hybridfree/eevblog-posts huggingface dataset:
how to solve and understand this opamp circuit - Page 1
Forum section: electronics / beginners

author: haseeb zaib
author_rank: Contributor
timestamp: August 12, 2021, 05:22:11 pm
content: Hello guysHere I have this portion of the circuit which I can't really understand what it is doing and I want to solve it, so I can understand it. The inverting input is having 2 signals and their peak is 5V, while on this inverting input we have this transistor with an analog switch, this analog switch is being switched by a delay signal whose "ON" time is 50us, this is the portion I am confused in. So I want tips/suggestions on how to understand this circuit and how to solve it, So I could understand why they used this transistor and switch part in this circuit. The value of the capacitor is 100nf.opamp rail voltages 10.6V and ground

author: tooki
author_rank: Super Contributor
timestamp: August 12, 2021, 11:36:06 pm
content: It’s impossible to say for certain without knowing more about the context. The resistors on the inputs sums their signals, and the cap as the feedback path tells us it’s an integrator. The switchable resistors in the feedback path let you add feedback.Your description of the circuit function is very unclear (as is the image itself, which is so overcompressed that some areas are nearly illegible) — what 100nF cap? There’s only one cap in the schematic and it’s a 470 (nF?), but it’s got nothing to do with delays. What do you mean by “analog switch”? The only switch shown is an actual pushbutton. And what about this delay signal? You haven’t described the circuit inputs at all.

author: rstofer
author_rank: Super Contributor
timestamp: August 13, 2021, 01:43:11 pm
content: You might consider modeling the circuit in LTspice. Substitute a signal source (square wave) for the pushbutton and see what happens. NNot knowing the intent of the circuit makes describing it a lot more difficult.
How to solve multiple voltage sources - Page 1
Forum section: electronics / beginners

author: sebdehne
author_rank: Contributor
timestamp: November 11, 2015, 06:06:00 pm
content: Can someone help me understand how to solve attached circuit? When I put it into the simulator I see that the Voltage is 1.666667V across R3, but I wonder how I can calculate this myself.Thanks

author: AndyC_772
author_rank: Super Contributor
timestamp: November 11, 2015, 06:22:10 pm
content: Start by working out the voltages you do know. The bottom end of R3 is at 5V with respect to ground, and the right end of R2 is at 10V with respect to that node. Therefore, the voltage at the right end of R2 is at 15V with respect to ground.Now apply Kirchhoff's current law to the junction between the resistors. KCL says that the sum of all currents into and out of a point in a circuit must equal zero. Call the voltage here Vx with respect to ground, and use Ohm's law to work out the current in each of the three resistors.You know the resistance of each resistor (1 Ohm, in every case), and the voltage at every point with respect to ground, except for the voltage at the junction.Don't forget that when you apply KCL, it's important to get all the signs the correct way round. It's easy to get this wrong.The current into the junction via R4 is given by I = V / R, so:I4 = (0 - Vx) / 1Via R3 it's:I3 = (5 - Vx) / 1Via R2 it's:I2 = (15 - Vx) / 1By KCL, these must all sum to zero, otherwise electrons would all be piling up somewhere!(0 - Vx) + (5 - Vx) + (15 - Vx) = 020 - 3Vx = 0Vx = 20/3 = 6.6667V with respect to GNDFinally, the voltage across R3 is just the difference between the voltages at each end individually, provided they're each measured with respect to the same point. Since they are (ground, in this case), the voltage across R3 is (6.66667 - 5) = 1.66667V

author: sebdehne
author_rank: Contributor
timestamp: November 11, 2015, 06:57:18 pm
content: Thanks a lot! It makes sense now :-)

author: sebdehne
author_rank: Contributor
timestamp: November 20, 2015, 04:49:05 pm
content: Thanks a lot Dave for the vids on this subject! :-)

author: Syntax_Error
author_rank: Regular Contributor
timestamp: November 21, 2015, 05:03:49 am
content: This problem is a fine example of when superposition is appropriate. Consider each voltage source separately, and then add the contributions of the currents from each and their sum is equal to the final currents. The currents permit discovery of any node voltages.
How to solve these types of circuits? - Page 1
Forum section: electronics / beginners

author: subhadeepbiswas!
author_rank: Newbie
timestamp: August 17, 2017, 03:57:51 pm
content: I've followed the trace of a LED fader PCB which consist of an OPAMP (LM358) and some resistors, a trim pot , capacitor and a transistor and made a schematic out of it.From the schematic what I can see is an integrator and a comparator. 47K resistance acting as a voltage divider to provide reference voltage to pin 3 and 6 of the OPAMP.I simulated the circuit in multisim and found that it is generating a low frequency ramp signal from pin 1 (output of OPAMP1) which is connected to the base of the transistor.I'm not able to get a clear concept on this. Mainly the feedback paths of the two OPAMPs as well as the functions of 100k, 30k resistors and 20k pot. Please guide me to understand the whole circuit in details. Thank you

author: Zero999
author_rank: Super Contributor
timestamp: August 17, 2017, 05:22:44 pm
content: It's a relaxation oscillator. The comparator has hysteresis, so the high level threshold is greater than the low level threshold and the integrator is inverting and the forms the delay element of the circuit.http://www.falstad.com/circuit/e-triangle.htmlThe comparator can be reconfigured, so it inverts the signal and the integrator replaced with a simple RC circuit, but it will produce a ramped waveform, rather than a triangle.https://en.wikipedia.org/wiki/Relaxation_oscillatorThere's nothing to limit the maximum current through the LEDs which isn't good. It would be better to use a constant current driver for the LEDs, rather than connecting them to an emitter follower.
TVM 802A - Page 1
Forum section: electronics / beginners

