hybridfree/eevblog-posts huggingface dataset:
Resonant circuit question from textbook example - Page 1
Forum section: electronics / beginners

author: biker.josh07
author_rank: Contributor
timestamp: February 02, 2014, 10:05:24 am
content: HelloI am reading RF Circuit Design by Chris Bowick.I am a little mystified by one of the provided examples within the resonant circuit section of the book. The images provide a description of the problem.I am wondering how the effective shunt resistance is calculated to be 4500 Ohms.First I calculated the resonant radian frequency ? to be (close approximation)?=1/?(LC)=1/?(0.05x10^(-6)H x 25x10^(-12)F) = 894.4x10^6 rad/sThe series resistance of the inductor is then calculated to beR(s)=X(s)/Q= ?L/Q = [894.4x10^6 rad/s x 0.05x10^(-6)H]/10= 4.472 OhmsThen using the formula for calculating the equivalent parallel resistance for a series resistance and reactance.R(p)=R(s)[1+Q^2]=4.472[1+10^2]=4.472x101=451.7 OhmsSo I am an order of magnitude from the given value in the book.Is there a mistake in the book?If not then please let me know where I went wrong.Thanks

author: jimmc
author_rank: Frequent Contributor
timestamp: February 02, 2014, 04:46:47 pm
content: Well spotted, your figures are correct and the book is wrong!I have the fifth printing of the same book (1987) and the 'Q' in this example has been changed to 100 which gives the correct result.By the way you could have saved a step in your calculation since R(p) = Q* X(Lp) [=Q*X(C)]Jim

author: G0HZU
author_rank: Super Contributor
timestamp: February 02, 2014, 05:34:21 pm
content: I bought my copy of this book about 25 years ago and it's a brilliant book. However, there are other poor design examples besides this simple typo error. Some of the network designs that aim for a specific loaded Q end up with a quite different loaded Q because he uses quite crude or 'rule of thumb' equations in the designs. So the example fails to meet the original loaded Q design requirement by a large margin. eg a design target of QL = 15 ends up with a designed QL of just under 10 if you independently analyse the final network. Quite an error.But for basic theory on component analysis, impedance matching and also for basic use of the Smith chart, this book is still one of the best despite its age
Resonant LLC Converter - Why theory does not match simulation ? (solved) - Page 1
Forum section: electronics / beginners

author: tigrou
author_rank: Regular Contributor
timestamp: December 12, 2021, 03:39:34 pm
content: Hello,I have created the following LLC resonant circuit (half bridge):FalstadlinkHere is the inputs :Cr = 0.001 FLr = 0.001 HLm = 0.001 HRac = 5 OmhsVin_ac = 5Vfs = 112.5 Hz (switching frequency)Based on equations from thisdocument, I have calculated the following (page 4 and 5) :fr = 159.16 Hz (resonant frequency)Q = 0.2 (quality factor)m = 2 (primary / resonant inductance ratio)Fx = 0.7069 (normalized switching frequency)K(Q,m,Fx) = 7.06 (expected gain)Here is gain vs switching frequency chart for K(.2, 2, Fx) :Since input is 5V this should give 5 * 0.5 * 7.06 = 17.65V but I got 22.6V from simulation.I multiplied by 0.5 is because it's an half bridge (1 for full bridge as explain in page 4).

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 12, 2021, 11:06:38 pm
content: I think you're missing a factor of 4/pi for the fundamental amplitude of the square wave.Tim
Resonator vs crystal size - Page 1
Forum section: electronics / beginners

author: e100
author_rank: Frequent Contributor
timestamp: September 17, 2021, 05:55:54 am
content: In the following images there are two rectangular objects to the left of the two upside down MCP2515 CAN controller chips which are smaller than traditional looking crystals in a can. Would it be fair to assume that these are resonators rather than actual crystals. If so is this a bad thing for something like a CAN controller where frequency accuracy is important?

author: fourfathom
author_rank: Super Contributor
timestamp: September 17, 2021, 06:42:12 am
content: Those could easily be quartz crystals, with the adjacent devices the load capacitors. Or possibly they are crystal oscillators and the adjacent components power bypass caps, but given the layout I would suspect the crystal and load caps. Either of these are available in packages as small or smaller than what you show, and the tolerance can be quite tight (20ppm is common).
Resonators vs crystal with load capacitance? - Page 1
Forum section: electronics / beginners

author: abdullahseba
author_rank: Frequent Contributor
timestamp: February 23, 2018, 07:48:48 am
content: HiI'm designing a circuit that uses the nRF24 IC. The nrf requires a 16MHz crystal with 2 22pF caps. So I'm wondering if one of these would workhttps://www.mouser.com/ds/2/741/LFXTAL062487Reel-1000954.pdf?It says it has a load capacitance of 22pF but does not say it has built in caps. Then looking at the arduino schematic, I saw that it used a resonatorhttps://www.mouser.com/ds/2/281/p16e-522700.pdfthat has caps shown.Only problem is I cant find a resonator with a 22pF and 27pF cap While I can find 4 or 3 pin crystals with that "load capacitance"So can I use a crystal with load capacitance? And Whats the difference between a crystal with load capacitance and a resonator ?Thanks in advance.

author: ogden
author_rank: Super Contributor
timestamp: February 23, 2018, 08:15:54 am
content: Ceramic resonators are not for RF application! They have awful tolerance compared to crystals, temperature drift as well.

