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0-30 Vdc Stabilized Power Supply

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If my theory is good, the wire between output and banana plug have a resistance of 2.82R.
How to calcul it :
R1=U*R2/U2 - R2

R1=5V*10R/3.90V-10R=2.82R.

That explain :
a) why the chinese voltemeter "see" 5V and not 3.90V after bananaplug

for 5V =>3.90V at output
for 8V = >6.90V output

for 10V =>7.50V output

c) why, when i test with my electronic load, with 100mA on my electronic load I have a current of 282mA !

This evening I try to measure the resistor of the wire, I will change it tomorrow.

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I find the problem of the fallen voltage, it is due to a Fucking wire like this who have a 2.8 ohms resistor :
So I can test now the current limiter function correctly !

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I use copper wire, not rice wire. They put rice in everything they make, especially batteries.

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Ok finally I test limited current and the voltage above R7  with 500mA is 165mV and 313.8mV with 1A. I measure with milliohmeter and I have 430mR for R7. I don't understand why the voltage drop is not 0.43*0.5=215mV and 0.43*1=430mV ?
So I make some test :

a) For max 3A output with Pot2 max I have to put 1.304V on U3+
b)It's works fine, if a put a 3.01A load (with my electronic load) the Led bright and the current limiter est working.
c) But I test to make a short-circuit I blow up my primary fuse (630mA T, maybe to low).

Why do you think about the voltage drop about R7 and for my 1.3V for 3A max ?

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2 hours ago, Tintin said:

Ok finally I test limited current and the voltage above R7  with 500mA is 165mV and 313.8mV with 1A. I measure with milliohmeter and I have 430mR for R7. I don't understand why the voltage drop is not 0.43*0.5=215mV and 0.43*1=430mV ?

165mV/500mA= 0.33 ohms that is wrong. 215mV/1A= 0.215 ohms that is also wrong.

So I make some test :

a) For max 3A output with Pot2 max I have to put 1.304V on U3+

1.304V/3A= 0.435 ohms which is close to your measurement of R7. Then trimpot RV3 is set for a max current of 3A or less.

b)It works fine, if a put a 3.01A load (with my electronic load) the Led bright and the current limiter is working.

c) But I test to make a short-circuit I blow up my primary fuse (630mA T, maybe to low).

When the output current is higher than the setting of P2 then the output of U3 goes low which turns on the LED and reduces the voltage at the output amplifier. Then the shorted output should have a current of 3.0A maximum.

The opamp used for U3 and the negative supply voltage must be allow the output of U3 to go low enough so that the input to the output amplifier is shorted to 0V when the output of the project is shorted. Then R7 is the load.

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Hi Audioguru,

Sorry I do not understand your last phrase
" The opamp used for U3 and the negative supply voltage must be allow the output of U3 to go low enough so that the input to the output amplifier is shorted to 0V when the output of the project is shorted. Then R7 is the load. "

If my memories are good, if I make a short-circuit when the POT2 is set to zéro, the Voltage output do not go down to 0V, and when I turn clockwise the POT2 the current go up.
But I remember with this method, I have 3 A maximum wioth POT2 set to the middle, or if I put a load for 3A the POT 3 need to be max for 3A max.

This is this difference who make me perplexed !

PS : I buy a new toroïdal 28VAC 160VA !

https://www.tme.eu/fr/details/tst150w_28v/transformateurs-toroidaux/indel/tst160013/

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When you turn down P2 to zero then the project's output current should be no more than a few mA. The circuit reduces the output voltage with U3 and D9 to reduce the current. When the current is limited to a few mA then the anode of D9 is 0V and its cathode which is driven from the output of U3 must be about -0.65V. That is why U3 is an opamp that has its input and output able to go close to its negative supply and why it has a negative supply.

When you turn up P2 then the current does not go up, the voltage and the load resistance set the current. The maximum current goes up.

The circuit is designed for a maximum current of 3A so you should set the current calibration trimpot RV3 so that with P2 at maximum and with the output of the project shorted then the current is 3.0A. If RV3 is set to its maximum of 100k then the maximum output current will be 1.33A as I showed in post #?.

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Hi,
I just finish my power supply !
It is in French but I will translate in English soon.

I thank all this community, who made a great job !

I join you some photos and my work on  a PDF format.

Alimentation0_30V.pdf

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Hi Tintin,

You have done excellent work building this power supply and your experience is valuable for all other members. I encourage you to translate the PDF in English so anyone can benefit from it. Looking forward seeing your measurements and thoughts building this PSU.

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• 2 weeks later...

Hi,
as promised I made an English translation of my working. Maybe there is few mistakes and I am sorry for that !

ExplicationEN.pdf

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Excellent measurements! Thanks for sharing.

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On 3/29/2018 at 10:26 PM, Tintin said:

Hi,
as promised I made an English translation of my working. Maybe there is few mistakes and I am sorry for that !

Hi Tintin nice effort.

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• 1 month later...

Hello. I have a question about the rectifier part of this project.

