hybridfree/eevblog-posts huggingface dataset:
Power Supply Selection Circuit - Page 1
Forum section: electronics / projects

author: krapht
author_rank: Contributor
timestamp: December 17, 2015, 01:40:43 am
content: Hey, just wondering if anyone could tell me how to fix this circuit I drew? The goal is to implement power supply source selection using low Rds PMOSfets. The load draws a maximum of 2.5 watts at any given time, but usually is in a low power sleep mode.USB_PWR_EN# is from an FTDI part, 3V3 push-pull capable of sinking/sourcing 4mA. When there is no USB power, I believe it's high-Z (47k pull-up into VUSB).I guess the reason I'm posting is because I'm worried about backflow into VUSB from the high-voltage aux (bat) source. If 17V ever appeared across the rails of my UART chip, it would be destroyed. Even overcharged 1.6V alkaline batteries would be exceeding the absolute maximum limits of the FTDI chip (i.e. 5.5V). Looking at the circuit as is, if VUSB were to be applied while the circuit had been previously on aux power, the stored charge on C11 would all of a sudden appear across the Q4A/B short. Not to mention VGSmax for the PMOSfets I'm using is -8V, which means instead of using the transistors as inverters I should be using them in some sort of open-drain configuration.I could restrict the battery voltage I'm willing to accept in, although I quite like being able to use lithium AA batteries. I could use a Schottky on VUSB with the appropriate reverse bias ratings and get rid of the PMOS high side switch. Efficiency is not so important when the device is powered from mains. Still, I wonder if there isn't something more elegant I could do.

author: fivefish
author_rank: Frequent Contributor
timestamp: December 17, 2015, 02:00:14 am
content: Why not just a relay? A latching relay if you're trying to conserve last bit of power. They also have very very small on resistance.

author: krapht
author_rank: Contributor
timestamp: December 17, 2015, 02:39:38 am
content: I considered it, but I really want fast switch time. The load is a data logger, and the RF power amplifier is the big power hog which consumes most of the 2.5W power budget. The data logger should be able to keep running even if the power goes out, which is why there's aux battery power in the first place. While I haven't done the complete analysis, if my load is drawing 700mA~ @ 3.3V, I have a gut feeling that I would need a very large amount of input capacitance at the dc-dc regulator.Which is its own problem since I believe USB is limited to 10uF bypass capacitance on hot-plug.

author: exmadscientist
author_rank: Frequent Contributor
timestamp: December 18, 2015, 04:46:43 pm
content: Is this for low or high volume stuff? If it's low volume, just use LTC ideal diode and/or hot swap parts. They're not cheap, but you'll spend more time trying to substitute them than they'll cost you. The 4412 and 4231 are good places to start but they have a decently broad lineup.
Power supply shorting problem - Page 1
Forum section: electronics / projects

author: buffalo960
author_rank: Contributor
timestamp: December 10, 2011, 10:36:02 pm
content: Hello,I put together this power supply a few months ago and it was working (as far as I could tell) because the LED shown in the schematic attached would light up just fine. I was having trouble getting the supply to vary. The project got put on hold for a while and I just came back to it today. Now every time I power it up I instantly get a 9ohm short between power and ground. I have replace the regulator 3 times all with the same result.I am puzzled by this because as soon as the regulator blows out the short is gone. I only have 3 regulators left and would rather not blow them out. Does anyone have any ideas on why this would be happening? Let me know if you need more information then I have given.I should also mention I am using the LM27342http://cache.national.com/ds/LM/LM27341.pdf

author: amspire
author_rank: Super Contributor
timestamp: December 10, 2011, 11:30:08 pm
content: Where is the schottky diode from the SW pins to ground? The regulator cannot function without it. You will get the regulator IC either latching or blowing.

author: buffalo960
author_rank: Contributor
timestamp: December 10, 2011, 11:34:12 pm
content: Quote from: amspire on December 10, 2011, 11:30:08 pmThank you for your reply. I am gunna go run to get a diode and try it out.

author: codeboy2k
author_rank: Super Contributor
timestamp: December 11, 2011, 10:01:47 am
content: Quote from: buffalo960 on December 10, 2011, 11:34:12 pm

author: buffalo960
author_rank: Contributor
timestamp: December 12, 2011, 03:32:54 am
content: Quote from: codeboy2k on December 11, 2011, 10:01:47 amo_O ?

author: metalphreak
author_rank: Frequent Contributor
timestamp: December 12, 2011, 07:02:27 am
content: Diodes are a critical component of any buck/boost/buck-boost converter ie the non-isolated types.Quote

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 12, 2011, 11:04:39 pm
content: Some buck converter chips will have a synchronous rectifier built in.
Power supply suggestion for Esp8266 - Page 1
Forum section: electronics / projects

author: Karamel
author_rank: Regular Contributor
timestamp: October 24, 2019, 01:53:13 am
content: Hi,I am currently thinking to create Apple HomeKit for my home. Accessories have esp8266 mcu on each board. But, I am really worried about their power supply units.The accessories are briefly lamps, fans, locks, blinds etc. Their common ground is that they are small and light. So, I am thinking, maybe, I can supply each one with mobile phone charger. However, I have doubts about that. There is no enough isolation between AC and DC, output not too much stable. etc.Have you ever tried to supply esp8266 via phone charger circuit for a long time? (probably iPhone charger or any other)Or Do you have any suggestion to me about that issue?
Power Supply Teardown question - Page 1
Forum section: electronics / projects

author: zerobrain
author_rank: Contributor
timestamp: November 26, 2014, 09:00:37 pm
content: Hi,i have take apart a power supply and came accross a construction Dave showed as well in one of his teardowns (see attached image).In the image you see lines L1 and L2 entering from the bottom, passing a fuse and an NTC. Then there seems to be an emc filter. But what i don´t get are the spark gaps being "parallel" to the current compensated inductors. Has anybody got a clue what they are being used for in this case?Not drawn in the picture: after the inductors a four-way- rectifier is applied...Thanks a lot..

