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Convert 0-30V 3A PSU to 5A or more


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This topic is about modifying the project for 5A of current.
The "Projects Q/A" forum has the topic about modifying this 3A project to work well and reliably. I posted a recommended parts list there many times.

The supply voltage rating of an ordinary 741 opamp is 36V absolute max and is the same for the TL081 opamps in the original project. This project with a 30VAC transformer and low load current has a supply voltage for its opamps of 50VDC. That is why I recommend OPA445AP high voltage opamps.

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The TL081 and most other opamps have an absolute max supply voltage rating of 36VDC. The project with your 24VAC transformer will have a supply voltage total of about 40VDC when it has low output current. A 741A opamp and a few others have a max supply voltage of 44V and the OPA445AP has a max supply voltage of 90V

You Said this earlier for the 3A PSU and by the way how is the heatsink for the 3A PSU.
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  • 4 weeks later...

Hi Roomi,
Welcome to our forum. ;D
Good idea!
The TL431 or TL432 adjustable voltage references are much better than the D8 zener diode and the project would be better with one. R4 in the project would power it and two resistors must be added to set its voltage to 11.2V.

The schematic for the project modified to work well and with up to 5A output has been posted in this thread by at least two people.

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The problem is that here in my place low current 5.6V zener is not available.So i am thinking about the second way... ???Here is another idea which i haven't been tested but think it will solve the problem of output voltage going down.Making R6 variable(27K) and by adjusting the pot greater than 10K we can increase the output voltage of OPAMP.What do you think guys... 8)

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Hi,

I am a beginner in actually "messing" around with electronic circuits but have been around them for a while and am very comfortable tinkering around.  For example, I've been working with FPGAs for several years, albeit mostly on the software side of things.  I have also made a robot which wanders around avoiding obstacles via infrared.

In any event, I am very interested in building the power supply as it is in its current state (0-30VDC, 0-5A, I believe).  I am interested in having a voltmeter and ammeter in place (will build it in a case and have these on the front of the case), and am interested in having a dual power supply.  Now, does anyone have the "final" schematic for this thing (including the voltmeter, ammeter, and dual power supply requirements), perhaps also a "detailed" parts list (i.e. a volt rating for all the capacitors, heatsink requirements, fan requirements, etc).  Even better would be like a parts list from mouser or something in order to ease the ordering process.  I know, this may be asking too much, but I figure why not ask.  You folks are really helpful from what I've been reading, and this seems to be a very cool place to wander around!

I have been reading a whole bunch about this stuff lately and seem to be moving from the software side to hardware.  I have messed around with simple circuits (built a battery charger to recharge store-bought alkalines at ~65mA, a MIRT, also one of those rotating persistence of vision LED thingies, etc).  I would very much like to build this power supply.  Any suggestions for a beginner?

Thanks for your help.

--Niksun

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  • 3 weeks later...

Hi I'm thinking about building this PSU but I want to make a dual supply that I can switch to 0-60V but I'm a little confused on what kind of transformer I should use.

I have read that you can make a dual output using seperate windings, i'm not sure how to hook up the secondary windings. I know that they would each need there own rectifier, filter capiciter ect.. Hammond makes a 60V center tap transformer that is in my price range (model 182R30) Can I use this transformer to achieve a dual supply? If not, what kind of transformer could I use? (specs would help) I'm hoping to keep it as a single transformer rather then two completely seperate transformers.

In addition if I cant use the Transformer I mentioned above for a dual supply, how about a Bipolor supply using the center tap as a common ground?

This would be for the improved 0-5A 0-30V PSU

Thanks in advance,
Trigger

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Good idea!
The TL431 or TL432 adjustable voltage references are much better than the D8 zener diode and the project would be better with one. R4 in the project would power it and two resistors must be added to set its voltage to 11.2V.



and

I looked at the zener diode D8 in the negative feedback loop of opamp A1 and they perform very well when the zener is a low current type and the value of R4 is reduced to provide it with enough current. It would be difficult to include a TL431 or TL432 in the same opamp circuit and I don't think it will perform as well by itself.



So which is it??

Adding a TL 431 to this circuit is VERY, VERY SIMPLE!!! A1 can even be used as a buffer. Your joking when you say a non-presision, non-temperature compensated zener will work better than a "real reference" ... right??
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  • 2 weeks later...

This project would need a complete re-design to get its output voltage up to 50V.
It still has nearly the same schematic as the original. The output transistor has an added emitter resistor then two more output transistors and emitter resistors are added in parallel on the heatsink. Many parts values were changed. Someone mentioned adding trimpots in series with the main pots for calibration.

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Gah!!  I apologize; I made a mistake.  I meant 0-30V and 0-5A.  Wow, the "5" key is awfully close to the "3" key, eh?  :P

As an aside, I've been investigating recharging regular, old alkaline batteries (I know, most think this is not a good thing) with this PS.  In any event, I figure that capping the current at ~65mA and setting the voltage to the appropriate value for the cell I wish to charge, it may just work.  What do you think?

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:D

I'll try a completely new way concerning the power stages. 2N3055 is something I have seen in the museum. Two main changes will apply to a power supply with high perfomance. First the transformer will be a ring type (excuse me, my English is not better but may be understood). You can drive a ring type transformer almost to saturation and it will still work. Secon change: through out the dinosaur transistors and replace with N-channel Power MOSFET with no higher restance than 0.04 Ohms, even having the luxory that each individial transistor has a FLAG output to indicate that it is tired of working and give the whole burden to his brother.

Just let me think two or three nights about the theme. I'll come out soon with a good and affordable power supply.

Kind regards to all being busy with the problem.

HtG

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