hybridfree/eevblog-posts huggingface dataset:
BJT transistor model - Page 1
Forum section: electronics / beginners

author: edba
author_rank: Contributor
timestamp: February 03, 2021, 01:27:32 pm
content: HiI have been wondering about creating a behavioral model for a BJT transistor using a sub circuit. The model would cover large signal (DC) and small signal (AC) behavior.I wondered if anyone knows how to do this. I have thought about using the Ebers-Moll model so DC would be an ideal diode and currect soure (HFE*IB) and AC uses re and (hfe*ib).I know spice offers the gummel and poon model but think the model is over complicated and takes some of the understanding away, having so many parameters when I only want to model a few. I don't know why it is so complicated as I have known analogue engineers from the 60s, 70s and 80s who don't even uses computers to design their circuits, so believe a more practical approach is better when you get a feel for how the model works,BrEdba

author: Terry Bites
author_rank: Super Contributor
timestamp: February 03, 2021, 01:49:07 pm
content: Why reinvent the wheel?

author: edba
author_rank: Contributor
timestamp: February 03, 2021, 03:10:19 pm
content: I want to know whats under the hood i.e. I just want a simplified model that you see in text books, or how do you disable the parameters of the gummel and poon so that it is just like the ebers moll. I know the spice documentation says it simplifies to this but it doesn't say what parameters you need to switch off.
BJT vs FET in dummy load - Page 1
Forum section: electronics / beginners

author: jay
author_rank: Regular Contributor
timestamp: September 25, 2014, 01:47:24 pm
content: All the dummy loads discussed on the forum seem to use a power FET (Or maybe I missed something while searching?). What are the reasons to not use power BJT? Base current? Min voltage?

author: Simon
author_rank: Unknown
timestamp: September 25, 2014, 01:51:33 pm
content: Base current could become a problem for high power loads as I believe larger BJT's have lower HFE although darlingtons could be used.Other than that no idea

author: Seekonk
author_rank: Super Contributor
timestamp: September 25, 2014, 02:41:03 pm
content: There is an abundance of FETs out there. I scavenge FETs from old UPS inverters. Can't remember when I have found something as once common in the 2N3055 range. They are easy to drive without having to go the extra steps as multiple darlingtons. You are still limited to the same power per package size. So I would say it is availability.

author: c4757p
author_rank: Super Contributor
timestamp: September 25, 2014, 02:59:39 pm
content: VCE(sat)means the load won't work at low voltages with a BJT. The required base current will cause an error term in the current sensing if sourced from the load's internal power supply, and if sourced from the DUT, this will increase VCE(sat)to that of a Darlington or worse, making the load even less useful. MOSFETs don't require gate current at DC, their only equivalent to VCE(sat)is (ID)(RDS(on)), and RDS(on)can be very low with a modern device.

author: David Hess
author_rank: Super Contributor
timestamp: September 26, 2014, 01:10:31 am
content: For a given current and die size at higher voltages (although not that high), the voltage drop from MOSFET Rds(on) will be greater than Vce(sat) of a transistor which is why IGBTs or composite transistors are used instead of MOSFETs in some applications.As far as dummy loads, the gate current of the MOSFET contributes insignificant error so current sensing can be single ended which is simpler.
BK Precision 1735(Non-A) PSU Recap Question - SOLVED - Page 1
Forum section: electronics / beginners

author: t1d
author_rank: Super Contributor
timestamp: May 29, 2019, 10:40:55 am
content: I am considering replacing the caps in my PSU, as it is decades old. In doing my homework before starting the project, I came across these photos of the PCB. Some of the caps have connections that I do not know. I expected just two pins for each cap, but...- C1 and C2 have four, maybe six, solder points. My guess is that two holes are bodged for a pin spacing that was not that drilled originally. And, that the remaining two might be for a jumper wire, between two pours... But, this would mean the jumper is under the cap?- C3 and C4 have two, maybe three, solder points. My guess is that one hole was bodged for a pin spacing that was not that drilled originally.- C9 looks as I would have expected, two pins.All of these caps have a "SSS" silk-screened between two of the pins. I could use some help with what this symbol means and its orientation, too.This is the Bottom PCB Photo. Top of PCB photo and Schematic are on the following posts.

author: t1d
author_rank: Super Contributor
timestamp: May 29, 2019, 10:41:37 am
content: Photo 2

author: t1d
author_rank: Super Contributor
timestamp: May 29, 2019, 10:42:10 am
content: Schematic

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: May 29, 2019, 12:16:35 pm
content: T1D and the group.Those extra pads are so BK can build the 1711 & 1715 (60V)models on the same PCB.In these models the capacitors are in series and resistor R1B an R1C are installed.On the 30V models the capacitors are in parallel.On these models the electrolytic capacitors will be rotated 90 degrees.C1B and C2B designations are used.Regards,Jay_Diddy_B

author: t1d
author_rank: Super Contributor
timestamp: May 29, 2019, 12:29:51 pm
content: Hi, Jay. Thanks for the info. You really are a knowledgeable guy and I always appreciate your input. Can you tell me what the "SSS" means? Is it a designater for the pin orientation for the specific model?

