hybridfree/eevblog-posts huggingface dataset:
Momentary button behaving as a touch button (unintended). (Video and schematic)  - Page 1
Forum section: electronics / beginners

author: Sysse
author_rank: Newbie
timestamp: April 26, 2018, 04:41:40 pm
content: I've been trying to make a toggle switch using transistors. I watched Dave's video (https://youtu.be/Foc9R0dC2iI) but I couldn't get it to work, so I tried coming up with my own design, but I ran in to a funny problem. The momentary button doesn't actually have to be pressed (most of the time). It's enough to touch it to turn on the circuit.This is beyond me and I'm not even sure what to google at this point. I've included a short video (listen for the click of the button) and a beautiful handdrawn schematic.Any and all idea are welcome!Schematic:https://photos.app.goo.gl/phRSDsSl0OWZzvg32Video:https://photos.app.goo.gl/ZibzJBReuho79zWD3

author: eev_carl
author_rank: Regular Contributor
timestamp: April 26, 2018, 05:36:05 pm
content: I created a few toggles the other day with a SN74LS74AN D-Type Flip Flop ($0.61 USD from Mouser). You might try to build your own D-Type flip flop from a series of gates like thishttps://www.electronics-tutorials.ws/sequential/seq_4.htmlAnd build the gates from transistors like thishttps://www.electronics-tutorials.ws/logic/logic_5.htmlThe IC I used is really simple...a single connection from the switch drives the CLK pin. The output voltage appears on a different pin. PRE + CLR are high. D + ^Q are tied together.-Carl

author: Sysse
author_rank: Newbie
timestamp: April 26, 2018, 07:34:27 pm
content: Thanks for the tip! For now I'm going to try to figure this out so I don't get sidetracked, but gates with discrete transistors looks fun!

author: Jwillis
author_rank: Super Contributor
timestamp: April 27, 2018, 01:54:23 am
content: Switch may not be rated for the voltage your putting into it .Probably arcing inside.That would be my guess

author: BradC
author_rank: Super Contributor
timestamp: April 27, 2018, 04:35:25 am
content: You have a very high open impedance on that switch. It is not outside the realm of possibility you are coupling some floating EMI into that switch with your finger. As an experiment, change the 1M to 100K and see if you can still make it happen.
Momentary Switch to directional DC motor - Page 1
Forum section: electronics / beginners

author: Skylimit
author_rank: Newbie
timestamp: January 07, 2020, 05:54:52 am
content: I have an application that involves a 12V/24Vdc motor that currently uses a momentary toggle switch to tilt forward and back, depending on the direction the switch is pushed.I need to switch the toggle to a momentary PushButton. Each time the PB is pushed, the motor alternates direction- only while the button is held down.Many thanks in advanced!

author: ebastler
author_rank: Super Contributor
timestamp: January 07, 2020, 06:39:06 am
content: This is a bit more complex than you might think. "Something" has to remember the current state of the system, i.e. which direction the motor will travel the next time the button is pushed. I am not aware of electromechanical pushbuttons which would do this directly, via a latching mechanism.You could use discrete electronics (transistors or an integrated flip-flop), but then they would need standby power to remember the current state. Or you could use a microcontroller with a bit of flash memory to remember the state. In either case, you would need a driver (bipolar transistor or MOSFET) to drive your motor current. This all gets a bit unwieldy.I would suggest a purely electromechanical solution with a "latching relay": Use a DPDT latching relay to switch the polarity of the motor. And use a DPST momentary switch, with one pole to provide a voltage to the relay's coil every time the button is pressed, and the other pole in series with the motor.Implementation details aside: Are you sure this is a good solution in terms of the user interface it provides? I would probably find it annoying that I never know which direction the motor will move first when I start operating this.
Monitor Repair Ideas - Page 1
Forum section: electronics / beginners

author: DrMag
author_rank: Regular Contributor
timestamp: October 08, 2016, 03:39:54 pm
content: One of my monitors has started flickering badly when it first turns on--it does this for as much as a full minute before finally staying lit. Obviously time for a new monitor!Or not... I'm trying to learn how to diagnose (and hopefully repair) equipment, and I'd like to try my hand at this one. My first guess, as I've learned from Dave's repair videos and seeing others' work, is to replace the capacitor. That would also make sense, because the flickering is quite periodic, which implies an oscillator (and thus likely a capacitor) is happening somewhere.For those with experience, what else might be good for me to look at or replace in debugging the problem? Has anyone experienced this kind of failure and fixed it? Given it's a flicker (and not something else like a delayed refresh), where is the problem most likely to be occurring--the power supply?

author: helius
author_rank: Super Contributor
timestamp: October 08, 2016, 03:58:14 pm
content: Likely the CCFL is worn out and should be replaced. It flickers at a particular frequency as the inverter tries repeatedly to start it and then waits to avoid overheating.
Mono output signal generator for stereo use. - Page 1
Forum section: electronics / beginners

author: Tomer
author_rank: Regular Contributor
timestamp: January 04, 2018, 11:14:00 am
content: HelloI am intending to work on audio applications in mono and in stereo. I am looking for a signal generator and thinking i will have to buy a box with 2 outputs.Then i was thinking maybe i can save money, and buy a signal generator with only 1 output and somehow split the signal from 1 to 2 in order to test stereo applications.Is that something that i can do ? if yes what will be the cons for such split.Also how can i split the output, adapter maybe ?Thank you very muchTom

author: Zero999
author_rank: Super Contributor
timestamp: January 05, 2018, 12:34:54 pm
content: Yes, it can be done, just connect the inputs to the stereo together and then to the signal generator. The output impedance of most signal generators is 50Ohm and most amplifier inputs are much higher than that, so it's no problem. There is no need for any additional circuitry.

