hybridfree/eevblog-posts huggingface dataset:
Surface Pro - External DC charging questions - Page 1
Forum section: electronics / projects

author: deanfourie
author_rank: Newbie
timestamp: November 06, 2022, 10:17:22 am
content: So, I'm out of ideas on this one! And really do need some help! There is NO information online.I have a Surface Pro 3 that I'm trying to power externally, this tablet will be used as a wall mounted tablet for Home Assistant. The issue I have is with getting it to charge. If I plug it into a standard wall USB charger, it charges just fine, but when trying to use a DC to DC buck converter, 12v to 5v 10A, it doesn't seem to want to charge.When flat, I've measured the draw given to the tablet. When dead flat and plugged in, its proving 5v @ 0.5A. I'm guessing this is not a limitation from the buck converter but rather what its demanding.I've tried powering the buck from a 7AH 12v battery, and now a 12v 3.8A AC wall adapter.When fully charged, it detects that something is plugged in to the charger port, but does not charge. The battery continues to decrease.I don't think there are any smarts in the charger as I said it charges off any AC to USB 3A fast charge adapter just fine .Any ideas? This tablet is worth nothing but perfect for a wall mount touch display for Home Assistant and would be a shame to let it go to waste.Thanks

author: mushroom
author_rank: Regular Contributor
timestamp: November 06, 2022, 10:36:11 pm
content: Could you explain how you charge a SPro 3 from a 5V USB charger ?Power supplies (SMPSU bricks) for S Pro 3, 4, 5, 6 and 7 are all more or less identical and 12V, not 5V. (I have S Pros 3, 4 and 7 by hand)
Surfact Mount Resistor Value - Page 1
Forum section: electronics / projects

author: bostonman
author_rank: Super Contributor
timestamp: July 08, 2021, 01:10:47 am
content: I believe this 0603 component is a resistor (not sure what else it could be).In circuit, it measured 1k, but looking at the value, I thought it was incorrect due to other resistors elsewhere causing the meter to measure wrong. After removal, it measures 1k (I expected a 1k resistor to be marked 102). Thinking maybe something was wrong, I removed one from a parallel circuit and it also measures 1k.During a repair job using hot air, this component blew off at some point, so I'm using the other circuits to determine the value.Looking online, I see the following:https://www.venkel.com/media/wysiwyg/categories/docs/0603-marking-code-venkel.pdfAfter process of elimination, it looks like my resistor reads 01B.Is this correct?

author: fourfathom
author_rank: Super Contributor
timestamp: July 08, 2021, 01:18:49 am
content: Yes, that's 1K. I recently got some reels of 0603 resistors from LCSC (associated with the JLCPCB PCB fab house), and they were marked:100 Ohm: 01A1K: 01B10K: 01C(etc.)

author: Miti
author_rank: Super Contributor
timestamp: July 08, 2021, 01:19:09 am
content: Search for EIA-96 marking. 01B is 1K.

author: bostonman
author_rank: Super Contributor
timestamp: July 08, 2021, 01:23:51 am
content: Thanks.QuoteThe link I provided is a EIA-96 marking, I just never heard of this type of marking and wanted to confirm.

author: Zero999
author_rank: Super Contributor
timestamp: July 08, 2021, 10:35:11 am
content: Quote from: bostonman on July 08, 2021, 01:23:51 amIt's quite common for 1% resistors. The first two digits, range from 1 to 96, index thepreferred E96 numberand the letter denotes the multiplier. The reason a letter is used for the multiplier, so it can't be confused with the other standard code, which uses the first to digits of the resistor value, followed by a multiplier.

author: bostonman
author_rank: Super Contributor
timestamp: July 08, 2021, 02:26:43 pm
content: It makes sense and seems like a good method.My opinion: if components have a standard marking that allows someone repairing it to replace them by cross referencing the number (E96 in this case), then I don't care how they are marked.Unfortunately I'm still dealing with a component (I believe it's back-to-back diodes) with a G21 marking. Sadly, G21 is used for various types of components, and, while I suspect these are back-to-back diodes (BAT 54S), I can't find a manufacture that produces a SO23 (it's approximate size) with such a marking which is making me scared to try replacing this.I already have a thread on this, and not asking to piggy pack on this thread, I'm just making a general statement on my frustration for trying to repair electronics today.
Surge Protector Ground Indicator Circuit Operation - Page 1
Forum section: electronics / projects

author: Bushougoma
author_rank: Regular Contributor
timestamp: November 03, 2017, 03:31:20 pm
content: I came across this ground indicator circuit inside a surge protector I disassembled and I have some questions about how it works. I've cut out much of the circuit not related to the ground indicator (extra MOVs, thermal fuses that disconnect power should the MOVs fail, etc).It consists of two LEDs the first green LED D2 just indicates power on and will go out if any of the thermal fuses (not shown) blow due to a MOV failure. The second red LED D3 is the ground presence indicator. If your outlet is properly grounded it will illuminate if not it will go out simple enough.We start out with 120 volts AC which immediately passes through a half wave rectifier D1 lowering the voltage to 60 V with lots of ripple. It then passes through R1 the current limiting resistor for both the green and red LEDs.Here's how I think the circuit works lets start when a proper ground is NOT present (the ground wire is not connected) and D3 the red LED should be OFF.A small amount of leakage current through the upper MOV which is connected to the line (forms a voltage divider with the lower MOV connected to neutral) this reduced voltage passes through R3 the base current limiting resistor for the KSP13 NPN darlington transistor. This causes it to conduct and it essentially bypasses the red LED across it's collector and emitter causing it to go out. So current would flow from the cathode of the green LED D2 through the transistor and to neutral. The transistors base is being fed AC so I guess they are using the base emitter junction as a rectifier. It won't conduct on the negative portion of the sine wave but since the LEDs are being fed through a half wave rectifier they don't see the negative portion and would be off anyway.With a proper ground present (the ground wire is connected) the red LED should be ON.As before a small amount of leakage current flows through the upper MOV connected to the line but this time a voltage divider isn't formed because the ground wire is connected and essentially both sides of the lower MOV from ground to neutral are at the same potential. The leakage current from the upper MOV connected to the line flows to ground instead of through R3 this means 0 volts is present at the base of the KSP13 transistor and it is essentially open circuit. This puts the green and red LEDs in series so both glow.Now to my question and hopefully I have the theory of operation right so far. What is the purpose of the parallel 10K resistor? It seems like the circuit would work just fine without it.Thanks for any help in advance.
Surge testing with remote power supply - Page 1
Forum section: electronics / projects

