hybridfree/eevblog-posts huggingface dataset:
Voltage regulator - Page 1
Forum section: electronics / beginners

author: neo
author_rank: Super Contributor
timestamp: October 24, 2016, 10:00:45 pm
content: What happens if the adjust pin gets positive voltage? lm338k

author: Andy Watson
author_rank: Super Contributor
timestamp: October 24, 2016, 10:09:45 pm
content: Positive ?With respect to what ?

author: Cliff Matthews
author_rank: Unknown
timestamp: October 24, 2016, 10:10:11 pm
content: PLS name part number in question...

author: neo
author_rank: Super Contributor
timestamp: October 24, 2016, 10:17:36 pm
content: lm338k i think i might have fried it testing it, test circuit below, positive with respect to ground. I would like to note this is to-3 package so me acidently confusing pin 1 and 2 is nowhere near as dumb as it sounds

author: Cliff Matthews
author_rank: Unknown
timestamp: October 25, 2016, 12:00:47 am
content: Drawing's a bit up-side-down, but this layout for current limiting. Did you see any smoke?It will try to maintain 1.25v across R1 and if R1 was a low enough value, you may have fried that pot.

author: neo
author_rank: Super Contributor
timestamp: October 25, 2016, 12:02:55 am
content: no smoke but it is hermetically sealed steel after all, and that should be a voltage regulating circuit ive used it before r1 was a hundred ohms

author: Cliff Matthews
author_rank: Unknown
timestamp: October 25, 2016, 12:25:47 am
content: Hook it up as a standard regulator to a 12v low current wall-wart and see what you get.Also Google "lm338k fakes", since lots of these are fakes from China.

author: neo
author_rank: Super Contributor
timestamp: October 25, 2016, 12:39:34 am
content: mine are old made in america ones, or were perhaps i broke them. How do you suggest hooking it up i took that straight from the datasheethttp://www.st.com/content/ccc/resource/technical/document/datasheet/group1/07/c7/47/cb/15/f7/4b/ec/CD00000548/files/CD00000548.pdf/jcr:content/translations/en.CD00000548.pdf

author: Cliff Matthews
author_rank: Unknown
timestamp: October 25, 2016, 01:02:07 am
content: It's a PITA to break those.. in my local, these are $10 each. Keep it simple, 12vdc in, R1=240, R2=1K and you should get ~6v out.

author: neo
author_rank: Super Contributor
timestamp: October 25, 2016, 03:09:42 am
content: well i feel like an idiot but im going to say it anyway as a message for the new players reading this, NOTHING is infallible if it works when you test it 5 times but doesnt in circuit test it in circuit, the voltage regulator wasnt working because the second current was applied the resistor, previously infallible, failed i changed that pot for a different one and the problem is instantly solved. Though in all fairness i started this thread for ideas as much as i did out of annoyance (when i posted i had just finished two hours of being teased by that pot)
Voltage regulator for micro amp loads - Page 1
Forum section: electronics / beginners

author: lk
author_rank: Regular Contributor
timestamp: August 01, 2011, 06:33:29 pm
content: Greetings,im building a pic12f683, light on sensor ting, and as im running it off a solar panel and a battery i would like to have the amp draw as low as possible, but now i have run into the interesting problem that i cant really figure out how to regulate the power for those small loads, the two regulators i have looked at, lm317t and lm2576, data sheet indicate that the minimum load is 10 miliamps, and my pic with voltage dividers is only drawing something like 65 micro amps at around 2.1 volts, so for now im just running the pic of a voltage divider, which im guessing will cause me problems down the road.my input voltage is between 11.8 and 13.8.I did try searching digikey, but it kept not returning any results.So could someone point me to the the regulator i should use-lk

author: ejeffrey
author_rank: Super Contributor
timestamp: August 01, 2011, 06:45:58 pm
content: Try searching for a 'micropower regulator'I come up with the linear technology LT1020, the national semi LP2952, and the analog devices ADP1720 that all have low quiescent currents. However, be warned: this is the sort of application where you have to really dig into the data sheet to see what the typical and worst case quiescent current is for your exact use case. It will vary from the nominal value with the input voltage and output current.

author: IanB
author_rank: Super Contributor
timestamp: August 01, 2011, 07:19:48 pm
content: You might get some ideas from here, concerning power management chips:

author: deephaven
author_rank: Frequent Contributor
timestamp: August 02, 2011, 07:59:07 am
content: How about the ON Semi MC78LC00 series?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 02, 2011, 08:53:40 am
content: There are plenty of micropower LDOs with quiescent currents of a couple of microamps. A few of my favorites are Holtek HT71xx (unusually high input range up to 24V) and Microchip MCP1700 and MCP1702 (Latter has wider input range)

author: eliocor
author_rank: Unknown
timestamp: August 02, 2011, 10:54:11 am
content: For low quiescent current I used the TI TPS62120 chip (some thousands used to this date).It works really well and even its price is not too high.

author: tecman
author_rank: Frequent Contributor
timestamp: August 02, 2011, 07:03:00 pm
content: For light loads like this, I use an op-amp with a reference diode. Either inverting or non-inverting configuration (depends on what you need for output) and a couple of R's and a C or two will do it. Low power and can be made very accurate.paul

author: lk
author_rank: Regular Contributor
timestamp: August 03, 2011, 08:02:28 pm
content: Thanks for all the replies with pointers, now i have something to work with-lk
Voltage regulator inrush current - Page 1
Forum section: electronics / beginners

author: LaserTazerPhaser
author_rank: Regular Contributor
timestamp: September 14, 2019, 08:48:27 pm
content: Is there any method to implement soft start into this regulator?With small filter cap & load current the overvotlage is large, however with larger caps and high load current there isn't any over voltage however over voltage can occur rapidly if load varies. The current surges during startup and will likely also surge during changes in load current.vreg.asc(2.89 kB - downloaded 68 times.)

author: ledtester
author_rank: Super Contributor
timestamp: September 14, 2019, 09:04:01 pm
content: Posting an image would help out everyone.

