hybridfree/eevblog-posts huggingface dataset:
Barrier Diode Substitution - Page 1
Forum section: electronics / beginners

author: joeyjoejoe
author_rank: Frequent Contributor
timestamp: September 24, 2022, 04:57:55 pm
content: Hello,I'm building a switching DCDC converter on a PCB. It will take 24VAC and output 3.3VDC.My full bridge rectifier is usingSS210Schottky's (100V 1.5A).My switching IC is theBD9G101Gwhich calls out aFB160L-60as the barrier diode.Can I use the SS210 diode from my rectifier instead? The maximum current is 500mA for my switching regulator. This would reduce my BOM count, and the SS210 is a slightly smaller footprint.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 24, 2022, 10:37:18 pm
content: The datasheet doesn't make any statement about allowable negative voltages. In fact... it doesn't at all, apparently you could apply a million volts, negative, to any pin besides GND and it would survive. Which I very much doubt, but, the datasheet doesn't seem to say otherwise.They also say almost nothing about the diode. Evidently it needs a diode. Evidently they don't care what type.So, it's probably fine.Most regulators have a -2V rating on the "SW" or "LX" or "PH" or whatever they call it, i.e. the diode forward voltage must be under 2V including transiently. (Sometimes a little more is allowed for short periods (some ns) as well.) The main thing with higher voltage schottky is the higher Vf, hence concern for this rating.Tim

author: joeyjoejoe
author_rank: Frequent Contributor
timestamp: September 25, 2022, 01:56:39 pm
content: Awesome, thank you. The Vf difference is only 0.1V so let's try it out and see how it fares. I did a test board with some test points and what not, I often design projects needing larger stepdown so it's about time to roll up my sleeves, venture into switchers and get a nice design I'm comfortable with to use in other projects. A wide VIN range on this IC and the nice reference document with popular voltages sure makes it that much easier. Hopefully I did alright on the layout!
Basic(?) Project Questions - Page 1
Forum section: electronics / beginners

author: Rigolon
author_rank: Regular Contributor
timestamp: March 28, 2018, 05:01:31 pm
content: I'm not sure how to name this topic, but i have some curiosity that perhaps are common knowledge.First, I have seen in some circuits, that use a relay output, that the output is inverted. The NO of the relay is considered NC, because when the circuit is powered on the relay is also powered. Why is that?I've seen this mostly on sensors, infrared ones, those used on automatic gates so the gate don't close on the car.I thought that maybe is made like this to identify that the relay might not be working, but in this case there are a lot of things that can be happening other than the relay is broken.Second question, when using a digital input of a MCU, is it better to project it as HIGH (with pull-up resistor) when nothing is happening or as LOW? Given the fact that I don't have anything that forces me to use one or another.

author: james_s
author_rank: Super Contributor
timestamp: March 28, 2018, 05:41:40 pm
content: Generally it's done so that if the device fails or loses power, the contacts fail closed but it depends on the circuit.Doesn't really matter, it depends on what you're driving it with and what makes the firmware easier to write. I generally use high = on for outputs but there can be reasons to use negative logic.

author: ataradov
author_rank: Super Contributor
timestamp: March 28, 2018, 05:47:29 pm
content: The coil of the relay is often normally energized on internal doors with key card entry. This is done for fire safety. If electricity is cut off, all internal locks will default to the unlocked state.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: March 28, 2018, 10:44:25 pm
content: Generally speaking, but not always, when a circuit is wired to a relay contact to the NO side of the contact and provides power when the relay is energized, it is a fail safe setup. If power fails, nothing is energized. Sometimes systems have battery backups and are driven on DC through the relay. Other commenters have stated similar reasons.As far as the digital input is concerned, this setup is so that you can utilize either, depending on your requirements or ease of use. If there are safety concerns, again use your logic (your brain) to best determine what would be the optimal fail safe situation. Otherwise, it is a function of the type of input that you are using. If you have to add extra components in order to achieve either a pullup or pulldown situation, it may be advantageous to use the opposite input logic (the one where you don't have to put extra components).Poorly explained, but I hope you get the gist.Hope this helps.
basic 555 astable oscillator issue - Page 1
Forum section: electronics / beginners

author: dacke909
author_rank: Newbie
timestamp: July 21, 2025, 05:31:00 pm
content: Hi,I'm having problem with astable oscillator, when I made a pcb it looks like ive made a mistake, and I cannot see it.

author: Grandchuck
author_rank: Super Contributor
timestamp: July 21, 2025, 06:17:55 pm
content: CV is not connected

author: edavid
author_rank: Super Contributor
timestamp: July 21, 2025, 06:54:16 pm
content: Quote from: Grandchuck on July 21, 2025, 06:17:55 pmThat's not an issue, but maybe it would help if you drew your schematic in a less insane wayTry making it look like the one in the datasheet.

author: PGPG
author_rank: Frequent Contributor
timestamp: July 21, 2025, 07:19:56 pm
content: Quote from: dacke909 on July 21, 2025, 05:31:00 pmCongratulations! You gave us comprehensive information that allowed us to find the error.We don't know:1. What is your problem:- not generating at all,- generating, but frequency is different than expected,- generating, but signal at scope is not stable rectangle.2. What is your expected frequency:- what is C value - may be you are trying to work over IC range,3. What is your supply:- is it battery (what voltage, not used too much),- is it lab supply (what voltage, connection enough short if you don't use blocking supply capacitor),- other supply source,- are you sure you didn't reverse the polarity.4. Are you sure IC is not damaged:- have you checked it working in another configuration.5. Are you sure your PCB is coherent with the schematic:- show PCB if you say PCB is not working.

