0-30 Vdc Stabilized Power Supply

[ante1]

Kain,

Yes it

 

[Kain]

Ok, now I got one of those digital meters but the either the description is not enough or the unit is not working, or I'm missing something... I put it on my test board and wired the thing with 9V battery is the way shown there. As far as I know the decimal point does not affect the range of measuring - the unit should still show the value without the decimal point. Good, but when I try to measure 3V battery and it goes all crazy and out of scale. I assume the unit uses the chip 7101 and I was looking at the schematic posted on this site realised with the same chip. They use resistors to switch ranges. Hum, am I missing something? This is copy of the description. :

View attachment 35492

 

[mav]

Hi! I have built this psu, but when I connect some load to it and I set voltage to some value and then I decerase current (by setting current limit), voltage decerases too. Has it to be so?

Thanx for answers. But what should I do when I need to regulate current at some constant voltage? For example for charging of accumulators ... sometimes I need 3.6V and 180 mA, sometimes 3.6V and 1.8 A. Should I build project http://www.electronics-lab.com/projects/power/011/index.html or is it still the same as this psu?

 

[ante1]

Kain,

With no external divider the 3V battery will show

 

[audioguru2]

Ante,
Heh, heh,
What do you call it that flows into jolly good "accumulators"?
Doesn't the same thing flow out during discharge?
But I have learned that when it is stored in there, it gets a new name.

 

[ante1]

audioguru,

I

 

[Kain]

True, I noticed that the sheme I was reffering to actually does have voltage devider. Hopefully I didn't blow up the thingy ;D.

 

[ante1]

Kain,

Everybody makes mistakes sometimes, don

 

[Capricious]

Ok, my PSU is nearly finished... and what I've tested works fine.
I've used a "Lochrasterplatine" (don't know the English word for the boards with many holes).
Tomorrow I'll use some car lamps to test the maximum current.

I think I will change the R1 resistor to a 4W version. The 1W version has at 3.7V and 0.28A a temperature about 40 C.

I have still one question...
I have a 100uA analog amperemeter. I want to connect it parallel to the circuit. Which resistor I have to use in series to I-meter to get max. deflection at 3A overall current?
I=3A
I(M)=100uA=0.0001A
I(L)=2.9999A
U(M)=U(L)=U
R(M)=?

 

[audioguru2]

Capricious,
R1 is across the unregulated supply voltage. Maybe you mean R2 or R3 gets hot with 3.7V across it.

A current meter is connected in series with the load to measure the current that is flowing in the load (and flowing through the current meter). You simply connect a very low value resistor in series with the load and use your meter to measure its voltage drop.
Instead of adding another resistor to this project, use your meter to measure the voltage across its R7, which is already in series with the load.
With 2.9999A flowing through the 0.47 ohms R7, its voltage drop is 1.41V. For your 100uA meter to have full-scale deflection with 1.41V, its total resistance must be 14,100 ohms. Add a resistor in series with your 100uA meter that is 14,100 minus the meter's resistance. Then connect the meter and its new series resistor across R7.

 

[Capricious]

Capricious,
R1 is across the unregulated supply voltage. Maybe you mean R2 or R3 gets hot with 3.7V across it.

A current meter is connected in series with the load to measure the current that is flowing in the load (and flowing through the current meter). You simply connect a very low value resistor in series with the load and use your meter to measure its voltage drop.

No, it's R1 and it is the output voltage. But I understand that the problem is not the output power. So the temperature will be constant at about 40 degrees C. I think it is too "warm".

Ok, I know that a current meter is connected in series. I will connect it in series but in parallel to the "shunt". And the "shunt" is a piece silver wire on the board from circuit. What I want to do is to split the current in two parallel flows. One with max. 2.9999A and the other with max. 0.0001A which is together the max. output current 3A. Then I can put in the A-meter in series to the low current part.
Now I only need the right resistor value to split it up like that.
Is this not possible?
I have the problem that I do not really know the resistance of the wire. It is too low for measurement and I think the "spezifische Widerstand" (specific resistance?) for silver isn't accurate enough to calculate the resistance of the wire in practice.
But maybe this way is too extreme so there must be a resistor with known value?