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 14, 2019, 09:42:11 pm
content: Quote from: LaserTazerPhaser on September 14, 2019, 08:48:27 pmYeah, by not using a freaking 555 timer as your controller; you might as well use a potato.

author: ledtester
author_rank: Super Contributor
timestamp: September 15, 2019, 05:31:24 am
content: It's only going to last for 40us... is that going to be a problem?

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 15, 2019, 09:56:16 am
content: Quote from: ledtester on September 15, 2019, 05:31:24 amInrush in the boost can be a problem if it causes the inductor to saturate and the switch starts switching at that time.And note (to the OP) that inrush is unavoidable in the boost converter because of the direct connection between the input and output, but in low power converters like this it is frequently ignored or only addressed by slowly ramping up duty cycle (because a saturated boost inductor will allow peak current to go too high). In commercial boost PFC stages some of the inrush current is routed around the inductor via another diode in parallel to it, and at higher power levels a conventional precharge resistor with relay/switch bypass is typically used.
Voltage Regulator - Selfmade? - Page 1
Forum section: electronics / beginners

author: Flunze
author_rank: Regular Contributor
timestamp: September 07, 2012, 06:47:27 am
content: I just wonder, if there is any way, to create your own Voltage Regulator.Just a circuit, that does the same job. Put in anything and get out a clean Voltage, as long as there is enought input. I mean, some digital sort of VR's are possible by measuring the voltage trhough a cap and instantly charge it up, if it drops 0.5 mV or more. But is there a way to do it simple? All the Regulators for higher currents can not give you high voltage. If I want a Regulator for 90 Volts DC Output at 16 Amps, I cannot do anything, cause they do not exist.I would need 2 Pieces: +90V and -90V. Is there any way to do that sort of job?

author: kripton2035
author_rank: Super Contributor
timestamp: September 07, 2012, 07:05:23 am
content: some help here :http://www.romanblack.com/smps/smps.htm
Voltage Regulator Thermal Dissipation - Page 1
Forum section: electronics / beginners

author: NivagSwerdna
author_rank: Super Contributor
timestamp: September 21, 2017, 04:06:37 pm
content: Given a regulator such as NCP1117 providing 100mA @ 5VIf I provide the regulator with say 6.2V, 9V or 12V or 20V etc. how does that affect the thermal dissipation? i.e. does it get hotter the higher the input voltage?I looked at the datasheet but can't puzzle that out. I would expect that I should supply nearer to 6.2V than 20V? (1.2V max dropout)Thanks in advance

author: rdl
author_rank: Super Contributor
timestamp: September 21, 2017, 05:28:37 pm
content: Dissipation in watts for a linear regulator is Vin - Vout x IThe higher the input voltage the more power must be dissipated as heat.

author: cdev
author_rank: Super Contributor
timestamp: September 21, 2017, 05:42:03 pm
content: I have a related question about voltage regulation and heat in a GPSDO controller context which I think I'm going to post in its own thread, maybe in the metrology section.

author: Zero999
author_rank: Super Contributor
timestamp: September 21, 2017, 06:23:54 pm
content: Quote from: rdl on September 21, 2017, 05:28:37 pmCorrected: you forgot the brackets.Yes, the higher the input voltage, the higher the power dissipation.Although it's usually negligible, the current flowing out of the regulator's 0V pin can be significant too. Especialy in low drop-out regulators, when the output voltage is fairly close to the input voltage. This normally isn't a matter for thermal design. It's more important when dealing with power consumption.

author: Damianos
author_rank: Frequent Contributor
timestamp: September 21, 2017, 06:24:59 pm
content: I think that it is better to answer by yourself. It needs just a little thinking.A linear voltage regulator is a box that somehow observes the output voltage and tries to keep it stable, by adjusting the conductance from input to output. Lets say that someone inside measures the output voltage and adjusts a resistor that the input with the output. This creates a power loss that converted to heat.The input power is Pin= Vin* IinRespectively the output power is Pout= Vout* IoutAlso according to the above description the Iinis about equal to the IoutThe power loss is the difference of the above two. Calculate it.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: September 21, 2017, 11:23:15 pm
content: Thanks for the responses.Looking at a related datasheet I found...PD = (VIN – VOUT) IOUTTJ = TA + PD (omegaJA)and a no heatsink 65 °C/WI think that probably tells me what I need to know.Thanks
Voltage Regulator Trouble (Solved) - Page 1
Forum section: electronics / beginners

author: laus
author_rank: Contributor
timestamp: June 07, 2018, 04:55:08 am
content: I circuit I build doesn't work as expected. Full 13V was on sections where I'd expected 5V and 3.3V from the voltage regulators.So I went back to he basic an tested a new LP2950-33LPRE3 volt regulator by itself. Low and behold I didn't get the voltage regulator do its thing. With and without the electrolytic capacitors the output voltage is just a little bit below the input voltage. I tried it with 13V and 5V. Measurements were taken with a multi meter. Otherwise there was no load.Specs:https://www.mouser.com/ProductDetail/texas-instruments/lp2950-33lpre3/?qs=iSMark9AYDUagDsOL8Eqdw%3d%3d&countrycode=US&currencycode=USDWhat am I doing wrong here?