author: capt bullshot
author_rank: Super Contributor
timestamp: February 23, 2018, 08:35:46 am
content: In general, do not use resonators for circuits that require a stable frequency. Resonators have large initial tolerances (in the percent range, compared to ppm range for crystals), and have real bad temperature drift. As your nRF24 would generate its radio frequencies from the resonators frequency, this would cause to RF frequency to be off the nominal value and your RF comms would not work.For the crystal, the load capacitance is usually added as these two external capacitors. The total load capacitance is calculated from then IC's internal and stray capacitance plus the external capacitors (as a series circuit) and shall match the crystals specification. So if you have a different load capacity specified for a particular crystal, you can adjust the external capacitors accordingly.Resonators have different load capacity requirements, most ICs can be used with resonators and crystals as well, just adjust the external capacitors according to the datasheet of the resonator - some of them might require no capacitors at all.
Resonators  - Page 1
Forum section: electronics / beginners

author: Aztlanpz
author_rank: Regular Contributor
timestamp: January 23, 2018, 12:06:02 am
content: I am looking for a resonator (16MHz) that is smaller then 3.2mm x 1.30mm; the smaller the better .Aztlan

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: January 23, 2018, 12:29:35 am
content: If size is the main factor, a crystal might be smaller.https://www.digikey.ca/product-detail/en/avx-corp-kyocera-corp/CX2016DB16000D0FLJCC/1253-1348-2-ND/4896402is 2.0 x 1.6 mm = 3.2mm2 vs 3.2mm x 1.30mm = 4.16mm2.Circuit to resonate a crystal is pretty much the same as a resonator, but a crystal has less pullability.

author: Aztlanpz
author_rank: Regular Contributor
timestamp: January 23, 2018, 01:19:11 am
content: what is the smallest by footprint to generate a 16MHz clock?Aztlan

author: retrolefty
author_rank: Super Contributor
timestamp: January 23, 2018, 01:23:25 am
content: I think it might be clearer to specify that there are quartz crystal resonators and there are ceramic based resonators. So just stating your are looking for a resonator is not specific enough unless you want to rely on assumptions of what kind of resonator your are looking for.

author: Zero999
author_rank: Super Contributor
timestamp: January 23, 2018, 01:36:30 pm
content: Was it really necessary to create a new thread?https://www.eevblog.com/forum/beginners/crystals/msg1404154/#msg1404154
Resources for learning how to design test/QA boards - Page 1
Forum section: electronics / beginners

author: seqvenzer
author_rank: Newbie
timestamp: August 09, 2024, 02:38:36 pm
content: Does anyone have books, notes or video clips they've come across on how to design and think around test boards for ensuring correct functionality of an actual board? Anything to share from your experiences? Not a particularly hot topic I know.I have a peripherals control board gathering dust that I'd like to test. It uses a (now defunct, go figure) 8-bit MCU as it's controller. MCU shorted somewhere but the board is probably good. I have a replacement I can plug in. Most of the peripherals are simple on/off, but some are analog sensors (temperature, flow) and fiber optic receivers and transmitters. There doesn't seem to be anything that would be sensitive to high speed timing circuits, the MCU feeds control signals to start/stop things and awaits for signals from the peripherals. Some of it is on the low side of driving motors, pumps and the like, but again it's a high/low signal type of situation.Was thinking of building a few protoboards of buttons/switches, potentiometers, LEDs and the like and hook it up to the control board connectors where normally the rest of the real equipment would be, and test the whole thing that way. Almost like an evaluation board that you'd get from a dev kit. But then I remembered companies have EEs doing this for their QA departments to ensure functionality and there is probably good material on the subject of what to keep an eye out on and common circuits/patterns for dealing with certain kinds of components.
Resources for learning how to use Keithley semiconductor analyzers. - Page 1
Forum section: electronics / beginners

author: Gumbysauce
author_rank: Contributor
timestamp: June 07, 2017, 04:19:36 am
content: Hey team,I was wondering if anyone had some resources they could suggest to learn about Keithley semiconductor analyzers. I am an undergraduate EE student and recently started work in a lab where having some knowledge of: how these things work, what they can measure and how they do it, would be pretty useful. I'm not sure of the exact model but I have looked for user manuals; unfortunately they tend to be more concerned with the exact interface and how to implement certain tests than giving you an introduction to the device. I would love it if anyone knew of some good resources or strategies for learning how to use these things.Thanks!

author: pigrew
author_rank: Frequent Contributor
timestamp: June 07, 2017, 05:10:06 am
content: My guess is that it would be a 4200 model. The major thing is to understand what you are trying to measure (the DUT). What is it? What do you need to know about it?The second thing to study is the SMU hardware. Understand Kelvin measurements, NPLC, and how current ranging happens (note that when auto ranging, the source is momentarily disconnected).

author: rfeecs
author_rank: Frequent Contributor
timestamp: June 07, 2017, 04:43:14 pm
content: Keysight does a good job with the basic app notes:The semiconductor parameter analyzer (device analyzer) basics for your device characterization:http://www.keysight.com/main/editorial.jspx?cc=US&lc=eng&ckey=2317167&nid=-33019.1048181&id=2317167The parametric Measurement Handbookhttp://www.keysight.com/main/editorial.jspx?cc=US&lc=eng&ckey=1832933-1-eng&nid=-32800.695943.02&id=1832933-1-eng&cmpid=1-5628735812

author: pigrew
author_rank: Frequent Contributor
timestamp: June 07, 2017, 04:45:22 pm
content: I should have also suggested the book "Semiconductor Material and Device Characterization" by Schroder.