author: Seekonk
author_rank: Super Contributor
timestamp: January 05, 2018, 05:27:24 pm
content: Don't see why you would need to test both channels at the same time. I think I would have the option of inverting one of the outputs 180 degrees. Two channels in phase would be rough on a power supply of an amp.

author: tszaboo
author_rank: Super Contributor
timestamp: January 05, 2018, 05:34:24 pm
content: Yeah, but if you want to save money, why dont you use something that is made for audio? It is going to be cheaper and better suited.
Mooc on Analog electronics - Page 1
Forum section: electronics / beginners

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: October 10, 2015, 08:58:31 am
content: Let me advertise this new MOOC on analog electronics from the EPFL (Ecole Polytechnique Federale de Lausanne).(edit link)https://www.edx.org/course/electronique-i-epflx-electronixIt seems to provide a solid classical course on analog electronics.There will be 3 coursesElectronique 1, 2, 3 and it looks very nice.The first one deals with OpAMPS and last 8 weeks. The only (minor) problem is that you first need to learn frenchlanguage for the few who do not know already.Quote

author: SteveLy
author_rank: Regular Contributor
timestamp: October 10, 2015, 09:09:10 am
content: That link won't work for people not already enrolled. Try this:https://www.edx.org/course/electronique-i-epflx-electronixedX has some great courses, but yeah, for this one instruction isin French!

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: October 10, 2015, 09:23:16 am
content: Thanks, I have edited the link.Jacques

author: Simon
author_rank: Unknown
timestamp: October 10, 2015, 04:50:28 pm
content: Hopefully and probably to better standards than courses in the UK where procedures are more important than content and actual existence of content and there is no way to complain about the lask of content or it's innacuracy.
Moore  Finite state machines in programming - Page 1
Forum section: electronics / beginners

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: March 01, 2016, 04:52:10 pm
content: 1. I had been viewing this on youtube/edx courseExplains use of Moore FSM in embedded. Who else use Moore FSM or any other FSM like Mealey?2. I am used to superloop concept in which I design my own state, step by step. I had tried to put this Morre FSM in my ealier written code for ECG code. I found it extremely difficult by Moore FSM. Since there are so many tasks running, interconnections with ISR, multiple inputs , multiple outputs & other things, I got stuck. What is better method in these kind of situation.

author: mazurov
author_rank: Frequent Contributor
timestamp: March 01, 2016, 06:00:25 pm
content: You may want to take a look at UML state machine. Several implementations exist, the one I'm using is explained here ->http://www.state-machine.com/

author: bson
author_rank: Unknown
timestamp: March 01, 2016, 07:35:18 pm
content: FSM is pretty much required produce non-blocking, asynchronous software that you don't want to become an unintelligible mess. It's very useful for interrupt-driven I/O. Above all, the state diagram forces you to think through the states and their transitions before writing a single line of code. The pro forma particulars aren't particularly important; for analysis you're better off expressing it as a DAG anyway. (But if the graph is that big you're probably doing something wrong and should refactor. An FSM graph really should be on the order of obvious when you look at it.)

author: zapta
author_rank: Super Contributor
timestamp: March 01, 2016, 07:55:04 pm
content: Quote from: bson on March 01, 2016, 07:35:18 pmDid you mean directed graph?In real life applications FSMs often have cycles.

author: Vindhyachal.takniki
author_rank: Frequent Contributor
timestamp: March 02, 2016, 03:33:33 am
content: Made a code from his course for street light.Code:enum{goN = 0U, waitN, goE, waitE};typedef const struct{uint32_t output;uint32_t wait;uint32_t next;}street_light;street_light sl_fsm = {{0x21U,100U,{goN, waitN, goN, waitN},},{0x31U,100U,{goE, goE, goE, goE},},{0x41U,100U,{goE, goE, waitE, waitE},},{0x51U,100U,{goN, goN, goN, goN},},};void all_tasks_manager(void){uint32_t state = goN;uint32_t input;uint32_t output;while(1){output = sl_fsm.output; /* set tthe output */wait_delay_us(sl_fsm.wait); /* delay for spcified time */input = goN; /* input is goN for testing, otherwise input is from pins */state = sl_fsm.next; /* determine next state *//* to remove compilre warming */if(output){__nop();}}} /* function ends here */
More dumpster finds of the day  - Page 1
Forum section: electronics / beginners

author: Shadetreeprops
author_rank: Regular Contributor
timestamp: March 03, 2016, 12:37:03 am
content: I tested these to make sure they are working. THEY AREi had some of these already. but they were just sitting there in a box, with some large relays, and a old laptop computer, and a few circuit breakers.

author: Shadetreeprops
author_rank: Regular Contributor
timestamp: March 03, 2016, 12:46:03 am
content: this was sopposed to go into GENERAL my bad for accidently posting that here.

