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0-30V Stabilized Power Supply


redwire
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Hi Bean,
The original project had many errors so it did not produce 30VDC at 3A but instead produced about only 25VDC with lots of ripple at 3A.
Many of its parts overheated especially the old fashioned and tiny transistor Q2 and the transformer.
The unregulated supply was a total of 40.3V without a load but the opamps in the original project have an absolute max total supply of only 36V.

I corrected some of the problems 5 years ago by using OPA445 high voltage opamps, a more powerful Q2 transistor and a few other changes but then this opamp became hard to find and expensive. So the latest version uses two types of opamps that are available almost anywhere, do not need a huge negative supply voltage and have a max total supply of 44V.

The datasheet is what you should look at because maybe Farnell missed that the max supply voltage for the TLE2141 is plus and minus 22V which is a total of 44V.

The latest version has a small negative supply for U3 and no negative supply for U1 and U2. Most opamps do not work with a small negative supply or no negative supply. The opamps for the latest version were selected because they work perfectly with a small or no negative supply voltage.

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Thank you Audioguru. I am going to build the 5amp that... Redwire? built... I am going to try to use the exact parts he used to try and avoid the endless troubleshooting. Another bonus is that since we are both using microwave transformers I might luck out and have a near identical power source eliminating all the problems I have read about concerning this. At worst I think I might end up short on x-fmr amps, but I will have a psu with a 5A potential.

I was wondering if that was the case with the opamps, but I have never seen a use for negative voltage so I have never had to consider that.

Also to correct myself in my last post: I said "MCU or TLE", and realized there is no U in the MCU part number. oops.

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The difference between a 3A project and a 5A project:
1) The 28V transformer must be 119W for the 3A project and must be 198W for the 5A project.
A little 28V x 3A= 84W or 28V x 5A= 140W transformer will be overloaded.
2) The 3A version uses two output transistors with emitter resistors and the 5A project uses three output transistors with emitter resistors.
3) R7 is 0.47 ohms/10W for 3A and is 0.27 ohms/10W for 5A.
4) The heatsink for the output transistors must be able to dissipate 109.8W for 3A or 183W for 5A. 

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Ok. I just ordered everything off newark (xcept xfr) for just over 20$. Actually, I got 3 of almost everything just in case. I ordered 3 power transistors in case I build the 5amp. I decided not to be cheap and bought some Aavid heatsinks with a thermal resistance of 4 degrees/w. Ok that was a lie, I did go cheap-they were 6 for 3 dollars, another 3 for shipping brand new. I was ready to pay 20+ if I had to, don't tell the seller that. I have an 1100 watt 250 dollar stainless microwave that works great but would work better if the xfer was rewound. I think I am going for the 5 amp. You guys put way too much effort into making such a wonderful product accessible to poor people like me, so I am going to make sure y'all's work is put to good use.

Thank you everyone with your infinite patience for helping us newbies through this, it is people like you who donate their time so that others can benefit that makes the internet so damn useful. We all appreciate you. Now wish me luck I am going to go electrocute myself.

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neither of the 2 opamps are availible here in SA.

The MC34071 is made by Motorola/ON Semi/Freescale Semi which is one of the largest semiconductor manufacturers in the world.
The TLE2141 is made by Texas Instruments which is also one of the largest semiconductor manufacturers in the world.

These opamps were chosen because their max allowed total supply is 44V and their inputs work without a negative supply voltage, and their outputs go much lower than ordinary opamps.

I don't know which opamps are available in South Africa. I don't know Oriental nor European opamps.

My transformer is rated 25V @ 5A AC, therefore open rectified voltage will be 35.4V, what other Opamps are recommended that I could use?

Thanks in advance!
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Hello, I'm new to the forum I'm from Argentina I want to assemble the source query and I have the following problem I can not offset lower intentions to 0 volts replace all integrated and I still have the same problem thanks for your help

Hi lu2dlt. Your English is not clear.
What is "source query"?
What is "offset lower intentions to 0 volts"?

You did not say if you made the original project that has many problems including errors with its offset voltage adjustment. Or maybe you made the latest circuit that has no problems.
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Hey guys, first off my son spilled something on my laptop and my keyboard hates me now so I apologize if my grammar/puncuation/spelling is crap, I will do my best. I have just about finished the PCB, I used two thin single PCB's and made a dspcb, and since I am using a dremel to do everything and precision is nearly impossible, I am unable to join the top layer to the bottom layer so I simply held the components off the top enough to solder the top and bottom layers. I knew that some things were missing on the birdy file, butI figured that is the board audioguru and redwire made so I made mine identical to the birdy file, but now that I am in the process of attaching the external components, I have noticed that the voltage fine adjust pot is nowhere to be found on the schematic, and I remember reading that it was an afterthought but 0 results turned up when searching the forum for voltage fine adjust. Is it simply ran series with the 10k coarse? If so, can I also use this method for a fine current adj since I am building the 5A? Also, with the birdy file there is a note to hit ratsnet to fill a groud plane under d7 which was eliminated. Since I have absolutely no idea what that is supposed to mean, I just used a wire in its place, is that the same as what redwire was saying? Also, I have read through this forum so many times that the I get the specifics confused so if you know of any mods off the top of your head that I need to do before applying power I would really appreciate the info. The updated design has not been modified at all on my project, from the board to parts list so I only need the mods to make the original ps-6 desing work properly. This is turning out a lot smoother than expected, the biggest delay I have had was my wife took the assembled pcb and tossed in in a pile of other stuff and I had to completely strip it and make a new one because some components were ripped off and took thecopper with them... Not exactly the setback I anticipated, but if it were too easy I guess it wouldn't be as much fun.

