0-30V Stabilized Power Supply

[mauriciovargas]

Thanks audioguru.

So, I can use any transformer on the project, but it will work at a limited power? All I need to do is change R7 and everything is gonna be OK? What more do I need to change?

 

[audioguru2]

So, I can use any transformer on the project, but it will work at a limited power? All I need to do is change R7 and everything is gonna be OK? What more do I need to change?

I don't know if you are making the original faulty circuit or which improved circuit.
Since your transformer is so small then you can make a simpler low power circuit.

 

[mauriciovargas]

Audiogurus, I'm doing the improved one. I did the original and now I have all the components waiting for something. This is why I want to do the good one. Actually my idea is use a transformer with 2A or around it. So, will it work?

Another question: Can I use a smaller capacitor than that ones with 6.800 uF? They're very expensive and if I use a smaller transformer I think they'll be unnecessary.

Thanks again.

 

[Enforcer83]

Mauriciovargas,

You can use a smaller capacitor,  but you will induce a greater ripple voltage into the system.  There is an equation that you can use to determine the ideal value for a capacitor given the desired ripple voltage and system current.  However, this equation eludes me at the moment.  Try doing a search for voltage ripple in google.

I will update when I find the equation.

 

[audioguru2]

A 2A transformer is also too small. Then the max current from the project will be only 1.4A DC.

I have a graph that shows the amount of p-p ripple in a full-wave rectifier with a 60Hz mains and with various sizes of filter capacitors:

View attachment 41216

 

[mauriciovargas]

Thanks audiogoru and Enforcer83.

I already know the ripple problem with a smaller capacitor and a big current. But,what I meant to say, is that I don't need more than 1 A. So, can I use this project (audiogoru's 3A version) with my little transformer (24VAC / 435 mA) and a smaller capacitor, like 3300 uF? What more I need to change in the project?

 

[audioguru2]

With a max output of only 300mA and a max voltage of only 25VDC then the two 2N3055 transistors can be a single TIP31 transistor on a heatsink that is not very big.

 

[mauriciovargas]

OK. I already have the 2N3055 so I'll use them. My idea is use the little transformer just for a while. When I can afford, I'll buy a good transformer and the 12.000 uF capacitor.

Thanks for everything.

 

[Enforcer83]

Ha,

Audioguru's pic has the formula I was looking for.

 

[mauriciovargas]

Hi guys...

I was thinking better, so I won't do this project right now. Do you know a good project for a small power supply? Like 0~24v 1A with current protection or something like that?

Thank you

 

[audioguru2]

There are many cheap weak little power supply projects on the internet. Some work but many don't.

 

[mauriciovargas]

That's my fear. It's why I came here and asked you. I found a lot of projects using LM317 but I didn't find a good one. Don't you know anyone?

 

[audioguru2]

I found a lot of projects using LM317 but I didn't find a good one.

The LM317 reduces its max output current to only 150mA when its input to output voltage is high.
An LM317 does not have adjustable current regulation. Instead it has simple abrupt current limiting at 1.5A to 2.2A when the input to output voltage is 15V or less.
An LM317's output does not go down to zero volts without an additional negative 1.2V regulated supply.

 

[albal59]

Hello

I'am french and i speak a basic english
I have a problem with my 0-30V Stabilized Power Supply.
The problem appeared when i use this power supply for charging lipo battery
The problem is a voltage variation is between Approximately 10V to 33V and the intensity variation is broken.
Have you got ideas of my problem?

Florent

 

[audioguru2]

The output voltage should not increase if it is set to one voltage.
What is "the intensity variation is broken"?

 

[albal59]

Excuse me, the intensity variation is the current control
The problem is under 10V there is no voltage variation.

Florent

 

[nemeszoli]

Hi everyone, I finished building this power supply with the three 2N3055 transistors version, but I couldn`t find 0,27/10W ohm resistor for R7 only 0,22 ohm but it works really nice, I measured the output current in short circuit it is adjustable from 0 to 11,38A  ;D, but with the current setting trimmer it can be calibrated to a smaller output current, the minimum output voltage is about 50mV cannot be adjusted with RV1 not even if I replaced C7 with a tantalum capacitor. I had the same problem as some other guys, when the current limit pot. is turned to min. the current limit led lights up,  I thougth if U3 is a comaparator on U3 pin 3 is the reference voltage for the current control, on pin 2 the voltage without a load was 10.6 mV, and when the current control pot. is at min. on U3 pin 3, I had 8.4 mV (the compared value was bigger than the reference value)  from this voltage difference the led was lighting up, so I replaced the 33ohm R17 to 100ohm  ;D (I don`t think I have to change anything else, correct me if I am wrong) so in this case the voltage on U3 pin 3 with the current set. pot. at min. is 11.4 mV finaly the led does not light up when the current set. pot. is at min. , but in my case from the voltage difference between pin 2 and 3 on U3 the minimum adjustable current is about 4 mA, which I don`t mind. I designed a board in eagle and I would like to make a 7 segment volt and ampere meter using PIC, I`ll upload some pictures of my project soon...

 

[audioguru2]

Hi Nemeszoli,
How can pin 2 of U3 have a voltage when there is no load on the project? Pin 2 is connected to 0V by R7 that has no current in it. Maybe you have leakage current in your 0V printed wire.

If C7 has "dielectric absorption" then there will be an output voltage when the voltage pot is at minimum. The capacitor type with the lowest dielectric absortion is a metallized plastic film type.

Which opamps did you use? 

 

[albal59]

Hi

The control voltage on output of U2 is OK but the current control is not ok.
Have you got an idea of my problem?

Florent

 

[audioguru2]

Hi

The control voltage on output of U2 is OK but the current control is not ok.
Have you got an idea of my problem?

Florent

What is the problem?
The output voltage is supposed to be regulated when the current regulation is not reducing the output voltage.
Does the warning LED for the current regulator light up when there is no load?