author: JS
author_rank: Frequent Contributor
timestamp: June 07, 2018, 05:05:12 am
content: Is your device ok fpr 13.6V input? 10V drop? At the requested current?Regulators need a minimum load to dp their thing, try 1k resistor from output to ground and test again, maybe try a second regulator in case they were fried, double check the pinout.JSEnviado desde mi LG-M250 mediante Tapatalk

author: laus
author_rank: Contributor
timestamp: June 07, 2018, 05:18:55 am
content: Quote from: JS on June 07, 2018, 05:05:12 amThanks,I added a 10k resistor from output to ground. Not really any difference with that.This is my second regulator I'm testing with and the pinout looks good to me.

author: JS
author_rank: Frequent Contributor
timestamp: June 07, 2018, 05:24:51 am
content: So you are probably wiring it backwards, note that the datasheet shows the package from the bottom, your drawing looks backwards, try them again in the other direction, but they might be fried.JS

author: laus
author_rank: Contributor
timestamp: June 07, 2018, 05:29:44 am
content: Quote from: JS on June 07, 2018, 05:24:51 amDoh! Thank you. Yes, I did wire them backwards.Claus

author: JS
author_rank: Frequent Contributor
timestamp: June 07, 2018, 05:34:21 am
content: Yeap, I double and triple check and always look for the picture description, as they are not always clear, I don't know who looks the components from the bottom!!!I love the 3D view as firchaild do, doesn't look so professional but you never miss a pinout because you thought it was the other way around.http://pdf.datasheetcatalog.com/datasheet/fairchild/LM317.pdfEven texas sometimes show components from the top, sometimes from the bottomIt fries components so maybe it makes the sells go up.Nobody will read this post ever again, so people will keep making the same mistaeJS
Voltage regulator vs. resistor for lowering voltage? - Page 1
Forum section: electronics / beginners

author: Elf Six
author_rank: Newbie
timestamp: January 30, 2014, 01:16:59 am
content: Hi guysThis is a sort of general question. If a voltage is to be lowered from, say,40V or 50V to 12V or 20V for a short duration, would a voltage regulatoror a resistor(cement high-W) be best? What are the pros and cons, anddo either induce any time of delay?I assume that the 78xx will be plenty for lamps etc, but can they also drivea strong 20V coil? Aren't they about 1 amp?Any insight is welcomeThanks

author: Rerouter
author_rank: Super Contributor
timestamp: January 30, 2014, 01:54:14 am
content: The voltage regulator has a limited current capacity, and as most globes are lower resistance when cold the surge could be more than it could handle without a npn or similar to dump the wattage and handle the current (look at a lm317, they have example circuits of this)the resistor is fine if your not concerned with it being be all and end all accurate, just be aware those cement resistors may be rated at a few hundred degrees for full load, and i have seen them desolder themself from the wires feeding in,

author: AG6QR
author_rank: Frequent Contributor
timestamp: January 30, 2014, 05:17:32 am
content: The problem with a resistor is that it obeys Ohm's law. In other words, the amount of voltage drop that it produces is proportional to the current. That might work if you have a steady input voltage and a steady current, but if not, your output voltage is likely to vary widely.A voltage regulator uses active elements and feedback loops to produce a relatively constant output voltage, regardless of variations in current, and regardless of variations in supply voltage, as long as you stay within the limits of the data sheet. A linear regulator sort of behaves like an automatic adjustable resistor, where the automatic machine watches the output voltage and quickly adjusts the resistance to provide the specified output voltage.Yeah, the 78xx is good for about an amp, when properly heatsinked. You can use a pass transistor (or several) to provide additional current capacity.Going from 50V or so to 20 V or so means dropping around 30V. At an amp, that's going to be around 30W. That's a lot of power to get rid of. You're getting into territory where a switching regulator is probably a better fit, though it has its own set of issues to deal with.
voltage regulators protection circuit - Page 1
Forum section: electronics / beginners

author: khatus
author_rank: Regular Contributor
timestamp: November 18, 2022, 02:17:58 pm
content: Hi, guys I want to know what is the purpose of the transistor Q2 in this circuit.I think it acts as a bridge between Q1 and the voltage regulator and balances the current between them. If the droop across RSC is higher then Q2 starts conducting and thus cuts the input current to the transistor Q1 and supplies current to the voltage regulator.

author: Grandchuck
author_rank: Super Contributor
timestamp: November 18, 2022, 02:52:03 pm
content: Rsc drop turns on Q2 and Q2 shunts R1 when on to limit the drive to Q1. So, the effect is to protect Q1 from a shorted output load.

author: khatus
author_rank: Regular Contributor
timestamp: November 18, 2022, 03:46:04 pm
content: But I think, in that case, the whole short circuit current flows through the voltage regulators???

author: wasedadoc
author_rank: Super Contributor
timestamp: November 18, 2022, 03:57:34 pm
content: No, the short circuit current is limited. If most of the current is passing through Q2 the voltage drop across R1 is not enough to make Q1 conduct. If Q1 is not conducting then there is no drop across Rsc and Q2 is not conducting. So there is some balance point where the total current through Q1 plus Q2 is limited.

author: MasterT
author_rank: Frequent Contributor
timestamp: November 18, 2022, 05:29:39 pm
content: Quote from: khatus on November 18, 2022, 03:46:04 pmDon't worry, most voltage regulators have current limits circuits built-in. Q1 doesn't, this is why Q2 needed.
Voltage scaling and shift with opamps - Page 1
Forum section: electronics / beginners

author: mrkva
author_rank: Unknown
timestamp: June 15, 2013, 09:53:11 am
content: Hello,I am trying to design a circuit to shift 0-5V AC signal to -/+5V range. So far I have came up with two methods. One is classic summing amplifier, where I sum the the signal with -2,5V and then give the output 4x gain (because of the summing). This however (as I understand) has quite high input impedance. My other solution is differential amplifier setup. The scheme speaks for it self.Any tips? The second option is more clean, but requires -1,666V voltage reference.Thanks for any help!

