hybridfree/eevblog-posts huggingface dataset:
Power supply resets when aircon comes on - Page 1
Forum section: electronics / beginners

author: new299
author_rank: Regular Contributor
timestamp: June 07, 2015, 09:55:33 pm
content: I have a E6340, every time my aircon comes on (portable unit on the same circuit). The E6340 resets. I assume this is something to do with the inrush current to the aircon. But what exactly is happening? And how to I rectify the situation?

author: electr_peter
author_rank: Unknown
timestamp: June 07, 2015, 10:23:57 pm
content: Few possible causes:AC line is dragged down too low by the inrush currentspikes on AC line manage to get though (conducted emission)RF noise emission induces noise around MCU forcing a resetMore detailed investigation is needed to know for sure. Check AC line, add noise filters, ...

author: new299
author_rank: Regular Contributor
timestamp: June 07, 2015, 10:30:16 pm
content: Quote from: electr_peter on June 07, 2015, 10:23:57 pmThanks, I'd guess not RF as it's a few meters away, and I'd would have thought I'd see other effects if it was that serious. Would adding ferrite cores to the power supply and aircon possibly help? This would provide some filtering?

author: flynwill
author_rank: Regular Contributor
timestamp: June 08, 2015, 02:38:35 pm
content: Most likely it's the voltage sagging when the AC compressor kicks in. An easy test: plug a small incandescent lamp into the same circuit and watch as AC kicks in. You'll likely see it dim.As to whether or not it is an issue: probably not. If the dip is really bad it might be indicative of a bad splice somewhere in that circuit that's on the edge of going up in smoke, or that the AC's compressor is on it's last legs. More likely it's just a long wiring run.

author: TimFox
author_rank: Super Contributor
timestamp: June 08, 2015, 03:48:08 pm
content: I agree about voltage sag.40 years ago, my apartment shared a utility transformer with a townhouse that had a badly-maintained central air unit. Whenever that unit cycled on, there was a serious transient sag in the voltage at my apartment, that screwed up my audio amplifier temporarily.
Power Supply Resurrection - Page 1
Forum section: electronics / beginners

author: An_Onion
author_rank: Newbie
timestamp: October 12, 2020, 10:59:53 pm
content: For the last month or so I've been working on resurrecting an older APC power supply for use with some older computers. I started by replacing all of the electrolytic capacitors, because they were quite old and several of them were swollen. With those replaced I figured I couldn't fry too much by powering it on. It would try to start, but one of the relays wouldn't stay on. I figured out which one it was, and there were two identical ones on the board. I switched them and the problem moved with the relay. I figured just replace them both, since they were both old. Now the thing would start up, but there was a lot of noise from the (lonely, unheatsinked) 317T voltage regulator. So I replaced that and added a heatsink to the new one.Hopefully that all made sense, and now you're caught up. Now the darn thing will start up, but will cut out and restart after it's been running for 15-30 minutes. The onboard software doesn't record the crash or whatever it is as a power failure, and does record if I pull the plug. I checked all of the film capacitors (out of circuit), since those are often iffy on old stuff, but they all test perfect. Next on my hit list is all of the MOSFETs. The main ones are all ST, marked "P80NF 55@ / GK03X V6 / CHN 828" I haven't been able to find the exact data sheet for that one, but I thinkthis oneis probably close enough. I've tested the forward and reverse voltage drop across gate and drain with the FET on and off and resistance across gate and drain with it in and off with my multimeter. On one of them I get a lot higher voltage drop across when the FET is on (2x the average of the others) and it has higher resistance when it's on (again, 2x). I know V=IR, so that makes sense.My intuition tells me that the outlier is probably bad. Since the thing runs for a while, maybe it's getting hot. I know Joule heating, our ancient enemy, is P=I2R, and with higher resistance it's getting hot. But it's got a MASSIVE block of aluminum to sink the heat away. So maybe not. The Al block never gets very warm.I know the test conditions on the datasheet for the MOSFET are not what my pos multimeter can put on it, but it's the best I can do with what I have. What do you guys think? Is that MOSFET probably the culprit? Or is there another more failure-prone part I'm overlooking? I know I could easily replace the whole thing, but I'm using this to learn. Plus, it's a LOT more alive than it was when I started, so I feel like I'm making progress. :VI'll include a pic of the board below.Test equipment I have:Klein MM400 multimeteran old analog 20MHz scope I picked up for a songA few DC power suppliesBasic soldering tools and skillsone lonely brain cell rolling around in my head like a ball bearing in an empty paint can
Power Supply Ripple Simulation?  - Page 1
Forum section: electronics / beginners

author: ROBOT
author_rank: Contributor
timestamp: March 02, 2016, 11:35:37 pm
content: I need to do some testing at different frequencies with a waveform generator. Simulating various amounts of system noise.I need a 5v signal with up to 1V pk sine wave at from 15KHz to 10MHz if possible. The device under test will be drawing no more than 100mA.I have tried a few ways online on how to modulate noise onto a power supply using FETS and Opamps. However as soon as I increase the frequency beyond 5KHz the peak voltage drops and the amplitude maxs out at 10v while hardly in giving me a 100mV signal.The circuit I tried was the first one on this linkhttp://www.electronicproducts.com/Test_and_Measurement/Benchtop_Rack_Mountable/Simulating_electrical_noise_from_power_supplies.aspxI would appreciate the help. I can spend up to $400 making this work. I have power supplies and function generator Agilent 31220a.

