hybridfree/eevblog-posts huggingface dataset:
Power supply for 12v hdmi screen and raspberry pi - Page 1
Forum section: electronics / beginners

author: LagStorm
author_rank: Newbie
timestamp: October 09, 2022, 03:14:19 am
content: HelloI wanted to use a DC jack charger with an Y adapter to power a 12V HDMI monitor adapter, and a 5V PiFor the Pi I would put a DC buck, how should I calculate to know if the charger will be sufficient? You have to add the amps of the two devices and see if the charger delivers them?Thanks

author: ledtester
author_rank: Super Contributor
timestamp: October 09, 2022, 03:57:46 am
content: The amount of current you need from your charger depends a lot on the efficiency of your buck converter.Let E be the efficiency -- it will be a number between 0 and 1.If your RPi needs I amps of 5V current, the amount of 12V current going into the buck converter will be$$ I_\pi = \frac{5}{12\times E}I $$So add this to the amount of 12V current the monitor needs and that's what you need from the charger.A good modern buck regulator can achieve over 90% efficiency (E > 0.9). The efficiency of those cheap buck regulator boards you get from aliexpress/ebay can be lower than 70% under high load conditions.

author: LagStorm
author_rank: Newbie
timestamp: October 09, 2022, 04:07:59 am
content: Thank you for your help, I measured the pi in condition, it does not exceed 0.6 amps, is this formula applicable to other situations?I was thinking of using a mini360 but obviously it's not a good idea

author: ledtester
author_rank: Super Contributor
timestamp: October 09, 2022, 04:40:21 am
content: What's a mini360?

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: October 09, 2022, 04:48:42 am
content: Quote from: ledtester on October 09, 2022, 04:40:21 amhttps://components101.com/modules/mini360-dc-dc-buck-converter-module

author: ledtester
author_rank: Super Contributor
timestamp: October 09, 2022, 05:48:43 am
content: Found this testing report of the mini360 done in 2018:https://goughlui.com/2018/07/04/tested-mini-360-mp2307-based-3a-buck-converter-module/About halfway down there's a graph of efficiency for 5V output. At 500 mA the efficiency is around 70%. (Search for "Moving up to 5V" in the page.)
Power Supply for a ZVS - Page 1
Forum section: electronics / beginners

author: Another Dave
author_rank: Contributor
timestamp: December 04, 2016, 10:08:58 pm
content: Ebay bargains have tempted me again, I have bought a 1000Watt ZVS induction heater.Seen several people blow them up due to not having a voltage or current limiter. I have tried itwith a MingHe BST400W boost converter. Only @24v and limited to 5 Amps just in case.Also wary that the power supply needs to hit the voltage instantly and can not rampup slowly. The BST400 does, but i set the voltage and current and allow that to buildbefore plugging the ZVS in.It seems a decent PSU is rather expensive, are there any budget options?As i started to type this i had a flashback to one of my previous questions about a caravan batterycharger. Seems like the type of thing that will work except the voltage.Adjustable upto 48V and 20Amps. Thought of a bench PSU but anything approaching that specis super expensive.Due to the rapid voltage required, is a linear PSU better than a switched PSU? Or is that not anissue as long as i allow the unit to power on first then plug the ZVS unit into it after its powered?Many Thanks.
Power supply for secondary elements in main circuit? - Page 1
Forum section: electronics / beginners

author: d4n13l
author_rank: Regular Contributor
timestamp: April 27, 2017, 06:27:15 pm
content: Hello, I'm new to electronics currently working on building a power supply. My plan is going from a simple unregulated oneand then build on it until I understand how all parts work, and so get to something like this one1. My problem now is that I want to add digital voltage and amp meters and also I'll need a fan for the heatsink that goes with the 2n3055, but I'm not sure if I should add an independent power supply that provide power for them independent from the rest of the circuit or draw power directly from the main circuit.2. The fan I have requires 12v while the meters need 5v which in the spirit of learning, I'm thinking of building a linear voltage regulator for them, but for what I understand they are not very efficient, any suggestion how would be better to approach this?

author: rdl
author_rank: Super Contributor
timestamp: April 27, 2017, 08:19:20 pm
content: You will probably need an auxiliary supply for the metering, with many digital meters it is actually a requirement. If you are intending to build a linear power supply such as those in the schematics attached, inefficiency in a small auxiliary supply will not be too significant. A fan could just be run directly from the transformer secondary, unless you plan some kind of speed control. Personally, I would add more convection cooled output capacity before I would use a fan just because it would mean less noise, both audible and possibly electrical.
Power supply for TFT LED backlight - Page 1
Forum section: electronics / beginners

author: Kaisha
author_rank: Contributor
timestamp: August 12, 2021, 03:20:58 pm
content: I'm looking for a way to power or current limit an LED backlight for a TFT display (https://www.buydisplay.com/download/manual/ER-TFT032A3-3_Datasheet.pdf). The backlight has a Vf of 3.2 - 3.4V, and requires 100mA. The LCD (and rest of components) are powered from either 2 lithium ion batteries in series (so 6.6V - 9.4V) or USB (5V) through a buck converter (https://www.ti.com/lit/ds/symlink/tps54331.pdf?ts=1628780714735&ref_url=https%253A%252F%252Fwww.google.com.br%252F) at 3.3V.Normally a resistor would suffice, but since the Vf of the leds is equal to the output of the power supply, I can't pick a resistor size of 0. I fear any small value like (1 or 10) wouldn't be safe (slight variations, supply ripple, etc... could potentially draw too much current).Most of the constant current power supplies I've looked at (like the TPS65165) are boost converters. But given the higher voltage of the bats/USB, I can't use these.A device like the TPS54200 (https://datasheet.lcsc.com/lcsc/1809051024_Texas-Instruments-TPS54200DDCR_C177139.pdf) looks like what I'm looking for. The LED backlight has 3 cathode pins, and I've read online that led strings should each be individually current controlled (since there is variation between individual strings which can cause some to light brighter than others). Does this mean I need 3 TPS54200's for a simple TFT led backlight?Any ideas/thoughts?
power supply grounding - Page 1
Forum section: electronics / beginners

