hybridfree/eevblog-posts huggingface dataset:
Power wiring help: 11.1V LiPo → 5V buck → 3.3V AMS1117 setup - Page 1
Forum section: electronics / beginners

author: ryanjm
author_rank: Newbie
timestamp: October 14, 2025, 05:41:52 pm
content: Are these connections accurate?Charging mode (battery ↔ charger):[AC WALL] ──> [SKYRC iMAX B6AC V2 (AC input)]│Charger main output (+) ──> + ──> [EC5 plug] ──> + on 3S LiPo(−) ──> − ──> [EC5 plug] ──> − on 3S LiPoCharger balance port ──> 3S balance plug ──> LiPo balance leadRunning mode (battery powering electronics):[3S LiPo pack]+ ──> [Inline fuse holder (5 A)] ──> + input VIN of DC 12/24→5V 5A buck converter− ─────────────────────────────────────────────────────────────────────────────> GND common[DC buck converter]VIN+ ← fused battery +VIN− ← battery −VOUT + (5V) ──> AMS1117 module VIN (or to 5V devices)VOUT − ──> common GND[AMS1117-3.3 module]VIN (from 5V output) → AMS1117 VINGND (common) → AMS1117 GNDVOUT 3.3V → 3.3V device VCCGND → device GND (common)

author: jwet
author_rank: Frequent Contributor
timestamp: October 15, 2025, 02:27:42 pm
content: That all makes sense from what I can see. The "ground" should be one point where all the ground connected things come together- this is called a star ground and insures that currents aren't flowing in different ground connections, bring all together and tie to one point near battery ground (minus)Good luck.
Powerboard failure - Page 1
Forum section: electronics / beginners

author: mrzoop
author_rank: Newbie
timestamp: September 06, 2023, 04:34:26 am
content: Hello All,I'm new to the site and have some basic understanding of electronics. After a couple days of google searching without finding what I'm looking for, I turn to you.This is an Orbit Irrigation International powerboard (WT-25) GEN1 that has failed on the common/ground. See attached pictures of the board.What I'm trying to identify is what's burnt out next to the R250 resistor? Is is just another R250 running in series?Any details would be helpful if you've seen this configuration before.Thanks in advance. Cheers

author: mrzoop
author_rank: Newbie
timestamp: September 06, 2023, 04:41:20 am
content: Here's a picture of the burnt part cleaned up a bit
Powered by an inverter - Page 1
Forum section: electronics / beginners

author: Kez
author_rank: Newbie
timestamp: December 25, 2017, 07:57:55 pm
content: Hi I'm new here, I used to be into hobby electronics in my younger years and getting back into the fun now mainly playing with microchip pics GPS, gprs and data transmission over as few wires as possible to control bit and bobs. Spent a few years fixing mobile phones and my main job is repairing hand held terminals/barcode scanners in retail.I have a bit of a problem I'm hoping I can get a bit of help with. I live on a narrowboat with 1kw of solar 480ah of battery bank and a pure sine wave inverter.I've just purchased a Rigol DS1054Z scope , I'm new to scopes and it looks like I'm getting a lot of noise from my inverter, would some fancy power conditioner work to clean up the power or could I make my own and where do I start?

author: David Hess
author_rank: Super Contributor
timestamp: December 25, 2017, 10:11:33 pm
content: I would spend some time figuring out exactly where the noise is coming from. It could be from the charge controller instead of the inverter or it could be common mode noise to ground instead of differential noise between hot and neutral or hot and hot.If the noise is high enough frequency, then they make big line side RFI filters which might work. If it is lower, then some type of resonate filter might be needed.If the noise is common mode, then a big low capacitance isolation transformer and common mode choke might help.

author: BrianHG
author_rank: Super Contributor
timestamp: December 26, 2017, 01:23:05 am
content: Show us a screenshot of your noise.a) Are you getting a regular approximate 6 fine spikes along a slow 50hz or 60hz sweep?b) Or, are you getting a continuous high frequency above 20KHz sine signal?c) Or a low voltage squashed 50/60hz sine wave permeating everything?If a), then your inverter may not be a pure sine wave type.If b), then, some high frequency is leaking through the inverter's output DC-AC converter. This one you might be able to filter with a quality AC power-bar or a dedicated line filter.If c), then your inverter is leaking current to your common ground, or you might call this a ground loop issue. Unfortunately, this might be by design and the only fix might be an AC line isolation transformer, at minimum for powering your scope.
Powered off microcontroller/ESP32 conducting significant current - Page 1
Forum section: electronics / beginners

author: petert
author_rank: Regular Contributor
timestamp: October 06, 2020, 02:59:03 am
content: Hello,This is probably a beginners mistake, but I am a bit puzzled by this behavior.When I have an ESP32 with only the GND pin connected to GND of a 3V battery (nothing on the positive power rail of the ESP32), and then connect the positive 3V pin of the battery to one of the ESP32 input pins with a 1K resistor, I will still have a current of a few milliamps, eventhough the measured input resistance of that pin is around 80kOhm.Only when I raise the resistor in series with the pin to 10k, does the current flow drop below my meter's resolution (in 10A mode).But using a 10KOhm series resistor is too high of an impedance when I power the ESP32 and want to sink current with it, when it's on.How can this be solved? Ideally with just resistors/passives, as I don't have much space left to add transistors on my board.

author: petert
author_rank: Regular Contributor
timestamp: October 06, 2020, 11:53:14 am
content: Thanks. It seems to be a protection diode issue, indeed.If I understand it right, it means I have essentially no resistance in this case, besides of the resistor I added myself?Reading this post:https://electronics.stackexchange.com/questions/517344/what-happens-to-esp32-module-io-pins-when-it-is-connected-to-ground-but-not-to-pit seems the most effective way to handle this issue is to ensure there is no voltage on the input pins (e.g., using an external transistor) when the µC has no voltage on its VCC/3V pin? Or are there other options?