author: danadak
author_rank: Super Contributor
timestamp: March 02, 2016, 11:46:43 pm
content: The NE5534has a 13 V/uS slew rate, so this might be part of yourproblem.https://en.wikipedia.org/wiki/Slew_rateOne way of injecting noise would be switch a load using a MOSFET witha random noise generator driving MOSFET. Very high speed can be achievedif you meet the MOSFETs gate drive requirements. Or use a bipolar to switcha load, base drive requirements might be easier for this application. Either caseswitching to 10 Mhz quite doable.Load switching works good in terms of evaluating regulator control loop performance.Regards, Dana.

author: vk6zgo
author_rank: Super Contributor
timestamp: March 03, 2016, 04:23:01 am
content: If you are trying to superimpose ac on a dc supply,run the dc through one winding of a transformer,& feed yourAC signal into the other.Back in the day,before we had purpose built "bump" generators,we used to test the clamping in Video Clamp Amplifiers by feeding the video through the secondary of a low voltage (3-5v) soldering iron transformer,with the primary Mains fed as normal.The winding inductance messed with the video a bit,but it was an effective test of the Clamp Amps.They all passed with flying colours,by the way!
Power supply selection - Page 1
Forum section: electronics / beginners

author: openthomas
author_rank: Contributor
timestamp: October 04, 2012, 10:34:23 pm
content: I have some equipment needs a -48v 3a isolated power supply. I am told it has 'internal Voltage Regulators to condition the internal DC voltages'.The difference between regulated, unregulated, isolated power supplies ? Should I choose regulated over unregulated or will that be a mistake being I know it is internally regulated already ?Why -48v ? I should reverse the polarity ?

author: Bored@Work
author_rank: Super Contributor
timestamp: October 04, 2012, 11:05:50 pm
content: -48V means it is telco equipment. And it is minus, not plus, because this prevents oxidation and destruction of wires due to electrolysis.When the manufacturer says you don't need a regulated supply, then you can use an unregulated on. Although a regulated one should not hurt. They should also have specified some limits for the unregulated supply (min and max allowed voltage).When the manufacturer says it needs to be isolated, then get an isolated one. Which also fixes your earth reference problem "should I reverse the polarity". If the supply is isolated you just need to connect its output correctly. They hopefully have marked the polarity on the equipment correctly. If in doubt, ask them. If still in doubt, open the thing and trace the wiring and circuit.

author: openthomas
author_rank: Contributor
timestamp: October 07, 2012, 04:00:32 am
content: Thats helpful Thank You

author: robrenz
author_rank: Super Contributor
timestamp: October 07, 2012, 06:22:54 pm
content: Wouldn't the built in regulation need a slightly higher input voltage than 48V to regulate properly? If so you don't want to feed it a regulated 48V.

author: Bored@Work
author_rank: Super Contributor
timestamp: October 07, 2012, 07:16:03 pm
content: Quote from: robrenz on October 07, 2012, 06:22:54 pmNo, there is stuff like SEPIC converters. But anyhow, just because it requires -48V externally doesn't mean it internally runs on -48V. In fact it is unlikely that any modern electronic inside will run on -48V.

author: robrenz
author_rank: Super Contributor
timestamp: October 07, 2012, 07:31:27 pm
content: Thanks. In re-reading the op I see that the 48V was the input voltage spec. not what it was regulating to internally.
power supply set up help - Page 1
Forum section: electronics / beginners

author: Axtman
author_rank: Regular Contributor
timestamp: February 23, 2022, 06:40:48 pm
content: I have an amplifier circuit that I want to test. It is uses a split supply bridge rectifier circuit. The transformer has a center tap that is grounded. The two outer secondary taps then go to a bridge rectifier and smoothing capacitors.I want to bypass the transformer, rectifier and capacitors and hook the circuit directly up to a power supply. The rails of the circuit are +43v and -43v. (Those votages are then knocked down to 12v and 15v.)I have a variable voltage/amp power supply that has three posts. Red for postitive. Black for negative. Green for ground.How do I set up the power supply? When I turn it up to 43 volts I only get 43 volts between red and black. I want positive and negative voltages.Thanks!

author: TimFox
author_rank: Super Contributor
timestamp: February 23, 2022, 06:44:48 pm
content: The third output post (ground) is not connected to the actual power supply. It is there to give a convenient way to connect either the red (positive) or black (negative) output to "ground" (i.e., protective ground, the third wire on the line cord, and the chassis of the power supply).You cannot use this supply to provide +43 and -43 V to your amplifier. You need a second power supply to get the negative rail.There are slightly complex circuits ("rail splitters", q.v.) that can provide a "center tap" to your single 43 V power supply to get +21.5 and -21.5 V, if that suffices, but they require a power device to handle the difference in current (which may be small) between the loads on the + rail and - rail.

author: Axtman
author_rank: Regular Contributor
timestamp: February 23, 2022, 07:01:33 pm
content: Thanks TimFox.So how would I set up two power supplies?Below is what I want to do.

author: TimFox
author_rank: Super Contributor
timestamp: February 23, 2022, 08:07:08 pm
content: Connect the negative of one supply to the positive of the other supply. That connection is your "0" point. The positive of the first supply is your "+" rail, and the negative of the second supply is your "-" rail. You may want to connect the ground posts of the two supplies to the common "0" point. Obviously, you need to adjust each supply to the same absolute value. Sometimes, it is convenient to use an AC power strip to supply mains to the two supplies so that you can turn them on and off together with the switch on the power strip.
power supply suggestion - Page 1
Forum section: electronics / beginners

author: LaserTazerPhaser
author_rank: Regular Contributor
timestamp: March 19, 2019, 08:42:39 am
content: Thishttps://www.mouser.com/ProductDetail/374-SW3477Dmade byStadium Groupis less expensive thanMean Wellwhich cost more and outputs out less power.Is anybody here familiar withStadium Groups'choice of components particularly capacitors?

