negative regulation with single power transformer

[thebadtall]

hello..
i have been looking for an easy way to make a +- 12v power supply, supplied by a single typical cheap transformer. without luck, because all i found was complicated and unstable designs.

a minute ago i saw a datasheet of negative voltage regulator, lm337.

my question is, can i use this to regulate the gnd of a dc single power supply?

to use it as typical application of datasheet

http://www.datasheetcatalog.org/datasheet/nationalsemiconductor/DS009067.PDF


if i can, then id combine with lm317 to make a dual power supply right?
or fantasy?

thank you

 

[tpetar]

This transformer have central out ?

If we need 12V regulated, trafo should have at least 15V-18V.


Example with LM317 and LM337 :

In your case you will adjust input voltage to 15-18V and output voltage to +12 and -12V over VR1 and VR2 pot.



One of example how to increase current/power of regulator :

**broken link removed**

**broken link removed**

 

[thebadtall]

unfortunatelly transformer has only 2 terminals and that ruins the
plans once more

 

[tpetar]

Ok then, there are lots of possibilities :




Your transformator can be used on that way.

 

[BradtheRad]

Here is a way to obtain a bipolar supply from a single coil secondary.

Made from two half-wave supplies of opposite polarity.

The bottom wire is ground as marked.

It will need sufficiently large filter capacitors, depending on the load.

 

[thebadtall]

aha ! interesting !! And can I use all the power of the transformer, or I need to be careful ?

dear tpetar why is 39Ω Resistor for ? Can I bypass it ? if not , I got on hand 2x 15 Ohm / 50Watt can I use those in series ?

thank you!!!

 

[BradtheRad]

On closer examination I see my schematic is a bare-bones version of tpetar's, post #4.

The transformer is used at 100% duty cycle. Keep track of temperature to make sure it does not overheat.

I believe the 39 ohm resistor is meant to limit current to 300mA or so. If you need more juice then you can reduce it. Nevertheless you should install some sort of component protection.

 

[tpetar]

You can exclude that resistor from circuit.


Here is another similar circuit with PCB :

https://circuitsbook.com/symmetricalauxiliaryps.html

**broken link removed**

 

[thebadtall]

You can exclude that resistor from circuit.


Here is another similar circuit with PCB :

https://circuitsbook.com/symmetricalauxiliaryps.html


**broken link removed**

i will build this,today. is it necessary for r1 and r2 to be of high watt rating?
may i use a couple of 1/4w 1k ?

 

[tpetar]

Use as described in text. 1W or 2W metalfilm have small dimension like carbon 1/4W.

Monitor them if they heat up change for higher power ratings.

 

[thebadtall]

ok thank you ! i will try it

 

[tpetar]

My friend, just do this easy, dont rush, pay attention on capacitor polarities and diode orientation. Check voltages with voltmeter.

 

[thebadtall]

i was born holding the soldering iron !

 

[tpetar]

Let force of iron be with You!

 

[thebadtall]

thank you for the wishes