author: robotdiggme
author_rank: Newbie
timestamp: August 18, 2016, 08:27:48 am
content: When you receive robotdigg TVM 802A pick and place machine, it is marked as a beta copy and asking you to run under windows 7 pro.The problem is fixed. We got updates on 64-bit trial. All DLLs should be reconfigured.I was feedbacked the machine works well.
How to start with microsoldering on iPhone logic board - Page 1
Forum section: electronics / beginners

author: extra22
author_rank: Newbie
timestamp: January 26, 2015, 09:32:01 am
content: Hi!First of all, thanks for letting me in to this forum!I do some kind of iPhone repairs (cracked screen etc) and want to expand it with micrsoldering. I have basic understanding of soldering. But I feel like this is a whole new world to me. Have seen tons off youtube videos, but still I have some question that I hope you will help me on:1. How do you test if a part is function or not? Do you use a multimeter and test, or do you just take the logic board under microscope and look for damage?2. How to you know what method to fix that part? I see some just reflow the part, other rework it. Some solder the parts back into the board again, and some other just heat it from underside and then the part "falls" into palce.3. Could anyone explain to me in detail step by step the process he is doing here:?Thanks for all the answers. Much apreciated

author: Yago
author_rank: Frequent Contributor
timestamp: January 26, 2015, 11:49:25 am
content: Have a look at Dave's soldering tutorials, he has iron, hot air, and demonstrates "Chip Quick" low temperature solder videos.There are links on the home page of this forum.
How to strip flat flex cable - Page 1
Forum section: electronics / beginners

author: ME
author_rank: Frequent Contributor
timestamp: August 19, 2025, 10:41:08 am
content: I have to strip about 4mm of the insulation from one end of a ffc to solder it to a laptop switch board , I have tried a dremel etc but no luck, is there a reliable way to strip the insulation? , I have thought of dunking the end in a chip frier to melt it so i can melt it and grip it with some rag to pull off the plastic insulation, Just to add my chip frier needs its oil changing and a clean anyway , Is there a better way?.

author: artag
author_rank: Super Contributor
timestamp: August 19, 2025, 10:59:05 am
content: They're normally supplied stripped. Is this a repair where you're shortening the cable ?It might be better to get a replacement.If you have to do it I think I'd try scraping - but it might need a few goes to do it without further damage.

author: jpanhalt
author_rank: Super Contributor
timestamp: August 19, 2025, 11:31:46 am
content: For cable with PVC insulation, I just use a spring clip and hot air gun down the channel in the clip. It will not work with polyester and higher melting insulations, which maybe yours is.

author: ME
author_rank: Frequent Contributor
timestamp: August 19, 2025, 11:37:24 am
content: i have a hot air station , I never thought of that ! .
How to switch a circuit when it drops below a particular voltage. - Page 1
Forum section: electronics / beginners

author: greatsenshi
author_rank: Newbie
timestamp: April 25, 2013, 10:34:31 am
content: Hey guys im a complete beginner when it comes to electronics, however im very keen and I have almost finished my very first project. However I have come across a bit of a snag, the project is portable and uses batteries. I am using theseLi-Ion Batteriesand they dont like being dropped under 10.8v. I was wondering what the best way of being able to switch the circuit when the voltage drops to around this.Thanks in advance guys, I hope the question wasnt too stupid.

author: kizzap
author_rank: Unknown
timestamp: April 25, 2013, 10:49:29 am
content: Comparator with a reference voltage, controlling the voltage source switch.http://home.cogeco.ca/~rpaisley4/xLowBattery.htmlfor a basic idea.-kizzap

author: Gall
author_rank: Frequent Contributor
timestamp: April 25, 2013, 10:52:37 am
content: A out-of-the-box solution: power supervisor IC. It's voltage reference plus comparator on a single chip.

author: greatsenshi
author_rank: Newbie
timestamp: April 25, 2013, 11:35:53 am
content: Wow thanks for the quick reply. I like the idea of using the TI chip, however im not sure how the Vref input is used.
How to switch a large-V load with a P-channel mosfet and small-V unipolar clock? - Page 1
Forum section: electronics / beginners

author: johnyradio
author_rank: Newbie
timestamp: October 13, 2018, 06:17:18 am
content: i can switch the supply voltage with a unipolar clock, if the clock has the same peak V as the source supplybut if i make the source V higher than the gate V, i get a flat line output.How to switch a high-V load with a low-V gate, on a P-channel mosfet? Prefer single-stageThx

author: exe
author_rank: Unknown
timestamp: October 13, 2018, 08:26:25 am
content: Do you need a high-side or low-side switching? If low-side, just put load at the drain.If high-side, I'd propose an additional bjt as level shifter. Something like this:https://www.chegg.com/homework-help/questions-and-answers/bjts-often-used-level-shifting-changing-voltages-microcontroller-outputs-control-parts-cir-q21548315or this:https://www.luisllamas.es/wp-content/uploads/2016/07/arduino-transistor-driver-bjt-mosfet.png. AFAIK, The Art of Electronics has a paragraph on this.Just be sure to thoroughly test it: mosfet should open/close reasonably fast, and it should be fully open. Also gate voltage should not exceed absolute maximum ratings (clamp it to 10-15V with a zener to be sure, if needed).
How to switch load using radio controlled module if it switches the ground? - Page 1
Forum section: electronics / beginners

author: ghostbanana34
author_rank: Newbie
timestamp: January 10, 2019, 08:48:12 am
content: I had old broken toy car. I wanted to use it's RC module to switch 12V fan. I measured original circuit, found the output, saw 3V there (fig. A). Then I assumed that RC module switches the 3V and designed my circuit accordingly (fig. B). It was always on. Only then I start analyzing it more deeply and to my surprise I found out that RC module output is permanently connected to 3V and only switches second output to the ground (fig. C).I used NPN transistor in TO220 package from old PC power supply, as that was only power transistor I had. Is it possible to modify this circuit so that switching to the ground would switch it?