author: t1d
author_rank: Super Contributor
timestamp: May 29, 2019, 12:48:15 pm
content: The "SSS" silkscreen is just a different way to indicate that it is an electrolytic. Maybe used by the Japanese?https://electronics.stackexchange.com/questions/105441/what-is-the-symbol-on-the-supply-voltage-that-looks-like-a-shaded-in-capacitor
BK Precision 8500 Resistance  - Page 1
Forum section: electronics / beginners

author: digitaladdictions
author_rank: Contributor
timestamp: December 20, 2012, 06:32:51 am
content: I am probably being a noob and neglecting some basic stuff here but I want to just make sure. I just received my BK Precision 8500 electronic load. I used the battery test function and plotted some characteristic curves for some batteries I had which worked great. The only thing was that based on the voltage and the current draw I calculated the resistance of the load and tried to measure it across the input posts and could not. I then switched to constant resistance mode and could not measure the resistance there either (no supply attached). Is this to be expected?Unrelated I just discovered you can interact with the 8500 via Python which is very cool.

author: dr_p
author_rank: Frequent Contributor
timestamp: December 20, 2012, 09:17:25 am
content: Resistance measurement works by forcing a known current through the resistor and measuring the voltage drop across it. If theDUTis in circuit, meaning there is some other voltage drop on it, the reading is erroneous.In constant resistance mode the BK is simulating the behavior of a resistor (U=I*R), meaning it eats as many Amps needed to keep the equation true. If the supplied voltage doubles, the current doubles as well, keeping R constant.However, it's not a resistor!Suppose you set your BK for constant R on 10ohms and connect a 10V battery. It will draw 10V / 10ohm = 1A. Now you want to measure those 10ohm with your DMM. Your multimeter tries to push let's say 1mA through it and measure voltage drop. It will then measure the 10V plus whatever drop you have on your circuit, but we'll ignore that. So the meter sees 10V "drop" on a 1mA current, meaning R=10V / 1mA = 10Kohm. And it gets nastier if you have an autoranging meter, because 10Kohm is on a different scale, it then changes scale, thus changing the test current. But the 10V are still there, so the DMM thinks the resistor has changed, and the displayed value jumps all over the place.Same goes for measuring an actual resistor while in circuit.EDIT:Similar rationality goes for measuring the load terminals (in constant R) with no supply connected. U=I*R, you've set R to whatever value, but U=0V (no battery connected), so the load draws no current (transistors switched off) increasing the actual resistance of the terminals to maximum, effectively isolating them, so resistance is not measurable with a DMM.

author: digitaladdictions
author_rank: Contributor
timestamp: December 20, 2012, 03:25:43 pm
content: Makes perfect sense. Yes I was just being a noob. Lifting one of the leads of a resistor before testing it is as basic as it gets but it is extremely rare I want to actually measure resistance and forgot.Thanks
BK Precision 885 LCR/ESR 4-wire test lead - Page 1
Forum section: electronics / beginners

author: r042wal
author_rank: Newbie
timestamp: November 03, 2022, 02:24:23 am
content: I am going to do some work on the crossovers in my speakers and got a good deal on a used BK Precision 885 LCR. It came with a 4-wire test lead set but I can't find any information on how to test components with this accessory. I realize it allows for higher accuracy but the manual for the 885 is marginal and also, it does not cover this accessory. Any help would be appreciated. I have never used an LCR before.Thanks in advance.

author: bdunham7
author_rank: Super Contributor
timestamp: November 03, 2022, 02:42:23 am
content: The manual is a bit terse. Fig 3.3 on p31 shows you how to set up a 4W test.https://bkpmedia.s3.amazonaws.com/downloads/manuals/en-us/885_886_manual.pdfFor best results, do this:1. With the test harness plugged into the LCR but all 4 alligator clips unconnected and not touching anything, perform a Cal OPEN (press the CAL button briefly).2. With all 4 leads connected together, preferably on one lead of whatever you will be testing, perform a Cal SHORT (press the CAL button for a few seconds and then release it)3. Connect the Hcand Hpleads to one side of your component and then your Lcand Lpleads to the other side.Now you are ready to test. You can continue using the meter for while without recalibrating it.

author: r042wal
author_rank: Newbie
timestamp: November 03, 2022, 09:16:25 am
content: Fantastic, thank you!
BK Precison 2709B or Extech EX505 ??? - Page 1
Forum section: electronics / beginners

author: kasumyku
author_rank: Regular Contributor
timestamp: July 07, 2012, 04:41:47 pm
content: Hi everyone, this is my first post ...I have watched Dave's $100 multimeter shootout and I really like the BK Precision 2709B, but then I've seen it has that annoying beeping sound everytime you turn the knob plus couple of more things including the Burden Voltage problem( I know there is a Precision Current Adapter for that problem) but its all about which multimeter of these would be better... And ya, about Extech EX505 from Dave's tests it shows that it has a bit more flaws than BK 2709B...Thnx, hope I'll get some repliesp.s.: English is my 2ND language so, yap u know what i mean...

author: T
author_rank: Newbie
timestamp: July 08, 2012, 01:43:59 am
content: Dave declared the BK the best of the bunch in the shootout, and I would agree, but it depends on your needs. The BK is the better quality meter of the two, however the Extech has a few more features, temperature, duty cycle, etc. If you need the features the Extech has then it's probably what you want, but if you don't need them then the BK is a slightly better built meter. I have several BK instruments and have always been pleased with them for the price. The beep would be a nuisance, but I think it's a small issue overall.