author: shobo
author_rank: Regular Contributor
timestamp: January 29, 2018, 06:25:30 pm
content: I bought a used old power supply - a Fontaine MC4020C.when i opened it up some wires were loose inside (not conected to anything but no conductor touching the metal).i used an ohmeter to see if the case is gounded and it is.Is it safe to use?i'll open it again an use some tape on the cables.

author: james_s
author_rank: Super Contributor
timestamp: January 29, 2018, 08:38:55 pm
content: Depends on what wires are loose, surely they're supposed to go to something?

author: shobo
author_rank: Regular Contributor
timestamp: January 30, 2018, 04:20:04 am
content: Quote from: james_s on January 29, 2018, 08:38:55 pmthere is space for someaditional circuit,i guess for remote sensing

author: james_s
author_rank: Super Contributor
timestamp: January 30, 2018, 10:01:39 pm
content: Assuming it works without them hooked up, just tape them off and tie them out of the way and it should be fine.

author: Shock
author_rank: Super Contributor
timestamp: January 31, 2018, 01:28:43 am
content: Proper way if wire is exposed and ok to remove it - cut cleanly then use glue/adhesive lined heatshrink and cover each end. Then cable tie it to another loom or back on itself so it doesn't interfere with the chassis or any hot components.

author: Brumby
author_rank: Unknown
timestamp: January 31, 2018, 03:26:32 am
content: I'd be curious to see a photo...
*SOLVED* Power supply grounding problem? - Page 1
Forum section: electronics / beginners

author: Aethelstan
author_rank: Contributor
timestamp: August 05, 2018, 11:52:03 am
content: ** EDIT I have tried a different PSU and the problem persists **** EDIT 2 Solved by tying the PGM pin to gnd. Funny how the problem manifested itself **Hi, I have a dual rail power supply made using a centre tapped transformer a pair of LM317/337 that I have built myself. I was trying to use it to supply a PIC18F on a bread board and flash an LED, which would work until I disconnected my PICKit3. After a bit of trial and error, I discovered the circuit will work correctly if I had the ground connected to the PICkit or to my oscilloscope. The power supply does power the breadboard, but the program doesn't run. If I connect the oscilloscope probe to my power supply with the ground part of the probe connected to the grounding tab on the scope, I see a +-8V wave at mains frequency, and adjusting the power supply does not change the magnitude of the wave. If I connect the ground part of the probe to the power supply ground, then I see a nice flat linear voltage that seems well regulated. I have checked continuity of the transformer, and also between the ground terminal and the centre tap.To my mind, the ground reference of the PSU is not staying at 0V, but I have no idea why.I have attached a schematic, the 12V supplies represent the centre tapped transformer. J2 and J3 are connectors for the potentiometers to control the voltage. J1 and J4 are connected to the LED voltmeter modules.Thanks for any advice.
power supply, I have only common cathode diodes - Page 1
Forum section: electronics / beginners

author: stefon
author_rank: Newbie
timestamp: December 20, 2019, 11:21:17 am
content: stupid question... I have only common cathode diodes schottky diodes.Can I do something like that to get symmetrical power supply?

author: MagicSmoker
author_rank: Super Contributor
timestamp: December 20, 2019, 12:24:17 pm
content: You sure can.

author: stefon
author_rank: Newbie
timestamp: December 20, 2019, 02:20:50 pm
content: well, this is how it looks... "-" is weird... why?edit: OK, I think I know.... reverse voltage of one schottky diode is only 30V and when I connected both 12V trafos, there is 40V peak to peak

author: StillTrying
author_rank: Super Contributor
timestamp: December 20, 2019, 03:01:45 pm
content: Quote from: stefon on December 20, 2019, 02:20:50 pmLooking at the scope that explanation doesn't make sense to me, but I can't explain why just 1 half of the -ve's cycles is floating about either.

author: Jwillis
author_rank: Super Contributor
timestamp: December 22, 2019, 05:00:56 am
content: Looks like you have one bad diode that isn't recovering very well.

author: ArthurDent
author_rank: Super Contributor
timestamp: December 22, 2019, 05:21:50 am
content: If the circuit is as shown and you have no real load, it may just be reverse leakage on one diode. Try just touching a 1K resistor across the output and see if the waveform returns to normal. The circuit may work just fine with a normal load but the scope you're using may be very high impedance and the diode has enough reverse leakage to show some voltage at this really low current load. I would still check to see which diode is causing this and perhaps replace it if you have spares, just in case.https://www.tutorialspoint.com/semiconductor_devices/semiconductor_devices_leakage_current.htm

author: schmitt trigger
author_rank: Super Contributor
timestamp: December 22, 2019, 05:29:42 am
content: What ArthurDent said

author: andy3055
author_rank: Super Contributor
timestamp: December 22, 2019, 07:24:02 am
content: Quote from: stefon on December 20, 2019, 11:21:17 amIf you need -ve voltage, should you not reverse the diodes in the bottom half of the circuit?