I recently made a transformer and a rectifier board that outputs the GND, 30VDC and -1,4VDC lines. Since the winding was made by hand, the output voltage got a little off. Instead of a 28AC output, i got something around 30,5AC. The problem starts when i connect the transformer to my rectifier board. The positive output gets to 45VDC and begins to slowly rise until it hits 49VDC. The negative line stays at -1,6V. I'm more worried about the positive supply since the OPAMP can only take 44Volts.

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The peak of 30.5VAC is 30.5V x 1.414= 43.13V. The bridge rectifier has diode voltage drops of 1.4V when there is no load so the positive supply will be 43.13V - 1.4V= 41.73V. If your mains electricity voltage rises then the opamps might be destroyed.

I do not know why your voltage measurements are wrong.

A 28VAC transformer is about 29VAC with no load. Then its peak is 41.0V and the bridge rectifier reduces it to 39.6V with no load which is fine for the 44V opamps.

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Then i should assume that my 30.5VAC transformer has a number of widings for a 29.5VAC. The widings are at a ratio of 2,44 turns per volt. So i need to remove 2 or 3 turns to get something near the ideal 28AVC.

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On 06/05/2018 at 7:28 PM, detonatorinf said:

Hello. I have a question about the rectifier part of this project.

I recently made a transformer and a rectifier board that outputs the GND, 30VDC and -1,4VDC lines. Since the winding was made by hand, the output voltage got a little off. Instead of a 28AC output, i got something around 30,5AC. The problem starts when i connect the transformer to my rectifier board. The positive output gets to 45VDC and begins to slowly rise until it hits 49VDC. The negative line stays at -1,6V. I'm more worried about the positive supply since the OPAMP can only take 44Volts.

I, I had the same problem of you. To fix it, make a minimum load with resistor. For me a 25mA load was the minimum to decrease this.
See there :

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Thank you, Tintin. Adding another 2k2 resistor in parallel solves the problem. Now the rectified voltage is 40,5 VDC and will not rise.

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• 1 month later...

Wow! After long 4 months of waiting, my package with five TLE2141CP finally arrived from China. And for my "surprise" none of them worked. Both U1 and U3 got extremely hot and began to smell. Turns out two resistor got burned!!

Just minutes ago i found a store in my country that sells the original MC34071. God... so much time wasted. I'm ordering them tomorrow ASAP.

Just a advice for Brazillians interested in building this project. The online store Proesi is selling the SMD version of the MC34071.

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I did not calculate it but I think a tiny surface mounted opamp for position U2 will get too hot if the hFE of the driver and/or output transistors is low.

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2 hours ago, audioguru said:

I did not calculate it but I think a tiny surface mounted opamp for position U2 will get too hot if the hFE of the driver and/or output transistors is low.

U3 only outputs 0,640 volts. When the voltage control pot is rotated to the left or right, the variation in the readings are minimal. The voltage only raises to 10v when U3 gets too hot. U1 outputs 33v and also gets hot. RV2 has no effect on the readings.

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My Rev 6 July, 2014 schematic shows that opamp U1 makes the 11.2V reference, U2 is for the voltage control and drives the output driver transistor with 0V to about +32V and U3 is for the current control and has an output from -1.0V to about +27V.

If the output has a low voltage (or is shorted) and a high current then the NPN output transistor in U2 will get hot. A tiny little surface mount package cannot dissipate much heat.

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4 hours ago, audioguru said:

My Rev 6 July, 2014 schematic shows that opamp U1 makes the 11.2V reference, U2 is for the voltage control and drives the output driver transistor with 0V to about +32V and U3 is for the current control and has an output from -1.0V to about +27V.

If the output has a low voltage (or is shorted) and a high current then the NPN output transistor in U2 will get hot. A tiny little surface mount package cannot dissipate much heat.

Sorry. You're right. I confused the order of the ICs. U1 (reference voltage) outputs 33v and U2 (voltage control) outputs 0,640V to the base of the BD139.

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1 hour ago, detonatorinf said:

U1 (reference voltage) outputs 33V and U2 (voltage control) outputs 0,640V to the base of the BD139.

No  and No.

U1 has a gain of 2 times and a 5.6V Zener diode. Therefore its output is 11.2V, not 33V. A 5.6V Zener diode does not change its voltage when its temperature changes but an 11.2V Zener diode increases its voltage if it gets warmer.

The BD139 and the output transistors are emitter-followers. Their emitter voltage follows their base voltage but at high current, their base voltage is 1V to 1.5V higher than their emitter voltage. Then when the output voltage is 30V the output of U2 must be 32V to 32.5V.

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• 2 weeks later...

Sorry, audioguru. My post sounded like i was describing how the circuit should work but i was just explaining the behavior of the opamps. None of the 3 opamps were working as intended. The problem was caused by my lack of atention while copying the schematic to Kicad. The opamp footprint for U2 was printed with the negative and positive inputs inverted. Two jumpers solved the problem and now i have a working power supply.  I attached some images.

Really ugly, ain't it? But it was my first time learning how to make one.

R7 resistance is 0R22. I couldn't find the 0R25 resistor recommended for a 5A power supply. Also, three 2sc5200 in parallel are used as output transistors.

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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!".

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