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0-30 Vdc Stabilized Power Supply


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Hi Newguy,
If you use this lab power supply to charge a Li-Ion battery then you risk having an explosion and/or a fire!.
When a Li-Ion battery is fully charged, it needs a "minimum current" detector circuit to shut-off the charger. This lab power supply doesn't have a method to detect the minimum current nor a way to shut it off.
If you use this lab power supply to charge a Li-Ion battery, you can set its current to charge at the regulated current that is specified for the battery.
You can also set the voltage so that the battery will not charge to a higher voltage than is specified for the battery.
When the battery is about 65% charged, its voltage will reach its specified maximum and the power supply's voltage regulator will keep it there. Then the battery will continue drawing current until it is fully charged and will continue drawing current as it is overcharging.
When the battery is overcharging, all the current is used to heat it.

Another problem with using a power supply to charge a Li-Ion battery is that you must detect whether the battery's voltage is lower than its specified minimum voltage for "normal current" charging. If its voltage is low, then the initial charging current must be reduced until its voltage rises above its specified minimum voltage.

Special ICs are made for battery chargers that incorporate all precautions as mentioned above, and also their circuits have back-up safety measures of maximum temperature cutoff and timer cutoff.
A good article about battery chargers is in our Articles Section, here:

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Hi audioguru
Thanks very much for telling me the limitation of the circuit.
Actually, I am a student, I am finding a circuit which can provide a constant current and constant voltage for charging. And both the current and the voltage must be adjustable for different kinds of batteries.
And I need not consider about the problem of over charging.

Secondly, I found that some regulators like L200(ST) and LM117 can be built to be a Voltage and Current Regulator. In the data sheet the voltage out put and current out put are controled in the same circuit with two variable resistor. I want to know that in these kind of regulator circuit the voltage and current are controled individulally or related.

However, I still can't find a suitable circuit after reading many web pages. Could you give me some hints?

Thanks a lot


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Hi Newguy,
How are you going to stop your batteries from overcharging?
Why not use a battery charger IC?
That is the most important part of a battery charger.

A power supply with voltage and current regulation, like our Lab Supply and fig. 23 of your L200 posting, have completely separate controls for voltage and current.
However, the output voltage is reduced by the current regulation, in order to keep the load current constant. For example you set it for 10V and 1A. The output voltage will be 10V for loads drawing up to 1A. But if you put a load that draws more than 1A at 10V, such as 8 ohms, then the output voltage reduces to 8V to keep the current through that resistor at 1A.

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Hi Audioguru
Thanks your suggestion. But since the overcharging part is not my responsiable, I have no need to worry about it. And The out put must be controled manually so I can't use IC.

So, in order to let user to choice between constant current charging and constant voltage charging, I have to built one voltage regulator and one current regulator in the same charger. right?

If I really built the voltage regulator, the output voltage will keep as my setting no matter the situation of the battery. And the current regulator is the same right ??? If not could you teach me how to find the rang of load for the constant current output and the constant voltage output.

Additionally, back to our circuit. Do you mean that both your lab supply and regulator in market are trying to keep the set current first ?
But by my limitted knowledge, I think your lab supply and the regulator can only limit the current not over a constant. Let say, if the load keep increasing and reach 80 ohm, (It just an asumption, is ture that in the actual world charging will only decrease the load of the battery ???) and the current drop to less than 1A(0.5A), then the circuit will still out put 10V and 0.5A. The circuit can not make sure that the output current is kept in 1A, if the load increase.

Thanks very much

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Hi Newguy,
Didn't you learn Ohm's Law?

10V across 80 ohms creates a current of 125mA, not 0.5A.
If you want 1A through 80 ohms, then the voltage across it must be 80V!

How many volts do you need to create a current of 1A to flow through a resistor with a value of 1M?
Steven (Sparky) knows.

If you build the constant voltage with constant current circuit for the L200, fig.23 and give it to a user for charging Li-Ion batteries, then run for cover to avoid the explosion and the user's heirs.
Run far, because over-charging is your responsibility.
You better worry about that.

What is "a ring of load"?