author: dmills
author_rank: Super Contributor
timestamp: March 19, 2019, 09:56:18 pm
content: I had work dump Stontronics supplies in favour of Meanwell because we were seeing way too many in field failures.Now our use case was high load 24/7 in sometimes high ambient temperatures, but the GST series stuff just seems to keep on going where we had no end of pain with the Stontronics product.IIRC ours were the 60W variant.I would take the Meanwell myself.Incidentally, Mouser/Digikey are no sort of indicator for pricing on this stuff, it gets MUCH cheaper in quantity from a specialist supplier.Regards, Dan.

author: dmills
author_rank: Super Contributor
timestamp: March 21, 2019, 10:26:31 am
content: It is a Stontronics, Stadium Group brought Stontronics and if you look at the datasheet it is one of the old Stontronics supplies.You can do whatever of course, but IMHO Life is too short to be dealing with poor power supply reliability.Now it is a different Stontronics to the one that caused me all the pain, but short of pulling one apart I can only advise based on what I saw when I had my 60W sample apart and on the reliability record we had with that manufacturer (Which IMO spoke for itself).Incidentally, adding an LED is a way to get around the standby power limit for consumer goods in the EU! Standard trick.Regards, Dan.
Power Supply Switching Off a Capacitve Load - Page 1
Forum section: electronics / beginners

author: piguy101
author_rank: Regular Contributor
timestamp: September 09, 2018, 07:31:15 pm
content: I am borrowing a Keysight N8928A power supply (rated 10 kW, 500 Vdc) to do some testing on an inverter and a permanent magnet motor. The inverter has about 400 µF of DC link capacitance. The power supply has an output on/off button. Can I use the on/off button to switch the output? I set a low current limit to reduce the capacitor charge current when turning on. But I worry that when I switch the output off, the DC link capacitance in the inverter could backfeed the power supply. Is this an issue? For now, I have been slowly stepping the output voltage on the power supply down to 0V in order to turn off because of my concern.

author: Eka
author_rank: Regular Contributor
timestamp: September 10, 2018, 03:10:13 am
content: It can be a issue. It all depends on how well protected the power supply is. See if you can find the manual for the power supply online and see what it says. You can put a diode inline with the positive rail to block discharging back through the power supply. That will create a voltage drop, and the diode does need to be able to handle the expected current, and be heatsinked if needed.

author: Paul Price
author_rank: Super Contributor
timestamp: September 10, 2018, 03:12:05 am
content: When in doubt, always download and read the manual for this instrument.In general, if the switch is directly connecting the power supply output to the output terminals, or even if it does the same thing with a relay, the surge current flowing into or out of the P/S would easily damage the relay or the switch upon turn on or cause the power supply to be severely damaged.The use of a series diode would certainly prevent a load dump back into the power supply, but would not protect the contacts of a switch or relay within the P/S from damaging surge currents into the power supply load.
Power Supply Timing specification clarification - Page 1
Forum section: electronics / beginners

author: Freshman
author_rank: Regular Contributor
timestamp: May 07, 2025, 11:16:14 am
content: Using this E51 (https://ww1.microchip.com/downloads/aemDocuments/documents/MCU32/ProductDocuments/DataSheets/SAM-D5x-E5x-Family-Data-Sheet-DS60001507.pdf) microcontroller in a project.On page 1853 of the datasheet, the rise rate specifications for the microcontroller's power domain are provided. I am supplying the device with a fixed 3.3V.According to the datasheet, the minimum and maximum allowable rise rates for the power rail are 0.2 mV/µs and 100 mV/µs, respectively. In my PCB implementation, the power rail rises from 0 V to 3.3 V in approximately 20 ms.Is this rise time is compliant with the datasheet specifications? If it is not, what potential issues could arise due to a non-compliant power rail rise time?

author: xvr
author_rank: Frequent Contributor
timestamp: May 07, 2025, 11:34:39 am
content: Quote3.3V/20ms = 3300mV/20000us = 0.165mV/us A little bit slow (less than minimum of 0.2mV/us)QuoteMCU may have unstable reset (may not start sometimes)

author: Freshman
author_rank: Regular Contributor
timestamp: May 07, 2025, 12:36:38 pm
content: If it's slightly slower than minimum, any expectation of malfunctions of the IC pads apart from having unstable reset?Also, these are simulation values only, so can they be deviated as 0.165mV/us, and work fine expecting no issues?

author: xvr
author_rank: Frequent Contributor
timestamp: May 07, 2025, 12:46:39 pm
content: Quote from: Freshman on May 07, 2025, 12:36:38 pmTheoretically everything is possible, practically only unstable reset is a most probable result.QuoteCould be, but there is no guarantees. I think it will work.

author: Ian.M
author_rank: Super Contributor
timestamp: May 07, 2025, 02:38:07 pm
content: The datasheet claims operation down to 1.71V. Therefore the rise time you need to meet should be measured to that voltage, not to 3.3V. The odds are this speeds it up enough to beat the 0.2 mV/µs limit.
Power Supply Tips - Page 1
Forum section: electronics / beginners

author: Balakumaran Selvaraji
author_rank: Contributor
timestamp: December 31, 2017, 05:27:55 pm
content: Hello,I am finally going to complete my 8-bit breadboard computer ( just the control logic left ). I am not dealt with this issue of power distribution across the breadboard. I have tried the following method and would love to hear some recommendations to it :I took my cell-phone charger | OUTPUT - 5.00 V 2A | and connected it onto the breadboard by soldering with some header pins. The LED's did glow somewhat better than before, So I tried connecting another power supply which I got it additionally when purchasing the breadboard. Its called a 'Power Module' and it gives me about 5V and then the LED's glow a lot better but could still be improved.....