author: ZeTeX
author_rank: Frequent Contributor
timestamp: March 03, 2016, 02:23:04 pm
content: what current do they output at their rated voltage?
More help with OpAmps. - Page 1
Forum section: electronics / beginners

author: jgalak
author_rank: Regular Contributor
timestamp: December 24, 2017, 04:15:59 am
content: This time, it's a practical circuit I'm building. I have a source voltage that varies 0-5V (right now I'm just manually setting the voltage, eventually it'll be fed a sine waves). I need to resale that to be 0-2.5V. Since the source isn't very stiff (it's an R2R ladder), and since the IC I have has two OpAmps in it, I decided to first use a buffer, for its hight input impedance, followed by an inverting amplifier with G=1/2.I am using an LMC6482 single supply rail-to-rail opamp, fed 5V and ground at its V+ and V- pins.Circuit attached.The buffer is working fine. Voltage at point B is almost exactly the same as at point A (it's.7V when Vin is 0, but I can probably live with that).However, the second stage doesn't seem to work. In my first attempt, I grounded the non-inverting input. That resulted in Vout staying around zero, regardless of Vin. Having done some reading, I tried binding the non-inverting input with a voltage divider. Now Vout sits around 2.5V, regardless of Vin.Am I doing something obviously wrong? OpAmps are fairly new to me, so I can't tell if it's a design problem or if I just effed up the breadboarding.

author: jgalak
author_rank: Regular Contributor
timestamp: December 24, 2017, 04:57:58 am
content: Never mind. Breadboarding error.I can't seem to delete the thread. Could an admin please do so?

author: grouchobyte
author_rank: Regular Contributor
timestamp: December 24, 2017, 05:08:53 am
content: Get yourself a spice simulator like LTSPICE. As you've probably already discovered, or soon to discover if you get more into this analog stuff, it can and many times saves you theHowever, don't get too addicted to it. Its alot like porn in that its not like the real thing...@grouchobyte

author: jgalak
author_rank: Regular Contributor
timestamp: December 24, 2017, 05:21:09 am
content: LT Spice I'm having a lot of issues with. Need to dig deeper into it. But circuitlab.com was quite nice for this - showed me that the design was correct, and motivated me to start re-tracing the breadboarding for the N-th time.Now if only it was as easy to do DC sweeps in real life as it is in the simulator...

author: danadak
author_rank: Super Contributor
timestamp: December 24, 2017, 12:23:35 pm
content: You can do a simple DC sweep easily with a PSOC, 8 bits (or PWM withfilter to 16+ bits) and measure any deviation from it with a PSOC,to +/- .1% accuracy. The sweep ramp amplitude 4V, if more is neededan external OpAmp could easily enhance.See attached.You can control ramp amplitude and frequency solely in code or by sensingexternal pot by adding mux to A/D to respond to controls.UART transmits error to windows or Linux terminal session, or to file. Orwith some coding over USB. Or datalog to a SDCARD.Or an Arduino and PWM approach. To << accuracy.Basically a one chip approach.Regards, Dana.
More questions about my VIC-20 - Page 1
Forum section: electronics / beginners

author: MrAureliusR
author_rank: Unknown
timestamp: August 19, 2013, 06:16:27 am
content: In another threadwe started talking about the VIC-20 but it was off-topic and I'm going to continue the discussion in a new thread.I've spent the last half hour or so going through the resources CrazyApe linked in that old thread about the VIC-20:Quote from: Crazy Ape on August 18, 2013, 11:35:17 amAnd my board is the "other type you might find" he linked above. I'm STILL not quite clear which chip is the actual KERNAL chip, as I found one listed on eBay as "901486-07" but I don't even have one of those in mine! I have a -01 and a -06 directly to the right of the 6502A. Obviously the ones in the far upper left are the keyboard controller. And the video chip is also very obvious. So those are all ruled out. About 1/3 of the way from the left there's a chip marked 901460-03 which is mysterious. It is probably the RAM but I'm not %100 sure. It's linked into the 74LS245's. In the bottom left of the board, among some plain 4000 and 7400 series logic chips is an ocean of mysterious, identical chips made by that manufacturer who I always forget, their logo is the two short zigzags on top of each other. Not National Semiconductor, I can't remember... it'll come to me in a minute. EDIT: Just figured out these are the RAM chips! Crazy, there's 11 of them, for a total of 8k ...I was told that my version of the VIC was a Canada-only version that might be slightly different... not sure if that's true or not.Any and all info is appreciated, Googling isn't getting me very far! My ASSY number is 324003, apparently that can matter a lot.

author: Clint
author_rank: Regular Contributor
timestamp: August 19, 2013, 07:39:40 am
content: The Kernal will be mapped at E000-FFFF and should be in UE12You can check which roms are mapped where as the Pin 20's will be mapped to the correct SELECT Line - i.e. E000 will be on SEL E on the BUS.

author: Crazy Ape
author_rank: Regular Contributor
timestamp: August 19, 2013, 09:51:39 am
content: 901460-03 is the character rom.901486-01 is the BASIC ROM901486-06 is the KERNAL ROM (for NTSC-M systems with 14318181/14 Hz clock frequency and a 6560 video chip)901486-07 is the KERNAL ROM (for PAL-B systems with 17734472/16 Hz clock frequency and a 6561 video chip)You can look up the MOS part-numbers here:http://www.cbmhardware.de/mosic/Here's a better image of your board.http://www.mainbyte.com/vic20/vic20_mb.jpgYou should have a look through these books:http://www.bombjack.org/commodore/books/pdf/SAMS_Computerfacts_(CC3)_VIC-20.ziphttp://www.bombjack.org/commodore/books/pdf/VIC_Revealed_(US_Version).ziphttp://www.bombjack.org/commodore/commodore/VIC-20_The_Friendly_Computer_Technical_Manual_%28PN_990440%29.pdfhttp://www.bombjack.org/commodore/books/pdf/The_VIC-20_Connection.ziphttp://www.bombjack.org/commodore/books/pdf/VIC-20_Users_Guide.zipLot's more books on the VIC-20:http://www.bombjack.org/commodore/books-kim-pet-vic.htm
More scope memory questions! - Page 1
Forum section: electronics / beginners