author: Paul Price
author_rank: Super Contributor
timestamp: June 15, 2013, 01:32:35 pm
content: Use the top picture non-invert but adj. the resistors to whatever value you want. If you want low impedance use low valued resistors. You can also always terminate the signal at the signal coming into the + input resistor to get whatever low valued impedance you want. You can set any reference voltage you want by using a potentiometer to a stable voltage source and feeding it into the offsetting resistor as in the non-invert schematic shown.

author: mrkva
author_rank: Unknown
timestamp: June 15, 2013, 02:38:55 pm
content: Thanks! Can you maybe quickly note what is wrong with the bottom solution (except inverting)?

author: Paul Price
author_rank: Super Contributor
timestamp: June 16, 2013, 04:20:09 am
content: Nothing wrong with inverting if you want it but adj. of the offset would also vary the gain by changing the feedback.

author: Harvs
author_rank: Super Contributor
timestamp: June 16, 2013, 05:53:10 am
content: If it's a purely AC signal as you say, why not just AC couple it with a cap into a standard inv or non-inv amp configuration with the required gain?

author: mrkva
author_rank: Unknown
timestamp: June 16, 2013, 06:50:41 am
content: Unfortunately it is not purely AC.
Voltage signal multiplying\dividing - Page 1
Forum section: electronics / beginners

author: Alex30
author_rank: Regular Contributor
timestamp: September 21, 2014, 08:46:01 am
content: So I have a circuit where a 10 volt reference signal comes in and then I have an inline 10K resistor and a 10K pot going to ground in order to vary the signal between these two resistors from 0->5 V to control a comparator.This 0->5V signal actually refers to a 0->3A current limit I am setting up.So I want to take that 0->5V signal and multiply it by a factor of (3/5) so I can throw that number on a voltmeter to display what I have set the current limit to. Obviously this means I cannot degrade the signal at all otherwise it will screw up the comparator. What is the best way of accomplishing this?Thanks

author: Rerouter
author_rank: Super Contributor
timestamp: September 21, 2014, 08:53:30 am
content: Use an op amp, one as a buffer so you do not load your signals, driving a voltage divider, and your voltmeters impedance should be high enough that you could throw a resistor dividor on the output for the voltmeter, or use a second op amp to properly divide the buffered signal down if you want the lowest possible power consumption,

author: Alex30
author_rank: Regular Contributor
timestamp: September 21, 2014, 09:42:54 am
content: Excellent thanks that worked

author: Alex30
author_rank: Regular Contributor
timestamp: September 21, 2014, 12:22:00 pm
content: Say there isn't a way to subtract 20mV from that signal without using more opamps is there?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 21, 2014, 01:47:08 pm
content: Just another voltage divider; compensate for its loading effect in the previous divider, or buffer the signal.Subtraction can be done by raising ground, if you can do this with your voltmeter. Otherwise, op-amp I guess (you don't need another, just tweak the inputs with a little bias current).Tim

author: Alex30
author_rank: Regular Contributor
timestamp: September 22, 2014, 02:41:43 am
content: Doh, why didn't I think of that? I'm already using a voltage reference in my circuit so I should be able to just divide that down to 20mV and run the voltmeter across these two signals. I think the mark of experience is just seeing these things in the simplest way. Thanks for that

author: macboy
author_rank: Super Contributor
timestamp: September 24, 2014, 01:02:47 pm
content: Quote from: Alex30 on September 21, 2014, 12:22:00 pmYou might also consider taking a good look at your grounds... where are you connecting the low side lead of the measuring meter? Do you have any resistive losses (V = I*R) contributing an extra 20 mV on that line? It should have a dedicated connection to the low side of the 0-5V voltage divider.You should also consider using a "precision" opamp. These are designed to introduce less DC offset for applications like this.
LTSpice Voltage source minimum parameters - Page 1
Forum section: electronics / beginners

author: GreyArea
author_rank: Contributor
timestamp: September 04, 2020, 08:34:22 pm
content: I was taking a look at Dave's Hakko mod video and thought I might have a go at coming up with a circuit using different Bi-colour LED types. I have a CAC type.I moved from the DC Operational voltage view to a transient view where I tried to put a voltage controlled switch as S1 & V2 to simulate an open collector transistor.For some reason, I get the error"V2 requires a minimum of 5 parameters, only 3 were specified", even though in this videoonly having 3 seems fine with a .tran directive.While I'm here, any comments on the circuit would be welcome - presumably theres a thread on this somewhere but I wanted to have a go myself before looking for "the answer" so to speak.