author: phil from seattle
author_rank: Super Contributor
timestamp: December 31, 2017, 05:35:29 pm
content: Probably the best tip is to calculate your load. Add up the draw of all your components and use a PS that is spec'd for 50% over that.If you must use USB cell phone chargers, get a USB connector. Breakouts for the jack are available. This is one example:https://www.adafruit.com/product/1833You might have to supply resistors to tell the charger to give you full/more power.

author: rstofer
author_rank: Super Contributor
timestamp: December 31, 2017, 05:59:02 pm
content: This is a perfect opportunity to use your DMM to measure the current required of the PS. While you're at it, measure the voltage while drawing full current.
Power Supply Troubleshooting Videos - Page 1
Forum section: electronics / beginners

author: SgtRock
author_rank: Unknown
timestamp: January 31, 2013, 03:04:57 pm
content: Greetings EEVBees:--See below links for a couple of the latest TV Power Supply videos from Norcal715. Though these are about TV Power Supplies, they are applicable to virtually any modern switching supply. In these two videos the emphasis is on troubleshooting, and component testing, with use of the Fluke DMM, an ESR tester and a scope. He knows a lot of tricks. This guy's videos are very watchable, and just what you need if you have seen all of the Dave videos."Where ignorance is bliss, 'tis folly to be wise."Thomas Gray 1716 - 1771Best RegardsClear Ether
Power Supply Voltage Conversion - Page 1
Forum section: electronics / beginners

author: spoon
author_rank: Newbie
timestamp: August 11, 2014, 09:15:54 pm
content: Hi all,EEV blog noob here. I have what is probably a rather noob question as well:I'm interested in converting an old 16V 4.5A laptop power supply to 10V 4.5A (partly to actually use for a project and partly just to see if it can be done). I found the TI LM338T/NOPB, which I think would work for this, correct?I know I also will need to dissipate the excess power, which I believe would be: (16V - 10V) * 4.5A = 27W. So I would need a heatsink capable of dissipating at least 27W.I'm a little confused as to how I actually adjust the regulator to output 10V. I've gathered that it has to do with feedback into the adjust pin, but I'm not sure exactly how that works.Anyway, I hope this isn't too noobish, and I appreciate any help you all might have!

author: mariush
author_rank: Super Contributor
timestamp: August 11, 2014, 09:43:07 pm
content: See datasheet :http://www.ti.com/lit/ds/symlink/lm138.pdfPage 2, footnotes. Power dissipation is internally limited, for TO-220 packages it's 25w. So even if you'd have a heatsink and fan capable of dissipating 27w of heat, the regulator will not do that, it will stop at 25w.27w is A LOT. It's not the way to go.(I suspect this is too much for you, as you really sound like a beginner) My advice would be to open up the laptop power supply and try to understand how the circuit works. There's a chip on the secondary side which controls the output voltage - by changing one, or a couple of resistors inside the laptop adapter, you may be able to reduce the output voltage down to lower voltages. I wouldn't say 10v, but something like 12-14v should be within possibilities.LM338 would need about 2v above the output voltage to regulate output voltage properly, so either way you'd need 12v+.But my advice would be to forget about it and switch to something like LM1084 or LD1084 or *1084 :http://uk.farnell.com/jsp/search/browse.jsp?N=2025+225134&Ntk=gensearch&Ntt=1084&Ntx=mode+matchallpartial
Power supply wine when running led contoller - Page 1
Forum section: electronics / beginners

author: shiftline
author_rank: Contributor
timestamp: May 19, 2016, 06:16:13 pm
content: I bought this susay 100w 12v 8.5a power supply for my DIY LED lightIt powers a TV420 contoller which outputs to the different led channelsEverything works except for this annoy whine outputted from the power supplyHow can I fix this?!

author: Wirehead
author_rank: Regular Contributor
timestamp: May 19, 2016, 06:21:31 pm
content: Can you put a capacitor on the input V+ V- of the controller? Probably the PWM'ing is causing spikes on the supply rail.

author: shiftline
author_rank: Contributor
timestamp: May 19, 2016, 07:49:17 pm
content: I will try it. Do you have a recommendation of what size to use?

author: ali6x944
author_rank: Frequent Contributor
timestamp: May 19, 2016, 08:54:44 pm
content: How much current dose the led driver draws from the supply , because some supplies will make a high pitch wine when high current is drown due to the fact that it shift in frequency and the increased duty cycle which is some times in hearing rang.

author: shiftline
author_rank: Contributor
timestamp: June 20, 2016, 06:00:05 am
content: I ended up finding a different supply but I'm still curious to test this to find out the cause. I'll put a meter on it later and see what is drawing
Power supply with reverse polarity - Page 1
Forum section: electronics / beginners

author: Code_Monkey
author_rank: Newbie
timestamp: July 18, 2020, 10:51:25 pm
content: Is it safe to power a device that has requirements in the specs of 0V and +5V with a power supply that provides -5V and 0V? If not, why?