author: Jebnor
author_rank: Regular Contributor
timestamp: November 27, 2014, 02:03:44 am
content: With inductors, sudden stopping of current will induce a voltage spike. The spark gaps are there to kill any voltage spike before it gets too bad. I think.

author: Seekonk
author_rank: Super Contributor
timestamp: November 27, 2014, 05:39:24 am
content: Spark gap? Are you talking about the cut gap in the board? The UL clearance for air is less than for just a circuit board. Notice the other side of the inductor the clearance is much wider and therefore acceptable for that voltage. Without the cut in the board it wouldn't have passed certification. That cut is not intended to be a spark gap.

author: Niklas
author_rank: Frequent Contributor
timestamp: November 27, 2014, 07:47:10 am
content: Quote from: Jebnor on November 27, 2014, 02:03:44 amSimilar issue, but for CAN bus. Energized inductor with one end fixed to DC, either through a short or a capacitor, creates a voltage transient.www.ti.com/lit/an/slla271/slla271.pdf

author: zerobrain
author_rank: Contributor
timestamp: November 27, 2014, 03:08:11 pm
content: Thanks for all the answers!@Niklas, Jebnor - that makes sense!@Seekonk - no i really meant the "spiky" things parallel to the coils.Your explanations made sense, but i won´t get still - after looking more deeply into the schematic: Why the the minimum distances not more an issue after the foru-way-rectivifer? I painted in the diodes forming that rectifier and i noticed (marked yellow) the minimum distance between Vmax and 0 is rather small.Is that an error or are the rules different here?thanks very muchDominik
Power Supply, two voltages  - Page 1
Forum section: electronics / projects

author: brue
author_rank: Contributor
timestamp: February 14, 2015, 12:32:00 am
content: Hi there,I have to design a device which can be powered from two different voltages, 5V and 3.3V on different input pins and common ground pin.The user can apply either the 5V on the 5V input or the 3.3V on the 3.3V input pin. If both voltages are present (Voltage on 5V Pin is > as 3,3V Pin), the device should take the 5V to power the device. We talk about <5 watts. Finally I need 3.3V for the controller, so the voltage drop of a simple diode in the 3,3V supply would be to high. And I need to have a regulator for the 5V. Any reverse current is not allowed.I'm looking for a nice way to design that, any ideas?Thanks!

author: sdg
author_rank: Regular Contributor
timestamp: February 14, 2015, 08:59:05 am
content: I believe Linear makes some controllers that do precisely what you're looking for.

author: jpb
author_rank: Super Contributor
timestamp: February 14, 2015, 11:03:24 am
content: I'm not sure if I understand your requirements correctly and I don't know if you need this all to be small and well integrated, but it sounds like you just need some sort of switch operated by the 5V supply to turn off the 3.3V supply if it is there (a reed relay to avoid any diode drops in the 3.3V supply?). So my rather basic circuit would be 5.5V in to 3.3V regulator with a connection to the reed relay on the 5V side of the regulator and the 3.3V in would just be passed via the reed relay.Perhaps reed relays are too noisy or power hungry - but it is just a thought.Even simpler would be a mechanical switch attached to the 5V input socket (in the same way head phone jack sockets have a switch to disconnect the speakers).

author: Kalvin
author_rank: Super Contributor
timestamp: February 14, 2015, 01:10:55 pm
content: LTC4415 might be something you want to take a look at. There are also other "ideal diode" products available, which may be suitable for your application."LTC4415 - Dual 4A Ideal Diodes with Adjustable Current Limit"http://www.linear.com/product/LTC4415

author: brue
author_rank: Contributor
timestamp: February 14, 2015, 06:48:25 pm
content: Hi,Thank you for your suggestions.Something like the LTC4415 or 4413 would fit pretty good I think, it's probably just a bit expensive solution for mass production.The circuit has to be relatively small, I have enough space for some ICs or some transistor/FET circuits but a relay would not fit, apart from that it is not reliable enough.Probably someone implemented something discretely?

