0-30 VDC Stabilized Power Supply 0.002-3 A

[CBETO3AP]

Limited by the 24V / 300W transformer this will give out 24 or 20V-10A.
I bought fake China MC34071 and now I'm doing tests with UA741, the truth is that there are going pretty well. I expect a TLE2141AIP and if it is the original'll ask the rest. What I will possibly do after testing is remaking the scheme to put LM311, open collector 50V out at currents as 50mA. This and a more powerful transformer allow me more output. The use of such power is for example the CNC machine cutting expanded polystyrene with hot wire.

p.p. By my calculations with 1 or 2 driver transistors BD140 is enough.

View attachment LM311-n.pdf

 

[audioguru2]

The peak voltage from a 24VAC transformer is 34V. It charges the main filter capacitor to this peak voltage and heats the load, rectifiers, series pass transistors, driver transistors and current sensing resistor. Then this 300W transformer is at its max current when the DC output current is 8.8A.

The inputs of some 741 opamps fail to work when their voltage is within 4V from the positive or negative supply so the 1.3V from the two diodes is not enough. Use the negative -5.6V supply in the original circuit.

The LM311 is a comparator, not an opamp. It its voltage gain is 200,000 times and it oscillates if it has negative feedback.

Maybe you calculated with "typical" current gain. Then you must buy a few hundred transistors, test their gain and use only the best ones. We usually design circuits so that all of them work well even if the transistors have minimum specs.

We do not use "China" transistors or ICs. Instead we use Name Brand genuine parts.

 

[CBETO3AP]

BD140 driver emiter current tested - 85mA max at 10A load  8) (200mA expected)

The peak voltage of this toroid transformer (filtered, no load) - 38v, i modifed the secondary from 12v/25A to 24V/12.5A

741 opamps is on negative -5.6V (4.7V in my case) supply, ofcorce

The LM311 is a comparator I know, will see...

"Then you must buy a few hundred transistors, test their gain and use only the best ones" I usually buy scrap and test

"Maybe you calculated with "typical" current gain" nop, i calculate well and have some luck with the gain

 

[CBETO3AP]

measured
24V/11A - 0.003V drop, for now

 

[audioguru2]

You got excellent voltage regulation.

 

[CBETO3AP]

Yes, I have been forced to change the shunt resistor. Now this place metal shunt 10A / 0.1V.Thus I am saving me 1.4V. Plus something like 0.5V to have 10 emiter resistor in parallel. Low Vdrop is because the shunt is bolted directly to the output. And the sensing cable to the out.

 

[OZ6YM]

This print-layout has a "to thin" returnline for MAX power 3 Amp.

You have to make a better layout, or make it stronger with a 0.6 m.m. wire, extra, between the end-point.

A fine Lab. Supply, I have made 3 of them until now, working perfekt!!
Good luck.

 

[audioguru2]

OZ6YM,

Which version of this project did you make:

1) The original Greek kit with many overloaded parts and it cannot produce 30V at 3A?

2) The improved circuit in the forums?

3) The Chinese copy of the Greek kit?

 

[OZ6YM]

I made nr. 2.
My comment is for the print on the Picture...

 

[audioguru2]

I do not like to look at a pcb that has nothing labelled.

 

[OZ6YM]

I am talking about this project http://www.electronics-lab.com/project/0-30v-laboratory-power-supply/
Look at the PCB...
The return-line for MINUS or the GROUND-WIRE is to thin...
Make it bigger to take 3 Amp at 30 Volt.

That is my comment....
...what a guru...

 

[CBETO3AP]

Hi
I work on Hristo PCB, member of this community.

http://diyfan.blogspot.com.es/2012/02/adjustable-lab-power-supply.html

By changing the shunt, as I feared, the current regulation is very slow, now I'm looking solution without increasing the shunt.

No load through the PCB and is cut so.

 

[OZ6YM]

Ohh.. Yes... This i much better... Thanks...
de OZ6YM, Palle

 

[audioguru2]

I am talking about this project http://www.electronics-lab.com/project/0-30v-laboratory-power-supply/
Look at the PCB...
The return-line for MINUS or the GROUND-WIRE is to thin...
Make it bigger to take 3 Amp at 30 Volt.

That is my comment....
...what a guru...

I have never seen this defective new copy of the original project before. It has all the errors of the original project and added some new errors. The parts numbering has been changed so it is difficult to say that a resistor is 1/4W but must be 1W and its value should be xxx. Many parts are overloaded and the opamps have a total supply voltage too high for them.

 

[CBETO3AP]

woala

 

[CBETO3AP]

 

[Mayoral]

Hi,

Audioguru, would you mind point out where can I find the improved schematic of the Chinese (banggood) and  Greek power supply kit?

I have one of those kits and I would not mind expending few dollars to improve it ... or I may  have the components in the shack.

Thanks!

 

[audioguru2]

Many parts are changed or added so a new pcb is needed.

Here are the latest parts list and schematic for the improved version:

 

[Mayoral]

Thank you very much! I see what you mean, it is not only changing few component.... I have almost every component I may make it next new project ! 

Since I was curious I was digging the forums and the web an I came across a very similar schematics. In this one, Q1, R13 and R14 have been included back to "mitigate transient surge issue". Since you look pretty knowledgeable (and my knowledge that does not go that far), do you have an opinion in this incorporation? Will it affect the overall performance of the supply?

Thanks in advance again for your time and comments.

 

[audioguru2]

I did not look into the transient that might occur when the power is turned on or off. Q1 was originally placed to short the output of opamp U2 because the old TL081 original opamps had a problem called "Opamp Phase Inversion" when an input voltage became too close to the negative supply voltage when the negative supply collapsed first when the power was turned off. It would have caused the output of the opamp U2 to suddenly go as high as it can which is bad for the speaker. The new opamps do not have this problem.

You can add Q1 and its resistors if you want.