LM723 and TL082 power supply - Page 1
Forum section: electronics / beginners

author: mike_mike
author_rank: Super Contributor
timestamp: July 13, 2023, 08:22:16 am
content: Hello ! The attached schematic is a power supply which I build using TL082 instead of LM358 because LM358 was oscillating.After replacing LM358 by TL082 I tested using the oscilloscope and it was ok. Also I used a 7812 and 7912 instead of that simple capacitor power supply, to power the TL082 and LM723.The "problem" that I found is that the minimum output current is about 170mA and I wanted to be 0 mA - as the schematic designer notified.Please let me know what can I do to make it going as low as 0 mA ?

author: iMo
author_rank: Super Contributor
timestamp: July 13, 2023, 08:38:03 am
content: Btw the C11 should be wired ti IN+, imho..

author: dietert1
author_rank: Super Contributor
timestamp: July 13, 2023, 08:41:20 am
content: If you are asking about the current limit, the lowest setting depends on R23. If you put a short there, you can adjust the limit to zero or near zero. There is an uncertainty of about 5 mV / 0.1 Ohm = 50 mA due to the unknown input offset voltage of U28. One could use a so-called precision amplifier there, for example OPA145, in order to reduce uncertainty to about 1 mA.Regards, Dieter

author: mike_mike
author_rank: Super Contributor
timestamp: July 13, 2023, 08:48:24 am
content: It is possible to adjust the input offset voltage by using a resistor to the +12V or to the -12V rail ?

author: dietert1
author_rank: Super Contributor
timestamp: July 13, 2023, 08:54:31 am
content: Yes, the TL081 supports offset voltage adjustment. Datasheet explains how it works.For TL082 one would use a voltage divider to provide a small offset below RV2. Maybe you can use the surplus 33R resistor for that.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 13, 2023, 09:37:09 am
content: The min value for the current comes from the OP- offset and R23. One could test a different sample of TL082 / TL072 or maybe an RC4558 as an alternative OP-amp to find one with a small offset.With a 0.1 Ohm shunt the regulation at low currents is limited. To get good current regulation also at low currents one may have to use 2 ranges for the shunt (e.g. 0.1 ohm and 10 ohm).

author: xavier60
author_rank: Super Contributor
timestamp: July 13, 2023, 10:53:07 am
content: A high value resistor from -12V to the non-inverting input of the CC opamp will make the CC range go to zero.

author: mike_mike
author_rank: Super Contributor
timestamp: July 13, 2023, 01:41:48 pm
content: Quote from: xavier60 on July 13, 2023, 10:53:07 amI added a 10M resistor from -12V (pin 4) to pin 5 but now when I set the minimum output current from potentiometer (RV2) then the output voltage goes to -1.5V.I also tried to test different values for R23 (33R), but if I change R23 to 4.7R, then the same negative output voltage appears at the minimum set current.If I change R23 to 10R, then the things change and now the minimum output current is 17mA.

author: dietert1
author_rank: Super Contributor
timestamp: July 13, 2023, 04:35:44 pm
content: Seems like with 10 Ohm or so you already have a good solution. You could try to fine tune with a 100R resistor parallel to the 10R.Near zero current it gets a bit complicated. For example the zero offset depends on hfe of Q3, as the current through R19 at 0.6 V gets measured by the shunt and is inside the current limit. This contribution may be a mA or so. Also when the output transistors get hot, the adjustment changes.R19 also is a path for negative output voltage. That's why they inserted D9. There could be another diode as protection of Q3 against reverse Ube breakdown.Regards, Dieter

author: xavier60
author_rank: Super Contributor
timestamp: July 13, 2023, 07:51:16 pm
content: The only place I can see causing the negative output is the current flow from Reference to the output via RV1.Explains why the design has the minimum CC setting above zero. D9 should be clamping the output to about -0.6V.Also there needs to be something added to protect B-E of Q3 from high reverse bias.

author: xavier60
author_rank: Super Contributor
timestamp: July 15, 2023, 04:40:03 am
content: One work-around is to add a preload circuit like your other PSU has. It just needs to be done with a PNP transistor or P-ch MOSFET.