author: I wanted a rude username
author_rank: Frequent Contributor
timestamp: October 06, 2020, 09:23:17 pm
content: The normal solution is to not switch off power to only the microcontroller. Put it to sleep instead, with the GPIOs configured correctly. The claimed current consumption in deep sleep is 10 uA ... although Espressif's current consumption claims tend to be slightly dubious.

author: petert
author_rank: Regular Contributor
timestamp: October 07, 2020, 08:34:57 am
content: I ended up using an N-channel enhancement mode MOSFET to disconnect GND of the battery from ESP32's GND, when the ESP32 is not powered (through normal ways, not due to the unintended powering through the protection diodes). That way a positive voltage from the battery has no effect on the pins.If the ESP32 is powered as well, its 3v3 pin switches the MOSFET and connects the battery's and the ESP32's GND, and everything works as expected.Was a little fiddly to fit the MOSFET on the board, but I could find enough space and a good layout still
Powering 6v leds - Page 1
Forum section: electronics / beginners

author: CharlesTT
author_rank: Newbie
timestamp: January 25, 2020, 06:26:50 pm
content: Hi, I have 6 6v leds that I want to run off of 12v what is the best way to do this ? I can't get a series + parallel circuit to workRegardsCharles

author: Ice-Tea
author_rank: Super Contributor
timestamp: January 25, 2020, 06:58:02 pm
content: Hi Charles,You will have to provide a little bit more detail. A 6V LED does not exist. So, you have LEDs + something. Without knowing what that something is, it's hard to comment.Ice-Tea

author: CharlesTT
author_rank: Newbie
timestamp: January 25, 2020, 07:41:52 pm
content: So the leds are surface mount on a small pcb,they take 6v to power them

author: Ice-Tea
author_rank: Super Contributor
timestamp: January 25, 2020, 08:02:17 pm
content: Herhaps a picture might help? Part number?

author: LateLesley
author_rank: Frequent Contributor
timestamp: January 25, 2020, 08:44:30 pm
content: If they are 6V, then you'll have to run each one off the 12V with a current limiting resistor. Without knowing the current required by them, it's hard to help any further. Also a diagram of how you have tried hooking them up would be helpful too.
powering a DC motor with plug in transformer... - Page 1
Forum section: electronics / beginners

author: oslin76
author_rank: Newbie
timestamp: February 08, 2017, 02:51:34 pm
content: Ok, this is weird but I can't figure out the problem. I have a inflatable mattress that is powered by four D batteries (6 Volt ) and I want to use a plug in type transformer (output 7.2 Volt DC, 500mA) instead of the batteries. But the motor will not turn... I tried a variety of different size transfo with no luck. Any ideas anyone???

author: grifftech
author_rank: Frequent Contributor
timestamp: February 08, 2017, 02:53:06 pm
content: use a 2.1 amp USB charger

author: oslin76
author_rank: Newbie
timestamp: February 08, 2017, 03:01:15 pm
content: ok I will try that

author: james_s
author_rank: Super Contributor
timestamp: February 08, 2017, 04:35:02 pm
content: If it runs off D batteries it could draw several Amps. I would start by measuring the current drawn by the motor when running from batteries. You might need 5 Amps or more.

author: jm_araujo
author_rank: Regular Contributor
timestamp: February 08, 2017, 05:56:24 pm
content: Also it's probably a brushed motor, which needs a high inrush current to start rotating.

author: Zero999
author_rank: Super Contributor
timestamp: February 08, 2017, 06:11:39 pm
content: Quote from: jm_araujo on February 08, 2017, 05:56:24 pmYes, the inrush current could be tens of Amps, which will cause a switched mode power supply, such as that used in USB charger, to shut down. You may need a soft start circuit to get the motor moving slowly before it can be run at full speed.

author: james_s
author_rank: Super Contributor
timestamp: February 08, 2017, 07:06:54 pm
content: Let's not get overly complicated here. A beefy iron transformer type AC adapter will tolerate the high inrush just fine, but it may be a prohibitively large adapter to be practical.I have a similar mattress inflater in which I use NiMH AA cells in adapters and that works fine. I have another one that takes 12V, I normally use a 3 cell LiPo pack on that.

author: Zero999
author_rank: Super Contributor
timestamp: February 08, 2017, 11:31:00 pm
content: An old low frequency transformer mains adaptor would do fine but as you've said it may be too big to be practical and they're getting rarer nowadays and are banned in some countries because they're to inefficient.A soft start needn't be complicated. A MOSFET, resistor and capacitor are all that's required. The attached example uses the Miller effect to make C1 look much larger, when the MOSFET is turning on. The simulation shows it will take about 3s for 90% of the supply voltage to appear across RL. If this is too slow, use a lower value capacitor or resistor.Note that it isn't a logic level MOSFET (I chose it because it will be slow) but should be fine for 10 or so Amps when the battery voltage is 6V. Check the MOSFET will pass enough current when given a gate voltage of 6V.I've used a similar circuit before to power a motor off a switched mode power supply and it worked quite well.
Powering a PC SATA Power Conenctor - Page 1
Forum section: electronics / beginners

author: DW1961
author_rank: Frequent Contributor
timestamp: May 25, 2021, 12:39:55 am
content: How would I g about powering an SATA power connector using a bench power supply?What I want to do is power a 5V LED controller so I can test computer ARGB lights before installing them. Unlike 12V RGB lights, which just require + and -, the ARGB requires a signal to turn them on. So, I have to get a cheap controller, and then power it. All of the controllers HAVE SATA connector. I don't have a problem just cutting the SATA connector and using a + and - connection from the bench power supply, if that is all that's needed.Controller:https://www.amazon.com/StepOK-Controller-Splitter-Plastic-Lighting/dp/B0899VYB16/ref=sr_1_3?dchild=1&keywords=5v+argb+controller&qid=1621903172&sr=8-3

author: macboy
author_rank: Super Contributor
timestamp: May 25, 2021, 12:59:04 am
content: Connect negative to the black wires and +5V to the red. If you need 12V, that's the yellow.