author: StillTrying
author_rank: Super Contributor
timestamp: December 22, 2019, 12:20:03 pm
content: I think it's more to do with capacitance across the transformer windings rather than anything to do with one of the diodes.A small load, even ~10k across the rectified -ve supply's DC output would probably fix it.
Power supply inductance and plane capacitance configuration - Page 1
Forum section: electronics / beginners

author: Freshman
author_rank: Regular Contributor
timestamp: February 17, 2025, 08:41:08 am
content: In this tool (https://pdntool.com/app/), If we set the quantity of all capacitors to zero and retain only the "plane capacitance" and "power supply" field values, the impedance plot exhibits a single sharp peak.This peak occurs at the resonant frequency determined by the interaction between the power plane inductance and the plane capacitance.Since the impedance peak is upward-facing, resembling the behavior of a parallel RLC circuit, I would like to understand how the power supply inductance and plane capacitance form a parallel configuration. Could you clarify this relationship?

author: mtwieg
author_rank: Frequent Contributor
timestamp: February 17, 2025, 01:48:03 pm
content: I drew a simple schematic of the model the tool is assuming. The tool is showing you the impedance seen from the load's perspective. From the load's perspective, the impedances of the "supply" and the "plane" are in parallel (remembering that for such an analysis ideal voltage sources like the supply become short circuits). This impedance has a peak, exactly like what the tool shows you.If we were to look at impedance from the source's perspective, then the two impedances are in series (remembering that ideal current sources like the load become open circuits). This impedance has a notch at the same frequency. But this is not what the tool shows you.

author: TheoB
author_rank: Regular Contributor
timestamp: February 18, 2025, 09:00:21 pm
content: Any active power supply uses feedback to control the output to a stable voltage. The most simple example is an unity gain buffer made with an opamp. Thanks to the large gain, the output barely changes with varying load. The output resistance is thus very low (mOhm range). But the higher the frequency, the lower the loopgain. The loopgain starts from 100k at DC and begins to drop at 10Hz and continues all the way to 1MHz where the loopgain drops below 1. The output behaves as a small resistor with a coil in series. Low impedance at DC and high impedance at 1MHz and higher. A cap at the output will thus create resonance, peaking. The tool you link to allows to see how all kind of loads can lower the peaking.

author: BillyO
author_rank: Super Contributor
timestamp: February 19, 2025, 02:48:04 am
content: Quote from: TheoB on February 18, 2025, 09:00:21 pmUnity (1) is a large gain?

author: TheoB
author_rank: Regular Contributor
timestamp: February 19, 2025, 07:19:15 am
content: There is a huge difference between open loopgain and closed. High open loop gain assures accuracy. Any difference between the plus and minus of an opamp is amplified 100k and makes the low output impedance.

author: BillyO
author_rank: Super Contributor
timestamp: February 19, 2025, 03:29:31 pm
content: Yes, I know how operational amplifiers work.
Power supply inside mainboard or as separate circuit board? - Page 1
Forum section: electronics / beginners

author: canol
author_rank: Contributor
timestamp: May 13, 2014, 07:28:13 am
content: Hello,I watched some teardown videos of different electronics devices. The power supply parts where the device gets 220V (or 110V) in and converts it to 5V or 12V for other components inside is usually a separate circuit board from the mainboard of the device where other components like processors, memory, logic gates, LCD drivers are present. But I've also seen some devices where the power supply is built into the mainboard.What is the reasoning of separating power supply from mainboard or including it into the mainboard? Is it for safety? Is it to be able to design them separately by different engineering teams? Is it for easier manufacturing (maybe designing a power supply and using it on two different products)? What are the advantages and disadvantages of both?

author: mariush
author_rank: Super Contributor
timestamp: May 13, 2014, 08:32:07 am
content: Sometimes they're made by other companies that specialize in power supplies (delta, astec, emerson etc).This way, the product manufacturer doesn't have to pass the power supply through various certifications, the oem manufacturers already did it. They also don't need to spend time designing it, testing it etc.Power supplies can also be built on cheaper pcbs (resin bonded paper/FR2 , semi-fiberglass pcbs etc) and can often be made only through hole or one sided only (means can be manufactured at cheaper pcb manufacturers).The main PCB of the product may be 2-4 layers or even more which is usually more expensive to make. PCBs are usually made in large rectangles (think 30cm by 20 cm at least), so if the pcb is smaller they may be able to fit more boards on one of those large panel and reduce the waste and make the pcbs cheaper (therefore more profit).
Power Supply Issues with RFID Access Control Backup System - Page 1
Forum section: electronics / beginners

author: charcowless
author_rank: Newbie
timestamp: November 20, 2024, 02:56:58 pm
content: Hello everyone,I'm new to electronics and need help troubleshooting an issue with a backup power system for an RFID access control reader in my residential complex.System Components:- RFID reader (12V, 6W consumption)- 12V/8A power supply unit (PSU) with 13.8V output- 12V/7AH VRLA battery as backup- MIC 6A8 diode installed on PSU +12V lineSetup:The PSU, battery, and access control system are connected in parallel. The PSU provides 13.8V to both the battery and the access system.The Issue:When there's a power outage, the system works as intended - the battery takes over and powers the RFID reader. However, when power is restored, the PSU fails to take control and charge the battery. Instead:1. The PSU output voltage fluctuates between 1V-10V2. The battery continues powering the system and discharging3. The system only works properly if I:- Disconnect the battery (which turns off the RFID reader)- Wait for the PSU to stabilize (returns to 13.8V)- Reconnect the batteryAfter this manual intervention, everything works normally - the PSU maintains 13.8V, powers the system, and charges the battery.I've already tried installing a diode to prevent reverse current, but the issue persists.Any suggestions on how to fix this so the system recovers automatically after power is restored?Thanks in advance for your help!