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  • 2 weeks later...

Hi i have just finished the 5 Amps version of the power supply , and it looks like work OK, i have loaded the P.S with 40 parallel connected bulbs ( 26 volts 100mA) and the voltage drop is only 0.1 volt when the current limiter is not on an the voltage drop is 0.5 volts when the current limiter is on, the R7 gets  hot with this load ( 2 parallel 7 watt 0.56 Ohm resistors), output transistors (3x MJ11016) are a Little bit warm, as far as voltage i have problem to bring it to 0 when potentiometer is at 0,  i get 1.1 volts i have electrolyte capacitor for C7 I'm thinking to change it to film type when I'm adjusting the RV2 so that at output i could have 30 volts I'm having 1.1 volt when I'm bringing the potentiometer to 0 and when I'm bringing down the RV2 voltage drops from 1.1 volts to 0.8 volts at the output with potentiometer bring down to 0, but then at the outup iw got 26 volts with the potentiometer put on maximum.
Guru how much should be the value of resistor that i should put at output so to bring the voltage to 0

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R7 gets  hot with 4A load ( 2 parallel 7 watt 0.56 Ohm resistors)

Each resistor is dissipating only 2A squared x 0.56 ohms= 2.24W.

i have problem to bring output voltage to 0 when potentiometer is at 0,  i get 1.1 volts i have electrolyte capacitor for C7 I'm thinking to change it to film type

Yes because an electrolytic capacitor has "dielectric absorption".

when I'm adjusting the RV2 so that at output i could have 30 volts I'm having 1.1 volt when I'm bringing the potentiometer to 0 and when I'm bringing down the RV2 voltage drops from 1.1 volts to 0.8 volts at the output with potentiometer bring down to 0, but then at the outup iw got 26 volts with the potentiometer put on maximum.

RV2 is adjusted for an ouput voltage of 0.0V when the voltage pot P1 is set to zero. RV2 is supposed to adjust only about plus or minus 0.05V to cancel the amplified input offset voltage of U2. C7 will hold a voltage if there is no load.

Guru how much should be the value of resistor that i should put at output so to bring the voltage to 0?

Maybe a 3.3k 0.5W resistor should be added to the output to discharge C7.
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Each resistor is dissipating only 2A squared x 0.56 ohms= 2.24W.
So its OK to get hot?



RV2 is adjusted for an ouput voltage of 0.0V when the voltage pot P1 is set to zero. RV2 is supposed to adjust only about plus or minus 0.05V to cancel the amplified input offset voltage of U2. C7 will hold a voltage if there is no load.
is it OK to adjust with RV2 to have 30 volts at the output without no load?

Maybe a 3.3k 0.5W resistor should be added to the output to discharge C7.
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So its OK for the power resistor to get hot?

The 7W power resistor is made to dissipate heat. it is made of substances that are fine when very hot. 2.24W is not near the 7W max rating so it is fine.  A power resistor operating at its max power rating will be extremely hot and will char the pcb, burn you if you touch it and melt plastic.

is it OK to adjust with RV2 to have 30 volts at the output without no load?

Yes. When the voltage adjust pot is set to maximum then RV2 in Redwire's schematic adjusts the output to be exactly 30.0V.

quote]"Maybe a 3.3k 0.5W resistor should be added to the output to discharge C7."
Connect it in parallel with C7??
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I have replaced C7 from electrolit type to film capacitor ( see attached datasheet) and conect the two paralel 6.8 Kohm resistors
to discharge the C7, but still cant bring down the output to 0 still reading 1.1 volts when voltage potentiometer is set to 0 .

Which opamp do you have for U2?
In the latest circuit the opamp must be an MC34071 or TLE2141 which have inputs that work at 0V and have outputs that go down to 0V. Ordinary opamps will not work at 0V.
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Dear Guru, i have tested and tested the power supply (5 amps version) and everything works perfect, i can bring down to 0 output voltage only when im bringing down to 0 the current potentiometer ( current limitng LED is on), is it OK?

Your power supply project has a fault. The voltage is supposed to be adjusted down to 0.0V.
Since the current regulation causes the voltage to correctly go down to 0.0V then since it reduces the voltage from the voltage-setting pot to 0.0V then your voltage-setting pot does not produce a low enough voltage when it is turned to zero.
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Your power supply project has a fault. The voltage is supposed to be adjusted down to 0.0V.
Since the current regulation causes the voltage to correctly go down to 0.0V then since it reduces the voltage from the voltage-setting pot to 0.0V then your voltage-setting pot does not produce a low enough voltage when it is turned to zero.

So what do you sugest? to change the voltage regulating potentimeter? and should my voltage regulating potentimeter bring down the voltage to 0 no mater in what position is my current regulating potentimeter?
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