hybridfree/eevblog-posts huggingface dataset:
Validate my noise simulation - Page 1
Forum section: electronics / beginners

author: Atomillo
author_rank: Regular Contributor
timestamp: April 04, 2021, 11:20:25 am
content: Hello to all:I'm recently designing a CSA for a X-Ray fluorescence project. I decided to simulate a circuit that has already been employed for a similar result (https://physicsopenlab.org/2017/06/22/x-ray-spectroscopy-with-pin-photodiode/) using OrCAD (because it's the program I'm using at uni). I asked for a Noise simulation with the current source I1 as the I/V source, and the Out node as the output.Because I'm not interested in the original noise spectrum, but instead in what results after passing the signal through a low-pass and high-pass filter with the same time constant (1us), I take the value provided by NTOTAL (ONOISE) (which is in V^2/Hz, right?) and multiply it by the module squared of the resulting transfer function (tau*w)^2/(1+((tau*w)^2))^2 using the following command:PWR(2*pi*Frequency*PWR(10,-6),2)/PWR((1+PWR(2*pi*Frequency*PWR(10,-6),2)),2)IfI understood this correctly, I now have the spectrum that results from the pulse shaping network in V^2/Hz units. I now take the square root of this to get a V/Hz spectrum, and integrate this to get the total RMS noise.The question: where did I screw up? (Because of my inexperience with both noise design and OrCAD, it's fair to assume I *did* screw up even if I don't know where!)Many thanks!
Validating anti static mat - Page 1
Forum section: electronics / beginners

author: sairfan1
author_rank: Frequent Contributor
timestamp: February 20, 2019, 09:31:19 pm
content: I bought anti static mat from ebay, when i check resistance any two points on the mat its always zero (no ready on meter)I was wondering then how current will flow through, does it mean that its low quality useless mat??thanks.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: February 20, 2019, 09:42:30 pm
content: You probably mean resistance is very high (inf) instead of zero.These thinks cant' be measured with a standard DMM.They need something similar to an insulation tester, which outputs a high voltage (500V or 1000V) and meaures curren then.These mats act a bit similar to a varistor, and they do not conduct current at low voltages.You can try using a piezo electic spark generator (such as in a regular lighter) on it.But I haven't tried that. Keep electronics away from such a thing though.

author: wraper
author_rank: Unknown
timestamp: February 20, 2019, 09:43:22 pm
content: QuoteThose two things are mutually exclusive. And you won't be able to measure any resistance by just sticking 2 probes.https://youtu.be/gqcv58nAd70

author: wraper
author_rank: Unknown
timestamp: February 20, 2019, 09:47:30 pm
content: Quote from: Doctorandus_P on February 20, 2019, 09:42:30 pmYou can do it with multimiter with a decently high upper resistance range, at least if mat resistance is on the low side. However you'll need 2 largish and heavy electrodes, not just sticking 2 probes.
validity of double probing - Page 1
Forum section: electronics / beginners

author: electrolust
author_rank: Unknown
timestamp: April 06, 2017, 08:30:25 pm
content: Keysight recommends in AN 5989-7894EN to double probe, to see the effects of your probe on risetime. Daniel also gave this recommendation in one of the livestreams for scope month recently. You probe once, save the waveform, then attach another probe and see what the difference is.How accurate is this method? I mean is it reasonable or would there be considerable error. ISTM you are doubling the capacitive probe load, so at least with a resistive circuit load it's reasonably accurate. (With capacitance in the circuit load, the effect of the 2nd probe is less than double so you can probably account for that.)

author: ebastler
author_rank: Super Contributor
timestamp: April 06, 2017, 09:08:16 pm
content: Yes.
Value of matching and very tight spec 1% 1/4 W resistors - Page 1
Forum section: electronics / beginners

author: SharpEars
author_rank: Unknown
timestamp: October 19, 2014, 06:01:21 pm
content: I have three 1% metal film 100 ohm resistors that measure dang near exactly 100 ohms on a pretty well calibrated 6.5 digit meter (i.e., 100.000 ohms), with a little lead trimming of each to well within what is needed for it to be mounted on a circuit board. So, aside from the fact that the threesome measure 100 ohms, they're a matching triplet. What is the value of a set like this above and beyond the usual 1% metal film resistor cost of something like ten US cents each?I am just wondering if they're valuable or not?Update: I've also got a pair of 180 ohm and a pair of 5.6 MOhm, that are spot on.

author: Simon
author_rank: Unknown
timestamp: October 19, 2014, 06:05:15 pm
content: as they are probably from the same manufacturing batch it is no surprise. At room temperature it's not unusual that they be "perfect", can you guarantee the resistance over time and at all temperature ranges ? just because they are 1% does not mean they are expected to measure +/-1% that often at room temperature when brand new.

author: SharpEars
author_rank: Unknown
timestamp: October 19, 2014, 06:10:30 pm
content: Quote from: Simon on October 19, 2014, 06:05:15 pmInteresting, so these were measured at room temperature (i.e., 70 degrees F = 21 degrees C) and they are a couple of weeks old. So, there is possible drift over time and possible drift over temperature in-line with that of metal film resistors. So, I suppose that is all that can be guaranteed. I am wondering what the premium on these resistors is within those constraints.

author: Zero999
author_rank: Super Contributor
timestamp: October 19, 2014, 07:07:54 pm
content: They're probably worth no more than any1/41% resistor which isn't much: under a cent each in quantities of 1000, from a typical distributor.