author: ajb
author_rank: Super Contributor
timestamp: February 15, 2015, 02:13:17 am
content: There are options from other manufacturers as well. Check out the TI TPS211x series, for instance, which is a tiny little 8TSSOP part.
Power supply using inductive charging from NFC terminal - Page 1
Forum section: electronics / projects

author: Tony.T
author_rank: Regular Contributor
timestamp: October 22, 2015, 11:00:44 am
content: I have read that normal NFC chip needs about 15mA to run properly. Suppose that one have a card with NFC chip onboard and some other sensors...also a small processor.HOW much energy could you take from a NORMAL nfc terminal...to be able tu run the circuitboard without having a battery? How much power can one gain from this inductive field that nfc terminal sends out.Depending on number of turns of the coil?(antenna).Of course that the possible amount of power is depending on the terminal but as i know there is limitations of how far the field can reach and the amount of energy it produces. One does not want NFC chip to react on distances further than 20cm.....But i just want to build something without battery that uses NFC field as a power supply....and wonders what MAX power consumption my board can have.Hope you understood my question :-)Cheers...
Power surge on hub port? - Page 1
Forum section: electronics / projects

author: Gizmo
author_rank: Regular Contributor
timestamp: November 23, 2016, 09:29:36 pm
content: I'm working on a USB device based on the SAMD21 chip. Up until now I've been using the Sparkfun breakout / dev board and have the USB comms working how I want. I've since created a custom PCB for my needs, but when I connect it to the PC I am getting "power surge on hub port" reported by Windows.I can run the device hooked up to a bench supply and it draws around 800ua according to the multimeter. I dont see any surge on startup, although that could be just down to the reaction speed of the multi-meter I guess.However the capacitance is just over 1uf (replacing the 10uf tantalum with 1uf ceramic) on the input side with a ferrite for filtering, feeding a 3.3v regulator. It doesn't look like it should be drawing anywhere near the 50ma required to trip the power surge?I've tried replacing the 10uf electrolytic tantalum in the schematic with a 1uf (as mentioned above) as well as using the 10uf with the same results.When connected to the bench supply I can program and use the micro no problem and it never draws more than 1ma.A bit confused.

author: Gizmo
author_rank: Regular Contributor
timestamp: November 24, 2016, 10:24:29 pm
content: Ok, it turns out I'm an idiot. Even though I double checked, I managed to get the footprint for the mini-b connector backwards so gnd and +ve were reversed, which explains the over current.I butchered a usb cable and wired it up the right way around and all is now working as expected.Live and learn.
Power switch brainstorming, DC in with battery failover. - Page 1
Forum section: electronics / projects

author: hitech95
author_rank: Regular Contributor
timestamp: August 28, 2022, 08:47:19 am
content: A friend asked me to help him with a small project he is working on.I've thinked of a couple of solution but are quite complicated and doesn't cover all the requirements at once:Two power busses- 12V battery in (standby)- 8-26V DC In (active)12V@3.5A (max not continuous) regulated outputDC IN must have reverse polarity protection, UVP, OVP (to protect switching converter)When DC IN fails, (no present, UV cut off, OV cut off) it must immediately switch over to 12V battery.When DC in come back switch over must be performed after DC IN has a power good signal for some time. (To prevent to switching when the PSU hiccups)The only solution for this that is coming to my mind is using an MCU.The OVP/UVP and the active/standby status must be capable to be monitored by and external MCU/CPU.My solutions fails to do this. In fact any additional load that i attach to the two voltage references to handle OVP/UVP will unbalance the gate network.Resulting in the P MOSFETs that I'm using as a switch are always open.And it must be Cheap!I'm attaching my idea below, but as I said before it is convoluted and not properly working. (It is also missing the reverse polarity protection.)In that simulator the voltage references component is not present, so i had to create them manually!And it is missing the DC DC part for the 12V stabilized output, but that should be the easiest part.Any idea is welcome!

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 28, 2022, 12:29:01 pm
content: Use a pair of Schottky diodes as the core of the switching circuit. On the main input, place an OVP protection circuit. On the backup input, place a LDO that's normally set for 7.5V or so. If the main input drops below 8V, then switch the LDO to 20V or so which effectively turns it into a bypass.If the Schottky diodes would cause too much loss, use an "ideal diode OR" circuit instead.

author: Peabody
author_rank: Super Contributor
timestamp: August 28, 2022, 02:43:44 pm
content: You might want to look at power mux chips such as the TI TPS2120, 2121 and 2124. They won't quite get you to 26V, but pretty close. This type of product usually lets you chose between automatically selecting the highest voltage source, or manually selecting a particular source to be the backup without regard to voltage. Other manufacturers have similar products.

author: hitech95
author_rank: Regular Contributor
timestamp: September 10, 2022, 09:16:10 am
content: Thanks for the replys.Unfortunatly those chips are a bit limited in voltage ranges. 26V was a bit of a stretch on the lower side.Going even lower is not possible.Anyway I've seen some interesting documents from TI I'll have to take a deeper look into them.Probably 2 diodes to an LDO to power a small micro (like an attiny) to control the flow would be the easy way.To actually switch the load a proper power switch would be awesome but all depends on costs!
Power switch distribution with ground control? - Page 1
Forum section: electronics / projects

author: Sarcarean
author_rank: Contributor
timestamp: August 01, 2018, 10:49:16 am
content: So I am having a bit of trouble with creating a circuit for some basic power distribution.I have a pin that needs to have either GND, +5V or +12V connected to it. And yes, GND instead of 0v, as in that scenario, it needs to pull down. I made various circuits with a slew-rate load switch, but then the issue is those lines have output capacitance that when in 0v would actually make the pin appear with 1-2V~.So does anyone have a good circuit or IC that can do this? For EN control, I have 2 IO pins that are used.

author: Sarcarean
author_rank: Contributor
timestamp: August 01, 2018, 11:13:48 am
content: Having thought about it some more, I actually can simplify it. I have one INPUT (Vcc) and OUTPUT and one high-side ENABLE. Does anyone know a part that the output is pulled low when not enabled? Voltage input will be 5-12V.