author: Doctorandus_P
author_rank: Super Contributor
timestamp: July 18, 2020, 11:13:58 pm
content: It's perfectly OK.There is no real "0V" in this world. It is just a naming convention.Take for example a regular Li-Ion battery. You can either define the terminals as "0V" and "+3V7" or as "-3V7" and "0V".This is also used for putting regular power supplies in series, to generate +15V and -15V when you want to power for example opamp circuits.But you have to be careful.With some mains connected power supply one of the outputs is tied to the "earth" connection of the mains voltage plug.It's also common to do this with a piece of metal on the front panel, so you can choose whether you want a floating power supply or not.

author: atmfjstc
author_rank: Regular Contributor
timestamp: July 19, 2020, 12:56:54 am
content: Well, it depends. In theory, an electronic device can only see the voltage difference between its inputs, so, yes, hooking up -5V and 0V to the GND and 5V inputs respectively will work, as will hooking up any voltage sources that have a value of X and X+5 respectively with respect to some arbitrary point you deem as "0V".However, you have to be careful if the device electrically connects to other devices (even unintentionally, like their metal cases touching). If the power supply is non-isolated, its "0V" will not be entirely arbitrary, but rather connected directly to mains neutral. Thus, your device's "ground" will be -5V versus mains neutral. If you try to connect it to some other device that is itself powered by its own non-isolated power supply, and thus with a "ground" of 0V versus mains neutral, fireworks will result.
power supply woes - Page 1
Forum section: electronics / beginners

author: glinjik
author_rank: Regular Contributor
timestamp: April 08, 2022, 09:59:03 am
content: Hi I have built the diagram below all works fine max voltage and current work etc but although I'm feeding in 24v I cannot get more than 3v out checked all connections all seems fine for the life of me cant figure this out I'm suspicious of the 2 zener diodes an was thinking maybe a tl314 would be better any ideas?

author: inse
author_rank: Super Contributor
timestamp: April 08, 2022, 10:24:44 am
content: This looks like an Elektor circuit, do you have the entire article?Usually the circuit is explained.

author: glinjik
author_rank: Regular Contributor
timestamp: April 08, 2022, 10:42:31 am
content: no just this diagram

author: bob91343
author_rank: Super Contributor
timestamp: April 08, 2022, 03:38:05 pm
content: The diagram is poorly drawn in that the crossovers and the connections are unclear. Perhaps you got one or more of them wrong.Having said that, the output voltage is compared to the zener voltage with a differential amplifier. Are the two inputs to that amplifier equal?

author: glinjik
author_rank: Regular Contributor
timestamp: April 08, 2022, 04:24:45 pm
content: TBH I think I'm gonna look for a different circuit, I've spent too much time faffing with it lol

author: magic
author_rank: Super Contributor
timestamp: April 09, 2022, 07:16:02 am
content: For up to 36V input voltage and 2.5V or higher output there is a fairly simple way to combine TL431 for regulation and a pass transistor for power, shown in the datasheet.I have used it with LM317 configured for constant current in place of the transistor to also get current limiting, but potentially some other solution could be devised for output currents in excess of what 317 can provide. Variable current limit would be harder to do, unless you are OK with doing it by swapping resistorsI'm not sure how stable such circuit would be with capacitive load.There is also a thread here in "beginners" about a fully tested, but somewhat more complex lab PSU using LM324 and a bunch of power transistors.

author: Zero999
author_rank: Super Contributor
timestamp: April 09, 2022, 08:47:15 am
content: That input-output voltage differential is too high to be practical. Is this running off a transformer? If so, tap switching should be implemented, so the input voltage is reduced, for lower output voltage settings.
Power supplys - Page 1
Forum section: electronics / beginners

author: alin_im
author_rank: Regular Contributor
timestamp: May 04, 2015, 12:41:21 am
content: Hi guys, quick question when it is safe to serie or paralel 2power supplies (floating ground point)If they share the same transformerNeed some tips

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: May 04, 2015, 02:21:46 am
content: If they are floating, with respect to ground, its ok. Its like you were putting batteries in series or parallel.

author: Rerouter
author_rank: Super Contributor
timestamp: May 04, 2015, 02:32:50 am
content: When you say they share the same transformer, grab something like a 10K resistor and put it between one supplies negative and the others positive with it running, if the voltage across the resistor is 0V or very close to, the supplies are both floating, if you get the supply voltage across it, they are not,as for putting the 2 in parrellel, measure the voltage of the 2 supplies, if there is a gap more than a few hundred mV, then likely not something to attempt, if very close then you may just need something like a 0.2 ohm resistor on both outputs before connecting them in parrellel to balance any loads used,

author: Ice-Tea
author_rank: Super Contributor
timestamp: May 04, 2015, 06:03:39 am
content: In parallel? Doesn't seem like the best idea. Might work albeit with poor load balancing with a simple trafo but will probably go (horribly) wrong with a SMPS.

author: jeroen79
author_rank: Frequent Contributor
timestamp: May 04, 2015, 11:19:17 am
content: Exactly how do they share the transformer?That they float relative to ground doesn't mean that they will float relative to eachother.Is this an existing powersupply or one that you are building?How are the transformer's windings wound?

author: alin_im
author_rank: Regular Contributor
timestamp: May 04, 2015, 11:47:45 am
content: Quote from: jeroen79 on May 04, 2015, 11:19:17 ami am building my own and i am trying to figure it out which is the best method.i am using a transformer like thishttp://uk.farnell.com/block/rkd-160-2x24/transformer-2-x-24v-160va/dp/2362171and it has an output of 2x42v DCand i want to build something like thishttp://uk.farnell.com/tenma/72-10500/power-supply-2ch-30v-3a-adjustable/dp/2251948any ideasso far i am thinking of using a lt1074 IC

author: Shock
author_rank: Super Contributor
timestamp: May 04, 2015, 11:53:28 am
content: Probably best at this point to draw what your suggesting out and label it.

