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0-30 Vdc Stabilized Power Supply


Sallala
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Hi Neo,
Using the recommended 30VAC transformer for this project, the unregulated positive voltage is about 40.4V which is much too high for a 12V fan. If a 5.4W resistor was added in series with the fan to reduce its supply voltage then there might not be enough extra current in the resistor to allow the fan to start running.

Make a two-resistors voltage divider of the 40.4V to reduce it to about 13.2V, then feed it to a darlington power transistor as an emitter-follower to drive the fan. The transistor will provide plenty of current for the fan to start if the current in the resistor divider is high enough.

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You can use a capacitive divider at the AC. Capacitive dividers can be used with AC input signals.  A DC input voltage would not pass through the capacitors, so you would have to use this type of divider where there is still an AC component to the circuit. The formula for determining the AC output voltage of a capacitive divider is:
Vout = Vin*C1/(C1+C2)

The output voltage is not dependent on the input frequency.  However, if the reactance of the capacitors is not large at the frequency of interest (i.e. capacitance not large enough), the output current capability will be very low.


MP


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I'm having trouble finding a few parts.

.47 ohm 10w
12,000uh / 63v electrolytic
47uf / 50v electrolytic  (found a 47uf / 35v)
100nf and 220nf Poyester
6-10a / 50v Diode bridge (is there another name for this?)
bzx79c5v6 5.6v zener
bc557
opa445ap

The site I ordered everything else from didn't have these. anyone know a good place to get them?

Also is there a difference between TIP31 and TIP31A (Sorry if that is a really dumb question, I'm a newbe. :)

Thanks to all ;D

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Hi Dosster,
All parts are available online at www.digikey.com and www.newarkinone.com .

Corrected spelling or re-phrased:
0.47 ohm/10W
12,000uF/63V Electrolytic capacitor
47uF/50V or 47uF/63V Electrolytic capacitor
100nF and 220nF Polyester capacitor
6-10 Amp/50V (or 100V) rectifier bridge module
BZX79C5V6 zener diode
BC557 transistor
OPA445AP opamp

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Hello!  ;D

I am looking this power supply for some time and I was planning to build it; in fact I still am interessted in this project, but I need some answers, so, please:

1. I have a 30/30 V transformer 100VA total, 1.7/1.7A secondary output. Can I use     
    it? What for output I will get?
2. What can I use instead OPA445AP?  ???  Not availabile, and as I hear,    expensive.
    TL081? +-18V will be enough?
3. Wich partslist to use? Modified or original one?
    I saw a part of conversation about this PS, (not all 60+ sites ;D) and I am
    confused. I do not need high-end tip-top extreme power supply, but I even do not
    want PS crashes, overheating etc. Just a nice, good working and reliable PS.
4. I assume that 10000uF/50V as C1 is gonna be just nice.

So long...

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1. I have a 30/30 V transformer 100VA total, 1.7/1.7A secondary output. Can I use     
    it? What for output I will get?

Unregulated will be 40.0VDC at 2.3A at full load to about 44VDC without a load. The negative 5.6V supply is additional for the supply to the opamps.

2. What can I use instead OPA445AP?  ???  Not availabile, and as I hear,    expensive.
    TL081? +-18V will be enough?

Your opamp's supply is 44V + 5.6V=49.6V. It is way too high for ordinary opamps with a 36V max rating and also too high for opamps with a 44V rating. Use OPA445AP opamps or get another transformer. Today, Digikey have 259 OPA445AP opamps in stock for $9.50US each.

3. Wich partslist to use? Modified or original one?

It doesn't matter. The voltage is too high for your opamps and the current is too small for the project.

I do not need high-end tip-top extreme power supply, but I even do not want PS crashes, overheating etc. Just a nice, good working and reliable PS.

If the project has enough voltage headroom, then the opamps will make its voltage and current regulation fantastic if you use the correct zener diode for its voltage reference.

4. I assume that 10000uF/50V as C1 is gonna be just nice.

Then it will easily reach 30VDC output at full current without ripple.
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Hi.

There is no way that this circuit will work with my transformer?
Adding a parrallel R to trafo output to drop voltage? Current will be too small?
Connecting together both trafo outputs is out of question, right?
Something else?
And I really cant afford 445 OPs to me... international shipping price + $30 for 445's is too much for me ???  :'(

There's really nothing to do? Only new transformer?

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There is no way that this circuit will work with my transformer?
Adding a parrallel R to trafo output to drop voltage? Current will be too small?

A parallel R is an AC load on the transformer and will drop the voltage only when the current and heating is so high that the transformer is grossly overloaded.

Connecting together both trafo outputs is out of question, right?

You need to parallel the secondary windings to get 3.4A AC.

There's really nothing to do? Only new transformer?

A 20VAC transformer will give about 22VAC without a load and about 29.7VDC for the positive unregulated supply. Adding the 5.6V negative supply and ordinary 36V rated opamps will be operating at 35.3V
The max regulated output voltage will be only about 20V to 21VDC.
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OK. Lets mess it out!