author: DW1961
author_rank: Frequent Contributor
timestamp: May 25, 2021, 03:14:56 am
content: Quote from: macboy on May 25, 2021, 12:59:04 amSATA has 12V lead? What uses that?

author: SeanB
author_rank: Super Contributor
timestamp: May 25, 2021, 09:16:32 am
content: Older SATA 3.5in drives use the 12V supply, though more modern ones do not. SSD drives use 5V only, and pretty much nothing uses the 3V3 supply, deriving it from the 5V rail instead. Optical drives also use 12V.

author: mariush
author_rank: Super Contributor
timestamp: May 25, 2021, 01:54:42 pm
content: Get a basic molex to sata adapter cable, cut the molex connector and connect the wires to your power supply. Example cable :https://www.amazon.com/12in-SATA-Power-Cable-Adapter/dp/B0002GRUV4/You only need the 5v and 12v wires ... red is 5v, yellow is 12v. Blacks are ground or negative.

author: Monkeh
author_rank: Super Contributor
timestamp: May 25, 2021, 03:08:04 pm
content: Quote from: SeanB on May 25, 2021, 09:16:32 amRubbish. 3.5" drives almost if not entirely exclusively use the 12V rail for the spindle.

author: DW1961
author_rank: Frequent Contributor
timestamp: May 25, 2021, 05:12:27 pm
content: HA!It's been so long since I used a mechanical drive, I'd forgotten about the 12V sata purpose!

author: DW1961
author_rank: Frequent Contributor
timestamp: May 25, 2021, 05:14:41 pm
content: Quote from: mariush on May 25, 2021, 01:54:42 pmCould I just cut one side of an SATA connector off and use the + and - wires with the power supply alligator clips?
Powering an ESP32 - Page 1
Forum section: electronics / beginners

author: paulca
author_rank: Super Contributor
timestamp: July 23, 2019, 06:07:05 pm
content: So apart from tonight bench work being rather disappointing in that everything worked first time, I have a conundrum.I'm using an ESP32 to run some WS2812 LEDs. 144 of them in fact. The WS2812 run on 5V and take a 5V signal of around 1Mhz. The ESP32 however is a 3.3V device.Having read a bit about this, I bought a 74 series TTL bus transceiver which has a suitably low logic trigger voltage and emits Vcc. Running it on 5V and feeding the 3.3V signal into it and 5V signal comes out, and it's fast enough to level shift the 1Mhz.So when I wired this up, it all worked, annoying the LEDs worked with the 3.3V signal, but that might not be reliable. First time I wired up the bus transciever on the breadboard and it also worked. Checked with a handheld scope and could see rougly 3.3V going in and 5V coming out.The conundrum is in powering the ESP32. It will run from USB 5V of course and has a 3.3V regulator. It also has a Vin pin. Here's the catch. The Vin pin takes 7-20V. Giving it 5V and the device does not start. How dumb is that? Why not just put a pin on the USB power and allow it to run from 5V?So either there is a 5V pin I'm missing or I'll have to use a boost converter to get 7+ volts or... I hack the board... or I use a USB plug to power it.It's intended to be hidden inside an IKEA floor lamp with the LEDs running up the middle. I have a beefy 10A 5V brick to power it. The LEDs claim 60mA max each, so that's around 8Amps, but I have yet to provoke them to pull more that 5Amps.

author: langwadt
author_rank: Super Contributor
timestamp: July 23, 2019, 06:24:25 pm
content: which ESP32 board?

author: paulca
author_rank: Super Contributor
timestamp: July 23, 2019, 06:26:31 pm
content: It claims to be an ESP32 DevKit V1, though I'm not sure as the Board that works in Arduino IDE is actually the NodeMCU-32Shttps://www.amazon.co.uk/JZK-ESP-32S-Development-Bluetooth-Antenna/dp/B071JR9WS9/ref=sr_1_1?crid=RDFOZTVU1M0N&keywords=nodemcu+esp32&qid=1563906555&s=gateway&sprefix=NodeMCU%2Caps%2C138&sr=8-1So this seems to depend on what board you get. Powered with 5V from it's VIN pin may not boot the MCU properly in many cases.https://github.com/nodemcu/nodemcu-devkit-v1.0/issues/9So I either buy a different dev board or I start hacking a USB plug to power it. Shame.In my case it took me to put 7V on the pin before it booted, although once booted it would run down to 5V or even 4.5V before browning out.