author: jeroen79
author_rank: Frequent Contributor
timestamp: May 04, 2015, 12:22:31 pm
content: Quote from: alin_im on May 04, 2015, 11:47:45 amThe transformer in your link has separate secondary windings that will float relative to eachother.Wether your transformer has this too can be checked with a multimeter.
Power switch using LTC4412; P ch. MOSFET does not open - Page 1
Forum section: electronics / beginners

author: zzattack
author_rank: Regular Contributor
timestamp: December 01, 2015, 03:22:34 pm
content: I built a power switch circuit based on a LTC4412 that will disconnect my battery when an auxilary power source is available. Schematic is built exactly as presented in the data sheet:The wall adapter input, when available, is a regulated 6V DC supply. The battery is a single-cell lipo that should be between 4.2-3.7V. The load goes toward a 3.3V low-dropout voltage regulator.Testing the operation of this circuit, I found that with just the battery hooked up, the LTC4412 pulls its gate low and Vbat is fed into the regulator. With the auxilary source enabled I verified that the gate pin measures a high. So far so good. Now for the problem: the MOSFET does not seem to open completely. I'm measuring 6V at both the drain and gate pins, but the PSU also hits the current limiter and I read about 5.5V at the source pin (thus going into the battery!). I've replaced the MOSFET but the problem remains.So, my best guess is that I did not choose a correct MOSFET for the job. The part I'm using is theNDS332p, with important parametersVDS(MAX): -20VVGS(VT): -0.6VRDSon: 0.4Ohms typicalThe VGS(VT)seems most important and should work with the 6V-4.2V difference between aux and battery supply.How can I figure out what's happening here?

author: homebrew
author_rank: Frequent Contributor
timestamp: December 01, 2015, 07:35:53 pm
content: Quote from: zzattack on December 01, 2015, 03:22:34 pmDid you put the FET in reverse? (Accidentally swapped drain and source?)Would at least explain the behavior as it would operate as a diode (but in reverse) ...Just an idea ...

author: Radiohead
author_rank: Contributor
timestamp: December 01, 2015, 08:23:59 pm
content: The Mosfet does not behave as an ideal diode, as it has an internal parasitic diode between drain-source. As you have noted, it charges your battery through the parasitic diode when the auxilary power source is connected. Use back-to-back mosfet configuration for ideal mosfet operation and connect CTL to GND, as described in the datasheet. See figure 4 and read "Ideal Diode Control with a microcontroller" above figure 4.

author: homebrew
author_rank: Frequent Contributor
timestamp: December 01, 2015, 08:48:34 pm
content: Sorry, äh, no!That is the REASON that this part exists. It should PREVENT reverse current flow! However FET does behave as a diode in one direction. Hence you could not turn the load off in that configuration and hence you need the back-to-back FETs to have that feature if desired. Not for the normal behavior of switching between two supplies...

author: zzattack
author_rank: Regular Contributor
timestamp: December 02, 2015, 03:03:30 pm
content: Quote from: homebrew on December 01, 2015, 07:35:53 pmI truly thought I had moved past this level of stupidity but must shamefully admit this was indeed the cause.. Thanks!
Power Systems HVDC - converting from DC to AC - Page 1
Forum section: electronics / beginners

author: EEBlackSheep
author_rank: Contributor
timestamp: January 02, 2017, 03:36:26 am
content: I live on an island and the undersea power cable uses HVDC to provide the island with 700MW of electricity. It is old and obsolete, using Thyristor tubes for rectification, but still in operation.The conversion to smooth DC seems to use roughly the same technology that we use in smaller systems (rectifier, smoothing reactors or capacitors). However I cannot seem to find how they convert it back to 3 phase AC. I looked at a great HVDC article from Siemens and nothing about inverting. On some sites there is an offhand reference that IGBTs or Thyristors are used to convert to DC (rectification) as weil as converting DC to AC, but no details.For high voltage DC power systems conversion to AC is it just like the smaller car inverters using PWM and IGBTs?thanks

author: Inflex
author_rank: Regular Contributor
timestamp: January 02, 2017, 05:14:33 am
content: Surprisingly, Wikipedia is quite useful in this case; key point being that the HVDC systems are supposedly bidirectional in most cases.https://en.wikipedia.org/wiki/HVDC_converter

author: T3sl4co1l
author_rank: Super Contributor
timestamp: January 02, 2017, 08:22:38 am
content: Using thyristors or thyratrons (tubes), you use a large series inductor on the DC bus (and usually a resonant circuit to help out), and that allows the inverter to commutate (switch from one set of devices conducting, to the next). This allows the grid to start up, and allows it to be bidirectional.IGBTs of course don't need any help to switch (just a pile of drivers), and you can save some cost on reactive components (smaller inductors). The voltage drop and semiconductor cost is higher, though.It's most definitely not like those shitty little automotive inverters.Tim

author: Richard Head
author_rank: Frequent Contributor
timestamp: January 02, 2017, 03:05:41 pm
content: It is old and obsolete, using Thyristor tubes for rectification, but still in operation.If it's old and still working it's probably a decent system. Most of the older generation equipment is so over-designed that it'll probably last forever.
power transformer to audio output transformer - Page 1
Forum section: electronics / beginners

author: christos
author_rank: Regular Contributor
timestamp: March 28, 2014, 05:55:41 pm
content: as the title says..can i make a power transformer 230v to 6-0-6v as a audio output transformer??if i can..then would the secondary coil be the input of the audio?