I parallel transformer secondary windings and i get 30V 4.3A AC.

No. Your transformer will provide only 3.4AAC, so the supply will provide only 2.4ADC instead of 3A.

And ... I buy OPA445AP's.

Yes.

And thing is gonna work.

Not yet. Your transformer doesn't have enough output current so the current setting pot should have a trimpot added in series with it and adjusted so that this project can supply a max current of only 2.4ADC.

And wich partslist to use?

Use the modified parts list.

It will perform very well and be very reliable. ;D
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Your transformer will provide only 3.4AAC, so the supply will provide only 2.4ADC instead of 3A.
Well, guess I gonna need satisfy with this...
If nothing else, there will be less heating problems...  8)

I will buy (or borrow, or steal  ;D) theese OP AMPs, add trimmer in series with current pot and use modified parts list.

And then...


And finaly, THANK YOU!!!
It was impressive and quick as always.
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Make a two-resistors voltage divider of the 40.4V to reduce it to about 13.2V, then feed it to a darlington power transistor as an emitter-follower to drive the fan. The transistor will provide plenty of current for the fan to start if the current in the resistor divider is high enough.


Sorry, i'm a newbie...
can u please include the circuit with the values?..i'm not sure how to connect it.. and what kind of Darlington power transistor sould i use?
is 2n6036 ok?

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can u please include the circuit with the values?..i'm not sure how to connect it.. and what kind of Darlington power transistor sould i use?
is 2n6036 ok?

The 2N6036 is a PNP type which is expensive and is not recommended for new designs so might not be made anymore.
I recommend a TIP-110 NPN darlington transistor that is made by many companies.

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hi,
thanx audioguru..

Now.. I have a analog voltmeter.. can I use the same meter to display voltage and current using a switch to switch between voltmeter and ammeter?
cause i know that a voltmeter can be converted into an ammeter by adding a shunt resistor..
how do i calculate the resistor value?
thanx

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Now.. I have a analog voltmeter.. can I use the same meter to display voltage and current using a switch to switch between voltmeter and ammeter?
cause i know that a voltmeter can be converted into an ammeter by adding a shunt resistor..
how do i calculate the resistor value?

A shunt resistor in series with the output of the project ruins its fantastic voltage regulation.
Just switch the voltmeter to read the voltage across R7, which is the load's current.
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I have a stupid question.
90% of profesional lab power supply is dual (floating). What is that?
Is like two 1,5V batteries? If I want, can I conect it in series and make a 3V supply or positive/negative supply +1,5V/-1,5V whith a virtual gound.
Supose I have 2 independent supply like "0-30 Vdc Stabilized Power Supply" wich are conected on two independent secondaries (double wound transformer), two independent bridge rectifier, and so on. Can I conect it in series whithout a big explosion?
Sorry for my ignorance, but I googling about a week for a good answer.


Adrian

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Hi fish2005, I am not sure if the dual power supply is also floating. One can think of the common as floating but in the case of laboratory PSU the common is very often ground as well, and as ground I mean earth. Even if it is not, the center point is called ground and positive and negative voltages are adjusted with respect to it. You can connect two of this in series without a "big boom" but I believe that the catch is that the current through them has to be the same if you want to use the full swing from 0-60V. If you use them as dual PSU I think still each stage will be on its own so you shouldn't have problems. I have done it actually.

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Thanks for your answer, Kain.
You are wright. Those PSU have a optional earth ground. On the front panel have 4 connectors for two positive PSU and one separate connector for earth ground. You can conect it in series and you have a double voltage PSU or a floating ground positive/negative supply (+ 0 -). This ground may be unconnected (floating), or conected to earth connector. You can also connect it in parallel for double amperage.
This kind of design is verry flexible.
In my searches I found many opinions about this subject. In my knowlege is OK to connect two transformers in series (or one transformer whith two independent secondary), but I hear people that say this is imposible after rectification (some kind of short thru diodes), so is imposible to conect two regulated supply.

GRRRRR... I'm verry confuse...
I whil try to find some service manuals whith schematics for original lab PSU.


Adrian

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Hi Ron,
I recommend this parts list for the project to work well and be reliable. A few months ago someone recommended adding trimpots in series with the controls for calibration.

hello agin
i have started building this project and i have left one capistor not in use where does it satnds?
C10 electrolitic 10UF

ron
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Leave R7 at 0.47 ohms. 3A through 0.47 ohms makes a voltage drop of 1.41V. If the meter is 200mV full-scale then it needs an attenuator.
If the internal resistance of the voltmeter plus its series calibration resistor is only 47 ohms or less then the calibration will be affected.


my voltmeter has range of 0-30VDC and a full scale current of 27.5mA.
what is the value of series resistor should i put to convert it into an ammeter with 0-3A range..?

thanx
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