author: timpattinson
author_rank: Contributor
timestamp: August 01, 2018, 11:18:57 am
content: Why can't you use a pull down resistor?

author: madires
author_rank: Super Contributor
timestamp: August 01, 2018, 12:31:22 pm
content: A circuit diagram would be helpful

author: Sarcarean
author_rank: Contributor
timestamp: August 02, 2018, 05:09:34 am
content: Quote from: timpattinson on August 01, 2018, 11:18:57 amI did think about that. And I am leaning on possibly putting a 50K-100K (very weak) resistor to ground. The reason I am trying to avoid that, is when the +12V rail is switched on, its being created by a charge pump that just barely manages to get to 12.0V and I am afraid that putting any path to ground would cause too much VCC loss.I was hoping there was just a simple MOSFET circuit that when logic ENABLE was not on, that it would instead pull the IO to ground, instead of just to a tri-state.
Power switch for TCXO - Page 1
Forum section: electronics / projects

author: Korken
author_rank: Regular Contributor
timestamp: January 21, 2017, 05:36:13 pm
content: Hi all!I have a design with a TCXO drawing about 2 mA nominal, and I need to be able to turn it off (when in power save) - but it does not have an EN pin and I cannot change TCXO.I had a google and found solutions using both an inverter gate as a "power driver" and P-transistor solutions for turning the VCC on/off.The solution will be controlled from an MCU (3.3V).Are there anyone here that has had the same problem and have compared these solutions?Is there any reason to use one over the other? Is there a better way?Thanks for all input!

author: DBecker
author_rank: Frequent Contributor
timestamp: January 21, 2017, 05:55:12 pm
content: With that low current draw you may be able to power it directly from an I/O pin if the supply voltage matches.If you do, make certain that the TCXO doesn't have a start-up surge (typically from overly-generous decoupling) and is tolerant of power supply noise (an I/O pin will be noisier than the MCU supply).If you don't need a solid ground, the typical approach is a low-side power switch. A 7002 MOSFET is about a penny ($0.05 if you only buy a few), needs no additional parts, and will have negligible losses. Otherwise a high side switch is used, which may just be a P-channel MOSFET. Again, at this low current a MOSFET rather than BJT is typically used.

author: Korken
author_rank: Regular Contributor
timestamp: January 22, 2017, 07:22:22 pm
content: Thank you for the input!A simple P-FET solution is probably the way to go.Should one add some inrush current protection when going with a small FET?There will be a 2.2uF + 100nF capacitor at the TCXO, though with that little capacitance it is probably not a problem but better safe than sorry.
Power switch relocation - Page 1
Forum section: electronics / projects

author: Ahyuan
author_rank: Newbie
timestamp: January 01, 2014, 06:50:33 pm
content: Hello!So I have a printer that is located in a shelf, and the power switch is inconveniently located on the side, and to turn it on I have to crouch down and reach inside to turn it on. I want to install a power switch on the front so it is easier to turn on the printer.The switch is a hard switch, and it is pcb mounted, so I can't really mount it on the front. The question is, do I have to switch both live and neutral? The board mounted switch switches both live and neutral, so that means I would have to route 4 wires to the front of the printer, and it is going to be tight, so I'm wondering if I could just short neutral and switch live?The switch is a Sony SDDF-3Thanks!

author: calexanian
author_rank: Super Contributor
timestamp: January 01, 2014, 07:29:17 pm
content: Just use a power strip switch like the rest of the world does!

author: Skimask
author_rank: Super Contributor
timestamp: January 01, 2014, 07:36:55 pm
content: First world problems???

author: mjrandle
author_rank: Contributor
timestamp: January 01, 2014, 07:52:28 pm
content: Really need to advise where you live when asking questions related to mains power. Switching neutral only is unwise if appliance plug is unpolarised. Safest bet is to use a powerboard with RF remote.

author: Ahyuan
author_rank: Newbie
timestamp: January 01, 2014, 09:36:11 pm
content: I wanted a more accessible switch because my parents find it difficult to reach…I thought about using a powerstrip, but making a little switch in the front was cleaner. It is polarized, it uses an IEC cable.I just finished, and it works fine.
Power Switch - Page 1
Forum section: electronics / projects

author: TRa757
author_rank: Contributor
timestamp: September 08, 2013, 11:24:43 pm
content: Hi All,I have an Arduino with a motor controller that I only need to use twice in a 24 hour period so I want to kill power to the motor driver unless I want to move the motor. Just wondering what is being used with Arduino boards to control power. I could just use an SCR but with all the activity on this forum, I figured I would get some interesting responses.Thanks!TimAustin, Texas, USA

author: tszaboo
author_rank: Super Contributor
timestamp: September 08, 2013, 11:36:25 pm
content: There are a ton of solutions to this. You can put a P or N channel MOSFET to the appropriate power supply. There are integrated power switches, which are basically low resistance analog switches. You can power the driver with separate voltage regulator, and use the enable pin on it. Or if the motor driver has Shutdown/sleep/enable pin, you can use that.