author: Dan Moos
author_rank: Frequent Contributor
timestamp: January 02, 2017, 08:49:06 pm
content: Ok, I'm still trying to wrap my head around how waveforms are stored in my scope (un-modded Rigol 1052e)I watched w2aew's excellent video on the matter, and that is where I get my process. The answers I get are usually not what I expect though.Ok, the manual says in long memory mode, I should have either 512 Kpts, or 1 Mpt. I assume that means I get the lower number with both channels active, and the higher with one active.With only one channel active, I have the scope set for 200us per division.the scope says I'm getting 100 Meg samples.Scope has 12 horizontal divisions.100,000,000 * .0002 * 12 = 240,000 points.Ok, since that's not the 1 Meg points I expected, I can think of three possibilities:1) The record length extends beyond the screen2) The scope doesn't always use its full memory, and changes it depending on horizontal settings.3) My math is done improperly.Any thoughts?

author: StillTrying
author_rank: Super Contributor
timestamp: January 02, 2017, 09:03:35 pm
content: Ok, I'm still tryingNo, that's me!1) The record length extends beyond the screenThat one I think, other than at the lowest time base speeds = roll mode.

author: JPortici
author_rank: Super Contributor
timestamp: January 02, 2017, 09:41:48 pm
content: easy to find out: single acquisition. now move the horizontal axis. if you see data from "outside" the screen, there you go.

author: tautech
author_rank: Super Contributor
timestamp: January 02, 2017, 10:51:30 pm
content: Dan, see the animated gif in this post by rf-loop.https://www.eevblog.com/forum/testgear/siglent-sds1000x-series-oscilloscopes/msg933997/#msg933997Observe the sample rate, memory depth and timebase settings.
more synchronous motor questions that make no sense - Page 1
Forum section: electronics / beginners

author: Simon
author_rank: Unknown
timestamp: January 25, 2019, 05:00:24 pm
content: QuoteSo how can (ii) be calculated? sure the new emf is now 90% so how can there be both an unknown PF and stator current draw? one determines the other ?

author: Simon
author_rank: Unknown
timestamp: January 26, 2019, 10:01:13 am
content: My take is that if i assume no load angle change i can calculate the new IXs vector and it's angle, but as load angle will influence the IXs angle and therefore the power factor one needs to be known. Can I make the assumption that given the exitation is reduced by 10% the load angle shifts by 10% as maybe the torque is now 90% of what it was?

author: Simon
author_rank: Unknown
timestamp: January 26, 2019, 10:04:48 am
content: Or given the attached i could indeed calculate the new current and it's angle or the angle of the E vector
More VHDL help! Compilation errors! - Page 1
Forum section: electronics / beginners

author: McPete
author_rank: Regular Contributor
timestamp: November 03, 2011, 01:16:18 am
content: Hi all,Sorry to be such a pain, but I'm having some trouble getting my latest VHDL project up and running- It's a strobing display, and I'd like some help picking out the lexical/syntax errors I may have created...Thanks!P.Errors;QuoteCode;Quote

author: joelby
author_rank: Frequent Contributor
timestamp: November 03, 2011, 02:51:42 am
content: This line seems to be missing some bits:IF count_op(2) <= '1' AND count_op(1) <BEGINThe 'if' statement needs a 'then' and 'end if' and the 'begin' needs a 'process'.
Morning clampers! - Page 1
Forum section: electronics / beginners

author: PerranOak
author_rank: Frequent Contributor
timestamp: December 03, 2020, 01:47:40 pm
content: I was intrigued to learn of the "clamper circuit" - see attached.I fiddled about in LTSpice but could only get the lowest peak to -164mV; so it's still a bit negative. The Schottky gives the best (i.e. closest to zero or +ve) even though its forward voltage is supposed to be 450mV.I saw another circuit that uses a voltage source (say, a battery) "under" the diode to boost the level but this seems like cheating(!)My questions are:Is a Schottky the best diode choice?Why is the lowest point 164mV and not 450mV?Is there a way to stop it going negative without a battery?Cheers.

author: Berni
author_rank: Super Contributor
timestamp: December 03, 2020, 02:04:46 pm
content: Yep schotkey is the best you can do with this setup.The way to prevent it from going negative is to use 4 diodes in a specific forward biased configuration like it is used here:https://www.maximintegrated.com/en/products/analog/analog-switches-multiplexers/MAX4936.htmlIts a bit of an unusual circuit that can handle very large voltages, while instead having the limitation of the signal it is passing getting clamped before it even gets to 0 so it instead needs a negative supply if you want your output signal to actually reach 0 at all. A very popular use of this circuit is medical ultrasound machines to protect the milivolt RX amplifiers from the >100V TX pulses.

