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Author Topic: ITTSB project: LM317 adjustable DC power source – High Power Pro version  (Read 643 times)

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Offline Kiriakos GR

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Intro
There is no home in this world not having at least one LM317 hidden in to an electronic device (appliance) this serving as voltage regulator.

From the other hand, by you inviting one LM317 alone this to operate as workbench power supply this is always a very bad idea.

LM317 specifications’ they are not generous speaking of watts handling.
Other common problems these are voltage stability and temperature issues.
 
While LM317 it does comes with Internal Short-Circuit Current Limiting and Thermal Overload Protection, the one million dollars question this is of how much trust you can demonstrate to such protections.

Most wise description for LM317 based circuits (them be controlled by a potentiometer), this is power source replacement of battery powered products.
Alternatively this can be a DC fan voltage controller.

 
Bellow I am going to present my very own LM317 based project which is a much safer approach so this to serve as Low-Power workbench power source.

My recipe includes combination of used parts that it’s one this adding valuable features which with out them, the sum would be another poor way about using an LM317.

1)  Case of Apple CD300 (1993 Vintage Computer part) this is full metal and at correct dimensions so this to be stacked above or bellow another heavy and professional power supply.
Bottom plate of Apple CD300 among with top cover in place, this is metal box able to handle 10 Kilos at least of weight on the top of it.

2) Switching power supply this is product of CANON and power source for printers.
Output of 24V 800mA has internal Short-Circuit Current Limit at 1.7A
Output of 3.3V this is at 150mA, this is nothing special but it helped me to under-volt one 5V tiny cooling fan.

3) 5V tiny cooling fan this is used part which previously this was cooling down the CPU of a color laser printer.

4) LM317 among with heatsink and PCB among with a tiny in watts transformer (28V AC), this was serving as motor power supply for whole lamb on BBQ.

5)  Mini DC 5~30V Voltmeter with three blue led digits (this is still on the way), this is my choice for my narrow in dimensions power source.

6)  Banana type output connectors and On/off load switch, they are last minute details for now.
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Offline Kiriakos GR

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Technical details and considerations,

Such choice of narrow and strong case was selected by me on purpose, but such a choice regarding dimensions this is not friendly for installing to it active cooling.
Practically what is important this is you avoiding exaggerations’ by seeking ultimate performing solutions for circuits which them has generic performance characteristics. 
All that matters this is LM317 to be kept cool enough at 1.5A full load at entire voltage range that this is able to deliver.

My very own load tests at 5V & 15V (which I performed by the use of my 110W constant current adjustable DC load)  they proved to me that I did followed the best practices so this DC power source to qualify for 24/24H operation.

In practice LM317 part which I have this delivered:
1.4A at 5.0V (long test) 70C with silent acting cooling
1.5A at 15V (long test) 52C with silent acting cooling
1.0A at 15V (long test) 40C with silent acting cooling


Sort circuit protection at my project this is now double, LM317 has it own, and this CANON switching power supply has it own too at 1.7A.

Selected Voltage (adjustment) at non-load condition to full load this is measured at 400mV less. 
For example if we aiming for 12.0 Volts (at medium or full load) we should adjust output at 12.4V (Non-load condition).


The good news for me this is that I spent one single Euro coin for getting a new digital volt meter, all other parts they are old used parts which they are carefully selected for this application.
If your own stock of older projects parts this is no as rich as my own, then you better think wise and follow the path of 70 Euro worth crappy power source (these looking as professional power supply but they are not) and use them for low importance applications.
 
My very own professional DC power supply, this was at price range of 1400 Euros, Made in Japan, clean DC and precise controlled current limiter, these are invaluable benefits that only one well made linear power supply this can deliver for several decades in your workbench.

Third part of this story will come later on  8)
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Offline Kiriakos GR

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Finally after several days of waiting all essential parts they are here.  :)

Today I did finalize front panel design, as material for my front panel I did use section of top cover of HP D4260 printer ;)
Personalty I am quite satisfied from my progress so far, despite the fact that I was working with 28C indoor. 

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Offline Kiriakos GR

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Dear viewers this project came to competition.  8)

In this last post you will see high quality pictures these demonstrating several product design details.
FYI this power supply it is the slimmest even composed (assembled).
Additional copper transformer at 8V AC added so to become DC power source for the panel meter.

In summary, this is the first LM317 based power supply, which it is compliantly assembled for professional use.
Over current protection this is double insured because of electronics working as power source for the LM317.
One Bourns 10K (ten turn) potentiometer this delivers necessary resolution for precision adjustments from 1.2V up to 22V DC.

Tiny DC fan this is capable fighting risk of overheat.
Banana plugs placement this aloud use or double banana testing plug.

Overall as in most LM317 based PSU only future missing this is adjustable current limiting, from the other hand there is no LM317 able to deliver reliability and features of 1000 Euro made in Japan, Professional grade power supply.
LM317 even build as armored  tank as is in my project, this always will be an medium quality secondary regarding priority power source. 

         
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