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0-30 Vdc Stabilized Power Supply


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See my reply in your other post for a discussion about heatsinks. Maybe you need to add an additional output transistor or two.

Yet another question to you gurus ::)

Have a look at the attached image ... is this circuit for the 2nd transistor correct?
Which values should R23 and R24 have? Should I use one variable resistor?



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You can use the 12V secondary for a 12VDC fan if you use 4 rectifiers. Put a filter cap and a series resistor to the fan if it buzzes.

Thermal grease is about 0.7 Kelvin/W. I don't know which insulator that you are using, it should be rated.

For the project to operate with 12VAC, the negative supply must be changed. I calculated values that will work on 12VAC and 24VAC:
1) R2= 39 ohms/2W
2) R3= 100 ohms/1W
3) C2 and C3= 100uF/50V
4) D7= 5.6V/1W zener diode.

Add a 10K-1/4W resistor in series (the high side) with the 10K voltage-adjust pot P1 for low output voltages and add it in series (the low side) with the pot for high output voltages. The voltage switch will need 2 poles to do this, plus another 1 or 2 poles to change the transformer secondary.

Your 2nd 2N3055 and the emitter resistors are drawn correctly. Use 0.1 ohms, 1W for each.

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I have also posted this reply on the modification thread.
would just like a reply if this could be a working model.

otherwise i'm starting building tommorow and see what i end up with.
so far it seems that it will work.

after 2 hours of posts reading this is what i have for mods

Transformer :
30VAC @ 5A = 30*5*1.5 = 225VA stepdown transformer

Resistors :
R2 & R3 --> 1/2 W
R7 --> 10 W
R1 --> 3 W

Caps :
C1 --> 4700 uF (prefer 10000 uF) @ 50V

Diodes :
Diodebridge : D1 - 4 --> Single chip diode bridge @ 8-10 A

P1 --> many turns (10)
P2 --> Cermet single turn

OPA445 @ 100V

Transistors :
Q1 --> stays same BC548/547
Q2 --> TIP29/TIP30 (R15 becomes 100ohm)
--> somebody also mentioned BD139/137??
Q3 --> Stays same BC557/BC327
Q4 --> stays same?? 2N3055

Heatsinks :
Q2 & Q4 gets TO-220 package heatsink

could someone please verify??
could this possibly be a workable mod or am i still missing something

sorry if i left something out,had to decipher my own handwriting at 03:00. please correct me


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Hi Guys,
I just realised that there is an error in the schematic and PCB for this project:
The emitter of Q1 should be connected to 0V, not to the negative output of the rectifiers as it is now.
While the circuit is operating, Q1 should be turned-off, since it is used only to quickly reduce the circuit's output to 0V when you turn-off the circuit's power. The way it is now, Q1 can be turned-on by the voltage-drop across R7 when the project is supplying current to a load. This will reduce the output voltage and may overheat both Q1 and U2.

Q1 should be changed to a TIP31A transistor, because the little BC547 specified cannot handle the current and power imposed on it.
The TIP31A has a different pin-out and will need the PCB layout to be changed. It will not need a heatsink.

If a transformer of 28 or 30VAC is used, then R14 should be changed to 1.2K, so that Q1 is not turned-on by the higher voltage during normal operation. ;D ;D

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Kobus, not I, is building this project and has asked for advice to modify it for 5A output current. I gave him advice. ;D

Didn't you see Capricious's recent serious problems with very high temperatures with this project, even when using less output current? :'(

Ask Mixos how poorly his project worked. :'(

Do you, or anyone else, want to discuss my theories and make this project work properly? ???

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It is just that I see your theories fail you so much. Hands on is the best way to solve hardware problems. Nothing can replace bench work.

Also, it is not so clear to some that you are not building anything, but only giving theoretical advice in all your posts. I just wanted to clear the air.


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It is just that I see your theories fail you so much.

Fail so much? No, only occasionally. I'm sorry that I am not absolutely perfect like you.
Where are your discussions for this project?
What's your big problem with my recommendations of project improvements for members?
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Guest Kasamiko

Ok after so much discussion and arguments. Can someone post the UPDATED and CORRECTED schematics for this project..
One that is "NEAR" perfect.. 8)

Rhonn ;) ;)

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Hello Kasamiko.
I don't know about 0-30V 0-3A power supply but see under electronic forums-->project design/ideas-->modify 0-30V supply
or something like that.On the last page is pretty much a summary of what audiophile thinks should be modified for a 5A supply.No-one knows yet if it works so no guarantees.I'm currently building the supply in my spare time and hope to have it done some time end of next week. Hope this helps.