author: capt bullshot
author_rank: Super Contributor
timestamp: January 10, 2019, 09:09:47 am
content: Add a small PNP transistor like this

author: Zero999
author_rank: Super Contributor
timestamp: January 10, 2019, 12:48:37 pm
content: Yes, it's very common to switch the 0V. It's often much easier, because N-channel MOSFETs have a lower on resistance than P-devices.If the RF module can switch enough current for the 12V fan, then add another transistor, forming a cascode with the internal transistor inside the module.If the module isn't rated to switch the current required by the fan, another option is to switch the motor's 12V with a PNP transistor.

author: ghostbanana34
author_rank: Newbie
timestamp: January 10, 2019, 03:22:14 pm
content: Thanks. The RC module isn't rated for such current, so I will have to add PNP.

author: spec
author_rank: Frequent Contributor
timestamp: January 10, 2019, 05:50:08 pm
content: Hi ghostbanana34Attached below is a schematic for another version:

author: Zero999
author_rank: Super Contributor
timestamp: January 10, 2019, 07:14:47 pm
content: Quote from: spec on January 10, 2019, 05:50:08 pmI did consider this option and it might work, but it's risky because the RC module's output stage is not a simple switch, as shown in the schematics posted previously. We don't know what the maximum voltage rating of the module's internal switching transistor and there will be a snubber diode across the transistor or an internal back-EMF diode to +V. I think the latter is most likely the case, as it's designed to switch a motor connected between +3V and the output. If this is the case Q3 will never turn off.It might be possible to remove the internal back-EMF diode, but one needs to be sure the internal transistor is rated to switch over 12V.

author: spec
author_rank: Frequent Contributor
timestamp: January 10, 2019, 08:05:55 pm
content: Quote from: Zero999 on January 10, 2019, 07:14:47 pmGood points. I did not have this additional information.
How to switch voltage inputs with MOSFET - Page 1
Forum section: electronics / beginners

author: paeion
author_rank: Contributor
timestamp: January 16, 2022, 03:41:51 am
content: Hi all,I am trying to switch-off 5V coming from a USB cable (USBVCC) when the input jack (VIN) is connected. I expect to use a 7V input voltage nominally, and the USB 5V only for programming the board (An ESP32). I have come up with the following schematic to feed the 3.3V regulator using a P-channel mosfet (datasheet:https://datasheet.lcsc.com/lcsc/1810171817_Alpha-&-Omega-Semicon-AO3401A_C15127.pdf).I have also seen the Arduino UNO schematic doing a similar thing with a comparator. Which is better and do I need to think about reverse-protection to stop the VIN going through the mosfet source-gate to the USBVCC?I could have simply had diodes at the junction going into the 3.3V regulator but the voltage drop makes the 5V USBVCC dangerously close to the NCP1117 limit. Note: The ESP32 gulps up to 600mA short current spikes as a worst-case.

author: Peabody
author_rank: Super Contributor
timestamp: January 16, 2022, 04:45:12 am
content: Your circuit is almost there, but not quite. If Vin is not connected to power, USB power will flow through the mosfet, into the Vin line, back through the 2K resistor to the gate of the mosfet, thus tending to turn it back off. So you need a diode in the Vin line going into the 10uF connection. It would normally be a Schottky diode so as to cause the lowest voltage drop. But it won't really matter in the 7V line. That will prevent USB power from messing up the mosfet gateAlso, you don't really need the 2K resistor, but if you use a resistor it should probably be a lot lower value, like 100 ohms, and technically it should be placed to the right of the pulldown resistor connection so as to avoid having a voltage divider.I don't see any advantage in this case to using the opamp version used in the Uno. And, no, you don't have to worry about current flowing back into USB. If Vin is powered, the mosfet will be off, and the mosfet is correctly oriented so its body diode will oppose any current flow back into USB.You could use two Schottky diodes instead of the mosfet, but might need to find a more modern regulator - one that will pass the 600mA but with a much lower dropout voltage. I would doubt 600mA is really needed, but if that's just spikes, perhaps a somewhat larger capacitor would make up for any shortfall in regulator current. The MIC5219, if you can find one, provides 500mA with a maximum 500mV dropout voltage.