author: Gumbysauce
author_rank: Contributor
timestamp: June 08, 2017, 02:04:50 am
content: Sweet, thanks so much guys. EEV-B community always comes in clutch.

author: w2aew
author_rank: Super Contributor
timestamp: June 08, 2017, 03:47:01 am
content: Quote from: Gumbysauce on June 07, 2017, 04:19:36 amThere are dozens of application notes and other documents on the 4200 on the Tek website:http://www.tek.com/search/apachesolr_search/4200?filters=type%3AdocumentAnd even a few videos and webinars:http://www.tek.com/search/apachesolr_search/4200?filters=type%3Amedia
Resources for O-Scope Current Measuring - Page 1
Forum section: electronics / beginners

author: ender4171
author_rank: Contributor
timestamp: July 20, 2018, 04:43:40 pm
content: Hello,I am a beginner to oscilloscopes and just purchased a DS1054z (on the recommendations of this forum and Dave). I have been reading and practicing a lot and have most of the basics down. I am trying to find information on measuring current without the use of an expensive current probe.Specifically, I am looking for info on using basic sense/shunt resistors like Dave did in the "How Secure Are Electric Safe Locks" video, or using a ferrite core current transformer (and resistor) like AvE did in the "Testing LED Bulbs For Bad Vibrations. Yep" video.All of the articles/tutorials/references I have found so far seem to always point to using a purpose-made OTC (i.e. way more expensive than my blood can afford) current probe or assume a level of knowledge I don't yet have. I have found some stuff discussing shunt resistors but then they have some overly elaborate setup instead of a simple single resistor like Dave used, and I would like to start simple and work up.I am not looking for any hand holding or for someone to ELI5, I was just hoping someone could point me to some good resources so I can learn for myself. I know it is possible to use a normal probe and a resistor/transformer to measure current/determine the current waveform.Any help is much appreciated!!-Keith

author: JS
author_rank: Frequent Contributor
timestamp: July 21, 2018, 03:52:14 am
content: There's a project running here to build a current probe, there are basically two types for isolated current probes, transformer and hall effect.The transformer is great for pecission, high bandwidth ac measurements, you can wind one yourself to match your requirements for thebresistor you want to use and the voltage range you need or use a standard transformer like the ones provided for power meters, where you can get the meter and the transformer for $7.The hall effect sensor allows to measure DC but specs don't go up as nice as in transformers, then you can use them cuttiing a toroid core in halfs to build a clamp or as pass elements with the available ICs, the one with the core is quite easy to go probing arround but the others come calibrated from factory but you have to pinch the wire.If you have a floating or ground referenced thing to measure you could do with a resistor and an amplifier as the μCurrent, wich is really nice in those cases, DC with really good precision and low burden voltage.JS
resources for standard/common design conditions - Page 1
Forum section: electronics / beginners

author: ratio
author_rank: Regular Contributor
timestamp: January 01, 2019, 05:25:37 pm
content: Are there any standard guides for the ambient temp & design temp rise (& other environment conditions?) for like cheap consumer goods, or an automotive accessory? In particular I'm looking for the above for a (one-off DIY, not any kind of production) battery charger that's going to plug into a cigarette lighter, will not be under continuous use but will probably spend a summer day in the car operating from time to time.

author: David Hess
author_rank: Super Contributor
timestamp: January 01, 2019, 07:44:01 pm
content: One of my first audio power amplifiers failed via thermal runaway when my car was parked in the sun.Knowing the power dissipation, junction-to-ambient thermal resistance, ambient temperature, and derating curves is enough but of course experience helps. A good rule of thumb is a maximum 75C case temperature for reliable long term operation.

author: spec
author_rank: Frequent Contributor
timestamp: January 02, 2019, 09:51:15 am
content: Quote from: ratio on January 01, 2019, 05:25:37 pmThe biggest killer long term is condensing humidity. And if you live by the coast, as I do, salt air.
restoring small brushed DC motor, can i delete the braided shield on the wires? - Page 1
Forum section: electronics / beginners

author: donbright
author_rank: Newbie
timestamp: October 14, 2020, 05:16:53 am
content: Helloi am trying to restore a handful of old small brushed DC motors, about 4 inches long, with an 1/8 inch shaft, slightly rusted and in need of some cleaning.the thing about them i am not used to seeing is that the 2 normal insulated motor wires are inside of a braided metal flexible tube which is soldered to a post inside the motor that is continuous with the negative wire. The braided tube comes out of a grommeted hole in the side of the motor case, with the two normal small insulated stranded wires resting inside of it.these motors were used in some old industrial application, but i just want to put them on a silly little robot. I am wanting to replace the old, dirty, frayed wires with new - but do I also need to replace this braided cable that surrounds them? Is it meant to carry current? Can I delete the braided tube?Thanks

author: james_s
author_rank: Super Contributor
timestamp: October 14, 2020, 05:41:08 am
content: That's just armored cable, it acts as a shield for radiated noise and protects the wires from damage, it's common in industrial equipment. You can remove it without any issues and it will be like any other DC motor.
Restricted Availability - Page 1
Forum section: electronics / beginners

author: Faranight
author_rank: Unknown
timestamp: August 10, 2023, 06:08:16 pm
content: Hey! Recently I was going to make a new PCB for a certain project. I wanted to use some parts that I've ordered and used in the past, but when I checked online for the same parts they were not available any more. What's the deal with thisRestricted Availabilityon some online stores? For example, I've ordered some#A914BYW inductorson Mouser in the past, but now the item is suddenly not available any more due to restricted availability. The parts do not seem to be obsolete, they're nothing special because they're just inductors and they're not military-related.Why do these become restricted, and more importantly, how does one pick parts so that they don't become restricted in the future to avoid having to update your existing PCB's with replacement parts?