author: paulca
author_rank: Super Contributor
timestamp: July 29, 2019, 06:44:11 am
content: Well, in the end I figured the onboard voltage regulator must be dropping the 5V to 3.3V and measured across it while running off USB and lo and behold, it was 4.89V and 3.27V, so ... I just soldered a mod wire onto the voltage regulator from my 5V supply and... the board powers up fine.I still have no idea what they were thinking, or how they even managed to make the Vin pin require 7V-20V.
Powering baby monitor with power through battery connector - Page 1
Forum section: electronics / beginners

author: Ajkza
author_rank: Newbie
timestamp: September 23, 2021, 07:55:18 pm
content: Hi AllI have a Motorola baby monitor, and after lots of wear and tear on the portable monitor (let's you view the camera), the micro USB port (used to charge and power the device) seems to have lifted from the board or become damaged in some other way, and the monitor stopped working unless you hold the USB cable at the correct angle.I ordered a new micro USB port to replace the one on the board, but unfortunately my surface mount soldering skills aren't great, and I lifted the pads and made a big mess of the USB input - it's totally disconnected from the device now.The monitor also has a rechargeable battery (3x Ni MH cells) which allowed it to be portable. Since the battery connector is nice and big, I thought I could just remove the battery and provide approx 3.8V - 3.9V into the battery connector on the circuit board. I tried using a bench power supply and the monitor worked fine - if I lowered the voltage to about 3.6V, its starts warning about low battery.My plan is to get a simple buck converter to provide 3.8V from a 5V USB wall power plug.I don't need it to be portable, so removing the battery isn't a concern for me.Am I missing something that could cause problems by powering the device through the battery input? The micro USB port is disconnected from the circuit board, so there isn't a concern of someone plugging in a USB cable and the monitor trying to charge the battery (which is actually my new power source [buck converter]).Thanks in advanceAjk

author: Manul
author_rank: Super Contributor
timestamp: September 24, 2021, 12:30:03 am
content: It is fine. If internal circuit does not have enough bulk capacitance at battery terminals, you could add some. Like 220uF, something like that. Often you can get away by using 5V directly. It is not unsual for NiMh cell to go 1.6V or above if fast charging, so 5V should be tolerated by circuits designed for 3 cells. If you are concerned, just add a series diode. With a diode drop you will get 4.2-4.4V which is for sure in the safe range for anything designed for 3 NiMh cells. So in my opinion, no need for buck converter in this case. Series diode and electrolytic capacitor would be my go.

author: Ajkza
author_rank: Newbie
timestamp: September 24, 2021, 06:21:30 am
content: Thanks so much, will give it a try.
Powering Concept - Page 1
Forum section: electronics / beginners

author: brue
author_rank: Contributor
timestamp: November 05, 2012, 01:14:24 pm
content: HiIm want to design a device. It contains a PIC24F32KA304 micro and a LCD EA DOGM163L-A.The LCD drives about 250uA. If the device is in use, the CTMU (Capacitive Sensoring) of all 16 Channels is active. If the device is OFF, it is in Deep Sleep Mode.If the device is OFF and in Deep Sleep mode, so i want to wake it up with a pushbutton on a interrupt input.I want to Power the whole thing with one or two CR2032 Cells.Its verry difficult for me to find out how much current the micro finally will draw.The LCD works with 3.3V, the micro with 1.8...3.6V.Should i use two CR2032 cells in series with a linear voltage regulator? The whole thing should draw the smallest current as possible.Any ideas?Thanks

author: Simon
author_rank: Unknown
timestamp: November 05, 2012, 09:24:34 pm
content: make sure you use a low quiescent current reg as standard ones can use upwards of 2mA! on standby
Powering DP30V5 from an unregulated DC supply? - Page 1
Forum section: electronics / beginners

author: ExtraThiccBoi
author_rank: Contributor
timestamp: April 25, 2020, 08:24:05 am
content: Hi,is it safe and possible to power theDP30V5module from a basic rectifier-capacitor power supply?ThanksDave

author: Mp3
author_rank: Frequent Contributor
timestamp: April 25, 2020, 08:49:30 am
content: Don't take my word as fact, but I run one of these which doesn't look too dissimilar off a 24v / 5a laptop style power supply until i get a nicer power supply to replace it. It has not given me any problems. (Edit: The highest amount of power I've used it for on the bench is 15v roughly 1a... so not a ton.)https://www.parts-express.com/7a-dc-60v-adjustable-step-down-regulator-nc-power-supply-current-voltage-meter-buck-module--320-615

author: Ian.M
author_rank: Super Contributor
timestamp: April 25, 2020, 10:16:17 am
content: Yes, but once you figure in suitable margins for mains line voltage variation and the regulation of the transformer feeding your rectifier, not to exceed the module's 40V max. input voltage rating during high line + minimum load conditions, you'll be lucky to get more than 24V out at full load current and normal line voltage without 100Hz ripple breakthrough.
Powering a Dyson V6 without original battery (for testing purposes) - Page 1
Forum section: electronics / beginners

author: tigrou
author_rank: Regular Contributor
timestamp: August 17, 2025, 07:26:02 pm
content: Hello,I have a Dyson V6 which start and stop. I think battery is dead and can't deliver enough power. It could also be electronic in the vacuum which is failing (eg: mosfets get hot quickly and stop)I have a perfectly working 24V battery from some other device (a electric wheelbarrow) that has enough power to run it.Would it be possible to connect that battery to the Dyson (bybassing the Dyson battery completely) for testing ?I have tested the battery few days ago (to find out the polarity) but just measured 0V. It seems Dyson batteries have a reed switch that need to be activated.AFAIK Dyson is running on 21.6V or something like that but 24V should be fine for a short time.

author: tigrou
author_rank: Regular Contributor
timestamp: August 18, 2025, 02:46:57 pm
content: I was able to get the V6 schematic from this topic:https://www.eevblog.com/forum/reviews/dyson-v7-trigger-cordless-vacuum-teardown-of-battery-pack/75/It seems there is no reed switch on the v6. All needed is to press a switch (that is activated once battery is in place).

author: Uunoctium
author_rank: Frequent Contributor
timestamp: August 18, 2025, 06:01:58 pm
content: Does the motor pulse on and off rapidly?That pulsing is Dyson’s built-in protection mechanism. It doesn’t always mean the battery is dead — more often the vacuum is starved of airflow or current. A blocked filter, clogged airway, or jammed brush bar can cause the motor to cut in and out to prevent overheating.A completely clogged fine filter can trigger this fault. After rinsing the filter thoroughly with water and letting it dry, the vacuum should run normally again.