author: Analog Kid
author_rank: Super Contributor
timestamp: July 21, 2025, 09:26:29 pm
content: Quote from: edavid on July 21, 2025, 06:54:16 pmLike this:And give us values (notmfr. part #s) for all the Cs and Rs, and for Vcc.
Basic Circuit Design Help - Page 1
Forum section: electronics / beginners

author: mrmagoo
author_rank: Newbie
timestamp: May 07, 2020, 08:06:05 pm
content: Very big electronics newb here. I can solder, wire things up, etc, but the most complicated circuit i ever put together was a blinking LED using a 555, led and resister. My projects usually side on the mechanical side of the fence (lathing, milling, etc), although i did rewire a whole car once, but thats getting off topic.So im in the middle of a project that requires me to deliver a small, controlled amount of compressed air at the push of a pushbutton. I am planning on usinghttps://www.alibaba.com/product-detail/3-5mm-Flow-Bore-2V035-06_60748410126.html?spm=a2700.galleryofferlist.0.0.3aeb35c1LxatxG,which is a simple solenoid valve that opens when 12v is applied (easy). Power source will be normal batteries in series to get 12vDC. But I need it to only open once per push of the button. To open the valve again, the user must release the push button completely and press it again. And I need to be able to dial in how long the valve stays open per button push. Doesn't have to be digital or anything fancy, tuning a Pot would be good enough.Everything i know how to do (which isverylimited (basically a 555, a potentiometer and a transistor) would cause it to pulse on/off/on/off or just stay open when the button is pressed (direct wire to the push button).I dont expect a full blueprint (although that would be absolutely fantastic), but just some help getting on the right track would be amazing. What components would I even need to do this?

author: xavier60
author_rank: Super Contributor
timestamp: May 07, 2020, 09:42:57 pm
content: Are you using a bread-board to experiment on?See if you can get this example to work, although it doesn't quite do the correct job.https://www.petervis.com/GCSE_Design_and_Technology_Electronic_Products/falling-edge-triggered-monostable/falling-edge-triggered-monostable.html

author: xavier60
author_rank: Super Contributor
timestamp: May 07, 2020, 11:14:49 pm
content: This should be closer to what's needed.Most of the component values have been picked out of a hat and aren't critical.For example the 10k resistors could be anything from 4.7k to 100k without causing problems.C1 ,R2 and R3 affect the timing adjustment range.The rail bypass, C3 an be just about anything upto 1000uF.A MOSFET would be a better choice for Q1 depending on what you have.I bought a heap of IRF44Z MOSFETs years ago so I'd use that although it's total overkill.Edit: The circuit draws some idle current so might not be suitable for being battery powered.

author: mrmagoo
author_rank: Newbie
timestamp: May 08, 2020, 03:12:28 pm
content: Thanks for the time/effort. I will give it a tryA breadboard is not a bad idea for setting up a prototype/experimenting. I will pick one up.
Basic Circuit Help - Page 1
Forum section: electronics / beginners

author: Adam60
author_rank: Regular Contributor
timestamp: August 22, 2018, 03:54:37 am
content: Can someone explain the current flow in this circuit to me. When the switch is closed, what happens in this circuit? Why am I seeing 5.5V on the base when my input voltage is only 4.5V? I am confused. Maybe it is because I understand everything in conventional theory and not electron theory? I think I understand it but not 100% sure about the voltage.EDIT: I just read that the switch that is closed is a variable capacitance switch. I have not measured the value but I am thinking this may have an effect on the voltage? Any thoughts?

author: rstofer
author_rank: Super Contributor
timestamp: August 22, 2018, 08:35:48 pm
content: What's it supposed to be?Where did it come from?It looks like a code practice oscillator with adjustable tone.Electron theory vs conventional current flow has nothing to do with anything beyond the physics level. Always use conventional current flow!The switch itself isn't 'variable capacitance', it simply changes the oscillator capacitance (I believe).It's entirely possible that when the circuit oscillates, the average base voltage rises up somewhat. I would expect to see an AC signal so if you are measuring DC, you might want to look at AC only on your meter.

author: james_s
author_rank: Super Contributor
timestamp: August 22, 2018, 10:52:04 pm
content: If it is an AC signal, your meter may be lying to you. Unless it is a true-RMS meter I would expect it to read incorrectly on anything other than a 50-60Hz sine wave. Even if it is true RMS it will have limitations and will only be accurate within a certain frequency range.

author: 6PTsocket
author_rank: Regular Contributor
timestamp: August 23, 2018, 08:23:16 pm
content: Quote from: james_s on August 22, 2018, 10:52:04 pmThat depends on the DMM. Some have better AC voltage frequency response than others. My old Tektronics TX3 is pretty flat through the audio frequencies, one of the reasons I bought it. .4% + 2 counts from 40 to 20k.Sent from my SM-G900V using Tapatalk

author: james_s
author_rank: Super Contributor
timestamp: August 23, 2018, 10:26:15 pm
content: The Tektronix TX3 is a true-RMS meter, so yes I would expect it to be fairly accurate over a wider range of frequency and waveforms, that's what True-RMS refers to.
basic circuit troubleshooting question - Page 1
Forum section: electronics / beginners

author: electrohobies
author_rank: Newbie
timestamp: May 28, 2017, 03:42:58 pm
content: I am troubleshooting an op amp based circuit and I notice that the PS drops on the negative rail from -15 to about -9 volts when I power up the circuit. on the other hand the positive supply stays the same (15V). is there a reason behind this issues? could the op amp be damaged and its loading the PS?Thank you

author: xrunner
author_rank: Super Contributor
timestamp: May 28, 2017, 03:47:02 pm
content: Quote from: electrohobies on May 28, 2017, 03:42:58 pmSchematics are helpful, but does the PS drop if you pull out the op amp?