author: Benta
author_rank: Super Contributor
timestamp: August 10, 2023, 06:24:01 pm
content: It's a supply chain issue that's been going on for the past few years. It simply means that demand is higher than availability.Some years ago, it was called "on allocation".The problem is, that it's self-amplifying. As soon as customers smell a whiff of supply problems, they double/triple/quadruple order the parts, making the problem much worse.Suddenly, the limitation ends, and the bottom drops outs of the market.Should happen within the next year.
Restricting USB power - Page 1
Forum section: electronics / beginners

author: msknight
author_rank: Regular Contributor
timestamp: November 10, 2023, 11:22:05 am
content: I have the following situation ... I have a Rasberry Pi 5 which I intend to hook up to a USB power bank which I believe is only going to be rated to 3A per port. The Pi has two modes, 3A and 5A. In 3A it limits the USB ports to 600mA which is fine for me... but I want to ensure that the pair only negotiate 3A and the Pi doesn't attempt to pull 5A.I believe that if I buy a 3A cable, there should be a 5.1K resistor in there which tells the Pi that the cable is only rated to 3A and not to pull above this.The testers out there for USB cables are running in the region of £70+, so I'm wondering if I can buy a few breakout boards and knock together my own for a few quid, just to detect that the cable is correctly going to limit the current by the presence of the 5.1K pull down resistor.Grateful for thoughts and insight please, before I start messing around and potentially melting things.

author: BillyO
author_rank: Super Contributor
timestamp: November 10, 2023, 11:18:13 pm
content: Before I went out and paid 70 quid on a tester, I'd get a 3A cable and try it out.
Reusing old laptop screen - Page 1
Forum section: electronics / beginners

author: sairfan1
author_rank: Frequent Contributor
timestamp: May 13, 2025, 06:49:19 pm
content: I need about a 14/15" inch screen (i dont have at this time) to use with camera, I was planning to use it from some old laptop.I want to know what kind of screens are easy to use with some video adaper (card) like thishttps://www.aliexpress.com/item/1005004302518914.htmlon aliexpressI also want to know if this card is not better choice what other options can be used.

author: amyk
author_rank: Super Contributor
timestamp: May 14, 2025, 05:22:06 am
content: Anything with LVDS is a safe bet, they're all pretty similar.

author: RoGeorge
author_rank: Super Contributor
timestamp: May 14, 2025, 05:51:08 am
content: If you have the old laptop, why bother dismantling the laptop to remove the screen?I'll use the entire laptop as it is, as a screen, and just connect the camera to the laptop.

author: Kleinstein
author_rank: Super Contributor
timestamp: May 14, 2025, 10:57:08 am
content: A problem could be the laptop part (e.g. hard disc, momory) not working anymore. Older laptops may also not be fast enough. I still have an old one with a really nice 15" screen, but only a pentium 3M CPU. It may not work with a higher resolution camera.

author: eugene
author_rank: Frequent Contributor
timestamp: May 14, 2025, 03:49:19 pm
content: I agree with amyk that LVDS is almost certainly the way to go. Unfortunately, there are a few different standards. A few years ago, when I was repurposing the screen in an old XPS13 I found this website useful:https://hackaday.io/project/179868-all-about-laptop-display-reuse/log/193081-common-lvds-laptop-panel-pinouts
Revers engineer single line rgb led driver - Page 1
Forum section: electronics / beginners

author: 97hilfel
author_rank: Regular Contributor
timestamp: December 26, 2016, 09:44:34 pm
content: Hi everybody,I'm working on a project (maybe as seen on the amount of stuff I write in the last days) and I work with the Thermaktake Riing 12 RGB fans here a link to the websitehttp://www.thermaltake.com/MICROSITE/Riing14RGBRadiatorFanTTPremiumEdition/index.htmland these thremendously expensive fans come with a software and a little neat controller box, which as soon as they arrieved whas thorn down following the motto "don't turn it on take it appart!!!". So in the box is just a LM1117-3.3 and a PIC MX32 Microcontroller.The point is I want to build my own open source fan controller for watercooled pcs with a lot of features. And one of them is to implement these Riing fans. These fans don't have a normal 4 Pin connector, they have a"propietary" (<- its just a Molex or Amphenol) connector with 5 pins, my first thaught was (after a half hour looking up if sb else already had done the teardown) that the connector is probably just a default 4 Pin fan connector an a single wire rgb led bus wire. And yes it is but I don't get the "encoding" of the signal, the speed of each data packet is around 400 kHz and each "bit" has a with of 2.5µs pictures will follow tomorrow afternoon, each packet is formed of 24 bits (how surprising for 3 colors ? 3*8Bit = 24Bit).Now to the real problem:The signal is composed of "bits" with a width of 2µs High pulse and of bits with a width of 0.5µ High pulse. (its difficult to measure because the MCU has a not quet enough driver power so I end up with banans like my ex teacher would call it)Has anybody already seen something like this and maybe knows a IC which could be build into these fans? I'm not gonna take one apart cause that would end in a destructive teardown and one of these consts around 25€.I hope I described my problem(s) right and you can help me, if further information is requered just ask for it.Have a nice day/evening/night its 22:44 where I live.Felix