author: Chopsticks
author_rank: Regular Contributor
timestamp: July 08, 2012, 04:11:25 am
content: I've got the bk meter dave reviewed in that shootout and sure the beeping is a little annoying but not enough to (for me anyway) be bothered by it. and i find it performs quite well with what i get upto in my lab

author: kasumyku
author_rank: Regular Contributor
timestamp: July 09, 2012, 12:56:30 am
content: thanks guys, I think I'll go with the BK Precision because I'll probably not be using anytime soon these selling features like temperature or other functions, and the beeping issue I guess I just have to get used to it...I was more worried about the high Burden Voltage, but apparently all multimeters have the same problem when measuring current ,its just this one is on high side...thanks again!!!

author: Chopsticks
author_rank: Regular Contributor
timestamp: July 09, 2012, 07:46:24 am
content: no worries mate, good luck with your electronic projects

author: EEVblog
author_rank: Unknown
timestamp: July 10, 2012, 11:16:06 pm
content: Quote from: T on July 08, 2012, 01:43:59 amAnd as always, that's just my opinion at the time. YMMV.Mos of the meters in that shootout were pretty good for the money.Dave.
BK4819 programming guide - Page 1
Forum section: electronics / beginners

author: u666sa
author_rank: Frequent Contributor
timestamp: December 25, 2024, 03:42:42 am
content: Can someone give me a full, official, private and leaked programming guide for the BK4819 with description of all the registers and ins and outs of this chip?The stuff I have, I'm not sure if that's the entire thing. Something tells me there is more.
Black powdery residue after changing tip - Page 1
Forum section: electronics / beginners

author: fixit7
author_rank: Regular Contributor
timestamp: June 05, 2019, 03:06:48 pm
content: When I changed my tip to a different type on my Chinese copy of a Hakko, I saw a small amount of black powdery residue that came out.I have used the soldering around 50 times. Is that part of a carbon rod?I plan on getting a better iron that actually maintains the right temp.Thanks,Andy

author: bob91343
author_rank: Super Contributor
timestamp: June 05, 2019, 04:28:11 pm
content: That's just oxide accumulation, very normal. Clean it up for best results, as it's not as good a heat conductor as metal. In the long run it can build up enough to make the iron less effective.
BLDC controller with fast response - Page 1
Forum section: electronics / beginners

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: January 19, 2018, 05:14:53 pm
content: I have a BLDC controller that I use to control a BLDC motor. The controller has 0 to 5V speed input and the speed of the fan is set based on this speed input voltage. What i have noticed is if I give a step input say 1V to 2V the controller responds only after a delay of 0.3 to 0.5s, that is the speed of the fan only starts to change after 0.3 to 0.5 seconds.1. Is this a normal delay for a BLDC controller?2. Are there controllers that can respond quickly within to the input speed signal?3. I have heard of Gecko drives for Stepper motor are there any similar companies that make drives for BLDC motors?TIA

author: Benta
author_rank: Super Contributor
timestamp: January 19, 2018, 09:11:47 pm
content: No, it's not normal, BLDCs respond as quickly as brushed motors. For whatever reason, your controller has a delay. Try another one.

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: January 20, 2018, 03:43:12 am
content: Are there any reputed BLDC controller manufactureres like Gecko, Leadshine are for steppers?

author: Belrmar
author_rank: Regular Contributor
timestamp: January 20, 2018, 10:26:34 am
content: actually texas instrumets makes some pretty good bldc controllers

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 20, 2018, 10:54:58 am
content: For fan type motors there are a lot of options - Microchip and Onsemi do several, I think Allegro also.Delay may be connected with the sensorless feedback algorithms, and that for most fan type applications you don't generally want the speed changing frequently so they may have some internal filtering

author: ZeroResistance
author_rank: Frequent Contributor
timestamp: April 06, 2018, 11:03:24 am
content: Quote from: mikeselectricstuff on January 20, 2018, 10:54:58 amI see that most controllers for BLDC motors are microcontroller based and not is this the right way to go? Are there any standalone controllers available for fan type motors?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: April 06, 2018, 04:14:41 pm
content: Yes, lots (dome use embedded MCUs but the user doesnt havw access) search bldc on digikey and filter by controllers, 3 phase
Bldc motor controller repair - Page 1
Forum section: electronics / beginners

author: diggitt
author_rank: Newbie
timestamp: February 19, 2025, 02:49:54 pm
content: Hi, I’m repairing a makita dsh680 saw. I have removed the potting compound from the board but I have knocked some smd components off whilst doing this. Please could you help me find out the values of the components knocked off, I can’t find a schematic. Thank youNumber on board:24V-02123 10PB-14G5-3111 V1 0

author: Infraviolet
author_rank: Super Contributor
timestamp: February 19, 2025, 05:38:01 pm
content: There's no guarantee that replacing the component(s) pulled off when removing the potting compound will be able to fix your saw, there might be corruption in the memory on some sort of microcontroller or in an EEPROM... or some other place like a microcontroller burned out by overvoltage/overcurrent where you can;t smply replace it because you don;t know what program would need flashing to the one you'd replace it with...But, for replacing the pulled-off parts, can you not examine the potting compound remnants and locate them within it? You ought to be able to either read colour codes (in the unlikely event of through hole older style parts) or text markings (commonly printed on SMD parts) on any such resistors or capacitors lost in this fashion, or otherwise measure their resistances/capacitances via a multimeter.
BLDC Motor Driver with BLE Control/ DFU - Page 1
Forum section: electronics / beginners