author: mike_mike
author_rank: Super Contributor
timestamp: October 19, 2024, 10:48:28 am
content: Hello, regarding the the original schematic (the one from the first post) I tried to check the stability at different types of load and at different output voltages.I found that at 4V output and 1.5 ohm load, the response has a little bump on the lower side (DS0031). I used 220pF capacitor (C10) in serie with 10k resistor.I tried different types of capacitors in series with resistor and finally I found that using 100pF capacitor (C10) in series with 1k resistor results in a good response (DS0034).And I also tested using the same capacitor and resistor but at 30V output voltage and 11 ohm load (DS0037).Please have a look and tell me what you think ?LE: My schematic use 4xTIP35C as power transistors and D44H11 as driver transistor. Also the +12V and -12V rail are stabilized using LM7812 and LM7912. The opamp is a TL082CP.

author: xavier60
author_rank: Super Contributor
timestamp: October 20, 2024, 03:13:00 am
content: There is something stubble in DS0034, not sure if it's small distortion or a little ringing. Either way, not a problem.Did you solve the problem of the output going negative at minimum current setting?

author: mike_mike
author_rank: Super Contributor
timestamp: October 20, 2024, 06:06:34 am
content: Quote from: xavier60 on October 20, 2024, 03:13:00 amI checked only the stability with the psu tester.I will try to solve it as fast as I can.

author: mike_mike
author_rank: Super Contributor
timestamp: October 20, 2024, 06:48:34 am
content: Tried different values: 1Mohm, 4,7Mohm, 10Mohm from pin 5 to -12V but only I got a negative voltage across output (-0.30V).The current limiting works, but I got -0.30V at the output when the PSU is in current limit mode.I think that it needs some negative voltage on the RV2 for having 0V and 0A at output...

author: xavier60
author_rank: Super Contributor
timestamp: October 20, 2024, 07:24:49 am
content: Quote from: mike_mike on October 20, 2024, 06:48:34 amI still think it's actually working normally. If pin 5 goes more negative than 6 by even a few mV, 7 will go full negative, reverse biasing Q3. The CV opamp will have no control. Remember, the opamp with the lowest output voltage takes control via the ORing diodes.Check the voltage on pin 7.

author: xavier60
author_rank: Super Contributor
timestamp: October 20, 2024, 07:35:08 am
content: Quote from: xavier60 on October 20, 2024, 07:24:49 amI did some calculations. 10M should have come close to fixing the problem depending on the opamp's input offset voltage. The next step could be to decrease R11 after fitting the 10M resistor.

author: iMo
author_rank: Super Contributor
timestamp: October 20, 2024, 08:44:28 am
content: Try to put a diode into the base of Q3 - cathode to the Q3 base (as it is in the standard designs).PS: btw., they always use a 2.2V to 2.4V zener with 10k in series wired to the common node of the CC/CV outputs - that has perhaps some reason too (you are missing that there)..

author: mike_mike
author_rank: Super Contributor
timestamp: October 20, 2024, 09:14:02 am
content: @xavier60I used a 10K in parallel with 6.2K for R11 (in total 3.8K) but now the voltage does not decrease when decreasing the current from the current pot, and now the red led does not lit, and the minimum output current is abou 0.07A

author: xavier60
author_rank: Super Contributor
timestamp: October 20, 2024, 10:56:40 am
content: Quote from: mike_mike on October 20, 2024, 09:14:02 amYou should be keeping track of what pin 7 is doing. Increasing the parallel resistor from 10K should cause the minimum CC setting to drop until a point is reached where pin 7 goes negative, and a small negative voltage appears on the output again.

author: mike_mike
author_rank: Super Contributor
timestamp: October 20, 2024, 11:57:36 am
content: Now I have 11.6V on pin 7 but no output voltage.I removed the 10Mohm resistor but no output voltage.Also I removed the 10K which was in parallel with R11 but no output voltage.On pin 1 I have -8.8V

author: xavier60
author_rank: Super Contributor
timestamp: October 20, 2024, 12:24:52 pm
content: Quote from: mike_mike on October 20, 2024, 11:57:36 amThe -8.8V from pin 1 will be caussing the Base of Q3 to be reversed biased.