author: Simon
author_rank: Unknown
timestamp: October 19, 2014, 08:34:44 pm
content: Just because you have found them to match under certain limited non repeatable circumstances does not mean they will be as matched in the future and adds no value to them unless your a qualified test house that can carry out proper testing. I'm sure that if there are trully so good the manufacturer would have already sold them as less than 1% tolerance.

author: rob77
author_rank: Super Contributor
timestamp: October 20, 2014, 05:06:55 am
content: drift over time, drift with temperature and drift after "burn-in" is guaranteedthose resistors got no special value, it's pretty common to find "spot on" resistors within a bunch of 1% ones.
Values for RC network - Page 1
Forum section: electronics / beginners

author: Psburg
author_rank: Newbie
timestamp: September 17, 2020, 01:46:38 am
content: Trying to figure out what capacitor and resistor value (and wattage rating) is needed for this on a 110v 15A outlet? (or just open ended without the inductor)Do I just use Ohm's law to get the resistor value (=7.3Ω)? and the wattage rating, V x I (1650W?)?

author: ledtester
author_rank: Super Contributor
timestamp: September 17, 2020, 02:50:55 am
content: What exactly are you trying to do? C and R can be anything, but supposedly you want certain values to accomplish some task.And is this a homework problem (which is ok) or a project?

author: bob91343
author_rank: Super Contributor
timestamp: September 17, 2020, 04:41:23 am
content: It appears to be a simple circuit, amenable to ordinary analysis. Perhaps if you explain what you want we can show you how.My keyboard is a pain when it comes to equations so I won't try to type them here. But you have two series impedances, one is the capacitor and the other is the parallel combination of a resistor and an inductor. The capacitor will pass current at 60 Hz, which is omega = 377. The reactance of the inductor is equally simple.

author: Psburg
author_rank: Newbie
timestamp: September 17, 2020, 05:59:40 am
content: Sorry I should have explained, I just want the 90 degree phase shift this is supposed to produce.

author: ledtester
author_rank: Super Contributor
timestamp: September 17, 2020, 07:19:05 am
content: Are you familiar with the "Element Impedance" table on this page:https://www.electronics-tutorials.ws/accircuits/series-circuit.html

author: Vovk_Z
author_rank: Super Contributor
timestamp: September 17, 2020, 03:08:22 pm
content: Quote from: Psburg on September 17, 2020, 05:59:40 am+90 degr. shift or minus 90 degr. shift? And in what exact wire?To current was shifted by 90 degree there must be only an inductor (without the resistor and the capacitor) or only capacitor (without the resistor and the inductor). Only a voltage source and a one reactive element.

author: Psburg
author_rank: Newbie
timestamp: September 17, 2020, 07:12:32 pm
content: + or - 90°, either would work, but not looking for a current offset from voltage like with an inductive load, but both offset 90° from the main line, I think it is called transient response or time delay?
varactor identification ? (Shyamalan twist its a zener (048J)) - Page 1
Forum section: electronics / beginners

author: algorithm
author_rank: Regular Contributor
timestamp: May 11, 2024, 02:08:32 am
content: So I have a varactor diode in a to-92 package.Im unable to find any documentation, so I have no idea what value it is.Its either04BJBB23BUOr048J88238UOther possibilities I guess are 238V?Though searching all arrangements have failed on my end.Any varactor specialists out there?(It looks more like B than 8 to me through my jewelers loupe)Thanks : )

author: algorithm
author_rank: Regular Contributor
timestamp: May 11, 2024, 06:10:35 am
content: I found other varicaps named "BBXXX" but somehow cant find what I have.If I test the capacitance on my fluke it reads thousands of microfarads. Reversing the leads I get a few microfarads.In diode mode I get a good diode reading 1 way, reversed leads I get 1.2v drop like 2 diodes. I am not sure it is a varicap but its a to92 package with only 2 legs so I figure it is. I tried googling again and found results that didnt show hours earlier but it still didnt help as it only listed "bb238 varicap" but "n/a" for brand. Weird...

author: algorithm
author_rank: Regular Contributor
timestamp: May 11, 2024, 08:40:40 am
content: Searching more, repeatedly, somehow found something! Though I still have no datasheet. Electronics-Today-1989-03.pdf - World Radio HistoryIf I copied the link it was a google redirect so for those curious search that pdf and flip to page 49, well 50, the diy radio project lists "048J 1.26v ref" as d2.I still am unsure what it is, but its something.Pretty cool magazine it seems. Ill have to look at this whole issue later. I wish I could have partook in the electronic magazine era.EDIT: actually im not so confident this reference is right, the layout diagram depicts d2 like a normal diode, and the schematic shows a zener symbol.Are zeners made in to92 with 2 legs? If it was a zener how could they get away with no polarity mark? (My part has no polarity denoted afaik)EDIT 2: its a zener...
Variable Circuit Breaker for Circuit Development? - Page 1
Forum section: electronics / beginners

author: JacobEdward
author_rank: Regular Contributor
timestamp: March 20, 2015, 12:43:36 am
content: I'm curious if there exists such a device that acts like a circuit breaker (a fuse that switch's off at a certain voltage or current), but is adjustable like a potentiometer and can be rated down to low voltages and currents like 1V to 60V for circuit development purposes? That would be pretty cool.

author: PeterFW
author_rank: Frequent Contributor
timestamp: March 20, 2015, 12:48:08 am
content: I think that i migh not have understood the question because you describe a common lab power supply.

author: JacobEdward
author_rank: Regular Contributor
timestamp: March 20, 2015, 12:52:43 am
content: Quote from: PeterFW on March 20, 2015, 12:48:08 amA lab power supply would essentially be the other side of the coin, vary the voltage instead of breaking the circuit.