author: x4ce
author_rank: Contributor
timestamp: August 10, 2024, 01:26:24 pm
content: Hi,I am prototyping a custom PCB with integrated ESC for a BLDC Motor (Datasheet attached). For this purpose, I plan of using STSPIN32F0 due to versatile options following thisSTM BLDC Motor Driver with BLE Control/ DFU. The article's design is based on 45A max consumption and looking at BLDC's datasheet this seems appropriate. In addition to this, I would like to add following capabilities i.e. Control/ Info through BLE along with BLE DFU.Please recommend/ suggest, any ST's SiP supporting BLE or war around to accomplish the sample.Regards
BLDC motor flavors - Page 1
Forum section: electronics / beginners

author: anvoice
author_rank: Frequent Contributor
timestamp: September 02, 2018, 07:45:27 am
content: I'm curious about a certain topic: looking online, I find some 36mm diameter BLDC motors rated for 5-25W (at 12V, so consuming about 2A tops) while other brushless inrunners can be found taking about 30A (on 3S-4S LiPoly batteries, and thus must be rated for several hundred Watts). So the question is: what would be the main structural difference between these motors? I'm guessing it's got to do with the number of windings, gauge of the wire used, etc., but could anyone provide an example of how the characteristics of one differ from the other (e.g. double the number of windings and performance changes in such and such a way)? Or point me to an information source? Thank you.

author: firehopper
author_rank: Frequent Contributor
timestamp: September 02, 2018, 12:25:09 pm
content: I'm into rc airplanes, and brushless motors have so many differences.. KV rating, wattage, max voltage, number of poles. and so on. to be honest, I dont know how they would achieve that, but I would guess like you, different winding methods and different gauge wire.

author: anvoice
author_rank: Frequent Contributor
timestamp: September 03, 2018, 05:14:24 am
content: Yep, that seems logical. I just want to know what makes the difference between 20W and over 300W (at the same voltage). I'm holding the 300W in my hand next to the 20W, and the 300W one is slightly shorter despite accommodating an impeller, plus a little lighter. I wonder if a can rewind the 20W for a higher power rating, and how the KV, recommended nominal voltage, etc. would change as a result.

author: mzzj
author_rank: Super Contributor
timestamp: September 03, 2018, 02:40:38 pm
content: Quote from: anvoice on September 03, 2018, 05:14:24 amSome possible differences:-Cooling (still air vs huge propeller directly on the nose of RC airplane)-insulation temperature limit-magnet temperature limit-lower loss stator iron (allows higher flux density and/or higher rpm)-magnets and stator iron with higher max flux density-and most importantly: rotational speed. There is not that much you can do about maximum torque in a given size of motor but if you can increase the max rpm from 3000 to 30000 rpm you get ~tenfold increase in output power.

author: anvoice
author_rank: Frequent Contributor
timestamp: September 03, 2018, 08:18:49 pm
content: The cooling issue can be mediated somewhat with an aluminum enclosure around the motor. It's true that some magnets can have a higher temp limit depending on the exact alloy.I would still guess that those points are not enough to make an order of magnitude difference, especially given that these motors have a similar RPM at 12V. So there must be a difference in how they're wound, I just don't know that difference. Worst case I'll open them up and check, it's just that to count the loops I'd have to actually unwind the coils.
BLE-STACK driver - Page 1
Forum section: electronics / beginners

author: u666sa
author_rank: Frequent Contributor
timestamp: October 23, 2024, 03:03:43 pm
content: Could someone please download this thing for me and upload it to some free file sharing thingy, like google drive or something. It says access denied when I go to download the driver. I never seen anything as dumb as this. You go to download bluetooth driver and it says access denied. Is this a driver download or I came across some classified documents??https://www.ti.com/tool/BLE-STACK

author: ataradov
author_rank: Super Contributor
timestamp: October 23, 2024, 03:55:44 pm
content: You are asking people at least in the US to commit a crime.
Bleed resistor - how? - Page 1
Forum section: electronics / beginners

author: amateur_25
author_rank: Regular Contributor
timestamp: March 22, 2012, 01:26:31 pm
content: I've used this website to calculate my bleed resistor but I would like to understand the formulas behind it ?http://www.welwyn-tt.com/products/resistors/calculation-tools.asp

author: Unknown
author_rank: Unknown
timestamp: March 22, 2012, 04:45:42 pm
content: http://en.wikipedia.org/wiki/RC_circuit

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 23, 2012, 05:18:17 am
content: Bleed resistors for safety reasons are rarely used nowadays since they waste power and even one that is assumed to be good cannot be trusted.

author: Kilroy
author_rank: Regular Contributor
timestamp: March 23, 2012, 02:36:36 pm
content: Well, in some cases, the use of bleeder resistors is absolutely prudent...like for when you want to throw away leakage current or from semiconductor devices like SCRs, triacs, diodes etc. Even in the "off" state these devices can leak enough current to potentially ruin your day, so it can be cheap and effective insurance to install appropriate leakage current bleeders.For example, when working with Programmable Logic Controllers, it is extremely wise to use bleeder resistors to pull down leaky triac field device switches, and such. Proximity switches are pretty bad for leakage current, too. You can see the signal present indicator flicker on the input modules and sometimes leakage current can actually be enough to switch the input module into the conducting state, with potentially scary results...CNC machines and industrial robots move *very* quickly.Similarly, you can have issues with outrush currents when triacs and SCRs are connected to inductive loads. When power is removed, the power is stored in the inductive load will try to make its way to ground any way it can, like taking a convenient path across a device such as a triac in the "off" state. This is a bigger problem if the current to the inductive load has been cut off at the voltage peak...it will not likely be noticed until the power is switched back to the "on" state. Installing suitable capacitance across the secondary side of the disconnect that supplies power to the inductive loads soaks up the outrush.
Bleeding resistors -- why - Page 1
Forum section: electronics / beginners

