power supply question

[iONic]

I am building a +/- 24VDC power supply and have built the 317T/337T voltage regulating portion. Since I would like to regulate the current also my question
stems from the position of the voltage/current regulation stages.

As it stands now I am in a more convient place to have the voltage regulation stage stemming from the Transformer and feeding the current regulating stage.

Does it matter which stage goes first, the voltage or current stage? If so what might be the pros and cons...

Thanks guys... or galls!

 

[audioguru]

If you use an additional LM317 and LM337 as current regulators then they should be ahead of the voltage regulators because they have a voltage loss across them of up to about 3.25V each. The voltage loss across the current regulators varies with current so if they were after the voltage regulators then the output voltage would have very lousy regulation.

 

[bananasiong]

Hi,
What is the purpose of current regulation usually? Is battery charger one of the application? To limit the charging current. Otherwise the battery will be charged by the maximum current produced by the voltage regulator?
Am I right?

 

[iONic]

essentially I am building a bench supply to test generally small circuit builds. I want current restriction so I don't blow parts when mis-wireing takes place.

 

[Hero999]

For a start the LM317/337 are already current limited so it shouldn't be an issue.

You might want to restrict current to below 1A so this is still a perfectly valid question. If look at the datasheets for the regulators you discussed in you post, you'll see that you can also congfigure them as current regulators. The idea is to connect a current regulator in series with you voltage regulator but you need to be aware of the fact that the current regulator requires a minimum extra 3.2V of overhead.

 

[Speakerguy]

Is that basically the dropout voltage + the 1.25V ref voltage?

 

[Hero999]

Yes.

There's also a circuit on the datasheet which reduces the voltage to 1.25V when excessive current is being drawn. It's probably good enough for most purposes, failing that, I have a circuit which enables you to achieve 0V that can be adapted to have current limiting.

 

[stevez]

Take a look at the LM723 - an old but still useful linear regulator. A relatively simple supply can be constructed that offers adjustable current limiting and variable voltage. I use the word "adjustable" in order to call attention to the fact that adjustments are made at higher levels of power that can't be handled with a common potentiometer.