author: TRa757
author_rank: Contributor
timestamp: September 09, 2013, 05:27:30 pm
content: I see they call these power switches, "Power Management" these days.Conveniently I have located lots of Semtech SC1566 regs with enable at work. I can desolder them from pilot or failed prod boards and they will work just fine. Just perfect for my needs, low cost ($0) and free shipping!I might wind up with a larger motor controller, as the one I have is very basic and I am not sure the motor has the power to turn the door. Thanks for the help!
Power system for DIY laptop - Page 1
Forum section: electronics / projects

author: UnbrokenMotion
author_rank: Newbie
timestamp: November 16, 2016, 05:01:43 pm
content: First off, i'm new to the forum, hello everyone!Anyway, I am currently building a laptop that uses an Realan LR1106-250W12VDC power supply. Thanks to the 11.8v ~ 12.5 volt variable input on the power supply I can power the entire computer off of a battery pack.However, I am unsure as to how to balance charge five 6P battery packs in series. I know I can use an 18650 protection PCB but I have no idea how to wire the battery pack itself. Do I need resistors between cells? Diodes? How does this work?Would it be easier or even feasable to put all of the batteries in parallel and use a boost converter?Also, is it possible to integrate the battery so that windows detects the battery as part of the system?

author: edavid
author_rank: Super Contributor
timestamp: November 16, 2016, 07:12:02 pm
content: How can you use a 5S pack when the maximum PS input is 12.8V?

author: grifftech
author_rank: Frequent Contributor
timestamp: November 17, 2016, 02:50:03 pm
content: Quote from: edavid on November 16, 2016, 07:12:02 pmbuck converter

author: zv_odd
author_rank: Newbie
timestamp: January 12, 2017, 02:20:04 pm
content: Having pulled apart a few battery packs... They are usually wired in series, 4 - 8 cells at a time with sense wires (center taps) between each cell. The ones I've seen (Lenovo) had Texas instruments ICs designed specifically for the task.The keynotes from this cyber security talk on battery firmware as an attack vector, has an good teardown and part explanation of a macbook battery.https://media.blackhat.com/bh-us-11/Miller/BH_US_11_Miller_Battery_Firmware_Public_WP.pdfIt also gets into the firmware component of the battery.An overview of the standard low level computer power management BIOS API (ACPI) can be found here:https://en.wikipedia.org/wiki/Advanced_Configuration_and_Power_Interface.So I'd guess it's usually the BIOS implementing this API and talking the System Management Bushttps://en.wikipedia.org/wiki/System_Management_Bususing Smart Battery Systemhttps://en.wikipedia.org/wiki/Smart_Battery_SystemBonushttp://www.pmbus.org/Specifications/CurrentSpecifications
Power transformer design - Page 1
Forum section: electronics / projects

author: Digibin
author_rank: Regular Contributor
timestamp: April 28, 2016, 09:29:22 pm
content: I'd like to design a relatively high power offline converter, 30V 5A. I've not designed a DC-DC converter at anything near this power level before so this is new to me. I've tentatively selected theLTC3721-1push pull controller, and I've run a few simulations using the part in LTSpice. However I'm not really clear on the design process. I don't own any reference books on the subject and whilst there is a considerable amount of material out there on the internet, I can't find anything that's of any real use. The simulation is working but is lacking a properly considered transformer design. So I need to read up on the subject and design one. This is just a one off so I will most likely be winding my own.If anyone could point me to some good reference material for designing a ~150W transformer that would be great.

author: cat87
author_rank: Regular Contributor
timestamp: April 29, 2016, 05:31:50 am
content: As far as I've seen, one of the best books around, where you have theoretical elements very well laid out and practical designs, step by step, is this : "George C. Chryssis High Frequency Switching Power Supplies Theory And Design"The book is quite old, but the same principles apply in transformer design. Also, most of the designs are in the ballpark of your needs, power-wise.There's also this book: "Power Supply Cookbook - Second Edition By Marty Brown". It's ok, and there's also a lot to read up on.There are a few more books that are nice to read on the subject of SMPS.Also, if it's magnetics that you want to design (and that;s mostly what you need in a SMPS), you would definitely want to read this : Colonel Wm. T. McLyman - Transformer and inductor design handbook Third edition. The fourth edition is even nicer, as it's a bit more recent (written about 5-10 years ago, or something like that) but it has a hell of a price tag on it, and I can't seem to download....ahem...buy it (wink wink) from anywhere. This, to me, would be you reference book when designing any sort of magnetics for SMPS.Hope these are useful to you.

author: Digibin
author_rank: Regular Contributor
timestamp: April 29, 2016, 07:40:54 am
content: Thanks for the recommendations, I will read up on reviews etc. The first one you mentioned is fairly old but is only £5 used on Amazon so may well be a no brainer.

author: tautech
author_rank: Super Contributor
timestamp: April 29, 2016, 07:44:59 am
content: Here's a link bookmarked from a thread some time ago, hope it's of some use:http://ludens.cl/Electron/trafos/trafos.html
Power transformer toroid Design - Page 1
Forum section: electronics / projects

author: MohamedSaleh
author_rank: Newbie
timestamp: August 05, 2013, 11:02:22 pm
content: I'm working on induction furnace project,, I'm facing a serious problem with my toroid transformer. As you may find in the attachment Pic, There's green toroid with 20 Turns, which transfer the current from 1500 Hz inverter to LC tank which in turn works in resonance. The problem is the core saturates before I reach the current level I need ( which 40 amps) as you may also find in the attachment file. It saturates at 3 amps. I'm seeking for help to design the core so that it doesn't saturate at the current level I needthe yellow waveform is the output voltage of the inverter,, the blue waveform is the output current , as u can see the spike happens like that at certain voltage level ,, but at lower voltage level ,, the output current is pretty much sinusoidal wave until I increase the voltage and current spikes up

