POWER SUPPLY DESIGN

ladyphoebe15 · Feb 25, 2014

I created a power supply design.

I use an Transformer with an 18v/3A. I wanted to have this output:
0-25 V
3A max

using only discrete components and having a course and fine to adjust the voltage but when i tried it by breadboarding, it doesn't work. What is wrong with this and how can i make it work

audioguru · Feb 25, 2014

Could somebody please copy this pastel schematic and increase the contrast so it can easily be seen?

It appears to have no error correction amplifier with negative feedback so its voltage regulation is horrible.

Its transformer is 18V x 3A= 54VA. The 18V transformer has a peak voltage of 25.5V. The load on the transformer is 25.5V x 3A= 76.5VA so the transformer will be overloaded.

The 25.5V peak voltage is reduced to about 23.5V by the bridge rectifier and the small value of the filter capacitor reduces it more. The maximum base-emitter voltage of the TIP31 transistor at 3A is 1.8V so the maximum output voltage at 3A is less than 20V.

The 27V zener diodes will do nothing.

The maximum base current of the TIP31 transistor at 3A is 300mA which will burn up the pot R10. The TIP31 will burn up if the circuit works and the output was 0V at 3A because then the transistor must dissipate 84W or more.

The five 1 ohm resistors in series with the output and the two diodes will cut the output voltage and current.

DerStrom8 · Feb 25, 2014

First of all, what is F- and F+? Also, what are the 1N4148 diodes supposed to be doing?

DerStrom8 · Feb 25, 2014

Here you go, AG:

JimB · Feb 25, 2014

What is wrong with this and how can i make it work

There is no easy way to say this, but that circuit is wrong on many levels.

You do not make this circuit work, you just abandon it and start again.

I suggest that you look at circuits using an LM317, or if this is some school project which must not use an integrated circuit,
try looking here:
https://eecs.oregonstate.edu/education/docs/ece322/Section3.pdf

Otherwise, try googling for "Voltage regulator using discrete components"

JimB

audioguru · Feb 25, 2014

Thanks for the contrast. My image editor software is trying to make me pay again.
The 1 ohm resistors have enough voltage drop with an output current of more than 1.2A to limit the output voltage and current like this:

DerStrom8 · Feb 25, 2014

audioguru said:
Thanks for the contrast. My image editor software is trying to make me pay again.

No problem. I own a copy of Photoshop so adjusting the levels wasn't a problem

ladyphoebe15 · Feb 25, 2014

DerStrom8 said:
First of all, what is F- and F+? Also, what are the 1N4148 diodes supposed to be doing?

It was actually for a fan.
I guess I really do have to start from scratch considering all audioguru said.

chemelec · Feb 26, 2014

audioguru said:
Could somebody please copy this pastel schematic and increase the contrast so it can easily be seen?

Get a copy of "ADC See".
It can Resize, Enhance, Change pictures from one format to another and Much More.

audioguru · Feb 28, 2014

chemelec said:
Get a copy of "ADC See".
It can Resize, Enhance, Change pictures from one format to another and Much More.

I had a free older version of ACD See for years but it got removed when I got Windows 7. Then I bought ACD See Pro (VERY complicated with millions of features) but now they want me to pay for it again. Maybe my anti-virus software removed its license number.

chemelec · Feb 28, 2014

I have the Install Version of the Older Free one.
Want it?

audioguru · Feb 28, 2014

Thanks, Gary.
Should I PM you with my e-mail address?

chemelec · Feb 28, 2014

audioguru said:
Thanks, Gary.
Should I PM you with my e-mail address?

Hotmail won't allow Sending EXE Files.
I recommend you Email me your Name and address.

Than I will put it on a CD and mail it to you.

DerStrom8 · Feb 28, 2014

chemelec said:
Hotmail won't allow Sending EXE Files.
I recommend you Email me your Name and address.

Than I will put it on a CD and mail it to you.

Put the exe in a zip folder, then email the zip. That's usually the best way to do it.

Regards,
Matt

JimB · Feb 28, 2014

Put the exe in a zip folder, then email the zip.

Even that does not work sometimes.

When one of my customers has tried to send me some of their software, my e-mail system refuses anything that looks vaguely like a .EXE file.
Rename it as a .TXT - no go
ZIP it - no go
Rename it as a .TXT and then ZIP it - no go.

I have been through this scenario a couple of times.
Not exactly sure where the problem was, with my email provider or with my anitvirus SW, but it always ripped out the .EXE files so that the thing was useless.

JimB

magvitron · Mar 1, 2014

Rename the .exe file as .doc, then attach and send. It will be a breeze.

Nigel Goodwin · Mar 1, 2014

chemelec said:
Hotmail won't allow Sending EXE Files.

Why would anyone not have a real email address?.

chemelec · Mar 1, 2014

I am also on a 56 K Modem. SLLLLOOOOOOW.
Besides, The Post Office Need Business.

audioguru · Mar 1, 2014

Snail mail?
The post office still delivers my mail directly to my door (but not anymore when it is raining or snowing).
Newer homes do not have mail delivery and the people must go up the street to a big postal stand of neighbourhood mailboxes.

My first pc had a 14.4k modem that I replaced with a blindingly fast 56k modem but it operated at only about 30k.
Now I have the second-cheapest cable-internet speed of 9.4M. My son and daughter have about 60M.

My pc still uses a mechanical hard drive that takes a couple of minutes to boot. My son's pc uses a solid-state drive that boots immediately.

My car has 4 cylinders. My son had a Mercedes with a V12 engine with two turbos.

chemelec · Mar 1, 2014

Nigel Goodwin said:
Why would anyone not have a real email address?.

Because When I Started, Hotmail was an Easy Option.
Ihave numerous other Email address's, But Changing it a few year of having my website would have resulted in problems with me missing older contacts.
Anyway Hotmail usually Works good for me.

magvitron, Yes I Know about Changing Extensions.
But SLOW Dial-Up Internet is Really a Problem.
And This Is not just ONE File, it is Probably a Gig of data.

In THEORY, (So were Told) We are suppose to get CELL Service in this town Soon, This Year.
I can than use the Cell, High Speed Internet.

POWER SUPPLY DESIGN

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