author: Jester
author_rank: Frequent Contributor
timestamp: March 15, 2019, 04:54:26 pm
content: Assume a product requires a MAINS to 12Vdc power supply < 50WA suitable power supply is specified and it meets all required surge testing requirements, it is located within the product.Now if the power supply is moved outside of the device, from what I recall once the distance of the interconnecting dc power cables exceeds a certain length (1M possibly), then I think surge testing is required on the DC input terminals in addition to the MAINS, can anyone confirm this?
Surge/spike protection for 36V chip (40V abs max) on 28V nominal rail - Page 1
Forum section: electronics / projects

author: Psi
author_rank: Super Contributor
timestamp: August 21, 2025, 10:44:47 am
content: I have the need to protect a 36V chip (40V abs max) on a 28V nominal rail.Doesn't have to to be full automotive load dump protection, something that is equal to a 2kW TVS diode would be fine.Does anyone have a good solution?I'm currently looking into surge suppression chips that use mosfets, but does anyone have any other ideas?There's not enough range to use a TVS with the large Vworking to Vclamp range

author: scottapotamas
author_rank: Regular Contributor
timestamp: August 21, 2025, 11:16:23 am
content: If you've got the budget for them, Analog have a pretty wide range of "SurgeStopper" branded parts which drive a (or back-to-back pair) mosfet with varying OV/UV/OCP features.LTC4365 is in one of my designs, and I still have a TVS to help handle larger transients.

author: Psi
author_rank: Super Contributor
timestamp: August 21, 2025, 11:27:19 am
content: Yeah, I found a few chips that work like that one.Also some ideal diode controllers that have an adjustable overvoltage shutdown.I already have a diode in the path so maybe i can reduce the heat from that and get some overvolt protection at the same time.

author: Stray Electron
author_rank: Super Contributor
timestamp: August 21, 2025, 05:18:03 pm
content: You might take a look at the circuit that was used on many of the older Lambda linear power supplies. It was a SCR connected across the output and with a variable resistance poteniometer connected to the gate and a Zener diode tied back from there to ground. They were optional on some of the Lambda PSs and they mounted directly onto the row of screw terminals on the rear of the PSs. If you can find an old Lambda PS catalog it should show them and you might even find a picture of one on a Lambda PS on Ebay. AFIK they worked fine but once the SCR triggered it latched On so you had to turn the PS off to reset the circuit. The zener diode roughly set the trigger voltage but you could fine tune it with the potentiometer.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: August 21, 2025, 10:16:45 pm
content: Quote from: Psi on August 21, 2025, 10:44:47 amWhat current/voltage are you looking to clamp and what current draw does your system have?Adding series resistance or even a current source can ease the task of the clamp device.I you pay a little bit more you get a lower clamp resistance and if you accept some small operating drain, you can nudge down the clamp setting.One example:A 'bigger' part like 5.0SMDJ26A Specs 28.90~31.90V at 1mA and can clamp 118.8A at 42.1V, so roughly 93A at 40V

author: Psi
author_rank: Super Contributor
timestamp: August 21, 2025, 11:54:48 pm
content: TVS3301 is looking like a good option.https://www.ti.com/lit/ds/symlink/tvs3301.pdfIt's a mosfet configured to act like a TVS, so much less gap between working voltage and clamp.~$0.20Standoff 33VClamp 40V @ 27A8/20 µs at 1.1kW10/1000 µs 120WCheap enough to use a few to spread the load around.
Surprising colour temperature shift when phosphor LEDs are coated in resin - Page 1
Forum section: electronics / projects

author: I wanted a rude username
author_rank: Frequent Contributor
timestamp: January 02, 2022, 11:47:16 am
content: Hypotheses suggested so far:Resin reacts in some way with the phosphorResin's light transmissivity is not linear with wavelengthRefractionSuppression of the internal reflection that would normally bounce blue light back at the phosphorAny other ideas?

author: I wanted a rude username
author_rank: Frequent Contributor
timestamp: January 03, 2022, 03:24:44 am
content: YouTube user CorgonCorgon has experienced this before and adds that silicone coatings also produce this effect, while cyanoacrylate doesn't ... even when subsequently overcoated with the same silicone. This may support the internal reflection hypothesis.
Surv. camera setup with pi? help! - Page 1
Forum section: electronics / projects

author: MyHeadHz
author_rank: Regular Contributor
timestamp: February 21, 2017, 10:11:31 am
content: So I just found out that someone has been trespassing and vandalizing my property. I need a surveillance camera...I have raspberry pi's, a good quality webcam, and SD cards/HDD's to spare. I need to set it up ASAP.It doesn't have to be super technical or efficient. I will be able to plug everything in to a wall. It can simply record the entire time in HD, and log it to the drive via USB.I have never done anything like this, so I'm a complete noob.Any resources for setting it up?