author: blueskull
author_rank: Unknown
timestamp: April 12, 2019, 11:45:29 am
content: Have a question about my new PXI system.The backplane has about 1A bleeding resistors on 5V, 3.3V and 12V rails on board, plus 1A on 12V using chassis mount resistors. Anyone can explain why did they do that?My theory is that the PXI is a dynamic environment. Many cards can ramp up power consumption in no time, and since it uses a standard ATX power supply, it may not respond that fast under light load, so the chassis has a bleeding to ensure the PSU is properly loaded and ready to respond.Don't know if that's the most reasonable explanation, but if that's the case, can I replace the archaic power supply with an Intel Haswell certified (rated for crazy fast di/dt) unit and remove the resistors?I plan to run the PXI as a remote access box, so I expect it to be constantly powered on, saving a few tens of watts is crucial to me.Thanks.

author: Psi
author_rank: Super Contributor
timestamp: April 12, 2019, 12:09:16 pm
content: 1A seems ridiculously large but yes, pre-loading some types of psu's does improve there response timeSometimes the switchmode controller will go into various lower power switching states under very light loads (or no load) because it's more efficient.hm.. so 1A at 5, 3.3 and 12 rails using chassis mount resistors.So 20.3 watts.More likely it's part of a heater system to keep everything at a more stable temp. Maybe prevent it ever dropping below 0 C in cold environments.Did you order the PXI - Antarctica edition?

author: AndyC_772
author_rank: Super Contributor
timestamp: April 12, 2019, 12:23:51 pm
content: Minimum load to ensure the PSU remains in regulation even if there's no cards plugged in?
blocking diode choices - Page 1
Forum section: electronics / beginners

author: m3vuv
author_rank: Super Contributor
timestamp: March 14, 2022, 11:57:07 pm
content: Hi all,i am building a psu kit, it has a 1N5408 blocking diode in it, i have a few mrb 5200 diodes,is it best using one of those instead,both 5amp but the later is a schottky ?

author: CaptDon
author_rank: Super Contributor
timestamp: March 15, 2022, 12:20:37 am
content: Probably would work. Watch the PRV and leakage. I just replaced 4 1N4004 diodes in an 8vdc supply with schottky devices. Easily got almost another full volt at the filter capacitor which gave me better brown-out protection during heavy motor startups. I also replaced the 7805 regulator with a low dropout version for additional protection during power sags. I put 130L20 MOV's on the primary of the power transformer to help protect the PRV of the schottky's during line switching spikes. So far so good!!!

author: Gyro
author_rank: Super Contributor
timestamp: March 15, 2022, 09:44:08 am
content: Double post...https://www.eevblog.com/forum/beginners/shitty-chinky-psu-kit/msg4061530/#msg4061530Edit: I'll get rid of the strikethrough then

author: magic
author_rank: Super Contributor
timestamp: March 15, 2022, 09:52:00 am
content: OP is talking not about rectification but about a signal diode which could easily be even 1N4148 - that's unless he switched to yet another schematic and another component numbering once again and I misunderstood which diode it is.

author: CaptDon
author_rank: Super Contributor
timestamp: March 15, 2022, 01:53:09 pm
content: Not sure either, his original part number in this current post was a 5 amp device and so I thought it was passing full power supply output current. Sometimes his posts are a bit vain. Yes I understand he was talking 'blocking' and my application was rectification. Simply conveying my very pleasing results going from 4 X 1N4004 to 4 X Shottky rectifiers. Less heat, more voltage at the filter, etc. I did notice the O.P. got beat up pretty bad in a previous post about a 3 legged device? Maybe I need to 'follow the trail' more closely?

author: Terry Bites
author_rank: Super Contributor
timestamp: March 15, 2022, 02:31:25 pm
content: Who knows what OP is talking about?No schematic or context!

author: magic
author_rank: Super Contributor
timestamp: March 15, 2022, 04:08:57 pm
content: See the link Gyro posted.It turned out to be a reverse voltage protection diode on the output of a lab PSU

author: MathWizard
author_rank: Super Contributor
timestamp: March 15, 2022, 09:42:11 pm
content: The 1N5404 is a typical main's rectifier diode, like 400V 3A, also I've seen them/or similar in places on SMPS too, like for the bypass of the PFC when not on.Yeah OP so what kind of PSU ? In a jam as long as it's around 400V 3A, you should be fine either way, if it's not exacly the same spec's or purpose.OK a reverse blocking, protection application.
Blocking Oscillator Measurements - Page 1
Forum section: electronics / beginners

author: jfoster
author_rank: Newbie
timestamp: December 05, 2023, 09:44:19 pm
content: I have constructed what I think is a simple blocking oscillator on a protoboard. When I simulate this circuit in LTSpice, I see the voltage on the transistor collector reach very high (kV). However when I measure the collector voltage using an oscilloscope in real life I see that the voltage reaches ~10 V and seems to be clamped. I don't understand the difference between simulation vs. reality. For a while I thought volt-second product of the transformer core might play a role but I don't think I am saturating the core.Attached are measurements of the transistor collector at supply voltage of 3 V, 5 V, 7 V and the LTSpice simulation.

