Help for Newbie.

[sandoza]

Oh i think you caught the problem. From all above discussion adding good knowledge to my brain i checked the work again. So the regulator is a little hot. Output voltage of regulator is 27V(what the hell?).I think i got too hot unnoticed by me or may be instantly damaged at first power up and get short itself.

Dam thing might have damaged my OP-AMPS, although they are rated at 38v. But when things get wrong any thing can happen.They are not cheap.

Sharing Knowledge with some one who has less knowledge may help both sides sometimes, i believe. Thank you.

 

[audioguru]

A cheap, poorly made and low current transformer has resistance in its very thin wires. To make it 20V at 100mA then it must produce 28V or more without a load because the load current causes a voltage drop in its very thin wires.

I have a 9V/100mA cheap power supply that is 20V without a load. It was made in .....(guess where).

I have a 9V/500mA good quality power supply that is 10.5V without a load. It was also made in .....

 

[sandoza]

Yeah now get it all. thank you audioguru. Your power supplies are made in ???? i know where, the products made there most of the time are...................(you know what i was going to say). My transformer is also made there.From your post i think i can figure out what should i buy next. Thankyou.

 

[audioguru]

So many junk things are made in China that it is difficult to see which are good and which are bad.
I avoid cheap Chinese parts.

 

[Mr RB]

Oh, If i dishonored those minds then i would think i owe them an apology. I am sorry.

Relax nobody would be offended or dishonoured by what you said it was perfectly ok.

I suggested the LM317 solution because you said you were "new to the field of electronics" and wanted to build "some small and simple transistor based projects". So based on that level of skill and that specific PSU requirement I still think a LM317 PSU is a great beginner PSU. They will hold voltage regulation very well, definitely good enough for most hobby circuit experiments, or for making a +5v supply for logic etc.

But with the LM317 most of the circuit you are building is already inside the LM317 device, making the PSU very easy to build.

Your transformer readings look pretty typical.

 

[QuietMan]

I'm going a different route for a similar problem. I have an old LM317 unit I built over 20 years ago. Its been pretty good for general work, but weak on the current.

I just bought a fixed 24V 1.3A switching wall wart for $5. I plan on putting a switching circuit to allow me to switch between the transformer or the switcher with it to boost this old units current.

I've also bought 2 24V 6.5A switching units (each under $15) for something similar. I'm going to be a bit more adventurous and make a variable switching power supply, if the schematic works I'm designing I'll post it. If the smoke escapes I'll start over, and you'll never see it.

Once you have a stable voltage with a known current you are halfway there. A LM317 can do a really good job with it, and regulating current doesn't have to be with a LM317, but it can do the job well.

With modern ICs there really isn't a reason to overcomplicate this. With switching modules even less so.