author: Delta
author_rank: Super Contributor
timestamp: February 21, 2017, 10:36:55 am
content: http://felenasoft.com/xeoma/en/articles/linux-cctv/

author: bobaruni
author_rank: Regular Contributor
timestamp: February 21, 2017, 12:48:00 pm
content: Just stick this image an SD card and plug it into your PI and a suitable wifi dongle and webcam, it couldn't be simpler and works a treat, has a built in web server and record, motion sensing etc.https://github.com/ccrisan/motioneyeos/wiki

author: MyHeadHz
author_rank: Regular Contributor
timestamp: March 09, 2017, 03:15:06 am
content: Thanks! I decided to do with your MotionEye OS suggestion. It was simple to set up, and I am impressed so far.I've now had it set up for a while. I set it to do videos, though it was set up for images while I was testing. It may be trying to do images and video... nothing interesting on the images. the motion sensitivity may be too high.The images seem to be fine, but all the videos are either 0 byte files, or corrupt/unplayable. any suggestions? It also seems to drop off the wifi (built-in Pi3 wifi module) a lot.My two thoughts so far are 1. perhaps using the camera, pi, wifi, and writing to memory card uses more power than my power supply can put out (700 ma at .5 volt, under recommended 1 amp). 2. Perhaps my memory card is too slow, causing aborted/failed writes. Any other suggestions would be greatly appreciated.I will try running the setup directly from a battery (so pure DC, little/no noise) which can output up to 3 amps at 5v for at least a few hours. That should rule out (or confirm) any power supply issues. I will update with results.
Suspect resistor value - Page 1
Forum section: electronics / projects

author: @rt
author_rank: Super Contributor
timestamp: August 01, 2016, 12:28:17 pm
content: Hi GuysI’ve reproduced this circuit schematic:http://gerdkautzmann.de/cd32gamepad/a100schematic.pngAt first I assumed the schematic had an error, because the physical hardware hasa 220R resistor (rightmost in the photo), rather than the 2K2 resistor at the bottom of the schematic.The buffer around it are tri-state buffers, and the 2K2 ? resistor holds the outputsnormally low if the buffers are switched high impedance between their inputs & outputs.Now it seems to me the 220R value is harsh for a pulldown resistor.If the outputs became high, the 220R seems a bit close to short to be in the logic circuit.Am I correct in my thinking, and it should be 2K2 ?

author: tatus1969
author_rank: Super Contributor
timestamp: August 01, 2016, 01:55:26 pm
content: the 74LS125 has a max output high current of 2.6mA, which is by far exceeded by the 220R. You could measure the high-level voltage and check if it is above 2.0V.2k2 seems by far more reasonable. Maybe they had timing problems, as they serially clock out data from the 74LS165. But I would rather solve that by software then...Did you reverse-engineer the circuit? The schematic seems to be incorrect.

author: @rt
author_rank: Super Contributor
timestamp: August 01, 2016, 02:14:10 pm
content: HiIt wasn’t me that drew the schematic, but I did a prototype from it, except I used a 220R resistor, and it does work.Quote from: tatus1969 on August 01, 2016, 01:55:26 pm
solved:SWD maxes out at "200kHz" (actually 62.5kHz, 3kb/sec) through relay board - Page 1
Forum section: electronics / projects

author: incf
author_rank: Frequent Contributor
timestamp: June 03, 2025, 09:23:05 pm
content: I've got a situation where I need to disconnect a SWD programmer from a board using signal relays. (STLinkV2-1 flashing a STM32 with a large amount of flash)At "240kHz" flashing failsAt "200kHz" flashing succeeds. (actually 62.5kHz?)I've attached an oscilloscope to the pin header that the SWD programming signal enters a small PCB under test.Without the test fixture, the PCB under test seems to work at "2MHz". It has 47 ohm resistors at the header - the local capacitance of the PCB traces and MCU pins provide a small amount of low pass filtering that is not visable on the oscilloscope capture.The signals look really clean to my eye. But perhaps the oscilloscope capture might be misleading about signal integrity in some way that I've failed to imagine?I'm looking for ideas about figuring out why the connection is so slow. (I only achieve 3kb/sec)Perhaps some sort of ground loop / noise situation.The MCU is powered from a Rigol bench power supply.The ST-Link is powered via a USB port.The fixture has 6" of 0.1" dupont header going into it, and another 6" going out of it. They relays are all within about 0.5" of the connectors.The relay test fixture PCB is double sided without a ground plane. But the traces don't really overlap. The relay board is powered off, and the connection is through the normally closed contacts.If anyone has thoughts, I'd appreciate it. Thanks!edit: solved - it was a software problem pertaining to a bug in the programmer firmware that made it unreliable at high speeds. The system was good up to about 5MHz (25kb/sec) just with software changes.