author: PeterFW
author_rank: Frequent Contributor
timestamp: March 20, 2015, 01:31:17 am
content: Quote from: JacobEdward on March 20, 2015, 12:52:43 amA decent power supply can disable the output when a set load is reached.You can set the power supply to 650mA and when the target circuit draws above 650mA it will shut down.Same for the output voltage, if the output voltage in constant current mode gets above the set voltage it will shut down.

author: JacobEdward
author_rank: Regular Contributor
timestamp: March 20, 2015, 01:33:34 am
content: Quote from: PeterFW on March 20, 2015, 01:31:17 amWhat if you need to develop something with more voltage sources than your power supply offers and you don't want to buy/build another power supply?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 20, 2015, 08:09:44 am
content: I've got something like that,http://seventransistorlabs.com/Fuse/Tim
variable dc power supply design - Page 1
Forum section: electronics / beginners

author: shibas
author_rank: Newbie
timestamp: July 10, 2013, 08:30:20 am
content: How can i build a variable dc power supply variable from 0 volt to 150 v?

author: airiclenz
author_rank: Contributor
timestamp: July 10, 2013, 08:59:27 am
content: Do you just want the schematic?...you need to give some additional details regarding your requirements to the final PSU. Where do you live (110V mains or 230V?), what amp-range should it cover? Do you need a clean output or can it be s switching PSU? ...Airic

author: mariush
author_rank: Super Contributor
timestamp: July 10, 2013, 09:40:05 am
content: Quote from: shibas on July 10, 2013, 08:30:20 amWith patience and carefully not to kill yourself ... kinda of a stupid question.Here's the design of a 0-120v 1A linear power supply, simplifying it to use regulator potentiometers only and adapting it for 150v wouldn't be such a big problem if you know the basics:
Variable DC power supply to Variable AC power source? - Page 1
Forum section: electronics / beginners

author: windsmurf
author_rank: Frequent Contributor
timestamp: March 31, 2019, 08:32:44 pm
content: Is it possible to build an AC power source by using a DC power supply and powering something like this?https://www.ebay.com/itm/DC-to-AC-Converter-12V-to-110V-220V-AC-150W-Inverter-Pre-Boost-Board-Transformer/271988347042I'm not sure if I'm seeing a voltage regulator on the board which might limit output to 110VAC or if this board will allow continuously variable AC voltages... I'm also hoping that this board will allow me to change frequency from 60Hz to variable (e.g. 5 Hz, 250 Hz, etc) using a pot perhaps?Other ideas... I have a signal generator that can generate signals up to 5V... can I feed this through something to create a variable AC output at higher voltages?

author: pelule
author_rank: Frequent Contributor
timestamp: March 31, 2019, 08:48:52 pm
content: What you are asking for is a inverter. Generating asinousodial (AC) signla with variable frequency out of a DC voltage. Thats the typical application to drive an AC motro (just in multipla pases. So you need an H-Bridge and a controller harrdware, able to control the H-Bridge in the right frequency and varaible DC levls to build a sinousodial output./PeLuLe

author: MrAl
author_rank: Super Contributor
timestamp: March 31, 2019, 08:52:57 pm
content: Quote from: windsmurf on March 31, 2019, 08:32:44 pmHi,What you are referring to is called a VFD or "Variable Frequency Drive". They are not that simple to build so if you have never built a DC power supply you would find it very difficult to build one of these which is much more sophisticated.When i worked in the industry we manufactured these things as well as single frequency units.
Variable delay nanopulser - Page 1
Forum section: electronics / beginners

author: Srg
author_rank: Newbie
timestamp: January 28, 2019, 04:11:58 am
content: Can anyone tell me about this unit. What it was used for and what it can be used for?Thanks for any help

author: Zero999
author_rank: Super Contributor
timestamp: January 28, 2019, 09:16:37 am
content: It's a pulse generator.It can be triggered by an external signal or generate a square wave, depending on the settings.

author: David Hess
author_rank: Super Contributor
timestamp: January 29, 2019, 07:35:54 pm
content: The high voltage on the "width" connector indicates that it is an avalanche pulse generator and the width is controlled by an external charge line.The sync output and delay indicate to me that among other things it was intended to be used with sequential sampling oscilloscopes that require a pretrigger signal.

author: GonzoTheGreat
author_rank: Regular Contributor
timestamp: January 30, 2019, 10:30:42 am
content: Quote from: David Hess on January 29, 2019, 07:35:54 pmI know this unit. Yes it is used as a pretrigger in older scopes but the generator is based on a DSRD - not on an avalanche breakdown.
Variable Frequency Current Source ? - Page 1
Forum section: electronics / beginners

author: alin_im
author_rank: Regular Contributor
timestamp: June 29, 2017, 05:59:14 pm
content: Hey guys,Can I use a function generator as a variable frequency current source ?If yes, how ?I want to model a photodiode to test a transimpedance amplifier and I need a variable frequency current source and a capacitor in parallel. The frequency rage is between 10 - 100 MHz and the current between 10 - 100 uAAlin I.

author: alm
author_rank: Super Contributor
timestamp: June 29, 2017, 06:18:00 pm
content: Sure, a voltage source in in series with a sufficiently large resistor (compared to the load) behaves like a current source (Thevenin/Norton). However, given the frequencies involved and the currents, I see problems.To have a decent amplitude accuracy at 100 MHz, you would want your load impedance as seen from the generator to be close to 50 Ohms. This would require a transimpedance amplifier input impedance well below 5 Ohm, but would require voltages down to 500 uV. And obviously the capacitor in parallel will screw up your frequency response (depending on the value). So I doubt it would work particularly well.Maybe if you calibrate your system over its frequency range. And regulation will not be amazing due to the low source impedance. Maybe coupling the signal through a transformer could improve matching and regulation?