author: Ian.M
author_rank: Super Contributor
timestamp: September 04, 2020, 10:12:22 pm
content: He's using LTspice IV (version 'four'), and you are probably using LTspice XVII (version 'seventeen') which seems to do more stringent parameter checking. Its *STUPID* and probably a design fail that you need to specify a fall time for a step function that will never fall, but that's the way it is.I wouldn't do it that way as using voltage controlled switches result in a cluttered schematic For simple timing functions I use abehavioral resistoras a function of time, (overriding the type of the current controlled switch symbol to make it a resistor). or for anything more complex I use a current controlled switch so i can place the control source remotely. Seehttps://www.eevblog.com/forum/beginners/ltspice-and-mechanical-switch-problem/for details.I also note you haven't selected models for the coloured LEDs, so their Vf will be very unrealistic. These generic LED models may help:Code:*Typ IR LED from optocoupler: Vf=1.2V @10mA.model LED0 D (IS=1p N=1.999644 RS=0 BV=6 IBV=10u+ CJO=10p EG=1.424 TT=500n)*Typ RED GaAs LED: Vf=1.7V Vr=4V If=40mA trr=3uS.MODEL LED1 D (IS=93.2P RS=42M N=3.73 BV=4 IBV=10U+ CJO=2.97P VJ=.75 M=.333 TT=4.32U)*Typ RED,GREEN,YELLOW,AMBER GaAs LED: Vf=2.1V Vr=4V If=40mA trr=3uS.MODEL LED2 D (IS=93.1P RS=42M N=4.61 BV=4 IBV=10U+ CJO=2.97P VJ=.75 M=.333 TT=4.32U)*Typ BLUE SiC LED: Vf=3.4V Vr=5V If=40mA trr=3uS.MODEL LED3 D (IS=93.1P RS=42M N=7.47 BV=5 IBV=30U+ CJO=2.97P VJ=.75 M=.333 TT=4.32U)*Typ small White LED: Vf=3.2V Vr=5V If=35mA.MODEL LED4 AKO:NSSWS108T

author: GreyArea
author_rank: Contributor
timestamp: September 04, 2020, 10:54:44 pm
content: Thanks for the comprehensive answer!Yes, I could see the video was old but and thought it might be something like that, obviously I'm at beginner level but it did seem unintuitive. I'll take a look at the current controlled switches..Thanks for the LED models too
Voltage Sources and Series Resistor - Page 1
Forum section: electronics / beginners

author: geratheg
author_rank: Regular Contributor
timestamp: October 09, 2014, 11:54:53 pm
content: Shown in the attachments is a circuit with the ground given, I hope I converted it to the second circuit correctly with the ground in the correct location of the circuit. I would like to know what the voltage across the resistor is?Since the ground is there I would assume 0V. If ground wasn't labeled, I would choose 5V. Which voltage is correct with ground there?Thanks!

author: Rufus
author_rank: Super Contributor
timestamp: October 10, 2014, 12:06:52 am
content: The voltage across the resistor is 5v (+5 if the resistor polarity markings mean something). Where or if a ground is connected to the circuit makes no difference.

author: geratheg
author_rank: Regular Contributor
timestamp: October 10, 2014, 12:11:03 am
content: Doesn't connecting the ground to the other side of the circuit the same thing as connecting the negative there, thus causing a short?

author: Rufus
author_rank: Super Contributor
timestamp: October 10, 2014, 12:37:33 am
content: Quote from: geratheg on October 10, 2014, 12:11:03 amCurrent flows in loops. Your circuit has one loop. A ground symbol implies a connection to the earth. That doesn't create another loop so the current in your circuit is not changed regardless of if or where the ground is connected.In more complex circuits it is common to call one of the nodes ground (without it actually needing it to be connected to the earth). Voltages in the circuit are often stated and measured with respect to that ground. The node you call ground doesn't change the circuit but does change voltages measured with respect to ground. You just asked what the voltage across the resistor was.

author: geratheg
author_rank: Regular Contributor
timestamp: October 10, 2014, 01:43:22 am
content: Thank you for the response.I didn't realize DC circuits can have an earth ground and always assumed the ground was actually the negative battery terminal.Thanks for the help.
Voltage Spike? - Page 1
Forum section: electronics / beginners

author: hotpointer
author_rank: Newbie
timestamp: April 15, 2015, 08:18:55 pm
content: Hellocould somebody look at the circuit diagram attachedthe problem i am having is intermittently the Atmega chip resets ...this only happens when the relays are d energised supplying the two solonoid valvesi think that maybe its a voltage spike ... i do have the circuit protected by flyback diodes(1N4004)5volts to the relay ...........12volts to the valvesany ideasthanks

author: HalfSpace
author_rank: Regular Contributor
timestamp: April 15, 2015, 09:48:48 pm
content: Hi hotpointer,Does the micro reset if you disconnect the solenoid valves and just have the relays switching?Having the flyback (Back EMF) diodes for the solenoids and relays is good, but their effectiveness is governed by the PCB layout and GND connections. A large current can flow through these diodes during flyback and the PCB tracks going to them can develop a voltage difference along their length. This voltage on the GND connections may be reducing the 5V supply long enough for the brown out detection circuit in the micro to generate a reset.Can you post a picture of the PCB layout?HalfSpace

author: hotpointer
author_rank: Newbie
timestamp: April 15, 2015, 10:14:03 pm
content: Hithanks for your reply i will take a picture and posti have just been told i have no decoupling on the atmega would adding caps help?i will try with the valves disconnected.rgds john

author: kizzap
author_rank: Unknown
timestamp: April 16, 2015, 05:52:01 am
content: Quote from: hotpointer on April 15, 2015, 10:14:03 pmIt will help 1000x. No decoupling means that any voltage spike/drop will cause the chip to reset. 100nF(0.1uF) caps on the V+ pins will help immensely.
Voltage supply circuit with current sinking capability - Page 1
Forum section: electronics / beginners

author: DanioIO
author_rank: Contributor
timestamp: December 02, 2014, 06:49:05 am
content: Hi,How can i make a LDO voltage power supply, which can also work as constant current sink if the connected device voltage exceeds the power supply output?

author: void_error
author_rank: Frequent Contributor
timestamp: December 02, 2014, 01:44:12 pm
content: If you provide more details (input voltage, output voltage, output current) I might be able to give you a solution.

author: DanioIO
author_rank: Contributor
timestamp: December 02, 2014, 04:20:36 pm
content: I need something working from 30V and the output voltage should be min. 15V, output current isnt very important i will be happy with 1A.

author: Zero999
author_rank: Super Contributor
timestamp: December 02, 2014, 08:54:28 pm
content: Then it's relatively simple. You need a voltage reference connected to a push-pull amplifier.