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Kasamiko, and others,
My replies in this forum and the Parts List that follows will allow this project to meet its own specs and to operate reliably.

Parts List for 3A Variable Power Supply

*T1 = 30VAC, 4.3A, 130VA stepdown power transformer
*R1 = 2,2 KOhm 2W
R2 = 82 Ohm 1/4W
R3 = 220 Ohm 1/4W
R4 = 4,7 KOhm 1/4W
R5, R6, R13, R20, R21 = 10 KOhm 1/4W
*R7 = 0,47 Ohm 10W
R8, R11 = 27 KOhm 1/4W
R9, R19 = 2,2 KOhm 1/4W
R10 = 270 KOhm 1/4W
R12, R18 = 56 KOhm 1/4W
*R14 = 1,2 KOhm 1/4W
*R15 = 100 Ohm 1/4W
R16 = 1 KOhm 1/4W
R17 = 33 Ohm 1/4W
*R22 = 3,9 KOhm 1W
RV1 = 100K trimmer
P1, P2 = 10KOhm linear potentiometer
*C1 = 10,000uF/50V electrolytic
C2, C3 = 47uF/50V electrolytic
C4 = 100nF polyester
*C5 = 220nF polyester
C6 = 100pF ceramic
C7 = 10uF/50V electrolytic
C8 = 330pF ceramic
C9 = 100pF ceramic
*D1, D2, D3, D4 = 6-10A/50V diode bridge module
D5, D6 = 1N4148
D7, D8 = 5,6V Zener
D9, D10 = 1N4148
D11 = 1N4001 diode 1A
*Q1 = TIP31A, NPN transistor, no heatsink
*Q2 = TIP31A NPN transistor
Q3 = BC557, PNP transistor or BC327
*Q4 = Two paralleled 2N3055 NPN power transistors with 0.1 ohm, 1W emitter resistors each
*U1, U2, U3 = OPA445AP, operational amplifier
D12 = LED

"*" is a change from the original design.

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I this is a little bit off topic but I want to do nice front pannel for the PSU and I wonder how I can project some writting on alumunium pannel... I was thinking of doing it in the same way as some of us do the PCB - tonner transfer. However, if I do so I don't know how strong the layer would be and if i won't loose it soon. Maybe I can apply some protective layer too ???? Any ideas?

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Hi to all electronic Guys!!!! Am new to this project. Hi AudoGuru it seems you are an expert in power supply designs. I would like to clear my elementry level doubt with all experts down there. Can I use a 15-0-15 V 5A transformer as a bridge circuit avoiding the centre tap? Could u plz attach a complete modofied circuit of this voltage regulator?

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Hi Mash,
Welcome to our forum.
Yeah, your transformer is fine for this 3A-DC power supply.
I am sorry that I can't revise the schematic, since I cannot manipulate GIF images. There isn't much difference, just an added 2N3055 and emitter resistors for each one, as shown earlier. Also, the emitter of Q1 should connect to ground, instead of the negative supply. Maybe someone will make these simple changes to the schematic for us.
The PCB also needs simple changes for the different pin-out for Q1 and Q2, and moving Q1's emitter as above.
The revised parts list has been given recently here. ;D

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  • 2 weeks later...

Ok, now I got really weird problem. As I posted earlier in this forum:

I'm trying to use digital panel meters for this PSU project. Everything seemed to be alright untill I tried to measure voltage from any power supply. What I mean is that these digital panels work fine when I measure potential from a battery, for example. However, once I hook it up to transformer based PSU it freaks out - it shows bogus numbers that fluctuate all over the scale. The weird thing is that even if I don't hook it up the voltmeter starts fluctuating a little bit. I powered up the panel as shown on the diagram by 9V battery. Any idea what could possibly cause this? ???

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Ante, I already tried this, and just to make sure I did it once again with no improvement. I tried cap in the iput before the voltage devider as well as after the devider - no change at all. I wonder how the unit would work if I hook it up in the other way - I mean powered by +-5V. I see it has a common ground with the inputs which might turn out to be the solution. What do you think about it? ???

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Ok, I managed to fix it finally. The solution was as I suspected - common ground. I used the same transformer as for the PSU and made zener stabilized +-5V with mid point output, and I filtered the output potential with 1000mF/25V cap. Now it works absolutely stable - the measured value does't fluctuate even for one digit. ;D

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