author: alin_im
author_rank: Regular Contributor
timestamp: June 29, 2017, 06:27:41 pm
content: My generator and my input impedance are 50 ohm, I was thinking of using a 1V peak to peak and a 10 kohm in series to obtain 100 uA current source, do you think it would work ?

author: alm
author_rank: Super Contributor
timestamp: June 29, 2017, 06:59:35 pm
content: Only if your cables are extremely short or you do not care about voltage accuracy. Try it: connecting the generator to a 10 kOhm resistor with a coax cable. Then vary the frequency and observe the voltage at the 10 kOhm resistor with a 10x scope probe. The behavior will be very similar to an unterminated transmission line, since the impedance of the 10 kOhm resistor is very large compared to the 50 Ohm impedance of the generator and cable.

author: Dave
author_rank: Super Contributor
timestamp: June 29, 2017, 10:30:43 pm
content: You could always terminate the coax with 50R right next to the input of your DUT and just connect a 10k resistor from the 50R terminator and DUT input. The additional 10k termination is barely going to affect the 50 ohm termination.

author: alm
author_rank: Super Contributor
timestamp: June 29, 2017, 11:01:04 pm
content: True, that would definitely help the termination issue.
Variable frequency drive and common mode voltage - Page 1
Forum section: electronics / beginners

author: Kemme
author_rank: Contributor
timestamp: November 22, 2017, 04:53:06 pm
content: Hello allIs there any way to measure the common mode voltage on a three phase motor driven by the variable frequency drive when the neutral point of the motor is not exposed?Maybe creating a virtual neutral point with three resistors would help?Or sum of all the output voltages ((U-V)+(V-W)+(W-U)) would do a proper measurement?Any help will be appreciated.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 22, 2017, 05:09:31 pm
content: Yes, resistors can be used, as long as modest bandwidth is acceptable (good for line frequency and harmonics, okay for switching frequencies, unreliable for RFI frequencies).You can also use three oscilloscope probes, and average them together (using the MATH / ADD function, assuming you can add two traces, then a MATH and a trace, together -- YMMV).Tim
Variable frequency drive control via Modbus, register read/write limit? - Page 1
Forum section: electronics / beginners

author: V_King
author_rank: Regular Contributor
timestamp: March 03, 2019, 04:11:27 pm
content: Hello,I am after variable frequency drive, to control the electric motor RPM via RS485(Modbus).There is a Bosch Rexroth EFC5610 VFD, which I really like, it has an in-build motor thermal protection, but in Modbus communication description it warns that the registers read/write limit is only 150000 times/register. I will be changing the frequency registers frequently and that worries me.I had a look at other VFDs (Siemens V20, Schneider ATV12, Parker AC10) and none of their manuals mention the Modbus communication limits for read/write cycles per register.A lot of the industrial electronics seem to have unwritten defaults and I wonder whether the 150k cycles mentioned by Bosch is default for majority of VFDs, or is it just the big drawback of the EFC5610 VFD?Thanks

author: Kalin
author_rank: Regular Contributor
timestamp: March 03, 2019, 05:35:30 pm
content: I have never hear of that with other drives and never run into a failure to write to memory with any drives I have used even the ones that use an eeprom for storing parameters. How often do you plan on writing to this value?Sent from my SM-G965W using Tapatalk

author: V_King
author_rank: Regular Contributor
timestamp: March 03, 2019, 08:41:46 pm
content: Quote from: Kalin on March 03, 2019, 05:35:30 pmThe motor is for a small test rig, to test parts. The test would use up to 10 different frequencies (not pre-set ones). The test could be run to to ten times an hour, 8 hours a day. So pretty much in theory, the registers would be shot within a yearI would have thought the read/write count would be much greater, considering todays interconnected controls in the industrial environment.

author: Kalin
author_rank: Regular Contributor
timestamp: March 03, 2019, 08:56:58 pm
content: Would you consider another manufacturer or have you already purchased the drives? It might be a typo because that is not really an acceptable number for any application I can imagine for a VFD.Sent from my SM-G965W using Tapatalk

author: V_King
author_rank: Regular Contributor
timestamp: March 04, 2019, 01:11:09 pm
content: Quote from: Kalin on March 03, 2019, 08:56:58 pmI was not far from placing the order, luckily found the info in time. I just wanted to make sure it does not apply universally throughout VFDs before considering different manufacturer.I do not think it is a typo, because the read/write limit is throughout a number of revisions I checked and they have warning in a number of manual sections.
Variable Frequency Sine Wave Generator - Page 1
Forum section: electronics / beginners

author: bgsteiner
author_rank: Contributor
timestamp: February 23, 2015, 07:04:57 pm
content: So for a project I am working on I would like to incorporate a variable frequency sine wave generator. The signal should be around line level (1.23V) or greater. The signal will be going to a 15W amplifier to drive a variety of speakers. I am trying to find the best or most cost effective way of doing this. My first Idea was to use a DAC like the MCP4725 to generate the signal. Really all I would need to do is generate 100Hz, 1kHz, 2kHz, 4kHz at best or just 100Hz and 4kHz. I may change the values in the future which made the DAC seems best.So I guess what my question boils down to is is this a good option or would something else be simpler and more effective for what I plan on doing?Thanks and have a nice day.

