Sallala

0-30 Vdc Stabilized Power Supply

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1 hour ago, audioguru said:

Surface mount ICs on adapters? Solder that was dripped on from up high and heated with a blow torch?

All I can say after seeing your project is "EEK!". 

Hahahaha. I promise i will make a better one.

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The original defective circuit had many overloaded parts that will blow up. The improved version fixes it.

Opamp U3 senses the output current in R7 and reduces the output voltage and output current to match the current set with P2. The maximum output current is 3.0A in the improved circuit and the two output transistors have a total maximum current rating of 30A so they will not blow up with only 3.0A. 

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Dear Sirs,

I followed the discussions on the topic of the power supply project and during the last few years I set up different boards, all with the suggestions and improvements that you have suggested. In all the tests and prototypes that I made happens a small drop in voltage every time a load is turned on. This voltage drop goes from 0.02V up to 0.08V at the most different voltage and current. That is, at lighter loads it is at 0.02V, but at heavier loads it can reach at 0.08V. Is it possible to correct this little problem? What do you think about it?

Thank you for your attention and I sincerely apologize for my English because I am from Brazil and I am using Google translator.

Algot.

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Simply test voltages in the circuit with a voltmeter. The opamp U2 controls output voltage regulation and it has an extremely high internal voltage gain (220 thousand times for a TLE2141).

The negative feedback of the circuit detects any output voltage loss and directs U2 to correct it.

I think your poor voltage regulation is caused by the wiring from the output of the circuit to your load is too thin and causes the voltage loss.

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Hello everybody. What modifications should i consider for making this project? My idea is:

1- A huge transformer with two 28v secondarys. One secondary has a low current for only driving the current and power regulation. Another secondary will deliver the high current and has multiples taps. Both have their own rectifier boards.

2- A voltage comparator will take care of the tap selection based on the output voltage of the power supply. A way to reduce power dissipation. I'm thinking about the lm339 or three lm311 and relays.

I already made the transformer and i'm following the guide of a Youtube user who made the same modifications on the tl081 version of this power supply.  This is basically how he explained the concept. This approach is similar to the elektor power supply but without the tap selection circuit.

Clipboard01.jpg

MULTITAP.png

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Each comparator in an LM339 has an output current of only 4mA. Relay coils need more current so transistors or Fets must be in between.

Your block diagram is missing the huge filter capacitor needed that might burn out the relay contacts when the relays switch taps.

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2 hours ago, audioguru said:

Each comparator in an LM339 has an output current of only 4mA. Relay coils need more current so transistors or Fets must be in between.

Your block diagram is missing the huge filter capacitor needed that might burn out the relay contacts when the relays switch taps.

I

InputVoltageSelector.jpg

I was thinking about the tap selection circuit being done before the rectifier diodes and filter capacitors. This image relates to a similar aproach using the lm338. Since the mc34071 needs a stable 40v supply and -1,4v. Another 28vac 600ma transformer is used for powering the opamps and generating the negative supply. Most of my concerns are about the right way to connect the second transformer.

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How can you use an LM339 without reading its datasheet? Since its output is "open collector" then it cannot turn on the transistor unless you add a "pullup resistor".

The output of your 10A rectifier does not connect to "regulator in". Instead it has a huge filter capacitor (12000uF) and it powers the driver and output transistors of the regulator circuit.

R13 should connect to the fixed +40V.

When you switch taps then the huge filter capacitor must instantly charge with an enormous current that will burn out or weld the relay contacts.

 

LM339 output pullup resistor.png

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Sorry. I was aware of the pullup resistor. I will stop from here and stay with the standard project. I will stick with the lm311 and a lm35 for cooling the heatsink.

Once again, thank you for your help and patience, audioguru.

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On 8/1/2018 at 1:46 PM, audioguru said:

Simply test voltages in the circuit with a voltmeter. The opamp U2 controls output voltage regulation and it has an extremely high internal voltage gain (220 thousand times for a TLE2141).

The negative feedback of the circuit detects any output voltage loss and directs U2 to correct it.

I think your poor voltage regulation is caused by the wiring from the output of the circuit to your load is too thin and causes the voltage loss.

I understood your explanations and I already know what I did wrong.
Thank you very much.

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Gentlemen,
I know I have a specific topic for the improved project, but I'm still trying to understand some things in the original project.
I can not understand the operation of transistor Q1 in the circuit. It has been said here in the forum that this transistor works as a protection system, could someone explain to me how this works?
Does the power supply need no protection fuse in the output? How does it protect itself in the case of a simple polarity change, for example: a battery being connected with the polarities exchanged in the output with the whole circuit without power in its entrance? Or even if it is powered, but with the polarities of a load on its output inverted? That is, is she going to protect herself against dodgems like me?
Thank you again,
Algot.

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The original old Greek kit used TL081 opamps that have a problem called "Opamp Phase Inversion" where the output goes positively as high as it can if an input voltage gets within a few volts from its negative supply voltage. The improved project used newer opamps that do not have this problem.

When the power supply is turned off then the huge positive filter capacitor for the rectifiers takes time to discharge but the low current negative supply capacitor discharges quickly. Then the output of this power supply project will have opamp U2 to force the output of the project to go positively as high as it can which will probably destroy whatever you were powering with it.

The resistors on the base of Q1 detect that the negative supply voltage is dropping and causes it to conduct and short the output of opamp U2 to 0V so that it cannot cause the output of the power supply to go positively as high as it can.

The circuit does not have a huge high current diode at its output to block a negative high current at its output from damaging it. A huge high current diode might be too slow to protect against damage.

 

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