author: paeion
author_rank: Contributor
timestamp: January 16, 2022, 09:53:43 am
content: Thanks heaps Peabody, the diode on Vin is definitely a trap for young players such as myself. I thought of the 2K resistor for current-limiting but no point making it a voltage divider as you said.I have been told off about the 1117 regulator already, need to find a better alternative so will investigate the MIC5219.Thanks again!
How to sync Sweep output of rigol MSO5000 ? - Page 1
Forum section: electronics / beginners

author: Gioreva
author_rank: Contributor
timestamp: November 29, 2019, 04:11:04 pm
content: HiFunction generator of RigolMSO5000 has Sweep function.To analyze the bandwidth of a circuit, need to synchronize Y of the oscilloscope with Sweep Cicle.How to do This ?
How to Take apart IR leds by wavelength? - Page 1
Forum section: electronics / beginners

author: Erwin Ried
author_rank: Regular Contributor
timestamp: August 17, 2012, 07:36:06 pm
content: I am testing with remote controls (I am making a global one), so I bought a cheap led pack, 50x850nm and 50x940nm. I had some unlabeled leds from an older 10x pack, there is a way I can tell the wavelength so I can 'join' the unlabeled ones with their new family??

author: TriodeTiger
author_rank: Regular Contributor
timestamp: August 17, 2012, 08:03:56 pm
content: 850 approaches visible light, I bet you that you may be able to see a slight glow under magnification or especially with a camera that normally sees infrared light more than others (my old cell camera was brilliant at it)850 may be stopped by black, and 940 may pass through - some materials such as black developing film may block 850 all together. Output/relative wavelength surely are different on some IR diodes as well if you can find a large enough difference and standardise a test.Alexander.

author: Erwin Ried
author_rank: Regular Contributor
timestamp: August 17, 2012, 08:56:12 pm
content: Thanks a lot! Checking now

author: Erwin Ried
author_rank: Regular Contributor
timestamp: August 17, 2012, 09:10:45 pm
content: Quote from: MmCoffee on August 17, 2012, 08:03:56 pmOK, old ones are VERY bright at 3V, without anything I can see a red dot inside, with the cellphone I see a lot of violet light840 ones at 3V are like 30% less brighter than the last ones, but I can see a very small red dot inside940 ones at 3V are like 30% less brighter than the 840, but I can't see a small red dot inside.Maybe my old ones are less than 840 nm?

author: TriodeTiger
author_rank: Regular Contributor
timestamp: August 17, 2012, 11:41:00 pm
content: Entirely possible the older ones are 'dirtier' (emit a wider band of the spectrum at higher intensities than the newer), alas I have not seen too many of them to know why they are brighter (if technology or brand or age is the reason) so maybe someone else can step in. :-)I see no real reason to approach red light (~700nm) for the obvious applications for IR leds and it may be 840 with the above issues.Alexander.

author: Jeff1946
author_rank: Regular Contributor
timestamp: August 19, 2012, 11:34:32 pm
content: This may work. You can use leds as current source. Put a suitable resistor across the led and measure voltage when you shine a flashlight on it. Assuming this works you can test the diodes in pairs. The 840 nm photons will give a signal with either of your leds whereas the 940 nm should only give a signal with the 940 nm leds. So play around with pairs of them and you should be able to decide which is which.I would also think the excitation voltage (whatever is the correct term) for the 940 should be less than the 840. Just pick a current (say 1ma) and measure the voltage across each diode.
How to tell a carbon mic and convert the signal to standed audio? - Page 1
Forum section: electronics / beginners

author: abdullahseba
author_rank: Frequent Contributor
timestamp: May 23, 2017, 10:23:49 am
content: HiI have a telephone headset but it just connected to the announcement system on a train. How can I tell if its a carbon mic? And what sort of circuit do I need to get a regular audio signal that I can plug in to a PC audio input not the mic input.Thanks in advance.

author: Paul Price
author_rank: Super Contributor
timestamp: May 23, 2017, 01:53:08 pm
content: If you take the headset apart, and measure the resistance across the microphone you can see if its resistance of the microphone.If you measure something >100 ohms and <500 ohms regardless of the direction you apply the DVM probes, then it is a carbon mike.A carbon mike is quite big, several centimeters across.A electret mike will read 10K or more resistance and will be about 1cm in diam.A dynamic mike will measure <100 ohms, have a >1cm diam and you will hear a small click when you apply an ohmmeter.You can use a small electrolytic cap to at the output of an amplifier to couple the output of a single transistor common-emitter amplifier or an op-amp(LM358 for example) you could use to amplify the output of a carbon mike to a PC audio in jack.If you have a carbon mike you must apply a voltage to the microphone through a resistor (depends on the voltage of your power supply) but a 560 ohm resistor would be a good value if your supply is <12V.If the mike is an electret mike you will also need to bias the mike to a level of 3-5Volts and use a capacitor (1uF) to couple the output directly to a PC aud in jack and the mike will have polarity, you should find out which are the + and - terminals by trial and error if it not otherwise indicated. You want to use a positive voltage to the + terminal and this terminal is also the output.

author: abdullahseba
author_rank: Frequent Contributor
timestamp: May 23, 2017, 03:08:46 pm
content: Thanks.Looks like its a dynamic mic as it measured 42 ohms and I tried the diode test to hear for the click, so its effectively another speaker.Makes work a lot easier been dynamic.It has the industrial look of a carbon mic tho.
How to tell current drawn from a schematic - Page 1
Forum section: electronics / beginners

author: asteinhorn
author_rank: Newbie
timestamp: August 19, 2012, 04:08:49 pm
content: Hi all,I am relatively new to the EE field, and while looking at the schematic for a VCO, I had the following question; if i wanted to build a bipolar power supply using a transformer for the VCO, what current should said transformer be able to draw? More specifically, how can I tell the maximum current the VCO will draw by looking at the schematic? I got the schematic from birthofasynth.com, and I will post a link to it below:http://goo.gl/88KuQAny comments/help would be greatly appreciated. Not to be picky, but I would prefer an explanation to an answer, that I may be able to learn and use the knowledge in future projects.Thanks!