author: mike_mike
author_rank: Super Contributor
timestamp: October 20, 2024, 02:24:17 pm
content: The problem was a broken trace on the PCB. The PCB is old and has a lot of rework on it.Now, with only the 1M ohm from pin 5 to -12V, the output is -0.30V and on pin 7 the voltage is 3.73V, while on pin 1 the voltage is 23.67V.And with the 10Mohm resistor from pin 5 to -12V, on pin 7 the output is 3.84V and on pin 1 the voltage is 23.67V. The output of the PSU is -0.3V.

author: xavier60
author_rank: Super Contributor
timestamp: October 20, 2024, 07:58:34 pm
content: Quote from: mike_mike on October 20, 2024, 02:24:17 pmVoltages in the control circuitry should be measured WRT the positive output terminal to make sense.Does the -0.3V on the output cause any problems?

author: mike_mike
author_rank: Super Contributor
timestamp: October 21, 2024, 02:55:20 am
content: I measured WRT the positive output terminal.Pin1 = 11.56V, Pin7 = -8.28V.The -0.3V output doesn't cause any problems, I think that I should leave the current limit as it is (without the 10Mohm resistor from pin 5 to -12V) and concentrate more on the stability of the PSU.

author: xavier60
author_rank: Super Contributor
timestamp: October 21, 2024, 05:28:19 am
content: Quote from: iMo on October 20, 2024, 08:44:28 amThe reason for the Zener is so that the output stage loses drive while there isn't enough control rail voltage for the opamps to work properly.This prevents a possible output voltage spike when the mains supply is removed.

author: mike_mike
author_rank: Super Contributor
timestamp: October 22, 2024, 04:39:07 am
content: Regarding the stability of the power supply. I wanted to make some tests with the PSU tester circuit and with the PSU shorter circuit.I am using for C10 a 100pF capacitor in series with a 1kohm resistor.How can I find the ideal combination of the capacitor and resistor values ?When I used a 220pF capacitor and 10kohm resistor, the response at 4V output and 3A was not so good, because I got a response as shown in the attached screenshot.

author: xavier60
author_rank: Super Contributor
timestamp: October 22, 2024, 05:09:52 am
content: I think you are close so go to a 470 ohms and something higher for the capacitor, 1nF or higher. The capacitor being too high wont affect stability, only will increase settling time.Confirm that it's stable then gradually increase the resistance until ringing at the dip is noticed then lower the resistance again depending on how much safety margin you want.Then decrease the capacitance to improve the settling time without causing any ringing. It's not a problem to leave the settling time a bit long.

author: mike_mike
author_rank: Super Contributor
timestamp: October 22, 2024, 04:34:52 pm
content: A test using Rload=10R, Vout=30.5V.R=470 ohms and C=1nF.Please find attached the screenshots.Edit: probably tomorrow I will do some more tests.

author: mike_mike
author_rank: Super Contributor
timestamp: October 22, 2024, 07:04:14 pm
content: I tested at Vout=4.5V, Rload=1.5ohms, C=1nF and R=470ohms = BMP0008and I tested at same Vout and Rload, C=1nF and R=680 ohms = BMP0010Also, at same Vout and Rload, C=1nF and R=560 ohms = BMP0011.In the last 2 tests I see a small bump.

author: xavier60
author_rank: Super Contributor
timestamp: October 22, 2024, 08:15:09 pm
content: If there is no bump, as small as it is, with the 470 ohm, leave it at 470.Although it's good enough to leave as is, Im not sure what's happening with the settling. Does the voltage ever fully recover?It also looks like the voltage setting has some effect on the settling. This would be a design characteristic and unavoidable.

author: mike_mike
author_rank: Super Contributor
timestamp: October 23, 2024, 03:15:27 am
content: It looks like the settling time is very long...

