Pls help a newb with a linear power supply

[Zacvining]

Bear with me and try not to get frustrated for I’m learning how to do this as I go . I’m wanting to reverse engineer this linear power supply from the early 90s . The power supply from 0 to 14 V with a capability of 2 amps One issue I have run into is the circuit board was painted black so that you are unable to identify components. another is some parts are now obsolete, but I have been able to find suitable replacements. There are two components that I’m not sure of , one that I am assuming is a transistor, and the other is a Varisitor . I’m hoping somebody here can possibly help me figure this out. I built a copy of the power supply using a 2N3055 transistor And omitting the possible varisitor component. I was able to get the power supply to run for a short period of time until the 47 ohm resistor caught fire. Attached file one is a drawing of the components. I have figured out and how they are laid out on the circuit. Attached file two is photo of possible Varisitor. attached file three is all the information I can figure out about possible transistor

 

[Kurenai_ryu]

for a LM317 power supply I would go with a PNP transistor. similar to this:

40V 2A LM317 & TIP42 Power Supply

A very good and powerful Regulated Power Supply section was implemented by simply adding a PNP power transistor to the excellent LM317T adjustable regulator chip. In this way this circuit was able to deliver much more than the power required to drive two Mini-MosFet amplifiers to full output (at...

electronics-diy.com

 

[pjmelect]

I think that your circuit is not right, for example, the Varistor should not be in series with the AC input to the bridge rectifier but in parallel with it and the diode 8 is the wrong way around.

 

[prairiedog]

The mystery component is not a varistor/MOV. It is PTC thermistor, polyfuse X185 50V which holds 1.85A, similar to a Littelfuse RXEF185.

You have the 1N4001 diode backwards. Band/cathode should connect to the output, not to GND.
Also missing are 1-2 other protection diodes used when charging batteries.

Can you show a pic of the transistor? 2N3055 seems reasonable.

 

[KlausST]

Hi,

please don´t use that huge pictures. It´s a waste of data space and makes loading the page slow - especially in areas with low internet bandwidth.
Just use your camera options, use a simple photo editing software that usually comes with your computer, or use simple online tools like https://www.img2go.com/photo-editor (tried here for the first time)
It takes less than one minute (as a toatal beginner) to get this result:

File size reduced to about 3% only.

*****
To your problem:
I personally would not invest time and money for a power supply like this. It´s probably more than 40 years old and - from my experience - don´t perform well. They produce a lot of heat - and as soon as you modify a little thing they tend to oscillate.

Please ask yourself if it´s worth it.

Klaus

 

[Zacvining]

The mystery component is not a varistor/MOV. It is PTC thermistor, polyfuse X185 50V which holds 1.85A, similar to a Littelfuse RXEF185.

You have the 1N4001 diode backwards. Band/cathode should connect to the output, not to GND.
Also missing are 1-2 other protection diodes used when charging batteries.

Can you show a pic of the transistor? 2N3055 seems reasonable.

All identifiable markings have been removed . I know it’s a to3 package but that’s it .

I think that your circuit is not right, for example, the Varistor should not be in series with the AC input to the bridge rectifier but in parallel with it and the diode 8 is the wrong way around.

I may have just drawn it wrong , I’ll check the actual circuit tomorrow

 

[Zacvining]

https://dragon.img2go.com/download-file/6bfe3b57-662b-434e-a049-8fd94dddef20/6abde210-b845-42bb-971f-fca2f2643361

 

[prairiedog]

"Sorry, the download link that you are looking for is either expired or invalid."

I thought a flipped diode would basically short the output. The 47Ω resistor burning up would be a bad (open E-B junction) power transistor when the PSU has a heavy load on it. I would recheck the schematic and pinouts etc.

An LM317 power supply is fine for basic electronics work, I had used my own homebrew one for over 20 years and they even had us build one in tech college.