author: Andy Watson
author_rank: Super Contributor
timestamp: June 03, 2025, 10:27:57 pm
content: Quote from: incf on June 03, 2025, 09:23:05 pmCould be many things. But lets kick off with the oscilloscope waveforms. Both traces show overshoot on the rising and falling edges - Is this real? Or is it an artefact of your probing technique. If it is real and exceeds 0.6V (I'm looking in particular at the negative edges of the blue trace) it could play havoc with any logic input - not enough to damage the input but it could slow it down (considerably) whilst it recovers. If it is not real, you need to adjust your probing technique so that you can see the true signal (the ground lead on the probe is usually the culprit).
SWD Not working on PCB! (STM32) - Page 1
Forum section: electronics / projects

author: AmeliaBuns
author_rank: Regular Contributor
timestamp: June 17, 2024, 03:10:33 am
content: Hi, I finally got the latest version of my PCB and soldered just a few necessary components (I forgot which ones...) and the board was working great! So I finish the board and connect it up, and all of a sudden, no target found, my STLink (Those cheap crappy ones) also blinks red when I plug it in. Thinking I fried the MCU with heat, I swapped it to a blue pill and it works perfectly there, so it's a configuration issue I assume...I checked the traces and they conducted to the pins on the MCU. I can't figure this out. I reviewed the datasheet again to see if I did something wrong with one of the pins (Like the wake pin or boot1) but it seems like my configuration is OK?Any ideas about what could be happening? I've been trying to get it to work for the past 2-3 days.. this happened again on a second board. This project was supposed to be a quick and cheap DIY solution but it's been taking more than a month so far xD

author: ataradov
author_rank: Super Contributor
timestamp: June 17, 2024, 03:43:28 am
content: Are you sure you don't set RDP2 by accident? Or redefining the function of the SWD pins to GPIO?Connect the reset pin to the programmer, it might help.

author: AmeliaBuns
author_rank: Regular Contributor
timestamp: June 17, 2024, 04:02:00 am
content: In a fit of desperate, resoldered a new MCU there and changed it. probably my resoldering but now it works?!!! it works perfectly!I've never been so happysorry for the post I genuinely had tried this before... weird... THIS PCB was with a white solder mask from JLCPCB and the quality was utter garbage, so I wonder if one of the pins was somehow not making good connection, strange still... two boards. same issue?
sweeter sine wave poly-organ with analog  - Page 1
Forum section: electronics / projects

author: dave_j_fan
author_rank: Regular Contributor
timestamp: January 15, 2015, 05:14:52 pm
content: wanted to make a analog sweet sounding organ where multiple keys i can press and chord like sound i can derivethe typical analog synths are little bulkier ,any proper simple design? with 555 etc?or may be twin-t oscillatorsi want to make a smooth keyboard too .. little but of plastic work any links to proceed
Switced mode LED mood lamp design  - Page 1
Forum section: electronics / projects

author: Zero999
author_rank: Super Contributor
timestamp: April 22, 2011, 01:34:56 pm
content: Here's an idea I had when looking at the schematic for a Velleman LED dirver kit.http://www.rapidonline.com/netalogue/specs/55-2036.pdfIt uses the same constant current driver but with three LEDs in series, each with a MOSFET in parallel so it can be bypassed to turn it off. A PWM circuit driven by three low frequency oscillators which will gradually shift causing the different colours to become out of phase creating different colours.I probably won't build it as I have no need to a tacky mood lamp but I thought I'd post it anyway. The N-channel MOSFETs should be logic level so they turn on properly.
Switch 60 Watt LED Bulb  - Page 1
Forum section: electronics / projects

author: electronupdate
author_rank: Regular Contributor
timestamp: April 23, 2013, 02:58:56 pm
content: I recently obtained a Switch LED bulb, it's claim to fame is that the area around the LEDs is filled with a liquid to provide cooling. Sort of like people who fill aquariums with mineral oil and then dip a PC into the tank I guess. Liquids are excellent at conducting heat away from electronics.On first glance it appears to meet specs, which is more than I can say about some of the early bulbs I sourced out of China a few years ago...Does anyone know how to drill through glass to be able to insert a thermal probe into the body of the lamp?
switch a LED with a MOSFET - Page 1
Forum section: electronics / projects

author: andoo2012
author_rank: Newbie
timestamp: May 10, 2021, 09:22:31 pm
content: Hello,I am working on a project where I need to turn a LED on/off by an FPGA pin (1.8V). It needs to work with up to 50 Mhz frequency. I am currently using a channel MOSFET(BSS138PW) but the switching is very slow. The schematic pic is attached. The gate capacitance might be too high for FET to switch efficiently. Can I use a buffer before MOSFET to solve this problem? are there other better parts that I can use? Could somebody please point me to any articles/videos related to this topic?

author: Nikan
author_rank: Regular Contributor
timestamp: May 10, 2021, 10:10:03 pm
content: I think your mosfet is too slow to handle 50mhz, could be more on the max side of the datasheet...Having a 0Ohm gate resistance can destroy your fpga.Try a generic 100mhz bjt with the correct base resistor.If it's not the fet, a buffer would only help if the fpga can't supply enough current to charge/discharge the capacitance at that switching rate. Duty cycle should be considered as well.If you don't have to use a discrete component you could also use something like the NC7WZ14 to directly drive the led.

author: Wolfram
author_rank: Frequent Contributor
timestamp: May 11, 2021, 08:26:14 am
content: In a common-emitter (source) configuration, a BJT will likely switch even slower due to storage time. The other suggestion of using an NC7WZ14 or any other modern fast gate (74LVC1G14, etc.) is more likely to do what you want. If you need more current than can be provided by a single gate, multiple can be paralleled through current sharing resistors, which can also serve the role as current limiting for the LED.

author: Terry Bites
author_rank: Super Contributor
timestamp: May 11, 2021, 08:49:34 am
content: MAX3966/7 for instance?

author: exe
author_rank: Unknown
timestamp: May 11, 2021, 09:02:56 am
content: Why do you need to switch the led so fast? Is it a laser or something?
Switch at the end of a long cable: Noise, protection - Page 1
Forum section: electronics / projects

author: JuKu
author_rank: Frequent Contributor
timestamp: July 26, 2013, 11:38:42 am
content: I have switches at the far end of a relatively long (3m) cable in a very noisy environment. There are motors and such; I measure up to + / - 3V peak noise at the other end of the cable, when the switch is closed(!). I need to reliably trigger an interrupt when the switch activates. I have no control on the microprocessor software or hardware. I have a connector that goes directly to the uC pins, and there are pull-ups on the uC board. I can have whatever I want between the switch and the connector. Direct connection triggers all the time, but so far, hasn't killed the micro (but it sure looks nasty on the scope).What would you do?

