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0-30V Stabilized Power Supply


redwire
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Ok thanks. I didn't mind clicking to page 55, but when I got there the train had already left :) What am I looking for on page 55? A new circuit diagram, parts list, a link to the info? There is nothing there like that from audioguru. Am I in a time warp?

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I did some work on the case for the PSU, but after I finish one of the PCBs doesn't work anymore. Perhaps a piece of wire could sortened something. But I clear the PCB several times, but the fuse continue to break. Somethimes the fuse is OK and I measured some values, but I'm not sure where exactly to measure. For sure the input voltage from the transformer is OK, after the filter capacitors also is good. What to measure ? May be the OAMPs? I want to find the problem before I replace all of the parts on the PCB :)

P.S. I think the input fuse is with low value. I put a bigger one and now it's working fine. How much should be the fuse for two PSUs and the transformer - 250VA 2x30V ?

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Hi.  This is my first post on here.  I have been reading through the entire thread on this revised PSU and it has been an enormous refresher for me.  I am using tesseract's revised pcb 5.0A and have a few questions.  First on the board layout, the power transistor terminal block is labelled B (pin 1) and C (pin 2) which I would assume means Base and Collector.  But on his shaltplan schematic it shows pin 1 going to the collector and pin 2 going to the base.  Which is correct?

Also, RV3 limits the max current, so am I correct in assuming that if I use a power supply less than the specified 7A and set RV3 to my power supply's amperage rating that it will limit the max current to what I set it at?

Sorry for the questions.  It's been about 15 years since I built a board.

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I am using tesseract's revised pcb 5.0A and have a few questions.  First on the board layout, the power transistor terminal block is labelled B (pin 1) and C (pin 2) which I would assume means Base and Collector.  But on his shaltplan schematic it shows pin 1 going to the collector and pin 2 going to the base.  Which is correct?

Tesseract's schematics are WRONG.
The collector of the driver transistor is correctly shown connected to the unregulated positive supply and the collectors of both output transistors also should connect there.
The emitter of the driver transistor should connect to both bases of the output transistors.

Also, RV3 limits the max current, so am I correct in assuming that if I use a power supply less than the specified 7A and set RV3 to my power supply's amperage rating that it will limit the max current to what I set it at?

No.
RV3 is a trimpot to calibrate the max output to 3A or 5A. The current setting pot (connected to the box labelled "current") sets the regulated output current.
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Audioguru, thank you so much for your quick reply and clarification.  One other question, which might seem elementry and mean that I need to refresh my understanding a little more.

On the above pcb that I posted, why are there 3 power inputs (+, alternating, -)?  Is this  because a full wave bridge recitfier was used on a center-tapped transformer prior to board connection?

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On the above pcb that I posted, why are there 3 power inputs (+, alternating, -)?  Is this  because a full wave bridge recitfier was used on a center-tapped transformer prior to board connection?

No.
This project does not use a center-tapped transformer.

You need a schematic that shows how the two wires from the secondary of the transformer connect to the bridge rectifier and how three of the wires from the bridge rectifier connect to the circuit.
I assume that + is the positive output from the bridge rectifier, - is the 0V output of the bridge rectifier and AC is the signal that feeds the 82 ohm resistor to make the negative unregulated supply.
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So from the above mod that I posted, I connected everything up and after about 2-3 seconds c5 blew its top.  What could be the cause?

C5 on the schematic you used is only 220nF (0.22uF) so it is an unpolarized metallized poly film or ceramic. Both types of capacitors do not have a top like is on an electrolytic capacitor.
The voltage rating of C5 should be 63V. The max voltage it will ever see is 43V.
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The problem I am having is that the led current limiting led never turns on.  When I increase the voltage pot and then adjust the current pot, the voltage drops as it should and the power transistors heat up, however, I never get an indication from the led.  I've tested the led and its good.

Suggestions?  Bad U3 maybe?  I'm using MC34071s on a dip8 socket.  (Note:  I had to cross-reference BC556 with NTE's part which is NTE159.  I assume the EBC pins are the same for both)??

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Hi guys, i am really interested into building this one.

Only thing is: What if my transformator doesnt supply 3A? Does the current regulation still work? Will there be a voltage Dropoff if current regulation is set to higher than the current supplied by the transformator?

Should i "redesign" some parts to stay in my range of current control? And which parts do i have to recalculate?

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What if my transformator doesnt supply 3A? Does the current regulation still work? Will there be a voltage Dropoff if current regulation is set to higher than the current supplied by the transformator?

Since the rectifier bridge peak detects the 30VAC to 42.4VDC then the 3A DC output from the project requires 4.2A AC from the transformer.
If your transformer is rated for an output of 3A then it will over-heat if the project has an output of more than 2.1ADC. Its voltage will drop when it is overloaded.

Should i "redesign" some parts to stay in my range of current control? And which parts do i have to recalculate?

The latest version has calibration trimpots. You can adjust the current trimpot so the max output current is only 2.1A DC.
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Since the rectifier bridge peak detects the 30VAC to 42.4VDC then the 3A DC output from the project requires 4.2A AC from the transformer.
If your transformer is rated for an output of 3A then it will over-heat if the project has an output of more than 2.1ADC. Its voltage will drop when it is overloaded.

Exactly. Thanks.
But it would only overheat if i set the current limiter HIGHER than 2.1A DC and also consume it. Fine.



The latest version has calibration trimpots. You can adjust the current trimpot so the max output current is only 2.1A DC.

Cool i also can go with lower voltage then. nice.
Wonderfull, exactly what i wanted to hear. Because this way i can first use a weak Trafo and after i found a strong and cheap one, ill switch.



Thanks you. Will try to double etch the board with my toner method ;]

EDIT: I gonna use this files, are they compatible? are there newer? because in part list it says rev3:

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The problem I am having is that I have no current control.  If P1 is at max and I turn P2 to max, then both the voltage and current drops to zero, and vice versa.  The LED never lights up.  And the max current never gets above 0.9A.

Tesseract's schematic does not show P1 or P2.
On my schematic, P1 is the voltage control and P2 is thew current control. If P1 is at max and the voltage trimpot is calibrated then the output voltage is 30V (or less when the current is higher than the current control setting). Since your voltage and current drop to zero when P2 is at max then you probably have P2 wired backwards.

R7 senses the output current. U3 controls the output current and compares the voltage across R7 with the setting of P2 and reduces the output voltage so that the output current (and the current in R7) is the same as the setting of P2.
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