author: electrohobies
author_rank: Newbie
timestamp: May 28, 2017, 03:48:57 pm
content: I did not pull out the opamp just wanted to know if this is an ok behaviour?

author: xrunner
author_rank: Super Contributor
timestamp: May 28, 2017, 03:54:53 pm
content: Quote from: electrohobies on May 28, 2017, 03:48:57 pmI was implying by my suggestion that there was indeed a problem to troubleshoot - but no it's not OK at all.

author: StillTrying
author_rank: Super Contributor
timestamp: May 28, 2017, 05:14:43 pm
content: Sometimesjust some-Ve supply is needed for an opamp circuit so that its inputs and output can work near 0V, and it doesn't matter too much whether it's -15 or -9 volts. But without the schematic who knows.

author: UnkleBidii
author_rank: Contributor
timestamp: May 29, 2017, 08:08:02 am
content: I would test the supply on another load. If it drops on that load then there is an issue with your power rail.
Basic circuits to demo op-amp datasheet - Page 1
Forum section: electronics / beginners

author: LoveLaika
author_rank: Frequent Contributor
timestamp: July 31, 2021, 09:16:03 pm
content: I'm attempting to expand my limited knowledge of op-amps by using LTspice to develop test circuits using op-amps to better understand them. That way, I can observe some fundamentals about op-amps (such as input bias current, input offset voltage, GBW, open/closed loop gain, etc.) and try to learn more. I was wondering, for this first circuit, my attempts to measure GBW via open/closed loop gain, I was wondering if my approach is correct?To summarize, I'm using the AD744 op-amp, with a GBW of 13 MHz (model taken directly from LTspice, no 3rd party model). With a closed loop gain of -1, you expect it to have a constant gain up until 13 MHz. I got around 15 MHz for the point where the gain rolls off. For the open loop gain, I'm not sure if my circuit is correct in order to observe it. Using an AC source with no DC component, how does the op-amp simulate open-loop gain? The input is INM, and the output is FB1, and V4 just injects an AC signal with amplitude of 1 and increase the frequency. How does that translate to an open loop voltage gain plot?
Basic Circut Question - Page 1
Forum section: electronics / beginners

author: sweekly
author_rank: Newbie
timestamp: April 21, 2014, 06:29:08 am
content: Hey guys, if I use this circuit and hook a battery charger to the battery while this circuit is connected, will it damage the components, if so how can I change the circuit to prevent this?

author: Psi
author_rank: Super Contributor
timestamp: April 21, 2014, 09:01:01 am
content: What type of battery is it? and what type of charger do you plan to use?If the battery is a generic NiMh/NiCa/SLA and the charger is a standard trickle or float charger it should all work fine as is.I wouldn't recommend using a pulse charger on it. Or any charger that does battery rejuvenation/reconditioning.

author: sweekly
author_rank: Newbie
timestamp: April 21, 2014, 02:59:56 pm
content: It is a sealed lead acid, however it has a very high Ah rating (around 90 Ah if I recall correctly), I could potentially charge it at up to 20 Ah, the charger will be any standard 4 stage battery charger that will work. Also if anyone knows a way to calculate how quickly different chargers will charge at battery based on amp hours of the charger that would be awesome, so I can select what charger I want to use. I'm undecided currently until I compare price vs time for different chargers.
Basic Comparator Problem - Page 1
Forum section: electronics / beginners

author: wardenclyffe
author_rank: Contributor
timestamp: September 22, 2015, 05:59:01 pm
content: Hey guys,I have a very simple circuit I am trying to use to detect a voltage change off a portable battery powered device. I am using a jellybean LM324 quad pack op amp for a prototype and feeding in 6V to the V- while using the same 6V source to bias the chip. Using another output on my bench power supply, I ran a second voltage into the V+ pin. The circuit works as I expected as the voltage will drop to the ground rail (single supply configuration btw) when the V+ voltage drops below the V-/Vcc voltage. However, this only occurs when the difference between the V+ and V- inputs is greater than 1V. The output will remain high even if V- is 6V and V+ is 5.5V. Can anyone tell me what is going on? Why does it take such a large delta for the comparator to trigger? If it matters, I have a 1Mohm resistor on the output pin acting as a load.Thanks!

author: alsetalokin4017
author_rank: Super Contributor
timestamp: September 22, 2015, 06:05:45 pm
content: How are you measuring the voltages? Are you just using the meters on the power supply, or are you measuring the voltages with a DMM (the same DMM) for both the reference and the signal voltage?

author: wardenclyffe
author_rank: Contributor
timestamp: September 22, 2015, 06:09:00 pm
content: I am using an HP/Agilent 34401 bench DMM to check the voltages from the PSU

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: September 22, 2015, 07:12:41 pm
content: Check out the "input common-mode voltage range" in the data sheet

author: rob77
author_rank: Super Contributor
timestamp: September 22, 2015, 07:48:01 pm
content: as far as i remember lm324 goes down to negative rail , but doesn't go up to positive rail on inputs.. (usually it's vcc - 1,5V). you need a rail-to-rail (input) opamp , or one that reaches to top rail on inputs without problems.