author: lgbeno
author_rank: Frequent Contributor
timestamp: July 26, 2013, 12:17:51 pm
content: You could consider using a current source and then measure the current though the loop to determine switch closure.Sent from my iPhone using Tapatalk 2

author: ElectroIrradiator
author_rank: Frequent Contributor
timestamp: July 26, 2013, 12:44:02 pm
content: Yep, switch a current loop, maybe even use an opto-coupler between the cable and the MCU to get 'perfect' isolation from the noise voltages. Look into MIDI cables and setups for schematics and more ideas.

author: SeanB
author_rank: Super Contributor
timestamp: July 26, 2013, 09:02:21 pm
content: A relay will work there, just use a 12V relay with a set of gold flashed contacts at the MCU end and a catch diode or zener diode across the relay coil is both cheap and rugged. If you have a 12V rail a 12V relay is simple and going to have the mechanical life. Will have some contact bounce which will be minimal with a reed relay unit and will have a few milliseconds delay on switch on and off, but if you are doing motors then this is not a problem.

author: Andreas
author_rank: Super Contributor
timestamp: July 26, 2013, 09:06:10 pm
content: Quote from: JuKu on July 26, 2013, 11:38:42 amWrong concept: never do a interrupt on external signals. If there are too many external events your system may hang.Instead I would debounce the signal within subsequent calls of a 1ms timed routine.also some filtering (at least a R/C filter) with about 1ms time constant is a good idea.with best regardsAndreas

author: Marco
author_rank: Super Contributor
timestamp: July 26, 2013, 11:47:42 pm
content: Quote from: JuKu on July 26, 2013, 11:38:42 amSTP?

author: fcb
author_rank: Super Contributor
timestamp: July 27, 2013, 11:04:21 am
content: STP = shielded twisted pair
Switch between Vrefs for DAC - Page 1
Forum section: electronics / projects

author: Penguin36
author_rank: Contributor
timestamp: January 30, 2018, 02:01:05 pm
content: Hi,I‘m playing with an 18 bit DAC and use a 5V voltage reference atm.Now I‘m thinking of using a second Vref (2.048) on the same DAC which gives a higher resolution below 2V.How to switch between the 2 references? Using an analog switch will produce a voltage divider, right?

author: David Hess
author_rank: Super Contributor
timestamp: January 30, 2018, 06:52:11 pm
content: The analog switch should be buffered by a precision high input impedance buffer which then drives the ADC. That will reduce the effect of the switch resistance to nothing.Another way to do it is to use two buffers with only one of them actively driving the ADC at a time. Then the analog switches are used to disable the buffer not in use.

author: Penguin36
author_rank: Contributor
timestamp: January 30, 2018, 08:19:34 pm
content: I think I will use 2 buffers with en/disable.Thank you :-)

author: BrianHG
author_rank: Super Contributor
timestamp: January 30, 2018, 10:07:14 pm
content: Depending on your 2v reference circuit, it may be nothing more than just using a P-Channel mosfet.Some dacs already have multiple selectable vref inputs as well.

author: David Hess
author_rank: Super Contributor
timestamp: January 31, 2018, 11:15:14 am
content: Quote from: Penguin36 on January 30, 2018, 08:19:34 pmThe disadvantage of using separate buffers is that they will have separate offsets complicating calibration.

author: IanJ
author_rank: Unknown
timestamp: January 31, 2018, 11:52:00 am
content: How important is tempco to your design, if so check the analog switch spec and make sure you are happy.I use a single Vref (LM399AH), an extremely low RDS(on) fet and a couple of low TCR resistors (voltage divider) and a buffer op-amp on my PDVS2 design to switch between two Vrefs for the 18bit DAC. The resultant tempco/stability is good.Ian.

author: Penguin36
author_rank: Contributor
timestamp: January 31, 2018, 11:56:07 am
content: Ian,I know your calibration tool, very nice :-)I want to built a similar by my own. Maybe the Max5420 divider is a good choice?Any hint on the used fet in your design?

author: MT
author_rank: Super Contributor
timestamp: January 31, 2018, 06:39:33 pm
content: Are you even going to get 18 bit resolution below 2V? I dont think so.

author: Penguin36
author_rank: Contributor
timestamp: February 02, 2018, 06:04:44 am
content: Yes, I do get 18 bit resolution below 2.5V (decided to use 2.5 instead 2.048).I‘m using the LTC2756 Eval board with Max6350 as vref. To get 2.5V I use a precision voltage divider (2ppm resistors). Atm all just mounted on breadboard, but it works very well. I can set output voltage to the 5th decimal place. Measuring the output with a fresh calibrated 34401A, powered on for days now.The eval board seems to be very well designed and grounded. The output voltage is very stable und repeatable.
Switch contact problem and fix. - Page 1
Forum section: electronics / projects

author: Moriniman
author_rank: Contributor
timestamp: August 26, 2015, 12:58:51 pm
content: I've got an Electroantennography (https://en.wikipedia.org/wiki/Electroantennography) instrument on the bench at the moment.I had to replqce the switch for the 1mV and 10mV test signals before modifying them to 0.1mV and 1mV. Although it seemed to work OK at first, it soon started misbehaving.Insect Antennae signals drift a lot over time, so there are manual and automatic 'zero adjust' or 'baseline return' circuits. The automatic circuit is really just a high pass filter, with a 1uF capacitor and resistor values ranging from 1 to 30 Mega ohm (giving 1 to 30 second time constants) that can be selected via a rotary switch.It's not a well enough known fact that switch and relay contacts can have aminimumcurrent rating. Below this rating the contacts can become unreliable. This was a failure mode on a lot of transistorised ignition projects, you needed to make sure the points still carried around 100mA for them to be reliable.Anyway the rotary switch for the filter resistors had unreliable contacts, which is why the instrument was playing up. My trick for fixing this was to pass an AC current of around 10mA through each contact on the switch.

