| Electronics > Beginners |
| All about Linear Power Supplies |
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| MarkF:
I have been using Diptrace 3.3 Freeware version for my schematic and PCB designs. It's free and easy to learn. It also generates 3D images of your PCB to check over before getting it made (Previous post as examples). Also, I have been using Elecrow to get PCBs made. You can get 10 PCBs for $4.90 There are a lot here that use PCBWay for about the same price. |
| queennikki1972:
Any opinions on using PLA or ABS 3D printed enclosures for linear power supplies such as a lm317T and 24vac transformer? PLA melting point is about 190c. ABS is around 240c. i have used these plastics for face plates only in the past. |
| MarkF:
I would think either would be fine. The max junction temperature of the LM317 is 150oC. You will have bigger problems than the case melting if it gets that hot. For your next supply project, one thing I noticed on your first power supply is that you didn't bring out earth ground. The 3rd prong on the power cord straight to the front panel to a green banana jack. And tied to the case if it is metal. Your power outputs will be floating and in some cases you might want to tie the common to ground. Here is an example (although HP used a black jack): |
| ArthurDent:
There is another power supply design thread on this site that goes into a lot of detail on all aspects of power supply design, including 3D printing an enclosure, in about 15 pages. It would be worth at least scanning the posts to see if there is something that you might be able to use in your design. https://www.eevblog.com/forum/projects/linear-lab-power-supply/ https://www.eevblog.com/forum/projects/linear-lab-power-supply/?action=dlattach;attach=578924;image |
| mariush:
If you want to keep it simple, you should look into other linear regulators like *1084 for example, or *1085 : See AZ1084, AP1084, LT1084, LM1084 : https://www.digikey.com/short/pzcfr5 5A maximum current output, input voltage up to 30v (but depending on who makes them, some are maximum 12v or maximum 15-18v) The *1085 regulators are 3A parts: https://www.digikey.com/short/pzcf2d You can use two in parallel with a small resistance to balance current... not the best way to do things but nevertheless it's possible. See page 15 in the Linear datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/108345fh.pdf ^ just replace the "two feet of awg18 wire" with a couple 0.01 ohm resistors and connect the output between the two resistors. Also keep in mind that most regulators have a maximum power dissipation limit, like let's say 35w .... so for example you can't have 12v IN from the transformer and output 3.3v at 5A ... because the amount of energy dissipated would be (12v - 3.3v) x 5A = 43.5 watts. You could work around that by using two 3A regulators in parallel but it would make more sense to use a transformer that has two secondary windings... for example, use a transformer that has 2 x 6.3v secondary windings.... and either add a switch on the front panel of your power supply or use a mechanical relay and a voltage comparator or something to switch between 1 winding or 2 windings. For example, if the output voltage is set to less than 5v DC, then switch to using only one winding, so that in worst case scenario you're gonna dissipate around (7v - 1.25v ) x 5A = ~ 28 watts when output voltage is set to your minimum of 1.25v (the reference voltage of the linear regulator) |
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