author: tigrou
author_rank: Regular Contributor
timestamp: August 18, 2025, 07:25:33 pm
content: Quote from: Uunoctium on August 18, 2025, 06:01:58 pmOK thanks I will try it. The vacuum cleaner has been completely cleaned off about 1 year ago (by tearing it down completely) maybe it's clogged again.Initially there was some issues with the brush. It would sometimes do not start, or will start then stop. But after some investigation it seems it's fine. I teared it down and there wasn't anything wrong with it, like the belt mechanism or the small DC motor. The brush would spin OK without interruption if powered by some external DC supply.Then I found out the vacuum cleaner would start / stop in a uncontrollable way, even without the brush and start to make theory it could be the battery dead (or the vacuum itself).
powering IR receiver from uC output pin - Page 1
Forum section: electronics / beginners

author: djacobow
author_rank: Super Contributor
timestamp: May 15, 2019, 05:13:11 pm
content: I've got a battery powered device under development that has IR remote control receiver. The receiver datasheet (https://www.vishay.com/docs/82471/tsop772.pdf) suggests that the supply current is 0.8 mA and the the max supply current is 5mA (presumably, when the output pin is driving 5mA)Right now I am powering it through a largish PFET that controls a bigger power rail shared by some high current consumers. I want to do the IR receiver separately. I could use another PFET, but not using anything is preferable.Can anyone think of a reason that I cannot power down this receiver by driving its Vcc directly from a microcontroller pin? The output current will never be anywhere near 5mA because the output is going right back to an input pin of the same microcontroller.

author: MosherIV
author_rank: Super Contributor
timestamp: May 16, 2019, 07:02:02 am
content: QuoteMicrocontrollers usually have a limited amount of current that ALL the gpio pins can soure, notjust on each individual pin. You need to check the total current that ALL the gpios are going to output.Hint: the amount of current microcintrollers can sink is higher than they can source.To control the ir receiver by sinking current, put the gpio in open collector mode. In effect, the micro is switching the 0V on/off instead of the power.This may not be an problem, do the check like a good engineer

author: perieanuo
author_rank: Frequent Contributor
timestamp: May 16, 2019, 08:05:24 am
content: Just add one transistor and one resistor, your BOM won't explodeEnvoyé de mon iPad en utilisant Tapatalk

author: bson
author_rank: Unknown
timestamp: May 17, 2019, 04:30:12 pm
content: It will probably be fine, but do wire it up on a breadboard to check. 5mA is probably the maximum output current into a shorted load, but a GPIO input pin will be very high impedance and draw very little current. So supply current will be dominated entirely by what the device itself needs, which is probably very little (the < 1mA figure). But you can't know for sure until you check for yourself.
powering lots of leds from 230v mains - Page 1
Forum section: electronics / beginners

author: ME
author_rank: Frequent Contributor
timestamp: April 06, 2025, 08:24:32 am
content: i have a hundred leds i want to run from the uk mains,could i use a capacitor dropper psu to do this?.

author: PGPG
author_rank: Frequent Contributor
timestamp: April 06, 2025, 11:48:53 am
content: Connect them in pairs against parallel.If this are red LEDs (no info of it) than about 1.8V voltage drop at LED can be assumed. So on the 50 pairs string you get 90V. From AC source with 325V peak (230*sqrt(2)) it should be possible to supply it with current set by capacitor charging and discharging.If you will be trying don't forget to add resistor to limit high current pulse when it is switched on in random AC phase moment.

author: ME
author_rank: Frequent Contributor
timestamp: April 06, 2025, 12:52:18 pm
content: So do i measure the vf of 1 diode and divide 230 by that? to calculate the number of diodes , my question should of been howto run 100+ diodes from the mains , what i want is to run as many diodes ie 100ish red . tester says vf=1.9v ir=2na and 100ish blue vf=2.67v ir=2na , They are the numbers my chinese component tester gives , hope that makes sense? ,its for a diy plant grow lamp.

author: Xena E
author_rank: Frequent Contributor
timestamp: April 06, 2025, 01:38:31 pm
content: What current do you want ?

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: April 06, 2025, 03:40:58 pm
content: Quote from: ME on April 06, 2025, 08:24:32 amYes. But of course you'll want to ensure that the voltage doesn't exceed what the series-LED's are rated for. Additionally, depending on the style of LED's, you may need to design an enclosure to prevent the LED's from being easily-accessed, as they'll now be referred to mains voltages and be a shock hazard. (Don'tunder-estimate this, even a low-voltage-referenced shock can be uncomfortable and is a safety hazard).BigCliveDotComon YouTube has taken about dozens (hundreds?) of LED bulbs, showing off their capacitive dropper design, as well as bulbs that incorporate constant-current limiting via a dedicated IC, like the SM2082 (but there's many, many alternative IC's for constant-current limiting mains LED's).

author: tunk
author_rank: Super Contributor
timestamp: April 06, 2025, 04:40:47 pm
content: This is mains voltage which may be fatal.Given your limited experience, it may be better(and simpler) to get a ready made lamp.If you want to learn, mains voltage isn't thebest place to start.