author: Simon
author_rank: Unknown
timestamp: November 25, 2024, 05:43:37 pm
content: Please don't post duplicate threads, you won't get any love for it.
Power supply  leads  - Page 1
Forum section: electronics / beginners

author: mottihoresh
author_rank: Contributor
timestamp: July 01, 2017, 01:50:50 pm
content: Hey all. I am about to order my first real precision power supply.In the past I build one kit and messed around with small boards from the net. I've kind of settled on going for the Rigol832 since I think it would be a good value for the future.I am not sure if there are any special leads I would need to buy (for current purposes) I don't see my self using more than around 1.5 amps per channel.I've seen couple of elanco leads on amazon but none of them specify the wire gauge or any power ratingsSent from my iPhone using Tapatalk

author: bson
author_rank: Unknown
timestamp: July 01, 2017, 09:30:39 pm
content: Pomonas are a good value...Stocked Pomona test leads at Digi-Key

author: alm
author_rank: Super Contributor
timestamp: July 01, 2017, 11:19:44 pm
content: Leads will not specify power rating. Good leads should specify a voltage (not an issue here) and current rating. For Pomona leads, see their datasheet. 10A is a common rating for regular leads. In addition to Pomona I have heard good things aboutProbemaster.Franky (iloveelectronics)on this forum also sells nice leads.Nothing special about leads for low voltage lab power supplies. Because power supplies generally have binding posts that do not accept safety leads with a fixed sheath, make sure the sheath is either retractible or not present. You probably want to connect to your device under test, whatever you are powering. For a bread board or prototype you might want something like grabber hooks (in my opinion alligator clips are rather useless). It is up to you if you want monolithic leads with grabbers, or a more modular system where you have banana-banana leads plugged into a grabber.

author: mottihoresh
author_rank: Contributor
timestamp: July 01, 2017, 11:24:30 pm
content: Bson and alm thank you for the informationSent from my iPhone using Tapatalk
Power Supply Noise - Page 1
Forum section: electronics / beginners

author: Legal_Planet
author_rank: Newbie
timestamp: April 07, 2018, 07:54:50 pm
content: I've been working towards getting a guitar to sound like an old game console and I have gotten some great advise from the forums. Someone had posted a schematic of an op amp circuit that turns the output from the electric guitar into a square wave. I've recently been working on trying to use an arduino nano to monitor some of the signals from the circuit to add on some effects. However I'm running into an issue with the circuitry. I'd previously powered the arduino straight from the adapter's power rail since the adapter's output read 9v. Sadly I didn't know such readings are usually false and ended up frying the nano with 13.1 volts. So I moved onto a little voltage regulator circuit I'd found online which would substitute my lack of having the physical part (trying to make due with what I have until summer comes around). I'm getting 7.3 volts from the regulators output but the issue is whenever I put the arduino nano into the board the op amp appears to resonate at a certain frequency. I assume this may be because of noise created in the Vcc from the crude regulator? Is there a way to fix this and what is the underlying cause that it doesn't currently work?

author: taydin
author_rank: Frequent Contributor
timestamp: April 07, 2018, 09:32:04 pm
content: Are you hearing the 60 Hz hum, or is it another kind of noise?If it's the 60 Hz hum, you can power the circuit with a battery to eliminate the power supply as the cause. If there is no hum with the battery, then it's the power supply. But I doubt it's the power supply, because this circuit wouldn't be drawing too much curring to cause ripple on the PS rail. The hum probably is picked up through magnetic coupling.

author: Legal_Planet
author_rank: Newbie
timestamp: April 07, 2018, 10:18:59 pm
content: Just checked the frequency and it appears to be humming at 120Hz. I've thrown 3 +1000uF capacitors from the positive to negative rail and the sound has gone down quite a bit but I'm sure there's a far better and reliable solution. I'll also note that the hum's amplitude rises up and drops off along when the LED on the microcontroller flashes so I'm 99.99% sure this is a voltage issue. Any other suggestions besides using a battery or my arsenal of capacitors? *Quite happy I'm going through these problems since I'm learning more than I typically would on a weekend.

author: Legal_Planet
author_rank: Newbie
timestamp: April 07, 2018, 10:22:30 pm
content: And I'm sure a battery would solve this problem but I'd just changed out all the smoke alarms last week and I'm a bit to lazy to pull them back out. Trying to stay with adapters as well since I'm currently lacking the junction piece to connect one to the board.Just tried using the guitar with it and I'm finding that the op-amp isn't functioning while the arduino's plug into it's slot. Not sure if that piece of information helps draw other conclusions.
Power supply ON/OFF switch help - Page 1
Forum section: electronics / beginners

author: onemanonelaptop
author_rank: Contributor
timestamp: November 14, 2023, 07:07:20 pm
content: Hi all,I am designing a power supply and want to be able to turn it on and off using a switch.I have wired 2 P channel mosfets into the circuit which (according to circuitlab) will do what i want, but I am doubting myself. I was wondering if anyone would be so kind as to give it an eyes over for obvious mistakes.The power supply uses USB as its primary power source and batteries if and only if the usb power is disconnected. (At least that is what it should do)Turning on the switch should connect the gates of both mosfets to ground, pulling the voltage to zero thus allowing the power to pass through. Am i correct here?

author: CountChocula
author_rank: Unknown
timestamp: November 14, 2023, 08:06:27 pm
content: Why not simply connect the switch between the battery/USB rail and the inputs of U7? Unless I'm missing something (very possible!), that would achieve the same objective with fewer parts. Also, U7 is a pretty pricey component… you could replacethatwith a Mosfet and a couple diodes.