author: SeanB
author_rank: Super Contributor
timestamp: August 19, 2012, 05:08:56 pm
content: Largest current will be drawn by the buffer, as it has the potential to be required to supply 30mA into the pot. The rest add up to about the same, so you need a power supply that can supply +-15V at 100mA per rail.Simplest is to build a power supply using a 7815 and 7915, to give a power rail of 15V, and use a transformer able to supply 15VAC at around 0.5A, with 2 secondaries, or a 30VAC unit with a centre tap. A 100V 1A or 2A bridge rectifier ( always use a bridge rectifier rated at more than double the current drawn as a good rule of thumb, or a 1A unit if the current is less than 100mA) and a capacitor of between 1000uF and 4700uF at 35V ( 1000uF gives a ripple of around 1V, and a bigger value will reduce this a little, but you have to look at peak current through the bridge diodes as too big a value can exceed the repetitive current rating of the nominal 1A Dc diode), will then serve well as a reservoir for each rail. Unregulated input to the regulator will be in the region of 20-21V, so a small clip on TO220 heatsink ( the regulators will be dissipating around 0.6W each, so a clip on will allow you to dissipate heat up to the full 300mA the transformer will be able to safely supply) will perform adequately for each regulator. They will barely get warm, and you will have the ability to drive at least 2 of these VCO's, and have a few mA available if you want to add extra buffer amplifiers to drive long cables.
How to tell if a random buzzer component is piezo or magnetic? - Page 1
Forum section: electronics / beginners

author: HwAoRrDk
author_rank: Super Contributor
timestamp: July 26, 2016, 03:14:08 pm
content: I have a junk board here with a buzzer on it that - if it's a piezo - I potentially want to de-solder and reuse, but I can't actually tell whether it's a piezo or a magnetic buzzer. How can I distinguish between the two?Based on the fact it's got a '+' marking on it (piezos are non-polarised, and wouldn't need such markings, right?), and that it measures approx. 47 Ohms resistance on the meter, I'd tempted to say it's a magnetic buzzer.However, if I do a search on the part number printed on the side ("AAC HC1206A"), all the references I can find claim it's a piezo buzzer.So, I'm confused.Any fool-proof ways of telling?

author: Ian.M
author_rank: Super Contributor
timestamp: July 26, 2016, 03:22:11 pm
content: Pizeos with integrated electronics will have a polarity marking and may give a misleading reading on an ohmmeter. If the resistance remains the same when you reverse the test leads, (after isolating it from its drive circuit), or if a small steel nut on the end of a drinking straw is even slightly attracted to any part of its surface, its likely to be magnetic.

author: HwAoRrDk
author_rank: Super Contributor
timestamp: July 26, 2016, 04:11:11 pm
content: Pretty sure it's externally driven, as the negative pin is directly connected to a SOT-23 of some description, via a 33 Ohm resistor. I checked the resistance of the buzzer both ways, and same ~47 Ohm reading. Experimenting with offering up a small pin to the side of the buzzer revealed a slight attraction - but ever so small.I guess that settles it - it's magnetic. And the Googles, they lie!Shame, I want a piezo to experiment with, and thought this would save me the trouble of purchasing one.

author: jeroen79
author_rank: Frequent Contributor
timestamp: July 26, 2016, 05:07:52 pm
content: If it is magnetic then it should have some effect on a compassneedle or another inductor.

author: klunkerbus
author_rank: Unknown
timestamp: July 26, 2016, 05:22:01 pm
content: Why not provide a picture of the buzzer?
How to tell if this transformer is faulty? - Page 1
Forum section: electronics / beginners

author: reddish75
author_rank: Regular Contributor
timestamp: July 30, 2022, 11:05:43 am
content: This transformer in and out of circuit lights up my dim bulb tester brightly and doesn't dim, how do I test the transformer to see whether its faulty? Here's some resistance and continuity measurements as I couldn't think of which other tests to do,Secondary resistance measurementAcross k25 0.64r continuity acrossAcross k23 3.45r continuity acrossAcross k22 0.52r continuity acrossAcross k24 pins 1-3 4.78r continuity3-2 2.49r continuity1-2 2.49r continuityPrimary resistance measurementAcross k21 pins AC 3-5 9.68r continuity5-4 2.25r continuity4-3 7.62r continuity

author: armandine2
author_rank: Frequent Contributor
timestamp: July 30, 2022, 12:50:55 pm
content: check for shorts - I wonder why the primary resistances are so different?

author: eblc1388
author_rank: Frequent Contributor
timestamp: July 30, 2022, 12:56:35 pm
content: Quote from: reddish75 on July 30, 2022, 11:05:43 amThese two 115V windings should have roughly the same ohmic values because they both have the same number of turns. However, because one is wound on top of the other I would expect ohmic difference of 10%~30% max. between the two.In your case, such large ohmic difference indicates a possible inter winding short circuit. Try back feeding the transformer using a few volts AC from the secondary side and measure any possible voltages on the primary.Another test you can try while using the dim bulb tester is to short circuit any pair of the the secondary windings. If the light doesn't shows brightness changes, then the transformer is definitely faulty.