author: chicken
author_rank: Frequent Contributor
timestamp: December 26, 2016, 10:20:09 pm
content: Sounds like the protocol for addressable RGB pixels, i.e. WS2812, SK6812, etc.https://cpldcpu.com/2016/03/09/the-sk6812-another-intelligent-rgb-led/

author: 97hilfel
author_rank: Regular Contributor
timestamp: December 27, 2016, 07:04:47 am
content: Quote from: chicken on December 26, 2016, 10:20:09 pmI dont know if they are adressable because in the fan are 4 leds which may be wired up in parallel/series with a single line driver because they work syncroneously.
Reverse a swtch. - Page 1
Forum section: electronics / beginners

author: davelectronic
author_rank: Frequent Contributor
timestamp: January 17, 2017, 10:59:14 am
content: So i bought a couple of thermal swiches (bi metalic) unfortunately tired i ordered NC instead of NO relised when they turned up. So not wanting to reorder again, i thought relay to reverse the thermal switch state over when activated to NO, closing on temperature rise. My question is, does anyone know of a better arrangement to this problem ? Thanks for reading.

author: danadak
author_rank: Super Contributor
timestamp: January 17, 2017, 12:28:59 pm
content: If the switch was operating line operated loads, relay good idea.If just a logic level signal you could use single gate logic to effectthe inversion.http://www.ti.com/lit/sg/scyt129f/scyt129f.pdfRegards, Dana.

author: davelectronic
author_rank: Frequent Contributor
timestamp: January 17, 2017, 07:31:58 pm
content: Its only for 12 Volt loads at a few hundred mA, thanks, i will take a look at this idea.

author: eblc1388
author_rank: Frequent Contributor
timestamp: January 19, 2017, 12:28:44 am
content: Quote from: davelectronic on January 17, 2017, 07:31:58 pmOn temperature rise, a NO thermal switch would operate and provide power to the load, if that's what you want.In order to use a NC thermal switch to provide the same function, you can use either a relay or better still a PMOS to save on idle power lost.Connects the S(source) pin of the PMOS to +12V, its D(drain) pin to the load. Connects the NC thermal switch between its G(gate) and S pin. Then connects the G via a 22K resistor to 0V. Because of the NC nature of the thermal switch, the PMOS is cut off so no power to the load. When temperaure rises, the thermal operates and becomes open circuited. PMOS is biased and power is then fed to the load. The idle power loss is the current through the 22K resistor only.

author: alanb
author_rank: Frequent Contributor
timestamp: January 19, 2017, 01:43:16 pm
content: Is there a mechanical solution to this whereby you disassemble the switch and re assemble with the bi-metallic strip the other way up?
Reverse battery protection - 2x Pmos in paralell - circuit check? - Page 1
Forum section: electronics / beginners

author: Cvijo
author_rank: Contributor
timestamp: March 21, 2025, 02:21:08 pm
content: Hi all,I just wanted to check if this circuit is OK for reverse battery protection.My battery source can be 12V or 24V that's why that zener diode 16V is to protect the gate, and i used 2 mosfets in parallel because it will be high current (40+A) to i think that would be a good idea.Thank you all for your suggestions and help.

author: Peabody
author_rank: Super Contributor
timestamp: March 21, 2025, 02:42:15 pm
content: It looks good to me, but only for the battery discharging into the load. If there's a charger in the circuit, things are more complicated since current can flow in the opposite direction.

author: Cvijo
author_rank: Contributor
timestamp: March 21, 2025, 04:52:37 pm
content: Quote from: Peabody on March 21, 2025, 02:42:15 pmThank you Peabody,well, there will be a charger in the circuit, the alternator will charge the battery, and solar panels will charge too. Can you point me in some direction on what to search for on the web in that case or how to fix that?

author: Peabody
author_rank: Super Contributor
timestamp: March 21, 2025, 09:19:18 pm
content: If there's a charger, then you have to protect both the load circuit and the charger circuit. But the problem is that current can flow in either direction even when polarity is correct. The solution is above my pay grade, but I seem to remember that this was all addressed in a thread here a while back. I just can't find it.One place to start would be this Great Scott video:He ends up with a circuit that might work. Or maybe someone else will remember that older thread, which I think had a number of different circuits proposed. Edit: It may have been this thread:https://www.eevblog.com/forum/projects/how-do-i-add-reverse-battery-protection-to-a-battery-charger-with-common-ground/
Reverse battery protection & Battery voltage measurement - Page 1
Forum section: electronics / beginners

author: Shark
author_rank: Contributor
timestamp: July 21, 2014, 06:15:39 pm
content: Hi guys!I'm making a small circuit with an ATmega328P and I would like to protect against reverse battery polarity. I will put a Schottky diode in series with battery as the circuit shows. I would also like to have battery voltage measurement directly on the battery, avoiding the Schottky diode, because I will have a boost converter (ommited from the circuit for simplicity).My question is, do I need to worry about reverse polarity when ADC input pin will see battery ground and GND pin will see 3.0V?Big thanks

author: lewis
author_rank: Frequent Contributor
timestamp: July 21, 2014, 07:21:39 pm
content: Yes you do need to worry about it. In your circuit, when the battery is reverse connected, the internal ESD diode in the MCU between the ADC pin and ground will be destroyed.Simple fix! Use a 100K resistor between the battery and the ADC pin. Put another 100K resistor between ADC pin and ground. Put a 10nF or 100nF cap across this second resistor (the ADC will usually have a maximum external impedance spec of 10K or so, the cap allows the voltage at the pin to remain stable during sampling).The 100K resistors form a potential divider, adjust them to suit your voltage reference. You may want to increase the values significantly to minimise current consumption.

