0-30 Vdc Stabilized Power Supply

[audioguru2]

Hi Kevin,
The voltage regulating zener diode, D8, is in the feedback loop of the very high gain opamp, U1, and together make a very good voltage regulator of 11.2V. The high gain of the opamp makes certain that the current through the zener is constant, regardless of how much the supply voltage is fluctuating. Since the zener's current is constant, the output voltage of U1 is also constant. The 5.6V zener was selected because a zener of that voltage has a low temperature co-efficient.

The negative voltage regulating zener diode, D7, does have a voltage change due to transformer voltage variations and system output loading, but that has no effect on the system's output voltage.

 

[Newguy1]

I wish I could increase the max. current from 3 AMPs to 5 AMPs e.g. by changing the transformer, diodes and Transisters and PCB tracks width and heat sink etc.

 

[audioguru2]

Hi Newguy,
Welcome to our forum.
Your wish has come true, because we already discussed modifying this supply for 5A. The discussion and detailed instructions are in the other forum, here:
http://www.electronics-lab.com/forum/index.php?board=13;action=display;threadid=196

 

[Emiliano86]

OK, I

 

[audioguru2]

Hi Emiliano,
When you turn the Current Control to the right side and the project current-regulates, then maybe the control is wired backwards and the project works normally if you turn the control to the left side.

If the project gives a maximum output voltage of only 26.1V, then its transformer voltage is probably too low. That's why I recommend using a 30VAC transformer.

If the output voltage goes to -0.6V when the circuit current-regulates, then either U3 is defective with more than -200mV input offset voltage (maximum spec is only about 10mV), or U3 is breaking down because it is operating with high supplies voltages that total beyond the rating for TL081 ICs. IC2 and IC3 should be replaced by MC34071AP or TLE2141CP ICs that are 44V-rated.

When the output voltage drops to 0V wth a load, does the current-regulating LED indicator light? If it doesn't, then Q2 is probably shorted. It should be replaced by a heatsinked TIP31A power transistor that I recommended before.

 

[Newguy1]

Hi audioguru
Thanks for telling me the source.
And I would like to ask one think more that can this circuit be used for charger.
I think that the current limitter can only limit the current not over one level, but it can not make sure the current is keeped in that level.
For example, if I am charging a Li-Mh battery the resistance of the battery may change. But I have to keep the charging current in a constant level.
Can I use this circuit for that kind of charging purpose.
Thanks!!! ???

 

[audioguru2]

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.
Ka-boom!

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:
http://www.web-ee.com/primers/files/fsect5.pdf

 

[Newguy1]

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

L200_ADJUSTABLE_VOLTAGE_AND_CURRENT_REGULATOR.pdf

 

[audioguru2]

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.

 

[Newguy1]

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

 

[audioguru2]

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"?

 

[tattoodanjapan]

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

 

[audioguru2]

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:
http://www.national.com/ds.cgi/LM/LM150.pdf

 

[Emiliano86]

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 .....

!!!!

 

[ante1]

Emiliano,

How much exactly is incredible ripple? And under which conditions? What value have you chosen for C1? What is the voltage over C1 at maximun power 25VDC x 3.10amp? Are you sure it is ripple you are measuring?

 

[audioguru2]

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.

 

[Emiliano86]

yes...but the problem is that it is imposible to find that OA in my country......I don't know what to do!!!!!!!......
I A M F R I E D!!!

 

[audioguru2]

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.

 

[ante1]

Audioguru,

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?

 

[Emiliano86]

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