC max
Do you think option 1) is enough? Or should I go for 2) or 3)?

You mentioned single sided board so I would be wary of just having the
regulator standing straight up anchored only by the legs. Without plated
through holes a s/s board joint cannot reliably support the weight of a
TO220 package if the unit is dropped or shaken. My preference would be to
screw it down to board if only for mechanical reasons-then the bolt
hardware and area of copper underneath provide a little bit of extra
heat-sinking it also gives more allowance against someone installing the
unit next to a furnace or somewhere hotter than 35degC

I think he has a 10:1 or so thermal safety margin. Most fets are rated
for 150 or 175 degC max Tj, and can stand a lot more in real life.

I agree about the standup vibration issue. Why not use a surface-mount
dpak?

[Jasen Betts]

Post by john larkin
On Mon, 16 Sep 2024 17:46:29 -0000 (UTC), piglet

Post by piglet

Post by Pimpom
I'm going to use a standard 7812 TO-220 regulator on a single-sided 1 oz
- Idle at 120-150mW
- 0.5W for 1-5 minutes at irregular intervals
- Up to 4W for 1 second at the start of each 0.5W phase
The interval between the 1-5-minute periods is variable and may be 1 to
10 minutes.
The ground pin is soldered to ~2 sq.in. of copper on the PCB.
1) As described. No extra heatsinking.
2) Mount it on a small Al heatsink.
3) Place the regulator horizontally on the underside and bolt it to the
copper.
Tamb = ~35ºC max
Do you think option 1) is enough? Or should I go for 2) or 3)?

You mentioned single sided board so I would be wary of just having the
regulator standing straight up anchored only by the legs. Without plated
through holes a s/s board joint cannot reliably support the weight of a
TO220 package if the unit is dropped or shaken. My preference would be to
screw it down to board if only for mechanical reasons-then the bolt
hardware and area of copper underneath provide a little bit of extra
heat-sinking it also gives more allowance against someone installing the
unit next to a furnace or somewhere hotter than 35degC

I think he has a 10:1 or so thermal safety margin. Most fets are rated
for 150 or 175 degC max Tj, and can stand a lot more in real life.

78xx is bipolar internallly and goes into thermal limiting at TJ of 125°C

But yeah, still losts of headroom in this application.

[Pimpom]

Post by john larkin
On Mon, 16 Sep 2024 17:46:29 -0000 (UTC), piglet

Post by piglet

Post by Pimpom
I'm going to use a standard 7812 TO-220 regulator on a single-sided 1 oz
- Idle at 120-150mW
- 0.5W for 1-5 minutes at irregular intervals
- Up to 4W for 1 second at the start of each 0.5W phase
The interval between the 1-5-minute periods is variable and may be 1 to
10 minutes.
The ground pin is soldered to ~2 sq.in. of copper on the PCB.
1) As described. No extra heatsinking.
2) Mount it on a small Al heatsink.
3) Place the regulator horizontally on the underside and bolt it to the
copper.
Tamb = ~35ºC max
Do you think option 1) is enough? Or should I go for 2) or 3)?

You mentioned single sided board so I would be wary of just having the
regulator standing straight up anchored only by the legs. Without plated
through holes a s/s board joint cannot reliably support the weight of a
TO220 package if the unit is dropped or shaken. My preference would be to
screw it down to board if only for mechanical reasons-then the bolt
hardware and area of copper underneath provide a little bit of extra
heat-sinking it also gives more allowance against someone installing the
unit next to a furnace or somewhere hotter than 35degC

I think he has a 10:1 or so thermal safety margin. Most fets are rated
for 150 or 175 degC max Tj, and can stand a lot more in real life.
I agree about the standup vibration issue. Why not use a surface-mount
dpak?

I considered using the D2pak version but decided against it. One reason
is that I live in one of the most remote regions of a third world and we
have nothing like Digikey here. So I've made it a habit to use only the
most easily available parts. The D2PAK version of 78xx isn't in that
category.

[Pimpom]

Post by Pimpom

Post by john larkin
I agree about the standup vibration issue. Why not use a surface-mount
dpak?

I considered using the D2pak version but decided against it. One reason
is that I live in one of the most remote regions of a third world and we
have nothing like Digikey here. So I've made it a habit to use only the
most easily available parts. The D2PAK version of 78xx isn't in that
category.

Forgot to mention that I've decided to place the 7812 on the copper side
and bolt it directly to the PCB. Changed the layout to accommodate the
reversed pin orientation.

[John R Walliker]

Post by Pimpom

Post by Pimpom

Post by john larkin
I agree about the standup vibration issue. Why not use a surface-mount
dpak?

I considered using the D2pak version but decided against it. One
reason is that I live in one of the most remote regions of a third
world and we have nothing like Digikey here. So I've made it a habit
to use only the most easily available parts. The D2PAK version of 78xx
isn't in that category.

Forgot to mention that I've decided to place the 7812 on the copper side
and bolt it directly to the PCB. Changed the layout to accommodate the
reversed pin orientation.

Once you have bolted it down you might as well flow solder between the
heat sink tab and the pcb. This will give you the best possible thermal
contact.