author: onemanonelaptop
author_rank: Contributor
timestamp: November 14, 2023, 08:43:55 pm
content: Thanks for the reply.... So the switch (which is the only one that fits the application) has a max current of 100ma and the circuit is likely to draw around 300ma.The chip is $2.67 from LcSC, while still expensive, space is at a bit of a premium.

author: CountChocula
author_rank: Unknown
timestamp: November 14, 2023, 09:24:20 pm
content: OK, understood. Then this looks like it would work. You could increase R27, R29, R1, and R2 100k to reduce waste when you're on battery (though be careful not to fall below the minimum current rating of the switch). Also, I don't think you need R15, and R14 should probably be smaller—with a 10k resistor, that LED is… unlikely to be very brightBTW, if space is at a premium, Q3 and Q4 seem a bit overkill for your application… they are rated for up to 7A at 60V! You could switch to a SOT-23 likethis one, which also happens to be in JLC's basic parts list.In case you change your mind on omitting U7 (which would save even more space), I've attached an alternative for you to consider.HTH,—CC

author: onemanonelaptop
author_rank: Contributor
timestamp: November 20, 2023, 11:15:52 am
content: Thankyou for the reply, turns out that chip is way too expensive when it actually came down to trying to order it.I have switched the mosfets as you are correct they were way too big for the task at hand.
Power supply op-amp selection - Page 1
Forum section: electronics / beginners

author: fenclu
author_rank: Regular Contributor
timestamp: October 06, 2012, 08:16:04 pm
content: HiI've been designing a little Arduino PSU (pretty similar to Dave's uSupply). I've got almost everything sorted except for the op-amp selection. What op-amp should I choose for amplifying the PWM signal before it goes into the SET pin on the voltage regulator (it needs to be precise and as cheap as possible)? I guess for a simple buffer I could use a jellybean component like an LM324?

author: Rerouter
author_rank: Super Contributor
timestamp: October 06, 2012, 10:50:05 pm
content: your looking for an op amp whose input and output include the lowest and highest voltage you need, being how its a pwm signal i presume you will be filtering it back to near DC, in which case slew rate wont be all that critical, if your looking for precision look for a low input offset voltage,realy to spec any specific one you need to give us some more details like the voltage range,

author: fenclu
author_rank: Regular Contributor
timestamp: October 07, 2012, 06:33:22 am
content: Well, it has to be at least 0-15V.

author: Rerouter
author_rank: Super Contributor
timestamp: October 07, 2012, 07:09:02 am
content: http://au.element14.com/stmicroelectronics/ts912id/op-amp-dual-cmos-rri-o-smd-soic8/dp/1094386i suggest you get the hang of parametric searches, as all of the information i gave you would have turned up the same or a similar part :/
Power supply outage detection - Page 1
Forum section: electronics / beginners

author: wicket
author_rank: Contributor
timestamp: June 15, 2014, 08:04:57 am
content: I'm running my circuit with 18V AC power adaptor. In case it fails, I've installed a 12V backup battery and it works fine. Now I'd like to detect this power adaptor failure and trigger an interrupt with my PIC when it happens.What would be the simplest way to do that? I thought about putting another Schottky right after Graetz and use an NPN transistor. But I read that Schottkys have high leakage current if there is another power source on it's cathode.Help please.

author: Fank1
author_rank: Regular Contributor
timestamp: June 15, 2014, 11:25:08 am
content: Add a 100K resistor in series with the transistor base or you will let the smoke out of it.

author: mariush
author_rank: Super Contributor
timestamp: June 15, 2014, 06:13:42 pm
content: Even with a base resistor (or especially with one), you still have a problem with that circuit, because right after the bridge rectifier you're still going to have 100-120 pulses of DC :So the transistor may turn off for very brief periods and your pic will incorrectly think you don't have AC adapter plugged in. So move the capacitor right after the bridge rectifier because the 7812 doesn't need it anyway if it's powered from battery (but it doesn't hurt).You could just use a 5.6v zener (or less) and set interrupt on pin change.. when adapter fails, pin goes to 0v from 5.6v and you can configure the PIC to detect that.ps. And what's the deal with C16 and C17? 100nF = 0.1uF ... makes no sense to use 2 of those of same size.ps2. I'm also bothered by how you connect the battery. The label says 12v Pb .. I assume that's a car battery? That will be 10.8-13.5v or something like that.The 7812 being a linear regulator it will need 1.5-2V *above* the output voltage to output a proper 12v. It's 2v for around 1A, less at lower currents. I'm ignoring the schottky diode voltage drop as that's only about 0.1-0.3v.So as you connected it, the battery would have to be about 13.5-14v all the time to see on the output of that regulator 12v - as the battery discharges, you will see 10-11v on the output of that regulator.Use a regulator with less voltage drop, for example 1117 which needs only 1v above output voltage... but be careful as some 1117 (depends on manufacturer) only tolerate up to 15-16v on the input.

author: thejamesclan
author_rank: Newbie
timestamp: June 15, 2014, 09:52:37 pm
content: I would use a opto coupler driven from the + on bridge rectifier through a 470R resistor to ground and pulled up on the pic input.

