I never go below 0805, and I use the 'hand-soldered' footprints in KiCAD. Unless you have a real need for super-miniaturization there no need and you're just making a rod for your own back. I'd avoid putting HV AC on the board, though the LV secondary input should be OK. Personally for this project I'd stick with through-hole parts, there not much space-saving needed, the regulators are leaded anyway as will be the 10k capacitors, and they're typically 30mm dia. You should have no difficulty fitting this on a PCB 80 x 60 with just THT parts. Heatsinks will be your limiting factor.

You definitely should use a ground plane. Convention puts it on the back but it doesn't have to be. You could have it on the front as well, as long as they are well stitched together. The layout for this will follow the schematic and there are relatively few tracks needed. I'd keep the tracks all the same width, there's no real need to go below 1.5mm, and that's good for at least 3A.

Did you chose a transformer yet? and heat-sinks? Also think about getting on and off the board - direct wire-to-board (not recommended), push-on connectors, screw terminals, etc?

Hi. This power supply is strictly through-hole. The SMD quip was about a practice board I bought because I am also refurbing a 1968 Magnavox console and adding a bluetooth board that has SMD on it, so I wanted to practice. The 10K caps are 30mm and sitting on my desk as I type this.

As for the board, I am doing a ground plane along the back, and using fat traces for all other nets. Heat sink is 2 of this:



So I think that this will do a great job of dissipating the heat out of TO-220 packages. I'm leaving some space between components as well.

Thanks!

 

So I think that this will do a great job of dissipating the heat out of TO-220 packages.

It will certainly dissipate some heat... but maybe not enough. Do you have the spec for them?

 

It will certainly dissipate some heat... but maybe not enough. Do you have the spec for them?

35mmW * 12mm D * 25mmH

They seem able to dissipate a boatload of heat...



As far as attaching the 24-0-24VAC in and +/- 15VDC out,. I was looking at soldering the wires to the board; I think that screw terminals and spade lugs might be better on second thought.

Thanks!!

 

If they are only 25mm high they are spec'd at a thermal resistance of 13degC/W ie for every watt of power the difference between the device case and the ambient air increases by 13degC (mounted vertically in free air).

Both the LM317 and LM337 have an internal thermal resistance, junction to case of 5degC/W. In total therefore, between ambient and the device junction you have 18degC/W. Ambient inside a box will be at least 30degC and maximum allowable junction temperature is 125degC though you should never run that hot, so say 110degC.

So between 110 and 30 you have an allowable difference of 80C at 18degC/W which gives a maximum power of 80/18W = 4.4W. At 1A, 4.4W = 4.4V, so that means a maximum input voltage to the regulator of 15 + 4.4 = 19.4V peak, or 14v rms from the transformer. This is why transformer sizing is important and you have to look at this holistically. You can't randomly pick components and expect them to work happily together.

Now that style of heatsink comes in various lengths
25mm = 13C/W -> max Vin 19.4v
38mm = 11C/W -> max Vin 20.0v
50mm = 9C/W -> max Vin 20.7v even doubling the size of the heatsink isn't really helping (especially as its not in free air).

So, what can you do?

Well obviously you could reduce your expected maximum output current. Does your preamp really need 1A (I doubt it), and that is probably your best option. A typical preamp producing 1 volt rms into 600ohm is only 1.7mW output power,, I'd doubt the whole unit takes more than a couple of watts, At 15v that's less than 130mA.

Now that heatsink makes sense, In fact, that heatsink with an 18-0-18 transformer would give you a maximum 'safe' current of 300mA, more than adequate. Your proposed 24-0-24 transformer would limit you to 200mA and is certainly over-sized. Of course your regulator won't blow up or fry, it'll just current limit and shut down so you'd never get 1A out of it anyway. In fact, with an 18-0-18 transformer you'd be OK at 120mA without a heatsink.

Other options:
You could use a bigger heatsink, but that's not really an option, it would need to be a lot bigger, with a lot more fins. This one is 3degC/W but its 33mm x 46mm x 150mm and quite expensive.


You could force cool it with a big (as in high flow rate, not diameter) fan, but that's not very practical nor effective for that style of heatsink, plus noise, etc.

 

What is the claimed benefit of putting a "ground plane" on the component side of the PCB??? Other than extending the useful life of the etching solution by dissolving less copper??

 

What is the claimed benefit of putting a "ground plane" on the component side of the PCB??? Other than extending the useful life of the etching solution by dissolving less copper??

It makes a stiffer board and better heat dissipation.

 

If they are only 25mm high they are spec'd at a thermal resistance of 13degC/W ie for every watt of power the difference between the device case and the ambient air increases by 13degC (mounted vertically in free air).

Both the LM317 and LM337 have an internal thermal resistance, junction to case of 5degC/W. In total therefore, between ambient and the device junction you have 18degC/W. Ambient inside a box will be at least 30degC and maximum allowable junction temperature is 125degC though you should never run that hot, so say 110degC.

So between 110 and 30 you have an allowable difference of 80C at 18degC/W which gives a maximum power of 80/18W = 4.4W. At 1A, 4.4W = 4.4V, so that means a maximum input voltage to the regulator of 15 + 4.4 = 19.4V peak, or 14v rms from the transformer. This is why transformer sizing is important and you have to look at this holistically. You can't randomly pick components and expect them to work happily together.

Now that style of heatsink comes in various lengths
25mm = 13C/W -> max Vin 19.4v
38mm = 11C/W -> max Vin 20.0v
50mm = 9C/W -> max Vin 20.7v even doubling the size of the heatsink isn't really helping (especially as its not in free air).

So, what can you do?

Well obviously you could reduce your expected maximum output current. Does your preamp really need 1A (I doubt it), and that is probably your best option. A typical preamp producing 1 volt rms into 600ohm is only 1.7mW output power,, I'd doubt the whole unit takes more than a couple of watts, At 15v that's less than 130mA.

Now that heatsink makes sense, In fact, that heatsink with an 18-0-18 transformer would give you a maximum 'safe' current of 300mA, more than adequate. Your proposed 24-0-24 transformer would limit you to 200mA and is certainly over-sized. Of course your regulator won't blow up or fry, it'll just current limit and shut down so you'd never get 1A out of it anyway. In fact, with an 18-0-18 transformer you'd be OK at 120mA without a heatsink.

Other options:
You could use a bigger heatsink, but that's not really an option, it would need to be a lot bigger, with a lot more fins. This one is 3degC/W but its 33mm x 46mm x 150mm and quite expensive.

View attachment 346368
You could force cool it with a big (as in high flow rate, not diameter) fan, but that's not very practical nor effective for that style of heatsink, plus noise, etc.

Hi --

I'm going with the recommended 18-0-18. Thanks!