author: Andreas
author_rank: Super Contributor
timestamp: July 21, 2014, 07:24:23 pm
content: Quote from: Shark on July 21, 2014, 06:15:39 pmHello,The bond wire of ADC input will melt due to input protection diode.You dont have to worry about: it will not work this way.You have to limit ADC input current e.g. by a resistor to a safe value (e.g. 1 mA).with best regardsAndreas

author: mij59
author_rank: Frequent Contributor
timestamp: July 22, 2014, 04:10:50 am
content: Hi,Take a look at this reverse protection method.http://afrotechmods.com/tutorials/2011/12/04/p-fet-reverse-voltage-polarity-protection-tutorial/Maybe you can omit the boost converter all together.

author: Shark
author_rank: Contributor
timestamp: July 22, 2014, 06:38:06 pm
content: Thanks for all your replies!I updated my schmatics with two 100k resistors and a capacitor, is this what you meant lewis?I will get half of the battery voltage on ADC input (I'll probably use an external reference 2.048V or 2.5V).

author: lewis
author_rank: Frequent Contributor
timestamp: July 23, 2014, 12:12:55 am
content: That's right, you could even try 220K or 470K instead to minimise divider current and increase battery life. And you can adjust the divider ratio to make the most of the reference if you need greater precision!Edit - sorry, just noticed I've been repeating myself
Reverse bias of Photodiode - Page 1
Forum section: electronics / beginners

author: alamwte
author_rank: Regular Contributor
timestamp: January 03, 2022, 08:49:57 am
content: Hi,I have a question about Photodiode in Reverse bias.Do you know that which parameters are related to reverse bias photodiode?What parameter can change by changing of photodiode reverse bias?Thanks,

author: Martin Miranda
author_rank: Regular Contributor
timestamp: January 03, 2022, 09:12:45 am
content: you might want to gather application notes.took a good time researching and deep diving about photodiodes.http://www.osioptoelectronics.com/application-notes/AN-Optical%20Communication%20Photodiodes%20and%20Receivers.pdf

author: jwet
author_rank: Frequent Contributor
timestamp: January 04, 2022, 05:14:04 pm
content: The reference posted by the last poster is excellent. A lot of parameters change some but the most profound and noteworthy change is capacitance- it decreases with increasing negative bias. C can be a decade lower at Max bias (<75% VBR) than zero bias. The depletion region is growing from the junction boundary into the N and P regions- a bit like making the plates of a cap wider. C is proportional to A/d. Area (fixed), distance- change by bias.

author: Martin Miranda
author_rank: Regular Contributor
timestamp: January 04, 2022, 05:31:10 pm
content: Quote from: jwet on January 04, 2022, 05:14:04 pmfor me it's like (vietnam war flash backs) hahaha.the cheat sheet is also in figure 1.5.

author: w2aew
author_rank: Super Contributor
timestamp: January 04, 2022, 09:09:31 pm
content: Quote from: jwet on January 04, 2022, 05:14:04 pmTo add onto this post - one other (negative) effect of reverse bias is increased dark current. In many applications, this won't matter. The primary reason for reverse biasing a photodiode *is* to lower the device capacitance, which will have the end effect of dramatically increasing the bandwidth - the primary end goal.

author: alamwte
author_rank: Regular Contributor
timestamp: January 08, 2022, 11:26:44 am
content: Thank you all for your guidness
reverse BJT conduction on peltz oscillator? - Page 1
Forum section: electronics / beginners

author: vivi-d
author_rank: Regular Contributor
timestamp: December 06, 2024, 07:38:18 pm
content: It looks like the current thru Q1 is positive and negative. How is this possible? I thought BJTs only conducted one way.What's going on?

author: mawyatt
author_rank: Super Contributor
timestamp: December 06, 2024, 07:51:35 pm
content: That's conduction thru the Base Collector PN Junction when the NPN Collector swings below the Base by a Junction Drop. This is shown as sourcing current from the NPN Collector rather than the NPN Collector sinking current in normal bias condition.Best

author: vivi-d
author_rank: Regular Contributor
timestamp: December 06, 2024, 08:15:28 pm
content: I see. That makes sense. Is there any current gain with this base-collector conduction?

