0-30 Vdc Stabilized Power Supply

[Sallala1]

Ok, then Q1 emitter go back to 0V. I will make the modification. Just a new hole  :-X
I made a summarize about the project on my homepage:
http://sala.sallala.hu/elektronika/szab_dc_tapegyseg/tapegyseg.html
This time only for my language, (Hungarian)
I will update this.

negative supply quickly disappears

And then what about the suggested 10..47uF capacitor paralell to D7 ?
When the mains turns off, and there is a capacitor, -5V will go down slowly, not quickly. Isn't it? It's not a problem?


Other question:
Can I charge NiMH and NiCd batteryes with my powersupply?

NiCd and NiMH bateryes doesn't need any special thing, just constant current, when you charge it in slow charge mode. (With 1/10C, 14h)

Can the batteryes damage my supply? For example, when I stay connected it to the output, and switch off the supply? Or other reason?

 

[Sallala1]

Can I list all of the posts on one page in this topic somehow?

 

[audioguru2]

And then what about the suggested 10..47uF capacitor parallel to D7 ?
When the mains turns off, and there is a capacitor, -5V will go down slowly, not quickly. Isn't it? It's not a problem?

C3 is only 47uF and will discharge a lot quicker than the huge main positive filter cap.
The problem is caused when the negative supply disappears then U2 loses its negative supply, causing its output voltage to rise if it was fairly low.

 

[Sallala1]

Audioguru: thank you for the quick answers again!

- Yes, I'm thought to use a series diode too! (But I'm sure now because you confirm)

- I think, timer doesn't neccesarry, only once.

1. Just charge the battery pack, with full voltage and adjusted current according to the battery.
2. Measure the fully charged battery's voltage
3. Next time, adjust the voltage to the measured in the 2. point. The constant current charging automatically "switches" to something like drop charging at the end.

Somebody suggested this method. It's right?

(Of course, this method not the same as use a timer. Just for start charging in the afternoon, and stop tomorrow morning.. And sometimes need to repeat to measure the fully loaded voltage)

 

[audioguru2]

I just use a wall-wart DC supply and a resistor to charge my batteries overnight. A regulator's current remains constant even when the battery is fully charged, causing overcharging. My resistor has less voltage across it as the battery reaches full charge so overcharging isn't as much a problem.

 

[Sallala1]

A regulator's current remains constant even when the battery is fully charged, causing overcharging.

If I use a 4,8V battery pack for example, and set the voltage to 5,2V the curent can't remain constant. A fully charged 4,8V NiMH batterypack's voltage about 5,2V. No voltage difference between the supply and the battery, -> no current isn't it?

I use several type of batteries, I need the adjustable curent, so I'm happy, that I have an adjustable current batery charger too

 

[Sallala1]

Yes, a fairly high current would flow into the output of U2. Use a series diode for isolation.

Hey, it's neccesarry for everyone isn't it?
For example, if I put a circuit with a bigger puffer condensator on it's input, that can damage the power supply if the mains off. Not?

I remember, on some three terminal stabilizer IC's manufacturer suggest a bypass diode between the leg 1 and 3. So the puffer condensator can discharge over the diode and the transformer.

What can I waste, if I place permanently a series diode into tha supply's case?
0,6V voltage drop, 3W additional dissipation. Any other thing? Because who's care about that 600mV if it can be save your circuit?

 

[audioguru2]

If I use a 4,8V battery pack for example, and set the voltage to 5,2V the curent can't remain constant. A fully charged 4,8V NiMH batterypack's voltage about 5,2V. No voltage difference between the supply and the battery, -> no current isn't it?

My Energizer Ni-MH cells reach 1.4V when I think they are fully charged and the voltage keeps climbing.
In the case for your 4.8V battery it will be about 5.6V.View attachment 37631

 

[audioguru2]

0,6V voltage drop, 3W additional dissipation. Any other thing? Because who's care about that 600mV if it can be save your circuit?

You will have a lot more than only 0.6V on a diode carrying 3A, unless it is a Schottly.
If it is external to the circuit then it will ruin the superb voltage regulation. You could protect the supply with a diode inside the feedback loop like this:
EDIT -View attachment 37633

 

[Sallala1]

My Energizer Ni-MH cells reach 1.4V when I think they are fully charged and the voltage keeps climbing.

While the voltage keeps climbing, your batteryes doesn't fully charged. See it's technical manual! When the voltage stops climbing, and start decrease about a few millivolts, at this point your batteryes fully charged.

