redwire

0-30V Stabilized Power Supply

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I have doubt on transformer that the current ratting mentioned in my transformer is correct.
So I need to reconfirm it by testing.
I want to know the correct testing procedure of transformer.
For example explain with a 30V/2A.

Please help me to find out.

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I have one small very cheap Chinese AC/DC adapter that has no safety certification markings and is rated at 9VDC/100mA. It produces a little more than 18VDC with no load and gets hot. With a load of 100mA its output is 8V with a lot of AC ripple and it is dangerously hot so I do not use it.

An overloaded transformer gets hot. A transformer with safe ratings gets pretty warm but not hot. Simply find a safe name-brand transformer with the ratings you need and compare its size with the unknown transformer. If the unknown transformer is smaller then it might be overloaded at its rating.

A 2A load on a 30VAC transformer is resistance that is 30V/2A= 15 ohms at 30V x 2A= 60W. If you find this resistor then load it on the transformer and feel if the transformer gets hot. 

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Shall I use TL081 instead of TLE2141 or MC34071

What are the changes need.

The original circuit used TL081 opamps. Its maximum supply voltage is only 36V and it needs a negative supply so it cannot produce +30V without risking damaging it with a supply voltage too high for it. It also has a problem called Opamp Phase Inversion that causes its output to go high when its negative supply voltage drops too low when the power is turned off. So transistor Q1 was added to short its output to ground when the power was turned off.

The MC34071 is not available anymore in a DIP package. It and the TLE2141 have a maximum supply of 44V and they do not need a negative supply so they work fine producing an output of +30V.

If you use TL081 opamps then they need a -5.6V negative supply as shown in the original circuit. But the positive supply in the original circuit was too high for them since it used a 24V AC transformer and without a load the positive supply was about +34V or more, then the opamps are powered with a total of 40V or more. If the transformer is 20V then without a load the positive supply will be about +28 but then the maximum output from the project will be only about +20V if you are lucky. 

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hello audioguru! i am a newbie in electronics. i want to know that why the opamps like CA3140, CA3240 etc do not work at all in this circuit though they are capable of operating with single supply. i know they have a max operating voltage of only 36 volts but still if i require a low o/p voltage from the supply, the circuit does'nt work at all with these opamps.

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hello audioguru! i am a newbie in electronics. i want to know that why the opamps like CA3140, CA3240 etc do not work at all in this circuit though they are capable of operating with single supply. i know they have a max operating voltage of only 36 volts but still if i require a low o/p voltage from the supply, the circuit does'nt work at all with these opamps.

The circuit might work with CA3140 opamps if the supply voltage is reduced by using a custom made 22V AC transformer but then the maximum output will be only about +22.5V DC at 3A if you are lucky. You might need to re-calculate a lower value many of its resistors so that the currents in the circuit are adequate. 

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Guest OO7O

Hi everyone.

I Draw this circuit with PROTEUS-ISIS but cant simulate because a error, can someone help me to find the problem pls.

Final.zip

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I Draw this circuit with PROTEUS-ISIS but cant simulate because a error, can someone help me to find the problem pls.

Very few people use your Proteus program. For us to see if there is something wrong with your schematic then please post it as a normal PNG file type that everybody can see.

Maybe you can "copy screen" then paste the schematic into a picture viewer like Paint program then save it as a PNG file type.

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Hi again :) There is the circuit in ".png" Format.

hi James Bond O ,
you may have to indicate the  error image and  to members.
Otherwise, getting some error message doesn't appear a good way of reporting.
you can capture the screen and  upload as  .png.
it helps  proteous gurus to study and comment.

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Guest thiagoas

Would NE5532 work in this circuit? I have no LME2141 in my country.

I also simulate the circuit in proteus, and it works, just have to change SPICE options for better convergence.

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Would NE5532 work in this circuit? I have no LME2141 in my country.

The LME2141 is not available anywhere because nobody makes it. You have the wrong letters.

The TLE2141 is made by the world's largest semiconductor manufacturer, Texas Instruments, and should be available everywhere.
It was selected because its maximum supply is 44V, its inputs work at 0V without a negative supply and its output goes down to almost 0V.