author: C
author_rank: Super Contributor
timestamp: September 23, 2015, 12:34:55 am
content: Or you divide the inputs to a range the Opamp is happy with.C

author: wardenclyffe
author_rank: Contributor
timestamp: September 24, 2015, 07:19:28 pm
content: You guys were completely right. That is what I get for not reading the datasheet.Thanks!
Basic counter in verilog - Page 1
Forum section: electronics / beginners

author: Dmeads
author_rank: Regular Contributor
timestamp: June 07, 2019, 02:40:59 am
content: Hi all!In my simulation picture below, there is a,b,c,d,e ect after the 9 in my counter.Why is this and can anybody help me fix this please?I am doing some research and i think it might be related to roll over?Thanks!You can view my code and testbench on EDA playground:https://www.edaplayground.com/x/5Wjrpicture of simulation below

author: Buriedcode
author_rank: Super Contributor
timestamp: June 07, 2019, 02:43:24 am
content: That would be because it is showinghexadecimalrepresentation of numbers rather than decimal. You have a 4-bit counter, so in decimal it counts 0 to 15 then rolls over to 0 again. 10 in Hex is 'A', 15 is 'F'. Hex is very common and quite handy because a single hex digit represents all possible states of 4 bits (a nibble).

author: Dmeads
author_rank: Regular Contributor
timestamp: June 07, 2019, 02:45:02 am
content: Ah, thank you!So if I implemented some PWM using this counter, it would work okay on the FPGA?It seems to work okay in the simulation

author: Dmeads
author_rank: Regular Contributor
timestamp: June 07, 2019, 02:53:59 am
content: Never mind I answered my own question lol it totally works!
Basic Diode Question on Oscilloscope - AC vs DC coupling - Page 1
Forum section: electronics / beginners

author: johnnystarr
author_rank: Newbie
timestamp: August 02, 2023, 12:51:02 pm
content: I am using the student edition of Multisim to learn basic electronics. A simple circuit with a 120vac 60 Hz supply and a 100 ohm resistor load shows the two figures below. With the Mulitsim scope on DC coupling all looks correct with positive voltage half waves. But on AC coupling, there is a shift in the peak (+) voltage and now it has a negative voltage component to it.Is the negative voltage when AC coupled due to the reverse recovery time? As AC couple, I have changed the supply frequency from 60Hz down to as low as 2Hz and except for the timebase change, the sine wave voltages look exactly as for 60Hz. I read that for typical diodes the Trr is measured in ns or us.Thanks in advance for the help.John

author: johnnystarr
author_rank: Newbie
timestamp: August 02, 2023, 01:19:19 pm
content: Ooops forgot to mention that the circuit has a 1N4004 in series with the resistor load.

author: ledtester
author_rank: Super Contributor
timestamp: August 02, 2023, 01:26:04 pm
content: Here's an explanation from the electronics stackexchange:https://electronics.stackexchange.com/a/173758Basically, in AC coupled mode the zero line represents the "average" of the input signal. See the comments in the first answer for a description of how this "average" is computed.

author: NY2KW
author_rank: Regular Contributor
timestamp: August 02, 2023, 02:40:02 pm
content: QuoteThat sounds correct but it doesn't jive with some repetitive DC pulse work I did recently with my Keysight 3000x scope. Maybe it's not that simple an answer. I used the repetitive pulse training signals at 100Hz and the scope reads it the same either in AC or DC coupled mode, that is all positive, identical signals. If it was just arbitrarily setting the 'average' signal at zero it should shift the pulse train down half-way but thats not the caseJerry

author: Terry Bites
author_rank: Super Contributor
timestamp: August 02, 2023, 02:51:11 pm
content: AC coupled. If there is no offset on the trace, the scope display is correct.Note the areas "under the curve" above and below zero on your scope; they are the same. The waveform centres on at the average of the halfwave voltage.Vav = Vpk/π eqn. 1seefor the derivation of eqn. 1

author: wasedadoc
author_rank: Super Contributor
timestamp: August 02, 2023, 03:11:53 pm
content: Quote from: NY2KW on August 02, 2023, 02:40:02 pmIf the pulse was already AC coupled somewhere before reaching the 'scope, then AC or DC coupling on the scope would make no difference.
Basic, good quality Bench Multimeter - Page 1
Forum section: electronics / beginners

author: Zx Spectrum
author_rank: Contributor
timestamp: January 07, 2019, 06:47:40 pm
content: HelloI am looking for :- not expensive- basic (no fancy features)- sturdy , well build- 4 1/2 countBench multimeteras i mentioned before i need very basic functionality, no fancy features, actually I need the functionality of normal handheld DMM but in a big case just to be able to run it from the mains, i cannot stand the idea of battery-powered DMM.so it should be below 200$ but very sturdy; i want to use it for years to come and don't want to buy another one one or two years later.so what do recommend??please don't recommend any second hand old stuff from ebay; i want my bench multimeter to be brand new

author: Cliff Matthews
author_rank: Unknown
timestamp: January 07, 2019, 07:20:14 pm
content: "very basic functionality" and >40,000 counts sounds like a contradiction. What about buying a pre-calibrated unit on ebay?

author: Zx Spectrum
author_rank: Contributor
timestamp: January 07, 2019, 08:21:55 pm
content: Quote from: Cliff Matthews on January 07, 2019, 07:20:14 pmcould you provide a link to such unit ?

author: Cliff Matthews
author_rank: Unknown
timestamp: January 07, 2019, 08:50:07 pm
content: Quote from: Zx Spectrum on January 07, 2019, 08:21:55 pmYou'll have to search for when units come up, but what's your budget anyway?For hi-rez volts-only you could calibrate a Keithley 181.. and use the front Mv connector with an outboard shunt for amps?https://www.ebay.com/itm/Keithley-181-Nanovoltmeter-1/254052042539https://www.axiomtest.com/documents/models/Keithley%20181%20Data%20Sheet.pdf
Basic level shifter going very wrong - Page 1
Forum section: electronics / beginners

author: Simon
author_rank: Unknown
timestamp: August 14, 2015, 06:55:52 pm
content: I have made this circuit, it should take a 10V input and provide a 24ish V output.for some reason all I get is a constant 24V output. I have loaded the output with 100K but nothing, I can try a base to emitter resistor on the input and did put one on the PNP but to no avail. Odly I only get 7.5V tops on the collector of the NPN transistor.Any ideas ? do i actually have to start using mosfets ?