author: macboy
author_rank: Super Contributor
timestamp: December 02, 2014, 09:04:15 pm
content: More explicitly, look at using a power op-amp such as LM1875 (3875 for more power), amplifying a voltage reference like TL431. You don't need symmetric supplies for the op-amp, -5V is enough for the negative supply, our use single supply (neg supply is ground) if the output never needs to go below about 5V.
voltage switch for bluetooth - Page 1
Forum section: electronics / beginners

author: pwsn
author_rank: Newbie
timestamp: March 04, 2016, 09:25:25 pm
content: Hi all,I'm trying to convert the buzzer from a kitchen timer into a switch for a bluetooth headset. I figure a capacitor would be able to smooth out the voltages changes in the buzzer, and an NPN would be able to act as the switch.The problem comes in that if the switch is kept on for longer than 8 seconds, the bluetooth will enter pairing mode and won't connect. How would I be able to open the switch with voltage and close it after a time delay even when voltage is still supplied?

author: michaeliv
author_rank: Frequent Contributor
timestamp: March 04, 2016, 09:42:25 pm
content: 555 timer circuit or arduino. What power sources do you have available, what's the max allowed power consumption ?

author: pwsn
author_rank: Newbie
timestamp: March 04, 2016, 09:46:32 pm
content: I have 3 volts from 2 AAA batteries. was hoping to fit all the components back into the kitchen timer.it seemed like such a simple task in the beginning

author: michaeliv
author_rank: Frequent Contributor
timestamp: March 04, 2016, 09:53:20 pm
content: It could be simpler, You can probably do it with 1-2 MOSFETs, a capacitor and 2-3 resistors, but will only be able to draw/check the schematic later.

author: michaeliv
author_rank: Frequent Contributor
timestamp: March 04, 2016, 10:16:33 pm
content: Also, do you have shared ground / power between the timer and bluetooth device ?If not, may also want to check what resistance the bluetooth device considers a press being made (by adjusting a potentiometer and see at what value a press begins).

author: pwsn
author_rank: Newbie
timestamp: March 04, 2016, 10:54:16 pm
content: I do have a shared power source

author: michaeliv
author_rank: Frequent Contributor
timestamp: March 05, 2016, 09:04:26 am
content: Attached is a circuit that might work. I say might because it depends on how the bluetooth button actually works ( connects a positive voltage to ground, etc ) and how the piezo buzzer is driven, if it even has enough voltage to charge the capacitor, if not you want to amplify it with another transistor. Also on what resistance the bluetooth device recognizes as pressed vs not pressed.Depending on all of those you're going to want to choose different values for the cap, resistors + different MOSFETConnect piezo on the left, and bluetooth button on the right.

author: pwsn
author_rank: Newbie
timestamp: March 06, 2016, 12:12:31 am
content: i'll need to order that pchannel mosfet and give it a try. thank you!
Voltage switch - selection of component values - Page 1
Forum section: electronics / beginners

author: Maciek12
author_rank: Newbie
timestamp: April 29, 2020, 10:57:48 am
content: Could someone help me choose the value of the elements in this key? I am total begginer and I don't know how to start with it.I want the 5V power supply to turn on when the voltage on the battery will be below 3.3V.

author: Ian.M
author_rank: Super Contributor
timestamp: April 29, 2020, 12:42:10 pm
content: Quote from: Maciek12 on April 29, 2020, 10:57:48 amNo, because that circuit is incapable of doing what you want. Q1 starts to turn on when its Vbe reaches about 0.6V. Until that point its emitter is held at 0V by R3. It then acts as an emitter follower, with a voltage drop from the input dependent on its load current, gain and the value of R1. Once Q2 Vbe reaches about 0.6V it starts to turn on and depending on its gain and the value of its base resistor R2, increasing the input voltage may cause it to draw enough current to short out the 5V supply. As a whole it doesn't have a 3.3V switching threshold and as far as it works (which wont be very well) has the opposite action to that you desire.Quote from: Maciek12 on April 29, 2020, 10:57:48 amTo meet your stated objective, you need some sort of a comparator circuit with a 3.3V threshold, driving a transistor as a switch, in series with the 5V supply, (or possibly in series with the ground to your load if its acceptable to leave its supply connected all the time and switch the ground). How to implement that depends on the parts you have available or can easily obtain, the accuracy required (and whether or not it needs a 'snap' action), the quiescent current you can afford for the circuit's operation, and the maximum load current.
voltage to bidirectional current converter - Page 1
Forum section: electronics / beginners

author: DanKalc
author_rank: Newbie
timestamp: February 16, 2014, 10:14:22 am
content: Hi,How to build a constant current generator from (-1mA to 1mA) controled by voltage. Google gives me links only to one direction current converters mainly 0-20mA. Is there a way to decaple DC from a current? I need my current source to measure impedance using 4 leads, so the current dont have to flow to GND but from lead1 to lead2.Anyone got any idea how to build something like that?

author: SeanB
author_rank: Super Contributor
timestamp: February 16, 2014, 10:21:46 am
content: Use a differential input amplifier to do the sensing, that way you just use a current source to the ground of the supply. That is very common.

author: Andy Watson
author_rank: Super Contributor
timestamp: February 16, 2014, 10:44:42 am
content: Look up Howland Current Source. You will need a pair if you want to avoid ground - they need to be matched and perfectly balanced.
voltage to current converter circuit analysis - Page 1
Forum section: electronics / beginners

author: manjunath
author_rank: Contributor
timestamp: December 03, 2014, 09:46:25 am
content: Hi all,I am new to electronics circuits and i know basics about the Op-Amp. I need to know how the voltage across inverting terminal changes wrt voltage change across non inverting terminal.Please help me to analysis the attached circuit.Thanks.

