Power Supply 0-30V @ 2 A Needed

[HelderS]

030v power supply

Hi!

I bought at a good price two transformers 220V-24V @ 2,5 A. So, I would like to use them in a Dual Power Supply variable wich can go from 0V to 30V and limiting current at 2 A for my lab purposes.

My transformers are not center tapped.
Some Circuit, pcb needed,

Thanks

Hope someone can help.

Helder Silva

 

[Borber]

0-30v variable power supply construction

Look at http://home.planet.nl/~heuve345/electronics/projects/ for Lab Power Supply.

 

[HelderS]

Ok, Borber, I already have seen that power supply, but tell me something, how do I change the circuit, once i don't have that kind of transformer?

My transformers are 24 Volt in secondary, with only two wire.

Thanks anyway...

Helder Silva

 

[Borber]

With such a transformer you can not build 0-30V/2A power supply. Transformer must have more than 30Vrms output if you want 30V at 2A. Transformer enables construction of 0-25V/2A power supply.
For missing secondaries use another low power transformer or if transformer enables, wind up missing secondary.

 

[Gorilla]

With such a transformer you can not build 0-30V/2A power supply. Transformer must have more than 30Vrms output if you want 30V at 2A. Transformer enables construction of 0-25V/2A power supply.
For missing secondaries use another low power transformer or if transformer enables, wind up missing secondary.

?

A 24 VAC transformer will give you 2^0.5 * 24 = 33.9 VDC with a (lossless) bride rectifier and suitable smoothing capacitor. Because of transformer regulation this figure will be even higher under low load.

Of course the bridge isn't lossless (you lose about 1V per diode), but this will still give > 30 VDC on the output.

It depends on your regulator circuit whether this is high enough (where will be a voltage drop over the regulator circuit).

 

[Borber]

It all depends on the type of transformer, is it toroid or EI core. I suspected it is EI core.

 

[Gorilla]

It all depends on the type of transformer, is it toroid or EI core. I suspected it is EI core.

No, it does not. Only the regulation often is a bit better on toroidal cores. Otherwise the calculations are exactly the same.

 

[HelderS]

Hell, again, I really would like you to help me how to substitute the transformer used in this circuit:

h**p://home.planet.nl/~heuve345/electronics/projects/

By those I have, because my transformer doesn't have two windings in the secondary. And by the way, my transformers are EI core, not toroidal.


Thanks, Helder Silva

 

[Gorilla]

For that particular design I would use a small transformer for the 20 VAC winding in the schematic. I think that is the easiest. (I see the same recommendation in section 10.4 of that page.)

As an alternative design, something like this may be interesting:
https://www.electronics-lab.com/projects/power/003/

Please note that I haven't built the designs discussed here, so I don't know of any flaws they may have...

Anyway, happy soldering.

 

[Borber]

For start I suggest an experiment. Build rectifier for PS. Use smoothing capacitor at least 4.7mF or greater. Connect transformer and load (with propper resistor) rectifier with 2A. Measure DC voltage. It should be at least 34V or more. Bottom ripple peaks should be greater than 33V. If test is OK then you can use your transformer as planned. For missing secondary 20V use small, 20-25V transformer.

 

[HelderS]

Hi!

First, thanks a lot Gorilla, for the electronic-lab design PS, although I've already seen it, I didn't decide for that design.
Second I want to apologize because of my persistence in this, but...
But I want to know if I can have any problems, once de design showed in the electronics-lab site use a transformer that can source a current of 3 A, but my transformer is 220V/24V - 60VA, wich we can say that it can source a maximum of 2,5 A maximum, am I right? My question is:

Am I going to have any problems because of this difference, or just have to be careful, to never apply a load that ask's for more than 2,5 A???

Can I put my transformer in the circuit without any changes?

By the way, I think this circuit is great, it is very well explained, but uses a transformer that here, in Portugal, it is a little bit expensive, and that's why I want to use my transf's of 2,5 A instead of buying the expensive ones of 3 A... ;-)

Regards, Helder Silva

 

[Gorilla]

No problem.

A transformer will not explode immediately when you overload it a bit, so I wouldn't worry too much about that. 60 VA for your transformer would indeed mean 2.5 A of output capability.

Besides the power supply has a current limit built in, so when you short circuit the output terminals, the current will not exceed the set limit. So no problems there as well.

I do agree with the experiment Borber suggests. With that experiment you'll get an idea about the actual performance of your transformer. For best insight, use an oscilloscope to see the capacitor waveform change when you apply a load.