author: 3roomlab
author_rank: Frequent Contributor
timestamp: August 27, 2015, 03:25:31 am
content: wow ! insert a tungsten wire into a single neuron (inside the wiki)? that is fascinating ! talk about soldering SMDs, this 1 takes the cake !

author: georges80
author_rank: Frequent Contributor
timestamp: August 27, 2015, 04:44:58 am
content: Contact resistance is a common problem with many switches that are operated at very low currents. Some have specs in their datasheets for minimum operating current.Just google wetting current.Nothing new...cheers,george.
Switch DC equivalent rating? - Page 1
Forum section: electronics / projects

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: June 24, 2019, 02:09:37 pm
content: I'd like to buy some switches for a project but since they are rated for AC current and I need them for DC, what would be a good approximation of their DC ratings?They're rated for AC 125V/6A or 250V/3A. I need them for 8A DC is that too much to ask or will it not go into thermal runaway?

author: ejeffrey
author_rank: Super Contributor
timestamp: June 24, 2019, 04:34:37 pm
content: Yes, that is probably too much. DC rating depends on the voltage even more than the current. Switches typically have much lower voltage ratings at DC than AC due to the arc extinguishing properties of AC waveforms. The load is another factor: an inductive load (such as a motor or relay coil) will tend to sustain the arc and needs snubber capacitors or diodes.Maybe your switch could handle 8A DC at a very low voltage (5-10 V) that produces little arcing, but trying to operate at (say) 48 VDC would almost certainly destroy it.

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: June 24, 2019, 04:44:33 pm
content: Quote from: ejeffrey on June 24, 2019, 04:34:37 pmIt will be used on a 5V circuit so it should be fine I guess

author: Nominal Animal
author_rank: Super Contributor
timestamp: June 24, 2019, 05:09:21 pm
content: Consider looking at automotive switches. Cars use 12VDC or 24VDC, and the switches are usually marked with 12VDC current rating (10A is common).Just a couple of days ago, I was looking at additional switches for switching ~12V LEDs, and automotive switches fit that bill perfectly.

author: ejeffrey
author_rank: Super Contributor
timestamp: June 24, 2019, 05:47:30 pm
content: Quote from: drummerdimitri on June 24, 2019, 04:44:33 pmMaybe? As long as it isn't thermally limited (8A will produce ~70% more heat than 6A) it is probably OK. But I agree with Nominal Animal: try looking at automotive switches to find one that has an actual low voltage DC rating.

author: drummerdimitri
author_rank: Frequent Contributor
timestamp: June 24, 2019, 06:15:12 pm
content: Quote from: ejeffrey on June 24, 2019, 05:47:30 pmI have a Flir thermal imager, what would be a safe max temperature as I will test it before inserting it into the circuit. Does 60C sound reasonable?
Switch for multimeter project ? - Page 1
Forum section: electronics / projects

author: dds
author_rank: Contributor
timestamp: August 30, 2013, 09:28:27 am
content: Hi,Can I somewhere buy a mechanical switch for multimeter - which can be used for switching between voltage like Volts AC, Volts DC, Ampere, Ohms (I'm in process of making multimeter prototype).Thanks!
Switch Mode Converter Controller IC - Choice of MOSFETs - Page 1
Forum section: electronics / projects

author: frasdoge
author_rank: Contributor
timestamp: February 08, 2024, 03:55:00 pm
content: Hello,I'm taking a look at building a switch mode converter for 120V DC input, 5V output. I've come across a controller IC that looks appropriate.LTC3895. Something I don't understand however is that they use different N channel MOSFETs between their MTOP-MBOTTOM pair shown in the example schematics usingBSC520N15NS3Gand MNDRV usingIPD320N20N3.I've taken a look at the datasheets and can't really see what difference compels them to use different parts here. Those parts of obsolete now but their replacements do not differ in price by almost anything either. Can anyone spot what the rationale is?Mostly just a curiosity as I plan to swap out the MTOP and MBOTTOM for much lower Rdon, and MNDRV is unnecessary as it's only needed for voltage following at low input voltages nearing the MOSFET VGS, which is not applicable to my application.Cheers

author: David Hess
author_rank: Super Contributor
timestamp: February 09, 2024, 03:22:39 am
content: Conduction losses are proportional to duty cycle and highest efficiency is about where conduction and switching losses are equal. So if the duty cycle is very low, as would be the case with a conversion from 120 to 5 volts, then the optimum MOSFET size for the high side will be smaller.