author: jfoster
author_rank: Newbie
timestamp: December 08, 2023, 03:11:07 am
content: I think I have finally figured it out...When the circuit is first powered on, current flows into the base of the transistor which opens the transistor. This causes regenerative feedback through the transformer and causes the transistor to saturate very quickly. The capacitor slowly discharges until the base voltage is too low and the transistor starts to turn off. The collector voltage rises and causes the base voltage to fall even more from regenerative feedback through the transformer. This causes the transistor to turn off very quickly.The magnetizing current from the transformer has nowhere to go so the collector voltage rises very quickly. However this causes the base voltage to go very negative through transformer action but the voltage is effectively clamped by the reverse emitter-base breakdown voltage of the transistor (only 6 V). I think this is what is causing my collector voltage to appear clamped.I tested adding two 2N3904 transistors in a Darlington pair configuration and I noticed the collector voltage rose to 20 V while the pulse length was considerably shorter. See attached.

author: RoGeorge
author_rank: Super Contributor
timestamp: December 08, 2023, 01:34:43 pm
content: Very large voltage spikes can only appear at very high Q (quality factor).An ideal coil (as in no internal losses) has infinite Q, and can produce infinite voltage spikes. A physical coil has losses caused by the internal resistance in the wires that makes the coil, and even more losses inside the magnetic core when ferrite or alike high magnetic permeability materials are used for the core (\$\mu_r\$ >> 1).Another observation is that the original schematic shows a transformer T1, which implies there will be a load in the secondary of the transformer, while in the LTspice schematic there is no load anywhere.You'll need to eitheradd some losses in the coil wires (right click on a coil and specify the parasitics R, for example a 5\$\Omega\$ as the 'Series Resistance')or add a 3'rd L3 as the secondary of T1 (also coupled with the other two, 'K1 L1 L2 L3 1') with a resistive load (a 100\$\Omega\$ or so R2, in parallel with L3)or maybe add both the parasitic R series and the L3 || R2 loadand the kV spikes will vanish from the simulation.
Blocking Phantom Power 48V from Audio output - Page 1
Forum section: electronics / beginners

author: Saimoun
author_rank: Frequent Contributor
timestamp: April 27, 2024, 11:20:08 am
content: HiI have a simple audio output circuit, the audio comes from an opamp with no negative rail, so the signal is from 0 to 3.3V (centered around 1.65V), so I have a coupling cap to bring it to zero volt.How could I make the output blocking +48V phantom power? Would it be enough to add a 63V cap (in the opposite polarity as the current caps) just before the output?What about if the plug is a TRS instead of XLR, thinking that pluging the cable in and out will momentarily create some shorts?Thank you!

author: radiolistener
author_rank: Super Contributor
timestamp: April 27, 2024, 11:40:55 am
content: Quote from: Saimoun on April 27, 2024, 11:20:08 amWhat do you mean with "phantom power"?

author: BennoG
author_rank: Frequent Contributor
timestamp: April 27, 2024, 12:15:39 pm
content: yes you can, I would also add a extra resistor of 100k or 220k to the ground after that to discharge the capacitor.However you need to double the capacity of the 22uF to 47uF or something like that, because capacitors in series act the same as resistors in parallel.Benno

author: Saimoun
author_rank: Frequent Contributor
timestamp: April 27, 2024, 01:33:52 pm
content: Quote from: radiolistener on April 27, 2024, 11:40:55 amLike the 48V that an audio mixer can send over an XLR cable for example. As I understood it is typically raising the DC voltage from 0 to +48V on both pins 2 and 3 through a 6.8k resistor.Quote from: BennoG on April 27, 2024, 12:15:39 pmVery good point I did not think about that!Actually what about the discharge - would that not damage the first cap and/or the opamp behind it?

author: donlisms
author_rank: Frequent Contributor
timestamp: April 27, 2024, 07:47:52 pm
content: A very thorough analysis is here, in AES Convention Paper 5335:https://www.thatcorp.com/datashts/AES5335_48V_Phantom_Menace.pdf

author: Terry Bites
author_rank: Super Contributor
timestamp: April 28, 2024, 12:22:26 pm
content: Have a good read.See page 11.

author: Saimoun
author_rank: Frequent Contributor
timestamp: April 29, 2024, 08:14:12 am
content: Quote from: donlisms on April 27, 2024, 07:47:52 pmQuote from: Terry Bites on April 28, 2024, 12:22:26 pmBoth very good read thank you!Though they only seem to cover the Phantom Powersourceprotection, i.e. the mixer/audio input side.I'm on the other side, I have an audio output which may or may notreceivephantom power. Are you saying I should simply implement their proposed protection on my opamp's outputs?I understand the 1N4004 diodes to the rails, though I am not sure I get what R4, R5, and RG are (I believe they are just part of the audio input - my design is an opampoutput). And what about the capacitor, would my little 6.3V cap not be in risk of damage while the plug is connected/disconnected?Thank you!
Blog Proposal - Page 1
Forum section: electronics / beginners

author: Shale
author_rank: Contributor
timestamp: March 27, 2012, 04:45:29 am
content: Dave. it would be nice if you did a couple of videos on just oscilloscopes. one on how to use them, and another taking a look at what is a good bang for the buck. I have watched your videos on youtube and know that you recommend the Rigol, but that was some time ago, I would like to see one on maybe the OWON (really like the big screen), or another brand for about 400-600 dollar range. I have done some reading on scopes but am even more confused than when I started.Thanks

