Ok, time for a "first post"!

Firstly, I would like to thank all those on here who have already helped me indirectly by answering other peoples' questions in the past. There's a reason I joined this forum and it wasn't the fancy graphics

Ok, now onto the proper reason for this post...

I have always been interested in learning about electronics since I was in school (a lifetime ago) but funds, commitments and/or time always got in the way.

Funds are still limited but I found myself with time to kill and in need of a new hobby so here we are.

My first project has been to convert an ATX power supply into a bench top format because I cannot currently afford the real thing but had a redundant ATX unit lying around.

Then I started looking at oscillator circuits (mainly because the one I built in school never worked!) and that's when I discovered the need for a dual-rail supply.
The ATX has a -12V option but it's only rated for 0.3A. I did manage to get a sine, square and a (nearly) triangular waveform out of an LM324N but was constantly worrying about current limit (worrying is my superpower) so I'd prefer to have enough headroom to never have to consider it until I am into the whole Amps range.

I played about with the LM317T but it doesn't do negative (got a decent variable supply working though) so

I've been messing around with a transistor (powered by an ~1500Hz astable 555) switching the primary of an IT243 1:1:1 transformer
Datasheet (including Primary impedance)
Unfortunately, my first and only experiment resulted in magic smoke so it was back to Google for more research which has led me to the twin BJT push-pull driver but everything I have seen so far has assumed an AC drive signal for the push-pull.

And FINALLY, my question....

I am aware that the 555 can sink up to 200mA and I wish to know if this will be enough to drive the PNP side of the push-pull and if the transformer is suitable for the job when the secondaries are wired in series and centre tapped to provide the dual-rails.

I could keep experimenting but, as already stated, funds are limited so I'd rather not burn up any more components.


Thanks in advance for any help.

 

A couple of things:

1. The LM337 is an adjustable negative voltage regulator that is similar to the LM317.
2. Given your limited funds, I recommend downloading and becoming familiar with the LTspice simulator from Analog Devices. It will allow you to experiment with ideas without the risk of starting fires or sustaining a potentially fatal electrical shock.
3. Set the ATX power supply aside for the time being and focus on building up your knowledge of basic circuits
4. To become knowledgeable about Switch Mode Power Supplies you're going to need to pick up a bit of college math. Do you already have that, or will this be something to add to the checklist? Check out the following to see if you know this:
   2.5 AC and DC waveforms, average and RMS values – Applied Electrical Engineering Fundamentals (umass.edu)

 

What you seem to asking for is an inverter circuit using a center tapped transformer.

This a a very common circuit. They will even self oscillate.

The trick is you put + side to the center tap and then alternately drive the other ends low with NPN transistor.

Simple inverter

 

The LM337 is an adjustable negative voltage regulator that is similar to the LM317.

Saw that at the time but couldn't find an affordable supplier.

Given your limited funds, I recommend downloading and becoming familiar with the LTspice simulator from Analog Devices. It will allow you to experiment with ideas without the risk of starting fires or sustaining a potentially fatal electrical shock.

I am well versed in the dangers of electric shocks as I used to be an electrician wiring and testing buildings at 240v or 415v 3-Phase.
I have already downloaded LTSpice but my PC is currently undergoing warranty work so it's not available. I also learn best when doing stuff rather than being told how to do it.

You're going to need to pick up a bit of college math. Do you already have that, or will this be something to add to the checklist?

My maths isn't bad although I have never understood calculus.
(It doesn't help when not-so-clever know-it-alls on the web post formulae which include unreferenced and/or unexplained values)

What you seem to asking for is an inverter circuit using a center tapped transformer.

This a a very common circuit. They will even self oscillate.

The trick is you put + side to the center tap and then alternately drive the other ends low with NPN transistor.

Simple inverter

And where in my question did you see me ask for 240VAC? I trained as an electrician. If I wanted mains power, I would USE mains power.

 

Saw that at the time but couldn't find an affordable supplier.

I am well versed in the dangers of electric shocks as I used to be an electrician wiring and testing buildings at 240v or 415v 3-Phase.
I have already downloaded LTSpice but my PC is currently undergoing warranty work so it's not available. I also learn best when doing stuff rather than being told how to do it.

My maths isn't bad although I have never understood calculus.
(It doesn't help when not-so-clever know-it-alls on the web post formulae which include unreferenced and/or unexplained values)



And where in my question did you see me ask for 240VAC? I trained as an electrician. If I wanted mains power, I would USE mains power.