author: srb1954
author_rank: Super Contributor
timestamp: July 30, 2022, 06:16:18 pm
content: Quote from: reddish75 on July 30, 2022, 11:05:43 amDo you have an LCR meter?Checking the inductance of windings is useful if you suspect that there is an internal shorted turn and often gives a better indication of a problem than resistance measurements.For a normal transformer the inductance ratios between the various windings should be approximately the square of the voltage ratios between the respective windings. Any significant deviation from these ratios indicates a possible shorted turn.

author: dietert1
author_rank: Super Contributor
timestamp: July 30, 2022, 07:31:01 pm
content: As the primary is one coil it does not have two parts of 115 V each that can be used in parallel for 115V operation. So it has one strong 115V partition with lower ohms and the whole primary for 220V with somewhat higher ohms. Thats OK.Regards, Dieter
How to test a MOSFET - Page 1
Forum section: electronics / beginners

author: awyeh1234
author_rank: Contributor
timestamp: June 02, 2015, 12:09:26 am
content: How would i test a MOSFET with a digital multi meter? I have data sheets and i know where the drain source and gate are, But how do i test them?

author: dacman
author_rank: Frequent Contributor
timestamp: June 02, 2015, 12:19:32 am
content: One way that works for some is to short the gate to the drain and check for resistance to the source. Then short the gate to the source and check resistance to the drain. It should be open one way and closed the other.

author: rolycat
author_rank: Super Contributor
timestamp: June 02, 2015, 01:24:17 am
content: Alan (w2aew) has made an excellent video on this subject:
how to test a scope - Page 1
Forum section: electronics / beginners

author: texane
author_rank: Regular Contributor
timestamp: November 22, 2009, 01:07:52 pm
content: Hi,A friend of mine gave me a PM3207 scope for free, and thisis the first one I am ever using. He told me some things maynot be working.I am doing some basic tests, and nothing but noise appearson the screen. I read a lot of doc about scope thus I dontthink I am missing the the point... so do you have a verybasic test for me to do? For instance, there is a ProbeAdj onthe front of the panel. When I connect my probe on it, I getnothing (chan is the one selected, I used every time/div andvolt/div I could, results a re the same).When I try to probe a 5v ttl gate, I get nothing too. WhenI probe my ethernet RJ45 socket, I get a waveform, showingthat the probe is not dead.Any idea?Cheers,t.

author: texane
author_rank: Regular Contributor
timestamp: November 22, 2009, 02:02:22 pm
content: self answer: I was not on the same mass. A thing very weird however: there are 2 chans A and B. When I probe on the chan A, I get the signal being displayed HORIZONTALLY, not vertically, as this should be the case... (that is for chan B). I guess some mods have been done the scope.

author: Zero999
author_rank: Super Contributor
timestamp: November 22, 2009, 04:16:19 pm
content: I've found the easiest way to test a 'scope is to hold the probe in my hand and look for mains hum on the display. If the 'scope is working correctly, it should be easy to get it to trigger and display a distorted waveform.

author: Simon
author_rank: Unknown
timestamp: November 27, 2009, 05:31:45 pm
content: what type of scope is it ? analog or digital ? any scope normally has a self calibratrng signal generator built in sotry that first, or as hero said your finger will make enough signal for any functional scope to pick up

author: qno
author_rank: Frequent Contributor
timestamp: November 27, 2009, 05:59:37 pm
content: This is ananalog scope.It could bein X-Y mode?If you get a noisy signal is the line horizontal?Can you place a picture of what happens?

author: EEVblog
author_rank: Unknown
timestamp: November 29, 2009, 09:31:42 pm
content: Yes, show us a big photo of the front panel and display while the probe is hooked up to the "1KHz calibrator" output. That way we can see if all the controls are set correctly.Dave.
How to test a Triac - Page 1
Forum section: electronics / beginners

author: tazelikechickn
author_rank: Regular Contributor
timestamp: October 07, 2013, 11:01:08 am
content: I'm repairing an adjustable soldering iron for a friend (2 identical ones in fact - I think they have a common fault).I have checked a lot of components and am currently testing the Triac, but am a little confused in the testing method.Some say, use a analogue meter or a digital meter on diode setting, red probe to MT2, black to MT1, high resistance or no continuity, then place red probe to gate and MT2, causing the Triac to turn on, creating low resistance and it will stay in this state even when the gate connection is broken (similar to a MOSFET?)- others say that when the red probe is taken off the Triac will switch off.Which is correct? The one I am testing switches off when the gate connection is removed.Any suggestions?Also is there aneasymethod to check an opamp? They use a LM358 and that is my next component to check.Soldering irons that use all their electronic components in the iron itself, where all the heat is kept - no wonder they have both failed! Bad design I reckon!Any whoo.......just my thoughts.

author: locoo
author_rank: Contributor
timestamp: October 07, 2013, 12:25:27 pm
content: Thre thing you can do .1.Test it2.Buy and replace it is very cheap and if it dies once it will again .3.Buy a new won from ebay or dx.comit looks like one i had bought from dx .you can bypass all the electronics and directly connect the heater to the mains it will work but wery hot .

author: zapta
author_rank: Super Contributor
timestamp: October 10, 2013, 05:31:22 am
content: Quote from: locoo on October 07, 2013, 12:25:27 pmIs this a proper test?The triac did not hold the DC current when the gate current was removed.