author: youngda9
author_rank: Regular Contributor
timestamp: February 09, 2024, 09:32:21 am
content: David's answer is correct. Also look at some other parameters.Top FET is 1/2 the price, and 2 are used in that location.RDS-on is a bit less than 2x the lower FET, so effective resistance will be lower for the two top FETs, and each will handle 1/2 the current, ideally, so switching losses will be reduced.Upper FET is <1/2 the capacitance of the lower FET, so switching losses will be reduced as well using 2x in the upper location as opposed to one of the lower FET types.Net results is better efficiency in this setup.Lower FET will conduct about 95% of the time. Went with a more costly lower RDS-on FET in that location. Could parallel FETs for better efficiency, but it would cost more.These are the trade-offs they chose.I've done similar designs recently.- LTC3891EFE based 24V to 12V converter @ 10A output. Used a single upper and lower FET since duty-cycle will be 50%.- LTC3892EFE based 24V to 20V converter @ 20A output. Used dual upper and a single lower FET since duty-cycle will be 83%. This setup resulted in more optimal efficiency.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 09, 2024, 10:03:04 am
content: I'd just go with a flyback. Forward or resonant if higher power (>50W maybe?). Direct bucking at that ratio isn't very effective.Also gets more headroom for transient protection; 150V rating for 120V (nominal?) doesn't exactly instill confidence. Or is that the peak including transients already?Tim
Switch Mode DC/DC Power Supply Design & Power Management - Page 1
Forum section: electronics / projects

author: varunkoganti
author_rank: Contributor
timestamp: January 02, 2022, 09:06:58 am
content: Preface-I am designing a drone, My choice for stepping down voltage is to use a DC/DC switching converter, after using the parametric search of Digi-key, I selected TPS54495RSAT‎ as my SMPS.TPS54495RSAT‎ is a dual SMPS capable of 4A@Output1 & 2A@Output2. My SMPS design will output 5V,4A@output1 & 3v3,2A@output2.My design also requires monitoring the Battery/Power. My choice was to go to PAC1933T-I/JQ .Hyperlink to the part(TPS54495RSAT‎ ).https://www.digikey.in/en/products/detail/TPS54495RSAT/296-TPS54495RSATCT-ND/4291940?itemSeq=386099797Hyperlink to the part(PAC1933T-I/JQ ).https://www.digikey.in/en/products/detail/PAC1933T-I%2fJQ/PAC1933T-I%2fJQCT-ND/9453208?itemSeq=386132900Problem Statement -monitoring Voltage, Current & power requires utilization of sense Resistor. Where should the sense resistor be placed? before the feedback of SMPS or after?Will placing the sense resistor before the feedback compensate for the voltage drop due to sense resistor?Calculation for sense resistor was done by me using the datasheet it is specified in section 4.7 Selecting RSENSE Values.resistor values -5V - 0.025 ohm considering IMax = 4A3v3 - 0.05 ohm considering IMAX = 2Asense resistor direct from Battery - 0.01, considering IMAX = 10A.Which one should be followed? Figure 1 or Figure 2?
Switch Mode DC/DC Power Supply Design - Page 1
Forum section: electronics / projects

author: varunkoganti
author_rank: Contributor
timestamp: January 02, 2022, 10:00:43 am
content: Preface-I am designing a drone, My choice for stepping down voltage is to use a DC/DC switching converter, after using the parametric search of Digi-key, I selected TPS54495RSAT‎ as my SMPS.TPS54495RSAT‎ is a dual SMPS capable of 4A@Output1 & 2A@Output2. My SMPS design will output 5V,4A@output1 & 3v3,2A@output2.It has 2 soft start pins, as per my understanding from datasheet they are used to protect devices ie to reduce inrush current during startup as the SMPS switches with full PWM.Problem Statement -What should my soft start time be?10ms ? 50ms? 100ms? this timing is what determines my capacitor value connected.Hyperlink to the part(TPS54495RSAT‎ ).https://www.digikey.in/en/products/detail/TPS54495RSAT/296-TPS54495RSATCT-ND/4291940?itemSeq=386099797

author: jwet
author_rank: Frequent Contributor
timestamp: January 05, 2022, 08:51:15 am
content: My advice is to commit to a PCB and build it. It will probably work ok but you might find some anomalies that you can investigate and correct. SMPS are very layout senstive- minimize high current loop area and have very low impedance grounds especially at these current levels. A 25 milliohm resistance (like a fuse) creates a 100 mV drop at 4 amps.

author: palpurul
author_rank: Regular Contributor
timestamp: January 05, 2022, 10:58:23 am
content: You can change your soft-start time later in your design.Just slap a 0805 cap footprint from ss to GND and test what works best for your design.4A is not low just focus on layout I think.
Switch-Mode Hybrid - Page 1
Forum section: electronics / projects

author: Jon86
author_rank: Frequent Contributor
timestamp: May 02, 2013, 09:19:23 pm
content: Now just tell me if I'm being stupid here, but how about a Hybrid Switchmode/Linear PSU?I know switchmode PSUs don't have a very stable/smooth output voltage, so why not use a linear regulator on the output to fix this?For example:7V 2A Switchmode PSU (Tiny and efficient) feeding into a simple linear voltage regulator, max heat dissipation of around 4W, producing a smooth 5V at 2A.Are there any problems with this? Has it been done? Am I missing something?

author: Bored@Work
author_rank: Super Contributor
timestamp: May 02, 2013, 09:21:27 pm
content: Yes it has been done. Yes, it has been discussed here. You didn't ask this, but Dave even made a few videos about it, as part of his power supply design videos.Sounds like an opportunity to use the new URL link shortener to point to the serieshttp://llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogo.ch/16d

author: Jon86
author_rank: Frequent Contributor
timestamp: May 02, 2013, 09:26:47 pm
content: Ah, I see. I didn't watch all of Dave's vids on the power supply design...Thanks anyway, sorry for bringing it up again.

author: c4757p
author_rank: Super Contributor
timestamp: May 02, 2013, 09:34:08 pm
content: Quote from: Bored@Work on May 02, 2013, 09:21:27 pmBookmarked.

