0-30V Stabilized Power Supply

[zulcao]

Page 55

[audioguru]

This website does not have "stickies" like most other electronics chat sites.
This website does not allow you to key in a page number so you must go back only 2 pages at a time which takes a long time to get to page 55.

[nzo]

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?

[zulcao]

Reply 767

[audioguru]

Page 55 of this thread has a reply from me where I attached the latest parts list and schematic for this corrected project for the millionth time. Since it was 7 months ago then I will attach them here again:

[jpmhdbest]

sir may i request for a PCB design of the latest schematic diagram... if its ok..

[audioguru]

I am not a SIR and I have never built this power supply. I simply corrected its problems and made it more reliable.
A few people have posted their pcb design for it.

[nzo]

audioguru - I didn't realize how tedious it must be for you to answer the same question over and over again. Thank you for what little patience remains in you. I found the files this time.  :)

[morpheous87]

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 ?

[audioguru]

When this project is turned on, the very high value filter capacitor C1 takes a very high current to charge in less than 1 second so your fuse blows.
Use a slow-blow fuse.

[morpheous87]

When this project is turned on, the very high value filter capacitor C1 takes a very high current to charge in less than 1 second so your fuse blows.
Use a slow-blow fuse.

How much A should it be?

[audioguru]

How much A should it be?

This project uses a max power of 3A x 40V= 120W from the mains. So if your mains is 120V then a 1A fuse might blow so use a 1.5A slow-blow fuse.
If your mains is 240V then use a 0.75A slow-blow fuse.

[bf2015]

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.

[audioguru]

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.

[bf2015]

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?

[audioguru]

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.

[bf2015]

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?  I thought that Q2 might be shorted to the heatsink, but it wasn't.  I have voltages that I can post if needed.

[audioguru]

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.

[bf2015]

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)??

[audioguru]

Since you changed the transistor part number then why didn't you look at its datasheet to see its pins??

The BC556 is European with the normal pins layout for there.
The NTE might be American with the normal pins layout for there.
Oriental transistors have a different pins layout than both of the others.

[fly3rman]

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?

[audioguru]

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.

[fly3rman]

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:

[bf2015]

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.

[audioguru]

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.