author: woodchips
author_rank: Frequent Contributor
timestamp: March 28, 2014, 06:51:57 pm
content: Presumably valve? Not if class A, there is substantial DC current flowing that will saturate the transformer, fizz, pop!I have never tried it, one day, but for class B why not? The DC currents should be equal and opposite so cancel, leaving the transformer happy. A toroidal transformer will be better than an EI type for frequency response. Might even be possible to use a thin cutting disc to make a slot so usable on class A?Have wondered why you can't use a standard transformer, and buck the DC current with an opposing current through another winding. Seems a reasonably simple bit of servoing, measure HT DC current and then provide the exact opposite? Will it work? Why not?

author: SeanB
author_rank: Super Contributor
timestamp: March 28, 2014, 07:10:24 pm
content: Try looking for 100V line transformers, they might be capable of handling DC through the primary. If you use a transformer with 2 115V primary windings and run the valves in push pull with a 100V HT rail then the current will cancel out in the core and you will get better linearity.

author: christos
author_rank: Regular Contributor
timestamp: March 28, 2014, 07:31:57 pm
content: hard to find a 100v...i just wanned to know if its possible..if not ill buy one..5 euros only

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 29, 2014, 03:05:52 am
content: Again, assuming this is for valves/tubes (you didn't mention), you can use a 115-0-115 primary in a PP circuit with reasonable results.Unless it's a toroidal type, don't expect useful bandwidth.Tim

author: Unknown
author_rank: Unknown
timestamp: March 29, 2014, 07:04:22 am
content: Quote from: woodchips on March 28, 2014, 06:51:57 pmThis was occasionally done in very early valve radios - not really as a servo, since there was little/no feedback (at least not completely deliberately) - by incorporating the filter choke for the HT supply (usually between the CT & gnd) into the output transformer to cancel out the field caused by the DC component of the class A output stage.It was as big a pain in the arse as it sounds...
Power Transformer Voltage Stress when Isolating - Page 1
Forum section: electronics / beginners

author: kg4arn
author_rank: Unknown
timestamp: February 25, 2018, 08:30:31 pm
content: I really cannot find this specific question answered on the web or in the forum. If I missed it, my apologies and please point me in the right direction.I understand why one should not isolate the safety ground, or float the oscilloscope with an isolation transformer, for operator safety reasons. I accept this and I am not challenging it.And although I believe what TEK says about the power transformer stress, I cannot visualize is how it causes voltage stress on the oscilloscope power transformer. Would someone be kind enough to explain it?From TEK:https://www.tek.com/document/technical-brief/floating-oscilloscope-measurements-and-operator-protectionThis is dangerous, not only from thestandpoint of elevated voltages presenton the oscilloscope (a shock hazardto the operator), but also due tocumulative stresses on the oscilloscope’spower transformer insulation.This stress may not cause immediatefailure, but may lead to future dangerousfailures (a shock and fire hazard),even after returning the oscilloscopeto properly grounded operation!

author: Benta
author_rank: Super Contributor
timestamp: February 25, 2018, 08:46:03 pm
content: Your quote seems to refer to a situation where the 'scope is floated...exactly what should be avoided.What they are referring to is probably transient conditions if the scope is floated. It's casing and really the whole circuit is suddenly moved to a different potential, which does stress the insulation.If the 'scope is not floated, there is no additional stress on its power transformer.

author: Paul Rose
author_rank: Regular Contributor
timestamp: February 25, 2018, 08:52:35 pm
content: They mention two (bad) ways of floating the scope:QuoteIf youjustdisconnect the grounding pin on the mains lead, but do not use an isolation transformer, then you still may stress the internal power transformer's insulation, because there may be a path from the device under test to the neutral mains wire ( which is grounded back at the breaker box ).

author: kg4arn
author_rank: Unknown
timestamp: February 26, 2018, 10:29:02 am
content: Thanks to both of you for the replies.
Power Transistor in Power Supply - Page 1
Forum section: electronics / beginners

author: cc1960
author_rank: Newbie
timestamp: October 23, 2011, 09:27:36 am
content: HiCan somebody explain to me how the TIP2955/MJE3055 is helping to regulate this powersupply?http://www.eleccircuit.com/5v-3a-regulate-power-supply-by-tip2955/orhttp://www.reuk.co.uk/High-Current-Voltage-Regulation.htmI think I understand every other aspect of the circuitsHow can it be that the output from TIP2955/MJE3055 is regulated?Christian

author: ejeffrey
author_rank: Super Contributor
timestamp: October 23, 2011, 09:48:07 am
content: The regulator draws a current through R1 that sets the transistor Vbe, which in turn sets the collector current that is transmitted to the load. If the output voltage is too low, the 78XX draws more current, Vbe increases, and more current is supplied to the load. If the output voltage is too high, the transistor is turned down. Thus, the LM78XX controls the voltage, but only up to about (0.6 V / R1) goes through the regulator, the rest goes through the external pass transistor.

author: cc1960
author_rank: Newbie
timestamp: October 24, 2011, 06:38:54 am
content: Thanks for the explanation.That makes sense.