author: TimFox
author_rank: Super Contributor
timestamp: December 03, 2020, 02:46:45 pm
content: Another name for this circuit, especially in analog video circuits, is "DC Restorer", which is a misnomer. It is used in AC-coupled signal chains to get the "black" level in a waveform that is known to be unipolar (i.e., positive or negative-definite). A better method for video purposes is to use a FET switch ("keyed clamp") that is turned on at a specific interval ("back porch") of the waveform, instead of the diode.
MOS current mirror with Early Effect formula derivation - Page 1
Forum section: electronics / beginners

author: Starhowl
author_rank: Newbie
timestamp: February 20, 2015, 07:09:57 pm
content: The current mirror ratioI_o/I_REF = ((W/L)_1 / (W/L)_2) * (1 + lambda*V_DS1)*(1 + lambda * V_DS2)can also be expressed asI_o/I_REF = ((W/L)_1 / (W/L)_2) * (1 + (V_o - V_GS)/V_A),which implies that(1 + lambda*V_DS1)*(1 + lambda * V_DS2) = (1 + (V_o - V_GS)/V_A).Can someone explain to me why?(You can see the identity on page 5 of the attached PDF or on p. 529 of Microelectronic Circuits)
Mosfet driver charge pump? - Page 1
Forum section: electronics / beginners

author: Tantalum
author_rank: Regular Contributor
timestamp: December 31, 2020, 10:09:39 am
content: HelloI needed to use a LTC7001 MOSFET driver with charge pump. It may be used to dim LEDs at a frequency of 100Hz-1kHz but most of the time it will be used to switch on and off loads.Datasheet:https://www.analog.com/media/en/technical-documentation/data-sheets/ltc7001.pdfWhat I don't understand in their application example is why the minimum voltage on Vcc changes.7...15V5...15V3.5...15V6...15VThe last example is the one which best resemble my application. But I'm concerned with its 6V minimum on Vcc, since I only have 5V available.Q1:The driver has a charge pump, what does it change to have 3.5V or 7V minimum on Vcc??? In both cases the transistor gate will have 12V, not?The charge pump is also feeded by the high voltage source anyway, after first start-up.I would say a low voltage on Vcc will only delay a little bit more the first start-up of the mosfet, right?(After that the boost capacitor is charged from the high voltage Vin)Q2:I only have 5V on my board. I could add a 12V LDO connected to 28Vdc, but only if that gate driver doesn't consume too much to avoid the LDO to overheat. But I have no idea what that chip consumes.225uA??? Really???And how much at ~1kHz switching?I find that very low since there are other drivers which uses several Amps.Thanks for your help.
MOSFET  60.000 V/usec slew rate? - Page 1
Forum section: electronics / beginners

author: MasterT
author_rank: Frequent Contributor
timestamp: February 04, 2023, 05:12:31 am
content: I wander, if math is correct. DS says rise time 5 nsec, test condition 300V, than slew rate is300 / 0.005 = 60.000 V/usec.https://www.st.com/en/power-transistors/std1nk60-1.htmlIs it really so high?

author: Kim Christensen
author_rank: Super Contributor
timestamp: February 04, 2023, 09:40:25 pm
content: I think so. As per figure 20 in the datasheet, it's a bit more than that since it's from 10% (30V) to 90% (270V).So: (270-30) / 5nS = 48V/ns.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 04, 2023, 10:49:06 pm
content: Not unusual -- SuperJunction type MOSFETs have considerably reduced Cdg (Crss) under bias (notice Fig.7, it's almost zero for Vds > 10V).t_f is limited by Coss and R_L, hence the asymmetry.Note that the transistor is basically off, much sooner than t_d(off) + t_f suggests; much of the time is spent at low Vds, charging the relatively massive capacitance down there. This occurs in less than 10% of the swing (the 0 to 10 or 20V range where C's are large; whereas 10% of the rise is a full 30V) so all happens before t_f begins as such. But channel current has completely stopped somewhere during t_d(off) and load current is simply charging capacitance the rest of the way. If you have a load which charges that capacitance much quicker (e.g. a half bridge in hard switching), you'll see comparable times for both rise and fall.Tim
Mosfet Active Rectifier Center Tapped Version - Page 1
Forum section: electronics / beginners

author: mercurial
author_rank: Regular Contributor
timestamp: January 22, 2024, 09:40:12 am
content: Was trying to build an active rectifier using mosfets (N channel), using a full wave configuration (that usually has 2 diodes and a center tapped transformer)My ac voltage would be regular mains 50Hz and trying to rectify a voltage of 10 - 0 - 10 Vac from transformer secondary, current would be around 100 to 150A.I saw a configuration on wikipedia (image attached), but see some flaws in the design.I see that in the positive half cycle when the top mosfet is conducting the bottom mosfet will short out through the internal diode also I think the output polarity is reverse of what is show, does this topology work at all.Could someone explain the correct way of doing this?

author: Andy Chee
author_rank: Super Contributor
timestamp: January 22, 2024, 10:01:33 am
content: Take a look at the LM5045 and UCC28250 datasheets for some examples of synchronous rectification.

author: Kleinstein
author_rank: Super Contributor
timestamp: January 22, 2024, 12:16:07 pm
content: The way the circuit is drawn, the MOSFETs should only conduct for the negative half cycle. The FETs are drawn to create a negative voltage relative to the center.