author: suicidaleggroll
author_rank: Super Contributor
timestamp: February 23, 2015, 07:18:38 pm
content: A DAC would work, just watch out for the bandwidth of the data line. How "clean" do you want your sine waves to be? If you want, say, 50 steps per period, then a 4kHz sine wave would need new values sent to it at a rate of 200 kSPS. With a 12-bit data resolution plus addressing, you're looking at a minimum of ~20 clock cycles per sample, which means you need an I2C clock speed of 4 MHz (these are all just back of the envelope calculations, you should look at the I2C interface details in the data sheet to confirm).For AC signal generation, a parallel interface DAC would probably be a much better choice.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: February 23, 2015, 09:31:03 pm
content: There's a great little application note (AN-263) that TI has:www.ti.com/lit/an/snoa665c/snoa665c.pdfTable 1 is a great place to start. You might find something on it that more fits your application than a DAC/ROM solution.
Variable frequency ZVS? - Page 1
Forum section: electronics / beginners

author: nsled
author_rank: Contributor
timestamp: March 31, 2024, 07:54:35 am
content: Would it be possible to create a switchable frequency ZVS by just adding relays into the parallel capacitor string? so more or less capacitors are active when running.Pic is an induction heater schematic from "schematix" on youtube. I drew in some relays to show what I mean. It'd be more convenient to have different value caps connected to a rotary switch I guess but is there technical difficulties preventing that?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 31, 2024, 09:36:24 am
content: Sure, but to what end? If you're doing much power, it better be a big relay (contactor). And you run the risk of creating resonant modes that heat the relay rather than the work coil. How often does it really need to change, what degree of control do you need? Bus bars and bolted connections are the industrial standard.Tim

author: radiolistener
author_rank: Super Contributor
timestamp: March 31, 2024, 02:31:45 pm
content: I think adding relay switch into LC circuit may be problematic, because connections between L and C needs to be very low resistance and high current rated in order to avoid excessive energy loss. So using relay in that circuit can lead to excessive power loss due contacts heating inside relay.

author: mag_therm
author_rank: Frequent Contributor
timestamp: March 31, 2024, 04:05:10 pm
content: Generally, in absence of application detail:In an induction heating inverter as shown with a parallel tank, the total capacitor current is approximately Heating_Coil Q factor times the inverter current.( typical Q range 5 to 12).The switched capacitor sections were usually 10% to 30% of the total capacitance.Switches have to be ZVS or no-volt switching with interlocks to prove inverter is off.3 types of switches were used:Bar contactors with the solenoid parts spaced from the contacts.Pneumatic knife switches with water coolingAnti-parallel semiconductors with water cooling and high voltage isolated gate drive.These days, switching is mostly avoided, as the inverter topologies can economically and seamlessly handle the range of reactive power.Here is a photo of typical contactor:https://www.homa-ob.de/en/produkte/ac-contactors.php
Variable input to 5v out - Page 1
Forum section: electronics / beginners

author: Falcon69
author_rank: Super Contributor
timestamp: April 01, 2013, 07:41:24 am
content: I have a pcb I am designing. The problem I'm running into is finding an SMD components that will do the function I am wanting.Suppose a voltage input of any value, up to 30v or even down to 3v is supplied (i.e. 3.3v-30v dc). 5v is always going to be the output. The amperage required for the circuit, according to bread board test, is 289mA. So I would like to find something that can perform this operation with 500mA at least, to leave me room for adding more circuits to the design.I was looking at the LM340MPX, and using a 3way jumper, pin 1 of jumper connected to pin 1 of LM340, and pin 3 of jumper connect to Circuit, while pin two of jumper connected to input supply voltage. If someone connects more than 5volts, then simply jumper between pins 1 and two to activate the lm304mpx and bypass a direct connection, saving the circuits. But, I need something that will require NO jumper and still have a small SMD footprint SOT-223 or, preferably, smaller.Any sugestions?

author: Rerouter
author_rank: Super Contributor
timestamp: April 01, 2013, 07:42:53 am
content: look up a "sepic" configuration switch-mode regulator, its more common than you would think,

author: Falcon69
author_rank: Super Contributor
timestamp: April 01, 2013, 08:38:29 am
content: Thank RerouterIt seems that they also require alot of external components as well. Including, in most cases, two inductors. I was trying to keep the number of components from being more.What I have now isPower in to fusefuse to jumper pin 2jumper pin 1 to LM340 pin 1jumper pin 3 to circuitLM340 pin 2 & 4 to gndLM340 pin 3 to circuit.If a 5 volt source is connected, leave the jumper on jumper pin 2 and 3If a voltage greater than 5 volt source is connected (up to 30v), leave jumper on jumper pin 1 & 2If this set-up works, maybe I'll just keep my current setup. It will just require a 3pin jumper, and a SOT223-4 component. Alot less then that sepic set-up. And cheaper it seems.
variable linear DC-DC switching regulator - Page 1
Forum section: electronics / beginners

author: maminej
author_rank: Newbie
timestamp: February 10, 2016, 11:17:37 pm
content: Gentlemen,I have been trying to build a DC-Dc switching voltage regulator using the LT3991. I was successful in designing the board for a fixed voltage of around 36V with a 48V power supply. the purpose of this is to drive a CO2 laser fans.the next step was to make the output voltage variable and tune the fan speed. I am not a big fan of using PWM with FET or a Darlington to change the fan speed as I believe this introduces additional vibration and the optical setup is sensitive to that.I re-watched Dave's tutorial on the variable power supply as a reference and tried to change the Feedback pin voltage of the LT3991.So I am using a dual stage dual stage sallen key active filter to get a dc from a 3khz pwm signal, the output has low ripple.I had a little success in changing the voltage but the result was highly non-linear. below is the schematic I used for this:here is some data for the Vout vs Vfb I got :any idea of what could have caused the huge discontinuity in the curve ?Thanks in advance

author: maminej
author_rank: Newbie
timestamp: February 10, 2016, 11:20:40 pm
content: forgot to mention that I also tried to add a voltage divider at the output of my filter to get a higher resolution in the range of 0-1.2V :for some reason I don't understand, I was not able to adjust the output voltage of the LT when changing the FB voltage all the way from 0 to 1.2/here is the second schematic I tried.