John

[Jan Panteltje]

On a sunny day (Wed, 18 Sep 2024 00:12:09 +0530) it happened Pimpom

Post by Pimpom
I considered using the D2pak version but decided against it. One reason
is that I live in one of the most remote regions of a third world

Wow I did not know you lived in the USA!

[john larkin]

Post by Jan Panteltje
On a sunny day (Wed, 18 Sep 2024 00:12:09 +0530) it happened Pimpom

Post by Pimpom
I considered using the D2pak version but decided against it. One reason
is that I live in one of the most remote regions of a third world

Wow I did not know you lived in the USA!

Cheap people make cheap shots.

[Bill Sloman]

Post by john larkin

Post by Jan Panteltje
On a sunny day (Wed, 18 Sep 2024 00:12:09 +0530) it happened Pimpom

Post by Pimpom
I considered using the D2pak version but decided against it. One reason
is that I live in one of the most remote regions of a third world

Wow I did not know you lived in the USA!

Cheap people make cheap shots.

No universal health care makes the USA distinctly third world.

It's not a cheap defect - health care in the US (when you can get it)
costs half as much again more than same health care in expensive places
like German, Switzerland and the Netherlands.

It showed up in the Covid-19 death rate. 3642 deaths per million isn't
the worst performance around, but it's surprisingly third world.

https://www.worldometers.info/coronavirus/

Having Donald Trump as your president when the pandemic was doing its
worst didn't help.

[Jan Panteltje]

On a sunny day (Wed, 18 Sep 2024 07:39:47 -0700) it happened john larkin

Post by john larkin

Post by Jan Panteltje
On a sunny day (Wed, 18 Sep 2024 00:12:09 +0530) it happened Pimpom

Post by Pimpom
I considered using the D2pak version but decided against it. One reason
is that I live in one of the most remote regions of a third world

Wow I did not know you lived in the USA!

Cheap people make cheap shots.

Some kill

[john larkin]

Post by Pimpom

Post by john larkin
On Mon, 16 Sep 2024 17:46:29 -0000 (UTC), piglet

Post by piglet

Post by Pimpom
I'm going to use a standard 7812 TO-220 regulator on a single-sided 1 oz
- Idle at 120-150mW
- 0.5W for 1-5 minutes at irregular intervals
- Up to 4W for 1 second at the start of each 0.5W phase
The interval between the 1-5-minute periods is variable and may be 1 to
10 minutes.
The ground pin is soldered to ~2 sq.in. of copper on the PCB.
1) As described. No extra heatsinking.
2) Mount it on a small Al heatsink.
3) Place the regulator horizontally on the underside and bolt it to the
copper.
Tamb = ~35ºC max
Do you think option 1) is enough? Or should I go for 2) or 3)?

You mentioned single sided board so I would be wary of just having the
regulator standing straight up anchored only by the legs. Without plated
through holes a s/s board joint cannot reliably support the weight of a
TO220 package if the unit is dropped or shaken. My preference would be to
screw it down to board if only for mechanical reasons-then the bolt
hardware and area of copper underneath provide a little bit of extra
heat-sinking it also gives more allowance against someone installing the
unit next to a furnace or somewhere hotter than 35degC

I think he has a 10:1 or so thermal safety margin. Most fets are rated
for 150 or 175 degC max Tj, and can stand a lot more in real life.
I agree about the standup vibration issue. Why not use a surface-mount
dpak?

I considered using the D2pak version but decided against it. One reason
is that I live in one of the most remote regions of a third world and we
have nothing like Digikey here. So I've made it a habit to use only the
most easily available parts. The D2PAK version of 78xx isn't in that
category.

Can you receive shipments from the USA?

[Pimpom]

Post by piglet

Post by Pimpom
I'm going to use a standard 7812 TO-220 regulator on a single-sided 1 oz
- Idle at 120-150mW
- 0.5W for 1-5 minutes at irregular intervals
- Up to 4W for 1 second at the start of each 0.5W phase
The interval between the 1-5-minute periods is variable and may be 1 to
10 minutes.
The ground pin is soldered to ~2 sq.in. of copper on the PCB.
1) As described. No extra heatsinking.
2) Mount it on a small Al heatsink.
3) Place the regulator horizontally on the underside and bolt it to the
copper.
Tamb = ~35ºC max
Do you think option 1) is enough? Or should I go for 2) or 3)?

You mentioned single sided board so I would be wary of just having the
regulator standing straight up anchored only by the legs. Without plated
through holes a s/s board joint cannot reliably support the weight of a
TO220 package if the unit is dropped or shaken. My preference would be to
screw it down to board if only for mechanical reasons-then the bolt
hardware and area of copper underneath provide a little bit of extra
heat-sinking it also gives more allowance against someone installing the
unit next to a furnace or somewhere hotter than 35degC

Good point. With TO-220s, particularly those without a heatsink, I
usually pull the middle leg out to form a triangle with the other two,
and bend them on the copper side for a netter grip. If it's mounted on a
heatsink, even a small one, the HS is almost always bolted onto the board.