author: Simon
author_rank: Unknown
timestamp: August 14, 2015, 07:14:46 pm
content: I have done a quick test on a breadboard with just the NPN transistor and pullup resistor and base resistor, I will only get 7.5V peak on the collector, but when the transistor is off it should rise to the 29V supply...

author: Andy Watson
author_rank: Super Contributor
timestamp: August 14, 2015, 07:28:56 pm
content: What is driving the input? I would be tempted to put a pull-down resistor on the base - to be sure.Have you got the Emitter and Collector the right way around?

author: Simon
author_rank: Unknown
timestamp: August 14, 2015, 07:37:59 pm
content: I tried a base resistor, will try turning it over but following datasheet pinout.

author: Simon
author_rank: Unknown
timestamp: August 14, 2015, 07:40:03 pm
content: Yep turning the transitor over worked, suppose i better breadboard the whole thing to make sure the PNP one is up the right way too

author: SeanB
author_rank: Super Contributor
timestamp: August 14, 2015, 07:56:47 pm
content: Load the output with 1k, it should pull down then. Your base emitter resistors will help with leakage, 10k on both transistors will work. It will stay at 24V just from leakage, you will need a pull down in any case.

author: Simon
author_rank: Unknown
timestamp: August 14, 2015, 08:03:52 pm
content: Yea i've loaded output and put BE resistors on both, works now it was just the upside down NPN

author: c4757p
author_rank: Super Contributor
timestamp: August 14, 2015, 08:06:53 pm
content: Quote from: Simon on August 14, 2015, 07:40:03 pmQuote from: Simon on August 14, 2015, 07:14:46 pmThis is a big clue - try to remember it for the future! VEBO- the emitter-to-base breakdown voltage - is around 7V, and flipping it upside down typically causes that breakdown. If you see that voltage on a "collector" when it should be much higher, check the orientation!
basic opamp AC coupling problem - Page 1
Forum section: electronics / beginners

author: RoadRunner
author_rank: Frequent Contributor
timestamp: July 08, 2013, 06:12:01 pm
content: sir, i am trying to do little things with opamp i wired up a circuit like in shown in the image.the problem is , the C4 2uf should clean out any dc offset in the signal , but it doesn't the input signal is same on both side of the cap, but if i apply a very low ~1K resistor instead the R7 1Meg the dc offset is gone.i know opamp is doing something but what?is there any problem with the circuit?

author: Paul Price
author_rank: Super Contributor
timestamp: July 08, 2013, 06:28:29 pm
content: If the 2uf cap is polarized, you probably have connected it backwards and the DC is leaking through.

author: RoadRunner
author_rank: Frequent Contributor
timestamp: July 08, 2013, 06:48:57 pm
content: thank you very much sir , it has solved my problem in the hardware.but i have simulated again with polarized cap in both ways, the simulator didn't show up?

author: c4757p
author_rank: Super Contributor
timestamp: July 08, 2013, 06:50:28 pm
content: The polarized cap in LTspice is just a symbol. It is still an ideal capacitor in the simulation.

author: RoadRunner
author_rank: Frequent Contributor
timestamp: July 08, 2013, 07:23:38 pm
content: thank you for support.

author: jimmc
author_rank: Frequent Contributor
timestamp: July 08, 2013, 08:17:36 pm
content: Over what timescale are you running the simulator?The time constant of 2uF and 1Mohm is 2seconds so after 2 seconds the DC voltage across the 1M resistor will still be 37% of the input.For this to reduce to near zero (<1%) you need to wait at least 5 time constants (10sec).Jim
Basic PLC Analog Input Question - Page 1
Forum section: electronics / beginners

author: am1
author_rank: Contributor
timestamp: April 25, 2024, 07:14:03 pm
content: Hi all,I am using a B&R X20CP0483 system, I am working with a X20AI4222 module (+/-10V) for a simple FSR sensor . I have it wired and working in arduino (see image below for diagram), I have also wired it the same way on my AI mod (A0 is the AI+ pin, and the GND goes to PSU V- and AI-) and have it successfully working. However, since it is a 2 wire device, is there a simpler way to wire this on my PLC (so I can reduce cable wires needed)? DO I need to use the external PSU, or does the module (A+ pin) simultaneously read the signal with power the device. Do I need a load resistor at all, or could it directly be wired to the module?

author: BeBuLamar
author_rank: Super Contributor
timestamp: April 25, 2024, 11:23:17 pm
content: The input of the B&R X20 which is like most other PLC's system. It expects a voltage which in your case from -10 to +10V. The sensor you have is just a resistor and it doesn't generate any voltage. You would have to somehow convert the resistance of the FSR to a voltage. Perhaps part of a voltage divider? Still you will have to do quite a bit of calculation within the PLC because the voltage won't be linear to the resistance of the FSR.
Basic question on audio mixer circuit - Page 1
Forum section: electronics / beginners

author: donturner
author_rank: Contributor
timestamp: February 16, 2017, 12:21:50 am
content: Hopefully this is a simple one: What is the purpose of the 27k resistor at the opamp's non-inverting input? Why wouldn't you just connect directly to ground?

author: danadak
author_rank: Super Contributor
timestamp: February 16, 2017, 12:24:55 am
content: Its the parallel equivalent of the 3 input Rs and is used to minimizeoffset due to bias current the OpAmp inputs need. If left out you wouldsee a DC offset at output of OpAmp.http://www.analog.com/media/en/training-seminars/tutorials/MT-038.pdfRegards, Dana.

