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Yet another DIY Power Supply, Almost done

Bassblaster said:
i beleive that would be D2 in the latest schematic drawing

What do you guys think about swapping the 2SD1047's for TIP3055's? the TIP's are a little cheaper ($1.61 vs $3.71) and have similar specs.
Click to expand...
D2 helps, but I was suggesting one between the output and the supply.
TIP3055 is a good less expensive alternative fo d1047. My choice for low cost power would be TIP35C. YMMV
 
This is the latest version of the PCB. i moved the outputs farther apart and moved U1 and C4. Does this look like a good layout? im not an expert in PCB design but maybe someone here is. the cap bank is a custom footprint made for nichicon LGU1H472MELZ. input and outputs are also a custom footprint for 0.25" quick disconnects 571-624091
If all looks good i plan to order these in the next couple days
upload_2017-11-5_17-36-31.png
 
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Have you tried testing this circuit on a breadboard?
I have studied the schematic more closely. If you connect the end of R2 that now goes to U1 pin 2 to the output (e.g. + of C7) the output transistors and resistors would be included inside the regulator feedback path and load regulation could be improved . . .
 
merlynski said:
have studied the schematic more closely. If you connect the end of R2 that now goes to U1 pin 2 to the output (e.g. + of C7) the output transistors and resistors would be included inside the regulator feedback path and load regulation could be improved .
Click to expand...
for clarity - disconnect the resistor from pin 2, then connect to output. I agree - good idea.+
 
No i haven't breadboarded it. i was going to place the mouser order then breadboard it, then if all good order the PCB's
sregor said:
for clarity - disconnect the resistor from pin 2, then connect to output. I agree - good idea.+
Click to expand...
Good idea moving the feedback resistor. i never thought of that, obviously
upload_2017-11-5_21-17-1.png
just like this?
 
After looking at the PCB layout some more I suggest an additional 0.1mfd cap across the DC input (left side) just like C6 is across the output.
 
When you order parts make sure to get a high wattage resistor for R5. With 24 volts across it it will dissipate 2.4 watts. You will need to make space for a bigger resistor on your PCB layout as well, or mount it off the PCB.

EDIT: more info
 
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Mouser part number for a load resistor (R5) suggestion: 284-HS10-250F. Mount on heatsink with transistors.
Also increase C5 to 10 mfd for improved ripple rejection . . .

EDIT: more info
 
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Updated C5 to 10uF. that chassis mount resistor i think would just be too big. datasheet says its the same size as the HS50's i have for my dummy load and they are reasonably big. i found mouser 588-TWW10J270E OR AXIAL 71-RS02B240R0FE12 and mount it vertically
 
I just find it odd that the 0.1 ohm emitter/transistor balancing resistors were chosen to be 5W but they only will dissipate closer to 2W or so (3W should be more than enough), maybe you can get more room for the 240 ohm resistor by decreasing the balancing resistors...

When dissipating heat, bigger is better, make the board bigger... squeezing everything together is just going to make it fry faster.
 
Musing over the LM317 some more I remembered that it has a minimum load current required to maintain regulation. Looking at the datasheet it shows a typical value of 3,5 mA. I suggest about a 1.2K ohm resistor to ground from pin 2 of U1 to supplement the Q1-3 base currents load on it.
 
Okay a few things changed. the 5W emitter resistors a dropped to 3W.
R5 i went with a 3W axial resistor and i'll vertical mount it. i think that will also keep more of the heat away from the PCB.
i added the 1.2K resistor from pin 2 of the LM317 to GND
 

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http://www.ti.com/product/lm317?qgpn=lm317
This is the datasheet I am using.
Look at page 10 for the adjustable regulator and compare how your R6 pot is connected to how their R2 pot is connected.
Also look at page 17, how they suggest a high current regulator be implemented.
This regulator works by using a constant current source to maintain a difference of 1.25 volts between the output and the adjust terminals. The base-emitter junctions of Q1-3 will eat up over half of that voltage the way it is connected now, and the transistor's gain will affect the current flow. My suggestion of moving R2 from U1 pin2 to the output may not be a good idea after all. Bread boarding may confirm one way or the other . . .
EDIT: more info
 
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So according to the data sheet I should change the 240 ohm resistor to 120 ohm and add base resistors to the outputs? OR should I re do the entire sechmatic to copy page 17, just with more outputs
 
If you are bound and determined to use an LM317 I would go with the page 17 model. The benefit of the LM317 is it is a simple way to implement a low power regulator with a low parts count. As you are seeing, increasing its capacity increases the complexity of the circuit and the parts count. Was the original intent to make use of your transformers in a variable bench power supply, with the LM317 looking like a simple solution?
 
i wouldn't say simple, just less complicated than a fully discrete circuit.
Now page 17, would i have to copy that OR can i modify what i have already to use that kind of circuit. like, could we keep R2 between pin output and adjust of the LM317 but run a 2nd feedback resistor? It would suck having to start all over.
EDIT: What about ditching the 317 and running a discrete driver transistor, like the TIP41C
 
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