author: Xena E
author_rank: Frequent Contributor
timestamp: April 06, 2025, 05:49:28 pm
content: This will work, gives about 20mA through the diode chain.Heed the shock warnings though, to paraphrase...One slip and you're fucked.X
Powering mcu question  - Page 1
Forum section: electronics / beginners

author: DarkZero
author_rank: Regular Contributor
timestamp: August 24, 2016, 09:17:12 pm
content: i wanted to build a small current meter panel and i stole Dave's design, now i want to use same power supply that powers the op amps for the mcu without messing the things about the GND i simply cannot wrap my mind around it plz some suggestions

author: danadak
author_rank: Super Contributor
timestamp: August 24, 2016, 11:00:05 pm
content: Several issues/solutions -1) I assume the MCU CM range is + only with respect to its ground. Thereforethe OpAmp feeding MCU input has to be offset appropriately to force this tohappen. Easy with a R network to gen the offset.2) MCU tied to ground as shown in schematic.3) Assuming MCU is 5V, then use a 2.5V zener from the positive supply sourceto MCU, one approach. 7.5 - 5V (assuming MCU is 5V) = 2.5V4) Or use a 3 term adj reg, gnd leg to - side 15V supply, input to + side of 15V supply,set it to 7.5 + 5 (assuming MCU is 5V) = 12.5V, and reg output goes to MCU Vdd pin.Regards, Dana.

author: danadak
author_rank: Super Contributor
timestamp: August 24, 2016, 11:45:13 pm
content: One consideration is U2 has to carry the MCU Vss ground leg current. Since it is7.5V above supply - leg for every 1 mA of MCU Vss current the OpAmp has to dissipate7.5 mW. So do a current budget on MCU and all its I/O load that flows thru its groundpin and calc Pdiss. If too much for OpAmp consider a power OpAmp, or another 3 termreg to establish the system ground potential. Note that reg would have to have a source/sink output capability, not in every 3 term reg.Also, for stability, if you use large C bypass from + or - supply to ground, examine OpAmpdatasheets for C loading limitations. If necessary add a zero into OpAmp feedback net tolift the phase to get adequate phase margin.Regards, Dana.

author: rstofer
author_rank: Super Contributor
timestamp: August 24, 2016, 11:58:05 pm
content: Section 4.3 of Op Amps For Everyone:http://www.cypress.com/file/65366/downloadBasically you use a 5V single supply rail to rail op amp to offset and scale the input to match the range of the MCU.

author: DarkZero
author_rank: Regular Contributor
timestamp: August 25, 2016, 05:27:12 pm
content: my whole circuit draws 75mA max but ill take it that's it's 100mA so i guess i can get away with 150mA supply. so either i find some op-amp that can source or sink 100mA or i get some chip that can do -V because i don't want to use transformer with 2x secondary.but let me ask maybe a stupid question is it possible to boost current capability with a transistor in this situation ? or should i just wack in 7660

author: danadak
author_rank: Super Contributor
timestamp: August 25, 2016, 10:32:20 pm
content: Then generate a - supply, some techniques -https://www.dropbox.com/s/k1yn4m7heaixvmg/ADinput%20negative%20inputs.zip?dl=0Regards, Dana.

author: Jeroen3
author_rank: Super Contributor
timestamp: August 26, 2016, 05:36:27 am
content: Why do you need a 15v supply?
Powering on phone with dead battery - Page 1
Forum section: electronics / beginners

author: Digitalio
author_rank: Contributor
timestamp: August 19, 2020, 09:59:48 pm
content: My phone's battery has died recently, so it doesn't charge at all and the charging LED just stays blinking forever and the phone doesn't turn on. I wonder if it's very difficult to start the phone without the battery at all, simply from a 3.6V power supply?

author: anvoice
author_rank: Frequent Contributor
timestamp: August 20, 2020, 07:22:58 am
content: Can you open the phone easily to get to the battery and circuitry? If so, get the battery out and try to find the exact voltage it nominally provides (might be 3.8V for example), and you can try providing that exact voltage to the correct terminals on the phone.I've also had luck opening an old tablet, taking out the battery, and charging it directly by applying a voltage to it (don't try unless you can limit the current going in, i.e. you have constant current capability on your power supply). It worked long enough for me to to turn on the tablet.Third, if you want to continue using the phone with any degree of convenience (and assuming again a removable battery) you could buy a spare and use that.If you can't open the phone to get to the battery, you're likely out of luck.

author: Daixiwen
author_rank: Frequent Contributor
timestamp: August 21, 2020, 06:16:51 am
content: If you manage to open the phone, the cell is completely flat (under 2.5V) and you want to try and recharge it with a power supply, be sure to use a very low current, until the cell voltage reaches at least 3.0V. Using too a high current on a flat cell can damage it and transform it into a fire hazard.

author: Renate
author_rank: Super Contributor
timestamp: August 21, 2020, 06:41:18 pm
content: If the battery is really dead, you don't want to replace it and you want to run the device tethered to power, you can.Many (most? all?) cell phone batteries have extra connection for thermistor and/or analog/digital identification circuits.If you want to destroy your battery pack, cut the actual cell foil connections and recycle the cells and hook up 4V.This way you can retain all the other circuitry in the battery pack.(This is also a good way to monitor sleep/processing/CPU throttling.)OTOH, I'm sure ebay has the replacement for cheap.
Powering one light off while powering the other light on.  - Page 1
Forum section: electronics / beginners

author: Equinoxrebounds99
author_rank: Newbie
timestamp: May 01, 2017, 07:30:16 pm
content: Hi, I'm fairly new to the making your own circuits scene so please bear with me if I have any trouble understanding. I'm currently working on an art project for a contest that is a box with two panes of glass in it one on top one on the bottom, on one pane the moon is printed, on the second the sun is printed. I'm using an outdoor day/night sensor to power led strips behind each of them. Right now when it gets dark both light strips are powered on, I want to make it so when the lights for the moon turn on at night the lights for the sun turn off and vice versa. Any help is very much appreciated, thank you for your time.