author: helius
author_rank: Super Contributor
timestamp: February 16, 2017, 12:40:15 am
content: Op amps drive their output in whatever manner causes the two inputs to be equal. If you tied one of the inputs directly to ground, the opamp would be unable to balance its inputs; the input bias current on the inverting input creates a voltage on the three 100K resistors, but there isn't any voltage on the non-inverting input, because it would be tied directly to the ground rail.This circuit is a "inverting summer". See page A-24 of Texas Instruments' Op Amps For Everyone.

author: Audioguru
author_rank: Super Contributor
timestamp: February 16, 2017, 03:57:52 am
content: The design of the 741 opamp is 48 years old and it was never intended to produce good audio like modern audio opamps do.

author: helius
author_rank: Super Contributor
timestamp: February 16, 2017, 04:40:42 am
content: Quote from: Audioguru on February 16, 2017, 03:57:52 amThe NE5534A is 40 years old and has been used continually during that time in mixer equipment. Age doesn't mean much.

author: b_force
author_rank: Super Contributor
timestamp: February 16, 2017, 04:49:35 am
content: Quote from: helius on February 16, 2017, 04:40:42 amWell, the 5532 or 5534 wouldn't my personal choice for new designs, unless the budget is exmtremely tight.There are enough (audio) opamps out there with better specs and most of all, less Iq.

author: JS
author_rank: Frequent Contributor
timestamp: February 16, 2017, 04:54:36 am
content: When noise is critical a cap could (should) be added bypassing that 27k resistor, so you eliminate the thermal noise of that resistor.In big mixers summing amps are one of the critical noise points, a ton of noise gain to get unity signal gain is calling for problems, so any noise in that non inverting input really gets amplified. For this same reason using as low resistance values as possible is a good practice and is very important the routing of such PCB, specially where that non inverting input is connected to.JS

author: neil t
author_rank: Regular Contributor
timestamp: February 16, 2017, 05:07:34 am
content: danadak said it, bias current offset
Basic Question regarding a peice of 9v AC audio equiupment - Page 1
Forum section: electronics / beginners

author: Unknown
author_rank: Unknown
timestamp: February 13, 2019, 12:30:31 pm
content: Right, so I bought a Midi interface device of Ebay... And they neglected to include the 220/110v Ac to 9V Ac wall-wart...right.. So, the closest thing I have is a 12v AC adapter.... I wonder if there is any chance this could work, or will the 12v fry the 9v circuit for sure?The caps are all rated 35v, there are two 16v caps, one on each of the two phono audio inputs. There is a L7815CV +15v regulator, and a L7915CV -15V regulator. At the input, and at the power-switch there is a L7805CV regulator (L7805CV - Linear Voltage Regulator, 7805, Fixed, Positive, 10V To 35V In, 5V And 1.5A Out, TO-220-3 ).

author: Doctorandus_P
author_rank: Super Contributor
timestamp: February 13, 2019, 01:10:59 pm
content: Small AC wall warts (transformers) tend to have a much higher output voltage under no or a light load. Your 12Vac adapter could easily output 16Vac, and when you rectify that you have around 16 * sqrt(2) = 22.6Vdc Corrected for 2 diode drops of the bridge 21.4V left.So if the caps are rated for 35V you have plenty of headroom there.Another concern is the temperature of your voltage regulators.These will produce more heat when being fed with a higher voltage.They do not have much cooling (just the a(aluminimum?) standoff nut ?) but they likely also do not have to deliver much current.If the voltage regulators get overheated, they lower the current / output voltage.This means that the circuit wont function properly anymore, but it's unlikely anything will get damaged permanently.You could run it for a while and then check the temperature of the voltage regulators.As a rule of thumb if you put a wet finger to it and it doesn't sizzle then it's probably OK, but most prefer to keep their electonics under 70Celcius.Some other things to check, (Even if jus to get more experience with datasheets)Get the datasheets of your voltage regulators (Same ST brand, datasheets from other manufacturers may vary) and check the maximum input voltages.For the 7815 It's probably 35V, but for the 5V regulators it's probably lower, but they are also likely to be fed from the output of the 15V regulators.U14 is probably also an voltage regulator (AMD1117-3V3?)

author: Unknown
author_rank: Unknown
timestamp: February 15, 2019, 09:27:25 am
content: Thanx, I just ordered a replacement psu from a UK store, wrong socket, but it's actually for this very device... Oh.. well extra costs..Geez these things where expensve. I did measure my 12v psu, and as you suggested it output nearly 15.5v no load..

author: Zero999
author_rank: Super Contributor
timestamp: February 15, 2019, 10:25:31 am
content: The LM78/79xx regulators include thermal protection, so won't be damaged if they overheat, just shut down. Try it on 12VAC. It won't do any harm. The worst that could happen is the regulators overheat and shut down, especially if it's in a hot room.
Basic RF circuit design - trace impedance or pi-network?? - Page 1
Forum section: electronics / beginners

author: roogadget
author_rank: Contributor
timestamp: November 18, 2018, 11:52:55 am
content: Michael Ossmann - RF Circuit DesignI am designing an RF antenna at the moment.My source impedance and output impedance (antenna) are both 50 ohm.I have calculated the microstrip impedance to about 50 ohms.Is that all that is required?What about the use of Pi-networks? L-networks..etc??I feel like I'm missing something here.cheers

author: Benta
author_rank: Super Contributor
timestamp: November 18, 2018, 01:21:47 pm
content: If the output impedance of your TX amp, the antenna and the microstrip are all 50 ohms, then yes, that's all for impedance matching. But usually you also want to filter out harmonics of the transmitted signal, depending on modulation type. This might be integrated in the TX amp already, can't say.