author: xavier60
author_rank: Super Contributor
timestamp: October 23, 2024, 03:26:38 am
content: It's maybe because of where the DSO is connected.Try to measure as close as possible between the top of R5 and the bottom of RV1.Edit: The 2nd reading does show very slow settling time, eventually reaching the original voltage.Maybe because the DSO is AC coupled.

author: mike_mike
author_rank: Super Contributor
timestamp: October 23, 2024, 03:34:51 am
content: Please find attached.

author: xavier60
author_rank: Super Contributor
timestamp: October 23, 2024, 03:41:30 am
content: Ok, it does get back to the original voltage. I suspect that the extra settling time is being caused by C2 and/or C3, which are there for a good reason, so nothing to worry about.

author: mike_mike
author_rank: Super Contributor
timestamp: October 23, 2024, 03:54:05 am
content: Should I reduce the value of the capacitor now ? Should I leave it as it is, and make more tests with different output voltages and loads ?

author: xavier60
author_rank: Super Contributor
timestamp: October 23, 2024, 04:07:47 am
content: Leave it as is. It's safest for the capacitor to be a little on the large size than being too small.

author: xavier60
author_rank: Super Contributor
timestamp: October 23, 2024, 04:29:15 am
content: Yes, test with different voltages and loads to be sure.No need to post the respopnse if it looks good.

author: mike_mike
author_rank: Super Contributor
timestamp: October 23, 2024, 08:46:56 pm
content: The response looks good, but that settling time is probably very long.At Vout=30V, Rload=10R, the settling time looks very long.Please find attached the screenshots. It was measured at the top of R5 and the bottom of RV1.

author: xavier60
author_rank: Super Contributor
timestamp: October 23, 2024, 09:09:39 pm
content: You could try decreasing the 1nF but nothing else. Do a search on power supply load tests and you will find that 50mV is acceptable.

author: mike_mike
author_rank: Super Contributor
timestamp: October 24, 2024, 03:27:42 am
content: I replaced the 1nF capacitor by 470pF capacitor.Now the response looks faster.I used average mode and selected 2 from the Aquire menu on the oscilloscope, because when I use sample mode the signal looks dim.

author: xavier60
author_rank: Super Contributor
timestamp: October 24, 2024, 03:44:14 am
content: I don't think it can be made much better than that.

author: mike_mike
author_rank: Super Contributor
timestamp: October 29, 2024, 03:45:39 am
content: If I connect the DSO probe to the PSU output positive or negative terminal, then the following waveform appears, and it is the same that appeared at the LM358 PSU.I left the negative clip of the DSO probe unconnected.

author: xavier60
author_rank: Super Contributor
timestamp: October 29, 2024, 04:41:30 am
content: 50Hz indicates that it's mains related. Likely common mode coupled across the transformer's interwinding capacitance.

author: xavier60
author_rank: Super Contributor
timestamp: October 29, 2024, 08:45:47 am
content: Actually, that's a lot of voltage there which should be ringing alarm bells. Best to unplug it for now, check the PSU's mains wiring and do some leakage testing.

author: mike_mike
author_rank: Super Contributor
timestamp: October 29, 2024, 09:01:38 am
content: Should I use another transformer ?If the ground clip left unconnected then why this measurement is still valid ?

author: xavier60
author_rank: Super Contributor
timestamp: October 29, 2024, 09:10:20 am
content: Quote from: mike_mike on October 29, 2024, 09:01:38 amNot necessarily. I'm now concerned about safety. I'm not an electrician, so not prepaid to give direct advice. Do some research on safety leakage testing for now.After you have determined that there is no hazardous leakage current, simply swapping over the primary connections might reduce the large common mode voltage.With the DSO probe's ground clip disconnected, you are measuring a large common mode AC voltage which is present on every part of the PSU's output side WRT mains Earth.

