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Everything posted by eggy

  1. I tried to build it, but...ha some troubles with programming atmega8 ( dil28 package) and finally voltage regulator 78L05 fried to short circuit...result? Atmega8 had 13V between Vcc and GND...it fried...haven't got new one yet. By the way....is it me, or the ISCP part of DIP package Atmega ( on the original page) has serious bugs in it...there are'nt all the pins needed for programming present in LCD connector...
  2. End pins of RV1 are connected to pins 1 and 5.
  3. Got mine working. Voltage is 0-30,0V. One problem remained...R2 is heating....quite fast, after few minutes I can also smell the resistor besides seeing it.
  4. Actually transformer output has 25V AC before diodes and caps. After, 31V. Capacitors are 4x2000uFx50V. Have to test this 3A load part, but what do you mean by "without 100Hz ripple"? PS! Now the R2 is heating....even without op-amps... PS2! Voltage on U2 pin3 is varying from 5.1 to 16.4V not from zero to 11V...Output voltage changes from zero to 31,5V, BUT there are only two stages...zero and 31.5V. Each other in one end of the voltage pot. No smooth voltage change.
  5. Okei, negative supply is now OK. I had some bugs with the AC wire from the transformer to R2. :)
  6. Just to be sure....I have to measure it between pin 4 and...pin 7 or negative rail(the one with R7)? I know, but when D7 is reversed then current led will not light up when 1,5Ohm resistor is connected between output terminals of PSU. Its like Op-amps stops working.
  7. Non of the diodes are connected reverse...when I revers any of[ D5,D6D7] diodes the current limit led stops working.
  8. So, reversed D7. Voltage across it is 5.6V, but....voltage across pins 4 and 7 of U3 and U2 is ~5 volts lower than U1's voltage at the same pins...it should be higher, not lower, right?
  9. Okei, Replaced Q4[actually connected wires to another transistor]. D10 was backwards...C2 and C3 seemed to be fine. I have replaced D5,D6,C2,C3,D7(R3 is OK, 230Ohms)...nothing-voltage drop across D7 is still near 0.7V...all op-amps has same voltage across pin 4 and 7. At least one thing is working...kind of...I connected 1.5Ohm resistor in series with digital ammeter[is it right term in English? ] and another digital multimeter showed me output voltage. First it showed 33V, resistor connected, voltage dropped to ~4,5V...although current pot has no effect...:( Still trying to get it work.... PS! I use that kind of PSU. AC for negative power [originally from AC pin 2]is taken before one diode... PS2! I had this negative 5.6V by using the same scheme...
  10. Okei, I was away from the PSU for a while. Voltage at the pin 6 on U2 varies from 4,1 t o 26.6V when voltage pot is turned. Pin 6 on U3 does hold its voltage at near the power supply voltage. I tested opamps within one test circuit and the worked fine, so the should be alive.[atleast at the moment] Somehow I have "lost" this 5.6V negative power supply...I tested diodes, resistors-the seems fine. Voltage drop across D7 zener is 0.8V [should be 5,6V?]. One more interesting thing...when I removed Q2, then output voltage of PSU vary from 4.1 to 26.6V. (It comes directly from op-amp?`No real current....) When I connect Q4 output voltage rises and is not changeable. PS! Sometimes R15 heats up quite quickly. This could happend if Q1 is shorted? It connects one end of R15 to GND and otger goes through D10 to Vcc`?
  11. a little mistake by me: Voltage on pin6 of U1 is 11V... >>>and the slider of the pot should change from 0V to 11.2V.<<< Which pin voltage should it change?
  12. I know that Q1 is for bringing output voltage lo. Base of Q1 is not short circuited to positive supply, only through r13 which is not connected at the moment. Let's assume that I remove Q1 temporarely, I loose thats protective idea in the circuit, BUT i should be able to chance output voltage, right? What voltage should be on pin6 of U2?
  13. Hi. I have just built the PSU but surprise-surprise it does not work. Output voltage of the PSU is constantly 33V. Voltage between pin4 and pin6 of u1 is chancing from 0 to 9.9V when turning voltage pot. I am using UA741 opamps. [+-22V] Voltage over pins 4 and 7 is 38V on U3 and U2. On U1 it's 33V. Chanced RV1 to 10k, short circuited R10[Like in the 741's datasheet] What purpose has D10? Doesn't it just feeds all the output voltage directly to the base of Q2? R15 is heating....voltage on it is ~33V. When I remove all opamps the output voltage stays up. When I remove Q1 or both(!) of it's base resistors then output voltage drops to zero. -Eggy
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