harp
Badcaps Veteran
Last Activity: 10-23-2025, 02:24 PM
Joined: 06-05-2022
Location: 45.2,14.4
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Some overcurrent testing............ https://m.youtube.com/watch?v=RdT-xWC4h4k -
Yes I read eevblog link, and see there is the same issue even with branded psu. Everything point to electrolitic capacitor on output, so that seems for that ammount of energy isnt controlled... ridiculus... for my perspective it is a mayor flaw in design, and wonder how and why that problem isnt yet consider by (analog) psu designer, even on cheaper one psu... Now I have to worry if my psu has silently destroy some components while "repairing" something.................................. Everything starts with try to test zenner, but now it really isnt it, it is about psu, has he deliver...Leave a comment:
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"I etched the provided board design and populated it."... on picture there is some to92 transistors rotated against silk screen (hopefully in that position it work)... have you check that?...
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"and forget about the current limit on the PSU."... and for me that is the only point of haveing lab psu in use........................... Have someone schematics of that psu UNI-T UTP3315TFL, I have noticed that they did a improvement in meantime by ommitting vr6 and vr8 in 2025 selling model... and flip over top to220 element... How hard can be that do a propper CC function, I dont think thay pay any attention at all for startup detail in firstplace... so perhaps it can be easely fix?...
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So, is that mean that smps lab psu are affected too with this issue?Leave a comment:
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I go with extend testing and kill some regular LED diode at "5mA". Now I can conclude, it is not issue about switching between taps and induction, but inertion of regulation circuit to do real "constant" current. I tested in first range on 7.6v (without switching occure), and noticed that led initialy briefly flash much stronger that can on 5mA. Then I set it to 10v, and visualy is the same even switching occure. LED stay undamaged. Then I setup to 30v, and led instant die after initial flash...................... as many as I watch lab psu review, in all is pay attention to...Leave a comment:
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For these who want to test your linear psu, this is setup: set the voltage of psu al least to pass to one higher transformer tap (or simply to 30v) then the testing zener is, and set fixed current at 5mA. For these who have 3 digit display, you can anyway set fine current using a external dmm with caution. Example and procedure for 9v1 zener is: set voltage to 19v, current to 5mA, and connect zener across the probe (anode to ground), then read voltage on display, it will be about 9v, write on papers all digits and disconect probes. Again connect probes and read voltages on display - if the zener...Leave a comment:
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The initial idea was to use psu as measure device, not only as power source. The whole purpose of haveing a current limit is to prevent damaging circuit, and I use and explore that option... if the current realy stay at 5mA level all the time I dont think that while switching taps there can be enough surge power to damage 1w diode........................... So function of CC is no acomplish his task for fine electronic, I see that on that way...Leave a comment:
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I just kill another 9v1 zenner at 5mA, that say, it is repetable indeed. I have no digital scope so I can do only a yt review, capture execution on video clip... so guys be aware of that. I think it is only issue specificaly with zenner and zener properties to conduct at some point and too slow regulation (or too fast letting go) that control current. When it switch to lower tap, current limit is fast release in gap while induction surge hit zenner and slowly initiate again when is diode yet damaged........................ This topic is for someone who has needed equipment (on mind eevblog), I...Leave a comment:
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I am not get it... the switching between taps is done before rectifier, and not interference with setted current limmit. If it generate a high voltage spike by induction, there is much control electronic on the way before get to the output. I am a bit worry, because, if it connected to some circuit (that has to be repaired) and start to switching between taps for any reason, it can silently kill protection diodes in mosfets, ICs, makeing them shorted........................... I like to hear from different users and psu (linear) model, if they can perform above zener test and worrylessly swipe...Leave a comment:
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question/caution note to usage of linear psu
I have UNI-T UTP3315TFL (2025 model) and just want to measure some zenner diodes directly with it. Set it to 12v and 7mA and connect BZX85C9V1 to it... shown on display 8.91v at 7mA... that seem fine to me. But, I guess I have in box a larger zener, let set it up to 16v, same current. Relay inside clicking to bigger range over 15v. When I test the sameone zenner accross probe, it clicks back to lower range, but displayed about 0v. The zenner was samehow killed by switching winding on 7mA limit... It was a 1W zenner, and can take up much higher voltage and current, so what is hapened realy, am... -
"I think this is the pmic and on testing"... why you think that? So, say, if turn it is not: "I think it might be faulty"... please explain why you think that ic is faulty? ?................. on picture is sot23 package nearby, so that little chip is not likely to be pmic. Ldo is about 150mA I guess, so must be ic with ground plane... search on schematic for ldo, and pwrbtn, then find this ic on mb...Leave a comment:
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As example of ldo in attach, it is useful to check what pmic you have and if it have ldo 3v3 on power button, sometimes with addition to 5v ok and they are working ok. Be systematic in repair, so do nor just repair on first sight. If is usbc data lines is broken, the pd controler not let charger to switch to 19v, nor enable batt charging... so, changeing pd controler before check continuity pin-to-pin endpin it may not solve the problem. Check on every mosfet if not shorted also, it is routine check like checking rails......
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You have 3.3v and 5v on coil, but also 3.3v and 5v ldo from pmic. What is resistance of ldo 3.3v and 5v to ground? Oh, you are all over the forum... I see that laptom has common fault on usbc connector, have you check if voltage reach board without battery?Leave a comment:
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Maybe is some lab psu with short circuit protection kick in... what model of psu you have?Leave a comment:
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I put ntc on negative rail, and feed npn inverter. That add resistance in sensing circuit, get rid of latching and heating, but complicate circuit (wanted chart parametars) that I cant anymore follow. I manage in practice to fan start increase speed at 30 deg.c, and at 50 deg.c it is nearly fully on. I expect that all between has to be - if not linear - some sort of simple curve... but no, it jumping all over from min to max... I make some pause now to this project, and I gues that start all over with opamp control....
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1.2A? Really I dont know, I see that on psu display second after pass 115mA... in that time, ntc and bd139 are be hot to touch, and ntc can not to be again colded by touching like usual and fan go crazy. BD139 are later put on biger heatsink, and not overheating again...................... But ofcorse, now I have second problem, because "my simplicity"... I used ntc in metal can for testing, and it has significiant thermal mass all over the sensor. That act like small heatsink on it. Now I put flat ntc, with no thermal mass, bare sensor, and it is over heated in split of second if not...Leave a comment:
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Thank you stj, you open my eyes
I always think there is some kiloohm in there on ntc... I add a 220 ohm in extend to ntc to 24v, and in brief test it solve problem, not latch anymore. The ntc is 10k, and other two resistor value is determined to function at specific graph, so I cant just change value too much. I know, it is not good circuit, high voltage large current, but it is simpe enough and in practice ntc should not be over 100 deg.C... I do future test and if not satisfied, I have to add some sort of protection, with zenner, transistor... that not affect to graph characteristics... if...
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simple 24v fan control problem
I am working on automated fan speed for lab psu... the fan is 24v 0.15A, and I am connected it to 820 ohm to ground, that provide minimum silent air flow on startup. It is powered around 4v at minimum point. Parallel to resistor I connected BD139, that drive a 10k NTC. Everything work like expected, but in extended test, where I isolate NTC, I have few issues, and like to ask here for help. 1. If ntc is not connected to heatsink, it go slowly to heat up and up and fan make noise than... At point "A" I measure voltage and put NTC in flame, everything is working ok till about 1.1v, and...
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