author: james_s
author_rank: Super Contributor
timestamp: May 01, 2017, 07:38:30 pm
content: One very simple way of doing this is to use a double throw relay, one contact is open when the other is closed. Connect power to the common contact and connect one light to either of the other two contacts. When the relay coil is energized one light will be powered and when it is not, the other light will be powered instead. Use the light sensor to control power to the relay coil.

author: Equinoxrebounds99
author_rank: Newbie
timestamp: May 01, 2017, 10:16:57 pm
content: I'll look into it thank you for the reply!!
Powering one section of a circuit when another comes up - Page 1
Forum section: electronics / beginners

author: fabiodl
author_rank: Frequent Contributor
timestamp: August 12, 2022, 07:29:57 am
content: I have a board (A) which exposes a parallel bus. I want to make a second board (B) which connects to (A) but does not draw too much current from it. I want (B) to come on only when (A) is powered, to avoid having logic gates on (B) that are powered to feed current to (A) through the parallel bus lines. (B) maximum current draw is around 500 mA, so a small mosfet should be ok to power it.I came up with the following schematic. 5V_pwr is where (B) draws current from, while 5V_sense is from (A). Do you see any problems / possible improvements?

author: jmelson
author_rank: Super Contributor
timestamp: August 12, 2022, 03:05:52 pm
content: You need a resistor on source to gate of Q3, so that it will turn off when the 5V sense goes off.Jon

author: jmelson
author_rank: Super Contributor
timestamp: August 12, 2022, 03:07:01 pm
content: You need a resistor on source to gate of Q3, so that it will turn off when the 5V sense goes off.Jon

author: JustMeHere
author_rank: Frequent Contributor
timestamp: August 13, 2022, 01:56:00 pm
content: You need to have a high value pull down on both of your gates. 10k or 20k should do. These will turn off your mosfets when the power is gone.This may do the job for you, but I don't know if there's a power off delay (or if that's a problem in your case.)https://www.teaching.eng.ed.ac.uk/open-educational-resources/rc-delay-use-timer

author: TC
author_rank: Contributor
timestamp: August 13, 2022, 04:51:19 pm
content: Look up bus isolator ICs and learn about their purpose/function. Also learn about power sequencing methods and latchup as a phenomenon.The ESD diodes of the unpowered devices can become forward biased and try to source power from the signal pins for the unpowered IC. Not good.

author: fabiodl
author_rank: Frequent Contributor
timestamp: August 14, 2022, 08:53:02 am
content: Thank you everybody. I modified it to the attached schematic
Powering part (or most) of a circuit? - Page 1
Forum section: electronics / beginners

author: nicbul
author_rank: Newbie
timestamp: December 31, 2017, 03:38:41 am
content: I have a couple channels from a Yamaha m1516 mixing console and I would like to power them up, do some signal tracing, and see how something like this works.The board is supplied by +/-25V, +10V(led indication), and +48V(phantom power). I would be powering it with a dual bench PSU.Is it generally safe to power the board solely with +/-25V to test the signal path?http://cloud.tapatalk.com/s/5a485924ba3d6/yamaha_m1516.pdfSent from my LG-H933 using Tapatalk
Powering touch screen from solder pads (Need advice) - Page 1
Forum section: electronics / beginners

author: DROUGA
author_rank: Newbie
timestamp: October 12, 2018, 06:09:46 pm
content: Hello there, new to the EEVblog, but long time viewer of the YT channel.IntroductionI bought a touch screen display on AliExpresshttps://bit.ly/2OR2H8JIt is powered by a USB cable, and a separate USB connection for touch.I Am going to 3D print a frame for it, and i want the bezels to as small as possible.So a have a right angle low profile HDMI adapter.But i still need to figure out the USB side of things.I noticed quite a lot of test points / solder pads on the PCB.And i wonder if i could just power it by soldering the USB wires directly to the board.Also potentially controlling the back light with a potentiometer.I own a multimeter and i could test it if i had some more insight.Tried to look up the model number (HFSECURITY 010327) but could not find anything useful.And the seller on AliExpress provided somewhat useless technical pictures in the description of the product.Soldered USB wires before, but otherwisekind of new to electronics so i could use your experience and thoughts on the high res images of the PCB:Translating the first chineese URL written on the PCB i dug up some more information:https://goo.gl/bG8aVv

author: malagas_on_fire
author_rank: Frequent Contributor
timestamp: October 13, 2018, 12:31:54 pm
content: First it is more easy if information regarding the board and its components are available.From this point check if the points of power supply to solder does not bypass any protection circuitry , decoupling capacitos, etc.About brightness, since it is a USB module does it presents as a peculiar device? It may have implemented brightness control using the USB communication, either USB to RS232 TTL or some HID device.. If it is serial you could use a microcontroler to read a pot and generate the pwm, signal onto the board.

author: sokoloff
author_rank: Super Contributor
timestamp: October 13, 2018, 01:27:14 pm
content: Well, J6 has the same number of pins as a USB connection J8. Might see if J6 is the same as J8.If it's not, you could blow J8 off the board and solder to the connections there if you chose to.You could also get a right angle micro-USB, which seems likely to be smaller than a right angle HDMI in any case. If this is workable, it's almost surely your best bet by a long shot!
Powering two color LED array - Page 1
Forum section: electronics / beginners