The newer -dV chargers stops charging at this point too.

 

[Sallala1]

Audioguru! I can't see your pictures attached!

 

[Spagbol]

Presumably output taken from top of C7 in new circuit rather than emitter of Q4, just to clarify.

 

[audioguru2]

I think it would be very difficult to set the proper voltage of this supply to the hiccup point in the charging voltage curve of a battery. If you set the voltage slightly too high, the battery will continue over-charging.

I forgot to move the supply output connection on my previous post. I've corrected it.

View attachment 37632

 

[audioguru2]

Audioguru! I can't see your pictures attached!

Doesn't your viewer show PNG? Here they are as GIF:View attachment 37634

View attachment 37635

 

[Sallala1]

Audioguru:
My browser (Firefox) can show PNG files. I don't know, what was the problem. Now I can see the images twice... Thank you anyway!
I will buy a high current shotky diode, and will build into the pcb or inside to the supply's case.

OK, I understand, what you tell about the batteries.

 

[Sallala1]

I have got another problem:

- My fuse (5A) at the secunder side of the transformer glowed.
- T3 went out
- Fuse at the output (5A) desn't damaged

I used a 1,5-3Ohm load at 3-4V at 3A. (Cutting polystirol foam with hot wire) I use only one 2n3055 at this time, with heatsink and a big fan. This worked with no poblem.

When I change the foam, I just turn the voltage and the current potentiometer down. (Or maybe just the curent pot?) But later, when I like to continoue the cutting see the problem.

What happend? Why the fuseage burnt?

 

[audioguru2]

Hi Sallala,
My Microsoft IE6 browser opens pics using my ACDSee viewing program that shows many file types.

- My fuse (5A) at the secunder side of the transformer glowed.

See second-breakdown below.

- T3 went out

What is T3? What happened? (shorted or open)

- Fuse at the output (5A) desn't damaged

If you have a fuse for the output, it should be inside the negative feedback loop to keep the good voltage regulation.

I use only one 2n3055 at this time, with heatsink and a big fan. This worked with no problem.

Maybe it had second-breakdown with such a high strain on it. I bet its chip 's temp exceeded 200 degrees C and it began melting. :'(

 

[Sallala1]

Audioguru:
Something wrong in my workplace's internet access. I can't see any pictures attached to the forum at work. At home everíthing fine  ???
But it's doesn't matter.

I'm sorry: T3=Q3
(In my country, Transistor=T)

Huhh, I checked it, but I don't remember exactly. It wasn't conduct between E-B or B-C. But I'm sure: the LED was bright always. Even if the supply was in constant voltage mode.

If you have a fuse for the output, it should be inside the negative feedback loop to keep the good voltage regulation.

Hmm, of course. As the diode, that you drawed. I must to modify the PCB.
But this is not makes a problem, if the fuse at the output glowed, and it's in the negative feedback?

Maybe it had second-breakdown with such a high strain on it. I bet its chip 's temp exceeded 200 degrees C and it began melting

But how can it's temp exceed 200 degress, when I turned down the votlage potentiometer?

As I wrote, while I working, tha supply was good, and Q2 wasn't too hot.
Then I leave the 2Ohm load at the output, but turned down the voltage potetntiometer.

When I go back, fuse at the bridge rectifier burned. 

 

[audioguru2]

T3=Q3

A BC557 operates well within its ratings here. You must have had a weak one.

But how can it's temp exceed 200 degress, when I turned down the votlage potentiometer?

With a positive unregulated supply of 40V and 6V on the output at 3A a single 2N3055 must dissipate 102W. It is rated to dissipate 115W when its case is held at 25 degrees C somehow. If yours was only warm then it was too hot inside. Beginning to melt.

As I wrote, while I working, tha supply was good, and Q2 wasn't too hot.
Then I leave the 2Ohm load at the output, but turned down the voltage potetntiometer.

When I go back, fuse at the bridge rectifier burned.

When a power transistor gets too hot inside, it leaks a lot of current that turns it on harder, making its output voltage to rise, making more heat..... Thermal runaway. 5A into 2 ohms is only 10V. The output probably rose higher, causing more than 5A and blowing the input fuse. A single 2N3055 is not enough for this project.

 

[smokyLED]

where can i buy the pcb from? it is hard to make it myself, since i hae no where to dispose of the chemicals.

what can be used to replace the 2n2219 transistor, and cna the TL081 be replace with a TL071