power supply explanation

Specific circuits are generally hard to come by on the internet.

Just google "circuit variable voltage supply" and you will probably find everything there is. Trying to make your own variable voltage supply is pretty uncommon these days, considering you can by them for $50 - $100.

I was trying for controlled current and controlled voltage regulation my old one had switch so that you could vary the current drawn using a pot or the voltage from a different pot if the switch was the other way. The regulated bench power supplies of 0to 20 or 30v up to 4A seem to be $200 or more

I have found a circuit which might do me

----- Original Message ----- From: "F Murtz" Newsgroups: aus.electronics,alt.binaries.schematics.electronic,sci.electronics.basics Sent: Wednesday, June 11, 2008 3:57 AM Subject: power supply explanation

We shall not name any names, of course! ;)

Perhaps at one time they did. Not any more.

I'm not familiar with power supplies that have separate controls for voltage and current regulation, where you would have to disable voltage regulation in order to achieve current control (limiting). You don't really need such a switch for most applications. Consider the standard, voltage-regulated, current-limited power supply: when current reaches the setpoint and the current-limiting loop kicks in, voltage regulation gets cut out of the loop anyway. So why have a switch? Here's an example of a voltage regulator with current limiting:

His claims for "performance" are a bit exaggerated. I think you might get better line regulation and a flatter temperature response with an LM317 or LM723. This link goes over the fundamentals of linear voltage regulation pretty well:

** Posted from **

I'd be tempted to repair the old circuit, first. Things like pots, caps and switches do eventually wear out, and it's simpler fixing something you're familiar with. The 3130/3140 is still alive and well as a replacement part, from distributors like DigiKey. It wouldn't be the first suspect in troubleshooting flakey behavior, though.

You might be surprized just how similar your old circuit is to the new kit you've found. Beefing your old circuit up might simply involve changing a few components and adding a larger heatsink.

RL

the switch on my old supply controlled weather current or voltage were controlling. the meter showed either current or voltage depending on the switch. The potentiometers controlled the current or voltage ie if the current was set at say .5 amps then that is the current regardless of where the voltage pot was unless it was too low. The voltage was limited for that current Visa versa if the switch was other way

You've been told what to do. Go to (Australian suppliers, since I read this in a.e):

or or another supplier, and get the data sheets from e.g.

or the manufacturer: , and just build the damn thing using the information that I found there in 2 minutes searching.

If you want adjustable fold-back current limiting (to protect the devices you're supplying as opposed to protecting the supply itself) you'll have to look a little further, but NatSemi's website really gives all the help you could need. If you find folk are a little cranky, it's because you seem happy to ask us to write answers, but you don't seem willing to read them and take their advice.

Clifford Heath.

--- They're common, and usually called CV/CC supplies:

If you want voltage regulation you start with both controls at zero and the switch set to VOLTAGE, then you crank the current switch to max and adjust the voltage control for the output voltage you want. The current into the load will then vary as required in order to keep the output voltage constant.

If you want current regulation then you start with both controls at zero and the switch set to CURRENT, then you crank the voltage control to max and adjust the current control for the output current you want. The voltage across the load will then vary as required to keep the current through it constant.

If you want current or voltage limiting, then you set the appropriate control to the limit it shouldn't exceed.

--- If you have a CV/CC supply then you certainly do. How else would you switch between Constant Voltage and Constant Current modes?

JF

--
Oops...

You don\'t need the switch to change modes, it\'s just there to switch
from ammeter to voltmeter.

 
JF

Well, I _did_ suggest that you check out the ARRL Handbook, which has a nice adjustable supply project with pretty much those specifications or better. I don't know how hard it'd be to get one in Oz, but certainly it isn't impossible.

And if Radio Shack has more for it than the bannana jacks and some overpriced, underperforming meters, I'd be surprised.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html

Radio Shack rescues me regularly. My local one has a nice supply of overpriced transistors, LEDs, switches, relays, connectors, etc, all stored neatly in extremely nice metal drawers, and a bunch of sales people who try to sell me cell phones and radio controlled cars. However, when I need a widget, and don't want to drive to Frys or wait for mail order, it occasionally has what I need.

Regards, Bob Monsen

Yep. I agree. In SoCal, Frys is about the best place that you can still drive to and get parts, but Radio Shack still can be useful certain ICs, transistors, leds, switches, connectors, and cheap/inexpensive project boxes. Of course, neither compares to Digikey.

Bob

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Some caps (electrolytics) are likely at their end of life. Just replace them.

Graham

Step by step uA723 regulator.

Maplin in the UK nowadays.

Chris

F Murtz wrote private email.... responding here.

I understand what you want better now. When you say "control current", you mean that you want your supply to act as a current source. That's the correct term to use when searching for information on that aspect. Current sources feign infinite impedance, voltage sources feign zero impedance.

Most power supplies do not act in this way. It's just not what people want from a power supply very often; and when they do, they often use a specialised current source circuit, not one that's built into their power supply. The CC/CV supplies that John mentions are the exception.

What people *do* want is for the power supply to detect overload conditions and rather than just limit the current, to actually reduce the current down to near zero. This means that for a given output current, there are two possible output voltages; the voltage that is set on the control pot, and the voltage that results in the circuit drawing that amount of current.

This sort of current limiting is called "foldback current limiting", and is almost certainly what you should be building into your supply. A CC supply does not do this, and unless used carefully will often blow things up by delivering an excessive current *and* voltage at the same time.

That said, if you can build a new supply, you can fix the old one. If you can't, you should buy a new one.

Clifford Heath

It all sounds great.

One thing though... how could you possibly expect to get an optimized power supply design by giving some arbitrary, not-quite-all-informative description of a couple of transformers?

Common sense should tell one that it would be easier, less costly on time and money, and better to start from the ground up.

Hell, you claim no fancy stores... I'll bet that you haven't looked for surplus or the like. There are usually those in any given town of any significant size anywhere in the world. If you have power, you likely have someone there running a store that has gear he collected in it.

Then, of course, there are all kinds of hobbyist stores online.

The learning kits... everything is all there.

Essentially, your question was simply to vague to give the answer you seem to have been wanting to it.

A $25 class D audio amp can be used as the driver front end to an infinitely variable, variable frequency, power supply.

You need to decide what voltage range and power range you want to operate in, and with that info, you can deduce what your power needs will be to achieve such a supply.

Then, there are noise considerations. Simple regulated supplies typically have a very high ripple figure and are not useable in some digital domains. There are also switchers that are "noisy" in some niches of the industry (HF transceivers, etc.).

So, your request was oversimplified, so any answer you would have gotten would have been just as simple in nature.

The smack across the face you got from a couple folks was a wake up and use some sense call. Consider this one to be similar in nature.

All drawn out... whoopie doo.

The smack down worked as well.

Me, too -- but they don't have _everything_.

I was in there last night buying jumpers, and it occurred to me that you could build entire amateur radio transceivers just from Rat-Shack parts and some creativity. It would be a cool contest, if you had the time.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

I smell a new reality tv show. That is one that I would spend my time watching or even participating in.

Bob

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