author: roogadget
author_rank: Contributor
timestamp: November 20, 2018, 09:36:45 am
content: What do you mean by "filter out harmonics", like EMI??

author: David Hess
author_rank: Super Contributor
timestamp: November 21, 2018, 01:51:40 pm
content: Benta means that the L or T matching network can also operate as a low pass filter to remove harmonic distortion from the amplifier which is commonly required to meet regulatory requirements. So even if matching is not required, a low pass filter likely is.
Basic safeguard - IEC 62368-1 - Page 1
Forum section: electronics / beginners

author: chagli
author_rank: Contributor
timestamp: March 05, 2019, 05:25:24 pm
content: Hello everyone,I am quite new to safety and norm things concerning electronics.I have designed a quite simple AC-DC module (42VAC to 6VDC, full bridge rectifier + cap followed by a buck).The problem is that, following IEC 62368-1, my AC source is ES2 (energy source type 2) and my regulated DC is ES1 (energy source type 1).It also says that I need a basic safeguard between ES1 and ES2.Do you have any idea what kind of component can be used to implement this requirement ?Thank you.

author: perieanuo
author_rank: Frequent Contributor
timestamp: March 05, 2019, 05:50:16 pm
content: Separation (safety) transformer, dcdc isolated module.maybe there are others too...There are industrial areas where more than 24ac is considered dangerous.depends also on country reglementations.like wet working areas like slaughterhouses.That is the meaning of that requirement.Envoyé de mon iPad en utilisant Tapatalk

author: chagli
author_rank: Contributor
timestamp: March 05, 2019, 07:50:04 pm
content: Thanks for your answer. I'll probably go for the smallest isolated DC/DC I can find then.
Basic switch question - Page 1
Forum section: electronics / beginners

author: jy0un9
author_rank: Newbie
timestamp: November 15, 2014, 11:16:11 pm
content: HiFirst post very simple questionI'm trying to change the switch on an old Weller soldering station to a illuminated switch i haveThe old switch has 4 pins (two wires from the plug and two from the transformer) the new switch has 3 pinsCan i use this switch if so what wires do i connect to what pinsAttached two low quality imagesThank you

author: German_EE
author_rank: Super Contributor
timestamp: November 15, 2014, 11:27:15 pm
content: DO NOT USE THIS SWITCHThe old switch was designed to switch mains voltages between the plug and the transformer primary, your replacement switch is designed to handle 12 volts and (almost certainly) contains a 12v bulb inside to indicate when the contacts are closed.Please go back to your local retailer and ask for a Double Pole MAINS RATED switch.

author: jy0un9
author_rank: Newbie
timestamp: November 15, 2014, 11:30:16 pm
content: Thanks alot
Basic toy ski lift. - Page 1
Forum section: electronics / beginners

author: garygav
author_rank: Newbie
timestamp: November 19, 2014, 01:29:23 am
content: Hi I have basically no knowledge of electronic circuitry so I am looking for some advice on the most simple way of constructing a motorised ski lift as a moving christmas decoration.I basically want it so that a motorised pulley will pull little cardboard ski lifts up and down in opposite directions. I want them to travel one way for a certain number of seconds and then reverse direction.I would appreciate if someone could point me towards something I could put into a simple battery pack and maybe two of these motors,http://www.jaycar.co.uk/productView.asp?ID=YG2741&form=CAT2&SUBCATID=983#1 , circuit that would auto reverse the motor direction every few seconds.Apologies for the terrible sketch attached i'm just in a rush at the moment.
Basic Transformer Experiment - Page 1
Forum section: electronics / beginners

author: Time
author_rank: Frequent Contributor
timestamp: June 20, 2014, 05:09:26 pm
content: I am playing around with a simple 1:1 transformer that I made. It consists of 1 turn on the primary and 1 turn on the secondary.I am charging up a 100 nF capacitor on the primary and letting it discharge through a resistive load on the 2ndary. It all seems normal with a little bit of loss in voltage but seemingly normal.The strange thing that happens though is when I go to to discharge the capacitor through the transformer with an inductance on the 2ndary instead of the resistance. Quite a bit of voltage is loss, about half but it appears to ring out correctly. Why does this operate correctly under the resistive load (up to the V-s rating of the core) but not under the oscillating/inductive condtion?The values I am using are 100 nF on the primary, 200 Ohm resistance, and 500 nH inductance.I feel like the answer lies in basic knowledge of transformers which I don't know much about just yet.

author: RazSlack
author_rank: Contributor
timestamp: June 21, 2014, 10:51:30 am
content: I think your answer might lay in the reactances of your inductor. The impedance (AC resistance at a given frequency) of your inductor might be much lower than the resistor's actual DC resistance on the frequency you discharge it on.Check the impedance here against frequency. You see that a resistor is pretty constant over the frequency range, while inductive reactance raises with frequency, capacitive reactance drops with frequency

author: Time
author_rank: Frequent Contributor
timestamp: June 21, 2014, 04:02:05 pm
content: Cool, thanks for the response. I actually figured out what the issue was. My leads on the 2ndary were quite long with a small cross section. The parasitic inductance was significant at the ringing frequency of ~1 MHz. I figured this out by shortening them as much as possible and using some flat copper strips I had laying around.