author: mawyatt
author_rank: Super Contributor
timestamp: December 06, 2024, 08:30:25 pm
content: Quote from: vivi-d on December 06, 2024, 08:15:28 pmNo current gain in this case. However, there's always a howeverone can operate a bipolar transistor upside down, or inverted by swapping the normal Collector and Emitter terminals, so in this configuration there is current gain altho it's much lower than normal operation.Long ago folks used this inverted configuration as a saturated switch since the saturation voltage is very low, sometimes below 10mv, where in normal saturated operation it's well above this. With modern FET switches this transistor inverted operation has generally been forgotten.Best

author: Zero999
author_rank: Super Contributor
timestamp: December 06, 2024, 10:50:49 pm
content: BJTs do work in reverse. The hFE is much lower and the saturation voltage a little lower. Here's a bidirectional level circuit which uses the reverse mode to translate 5V logic levels to 3.3V and the forward mode to go from 3.3V to 5V.
Reverse breakdown voltage of LEDs in matrix on cheap LED cube - Page 1
Forum section: electronics / beginners

author: ian121
author_rank: Newbie
timestamp: July 18, 2016, 01:51:59 am
content: I bought one of those very cheap LED cubes as a soldering exercise. Quite fun to build, but predictably quality control doesn't seem to be great ... I see a lot of "ghosting" and not quite right effects. Upon trying various debugging points, I hooked up 3V on two cathode lines and to my surprise start seeing LED's light up dimly. There are no shorts and all LEDs are in the right way.It seems a bunch of these LEDs have very-low breakdown voltages and let current through at even as low as 0.8V (~1 mA) and at 3V about 5mA (enough to get things lighting up). Now I've learnt that LEDs have a much lower breakdown voltage than diodes -- from what I read more light == lower breakdown. But this low seems out of spec. The thing is that in correct polarity, these LEDs seem to light up just fine -- I would have thought that if they're breaking down at such a low reverse voltage they'd be duds in the correct polarity. During testing I did put a forward voltage across each LED to QA it ... but didn't think to check it backwards!Is this within any normal variation for LEDs? Or are these just reject-bin LEDs that have been stuffed into this cheap kit? The circuit board and micro seem to work fine (I even managed to reprogram it via the TTL lines) but there's so many connection points I'm sure there could be other things wrong.

author: mikerj
author_rank: Super Contributor
timestamp: July 18, 2016, 05:38:00 pm
content: It's more likely you are seeing the effect of reverse leakage currents rather than true breakdown. The Chinese LEDs that can be bought in bulk for almost pennies tend to have very little in the way of quality control so this isn't overly surprising.At the real breakdown point you will see the dynamic resistance fall fairly sharply, in a typical zener diode-like response. If it's just leakage current the slope will be much more shallow.

author: wraper
author_rank: Unknown
timestamp: July 18, 2016, 06:06:27 pm
content: IMO that current leaks through the driver circuit, probably parasitic diodes in MOSFETs, unless you test LEDs disconnected from the other circuit.

author: amyk
author_rank: Super Contributor
timestamp: July 19, 2016, 11:06:36 am
content: Modern LEDsdo not need much current to light visibly, and their reverse leakage current is usually and unsurprisingly not specified. They may also be quite leaky in the forward direction too; this video has a good explanation:
Reverse charger protection - Page 1
Forum section: electronics / beginners

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: August 12, 2016, 08:32:47 am
content: 1. I have to give reverse charger protection for battery management system in which N-channel mosfets are in ground path.2. Attached is the ckt for bq40z50 in which N-channel are on +ve path i.e Q2 & Q3.Battery is coonected across Bat+ & bat- & charger is connected across Pack+ & pack-.In this circuit Q4 is for reverse charger connection protection. Suppose charger is connected in opposite direction then there is +ve voltage at gate of Q4 & ground at its source. It turns on the Q4 & it then it shorts gate & source of Q3, so protecting any current to flow.3. Now i have a circuit in which n-channel are on ground path, I have to add reverse charger polarity in it also. Current Circuit without protection is attached with name actual4. I have attached modified circuit. three components added are R1,Q4 & R2. Its P channel mpsfet. When charger is connected in correct configuration then gate at +ve & source at -ve, it turns off the mosfet Q4, but if reverse charger is connected then gate become negative & source become +ve, it turn on Q4 which in turn connect gate of Q2 & its source, effectively turn off the mosfet & save any current in/out of battery.Query:1. Is the modified circuit is ok?Bat volatage in 1S configuration is 2.5V to 4.5V & charger voltage is +4.5V maxBat volatage in 2S configuration is 5V to 9V & charger voltage is +9V max2. Can Q4 mosfet be replaced by any n channel mpsfet as in original circuit as I have 2n7002 in use.

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: August 13, 2016, 03:38:48 am
content: 1. Cant use series diode as voltage at input is low. Even 0.3V drop at around 2A can cause significant capacity drop at output.Ideal diode are very expensive, product is very cost sensitive.2. Attached is modified ckt. It looks ok to me.Can it be done with one single mosfet.
Reverse Current on Arduino in Sleep mode?  - Page 1
Forum section: electronics / beginners

author: Twonius
author_rank: Contributor
timestamp: June 10, 2013, 10:27:31 pm
content: So I've got my arduino sleeping the deep sleep in power down with the ADC off.in order to measure this I'm using the micrucurrent DMM box.Curiously when my arduino is operating it's drawing 3ma (arduino + bluetooth 4.0 module) but when I put everything to sleep the dmm is now showing -190 mV (1mV/1uA scale).Did I miss something in the manual? I don't have any other pins connected to the 3V rail that it could be drawing power from so I'm a bit perplexed.

author: David_AVD
author_rank: Super Contributor
timestamp: June 10, 2013, 10:49:12 pm
content: Are there any other connections to other voltages at all?