author: kripton2035
author_rank: Super Contributor
timestamp: October 10, 2013, 06:17:05 am
content: a simple and efficient triac scr tester :http://translate.googleusercontent.com/translate_c?hl=el&ie=UTF8&prev=_t&rurl=translate.google.com&sl=es&tl=en&twu=1&u=http://www.soloelectronica.net/thyristor_and_triac_tester.html&usg=ALkJrhju_Ab3Is2aVcukNoNA4kJRgvE9yw

author: tazelikechickn
author_rank: Regular Contributor
timestamp: October 13, 2013, 05:40:28 am
content: Thanks for your comments guys, but as you can see, there seems to be different ideas about testing.Should the triac stay in the on postition when the red probe is removed from the gate?

author: Zero999
author_rank: Super Contributor
timestamp: October 13, 2013, 06:48:11 pm
content: Have you researched TRIACs/Thyristors to find out what they actually do first? Perhaps you should, then devising a simple test is easy.

author: geraldjhg
author_rank: Regular Contributor
timestamp: October 14, 2013, 12:44:59 pm
content: hitriacs are easier replaced than waste time testing themi woul insert them into a dimmer but y personallyprefer to change themsaludos
How to test an N-Channel MOSFET?? - Page 1
Forum section: electronics / beginners

author: Azhar
author_rank: Regular Contributor
timestamp: July 20, 2014, 01:20:11 pm
content: I have an LED TV which is dead. The main component in the power supply board is theMDF7N60Bwhich is anN-Channel MOSFET, I suspect it is the cause of the TV being dead, I already removed this component, but I am not sure how to test it!is there a way to test it with a DMM?Can I replace this MDF7N60B with any other equivalent component?Thank you in advance!MDF7N60B datasheet:http://www.datasheet-pdf.com/datasheet-html/M/D/F/MDF7N60B-MagnaChip.pdf.html

author: mij59
author_rank: Frequent Contributor
timestamp: July 20, 2014, 01:27:07 pm
content: Hi,Please take a look at this video.No its better to replace with the same mosfet.

author: Neilm
author_rank: Super Contributor
timestamp: July 20, 2014, 08:41:05 pm
content: First thing I do is check to is if there is a short between any of the pins.There are many factors that go into choosing a FET for a particular application. On resistance, off resistance, max peak current, max steady state current, max voltage, gate charge and others. If you have to replace a FET with a different one all these have to be taken into consideration. That requires an understanding of why that particular component was chosen. "Better" values might lead to unintended consequences.
How to test current on the negative rail with a Multimeter? Solved - Page 1
Forum section: electronics / beginners

author: t1d
author_rank: Super Contributor
timestamp: April 28, 2020, 02:42:13 am
content: I know how to do it, on a positive rail. Just put the meter in series. Have the probes aligned to have the power flow through from positive to negative.But, I have never measured current on a negative rail. And, I know that you must be very careful with your setup, when measuring current.So, how to do it properly? And, if you get it reversed, will the current reading just be negative, or will you blow a fuse, or destroy the meter?Just can't think well, tonight. So, thank you for your help.Here's the power supply schematic...

author: bob91343
author_rank: Super Contributor
timestamp: April 28, 2020, 03:07:41 am
content: You also put the ammeter in series with the negative rail. The reading will be negative.

author: rdl
author_rank: Super Contributor
timestamp: April 28, 2020, 03:22:39 am
content: Depends on how it's connected whether it is shown as negative or not, because the meter is actually measuring a voltage drop across an internal current sense resistor.

author: EEVblog
author_rank: Unknown
timestamp: April 28, 2020, 03:36:51 am
content: Just put it in series like on the positive rail. If the fuse is removable, then just remove F2 and put the meter in series.The measured current will include a small amount for the regulator, but it should be near enough.

author: t1d
author_rank: Super Contributor
timestamp: April 28, 2020, 03:54:48 am
content: Great! Thank you, everyone. I thought that if I had the polarity backward that the meter would just read negative. But, I didn't want to damage a meter.I can jump in at the fuse - Good suggestion.

author: EEVblog
author_rank: Unknown
timestamp: April 28, 2020, 04:08:01 am
content: Quote from: t1d on April 28, 2020, 03:54:48 amIt's next to impossible to damage a meter. Worst that can happen is you blow a fuse by testing voltage on the current rangeQuoteThat's the beauty of linear regulators like 7815/7915, current in is almost equal to the current out.
How to test dead components on a board? - Page 1
Forum section: electronics / beginners

author: Mechatrommer
author_rank: Super Contributor
timestamp: April 15, 2010, 04:32:11 pm
content: Can anyone teach a proper way of testing a working or broken components without separating it from its board?a) Resistorb) Capacitorc) Inductord) Diodee) Transistorf) FET/MOSFET?g) chipsAnd Dave, can u make a video on many types of diode and/or transistor and/or FET/MOSFET. Diode alone have many types (Scmith, Schotky, i dont know the names and differences), all i know diode is a one way ticket for the current to flow.

author: dds
author_rank: Contributor
timestamp: April 15, 2010, 05:27:44 pm
content: Oscilloscope, Huntron tracker, (component tester) while DUT is turned off.

author: dds
author_rank: Contributor
timestamp: April 15, 2010, 05:28:20 pm
content: ESR meter for elco capacitors.