author: rob77
author_rank: Super Contributor
timestamp: February 11, 2016, 12:01:29 am
content: you must have a voltage divider on your feedback pin set to the max voltage - so resistor from Vout to FB and resistor from FB to ground... then you can add a resistor between FB and your filter's output - this way you can inject current and fool the feedback to lower the Vout.

author: maminej
author_rank: Newbie
timestamp: February 11, 2016, 04:19:05 pm
content: Thanks for the reply.I just made the changes you suggested and it's working just like you said.Thank yo very much
Variable low voltage AC supply - Page 1
Forum section: electronics / beginners

author: drakke
author_rank: Regular Contributor
timestamp: March 31, 2015, 03:28:02 am
content: There are a lot of DC lab powers supply design circuits (AC to DC conversion) but how do you experiment with them when you don't have any safe AC supply?I have been looking for a variable AC supply but there are very few compared to DC supplies. I suppose I don't need 120v but possible 0-24v at 50-60Hz.I want to be very safe. What are the options?Thanks.

author: AG6QR
author_rank: Frequent Contributor
timestamp: March 31, 2015, 03:58:38 am
content: A Variac (common brand name for a variable autotransformer) is a way of providing an adjustable AC voltage from mains. Usually, they go from near-zero to about 120% of the supply voltage, or thereabouts. Normally, you plug it straight into the mains, but if you plugged one into a step-down transformer with a 24VAC output, the output of your Variac would be capable of about 0 to 26 VAC, or thereabouts. A Variac has a current limit, which must not be exceeded, neither on the input side nor on the output side, so beware of this.Or you could use a function generator, perhaps followed by a buffer amplifier. That would give you flexibility in frequency as well as voltage.

author: edpalmer42
author_rank: Super Contributor
timestamp: March 31, 2015, 04:26:42 am
content: Model train transformers have an isolated AC output of up to 20V or so. Power rating can be as high as 50 - 100 watts.Ed

author: 3roomlab
author_rank: Frequent Contributor
timestamp: March 31, 2015, 08:20:04 am
content: a 50/60Hz signal generator + a small audio power amplifier (maybe car amplifier?) or even just a DIY BJT/MOSFET module?

author: drakke
author_rank: Regular Contributor
timestamp: April 05, 2015, 06:38:18 am
content: Is this another possibility?Class 2 Plug-in Transformer 120VAC - 24VAChttp://www.mroelectronics.com/mro/product.php?id_product=4793... then wire the output terminals of the transformer to the binding posts on my breadboard.

author: Zero999
author_rank: Super Contributor
timestamp: April 05, 2015, 08:39:05 am
content: Quote from: drakke on April 05, 2015, 06:38:18 amThat's a transformer which outputs a fixed voltage. The original poster wanted a variable transformer.
Delete Delete Delete - Page 1
Forum section: electronics / beginners

author: The_Almighty_Bacon_Lord
author_rank: Contributor
timestamp: July 28, 2016, 03:06:52 pm
content: Delete Delete Delete

author: MosherIV
author_rank: Super Contributor
timestamp: July 28, 2016, 03:34:17 pm
content: Quote30V * 4 = 120WThat is a lot of power to dissipate, are you sure you can get rid of that much power without getting the heat sink too hot?In any case, here is a project with a single channel PSU which allows you to set the volts and current limit.http://www.microsyl.com/index.php/2010/03/31/bench-power-supply-0-25v-0-5amp/The project does show set V acutal V, set A limit and actual A.The schematic is the easiest that I have found to follow for this kind of PSU.EDIT : I wish beginners would stop refereeing to the current limit as constant current - that is a totally different type of PSU.

author: MosherIV
author_rank: Super Contributor
timestamp: July 28, 2016, 04:47:20 pm
content: QuoteCommon newbee mistake. Most buck/boost converters can be used in either Constant Voltage OR Constant Current mode.They CANNOT do both at the same time.Your description did not make it clear that you are using buck converters.To use buck converters as CV, you take the output V and feed it back to the controller sense via a voltage divider (eg a potentiometer).I would suggest looking at the design I posted for how to add current limit.It works by using a current shunt (accurate low ohm resistor) and comparing the current output against a set limit.If the current output reaches or tries to go over the set limit, the op-amp starts to try and drive the output voltage down - there by maintaining the current limit.In order to make this work with the buck regulator, you will have to do a similar ORing arrangement with the set voltage ( the feed back to the controller sense )Never done this before, so good luck
Variable resistors and loss of wiper contact - Page 1
Forum section: electronics / beginners

author: ifonlyeverything
author_rank: Regular Contributor
timestamp: October 08, 2024, 05:55:19 pm
content: I feel dumb for asking this, but I need to take a 12V input and divide it down to 0-5V. I know that it's best practice to tie the wiper to one of the other legs to protect against the wiper losing contact -- which would be bad. So something likethisappears to work in that regard. However, as I have the schematic drawn, if the wiper loses contact then the resistor maxes out at 10K and the output voltage goes to 5V. Is there a way to do this so loss of contact instead outputs 0V?