author: tggzzz
author_rank: Super Contributor
timestamp: December 03, 2014, 10:07:15 am
content: Quote from: manjunath on December 03, 2014, 09:46:25 amGeneralstartingprinciple with any opamp circuit that is operating "normally": the output does whatever is necessary to ensure that the inverting and non-inverting inputs are at the same voltage. If they aren't then the output voltage will be the (very high) open-loop gain times the voltage difference.There are many many introductions to opamps on the web; google is your friend.

author: manjunath
author_rank: Contributor
timestamp: December 03, 2014, 11:30:45 am
content: ya i have gone though some basics about op amp. Here my doubt is for a voltage above 1.7V across non inverting terminal i can able to get both inverting terminal and non inverting voltage at same value (I think at this time gives high output voltage) and for a voltage level below 1.7V across non inverting terminal i am getting a voltage of 2.5V across the inverting terminal. Why i am getting this difference ?

author: Seekonk
author_rank: Super Contributor
timestamp: December 03, 2014, 02:41:04 pm
content: R3 is going to have the drive current & the transistor current.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 03, 2014, 08:01:21 pm
content: What is the arrow at the base of R3? That doesn't look like a Multisim standard.Tim

author: IanB
author_rank: Super Contributor
timestamp: December 03, 2014, 08:14:14 pm
content: Quote from: T3sl4co1l on December 03, 2014, 08:01:21 pmIt looks like the numeral 4 overlaid on top of the line?
voltage usage question - Page 1
Forum section: electronics / beginners

author: willbanks
author_rank: Contributor
timestamp: July 14, 2017, 03:08:42 am
content: i have a 12V 3A switching psu. i want to turn it into a lab psu with multiple outputs.if i make a circuit that makes 12V into 5V, can i still make a separate output for the 12V?basically i know if i attach a load to a psu it takes away current, but does it take away voltage too?

author: MK14
author_rank: Super Contributor
timestamp: July 14, 2017, 03:19:43 am
content: You can connect as many things as you like, to the 12V supply. As long as the total current draw, is no more than 3 amps.So if your 5V supply (derived from the 12V), used up to an amp, from the 12V side.The 12V supply, could supply up to another 2 amps.EDIT:So to be clear. A power supply, keeps its output voltage (e.g. 12 volts), as long as the total output (load) current, is no more than it can handle. E.g. 3 Amps.I.e. NO voltage is lost/removed, by other uses of the output.

author: willbanks
author_rank: Contributor
timestamp: July 14, 2017, 05:50:43 am
content: thanks for the clarification!
VoltAlert picks up desk lamp from 50 cm away, crashes printer - Page 1
Forum section: electronics / beginners

author: mixiom
author_rank: Contributor
timestamp: January 22, 2022, 08:38:44 pm
content: Hello! On my desk is a desk-lamp and a 3D-printer ("Ender"). The moment Iswitch the lamp on or off, many times the 3D-printer crashes and restarts. The desk-lamp is a "Class II appliance", meaning itdoes not have a earth cable. The VoltAlter function of my multimeter, which senses AC voltage, beeps at 50 cm distance from the desk lamp (off), which to me indicates a nonexistent shielding. My theory is this: the unshielded cable of the desk lamp makes its metallic armsact as antenna. When the lamp is turned on/off, change of current increases that electric field and the 3D-printers mainboard, which does only have aplastic case, picks up that field and overloads/crashes. I omitted that other devices on my desk, for example a lab power supply, also at times cause the printer to crash at turn on/off events.Is this reasonable thinking? I also wonder if there is aelegant solution. At the moment I am thinking about a DIY metal enclosure for the printers mainboard, that seems best, or am I missing something?

author: Manul
author_rank: Super Contributor
timestamp: January 22, 2022, 10:02:02 pm
content: There is something wrong with 3D printer board. It should not be so sensitive. Maybe some digital lines are floating or pullup resistors are too high value. Maybe it picks up interference from external wiring, maybe some wire is disconnected. Hard to say, only you could investigate.

author: mixiom
author_rank: Contributor
timestamp: January 24, 2022, 12:36:33 am
content: Is there a nice way to trigger such interference related problems in a controlled way, without having to turn my lamp on/off hundreds of times? I am not sure how to actually investigate the matter.

author: SmallCog
author_rank: Frequent Contributor
timestamp: January 24, 2022, 01:37:22 am
content: Does moving the 2 apart have an affect?

author: Vtile
author_rank: Super Contributor
timestamp: February 07, 2022, 08:10:16 pm
content: As above.Are the lamp using a tungsten lamp or some energy saving bulb? If you measure the lamp metal frame with voltage meter it does propably have several tens of volts of potential difference to ground. This is normal for a such lamps and the value depends the input impedance of meter. If you then connect a meter with current measurement (equivalent to short circuit) between ground and lamp body it should read zero or a few microamps.

author: Terry Bites
author_rank: Super Contributor
timestamp: February 10, 2022, 10:53:57 am
content: Have you tried a Common mode ferrite on the lamp lead?https://www.google.co.uk/url?sa=i&url=https%3A%2F%2Felectronics.stackexchange.com%2Fquestions%2F320733%2Fwhat-exactly-happens-to-the-signals-hitting-a-common-mode-choke&psig=AOvVaw02DMe3MyFMa51jNWXIUwCR&ust=1644576793979000&source=images&cd=vfe&ved=0CAgQjRxqFwoTCKiHj4_89PUCFQAAAAAdAAAAABAF
Voltcraft DSO 1022 M oscilloscope - Page 1
Forum section: electronics / beginners

author: viorelcaia
author_rank: Newbie
timestamp: December 21, 2022, 10:51:12 pm
content: Hey there!I just bought a ''new'' old Voltcraft DSO 1022 M oscilloscope..working great so far..but I can't find any info, no manuals or software..can you give a hint? Thanks!!