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Sorry i took so long to reply but i got really swamped at work. I need at least 1 amp but i have seen tattoo power supplies up to 3 amps. Voltage i regularly use between 6 to 9 volts. I would like a unit that goes to at least 15 for the sake of just in case some weird setup comes into play. I apprecaite the response and info. The real key to the system I need is one in which i can set up to 4 diffrent voltage settings and and go to each by the flick of a switch or the push of a button

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Hi Dan,
If all that you need is up to 15V at up to 3A, then our 30V lab power supply project is too much for you. A simple LM350T 3A, variable-voltage regulator IC will work well. Its voltage adjusting pot can easily be replaced by switched resistors like I showed before. The datasheet is here:
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hi audiogoru!!......how are you?.....i am fighting with this PSU.....i could repair the current and voltage regualtor, i 've added two more 2n3055 transistors and it works fine.....it gives 3.25487 amps.....but the real bad thing apperared qhen i connected and test it in the osciloscope.........it was a desaster!!!!....the ripple is incredible!!!......and to get the thinsh wors it get to acsilate at maximun power 25VDC x 3.10amp......

I don't know .....


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Hi again Emiliano,
I am sorry that you also discovered ripple with this project. Many members have the same problem because the transformer is "only" 24VAC and needs to be 30VAC in order for this project to produce regulated 30VDC at full load.
As Ante suggests, try using 10,000uF or more for C1 and you might get regulated 24VDC at 3A. You might also get a couple of volts more output if you change R15 to 100 ohms, as I suggest.

If you do change the transformer to 30VAC and 130VA or more, then you must also change the opamps to OPA554AP high-voltage ones, and the resistor changes that are on my list.

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Hi Emiliano,
Please don't get fried. The OPA445AP is the only very high supply voltage rated opamp that I could find that is still being manufactured. It is made by Texas Instruments (previously by Burr-Brown).

What country are you in?
Look for your flag at www.farnell.com and you might be lucky. They have branches in many countries. My country's catalog has 2448 pages of the latest electronic components. For years I didn't know that they had a branch office right in my city.

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Did you understand if the ripple was on the whole voltage range or just on the highest part? And was it with or without load or both?
So, you have Farnell round the corner? And did not know it? Well what do you think of them as a supplier then? And another one: how is their prizeing compared to others you have over there?

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hi ante,

The ripple appeared when I'd connected a load at maximun voltage that it gives (in my case 27V) and at 2.35 Amp, i know that it is very uncommon situation, it was only a test, ofcoures that without load it does'nt gives ripple.

The solution is to connect a higer voltage transformer, change the opamp, and improove the filter, like said audiogoru, instead of using a 24VAC trafo, a 30VAC one (or 16 + 16), but in that case the opamp MUST be changed by other with a higer volt range .

Good luck!!..

thanks audiogoru for your help!!!!....thank you ;)

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My transformer is : 24 VAC - 75W

please help me!!!!!


Hi Ante,
His 75VA transformer is already overloaded since its peak voltage of about 34V must supply the project's rated DC output current of 3A, which is 102VA. At the transformer's limit, this project can supply a DC output current of only 2.2A.

I figure that with a very light load or none, the transformer's voltage will be 26VAC, 36.8V peak. The rectifiers will drop it to 35.4V. Therefore adding the 5.6V negative supply, the 36V rated U2 and U3 will be operating with a total of 41V!
Over here, if I use a 24VAC transformer that has a 115V primary on my 121V (very common) mains, the ICs will get 43V!
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Hi Ante,
A transformer doesn't dissipate much because it isn't the load, unlike a linear power transistor that is in series with the load. A transformer passes VA to a load, therefore shouldn't be rated in Watts. Its rating in Watts is how hot it gets (power input minus power output).
Since Emiliano's transformer is rated to pass a current of 3A at 24VAC, its VA rating is 3 X 24 = 72VA. It is expected to give 24VDC at 3A to a load (72W), plus maybe about 18W to heat the transistors and circuit, plus maybe about 12W to heat the rectifier bridge. So the total load on the 72VA-rated transformer is 102W and it is expected to pass 102VA. It is seriously overloaded.

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Hi Ante,
Thanks for the power factor article.
I don't think that a reactive load that is supplied by our Lab Power Supply will feed back into it. Even the huge filter cap isn't reactive because all of its charged energy ( ;D) flows as current in the load, or if the load is very light then the filter cap does almost nothing. If the transformer has reactance to the mains, it will have no effect on the output of our rectifiers.

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Hi, i'm thinking of using this cap as C1 but I'm not sure if its a good one for this project.
Some pictures:

There are four pins at the bottom, 1,2,3 and 5. The arrows for indicating the negative side are pointed towards pin 5.

My question: can this cap be used as C1, and how do i connect it (what pins do i use)?


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