The NE5532 also has a maximum 44V supply but its inputs do not work below 3V and its output does not go below 2V so the circuit and spec's for the project must be changed for it to be used. 

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Guest thiagoas

Ops, sorry, I was thinking in another piece at the time.  :P

Not even farnell have this one in DIP socket here.

I will have to find something similar to this.


Edit.
I requested samples from TI, let's see what I get. :D

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Ops, sorry, I was thinking in another piece at the time.  :P

Not even farnell have this one in DIP socket here.

I will have to find something similar to this.




Then build it with the SOIC 8 package.  You will have a choice between  the TLE2141 or the MC34071.

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Guest rvendrame

Hello all,

That's a very nice initiative + community + development here in this post.  Congratulations to all of you!!!

I will start to build my PS soon, and I have a quick question.  In case I make two of them, as liquibyte did  ---  Does the short-circuit protection will still working across the + 0 - outputs?  Or will it blow up in case of short-circuit between the + and - output, or even between the +/- and the zero?

Thanks
Ricardo

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When you make two completely separate supplies, one can be 0V to +30V and the other can be 0V to -30V. If one or both outputs are shorted to 0v then that supply will safely regulate its output current to the amount of current that is set at.
The supplies have no protection from an output voltage or current of the wrong polarity so if +30V is shorted to -30V then one or both supplies might blow up.

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Guest rvendrame

When you make two completely separate supplies, one can be 0V to +30V and the other can be 0V to -30V. If one or both outputs are shorted to 0v then that supply will safely regulate its output current to the amount of current that is set at.
The supplies have no protection from an output voltage or current of the wrong polarity so if +30V is shorted to -30V then one or both supplies might blow up.


Thanks.  In that regard,  a dual supply with a central-tap transformer (like this one http://www.electronics-lab.com/projects/power/030/index.html) would be more 'fail proof'?  Or will blowup / smoke exactly like?  My goal is to work with audio in hobby projects (preamps, amplifiers etc)


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I have never seen a power audio amplifier that needs a regulated dual-polarity supply. They use a center-tapped transformer, bridge rectifier and two big filter capacitors.

If you build two of this project and power them from a center-tapped transformer, joining the projects at the tap then I think the negative supply in each project will not work properly.

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Guest rvendrame

I have never seen a power audio amplifier that needs a regulated dual-polarity supply. They use a center-tapped transformer, bridge rectifier and two big filter capacitors.

If you build two of this project and power them from a center-tapped transformer, joining the projects at the tap then I think the negative supply in each project will not work properly.


Sorry, I want a dual PS to use in the bench.  I've build some power amplifiers and might use the PS just for testing them during repair.  I'm just trying to find one more 'fail proof' to short circuits, nothing else.

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A transformer with a dual 28V secondary winding will do.

D11 will protect the output in case of reverse polarity.

Another diode can be placed with the anode on +Vout and the cathode to the positive of the bridge rectifier to protect against brief positive high voltage spikes entering +V. You could also consider a transorb across the bridge rectifier to protect against transients.

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Guest thiagoas

What are the parameters I should look in the opamp selection? I am a bit confused looking the datasheets.


Now I find MC34074 here, It is good?

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The corrected and improved circuit used MC34071 or uses TLE2141 SINGLE opamps. They have a case that has 8 pins. The single opamps have 2 of the pins for the input offset voltage adjustment trimpot used on opamp U2. The MC34071 single opamp is not available anymore as a through holes type and is now only available as a surface-mount type.

If you use the MC34074 QUAD opamp (it has 4 opamps in its 14 pins case) then all the pins numbers must be changed on the schematic, a different pcb must be designed and it will probably overheat. Its opamps do not have input offset voltage adjustment pins.

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Guest thiagoas

I will be using 3 of them, to avoid overheat.

Offset adjustment is something I can live without?

Thanks for the help.

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You must properly disable the opamps you will not be using. Even though they are not used their idle current causes heating in opamp U2 which might be too high.

The opamps in an MC34074 have a maximum input offset voltage of 5mV so when the voltage setting pot of this project is set to zero volts, the gain of opamp U2 will cause the output to be from -15.4mV to +15.4mV.

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