author: viorelcaia
author_rank: Newbie
timestamp: December 22, 2022, 09:35:33 pm
content: I just found it ! It's the same like UNI-T UT2025B Digital Storage Oscilloscope 25MHz.
Voltmeter with Multiple Input - Page 1
Forum section: electronics / beginners

author: MARSHALBSB
author_rank: Contributor
timestamp: July 31, 2014, 08:04:28 pm
content: Hello Everyone... I need some help here...I want to switch the input of a voltmeter to measure different Power Source by selecting the input on a select button.... The same to current...What kinda solution I can use to do it...?

author: omgfire
author_rank: Regular Contributor
timestamp: August 01, 2014, 06:33:42 am
content: Keithley 199rotary selector switch
Volts / Turns - Transformer winding question - Page 1
Forum section: electronics / beginners

author: made2hack
author_rank: Frequent Contributor
timestamp: May 28, 2015, 06:27:27 pm
content: Hey,So as per my previous topic post regarding a1kVA transformerI'm rewiring, I have some issues with the primary and secondary winding.As perLudens Transformers & Coils, I should be using roughly 412 - 495 turns per 220V. 412 volts assuming 1.2 Tesla and 495 assuming 1 Tesla. Since I don't know the quality of the lamination, I will assume the crappier 1 Tesla coefficient. I used the calculation as follows: 220V / 4.44 / 0.002m2 / 50Hz / 1T (or 1.2 T).When I look at the primary and attempt to estimate the number of turns, I get approximately 620 - 660 turns. There are around 70 turns per layer, 8 layers (560) + around 60 turns on the last layer. This would indicate around 620 turns / 220 V (or close to 3 Turns / 1 Volt).When I wound 9 turns to form a secondary, I was getting roughly 2.6V on the secondary, which seems to uphold the 3 Turns / Volt theory. However, I only assembled the E Core, without really clamping it down too hard. Thus, lots of vibration. Could this loose me 1-2 Volts? Should I use the calculation of 2 - 2.5 Turns / Volt and not the apparent 3 - 3.5 turns / volt?I don't want to wind all my secondaries and then find out I messed up.

author: made2hack
author_rank: Frequent Contributor
timestamp: May 28, 2015, 06:46:37 pm
content: OK,So I redid the test today, same 9 turns on the secondary but this time I bolted the EI core and significantly reduced the vibration. I am now getting a relatively stable 4.2V on the secondary.Or, as the math suggests, 2.2 turns / volt.
Volume control circuit for Balanced Signal  - Page 1
Forum section: electronics / beginners

author: Jbliss
author_rank: Regular Contributor
timestamp: January 18, 2016, 06:01:21 am
content: Volume control circuit for Balanced Signal using a double ganged pot? what value would you recommend?

author: Dave
author_rank: Super Contributor
timestamp: January 18, 2016, 01:34:06 pm
content: The one that smells like raspberries.

author: tggzzz
author_rank: Super Contributor
timestamp: January 18, 2016, 02:06:25 pm
content: Quote from: Jbliss on January 18, 2016, 06:33:09 amSee thesehints.

author: Zero999
author_rank: Super Contributor
timestamp: January 18, 2016, 02:49:50 pm
content: A bit more patience wouldn't go amiss either. Bumping your thread because no one answered within half an hour is just rude. Sometimes it can take a couple of days for the person who knows the answer to log on and post. Most people here have a life outside this place.
Volume control encoder - Page 1
Forum section: electronics / beginners

author: nicksydney
author_rank: Regular Contributor
timestamp: January 17, 2015, 11:18:15 am
content: Hi,Thinking of playing around with a volume control kind like in a amplifier system but in my case want to drive LED (something like thishttp://designshack.net/images/designs/ui-volume-control.jpg). What I'm a bit confused is the normal potentiometer that are used in Arduino project are something like this (http://www.ebay.com/itm/1PCS-KY-040-Rotary-Encoder-Module-Brick-Sensor-Development-For-Arduino-/201190586723?pt=LH_DefaultDomain_0&hash=item2ed7e4b963) which is coarse in terms of turning it and not as smooth as volume control in amplifer, was wondering where can I find this kind of volume control thingy and what is it called actually ?. Googled around rotary enconder it came out mostly like the one on ebay link.Cheers

author: JuKu
author_rank: Frequent Contributor
timestamp: February 05, 2015, 07:08:38 pm
content: It is still a rotary encoder, just nicer.You are looking for a detent-less ball bearing optical rotary encoder. The nice ones are expensive. Bourns is one compane making these.
Volume control, using opto couplers, nead help to calculation. - Page 1
Forum section: electronics / beginners

author: FriedMule
author_rank: Frequent Contributor
timestamp: January 05, 2020, 04:35:58 pm
content: Hi I am trying to build a volume control that controls two opto couplers per channel.The two opto couplers have to work in reverce of each other, to maintain impedance.I have copied the 1A current source that Dave designed in one of his videos. The volume control is slammed together by me, so I hope it works.Each side is a copy of the other. I have tried to build a current divider to be amble to adjust from 0.1uA to 50uA while still having a larger current to run trough the pot. The second pot on the current divider is a multi turn that can be adjusted by a screw, it's for fine adjusting the exactly value needed.I know the formula for the current divider, but I do get lost when I try to calculate what happens, what values I get when turning on the volume control. Also how much current to run, the Dave-design, gives 1A.