author: djsb
author_rank: Super Contributor
timestamp: April 16, 2010, 09:43:16 am
content: Hi,Circuits should be checked using a top down approach wherever possible working from the front panel of a unit and finally down to component level. This helps to isolate a fault to a specific subsystem.1/ Visual check for burnt components,leaking capacitors,loose components,shorted tracks etc.2/ Voltage checks using Schematic or service manual if available.3/ Signals can be injected and traced to narrow down a fault.4/ When the specific suspect area is isolated then individual component checks can be done.5/ Most checks can be done with a multimeter using the ohm meter,continuity tester and diode test feature.a/ Resistor-Check for correct value, open or short circuitb/ Capacitor-Check if the capacitor charges using the ohm meter.c/ Inductor-Check for open circuit.d/ Diode-use diode check for correct forward voltage drop (0.7 for Silicon or 0.3 for Germanium etc) and infinite reverse resistance.e/ Transistor-Use diode check to test individual PN junctions.f/ FET/Mosfet-Check drain source resistance.g/ Chips-Check voltage at power pins and refer to schematic/data sheet for other voltages.That's the fault finding method I use anyway.Practice and persistence also helps.HTHDavid.

author: Kiriakos-GR
author_rank: Super Contributor
timestamp: April 24, 2010, 05:08:40 pm
content: I believe that all the "Ideas" , that David added so far , are all that you will ever need.But as Mediterranean technician , I would add and the most famous one .. the hammerIf everything else fails , its your only option !!
How to test if my oscillator is working? - Page 1
Forum section: electronics / beginners

author: davidleverett30
author_rank: Contributor
timestamp: July 20, 2016, 06:12:01 am
content: I am currently making a digital clock out of logic gates and an oscillator.I would like to check the output of the oscillator before using it in my project.What is the ideal way to test the oscillator? Using a multi-meter and it's frequency feature or my oscilloscope?

author: MosherIV
author_rank: Super Contributor
timestamp: July 20, 2016, 06:45:52 am
content: Oscilloscope

author: SeanB
author_rank: Super Contributor
timestamp: July 20, 2016, 07:00:14 am
content: Both of them will work. The multimeter will give the frequency only, and the scope will show you the frequency, the voltage and just how bad a waveform can be in a digital signal and still work. But both are valid, and usable.A frequency counter will however have more resolution and probably slightly better accuracy.

author: Brumby
author_rank: Unknown
timestamp: July 20, 2016, 07:42:41 am
content: To see what is actually happening, definitely start with the scope.Once you know that it works and what the signal looks like, you will know if it is sufficient to drive your meter's frequency measurement.Timing accuracy and stability will be dependent on the oscillator - and measurement thereof dependent on the meter's capability.
how to test IR2108 MOSFET driver - Page 1
Forum section: electronics / beginners

author: hussamaldean
author_rank: Unknown
timestamp: July 29, 2018, 09:14:25 am
content: Hi allis there a way to check if the IC work or not ?because when I apply 12V to the IC and 5V to HIN and inverter one to LIN the output remains high for both mosfetthis is the circuit from datasheetI used normal rectifier diode, 22uF 50V capacitor between Vb and Vs and 100Ohm resistor for the gate of the MOSFETplease helpregards

author: Andy Watson
author_rank: Super Contributor
timestamp: July 29, 2018, 02:11:14 pm
content: How are you measuring HO ? Remember that this output is relative to VS. Also, to properly function, the LO mosfet must conduct for a period such that the capacitor between Vb and Vs is charged.

author: hussamaldean
author_rank: Unknown
timestamp: July 29, 2018, 06:02:32 pm
content: Quote from: Andy Watson on July 29, 2018, 02:11:14 pmthe pin and the ground using oscilloscopeI tried the gate of the mosfet and same result

author: alsetalokin4017
author_rank: Super Contributor
timestamp: July 29, 2018, 06:46:12 pm
content: The "LIN" is an inverting input, right, indicated by the line above the letters?

author: hussamaldean
author_rank: Unknown
timestamp: July 29, 2018, 06:56:45 pm
content: Quote from: alsetalokin4017 on July 29, 2018, 06:46:12 pmI used NAND gate to get the invert state (my NOT gate is burnt) and still no hope to get the output

author: alsetalokin4017
author_rank: Super Contributor
timestamp: July 29, 2018, 07:17:23 pm
content: OK, let's back up a moment. Forget about the NAND and inverting your input. What happens when you simply apply the +5V signal to _both_ control inputs at the same time? This should produce HO high level and LO low level.And if you connect both inputs to COM (ground) you should see HO go low and LO go high.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: July 29, 2018, 07:26:01 pm
content: Quote from: hussamaldean on July 29, 2018, 06:02:32 pmNot ground, measure HO output relative to VS ! Which may or may not be at the same level as COM (ground). Measure LO output relative to COM (ground).

author: hussamaldean
author_rank: Unknown
timestamp: July 30, 2018, 07:05:55 am
content: Quote from: alsetalokin4017 on July 29, 2018, 07:26:01 pmwell, I will test it back when I get back from the vacation and I will update you
How to test LTV817 in circuit?  - Page 1
Forum section: electronics / beginners

author: Crambone
author_rank: Frequent Contributor
timestamp: July 14, 2024, 01:49:55 am
content: Is it possible to test LT817 Optocoupler in circuit?Andrew

author: Konkedout
author_rank: Frequent Contributor
timestamp: July 14, 2024, 02:26:59 am
content: What device are you asking about?Please give everyone a link to a datasheet.

author: StyxF2
author_rank: Contributor
timestamp: July 14, 2024, 02:28:47 am
content: https://optoelectronics.liteon.com/upload/download/DS-70-96-0016/LTV-8X7%20series%20201610%20.PDF

author: Crambone
author_rank: Frequent Contributor
timestamp: July 14, 2024, 03:22:56 am
content: Ok I got it guys thanks!Andrew