author: morzek
author_rank: Newbie
timestamp: March 01, 2015, 07:36:33 pm
content: Hi!I am trying to make a LED array of 60 diodes using red and blue HPLEDs (~3w each, cooling solved).I am planning to use 12v 250w 21A led power supply fromebay. In electronics, I am a total newbie, but I did some reading and thus far I have a vague idea of how the circuit might look like:There are a few problems that I see:Problem 1:Since diodes are connected in series and then in parallels to get 800mA on red and 750mA on blue, each series of LEDs should have the following resistances:n * resistance_of_LED + resistance_of_resistor = 4 * 3,5 + 1,2 = 15,2 ohms // for series with 4 red LEDs..... = 2 * 3,5 + 8,2 = 15,2 ohms // for series with 2 red LEDsn * resistance_of_LED + resistance_of_resistor = 2 * 6 + 4,7 = 16.7 ohms // for series with 4 red LEDsThe problem is that resistances might not be exactly as calculated, because of diodes coming from different batches and resistors having around 5% variation in resistance. This would make each string in parallels having a different current flowing through, possibly damaging the one with the least resistance and then destroying the rest in an avalanche, because of increased current.One plausible solution to this could be having resistors with higher resistance, but maybe there are better options available?Problem 2:I am clueless on how to power two 12v 0.3A fans and a 12v 0.4A water pump for cooling, especially if I would like to adjust the fan speed.Any advice appreciated, thank you and have a nice day!

author: hamdi.tn
author_rank: Frequent Contributor
timestamp: March 01, 2015, 10:06:27 pm
content: for such application i think it's better to use a led driver chip it will provide better efficiency.can adjust fan speed with PWM
Powering two dc-dc isolators off one dc signal - Page 1
Forum section: electronics / beginners

author: Mp3
author_rank: Frequent Contributor
timestamp: April 25, 2020, 09:38:18 am
content: I will draw up a mock schematic and post it later when i have more time but this is my question for how.Source: 5v from USBProblem: Need to power two separate 5V 1W DC-DC isolators from USB power (B0505S-1W). Running two diodes straight off the USB 5V would drop voltage to 2.5V as I understand it.Solution: 5v to USB powering DC filter caps, ferrite bead, and power both 5V 1W isolators off that?

author: Manul
author_rank: Super Contributor
timestamp: April 25, 2020, 03:46:39 pm
content: Yes, will be perfectly fine. But I recommend to not put ferrite bead on the input of this isolator. Put a capacitor on the input. Preferably electrolytic + ceramic. And if you want to use ferrite bead, do a pi filter. Capacitor - ferrite bead - capacitor.

author: Zero999
author_rank: Super Contributor
timestamp: April 25, 2020, 05:07:05 pm
content: There is no need for any diodes. A USB power supply can power as many circuits, as required, so long as the maximum current rating isn't exceeded.Diodes are only required when there are two power supplies and one load.

author: james_s
author_rank: Super Contributor
timestamp: April 25, 2020, 05:10:13 pm
content: Also why would diodes drop the voltage to 2.5V? I must be missing something, post a schematic of your proposed circuit and you will get a lot more useful help.
powering up GPU card without laboratory psu - Page 1
Forum section: electronics / beginners

author: debi
author_rank: Contributor
timestamp: November 11, 2022, 12:45:47 pm
content: Hello guys,i have a faulty GPU (RX580) no short on any rail but 12V blown fuses (8pin connector side), and no motherboard to plug it, No Vcore, but Core takes amps if i inject voltage right at the coils of the power stage. I have 3 lab psu at home, id like to track all voltages on the board (at this point, i target fault there : 1,8V output from GS7103 and Phase Driver pins from NCP81022). Is feeding 12V rail, 12V bus rail (pcie) and 3.3V (pcie) with the PSUs to simulate the environment of the gpu is right ?cheers
Powering up IC with active-low reset - Page 1
Forum section: electronics / beginners

author: jayalt
author_rank: Contributor
timestamp: January 13, 2023, 05:53:27 am
content: I’m struggling to understand the power up sequence of an IC that contains an active-low reset pin.I currently have a microcontroller that is toggling both the voltage rails and reset pin running into an IC. What state should the reset pin be in when I turn on the voltage rails? Since it is an active-low pin, should my GPIO toggle the pin high prior to powering on? Or is this creating a latch-up condition, similar to applying voltage to GPIOs on a device that’s completely powered off?

author: srb1954
author_rank: Super Contributor
timestamp: January 13, 2023, 06:08:50 am
content: Quote from: jayalt on January 13, 2023, 05:53:27 amHold the reset line low while turning on and toggle it high after a short delay when the power rails to the chip have stabilised. This is similar to the action of the most basic power-on-reset circuit where the reset pin would have a capacitor to ground and a resistor pull-up to the supply rail.

author: BillyO
author_rank: Super Contributor
timestamp: January 13, 2023, 10:08:32 pm
content: I've attached a simple reset circuit that provides both power-on and running reset. It's quite a bit better than just a resistor and a capacitor but still cheap and simple.Typical vlaues might be:R1, R2 = 5KR3 = 22RC1 = 10uF
Powering USB from PCB (no data) - Page 1
Forum section: electronics / beginners

author: logancane
author_rank: Regular Contributor
timestamp: September 04, 2021, 01:13:23 am
content: Hi everyone,A quick question that I can't seem to get a proper answer for. How does one go about powering a USB peripheral (in this case a camera) from a PCB? I don't want to send data, just keep the battery topped up. Can you simply connect the power lines and leave the data lines disconnected, or do you need a special USB controller?Cheers

author: langwadt
author_rank: Super Contributor
timestamp: September 04, 2021, 01:17:37 am
content: Quote from: logancane on September 04, 2021, 01:13:23 amshorting the data lines together is the USB standard way of signaling that it's a charger ( that not everyone uses )

author: logancane
author_rank: Regular Contributor
timestamp: September 04, 2021, 01:53:10 am
content: Quote from: langwadt on September 04, 2021, 01:17:37 amCool, thanks.