author: retrolefty
author_rank: Super Contributor
timestamp: June 15, 2014, 10:09:56 pm
content: I too would go with an optoisolator. Your Q2 in your circuit is lacking a base resistor resulting is a deceased transistor, not just resting.
Power Supply Output? - Page 1
Forum section: electronics / beginners

author: almamater
author_rank: Regular Contributor
timestamp: August 15, 2020, 12:31:49 am
content: Hello.This is an old Monitor (samsung syncmaster 171n) that decided not to work anymore.., no image, nothing.I checked the power supply (BN44-00054C) and the controller board, initial i measures the output pins and i read ~7.9V and 12V.. so i thought that it was Ok with PS.I tried to follow the traces and i stoped at the component IC112 (Mosfet Dual Channel), because the pins D1 (Drain1) have 0V but all the others seems ok: S1 \ G1 \ S2\ G2 \ D2 => ~5v, just D1 have 0V.I bought a new IC and change it but the problem remains and is the same behaviour, D1 with no output voltage (0V).I changed all the capacitores (metal ones), but still no luck.Then i tested the big capacitors from power supply and all have the right values.. i soldered some old joints and turn everything on again.. but now the voltages changed.. 7.9V => to ~3.2V and 12V => ~7.6V, but i just only removed the capacitors and put them again..Anyone knows the if the initial voltages were oK? (7 and 12V).Note: Before removing the capacitors, when i switched the IC112 for a new one, i turned everything On (he was off for a month or two), and it worked.. but only for one minute or 2.. :

author: bob91343
author_rank: Super Contributor
timestamp: August 15, 2020, 12:44:54 am
content: You need to post a diagram, as the people who read this would not be expected to do that research. I have no idea what the unit is or even if you reinstalled the electrolytic capacitors backwards.
Power supply plus minus ground hmph - Page 1
Forum section: electronics / beginners

author: The Magic Rabbit
author_rank: Regular Contributor
timestamp: November 15, 2015, 10:34:16 pm
content: Is there any reason I couldn't take a 12VDC power supply, use a 5VDC regulator to give me 12VDC, 5VDC, Gnd, and treat it as if it were +7VDC, Gnd, -5VDC?If this is the case, why would you then use a single rail OP Amp and bias the input to it, since you have to then filter the DC at in and out?Sent from my XT1039 using Tapatalk

author: jeroen79
author_rank: Frequent Contributor
timestamp: November 15, 2015, 10:56:50 pm
content: Depends on what you are using it for.If the load between +7V and GND is passing more current than the load between GND and -5V the regulator will have to be able to sink current.If it can't then it's voltage will rise above what it is trying to maintain and it will just stop passing current, leaving you with the two loads in series on a 12V supply.You could of course add another load between GND and -5V that is drawing enough current to always keep the regulator sourcing current.

author: The Magic Rabbit
author_rank: Regular Contributor
timestamp: November 16, 2015, 01:41:16 am
content: Quote from: jeroen79 on November 15, 2015, 10:56:50 pmI was hoping to build an 8 channel pre-amp that will connect to my computer audio interface inputs (unbalanced line level at 20k impedance) and take a variety of things as inputs (mics without phantom power, synthesiser, line output from amplifiers, etc)I want to drive a set of 8 LM358NG OP Amp chips, plus possibly a set of 8 YL071CN Op Amps with standard 3mm LEDs as overload indicators.My main thinking was that all these capacitors and biasing seems to add a lot of components that might simply be unnecessary.Sent from my XT1039 using Tapatalk
Power Supply - Power/Current Question? - Page 1
Forum section: electronics / beginners

author: StuUK
author_rank: Frequent Contributor
timestamp: October 17, 2016, 10:20:35 am
content: I've taken the attached power supply out of an old SKY box, the power supply works fine and could be very useful for something else but I've drawn a blank on trying to find any product info for it.What i'd like to try and work out is what power/current I could expect to draw safely from the 5v/12v supply.I suspect I'm missing a simple answer here but is there anyway of working this out?

author: tron9000
author_rank: Frequent Contributor
timestamp: October 17, 2016, 10:35:08 am
content: I suspect there are surface mount componets on the other side of this board? may we have a photo on that side? quite close up so we can see any IC idents

author: joseph nicholas
author_rank: Frequent Contributor
timestamp: October 17, 2016, 10:57:15 am
content: It looks to be probably around 10 amps. Try load testing it using your multi meter. This can be done by short circuiting it through the 10 amps range for a few seconds.

author: Cliff Matthews
author_rank: Unknown
timestamp: October 17, 2016, 10:58:54 am
content: Used in this product:http://electronics360.globalspec.com/article/3556/bt-vision-gen2-dvr-set-top-box-teardownauthor says it's 34 watts, so I'd guess both 12 and 5v rails can offer 2amps. There's at least 2 DC-DC convertors on PCB (left) likely ran 3.3v to the CPU and maybe 9v to th ethernet phy driver.Similar box shown here:

author: StuUK
author_rank: Frequent Contributor
timestamp: October 17, 2016, 11:08:46 am
content: Quote from: tron9000 on October 17, 2016, 10:35:08 amNothing, it's a single sided board.

author: StuUK
author_rank: Frequent Contributor
timestamp: October 17, 2016, 11:10:37 am
content: Quote from: Cliff Matthews on October 17, 2016, 10:58:54 amYes, that's the board, in fact I think it was a BT box not SKY box as I mentioned above.
Power supply purchase - Page 1
Forum section: electronics / beginners

author: OC71
author_rank: Contributor
timestamp: November 18, 2014, 11:49:07 am
content: Hi all,Does this PS look OK for general DIY projects? The price fits my budget and it has some good reviews.Thanks,OC71http://www.banggood.com/CPS-3205-0-32V-0-5A-Portable-Adjustable-DC-Power-Supply-110V220V-p-934530.html

author: teslafan
author_rank: Regular Contributor
timestamp: December 04, 2014, 09:41:20 am
content: I'd suggest seeing our forum founder, Elec. Engr. Dave Jone's, "How to set up a basic electronics lab", a YouTube video. Hope this helps.