author: Konkedout
author_rank: Frequent Contributor
timestamp: January 23, 2024, 05:36:32 am
content: Yes this is a "full wave center tapped synchronous rectifier." When using a MOSFET as a rectifier, current direction is opposite to normal use and it must be the same as the drain body diode which is shown in the schematic. A full wave center tapped rectifier conducts only from one side of the secondary winding at a time. So the transformer power output versus size and weight is not the best.N channel MOSFETs are more better than P channel MOSFETs in performance versus (size and cost) so that aspect is also OK. But with positive gate drive that means that they end up rectifying on the negative side of the output as this one does, not the positive side.Fundamentally I don't see any problem with the design as shown, but it is missing details regarding the gate drive. In simple terms you can drive the gates with RC coupling and clamp zener diodes driven by the opposite side of the winding. But I recommend care and simulation before blowing up any parts.You can get better performance out of a transformer with a "current doubler" rectifier design but that requires two inductors.https://www.how2power.com/article/2016/february/how-it-works-the-current-doubler-demystified-.php
MOSFET as amplifier: Can voltage after amplified can be calculated? - Page 1
Forum section: electronics / beginners

author: Walt Peter
author_rank: Newbie
timestamp: March 19, 2016, 08:07:30 am
content: Hello. I am going to start my first project. I now wants to use a N Channel Enhancement MOSFET, named TO-220 AB to as an amplifier. The bellow is a circuit I created a moment ago.The main voltage input is 9 Volts and there is another input I used as a controller of voltage in the circuit, which is 1~9 Volts. If, I run this circuit:How can I know the voltage received by the DC motor (after the original voltage is amplified) ?ORHow can I calculate the voltage after amplified? Can I simply sum up the voltage at Gate and Drain and I will get it?Thank you.

author: Zero999
author_rank: Super Contributor
timestamp: March 19, 2016, 08:36:51 am
content: You have a source follower there which has no voltage gain. If anything it has voltage loss. When the input is 9V, the voltage across the motor will be the MOSFET's threshold voltage less.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: March 19, 2016, 10:36:30 pm
content: @Walt Peter:The "TO220AB" refers to the mosfet's package style, it is NOT a mosfet part number. There are many many different mosfets available in the TO220AB package, and they will all have different relationships between the applied Gate voltage and the Drain-Source resistance. If you know the _part number_ of the actual mosfet you want to use, you can then look at the Data Sheet for that part number and you will usually find typical graphs which will show you the relationship for your particular part.However, mosfets are not usually used in the way you seem to be intending. Usually we would expect a mosfet to be fully OFF or fully ON, not in-between, because mosfets operated in the "linear region" (partially ON, determined by Gate voltage) will waste a lot of power by heating up. Also the "linear region" is typically a very small range of Gate voltage. Mosfets function differently than bipolar junction transistors in this way.If you are trying to control a motor's speed with a mosfet, you should use a Pulse-Width Modulation scheme, which turns the mosfet fully ON and OFF but in brief pulses. The width of the pulses are varied by the circuit in order to control the motor's speed.
Mosfet curve question - Page 1
Forum section: electronics / beginners

author: jomosoft
author_rank: Contributor
timestamp: March 16, 2025, 01:09:15 pm
content: Can anyone explain me why there is a dip in the Id curves ? Made this curve with the Rigol DP832 power supply just clipped on a BS170.

author: mtwieg
author_rank: Frequent Contributor
timestamp: March 16, 2025, 01:58:36 pm
content: Quote from: jomosoft on March 16, 2025, 01:09:15 pmGuessing the part is being cooked to death during the test. Typically these tests are done while applying the bias in brief pulses, with time in between to keep average power dissipation low.

author: jomosoft
author_rank: Contributor
timestamp: March 16, 2025, 03:42:39 pm
content: Not according to my component tester, I used rather conservative voltages with current limits programmed in the dp832.

author: David Hess
author_rank: Super Contributor
timestamp: March 16, 2025, 03:55:02 pm
content: 1 volt at 50 milliamps is only 50 milliwatts and well below the power limit of 840 milliwatts with 6.6 mW/C derating, and the curve is still bowed.It could be oscillating. I would put some resistance in series with the gate close to the MOSFET, or add some ferrite suppression beads.

author: jomosoft
author_rank: Contributor
timestamp: March 16, 2025, 05:15:27 pm
content: I was trying to replicate the datasheet curves using voltages in the same range. My goal was to use a python program in combination with the dp832 to do this. I found this procedure on an older post in this forum.

author: RoGeorge
author_rank: Super Contributor
timestamp: March 16, 2025, 07:08:55 pm
content: I guess the script is this one:https://www.eevblog.com/forum/testgear/rigol-dp832-power-supply-as-automated-curve-tracer/msg3745039/#msg3745039I didn't test it at smaller currents. Only measured back then a few power MOSFETS (with radiator) and didn't notice any oscillations. Could be.

author: David Hess
author_rank: Super Contributor
timestamp: March 16, 2025, 07:38:16 pm
content: Quote from: RoGeorge on March 16, 2025, 07:08:55 pmThe oscillation could be 100s of MHz for such a small MOSFET, so not so easy to detect.
mosfet datasheet missing specs - Page 1
Forum section: electronics / beginners

author: LaserTazerPhaser
author_rank: Regular Contributor
timestamp: August 19, 2019, 07:16:03 am
content: Obtained a many of thesehttps://lcsc.com/product-detail/MOSFET_Foshan-Blue-Rocket-Elec-BR13N50_C328554.htmland datasheet is missing transient thermal impedance and safe operating area tables.From the supplied data it be determined if it can handle a constant ~1amp @ ~175V without incurring damage?

author: amspire
author_rank: Super Contributor
timestamp: August 19, 2019, 07:31:46 am
content: Quote from: LaserTazerPhaser on August 19, 2019, 07:16:03 amIf you can keep the case temperature at 25 degC, you can, but it still would be a bit close to the absolute maximum rating for comfort.It is also not that easy keeping the case at 25 degC or lower. That is not the heatsink temperature - that is the case temperature and so you would need a heatsink that was well below 25 degC while dissipating 175W. Depending on the heatsink design, it could mean keeping the heatsink average temperature below 15 DegC.Richard

author: LaserTazerPhaser
author_rank: Regular Contributor
timestamp: August 19, 2019, 07:35:57 am
content: Quote from: amspire on August 19, 2019, 07:31:46 amThe question really was whether the safe operating area would permit ~1A @ ~175V.Going to gang at least 3 of these.