author: vk6zgo
author_rank: Super Contributor
timestamp: March 27, 2012, 09:04:06 am
content: Have a look on this forum for anything posted by w2aew.He is a fount of information on OscilloscopesPS:look up two threads!
Blown bulb in a device - Page 1
Forum section: electronics / beginners

author: Kerkana
author_rank: Contributor
timestamp: July 31, 2023, 10:18:25 pm
content: Hello, I have a 'keep warm' bulb that no longer lights up I think it has burned out, how can I test it? I don't even know where to find itThe resistor seems to be a 150k I measured the one next to it that works

author: Kim Christensen
author_rank: Super Contributor
timestamp: July 31, 2023, 10:29:53 pm
content: It's just a neon bulb. NE2 maybe? Pretty much any neon bulb that size will work.

author: TimFox
author_rank: Super Contributor
timestamp: July 31, 2023, 10:34:13 pm
content: The neon bulb in your photo requires a substantial voltage before it conducts at all (roughly 90 V for a NE2); after ignition, the voltage across the bulb at a given current falls to a lower level.Eventually, the metal on the interior electrodes poisons the gas and coats the glass, and the device goes dark.

author: Vovk_Z
author_rank: Super Contributor
timestamp: July 31, 2023, 10:49:00 pm
content: Quote from: Kerkana on July 31, 2023, 10:18:25 pmI guess it must lights with 120/220 VAC (from the wall socket voltage).If it is used as an indicator (as a lamp) only but not as something special like a noise source etc. then it may be replaced with a sensitive 3-5 mm LED diode (of course with 150 k resistor in series, or even larger resistance). Or two LED diodes in parallel and opposite directed (so you'll have 100 Hz light pulsation but not 50 Hz light pulsation).

author: Kerkana
author_rank: Contributor
timestamp: July 31, 2023, 10:51:17 pm
content: Thank you for your help, the resistor value is OL is it dead?I don't have a 150k resistor I'm going to put 100k and 50k in series

author: Vovk_Z
author_rank: Super Contributor
timestamp: July 31, 2023, 10:55:11 pm
content: Quote from: Kerkana on July 31, 2023, 10:51:17 pmYes, the resistor could die, and 100k+50k may bring it back to life. Exact value doesn't matter. It may vary by 10 or 20 %. Neon bulbs are quite reliable and long life parts (those I've seen).

author: Kerkana
author_rank: Contributor
timestamp: August 01, 2023, 12:26:27 am
content: It works, thanks for your help, maybe an alternative to replace this one for the future ?
Blown DSO150 scope with shorted 3.3V rail - Page 1
Forum section: electronics / beginners

author: dazz
author_rank: Frequent Contributor
timestamp: June 21, 2023, 05:15:25 am
content: Quick question, please. I have this DSO150 oscilloscope that won't power up, apparently because the 3.3V rail in the main board is shorted. I removed the 3.3V regulator and the cap to ground next to it but the short remains. The 9V main voltage is present. Guess something downstream must be shorting the 3.3V rail, the uController perhaps? Any ideas on how to troubleshoot it, please?Here's the schematichttp://www.jyetech.com/Products/LcdScope/Schematic_Shell.pdfThanks in advance.

author: Kim Christensen
author_rank: Super Contributor
timestamp: June 21, 2023, 05:27:13 am
content: Many times, it's one of the many bypass capacitors across the 3.3V rail. Tantalums, if there are any, are your prime suspect.A thermal imaging camera can help if the power supply doesn't completely shut down. Look for a hot component when it's powered on.Another method is to use a milliohm meter to narrow down the area on the PCB where the short is.ie: If the resistance to ground was lower at TP4 vs TP8 then your prime suspects would be C6, C5, and then U1.

author: Infraviolet
author_rank: Super Contributor
timestamp: June 21, 2023, 05:36:33 am
content: Another trick might be to try setting up a bridge circuit to use for low value ohm-meter measurements, then use this to try to trace where a short is occuring.I think this was the vid I saw a while ago explaining the method:

author: dazz
author_rank: Frequent Contributor
timestamp: June 21, 2023, 05:49:24 am
content: Thanks, guys. With the regulator in place, that's the area that gets hot. Obviously, once I removed it, there's no voltage supply in the 3.3V rail and nothing heats up in the board.I'll try your suggestions

author: dazz
author_rank: Frequent Contributor
timestamp: June 21, 2023, 07:27:26 pm
content: Turns out the microcontroller is shorted. Tried removing all the caps in the 3.3V rail, no dice. Removed the uController, boom, short gone. So yeah, the scope is toast.Thanks for the help everyone.
Blown fuse on USB port? - Page 1
Forum section: electronics / beginners

author: Kjetil
author_rank: Regular Contributor
timestamp: March 08, 2014, 01:40:33 pm
content: A while ago a friend was helping me to get stepper motors running off an arduino with a L298N bridge, when some of the power intended for the steppers accidentaly got routed into the USB port instead. The computer wasn't too happy about this, and instantly rebooted, but came back up without any apparent issues (and a nasty error message saying it had rebooted due to a power surge on the USB port).The USB ports still work fine for most equipment, but they only work as USB 2.0 ports (they are USB 3.0). This is shown clearly from both the performance, and that Windows asks me to plug USB 3.0 devices into a faster port. The drivers haven't changed, and reinstalling them haven't changed this behaviour. I am also unable to run power hungry devices off two of the four ports, such as cellphone charging.Could this be something as simple as a blown fuse or other component, or is it likely that the controller is fried? I find the last one less probable as it apparently retains most of it's functionality.