author: peter.mitchell
author_rank: Super Contributor
timestamp: May 03, 2013, 03:26:10 am
content: Quote from: Bored@Work on May 02, 2013, 09:21:27 pmBRAVO!

author: LaurenceW
author_rank: Frequent Contributor
timestamp: May 03, 2013, 10:12:16 pm
content: One GOTCHA to watch for is that 78xx (and maybe many other) simple linear regualtors have really quite poor high frequency regulation/attenuation.In other words, high frequency noise at the input can go straight through 'em like a damn good curry. So you'll need some sort of filter inductor between the SMPS and linear regs, and input caps around the linear reg, too. I don't think the components need to be huge - a cut-off freqnecy of a few KHz will more than cover it, I would think.

author: Frant
author_rank: Regular Contributor
timestamp: May 03, 2013, 11:22:29 pm
content: Quote from: LaurenceW on May 03, 2013, 10:12:16 pmThere are actually not so many voltage regulator ICs with well documented frequency characteristics (i.e. with a ripple rejection vs. frequency diagram up to at least 1 MHz given in the datasheet). Of those well documented only a few are really good at it. I found these: TPS7A4700, TPS796xx, TL1963A, LT1129.Regarding the mentioned passive filtering, one must exercise caution not to make the SMPS feedback loop unstable.
switch mode power supply  - Page 1
Forum section: electronics / projects

author: mohamedgad
author_rank: Newbie
timestamp: October 12, 2016, 04:40:19 pm
content: i need help fast iin transformer have 5 out put +12 5A, -121A, +/-95V200mA,+/-85V300mA and 1 inputmy all circuit take universal input from 85-220 AC and give these out put i want to design PSB by altium and i need help to dray schematicplease all in here help me how to begin how to select components.

author: calexanian
author_rank: Super Contributor
timestamp: October 12, 2016, 09:46:09 pm
content: I would review the materials at Power Integrations websitehttps://ac-dc.power.com/The website has changed recently but i believe they have a power supply design program that may be helpful to you.

author: mohamedgad
author_rank: Newbie
timestamp: October 13, 2016, 07:23:13 pm
content: please can draw it to me

author: rx8pilot
author_rank: Super Contributor
timestamp: October 13, 2016, 07:25:03 pm
content: Are you asking for someone to design this for you?

author: mohamedgad
author_rank: Newbie
timestamp: October 13, 2016, 07:27:31 pm
content: i want to design it by myself but i need help

author: mohamedgad
author_rank: Newbie
timestamp: October 13, 2016, 07:33:51 pm
content: thanks i will read it

author: rbola35618
author_rank: Frequent Contributor
timestamp: October 13, 2016, 08:07:46 pm
content: Watch videos 1 2 and 3. and then email me at rbola35618@aol.com and I will send you the TopSPICE files that I used in the videos.There is a total of 20 videos so far as I continue to add to the series.

author: rx8pilot
author_rank: Super Contributor
timestamp: October 13, 2016, 10:04:58 pm
content: Quote from: blueskull on October 13, 2016, 07:30:56 pmThere is a great YT video series on power electronics from University of Colorado.https://www.youtube.com/playlist?list=PLU0FYX-iPphekjedgxKuY4NsdtubodE20
Switch mode power supply common mode AC input filter. - Page 1
Forum section: electronics / projects

author: aargee
author_rank: Frequent Contributor
timestamp: June 28, 2013, 06:24:37 am
content: Hi all,I have a couple of small 12V/4A switchmode power supplies that have failed by one of the AC input rectifier diodes going short circuit and then compromising the winding on the common mode filter choke (melting the enamel/varnish).I would like to keep using the supplies due to the space where they fit is rather tight and there is no easy off the shelf substitute. The filters themselves are rather small and made of unobtanium - not easily found.Question is, can the supplies be run without the common mode filter? If so, what would be the consequences - noise put back onto the mains?Thanks in advance.

author: dr_p
author_rank: Frequent Contributor
timestamp: June 28, 2013, 07:18:12 am
content: Quote from: aargee on June 28, 2013, 06:24:37 amThe Chinese seem to get away with not using proper filtering in their switchers. I guess you can try eliminating them and see if there's a problem with the noise injected into the mains. If so, maybe build/buy a filtered outlet, something like this:

author: aargee
author_rank: Frequent Contributor
timestamp: June 28, 2013, 07:25:41 am
content: Yes, I was thinking of replacing the fixed power cord with an IEC socket with built in filter as a substitute.

author: SeanB
author_rank: Super Contributor
timestamp: June 28, 2013, 08:11:24 pm
content: Soable, just do not use older Schaefner units, only ones made within the last decade. The old ones of this brand have a reliability problem. Hopefully you are replacing the diodes with ones of at least a 3A 1000V rating.

author: Niklas
author_rank: Frequent Contributor
timestamp: June 28, 2013, 11:02:57 pm
content: Quote from: dr_p on June 28, 2013, 07:18:12 amThe reason why they can do it, at least for export to the EU, is that they have no responsibilty at all. The importer will be punished if, and only if, any problems occur and the units are tested by the authorities and fail the tests. Usually it will take some time between the time a product is introduced and the problems and testing occurs. During that time period a large portion of the batch is sold and the importer will have the invested money back together with some profit. Remember the video Dave did on the fake 5$ iPhone chargers a couple of months ago?There is a joke about what CE stands for in China: China Export

author: pinank
author_rank: Newbie
timestamp: May 12, 2016, 03:48:51 am
content: Can anyone please elaborate on the common mode choke? I am designing a smps (15Watts: 24V 625mAmps). I want to add the filter to it but can't decide how to select the filter? Any help will be appreciated thanksSent from my Nexus 4 using Tapatalk