 

[audioguru2]

Capricious,
Are we talking about the same circuit?
C7 is with the output voltage of this project across it, not R1. R1 is 2.2K ohms, and has the rectified and filtered supply voltage across it. If you are using a 24VAC transformer, R1 will have about 35VDC across it when the project has no load, and will dissipate only 0.56W. A 1W resistor will be quite warm, but not too hot. Use a 2W resistor if you are worried about its temperature.

Why make a "silver shunt" when R7 makes a perfect shunt that has a known resistance? The current will be split because R7 will pass up to 2.9999A, and your 100uA meter and its series resistor wil pass the remaining 0.0001A.

View attachment 35514

 

[Capricious]

Capricious,
Are we talking about the same circuit?
C7 is with the output voltage of this project across it, not R1.

We are talking about the same circuit ... and you are right but misunderstand me. I've never been talking about voltages across resistors. I've simply measured the output voltage and current of the PSU to know the load.

Thanks for the hint with R7.

My thingy is finished ... some technical data:

It has a max. output power of 73W.
30V => 2.5A
24V => 3.0A
14V => 4.3A => 60W
The max. current is limited to about 4.3A.
The max. output voltage is about 34V.

I try to find someone with an oszi to check the output quality.

View attachment 35516

 

[kobus1]

Hi all
Im new to this forum

Im attempting to build the 30 V supply

2 questions.

1 -> can i put a LED & R right after the diode rectifier bridge in parallel with the rest of the circuit or will the say 20mA reduction(parallel current flowing away) caused by the LED have an effect on the rest of the circuit?? If so any suggestions.

2 -> Has anyone started on the negative supply that can be connected in junction with this circuit with same specifications and which has a common ground? If so where can i find schematics. If not any suggestions on how this can be accomplished.

Thanks

 

[audioguru2]

Capricious,
That's good that you finished it and its wiring looks excellent.
A few questions:
1) Did you use a 24VAC, 3A transformer?
2) What is the total supply voltage of U2 and U3 without a load?
3) How hot does Q2 get with 5V or less output at 3A?
4) How hot do the rectifier diodes get at full current output?
Thanks.

 

[MP1]

Capricious,
It is a very organized and clean looking unit. Very nice work.
Thanks for sharing the results with us.

MP

 

[audioguru2]

Kobus,
Welcome to our forum.

1) You can put an LED "power-on" indicator in series with a 1.5K, 1.5W resistor in parallel with R1/C1. Since it draws 20mA, the output current of the project may be restricted to only 2.98A, instead of 3.00A. The difference will not be noticeable.

2) You could build 2 of this project, each one using its own transformer, and connect them in series for 60V output. If you use their junction point as ground, then its output becomes + and -.

 

[MP1]

Kobus,
In regards to the LED, you could also put it on the primary side of the transformer. Hotwaterwizard has posted a diagram here on the site showing how to do so. Let me know if you cannot find it and I will search.

MP

 

[Capricious]

Capricious,
That's good that you finished it and its wiring looks excellent.
A few questions:
1) Did you use a 24VAC, 3A transformer?

I use the 24V secondary of a 75VA trafo.

2) What is the total supply voltage of U2 and U3 without a load?

Both 41.5V.
Specified max. of TL081 is 36V.
Is there a simple pull out and put in replacement in DIL8 with higher max. ratings?

3) How hot does Q2 get with 5V or less output at 3A?

1.75V 3A => 130 deg. C
4V 4.3A => I switched it off at 175 deg. C
Should buy an heat sink ...

4) How hot do the rectifier diodes get at full current output?

14V 4.3A => 120 deg. C

The 2N3055 gets really hot, too.
But it is below the spec. max. of 200 deg. C.
Nevertheless I should not touch the heat sink at the back of my case. 120 degrees at heat sink are hot enough.

 

[ante1]

Capricious,

The 200 deg.C apply inside (junction) not the surface of the capsule, when it reaches 200 deg.C outside it