author: Harry_22
author_rank: Frequent Contributor
timestamp: November 02, 2024, 09:34:04 am
content: Quote from: mike_mike on July 13, 2023, 08:22:16 amHi!I found that TL082 circuit also oscillates. The self-excitation frequency is about 7 kHz. Could you check your circuit under such operating conditions?U=27V, Current limit 270mA, Load 100 Ohm

author: xavier60
author_rank: Super Contributor
timestamp: November 02, 2024, 09:53:05 am
content: The CV and CC loops should be checked separately, CV first. Set the current limit to maximum to ensure that only the CV loop is in control of the output stage,

author: Harry_22
author_rank: Frequent Contributor
timestamp: November 02, 2024, 10:26:49 am
content: Yes, you are absolutely right.The situation turned out to be very uncertain.I increased the current cutoff to the maximum.

author: xavier60
author_rank: Super Contributor
timestamp: November 02, 2024, 10:31:11 am
content: Try increasing C10 to 1nF. If there is still oscillation, try adding 470 ohms in series with C10.

author: Harry_22
author_rank: Frequent Contributor
timestamp: November 02, 2024, 10:38:23 am
content: The source file for Microcap is in attachment.I deliberately do not install capacitors in parallel with the voltage sources, so as not to overload the simulator with useless calculations.

author: Harry_22
author_rank: Frequent Contributor
timestamp: November 02, 2024, 10:43:47 am
content: Quote from: xavier60 on November 02, 2024, 10:31:11 amIncreasing the C10 solved the oscillation problem.Apparently LM358 works too.Sorry I missed the following manipulations:Quote from: mike_mike on October 19, 2024, 10:48:28 am

author: xavier60
author_rank: Super Contributor
timestamp: November 02, 2024, 10:48:18 am
content: I have settled on the TLC072 for linear PSU applications.

author: mike_mike
author_rank: Super Contributor
timestamp: November 02, 2024, 03:46:20 pm
content: Hello@Harry_22, please find attached the results of the test at Vout=27V, I=270mA, Rload=100R, C10=47pF.

author: Harry_22
author_rank: Frequent Contributor
timestamp: November 02, 2024, 05:13:35 pm
content: Hi Mike!Thank you for test.Is your current diagram exactly the same as the original one?

author: mike_mike
author_rank: Super Contributor
timestamp: November 02, 2024, 08:14:37 pm
content: The circuit diagram is different.I made the following modifications:1. I used a 2x12V/500mA transformer and L7812 and L7912 for powering the LM723 and the OpAmp.2. I removed C13, C14, C15, C16.3. I replaced C6 by 2x4700uF/63V in parallel.4. BD139 replaced by D44H11.5. BD911 replaced by 4xTIP35C, and 4x 0.1R/5W.6. RV1 = 50k.7. U2 replaced by TL082.8. R23 replaced by a strap.9. R9=22k, R5=22k in parallel with 22k.10. New PCB design.

author: mike_mike
author_rank: Super Contributor
timestamp: November 03, 2024, 08:32:20 am
content: Please find attached the schematic.Power transistors (trz connector) were mounted directly on the heatsink.

author: iMo
author_rank: Super Contributor
timestamp: November 03, 2024, 08:42:22 am
content: Btw the uA723 has been used here as a voltage reference only (with some output current capability), you may use more recent cheapo chips there, like 78L05/6/8 or any similar..PS: the filtering capacitor at the uA723 Vref's output is not good, imho, it should be wired at the uA723's +IN input instead..It is meant to create an RC low pass filter with the R there (to filter out the noise of the uA723's reference)..Also doublecheck in your other schematics..Quote from: iMo on July 13, 2023, 08:38:03 am

author: Harry_22
author_rank: Frequent Contributor
timestamp: November 03, 2024, 10:13:31 am
content: Quote from: mike_mike on November 02, 2024, 08:14:37 pmWhat about C10, have you changed it?Could you measure the pimary and secondary weel resistamce on main transformer, approximately.What rectifier diodes do you have?

author: mike_mike
author_rank: Super Contributor
timestamp: November 03, 2024, 10:19:10 am
content: The last test was with C10 = 47pF.I also made test with C10 = 470pF in series with R=470 ohms. Also with C10=1nF and R=470 ohms.I used a main transformer with 2 outputs of 15V, connected in series. It is a transformer from an UPS, it has about 300W-350W, and it is using aluminum wire for secondary windings.The primary is at 230V (and I don't know if it is copper or aluminum wire).The secondary resistance is about 6.0 ohms in primary and about 0.2 ohms in secondary.I use a KBPC1010 rectifier bridge.

