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  1. 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.
  2. I 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.
  3. 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.
  4. Hahahaha. I promise i will make a better one.
  5. 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.
  6. 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.
  7. 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.
  8. 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.
  9. Thank you, Tintin. Adding another 2k2 resistor in parallel solves the problem. Now the rectified voltage is 40,5 VDC and will not rise.
  10. 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.
  11. 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.
  12. What is the consensus about the voltage spikes discussed on older posts? REV8 adds a darlington transistor to solve this problem. But even after that, other solutions are still being presented for the same problem.
  13. Thank you. I will choose this project in that case.
  14. I found this. Since the same model number is shared by other 4 brands. I can't tell if the actual hardware still true to the schematic.
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