author: Experimentonomen
author_rank: Regular Contributor
timestamp: August 06, 2013, 06:52:36 pm
content: At that low frequency you need alot more turns. I built a induction heater using the core from a 3.5kW smps, the thing ran at ~30kHz and had a primary of around 20 turns.Primary current peaked at around 60A and secondary current was in the hundreds of Amps.Some pics of my project:http://imgur.com/a/AxfCUA video:Making some aluminum brass:

author: megajocke
author_rank: Regular Contributor
timestamp: August 07, 2013, 04:26:08 am
content: Quote from: MohamedSaleh on August 05, 2013, 11:02:22 pmAssuming it is the resonant circuit current you want to increase, you need to increase its drive voltage coming from the secondary of this transformer. So you need to increase the number of transformer secondary turns, increase the core cross sectional area and/or use a core material with higher saturation flux density to allow a higher secondary voltage without saturation.Changing the number of primary turns will not change the LC tank drive voltage (and hence current) at which the transformer saturates, but only the primary parameters at this point.You should start by determining how much drive voltage and current the LC tank needs and design your transformer based on that (the transformer secondary parameters).
Power up multiple motherboards from a single PSU? - Page 1
Forum section: electronics / projects

author: olkipukki
author_rank: Frequent Contributor
timestamp: April 05, 2020, 10:38:32 am
content: I have a few vintage MBs that I would like stack up and "encapsulate" into a custom build enclosure.The main issue is a space and would prefer to avoid 1:1 (MB:PSU) ration. The most MB setups consume in 150-300W range.I'm no planning to power these up altogether, max 2 at the same time. The whole thing should allows connect 8 MBs (yes, like eight as number)My idea is marrying a prefabricated industrial 48V ~600W PSU (aka TDK Lambda etc) and layout a custom board that fit an enclosure nicely.Key points:- cabling are okay to make in house- access to a proper components unrestricted- my pet project: no budget constraints, but reasonableAny suggestions?
Powerful (and hackable!) Flashlight Kit - Page 1
Forum section: electronics / projects

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 06, 2017, 12:15:28 am
content: This is the design I've shown and discussedelsewhere, now realized in non copper-clad-prototype form as well.Powerful enough to suck down an 18650. Not sure if these cells are in need of a charge, or just old and weak, but I'm only getting 50% of rated power out of these. Nothing wrong with that, of course -- the undervoltage limiter circuit prevents brown-out failure. That's why I know I'm getting only 50%.Very hackable design. Lots of test points. Two resistors change it to a portable, adjustable bench supply!Tim

author: CJay
author_rank: Super Contributor
timestamp: December 06, 2017, 06:55:59 am
content: At that implied power level I bet it makes a nice hand warmer too

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 06, 2017, 09:15:28 am
content: Th old 1W flashlight I made, you can feel it, particularly in a sensitive area like point blank on your lips.You can feel these in your hand, unmistakably.Tim
Powering 70 LED’s from 24VAC. - Page 1
Forum section: electronics / projects

author: matt6ft9
author_rank: Contributor
timestamp: June 29, 2018, 03:17:29 pm
content: A question came up recently on how to power 70, white LED’s from a 24VAC, 60Hz source. (This is no longer a project) The application was a backlight. The LED current would have been 60mA. The existing backlight (pictured below) uses less LED’s and was said to be “very unreliable”. The surface mount electrolytic cap on the PCB was tall enough to cast shadows.The “standard” (unimaginative) way to power 70 LED’s from 24VAC would have been to use a bridge rectifier, then a large filter cap, a DC-DC regulator to 24VDC, and finally 10 linear regulators to power ten strings of 7 LED’s. After some preliminary testing, the filter cap would need to be a roughly 2200uF, 50V part to have a reasonable amount of ripple. (very large physical size) The load on the DC-DC regulator would have been (10 strings)(60mA)=600mA.The main goals at the time were to: minimize 120Hz flicker, use only low profile SMT parts (less than 7mm?), and keep costs minimized. What would have been a creative way to achieve these vague goals?Matt

author: Zero999
author_rank: Super Contributor
timestamp: June 29, 2018, 03:39:50 pm
content: Any reason why you didn't consider a capacitive voltage dropper? That would have been the most efficient solution.

author: Ice-Tea
author_rank: Super Contributor
timestamp: June 29, 2018, 03:49:58 pm
content: Some more imaginative ways:- Booster in constant-current configuration after the bridge/rectifier, single string. So no LDO losses.- Trafo back to 230VAC and then use whatever of the shelf solution/circuit for 230VAC LED drivers.

author: Siwastaja
author_rank: Super Contributor
timestamp: June 29, 2018, 07:11:02 pm
content: With 24VAC, you'd probably rectify and filter it with an elcap first. But for the resulting DC, the market is literally saturated with easy-to-use, unbelievably inexpensive and small, single-chip solutions for constant current high-efficiency switch mode LED power.