author: amspire
author_rank: Super Contributor
timestamp: August 19, 2019, 09:13:22 am
content: Quote from: LaserTazerPhaser on August 19, 2019, 07:35:57 amIf you look at 13N50 mosfets from other manufacturers, the rating is for about 400mA at 175V at 25degC. So three in parallel would be right on the limit.If the mosfets could be in series with 60V across each, there would be no problem at 2A.

author: David Hess
author_rank: Super Contributor
timestamp: August 19, 2019, 04:54:19 pm
content: Quote from: amspire on August 19, 2019, 07:31:46 amPower MOSFETs can suffer from thermal instability at high drain voltage because the temperature coefficient of the current versus gate voltage reverses. This limits SOA (safe operating area) in the same way that secondary breakdown in bipolar transistors does.Just because the power MOSFET datasheet does not show the thermal instability line in the SOA graph does not mean that it has a square SOA. On the contrary, it usually means that the SOA at high drain voltage is horribly bad and the MOSFET is only intended for switching applications.For the highest performance switching power MOSFETs, the start of the thermal instability region is no better and may be worse than a comparable bipolar transistor.
Mosfet drain/source minimum voltage - Page 1
Forum section: electronics / beginners

author: speedy_rudolf
author_rank: Newbie
timestamp: June 20, 2015, 02:35:35 pm
content: Hi, everyone.I have a very basic question. I have a couple mosfets in half-bridge configuration. I would like to know what could happen if I turned the mosfets on, but there was no current on either drain or source pins.A basic circuit representation is as in the image attached. So, basically, both h-bridges are turned on by the same driver, but only one of them gets any voltage at all. What would happen to the mosfets when the opto-triac is switched off and the mosfet switched on?Thanks in advance.

author: PSR B1257
author_rank: Frequent Contributor
timestamp: June 20, 2015, 02:41:05 pm
content: QuoteYou can't turn them on in this configuration.Just applying a potential on the gate of the MOSFET does not turn it on. That requires a potential difference from gate to source. In your case it requires more specifically floating voltages for each MOSFET.What are the opto-triacs for (in your mind)?

author: speedy_rudolf
author_rank: Newbie
timestamp: June 20, 2015, 02:55:17 pm
content: Well, the optos are there to "apply" voltage only to specific group of mosfets/h-bridges. I know, i could have used other components as wel (mosfets for one), but i chose opto-triacs because of reverse voltage spikes (the h-bridges will eventually be used for switching inductive loads).but back to my main question. Let me rephrase: will it be a problem (maybe destroy the mosfets) if i apply voltage to the gate, but there is no voltage/current on either drain and source pins?

author: PSR B1257
author_rank: Frequent Contributor
timestamp: June 20, 2015, 03:31:12 pm
content: QuoteI dont see the point. You already have two switches. If you have no driving voltage, the MOSFETs will block any current anyway.A H-bridge consists of two sides. Just applying voltage to one side is meaningless since there is no current flow at the other side.The bipolar supply voltage is also not necessary. The bridge applies the total supply voltage (in your case 440V) to the load. It does not matter whether it is a uni- or bipolar supply voltage.QuoteWhat should the triacs do about these voltage spikes, haYou need to put free wheling diodes aross the MOSFETs in order to clamp these voltages.QuoteNo.
MOSFET driver as buck converter? - Page 1
Forum section: electronics / beginners

author: step_s
author_rank: Regular Contributor
timestamp: September 09, 2016, 05:59:29 pm
content: Hi.I was messing around with the TC 4420http://ww1.microchip.com/downloads/en/DeviceDoc/21419D.pdfdriving a bigger MOSFET in a asynchronous buck converter.Looking at the internal schematics of the TC 4420, it contains a CMOS configuration, and it had me thinking that it could be used directly as a synchronous buck converter, with just 1 PWM module to the input.Would this even be possible? Anything I need to take into consideration here?Hope you can help.

author: tatus1969
author_rank: Super Contributor
timestamp: September 09, 2016, 06:47:18 pm
content: that would result in a really low power device, as the chip has ~ 5 ohms output resistance. There are stronger ones of this type. I have used a similar one like yours to build up a simple unregulated DC/DC, schematic attached. Works like a charm.

author: step_s
author_rank: Regular Contributor
timestamp: September 09, 2016, 07:16:57 pm
content: Ye, I see the problem. It's around the 2.5ohms output resistance (or so it says in datasheet).So theoritically it would work, but I just need to adjust the parts for a very low power output?

author: tatus1969
author_rank: Super Contributor
timestamp: September 09, 2016, 07:26:30 pm
content: Quote from: step_s on September 09, 2016, 07:16:57 pmYes, but you'll need to add a PWM stage, feedback circuitry, and error amplifier, and I guess that would end up more complex and costly than just using an integrated solution including the MOSFETs. There are even modules that include the inductor, like EP5348UI. Cost less than 2$, incredibly small, just 2x1.8mm. You only need to add a few R and C.

