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0-30V Stabilized Power Supply


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Hi PicMaster,
The OPA445 high voltage opamp will not work in the latest modification.
I didn't keep a schematic for the project with the OPA445 opamps because it was nearly the same as the original except for a couple of corrections. Here is the parts list for it:

EDIT: Dec 13, 2013.
1) The MC34071 is not available anymore in a through holes package.
2) The value and size of R22 was changed.
3) The value of R17 was changed.
4) The 10V zener diode was added.
Here is the latest parts list:


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Audioguru,  do you have a copy of the last parts list using the alternate chips.  I seem to remember some of revisions were in red.

EDIT:  The first post contains REV 5 in the zip file.  Audioguru's post directly above this also contains the same update.  No need to read the next 125 pages except for fun

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Hy Guys!

Okay - after 1 damaged Zener and 2 damaged power transistors my power supply is now finished.
My experience:
- I used the MC34072 oamps with max.44V instead of the MC34071. With the MC34072 I was not able to do the offset compensation. So the current limiting became a problem. ( When I turned the current limiting to minimum, it stopped limiting the current and damaged the power transistors with 24A  output >:( ). So I used a 68Ohm resistor for R17 and all worked perfectly.
- I used a 2x30V - 230VA Transformer with 32.47VAC without load. The problem is the voltage without load of about 45.91VDC  -  too much for the oamp. So I decided to use D15 in my shematics.
In practice, the max voltage is about 44.1V so it will also work without D15.

Here are pictures of my working Power Supply, my shematics with the (hopefully...) correctly bill of materials for my shematics.
I decided to give you my bill of materials because there are a view mistakes and missing parts in the existing list.

Sorry for my bad english - hope everyone can understand me  :-[

means Markus

PS: More pictures in my next reply

Update: After a view tests at maximum output (30V 3A) I saw that D15 (10V Zener) in my schematic only allows an max output of about 24V at 3A. Or about 2.7A at 30V...
So I decided to throw D15 away and replaced it with a peace of wire. Now I am able to get 30V with 3A.
If someone has the same problem as I (The rectifier voltage is to high for the oamps with 44V) you can use D15 which should have only as much voltage as you need to get under the 44V. The voltage in my circuit is about 39.6V - 44V and nothing is damaged.




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Hi Limbo,
Your power supply looks good.
I think the tiny 2N2219 Q2 driver transistor will melt if the output is shorted and the gain of the 2N3055 transistors is low. It will try to dissipate more than 3w which it cannot do even with a clip-on heatsink. A BD139 real power transistor should be used with a medium size heatsink.

I do not understand why the current regulation failed when it was turned down.

Since you reduced the unregulated positive supply by 5.6V with a zener diode can your project supply +30V at 3A without ripple?

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Hi audioguru!

Thank you  :D

The schematic is for simulation only. I added a small statement in the schematic: "For parts value see bill of materials". There you can see that I used a BD139 for Q2. In LTspice IV there is no BD139 in the database  ::)

I also don't know why the current limiting failed by min current. I was not able to find a mistake in my circuit. I decided to say it is because of the oamp offset  :P

I have no oscilloscope to see if there is a ripple by 30V at 3A. I only have the small multimeter which shows 30V and 3A. But if I get the chance for an oscilloscope I'll post a picture.
Do anyone have a 10Ohm 90W resistor for testing the power supply at maximum?  ;)

by limbo

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I would like to add to that circuit fine tuning for voltage and current. So i am asking where to put it on that circuit on first post?
My minimum output is 40mV not 0V and i cannot correct it with RV1 it has no effect. 
Did i do something wrong or is it normal to get 40mV?

TNX in advance

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I would like to add to that circuit fine tuning for voltage and current. So i am asking where to put it on that circuit on first post?
My minimum output is 40mV not 0V and i cannot correct it with RV1 it has no effect. 
Did i do something wrong or is it normal to get 40mV?

TNX in advance

You can add fine-tuning pots in series with the coarse adjustment pots but they will be always set to the wrong position.
If you made the latest circuit with MC34071 or TLE2141 opamps then RV1 adjusts the 0V output to 0V if your voltage adjustment pot can give a 0V output.

The output capacitor C7 makes the output positive without a load if it is an electrolytic type. A film capacitor will not.
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hello. ;D
could you please tell me if there are any other equivalents to opamps used in the final version of the schematic? because i could not find tle2141 or mc34071

The opamps chosen are sold everywhere in the civilized world. Maybe not on your different planet.
Digikey in North America and Farnell in many other countries sell the popular opamps.

There are many newer opamps that can also work.

Where are you??
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Yesterday I got an oscilloscope to see if there is an output voltage ripple.
And I have to say: I was not able to see a ripple. Not even by 0,05V/div.
I measured  it by 30V 0A; 30V 3A; 1V 3A;... with current limiting and without
My power supply works very fine!  ;D

Thx for all your help!
bye Markus

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I can't remeber now and I know the Schematic say 28V AC but for the TLE2141 or MC34071 does the transformer have to be 28V AC or can it be a 30V AC ?

Looking at the data sheets the OPA445 is 45V and the other 44V. Only I thought I ordered 10 OPA455 but wrote the wrong part number down which was good really becasue when I did find the right part number I was shcoked to see they where

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Hello PicMaster!

Have a look at my post from August 27, 2009, 05:18:37.
I posted my schematic with my bill of materials. I built this power supply and it works perfectly!
I used a 2x30V/230VA transformer in order to build a dual version.
Link to transformer: http://shop.conrad.at/ce/de/product/518458/RINGKERNT2X30V230VA

My tip for using a 30V transformer: Build up the circuit with D15 (in my schematic). And then measure the positive supply voltage. If there are 44V you don't need D15. If the voltage is higher - use a Zener-diode which fits to your circuit. For example:

Positive Supply: 45V
Max OAMP Supply: 44V
45V-44V= 1V Zener-Diode.

In my circuit, I did not need D15, although I used a 30V transformer!
I don't know if the OPA445 will work. The MC34072 I used was 0,97

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The OPA445 opamp is rated for a positive and negative 45V supply which is a total of 90V. It needs a different circuit to the latest one, U2 and U3 use a -5.6V supply and is similar to the original circuit. Its total supply was 48V.

A 30VAC/4.3A transformer will be about 31VAC without a load. Its peak voltage is 43.8V and the rectifier bridge will drop it to 42.4V without a load which is fine for MC34071 or TLE2141 opamps that have a rating of 44V. A 28VAC transformer will be safer.

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