I did not. An inverter does not imply 240V. If use use a 1:1 transformer, as you said you would, you will get roughly a 12V square wave out. Why the attitude when I am trying to help?

 

I apologise if it seems abrupt but your answer doesn't resemble my question apart from the phrases "transformer" and "centre tapped". All the examples in the article you linked show step-up circuits for between 100 and 240 volts and they all seemed to have a centre tap on the primary.
If you looked at the transformer I was considering, you would have seen that it it isn't centre tapped and has two secondary coils.

To clarify, all I am looking for is to create +12V on one rail and -12V on the second rail with at least an amp of current available on each and doing it as simply and cheaply as possible.
If it can't be done simply and within my very limited budget with the design I thought of, then so be it and I will move on to a different design.

 

I apologise if it seems abrupt but your answer doesn't resemble my question apart from the phrases "transformer" and "centre tapped". All the examples in the article you linked show step-up circuits for between 100 and 240 volts and they all seemed to have a centre tap on the primary.
If you looked at the transformer I was considering, you would have seen that it it isn't centre tapped and has two secondary coils.

To clarify, all I am looking for is to create +12V on one rail and -12V on the second rail with at least an amp of current available on each and doing it as simply and cheaply as possible.
If it can't be done simply and within my very limited budget with the design I thought of, then so be it and I will move on to a different design.

The circuit I posted is the simplest way to get ±12V from 12 V in. With the right transformer. You cannot do it as easily with a single primary. You asked for a simple circuit and I gave you one. You could at least say no politely. I am sorry I overestimated your knowledge level.

 

Ok, time for a "first post"!

Firstly, I would like to thank all those on here who have already helped me indirectly by answering other peoples' questions in the past. There's a reason I joined this forum and it wasn't the fancy graphics

Ok, now onto the proper reason for this post...

I have always been interested in learning about electronics since I was in school (a lifetime ago) but funds, commitments and/or time always got in the way.

Funds are still limited but I found myself with time to kill and in need of a new hobby so here we are.

My first project has been to convert an ATX power supply into a bench top format because I cannot currently afford the real thing but had a redundant ATX unit lying around.

Then I started looking at oscillator circuits (mainly because the one I built in school never worked!) and that's when I discovered the need for a dual-rail supply.
The ATX has a -12V option but it's only rated for 0.3A. I did manage to get a sine, square and a (nearly) triangular waveform out of an LM324N but was constantly worrying about current limit (worrying is my superpower) so I'd prefer to have enough headroom to never have to consider it until I am into the whole Amps range.

I played about with the LM317T but it doesn't do negative (got a decent variable supply working though) so

I've been messing around with a transistor (powered by an ~1500Hz astable 555) switching the primary of an IT243 1:1:1 transformer
Datasheet (including Primary impedance)
Unfortunately, my first and only experiment resulted in magic smoke so it was back to Google for more research which has led me to the twin BJT push-pull driver but everything I have seen so far has assumed an AC drive signal for the push-pull.

And FINALLY, my question....

I am aware that the 555 can sink up to 200mA and I wish to know if this will be enough to drive the PNP side of the push-pull and if the transformer is suitable for the job when the secondaries are wired in series and centre tapped to provide the dual-rails.

I could keep experimenting but, as already stated, funds are limited so I'd rather not burn up any more components.


Thanks in advance for any help.

You can create a Negative supply output using the schottky diodes in reverse, and using the electrolytic capacitors also in reverse ( + to ground) you can do it on the 5V or 12V rails.

 

There is no particularly "cheap" way to create a proper Plus-Minus-Supply as You describe..

Here is a ~$25.oo solution, packaged in a nice, small Module.
.
.
.

 

There is no particularly "cheap" way to create a proper Plus-Minus-Supply as You describe..

Here is a ~$25.oo solution, packaged in a nice, small Module.
.
.
.

Actually, there do exist "cheap" ways but they often utilize used and surplus components. A low voltage supply is a very reasonable first project for one with electrician experience and skills. But I will not recommend the cartoon channel for education, although many others will. A transformer stepping down from mains voltages to a much lower voltage can be the basis for a very useful experimenter's power supply, as well as providing the needed isolation. It is, however, not the current vogue switching mode supply. One really interesting concept that I have not experimented with is using a triac light dimmer to reduce the input power to a transformer to provide a lower output voltage. That could provide the safe isolation but I have not investigated to learn if it would actually work.
The question is about what sort of parts the TS may have on hand, accumulated over the years. Or possibly not. A used 24 volt controls transformer could be a very good start. A new one would be way to costly.