author: Simon
author_rank: Unknown
timestamp: October 24, 2011, 07:00:15 am
content: in the first link the comment about just adding more transistors in parallel for more current is not quite correct. each additional transistor will need a resistor to make the transistors current share. BJT's unlike mosfet won't current share, as one gets a bit hotter it will let more current through and the effect will snow ball until magic smoke comes to the scene.
Power Up AD5683R - Page 1
Forum section: electronics / beginners

author: auccapuclla
author_rank: Newbie
timestamp: February 06, 2021, 04:49:20 am
content: Hello all. I am trying to power up the AD5683R with an Arduino Uno. Checking the datasheet I came upon the attached image.Could you please tell me how to power up this chip with Arduino Uno?Btw, I will communicate both through SPI.https://www.analog.com/media/en/technical-documentation/data-sheets/AD5683R_5682R_5681R_5683.pdf?fbclid=IwAR1fKapaSx58ITTJm9vib4YxC621ALToNl1SYDtX4c80U07FQkNBnELPjeYHope someone could help me.

author: mvs
author_rank: Frequent Contributor
timestamp: February 06, 2021, 11:13:53 am
content: You will need to connect SDI to MOSI (D11), SCLK to SCK (D13), /SYNC to any unused digital pin, GND to GND, Vlogic and Vdd to 5V./LDAC and /RESET are optional, you can connect them to any unused digital pins or to 5V if you do not want to use them. Add also decoupling caps on Vlogic, Vdd and REF.Configure arduino peripherals:set SPI mode to 1 or 2, MSB firstconfigure pins connected to /SYNC, /LDAC and /RESET as outputs and set them high.To write 3 bytes do following:set /SYNC lowwrite 3 bytes to SPIset /SYNC highIf you use software /LDAC, you can issue "update DAC register" command to load the data from input register to DAC register.As alternative you may load data directly with "write DAC and input register" command.If you use hardware /LDAC, you can set it low and then high to load the data from input register to DAC register.

author: auccapuclla
author_rank: Newbie
timestamp: February 06, 2021, 02:33:40 pm
content: Thanks for your answer.I was thinking in connect Vlogic and Vdd to the 5V output pin of the Arduino and the Vref to the 3.3V pin, and connect a capacitor in parallel in each connection. Do u think connecting in this way will cause me trouble?Btw, is it necessary to power Vref or can I leave this pin open?Thanks in advance.

author: mvs
author_rank: Frequent Contributor
timestamp: February 06, 2021, 02:56:58 pm
content: AD5683Rhas build in 2.5V reference with better accuracy and lower drift, then 3.3V LDO of Arduino Uno.You can left Vref pin open or just connect 10nF cap to it to decrease noise.
power-up circuitry for a MCU in series with a load - Page 1
Forum section: electronics / beginners

author: lixen
author_rank: Newbie
timestamp: March 02, 2017, 03:36:57 pm
content: I'm trying to create power-up circuitry for a MCU that will be place in series with a load it will control. The system will be powered by mains (240V AC). The MCU will be driving a power MOSFET in order to control the current through the load. Due to the nature of the load (LED), the total current through it must be practically zero (<1mA) for it to turn off. This means the power circuitry can only draw current during the parts of the mains sine wave that are below the threshold voltage for my LED load.To obtain this, I came up with the following:In the picture, only the power-up circuitry is present, V2 is mains voltage, V1 is there to simulate the MCU. The power MOSFET that switches the load on or off is not present in the picture.M1 is a depletion mode MOSFET. When powering up the system, M1 will act as a closed switch and the capacitor will charge up. This capacitor will be the input for a linear regulator that provides power to the MCU. As soon as the MCU is powered up, it has control over when the capacitor can be charged. It controls this by turning M2 on (closed switch), then due to the zener D6, Vgs(M1) will be -10V and M1 will act as open switch. Turning M2 off will lead to R1 acting to equalize gate and source of M1, so Vgs will be 0 again and it will act as closed switch.In my LTspice simulation, the circuit is behaving as anticipated:Now on to the issue: when implementing this on breadboard, Vgs of M1 will remain 0V instead of going to -10V when closing the M2 switch. The MOSFET I use for M1 is DN2540N5. During troubleshooting this, I tried replacing M1 by a short, and in that scenario, the voltage across D6 does become -10V as expected. Any ideas why this isn't working as desired with M1 in place? Did I overlook something? What else can I do to troubleshoot this? Or do you know of a better way to obtain the behavior I need?
Power Usage of Neon Light in Light Switches - Page 1
Forum section: electronics / beginners

author: kilimar
author_rank: Newbie
timestamp: July 22, 2024, 11:00:07 pm
content: Does anyone have any specifications or real world data (i.e. using a kill-a-watt or similar) on how much power is being used by the neon lights that are in the wall light switches or a neon light in the small plug switches (see photos)? Neon not LED.

author: coppercone2
author_rank: Super Contributor
timestamp: July 22, 2024, 11:01:15 pm
content: the load is between 50 to 200 kilo ohmsso around 1mA

author: Circlotron
author_rank: Super Contributor
timestamp: July 23, 2024, 12:07:20 am
content: Often saw a 220K series resistor with 240V neons (haven't looked for decades) so if the neon was shorted it would use 0.26 watts, so just a very tiny bit less than that.

author: Refrigerator
author_rank: Super Contributor
timestamp: July 23, 2024, 07:48:47 am
content: Neons run at about 60V IIRC, so (240V-60V)/220k = about 800µA or 200mW total power consumption.

author: kilimar
author_rank: Newbie
timestamp: July 23, 2024, 05:55:39 pm
content: Thanks for all the replies. FYI -- I'm in the US.

author: wasedadoc
author_rank: Super Contributor
timestamp: July 23, 2024, 06:52:44 pm
content: Quote from: kilimar on July 23, 2024, 05:55:39 pmSo about 100mW.