0-30 Vdc Stabilized Power Supply

[audioguru2]

my voltage out of u2 was always 17 volts now when i fixed the bad trace i can adjust up to 17 volts only. i get a max voltage of 34 volts between ground and positive rails i get a max at pin6 of u2 of 34 volts but only get 17 at output.

The driver and output transistors are simple emitter-followers so their output voltage should be 1.2V to 2V less than the voltage at the output pin 6 of U2. Since your output voltage is much too low then either your transistors are connected backwards or they are blown up.

does a heatsnk on transisters have to be grounded?

The collectors of the driver and output transistors are both connected to +34VDC. They are also connected to their metal case so they must be insulated with thermally-conductive insulators from the heatsink or the heatsink must be insulated from 0V.

 

[tolcty]

Hi guys. I have a few questions. Can I use 2n3055 instead tip3055? And how do I connect two such devices to receive power supply positive and negative voltage? If you can please give a picture.

 

[audioguru2]

Hi guys. I have a few questions. Can I use 2n3055 instead tip3055? And how do I connect two such devices to receive power supply positive and negative voltage? If you can please give a picture.

The latest parts list for the improved circuit shows real 2N3055 transistors in a metal case, not little TIP3055 transistors that might melt.

The transistors have only a positive supply, no negative supply. Opamp U3 has a negative supply.

Maybe you are looking at the original project that is full of overloaded parts and does not produce 30V at 3A.

Maybe you want to make a 0V to 30V positive supply and a 0V to 30V negative supply?

 

[tolcty]

Maybe you want to make a 0V to 30V positive supply and a 0V to 30V negative supply?

Yes. I want to make a power supply for both positive and negative voltage. To be able to connect the amplifier circuits for testing and tuning. This scheme I liked it because it has a current limit that is very important. But unfortunately it is only a positive voltage.

The latest parts list for the improved circuit shows real 2N3055 transistors in a metal case, not little TIP3055 transistors that might melt.

Sorry, have not looked at the parts list. now look :-[

 

[audioguru2]

You can easily make a negative supply from a second circuit that is completely separate from the first positive circuit (also a separate transformer winding) if you use its positive output as the 0V and use its 0V as the negative output voltage.

 

[tolcty]

And so you can connect?

 

[audioguru2]

And so you can connect?

No.
The positive input (ground) to the negative regulator is shorted to its positive output (ground).

The negative regulator needs a transformer winding, bridge rectifier and filter capacitor that are completely separate from the circuit of the positive regulator. 

 

[tolcty]

And so right? I am a beginner in electronics so I do not understand some things. And my bad English ...

 

[audioguru2]

And so right?

Yes. Your new circuit is correct.

 

[tolcty]

This is great. Now I can make a new power supply. Thank you for the scheme. I hope that no more questions. No problems there. What is TB4? What is a shunt resistor should I put it?

 

[audioguru2]

What is TB4? What is a shunt resistor should I put it?

"TB4" is not on my parts list and not on my schematic. Where did you see it?
A shunt resistor is used in a current-meter.

 

[tolcty]

Where did you see it?

Reply # 1602
  I downloaded the file. There is a scheme and PCB. Now I realize that TB4 is output for current-meter.

 

[audioguru2]

In reply #1602 you are looking at PicMaster's schematic and pcb. His "shunt resistor" is R7 on all the other schematics and senses the output current. It is 0.47 ohms for 3A max and is 0.27 ohms for 5A max. It can also be used as the shunt resistor in a current meter.

 

[tolcty]

Thank you! No more questions. I will start the construction.

 

[fikic]

Hy guys. I've made a little mistake, when I connected a diode bridge. I accidentally swapped - and AC connector. I then saw some smoke and litle bang. On the output of psu, I now only get constant 33V and I can't regulate it. I thought, that opamps may be the reason and I replaced them, but this is not the case. So, what should I check next. What could happen in that case, when you swap - and AC of rectifier.

PS.: PSU worked perfect before that.

 

[audioguru2]

Hy guys. I've made a little mistake, when I connected a diode bridge. I accidentally swapped - and AC connector. I then saw some smoke and litle bang. On the output of psu, I now only get constant 33V and I can't regulate it. I thought, that opamps may be the reason and I replaced them, but this is not the case. So, what should I check next. What could happen in that case, when you swap - and AC of rectifier.

PS.: PSU worked perfect before that.

Your mistake might have damaged the BD139 driver transistor or the 2N3055 output transistors.

 

[fikic]

I replaced BD139 with BD135, becouse I don't have any BD139 left. Is this ok? How can I check 2N3055 transistors - I don't have transistor tester. Should one conduct between base and emmiter and between collector and emittor? If not, where it should?

 

[audioguru2]

I replaced BD139 with BD135, becouse I don't have any BD139 left. Is this ok?

The unregulated positive voltage is  higher than 42V (when there is no load) which is very close to the max allowed voltage of 45V for a BD135. A BD139 is rated at 100V.

How can I check 2N3055 transistors - I don't have transistor tester. Should one conduct between base and emmiter and between collector and emittor? If not, where it should?

A transistor is measured like two diodes. The base-emitter is one diode and the base-collector is the other diode. When a diode is forward-biased then it should conduct. With reverse bias then a diode should not conduct. But some ohm-meters use a voltage that is too small to turn on a diode.
A transistor should not conduct between collector and emitter unless it has base-emitter current to turn it on.
Since your output is always 33V then the 2N3055 transistors are probably shorted from collector to emitter.

 

[fikic]

Ok, so Ohm-meter must show nothing between collector and emmitter of 2n3055, becouse it's infinite resistance? Mine show something between 100 and 200 kOhm (on both of them, on one even less).

 

[fikic]

I changed output transistors and it works. I get maximum 24V on output. Is this ok?