author: jmelson
author_rank: Super Contributor
timestamp: June 29, 2018, 08:43:04 pm
content: Quote from: matt6ft9 on June 29, 2018, 03:17:29 pmYUCK, how OLD SCHOOL!I have built some LED light strings using current regulator chips. There are boost converter chips available, but usually the buck regulator is slightly simpler. You could use a buck current regulator, and then small series resistors on each string to balance current. First, do your REALLY need 70 LEDs? That seems like too many. But, if you do, the buck regulator chip will make the flicker practically go away, although you will still need a capacitor after the rectifier.Jon
powering a diy antenna matching unit illumination with rf - Page 1
Forum section: electronics / projects

author: p.larner
author_rank: Frequent Contributor
timestamp: December 05, 2023, 04:38:56 am
content: i have a homebrew t match atu with a big roller inductor and 300+300pf differential cap,ive just made a stockton bridge and fitted twin needle meters,i have a white led in the meter,can i power that using a torroid over the internal coax rectified to the led ,just would be nice to have meter light when transmiting without more wires to a psu,is that a workable idea?.

author: Terry Bites
author_rank: Super Contributor
timestamp: December 05, 2023, 09:38:08 am
content: A high value resistor and neon on the line?

author: CaptDon
author_rank: Super Contributor
timestamp: December 05, 2023, 03:30:19 pm
content: Sounds like a pretty horrible idea. LED's will blink when on SSB and their brightness will vary with SWR and CW power level. The best you might hope for is to rectify some of the RF and filter it with with a couple of hundred microfarads of capacitance then run that positive voltage to something like a 78L05 and drive your LEDS through a resistor or constant current diode. What power level are you typically transmitting at? It may take some digging to find a suitable rectifier diode that works well up to 10 meters and at your P.R.V. based on maximum expected power level at the 50 ohm input side of your A.T.U.

author: p.larner
author_rank: Frequent Contributor
timestamp: December 05, 2023, 03:53:36 pm
content: its only for tuning at 10watts max in am or cw,as soon as the adjustment is ok i dont realy need to look at the meters,i am trying to cut down on the untidy wires hanging from my psu,thought using constant rf when tning a way of doing it?.
Powering a <5volt device from 5volt rail - Page 1
Forum section: electronics / projects

author: law_freak
author_rank: Contributor
timestamp: May 08, 2017, 06:07:08 pm
content: Im interested in using the PCF2127 in my project over the DS3231, but do not want to change the power supply of the design.The PCF2127 is much cheaper and has more flexible IO options.Is it suitable to power the PCF2127 from a series diode to the +5V rail? The device accepts up to +4.2V.What variety of diode should I choose? Any diode with a Vf of 0.8V or more?

author: keymaster
author_rank: Regular Contributor
timestamp: May 08, 2017, 06:27:21 pm
content: Any normal diode will do. But 4.2v is the absolute max voltage , so 2 diodes in series will do the trick.What ever diode you choose ,check the datasheet of the diode for the plot graph of Forward Voltage to be sure.

author: ajb
author_rank: Super Contributor
timestamp: May 08, 2017, 06:41:53 pm
content: The absolute maximum voltage is actually 6.5V, however the device is not specified above 4.2V. So it shouldn't be harmed by running it at 5V, but it may not perform to its specifications.The PCF2127 claims to have a typical Idd as low as 470nA, so even two jelly bean diodes in series may not be adequate to drop the 0.8V required. A separate regulator (even a zener as a shunt regulator) could be a better bet.Also note that you'll need to make sure that logic levels are compatible among the devices in your system.

author: TimFox
author_rank: Super Contributor
timestamp: May 08, 2017, 08:12:30 pm
content: If you worry about the minimum current through the series diodes, then add a suitable resistor from Vdd to Vss to pull a mA or so through the diodes at all times. Again, see the I-V curves for the P-N diodes, including at any extreme temperatures you may expect.

author: BrianHG
author_rank: Super Contributor
timestamp: May 08, 2017, 08:28:36 pm
content: If you are using a signal diode like 1N914, or, 1N4148, you must use at least 2 since at low current, the voltage drop will only be 0.4v, especially if the temperature goes up.Or, if you are using 2ma or less, and you don't mind a slightly larger voltage drop, you can try a red led.

author: law_freak
author_rank: Contributor
timestamp: May 08, 2017, 10:40:54 pm
content: I will try the series pair diode suggestion. After seeing that +5V is within the absolute maximum range, I will also see how the device performs from full +5V.I am not a fan of the cost of the DS3231Z, but would like an integrated-crystal RTC solution. I'll spin up a cheap breakout board and see how the PCF2127 performs.Thanks for the suggestions all.

author: technix
author_rank: Super Contributor
timestamp: May 09, 2017, 11:38:10 am
content: Or if your board have a white or blue power indicator LED, tap off there like a Zener shunt. Only white or blue LEDs have enough voltage drop across them for this.

author: law_freak
author_rank: Contributor
timestamp: May 11, 2017, 01:25:42 am
content: My board has three indicator LEDs. One happens to be blue. For curiosity's sake, I will try that too.My first test is to try running the PCF2127 at +5V and see how it fairs.
Powering HDMI Audio Extractors vs HDMI-VGA-Audio Converters  - Page 1
Forum section: electronics / projects

author: Koray
author_rank: Regular Contributor
timestamp: May 10, 2020, 08:14:42 am
content: Hi all,I have a Google Chromecast device with a single HDMI output which I want to use with a HDMI projector. Unfortunately the projector has no audio output and I have no way to get sound out of such system.When I search for in-line HDMI Audio Extractors I only find tiny USB powered items at around 10USD range, but when I search for HDMI-VGA Converters (with audio output) I find self powered in-line adapters for about 2USD price range. Price is not important, but I don't want to complicate the setup with an extra power cable for the audio extractor.Here are some questions:What is the difference?Why can't they build cheap and simple audio extractors without audio output?Can I re-purpose an audio capable in-line HDMI-VGA converter to HDMI audio extractor?I am attaching two sample devices for reference.K.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 10, 2020, 12:52:00 pm
content: Have you considered opening up the projector and rewiring the speaker output to external speakers?