author: marshallh
author_rank: Unknown
timestamp: March 08, 2014, 04:57:00 pm
content: If you drove a bunch of current into the superspeed pairs on the controller you probably fried the serdes in it.This is why you always use a hub when dorking around, or an isolator.
Blown fuse with high but finite resistance - Page 1
Forum section: electronics / beginners

author: kenshi
author_rank: Contributor
timestamp: May 30, 2015, 09:59:19 am
content: At work this week, a device blew an HRC fuse, although it wasn't completely blown. When I put the multimeter on it, it measured a few megaohms of resistance. To me, this seems like an incredible unlikely scenario. I would think this could only happen if there was an overload of current which caused the conductor to start vaporizing, but the current abruptly shut off just as there was an extremely tiny thread of conductor remaining. Is this a less rare phenomenon than I think? What's going on here?

author: Rerouter
author_rank: Super Contributor
timestamp: May 30, 2015, 10:01:55 am
content: your talking megaohms, the vaporised metal may have been deposited along the line of the arc, reducing the gaps between pieces of metal enough to form a leakage path,

author: mikerj
author_rank: Super Contributor
timestamp: May 30, 2015, 10:03:48 am
content: It's probably just a film of metal deposited on the filler inside the fuse when it ruptured.To get a resistance of megaohms in a piece of wire an inch or so long would be almost impossible.

author: kenshi
author_rank: Contributor
timestamp: May 30, 2015, 10:23:42 am
content: That makes sense. I hadn't thought about the fact that that metal vapor would condense somewhere.

author: Kedar264
author_rank: Regular Contributor
timestamp: May 30, 2015, 11:43:33 am
content: Its the resistance of your handsIts No Magic, dont touch at end of your dmm probes

author: Ian.M
author_rank: Super Contributor
timestamp: May 30, 2015, 01:02:58 pm
content: Quote from: Kedar264 on May 30, 2015, 11:43:33 ams/Its the/It may be the/Don't *ASS*U*ME* the O.P. is an idiot. Ask!

author: miguelvp
author_rank: Super Contributor
timestamp: May 30, 2015, 04:32:14 pm
content: Quote from: Ian.M on May 30, 2015, 01:02:58 pmHipChat much? (allthethings)

author: Ian.M
author_rank: Super Contributor
timestamp: May 30, 2015, 04:43:08 pm
content: No. The use of SED substitute command syntax by hackers/programmers to highlight mistakes in a previous non-editable message goes back to long before the likes of snapchat. I don't know when I picked it up, but it was probably on USENET, though it may have been on FidoNet in the late '80s.
Blown Laptop Fan Transistor - Page 1
Forum section: electronics / beginners

author: Sanctor
author_rank: Newbie
timestamp: October 20, 2015, 04:42:22 pm
content: Hi guys,I have a Toshiba Satellite A200 1LA that was overheating. I disassembled it and while pulling the 3pin fan header out, I broke it. Then I remembered the pinout wrong or I shorted the pins while trying to put them in their place. When I turned it on, a small puff of magic smoke came out and the fan would no longer turn on.I removed the motherboard and on the other side I could see a blown transistor. I can't see what it says on the component because half of it is burnt off, but there is a "6" visible.I have attached a photo of it.Is there a way I can replace or bypass this part?Thank you in advance.

author: Sanctor
author_rank: Newbie
timestamp: October 20, 2015, 08:20:01 pm
content: Hello again,I bypassed the transistor, which I assume was used to control the fan, by soldering a wire shown in green in the attached photo.Now the fan works at full speed whenever the laptop is turned on. Which is exactly what I wanted.I am posting this for future referance, in case someone has the exact problem

author: Simon
author_rank: Unknown
timestamp: October 20, 2015, 08:32:59 pm
content: The fan was probably PWM driven off that transistor. In general it is not possible to identify such a SMD part. But the good news is that most SMD mosfet transistors in a SOT23 package seem to follow the same pinout so if your sure it's a mosft and know if it should be P or n channel you may stamd a chance at replacing.

author: amyk
author_rank: Super Contributor
timestamp: October 21, 2015, 02:29:13 am
content: Rule #1 of repair: always look for a schematic first.Your laptop model is made by Compal and its original model number is LA-3481P. The transistor is anFMMT619.

author: Sanctor
author_rank: Newbie
timestamp: October 21, 2015, 12:01:14 pm
content: That is awesome!How were you able to find the part number for the motherboard and the manufacturer? I thought the schematics would be confidential.Is there some sort of database I'm not aware of or is it just Google skills?Thanks!

author: Cliff Matthews
author_rank: Unknown
timestamp: October 22, 2015, 02:37:01 am
content: http://www.s-manuals.com/notebook/toshiba_satellite_a200

author: amyk
author_rank: Super Contributor
timestamp: October 22, 2015, 03:56:55 am
content: Quote from: Sanctor on October 21, 2015, 12:01:14 pmGoogle the model number and add "schematic". (Make sure you use quotes, otherwise Google thinks you're stupid and are looking for user manuals and other irrelevant crap too.)QuoteTheywere... but no longer though.