author: mike_mike
author_rank: Super Contributor
timestamp: November 03, 2024, 10:55:19 am
content: Probably it should be a good idea to use the tap changer circuit with this PSU, but without using the switch.I attached the schematic used for tap changer, maybe it needs some modifications.I havent't tested it yet with load, I only connected it in the circuit and it works.

author: B0B45
author_rank: Contributor
timestamp: November 03, 2024, 03:11:12 pm
content: Hey,the schematics you use looks like the old Elektor power supply from 1982.Link to the plan:https://elektrotanya.com/files/forum/2014/06/0_35v_3a_labor.pdf(an eng. version of the text also exists somewhere in the internet)I'm currently planning to build one of my own. So I redraw the plan myself and add some changes that where suggested in the german mikrocontroller.net forum.Maybe it can help you.GreetingsBob

author: mike_mike
author_rank: Super Contributor
timestamp: November 03, 2024, 05:54:41 pm
content: I made some tests using R=470 ohms and C10 = 470pF.1. using TL082 - 275_003, 0042. using LM358 - 275_005, 006When I used LM358 appeared a small oscillation, you can see it in 275_005.jpg

author: Harry_22
author_rank: Frequent Contributor
timestamp: November 03, 2024, 08:32:42 pm
content: Just have adapted my old calculation of tube output stage transformer for this power supply.A little later I will add it to the diagram for the purity of the experiment.Transient analysis works, but you can look at the rest of the calculations, some of them are fascinating.

author: Harry_22
author_rank: Frequent Contributor
timestamp: November 04, 2024, 09:45:43 pm
content: Quote from: mike_mike on November 03, 2024, 08:32:20 amHi Mike!You and I got caught and made the same mistake.@Bob, what a time you came with Elektor power supply!So, R6 must be connected to R18 (please see diagram in appendix). Then the circuit is not excited.Once again I am convinced that Microcap is not mistaken. You get out exactly what you put into it.

author: xavier60
author_rank: Super Contributor
timestamp: November 04, 2024, 09:54:23 pm
content: From here, it looks like R6 should connect to the PSU's + output/GND, to get good regulation.

author: B0B45
author_rank: Contributor
timestamp: November 05, 2024, 12:42:38 am
content: According to the plans you shoud connect the R6 after the shunt on the +output.

author: mike_mike
author_rank: Super Contributor
timestamp: November 05, 2024, 05:28:40 am
content: So the blue line is the correct connection ?

author: xavier60
author_rank: Super Contributor
timestamp: November 05, 2024, 05:42:01 am
content: Yes. The physical location of the connection can have a small effect on regulation, try to put it close to the PCB output point.

author: mike_mike
author_rank: Super Contributor
timestamp: November 06, 2024, 03:44:04 am
content: I want to ask if I should start doing some tests with the PSU, using the R=470 ohms and C10= 470pF ?

author: xavier60
author_rank: Super Contributor
timestamp: November 06, 2024, 03:47:11 am
content: Yes, With which opamp?If there is any instability, reduce or totally bypass the resistor. Because the CV opamp is non-inverting, its proportional gain can't go below 1.

author: mike_mike
author_rank: Super Contributor
timestamp: November 06, 2024, 04:02:54 am
content: Quote from: xavier60 on November 06, 2024, 03:47:11 amWith TL082.Edit: Probably I could test with both TL082 and LM358....

author: mike_mike
author_rank: Super Contributor
timestamp: November 06, 2024, 09:35:48 am
content: Should I start testing with LM358 or with TL082 ?

author: xavier60
author_rank: Super Contributor
timestamp: November 06, 2024, 09:38:54 am
content: The TL082. Then try it with the LM358 just to see if there is any difference.