author: Kim Christensen
author_rank: Super Contributor
timestamp: October 08, 2024, 07:02:36 pm
content: Loss of wiper contact with this circuit would result in 0V at the voltmeter:EDIT: Or do you wanttwoPOTs? (Trimmer and regular)

author: PGPG
author_rank: Frequent Contributor
timestamp: October 08, 2024, 07:12:35 pm
content: You can do the divider with 14k resistor and 10k variable resistor and take output from viper.

author: Gyro
author_rank: Super Contributor
timestamp: October 08, 2024, 07:27:11 pm
content: A lesson from Metrology... For voltage dividers, put the variable resistor in parallel with one of the fixed resistors. Calculate the resistor values so that the variable resistor adjustment range is only sufficient to compensate for worst case resistor and other tolerances. That way, if the wiper goes open circuit, nothing dramatic will happen. Always start with two fixed resistors for the divider and provide the minimum adjustment needed.

author: ifonlyeverything
author_rank: Regular Contributor
timestamp: October 08, 2024, 10:26:35 pm
content: Quote from: Kim Christensen on October 08, 2024, 07:02:36 pmI did want a trimmer and a regulator potentiometer but I figured it out from your schematic. Thank you, I don't know why I didn't think of this!

author: Doctorandus_P
author_rank: Super Contributor
timestamp: October 08, 2024, 11:00:50 pm
content: Another method is to put the ends of the potentiometer to GND and 12V and the wiper to 5V.And of course add resistors to the end to limit the adjustment range and add precision.
Variable Voltage supply - Page 1
Forum section: electronics / beginners

author: alin_im
author_rank: Regular Contributor
timestamp: June 06, 2015, 10:30:08 pm
content: Hi guys,Can you help me with a schematic for a variable voltage supply 0 - 40 with a constant voltage independent of the load. like the variable supply that you set without any load attached and then attache the load and the voltage is the same. I manage to make the current limiting circuit but now i am struggling with the voltage part.

author: nickn4
author_rank: Contributor
timestamp: June 07, 2015, 05:23:55 am
content: I am at the point of starting a new project to build my own power supply, so i'm very interested in similar projects of other people, but i doubt i will be of any help.none the less i notice, where is the input coming from? i'm not familiar with power supply schematics so maybe i'm missing something really obvious?nickedit; i noticed the ground i the middle of the schematic, maybe i am starting to sort it out, but please still point it out for me please?vcc- 1 and vcc+ 1 are output?

author: Matty272
author_rank: Contributor
timestamp: June 11, 2015, 09:42:03 am
content: Have you looked at this video that Dave posted?
Variable voltage with high power, from a µC - Page 1
Forum section: electronics / beginners

author: PinheadBE
author_rank: Regular Contributor
timestamp: March 15, 2025, 01:41:37 pm
content: Hi,I'm in the need of being able to generate a variable voltage between 3.0 V and 5.0 V, with an output current that can go up to 6 A.This will be commanded by a micro-controller.What I already have thought of:- Using PWM, commanding a MOSFET. But I have to place a cap somewhere (a low-pass filter). Since the current is not stable and can vary largely up to 6 A, where do I have to place it, and what value to use ?- Using DAC. After that, I have to amplify the current. A BJT transistor mounted in an emitter-following configuration seems adequate. But can I do that with a MOSFET ?Any help welcomeThanks

author: DavidAlfa
author_rank: Super Contributor
timestamp: March 15, 2025, 02:00:37 pm
content: TPS55289 ? Has i2c control with 10mv steps.You can use the DAC, but feed it to an op-amp and let it control a BJT.Mosfets are harder to control, better use a BJT for this.

author: PinheadBE
author_rank: Regular Contributor
timestamp: March 15, 2025, 02:23:48 pm
content: VQFN..... Not a chance I'm able to solder thisIn fact, the micro-controller already exists and generates 6 PWM signals driving each a mosfet for a part of the circuit (a lot of LED's) that can work with that.In another part of the circuit, I have to be able to slightly dim special LED's (like blinking ones, flame effects,....) . Those LED's do integrate an IC, and I suspect it will not be happy with PWM....I made some tests, and to dim them, I can make the voltage vary between 3 V and 5 V.So, my preference would go to a simple circuit able to convert the existing PWM signal in a voltage. That way, I will be able to use the same control board as for the simple LED's, with a simple add-on. This circuit having to be repeated more than 20 times, it should be very basic (I cannot afford a buck/boost converter for each channel)

author: DavidAlfa
author_rank: Super Contributor
timestamp: March 15, 2025, 06:05:48 pm
content: Do you really need 6amps for each channel?A linear regulator will cause a ton of heat.There're very inexpensive buck converters for 2-3A, if you could use one for each channel then you could control then by filtering the PWM to control the feedback signal.Googling "dac controlled buck converter" shows plenty of topics.
Variac Inrush advice - Page 1
Forum section: electronics / beginners

author: orbiter
author_rank: Frequent Contributor
timestamp: January 20, 2013, 02:53:44 pm
content: Hi fellas,Could you advise on where abouts, or in what sort of configuration I can fit an NTC to prevent my 8A variac's inrush tripping the RCD on switch-on please?I have my variac plugged into the wall via an RCD and I also have an 13A RCD (10A fuse) plug socket on the front of the variac. It's getting to the stage though were I'm getting annoyed with the breaker tripping every few times I switch-on. I seem to be timing the switch-on perfectly in sync with the AC peaksI have various values of NTC going up to 20A.Any advice appreciatedThanks guys

author: SeanB
author_rank: Super Contributor
timestamp: January 20, 2013, 02:58:41 pm
content: In series with the incoming mains live inside the variac. Use a 8/10A unit in it. If you do not have then use the next higher current one.