author: MrFarag
author_rank: Newbie
timestamp: August 28, 2015, 05:36:29 am
content: RazSlack : Plz send me a refrence for your graph Thanks
Basic Transister Tester Circuit - Page 1
Forum section: electronics / beginners

author: queennikki1972
author_rank: Regular Contributor
timestamp: May 01, 2019, 07:11:03 pm
content: I can confirm this little circuit works. I thought it was perfect for me since I'm just starting out. I know the wires are a mess, I like to jump them on the top for now. I added hot glue to the 3 pin holes to hold it better after I took the picture. Green is good, Red is Bad, Red and Green is Open.

author: Old Printer
author_rank: Frequent Contributor
timestamp: May 01, 2019, 07:26:43 pm
content: I think it is nicely done. Some of the wires could be a little shorter, but I am loath to cut wires to the minimum as well. I like the 3D printer battery holder and base-plate. May I ask where you found the circuit?

author: queennikki1972
author_rank: Regular Contributor
timestamp: May 01, 2019, 07:32:57 pm
content: I forgot the link.https://www.elprocus.com/simple-transistor-tester-circuit/
Basic Transistor Circuit - Page 1
Forum section: electronics / beginners

author: Thirtyniner
author_rank: Newbie
timestamp: October 15, 2014, 01:08:08 pm
content: Good afternoon!I have spent many hours reading about transistor circuit theory but I am still confused so I have come here for some much-needed help!I want to use a 12v, 20ma (max) source to switch on an array of 12v devices with a 12v supply and ground.I figure I can achieve this with (let's say) a 100ohm relay, requiring 120ma to energise. Not wanting to load my source too much, would it be a safe bet to find a transistor that will saturate at 5ma, thus needing Hfe > 24?Furthermore, will a high-side switching circuit be the best format for what I want?And what value of resistor do I place between my source/input and the transistor base:One that will limit it to 5ma?One that will limit it to 20ma?Or somewhere in between?I would appreciate any and all input as this has been racking my brain for days and the more I read the more confused I become.Thanks,Oliver

author: w2aew
author_rank: Super Contributor
timestamp: October 15, 2014, 02:13:20 pm
content: Quote from: Thirtyniner on October 15, 2014, 01:08:08 pmWe need more information.What type of "devices" are you powering up?Do they need to be grounded when off (thus need high side switching)?What is going to drive or control the transistor?

author: Thirtyniner
author_rank: Newbie
timestamp: October 15, 2014, 02:58:06 pm
content: Thanks for your reply. I shall divulge...I have an Audison Bit One (12V Digital Signal Processor for automotive use) which outputs a 'trigger' for turning on multiple amplifiers, fans and a 12V DC-DC USB charger (down converts to regulated 5V for powering a Nexus 7, USB hub, powered hard drive).Problem is, this trigger is limited to 20mA. I want the 'best' (read: easy and efficient) way of achieving this, basically.Having reconsidered, there isn't any reason this circuit can't appear on the low side. I've been looking for relays with a higher coil resistance but the most common type that are easily accessible are around 80-90ohm, with capacity to switch 30-40A which is right on the money.I hope that helps!Thanks again.

author: mrkev
author_rank: Regular Contributor
timestamp: October 15, 2014, 06:15:46 pm
content: It looks like one power mosfet (like f.e. IRF530, AP23xx, IRLMxx) should be enough. You won't even need whole 20mA, and whole swich can be done with just that mosfet and one resistor between gate and ground to discharge... That is if you don't mind that in the off state, your DC/DC switch is connected just to +12V.

author: IconicPCB
author_rank: Super Contributor
timestamp: October 15, 2014, 08:56:32 pm
content: Check out Omron G5V-2-12VDC relay. Coil resistance in high 200s.
Basic Transistor question - Page 1
Forum section: electronics / beginners

author: Everton
author_rank: Contributor
timestamp: November 08, 2013, 04:07:10 am
content: I am playing with some basic transistor circuits and seem to be having a problem getting theory to match practice and simulation alike!I have built the common emitter amplifier seen below and am not getting the expected base bias of about 15V.Here is my thought process:1 - Set Quiescent current to 15 mA2 - Calculate V Emitter needs to be 15V3 - Set V Base at approx 15V4 - Impedance looking into base = hfe * RE = approx 100k so I selected 10K resistors for my voltage divider to get about 15V.When I simulated (and built this) I got V base at ~5V. What gives?I redid the same circuit with a quiescent current of 1mA and everything seems to work as expected. Does the impedance looking into the base not equal hfe*RE as quiescent current goes up?

author: c4757p
author_rank: Super Contributor
timestamp: November 08, 2013, 04:32:07 am
content: If there is 15V on the base, then there is 14.35V on the emitter resistor, giving 14.35mA quiescent. Good so far. But if there is 14.35mA flowing through the 10k collector resistor, it must drop 143.5V, which it obviously cannot do, so instead the transistor saturates. The base-collector diode becomes forward biased as it tries as hard is it can to pull the collector downward, and this draws extra current from the base and drops the base voltage.You have to either lower the quiescent current or lower the collector resistance.

author: KJDS
author_rank: Super Contributor
timestamp: November 08, 2013, 08:19:38 am
content: You should aim to get the collector to half the supply voltage by setting the base voltage to something suitable.If you want to keep the emitter and collector resistors as they are, then you'd have 1.5mA across the collector resistor, (from 15V and 10k) and that current will also flow through the 1k resistor, causing 1.5V drop across it so the voltage at the emitter is 1.5V. Add 0.7V for Vbe and the base voltage needs to be set to 2.2V using the resistors on the left of the circuit.

author: Everton
author_rank: Contributor
timestamp: November 08, 2013, 02:44:29 pm
content: Does zeroes get me every time!For some reason I was thinking that 15mA through 10K would give a 15V drop. Sorry for the dumb mistake.Thanks guys.