author: step_s
author_rank: Regular Contributor
timestamp: September 09, 2016, 07:58:51 pm
content: I understand what you are coming from. It was just meant as a thought experimentI tried hooking it up to a couple of caps and an inductor, and got some pretty strange performance. The waveforms were not what I expected, so I guess it's not really plausible.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 10, 2016, 07:57:33 am
content: Downside: it has to be switching constantly, because it has no tristate option.Current feedback and hysteretic oscillation (followed by an op-amp for voltage control) would probably be as good as anything. You can't really current-protect such a circuit because, under short-circuit conditions, it simply switches as fast as it can. It's doomed either way...Tim
MOSFET driver for controlling common cathode LEDs - Page 1
Forum section: electronics / beginners

author: Remark
author_rank: Contributor
timestamp: August 04, 2024, 04:31:55 pm
content: Hello,I have encountered a problem controlling 24V LEDs using a transistor. According to the common cathode LEDs configuration, I finished my design with N-channel and P-channel MOSFET drivers for high-side switching, where the MOSFET is turned on with a low signal and turned off with a high signal. However, when simulating the schematics, I noticed some voltage across the simulated 'LED' when the 'driver' is switched off. Could I ask where this voltage comes from and why it isn't zero or near zero when switched off?

author: tooki
author_rank: Super Contributor
timestamp: August 04, 2024, 04:57:03 pm
content: Quote from: Remark on August 04, 2024, 04:31:55 pmUmmm… take a closer look at the “some voltage”: it’s 5.8ᴇ-5.Youdoknow how to read scientific notation, right?That means 5.8 x 10-5V = 5.8/100000 V = 0.000058 V = 58 microvolts.That’s very much “near zero” in the context of 24V.

author: PGPG
author_rank: Frequent Contributor
timestamp: August 05, 2024, 09:02:13 am
content: Quote from: Remark on August 04, 2024, 04:31:55 pmI think you have bigger problem in your design than 58μV at LED when switched off.Have you read Absolute Maximum Ratings section of IRF9540NPBF datasheet?

author: MrAl
author_rank: Super Contributor
timestamp: August 06, 2024, 02:34:40 pm
content: Quote from: Remark on August 04, 2024, 04:31:55 pmHi,What current does each LED draw and how are they wired, in series parallel, and if so how exactly?The IRF9540 seems to have a pretty high current rating but you also have to watch out for power dissipation.For your original question, LEDs do not draw much current when the voltage is below the normal operating voltage. That means the resistance of the LEDs may be high until they start to light up. The mosfet will have leakage current, and that will 'power' the LEDs, but they probably will not light up because this current would be far too small in most cases. So nothing to worry about. The leakage current could be from 2.5ua to 250ua, which is still not that much but could light up one or more LEDs slightly. That's at max temperature though, which would only occur if you were using the transistor at the maximum current with minimal heat sink.Is that voltage of 5e-6 volts correct? If so, that's nothing to worry about. It's from the leakage current of the mosfet and/or part of the internal voltage of either a diode or the LEDs (the models sometimes use small biases they may refer to as the band gap voltage although that may not really be the reason for every model).
Mosfet driver PWM behaviour  - Page 1
Forum section: electronics / beginners

author: Iali
author_rank: Newbie
timestamp: March 30, 2021, 05:22:48 pm
content: Hi,I have a simple dual D4184 mosfet pwm driver board that I’m testing with a 3Mohm dummy load trying to understand how a perfect square PWM signal translates on the power side of this circuit. I’ve attached a picture of what I’m seeing on my oscilloscope. The yellow signal is the driving PWM and the blue one is the output across the dummy load. To me it appears that the reason the power output has a trailing end is because the mosfets have capacitance due to the nature of how they are constructed. Is my understanding correct and is there anyway to correct this behaviour?

author: Manul
author_rank: Super Contributor
timestamp: March 30, 2021, 07:33:32 pm
content: There is no schematic, so it is unclear. Anyway, if the output is two mosfets in half bridge (aka push-pull) configuration, then this is not normal. It looks like maybe the low side mosfet is not turning on, so the capacitance disharges very slowly through resistor. Yet, the trace shows very linear voltage drop, it is not a typical RC exponential curve, so I don't know. Schematic needed. By the way, 3 megaohm resistor is a very high resistance. It is more like a dummy leak, then a dummy load

author: Iali
author_rank: Newbie
timestamp: March 30, 2021, 08:27:23 pm
content: Thanks for the response Manul. Here is the link to the board I’m testingmosfet driverNot sure how it’s configured but I’m guessing not H-bridge as far as I know. I measured the output signal across the Vout +/- and I can see on the board that Vout+ is wired directly to Vin+, so looks like the mosfet is switching the ground side which I believe is a typical configuration. I’m assuming the mosfets are wired in parallel to increase power capacity.

author: Manul
author_rank: Super Contributor
timestamp: March 30, 2021, 10:10:13 pm
content: Yes, by looking the image of the board there are two mosfets in parallel switching on the low side. Your measurement also explains why the scope trace looked inverted (fast rise, slow fall). It happened, because you measured in reference to +DC, not ground. It is ok, but more common is to measure in reference to circuit ground.So, if we think about mosfet switching on the low side, we can say that it will produce fast falling edge when it turns on (because on resistance is very small). When it turns off, the voltage at its drain will rise, because it is pulled up by your dummy load. The output capacitance of two D4184 mosfets at low applied voltages can reach 2nF (look capacitance graph in the datasheet). It is quite a lot. Your resistor is also huge. If you would use smaller resistor it would look more rectangular, because it would pull up a lot stronger. Try 1K resistor.

author: Iali
author_rank: Newbie
timestamp: March 30, 2021, 10:32:02 pm
content: Thanks for this explanation Manul. You are right and I'm not sure why I didn't reference ground instead of V+ but I'll definitely try that next and also use a smaller resistor and see if the results are more square. Much appreciated!