author: Harry_22
author_rank: Frequent Contributor
timestamp: November 07, 2024, 09:03:35 am
content: Quote from: xavier60 on November 05, 2024, 05:42:01 amYes, you are right.I have redrawn the voltage regulator diagram to make it more intuitive. Unfortunately, it takes some time to do a comprehensive and conscious analysis.

author: iMo
author_rank: Super Contributor
timestamp: November 07, 2024, 09:46:54 am
content: Most people play with LTspice, imho..You may put it there and simulation would be easy..For example the analysis of almost similar PSU below..

author: mike_mike
author_rank: Super Contributor
timestamp: November 07, 2024, 04:16:48 pm
content: I could use a tap changer circuit for this PSU, using a sigle opamp (1/2 of LM358). Am I right ?Also the other half of LM358 I could use for controlling the fans which are mounted on the heatsink.

author: B0B45
author_rank: Contributor
timestamp: November 07, 2024, 10:24:23 pm
content: Hey,do you have some suggestion for the power transistor in a TO-247 package? Whats are the important characteristics on the datasheet I should look at?Thanks - Bob

author: mike_mike
author_rank: Super Contributor
timestamp: November 08, 2024, 04:12:58 am
content: @B0B45I am using TIP35C and TIP3055. I chose those transistors because they have high collector current and high power dissipation. I am using fans mounted on the heatsink to cool them better, but only on the final PSU, when I will install it into a case. I use a fan controller for turning on/off the fans. I will use 2 fans of 80x80 mm, at 12V.

author: mike_mike
author_rank: Super Contributor
timestamp: November 08, 2024, 05:04:41 am
content: I can't do right now the tests, I have problems with the software which is copying the screenshots to the pc...

author: B0B45
author_rank: Contributor
timestamp: November 08, 2024, 08:17:07 am
content: thank you for your reply, what about theMJL3281? Would that transistor also fit?Link to datasheet:https://www.onsemi.com/pdf/datasheet/mjl3281a-d.pdf

author: mike_mike
author_rank: Super Contributor
timestamp: November 08, 2024, 09:43:53 am
content: I think that it will do the job.

author: mike_mike
author_rank: Super Contributor
timestamp: November 08, 2024, 05:50:27 pm
content: The results:1.1, 1.2 - Vout=30V, Ilim=3.15A, Rload=10ohms2.2 - Vout=30V, Ilim=3.15A, Rload=27ohms3.1 - Vout=30V, Ilim=3.15A, Rload=47ohms4.1 - Vout=12V, Ilim=3.15A, Rload=4.7ohms5.2 - Vout=3V, Ilim=3.15A, Rload=1ohms6.1 - Vout=3V, Ilim=1.45A, Rload=4.7ohms7.1 - Vout=3V, Ilim=1.45A, Rload=47ohmsEDIT: The above tests were made using R=470R and C10=470pF.

author: Harry_22
author_rank: Frequent Contributor
timestamp: November 08, 2024, 07:07:45 pm
content: Hi, Mike!Could you explain what is the blue curve no.2 that dropped from 10V to 0V?Sorry I didn't find explanation.

author: mike_mike
author_rank: Super Contributor
timestamp: November 08, 2024, 08:44:57 pm
content: The blue waveform is the output of the NE555. The NE555 is located in the PSU tester schematic, which I will attach below.

author: mike_mike
author_rank: Super Contributor
timestamp: November 09, 2024, 10:48:41 am
content: @xavier60, I made the test from reply below:Quote from: mike_mike on November 08, 2024, 05:50:27 pmI saw that there is some noise on the yellow (the output of the PSU) waveform.What should I do next ? are there any other test that I should make ?

author: xavier60
author_rank: Super Contributor
timestamp: November 09, 2024, 08:56:30 pm
content: Try to find where the noise is from. Does the noise stay when the mains power is turned off?

author: mike_mike
author_rank: Super Contributor
timestamp: November 09, 2024, 09:09:30 pm
content: Yes, the noise stay when the power is off, even if I unplug the main transformer and the 2x12V transformer from the 230VAC mains .The big noise appears hwen the load consume low current.