author: orbiter
author_rank: Frequent Contributor
timestamp: January 20, 2013, 03:05:41 pm
content: Quote from: SeanB on January 20, 2013, 02:58:41 pmBelieve it or not my friend I actually thought that was the case, but I just wanted some confirmation first beforeshoving 240v through one of these lil' black thingsMuch appreciated Sean.Thanks

author: SeanB
author_rank: Super Contributor
timestamp: January 20, 2013, 04:39:15 pm
content: Just remember they can run very hot, mount in a space where the heat will not cause a problem.

author: orbiter
author_rank: Frequent Contributor
timestamp: January 20, 2013, 06:07:16 pm
content: Quote from: SeanB on January 20, 2013, 04:39:15 pmNo problem, I've got it installed now and nothing is touching it etc, also air can move through the area I've fitted it so it should be ok. I will test it as-well though just to make sure everything is safe.Thanks again

author: smashedProton
author_rank: Frequent Contributor
timestamp: January 23, 2013, 05:52:25 am
content: If you want to be lazy, you can always have the secondary switch a relay that would short the input over a 10 ohm resistor(series). I did something like that for a car audio capacitor I have done some time ago.
variac project - Page 1
Forum section: electronics / beginners

author: corporalspiffy
author_rank: Newbie
timestamp: July 28, 2015, 06:20:51 pm
content: before i turn this thing on; is this wired correctly?thanks

author: Simon
author_rank: Unknown
timestamp: July 28, 2015, 07:07:53 pm
content: unless there is some standard connection layout on variacs you will need to post a proper diagram explaining what stuff is.

author: Unknown
author_rank: Unknown
timestamp: July 28, 2015, 07:11:15 pm
content: This may be unnecessarily picky, but if this was mine I'd want some cable ties and ring crimps in with that lot...

author: electr_peter
author_rank: Unknown
timestamp: July 28, 2015, 07:30:39 pm
content: Both input and output must be fused - otherwise in case of short circuit on output with low voltage condition you will burn variac wiring.As for wiring - could you get some 2 wire or 3 wire flex cord? It is not expensive. Wiring with a flex cable (with 2 or three wires inside one) will make much neater cabling. Some heatshrink would help to isolate connections.Also, add some labelling on outside and/or inside. Current configuration will not be obvious next time you try to use itLabels also should note danger and setup to passers by who might try to use this thing - it is preferable to know that reasonable person will be both alive and variac will be undamaged if some proper labelling is here.Very nice project, by the way

author: Unknown
author_rank: Unknown
timestamp: July 28, 2015, 07:36:01 pm
content: You could at least use north american standards for wire color (green/ground, white/neutral). If your incoming mains is only secured with hot snot, you'll probably experience some sparks if you trip on the wire.

author: Postal666
author_rank: Regular Contributor
timestamp: July 29, 2015, 12:30:08 am
content: Found this on Antique Radio's forum. Looks like it's wired right, and by that I only mean the connections are in correct location. I agree with electr_peter, fuse both sides of the powerstat...you just never know, then it's too late. Bullet hit the mark (pun intended) with the cable ties; neatness counts and will save you massive headaches when troubleshooting. steverino also makes a good point about wire color standards (they were adopted for a reason) and securing the line cord. Only thing I would add is to make sure your wiring is the correct size. Some of those wires look small to me (16awg?), which might be ok if it were stranded cable, imo. At least on the output wiring. Tapping off for voltage reading with solid 16ga is fine.::edit:: If it were me, I would enlarge the hole for the receptacle a bit, mount it on the outside face, and put a coverplate on it as well. Would look very clean.

author: corporalspiffy
author_rank: Newbie
timestamp: July 30, 2015, 06:19:14 pm
content: thanks for all the replies, ill change the wiring, secure the power chord and put a nice cover plate on the outlet.
Variac wiring - Page 1
Forum section: electronics / beginners

author: Crambone
author_rank: Frequent Contributor
timestamp: May 29, 2024, 09:02:27 pm
content: Can someone help me with the wiring of the input and output? Can this be wired using 120vac in for 240vac out?If not I do have a 240vac available.Thanks

author: Andy Watson
author_rank: Super Contributor
timestamp: May 29, 2024, 10:36:28 pm
content: No.If I've read this datasheet correctly, you need to have terminals 6 and 7 for the 120V "STEP UP" option.

author: Ian.M
author_rank: Super Contributor
timestamp: May 29, 2024, 10:37:44 pm
content: Seehttps://www.farnell.com/datasheets/1761458.pdfIt hasn't got terminals 6 & 7 so cant be wired for 120V in, 0-240V or 0-280V out.

author: Shock
author_rank: Super Contributor
timestamp: May 31, 2024, 01:00:55 pm
content: Nice variac I have a similar model. I think the missing terminals on yours are the model that has a fuse holder in that spot. But you will have to check, it looks modified so takenothingfor granted. You may even find (if lucky) the winding has both the 120/240 taps present.Really though you should be competent before messing around with these things.

author: Crambone
author_rank: Frequent Contributor
timestamp: June 01, 2024, 12:10:49 am
content: I got it guys thanks