author: electr_peter
author_rank: Unknown
timestamp: December 04, 2014, 10:06:17 am
content: Quote from: OC71 on November 18, 2014, 11:49:07 amThis looks like Gopher CPS-3205 model. It is a switchmode type, works ok for a price. It is light, user interface is easy, inside construction is solid. It has some switching noise when in some operation modes, also stability/turn on performance is not the best.If your requirements are not super strict on noise/voltage ripple/accuracy, this DC supply is good choice.Search around this forum for "Gopher" to find discussions about these suplies.CPS-3010 review5A model teardown and description

author: tautech
author_rank: Super Contributor
timestamp: December 04, 2014, 10:12:40 am
content: Its a SMPS and thats why the ripple spec is 30 mV.A linear PSU will have much better ripple specs, but also be much heavier and probably larger.It not be possible to find a new linear PSU for a similar price as the shipping fees will be much more due to its weight.For project use just ensure you add additional bulk capacitance to reduce SMPS ripple.Have a look in Davids (Hiplane) Aliexpress store, he can advise you:http://www.aliexpress.com/store/group/DC-Power-Supply/917544_250094495.html

author: OC71
author_rank: Contributor
timestamp: December 04, 2014, 10:41:33 pm
content: Thanks for the replies everyone.OC71
Power supply question.  - Page 1
Forum section: electronics / beginners

author: IonizedGears
author_rank: Regular Contributor
timestamp: February 17, 2013, 10:55:54 pm
content: The circuit pictured requires a 15 V and a -15 V rail. There are no grounds and the only power connections are the 15 and -15 voltage rails. Wouldn't this circuit still work if there was 30 volts and a ground in place of the other two voltage rails. I marked the two rails on the picture.

author: IanB
author_rank: Super Contributor
timestamp: February 17, 2013, 11:12:50 pm
content: It would work in a way, but there is an implicit ground not marked on the diagram. The output waves are going to be referenced to 0V so they swing symmetrically positive and negative as AC signals. If you powered the circuit from a 0 to +30 V supply the output signals will be DC biased to +15 V. This most likely is not what you need.

author: w2aew
author_rank: Super Contributor
timestamp: February 18, 2013, 03:10:41 am
content: Quote from: IanB on February 17, 2013, 11:12:50 pmDitto the above. The paragraph on the upper right of page 6 of this data sheet describes this exact situation.http://www.intersil.com/content/dam/Intersil/documents/fn28/fn2864.pdf

author: IonizedGears
author_rank: Regular Contributor
timestamp: February 18, 2013, 03:19:44 am
content: Oh, thanks

author: smashedProton
author_rank: Frequent Contributor
timestamp: February 18, 2013, 07:07:59 am
content: you could put a series 1 uf cap on the output to ac couple it. It could attenuate your really low frequencies though.

author: funk1980
author_rank: Contributor
timestamp: February 18, 2013, 07:58:22 pm
content: You could indeed use a cap on the outputs to remove the CD bias as smashedproton suggests, but it should be calculated depening on the impedance of the next stage and lowest desirable frequency: C=1/2piFR
power supply question - Page 1
Forum section: electronics / beginners

author: sal_park
author_rank: Contributor
timestamp: June 12, 2016, 08:47:30 pm
content: Hi,I've got a power supply situation that I could do with some help on. I'm powering a raspberry pi (5v, 400-500mA) from a powerbank (http://www.clasohlson.com/uk/Clas-Ohlson-2600-mAh-Powerbank/Pr386941000rated at 5v 1A).Anyway I want to be able to cope with the situation when the power coming in to the powerbank is removed. The powerbank will then take over and supply the 5V, but there is a 100ms gap where the voltage drops to around 3 volts which causes the raspberry pi to crash.Question is, what kind of a circuit can I place inbetween the powerbank and raspberry pi to fill in this 100ms gap ? I know which end of a soldering iron to hold, but I'm not an EE.So, any pointer are welcome as I'm a bit stucksal

author: Kjelt
author_rank: Super Contributor
timestamp: June 12, 2016, 08:51:25 pm
content: A huge elco or goldcap capacitor is needed.

author: hushaoxin
author_rank: Contributor
timestamp: June 13, 2016, 09:00:30 am
content: Add a Super capacitor between the powerbank and raspberry pi, That's OK!

author: danadak
author_rank: Super Contributor
timestamp: June 13, 2016, 10:03:16 am
content: You can calc the capacitance. See attached.Regards, Dana.

author: TheAmmoniacal
author_rank: Unknown
timestamp: June 13, 2016, 10:06:27 am
content: http://www.ebay.com/itm/2-PINs-Super-Capacitor-Button-Type-5-5V-1-5F-Ultra-Capacitor-2pcs-/272225538535These should be more than enough

author: Kjelt
author_rank: Super Contributor
timestamp: June 13, 2016, 10:36:21 am
content: But I would choose a decent brand of goldcap like Nec or similar.

author: Ammar
author_rank: Regular Contributor
timestamp: June 13, 2016, 12:42:04 pm
content: Your load is effectively R = V/I = 5/0.5 = 10 ohms. You want to smooth over 100ms, so say you want a time constant of 3 times tau for your capacitors. tau = R*C. Looks like you might need about 30mF.Try a 47mF or higher super cap. Then put a few electrolytic caps in parallel (several hundred microfarads), and then a ceramic 0.1uF cap. Super caps tend to have high ESR and probably will not be able to deliver pulses of current. Hence, the extra types of other caps.
power supply question - Page 1
Forum section: electronics / beginners

author: funkimunky
author_rank: Contributor
timestamp: July 10, 2012, 11:45:04 pm
content: I got this ancient power supply on fleabaycoutant lc60 variable power-supply DC 30 V 2 A with current limiter.It doesn't seem to be working but I am not sure as I am pretty new to electronics.I have been trying to get the power supply working but it does not seem to supply any current when there is any load in a circuit. I set current limit to 250mA I connect a small resistor of 100ohms to the power supply no current is pushed but if I connect an led I get current and light but then as soon as there is any resistance by including a resistor in the circuit the power stops.Does this mean that the supply is broken?