author: Koray
author_rank: Regular Contributor
timestamp: May 10, 2020, 03:51:49 pm
content: The projector has no audio. I wouldn't do that anyway, I can just use a powered audio extractor.But I wonder if the HDMI VGA cable can be converted into a HDMI bypass with audio output?K.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 10, 2020, 06:23:23 pm
content: Quote from: Koray on May 10, 2020, 03:51:49 pmNot easily. HDMI operates well into the GHz and the only proper way to split it is to use active circuits. You might manage to get away with a parallel connection for such a short distance, but HDMI is fine pitch enough that I wouldn't consider it trivial to solder.
Powering led strings with higher voltage than led driver input voltage - Page 1
Forum section: electronics / projects

author: mariush
author_rank: Super Contributor
timestamp: July 03, 2024, 06:32:02 am
content: I think I'm right but I want a confirmation.With linear led drivers, they usually have a maximum input voltage for their internal circuitry but they basically limit the current going through the string of leds by measuring the voltage drop across a sense resistor, right? So the number of leds in the string and the voltage at the first led shouldn't matter, because the led driver is on the low side just measuring a drop of under 1v on the sense resistor and maybe dropping a few volts behaving like a linear regulatorI'm looking in particular at a driver like AL1793AFE :https://www.diodes.com/assets/Datasheets/AL1791_1792_1793_1794.pdfIt has 3 channels, all are set to a maximum current with a resistor, and the driver IC can be powered with ~ 6.7v to 30v, but it looks to me like that's independent of the voltage used on led strings.So I should be able to power this driver chip with 9v or 12v (as it's above 6.7v and below 30v), but can I have 48v powering 14 x 3.4v leds = 47.6v leds on one channel?The driver's channel should drop only ~0.4v - 0.1v dropped on the resistor.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: July 03, 2024, 09:50:19 am
content: Yes, you can use led drops to run from higher supplies, but you need margin for led temperatures and process variations and supply ripple and variations, and driver saturation.47.6v led drop from 48v does not give much headroom.

author: ArdWar
author_rank: Frequent Contributor
timestamp: July 03, 2024, 10:00:02 am
content: Put a 21v zener or something across the pass element if you're concerned that the voltage across pass element may rise up too high. Just a small one since it only need to shunt whatever forward current the LEDs may conduct at 2V VF(very small) when the pass transistor is not conducting (very rare, maybe only at startup or fault condition unless you're actually PWMing it).

author: ajb
author_rank: Super Contributor
timestamp: July 03, 2024, 03:11:15 pm
content: Quote from: mariush on July 03, 2024, 06:32:02 amAs PCB.Wiz pointed out, that isn't a lot of headroom. It seems fine per the datasheet, but more LEDs in series means a larger change in the total Vf with current/temperature, so you'll have to make sure that you can meet minimum headroom requirements at max Vf, but also won't trip the short circuit protection at min Vf. That's probably not an issue unless you're doing analog dimming, though.
Powering LEDs from single Li-Ion cell - Page 1
Forum section: electronics / projects

author: rexxar
author_rank: Frequent Contributor
timestamp: May 06, 2015, 04:52:14 am
content: I'm suffering project blindness and can't settle on a design decision. I'm powering a custom RGB LED controller from a single Lithium cell. I decided to add a 5V SMPS for the microcontroller and other peripherals, and I went ahead and used that supply to feed the LEDs, since it had enough current capability. It works well enough, and it's a lot brighter than how I was doing it before (the mosfets weren't going into saturation), but I underestimated how much power the SMPS controller dissipates, and it can sometimes go into thermal shutdown.My question is should I rearrange the board to get better heatsinking, or should I just go back to using the battery voltage to drive the LEDs? The problem with that is brightness will go down over the battery's voltage range, but the current limiting resistors should dissipate less heat (max I is 700mA).What do you guys think I should do?

author: PeterFW
author_rank: Frequent Contributor
timestamp: May 06, 2015, 05:30:58 pm
content: Quote from: rexxar on May 06, 2015, 04:52:14 amYou are using a step up regulator from a Li* cell to step up the voltage to 5V and then drive the LEDs through current limiting resistors from the 5V rail?You are wasting a lot of power, my advice would be to use a proper constant current boost LED driver on a battery powered application.You should check that you do not exceed your discharge rate of the Li* cell too.

author: Fungus
author_rank: Super Contributor
timestamp: May 06, 2015, 05:43:53 pm
content: Quote from: rexxar on May 06, 2015, 04:52:14 amGet a better power supply.(nb. You haven't told us anything at all about the existing supply or the power requirements)
Powering off LCDs - Page 1
Forum section: electronics / projects

author: pyrohaz
author_rank: Regular Contributor
timestamp: July 28, 2015, 11:20:06 am
content: Hi guys,I'm wondering what sort of damage occurs from LCDs when you power them off without the correct shut down procedures. Many datasheets say that certain power supplies should be removed first etc. Could somebody enlighten me on this? For reference, I'm talking COG LCDs as opposed to OLEDs.Cheers