author: Twonius
author_rank: Contributor
timestamp: June 11, 2013, 03:45:22 pm
content: Nope, I know these micros can sometime route current in strage ways but this is just strange.

author: Rerouter
author_rank: Super Contributor
timestamp: June 11, 2013, 08:56:27 pm
content: i did not think the ucurrent was capable of reversed polarity measurements, did you turn the device around?

author: c4757p
author_rank: Super Contributor
timestamp: June 11, 2013, 09:04:11 pm
content: Quote from: Rerouter on June 11, 2013, 08:56:27 pmThe whole circuit is symmetric about a middle rail, actually.Schematic- I don't have one, but it looks like it can go in either direction.

author: ConKbot
author_rank: Super Contributor
timestamp: June 13, 2013, 12:22:08 am
content: is the ucurrent zeroed properly?
Reverse current protection with P Mosfets circuit - Page 1
Forum section: electronics / beginners

author: Joddy
author_rank: Newbie
timestamp: July 17, 2021, 07:15:39 am
content: I'm trying to create a reverse current protection circuit for a battery charger using discrete p-channel mosfets, with a low voltage drop.The goal is to disconnect the battery from the load when USB is plugged in using back-to-back Si2323 P Mosfets rather than schotkey diodesSo far I've drawn this circuit.When USB is connected VOut won't be any higher than 4.2V, if it's disconnected Vout will act as a normal load.Would there be any risk of current flowing back into VBat if VBus is active at ~5V?

author: cortex_m0
author_rank: Regular Contributor
timestamp: July 17, 2021, 06:25:24 pm
content: I think the fundamental question you are asking is: do zener diodes also conduct forwards, and the answer is yes. They may be less ideal than a standard silicon diode, but they will conduct with ~0.7V forward.Knowing that, provided that the P-channel MOSFET is not enhanced, you're looking at the MOSFET's leakage current flowing into the battery, which is ordinarily single-digit microamps.

author: Faringdon
author_rank: Super Contributor
timestamp: July 17, 2021, 06:30:54 pm
content: Yes, and also , you wont need that zener, since SI2323 can do up to 8V gate to source

author: Peabody
author_rank: Super Contributor
timestamp: July 18, 2021, 03:51:29 am
content: When VBus is connected, the left mosfet will be off, so the battery will be protected against reverse current flow from VBus. But the problem is the second mosfet will also be off, so no VBus current can get to the load either.Also, it's not clear what you intend by having a charger downstream from this. Normally the charger would be upstream from the battery.Normally, it would be done like this:

author: Joddy
author_rank: Newbie
timestamp: July 19, 2021, 01:33:15 am
content: Thanks everyone!Quote from: Peabody on July 18, 2021, 03:51:29 amI'm creating a custom PCB for an Adafruit Feather but using my own Solar Charging instead of the downstream charger. This circuit is just to protect my own circuit from any reverse current from the on-board charger. VBus is connected separately to the load and charger.I'm using a BQ24074 IC which has it's own power path but I will be using something similar to your design for a power mux on the input (usb + solar).
Reverse engineering a car radio amp IC - Page 1
Forum section: electronics / beginners

author: Nickk2057
author_rank: Regular Contributor
timestamp: October 14, 2017, 04:20:20 pm
content: Hello all to our remarkable engineers.I have been trying to find out how to turn on this amplifier IC but could not find out how. This is a TDA7850A chip. It is at a total of 200W combined watts with all channels driven. I looked at the scamatic of this IC but could not find out what it means for input high or input low for the standby pin and the mute pin. Help would be great. Thanks.PS. The images from my phone was too large. Will have to resize them when I get home.

author: capt bullshot
author_rank: Super Contributor
timestamp: October 14, 2017, 04:43:07 pm
content: It's all in the datasheet, p. 8:http://www.st.com/content/ccc/resource/technical/document/datasheet/24/f1/fe/de/11/c2/4d/15/CD00173410.pdf/files/CD00173410.pdf/jcr:content/translations/en.CD00173410.pdfLow level means mute / standby, high level means "let's make some noise".

author: Nickk2057
author_rank: Regular Contributor
timestamp: October 14, 2017, 05:02:05 pm
content: But what does it mean? Am trying to figure this out and it is rattling my noggen.

author: stj
author_rank: Super Contributor
timestamp: October 14, 2017, 07:11:09 pm
content: low = ground, high = the supply voltage - or more usually anything over a few volts.

author: Zero999
author_rank: Super Contributor
timestamp: October 14, 2017, 07:59:45 pm
content: Quote from: Nickk2057 on October 14, 2017, 05:02:05 pmAs mentioned above: it's all in the data sheet. See page 8. Standby out threshold voltage (Amp: ON) 2.75V, Standby in threshold voltage (Amp: OFF) 1.5V.Beware of the maximum output power specification, which is quoted when the output is a square wave, which bears no resemblance to music or voice! It will be a horrible buzzing noise. The power output with virtually imperceivable 1% distortion is half the maximum power output specification.

author: Nickk2057
author_rank: Regular Contributor
timestamp: October 14, 2017, 08:59:04 pm
content: So basically it has to be anywhere around 2.75V to actually turn on. Would a resistor across the supply suffice?

author: Zero999
author_rank: Super Contributor
timestamp: October 14, 2017, 10:09:37 pm
content: It's all on the data sheet. Refer to page 12, section 4.3 "Standby and muting"