author: Psi
author_rank: Super Contributor
timestamp: July 11, 2012, 12:48:13 am
content: What happens if you set the current limit to 2A, the voltage to 12V and try a light bulb?I googled for a pic so others dont have to

author: funkimunky
author_rank: Contributor
timestamp: July 11, 2012, 06:16:15 am
content: Hey that was the actual one that I bought lucky find on the picture.I set the current at max 2.215 and voltage a little over 12.59v as the voltage is not that accurate. I hooked up a bulb and and it only drew 45mA no light no amp limiting happened.I have also attached pictures of set up then running of test.

author: Psi
author_rank: Super Contributor
timestamp: July 11, 2012, 06:56:13 am
content: Hm.. it does look like something is broken, probably the output driverThat lightbulb is 12V. correct?If you short the terminals together does the "LIMIT" light work?

author: funkimunky
author_rank: Contributor
timestamp: July 11, 2012, 07:33:17 am
content: doh no its not 12 volti'll pick one up in maplin later and test. thanks for help so far.

author: funkimunky
author_rank: Contributor
timestamp: July 11, 2012, 05:30:44 pm
content: I got a 6 volt bulb (2.2ohm) to light up (and it was drawing 220mA according to power supply) even with a 47 ohm resistor in series with it so the power supply must be ok. I need to test with a 12v bulb but the only one I have is busted. I even popped the fuses on 2 multimeter 0.5 A and 0.25A fuses. This must be a bad case of noob'itis.Only problem I can see is the voltage is a bit off about 0.4V higher built in display than what my multimeter says its at.

author: Monkeh
author_rank: Super Contributor
timestamp: July 11, 2012, 11:31:11 pm
content: Well then, fix the meter!

author: funkimunky
author_rank: Contributor
timestamp: July 12, 2012, 07:26:08 am
content: yeah thats what the guy said that sold the power supply to me when I told him about it
Power Supply Question - Page 1
Forum section: electronics / beginners

author: duggerd
author_rank: Contributor
timestamp: July 12, 2011, 12:44:55 am
content: I was wondering for a project what I could use to power a RFID reader at 12 V DC at 20 mA? Is there a power supply I could build to create this?

author: ivan747
author_rank: Super Contributor
timestamp: July 12, 2011, 12:50:53 am
content: Are you powering these from batteries?

author: duggerd
author_rank: Contributor
timestamp: July 12, 2011, 12:52:13 am
content: No I wanted to power it from a 12 V 0.15 A wall wart.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 12, 2011, 12:52:28 am
content: You will probably need something small but stabilized .Search for 12V stabilized power supply at 500mA , I do not think that you will find smaller than that.They have small transformer inside and they do the job.They cost 5-6$ .

author: duggerd
author_rank: Contributor
timestamp: July 12, 2011, 12:55:51 am
content: This is what I want to power.http://cgi.ebay.com/New-Design-Wiegand26-RFID-Reader-125KHz-Bell-/130411597050

author: ivan747
author_rank: Super Contributor
timestamp: July 12, 2011, 12:57:31 am
content: Easy, get one of these:http://www.sparkfun.com/products/9442It will do the job perfectly.

author: duggerd
author_rank: Contributor
timestamp: July 12, 2011, 12:59:01 am
content: Doesn't the output have to be 20 mA?

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: July 12, 2011, 01:02:32 am
content: Quote from: duggerd on July 12, 2011, 12:59:01 amThis is what your device needs to get, what the PSU can deliver its another story.

author: duggerd
author_rank: Contributor
timestamp: July 12, 2011, 01:05:20 am
content: Is there anything I can to build that takes 12V at a higher mA, and brings it down to 12V at 20mA?

author: nyo
author_rank: Contributor
timestamp: July 12, 2011, 01:45:32 am
content: Duggerd,Your RFID reader draws 20 mA, the ones suggested here are capable of supplying 500 mA and 600 mA. As long as the voltage is right, these will work, your device will only draw the necessary current from those, 20 mA.You can connect any 12V device to these as long as it uses less then 500 and 600 mA
Power Supply Repair (PowerMac G5) and Thermistors - Page 1
Forum section: electronics / beginners

author: Bskitter
author_rank: Regular Contributor
timestamp: February 01, 2017, 02:13:17 pm
content: Hello Everybody,I got a beautiful G5 Macbook yesterday with two broken power supplies.Apon investigating I found the NTC Thermistor's just before the primary transformer have failed.I need some help on identifying the failed NTC Thermistors,After struggling my balls off to remove these components I am now struggling to identify them.They are labeled "SCK206L545" after some brief googling I came accross the data sheets for these components.http://www.thinking.com.tw/documents/en-sck.pdfBut from looking on the sheets I can only find "SCK206R0"Could someone briefly explain the different in labels here ?Also what would cause both of them to fail so dramatically ?Here are some pictures.Bid red circle is where the Thermistors were removed.

author: Bskitter
author_rank: Regular Contributor
timestamp: February 02, 2017, 04:34:52 pm
content: Anybody ?

author: bson
author_rank: Unknown
timestamp: February 03, 2017, 06:54:47 pm
content: SCK-206 would according to that numbering scheme be 20ohm at room temp, 6A max.5mm lead spacing, 0.8mm lead diameter, 10mm length, 5mm width.