hybridfree/eevblog-posts huggingface dataset:
Why <150W PFC stages  use BCM boost  PFC and  not CCM boost PFC - Page 1
Forum section: electronics / projects

author: ocset
author_rank: Super Contributor
timestamp: November 14, 2017, 09:38:30 am
content: Please confirm that the reason that most <150W Offline Boost PFC designs are done with Boundary conduction mode (BCM) PFC controllers rather than continuous mode (CCM) boost PFC controllers is because the BCM controllers more easily facilitate a faster transient response of the boost PFC stage......and yet still slow enough voltage feedback loop to get a good power factor.(aside from the obvious advantage of BCM vs CCM which is the lack of reverse recovery in the boost diode)Its noteable, that CCM PFC stages can be done with a plain inductor, rather than the BCM boost inductors which need the extra winding for the zero cross detection (to tell when the inductor has discharged)......and yet you don’t see CCM PFC stages being used below 150W... in spite of the potentially cheaper inductor......which could even be offtheshelf. A BCM boost inductor must be a more expensive custom wound part.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 14, 2017, 09:50:19 am
content: Cost, economy of scale for various components.Tim

author: dmills
author_rank: Super Contributor
timestamp: November 14, 2017, 12:17:03 pm
content: Thats about the size of it, a custom inductor is not particularly expensive if you are taking 10-100k quantities, and particularly if you are trying for an overall power system meeting 97% or so efficiency, saving a half watt or so in that diode matters.There is a really interesting BOM optimisation problem in small switchers as they often have to meet mandatory efficiency standards and where to distribute such losses as you can tolerate has an impact on total BOM cost that is quite distinct from the impact on the PFC or flyback taken in isolation.Regards, Dan.

author: jbb
author_rank: Super Contributor
timestamp: November 15, 2017, 06:56:54 am
content: Power electronics is tradeoff city.DCM tends to have (compared to CCM)- reduced switch turn on loss- no diode reverse recovery loss- increased switch turn off loss- increased switch RMS current- increased capacitor ripple current- possibly reduced EMC filter size- smaller inductor- increased inductor RMS current- increased inductor core losses- (and we haven’t even talked about thermal considerations)So you can see that here are a lot of considerations. It happens that the balance of the pros and cons change with power level. And I think it’s fair to say that CCM might be a good choice for lower power designs but becomes less favourable as power level increases.Hope this helps explain things.

author: ocset
author_rank: Super Contributor
timestamp: November 15, 2017, 07:29:28 pm
content: Thanks, i believe you meant "CCM" is better for higer power

author: jbb
author_rank: Super Contributor
timestamp: November 15, 2017, 09:32:35 pm
content: OopsYes. DCM for lower power, CCM for higher power. Sorry.
Why might my DC-DC converter efficiency be off 20%???? - Page 1
Forum section: electronics / projects

author: MeganVonTincan
author_rank: Newbie
timestamp: September 11, 2014, 01:05:40 am
content: I'm wondering if anyone has some thoughts on why I'm getting only 67% efficiency out of my MAX757 when I was expecting closer to 85%. I'm using the standard application circuit straight out of the datasheet (Figure 1) sans the LBI resistor divider. I'm using large voltage divider resistors on the FB pin, LBI and SHDN are tied to Vin and LBO is floating. I have high quality caps and 22uH inductor. I'm using a ucurrent-like (low burden) device on the input to measure a voltage of 2.56v (2x AA Eneloop batteries) @42ma. On the output side I'm getting 5.13v @14ma. I'm using a breadboard (bad, I know) but I've arranged the components to minimize the need for wires and I kept all wires(22AWG) as short as possible (especially the grounds).

author: mariush
author_rank: Super Contributor
timestamp: September 11, 2014, 01:44:39 am
content: What diode did you use?What secondary capacitor did you use? It should be ceramic or tantalum, not electrolytic.Read the datasheet carefully, note that they recommend a 100uF tantalum capacitor, which will work much better at frequencies up to 500kHz compared to electrolytic capacitors. Maybe a polymer capacitor will work.Also breadboard... tough, pay attention to page 6 and 7 in the datasheet :http://datasheets.maximintegrated.com/en/ds/MAX756-MAX757.pdf

author: PChi
author_rank: Frequent Contributor
timestamp: September 11, 2014, 05:23:38 pm
content: Is the Inductor suitable? It's going to need to be low loss at I guess a couple of hundred mA and a few hundred kHzAs the input and output aren't pure DC but have high frequency noise Multimeters can get confused.
why my DPH5005 voltage showing 00.01V - Page 1
Forum section: electronics / projects

author: pc1093
author_rank: Newbie
timestamp: March 06, 2021, 07:00:22 pm
content: why my DPH5005 voltage showing 00.01V

author: m k
author_rank: Super Contributor
timestamp: March 07, 2021, 08:56:46 am
content: Its probe is disconnected.(wild guess)

author: Medved
author_rank: Contributor
timestamp: March 09, 2021, 05:47:24 pm
content: And/or not calibrated exactly.There should be somewhere a calibration manual, the calibration uses to be acessible from the front panel controls + the input power switch (some crazy combination of "hold these two keys while turning the power ON" or something along these lines). You need just an accurate multimeter, plus maybe some 1 Ohm power resistor (to not calibrate the current with a hard short, as that tends to lead to regulation inaccuracy).But in any way, I'm pretty convinced it is still within the specified tolerance (uses to be +/-(few 10's of mV + few %), you have to count with that error any time you are using it even when it displays 0).
Why no datasheet KS74HCTLS162AN?  - Page 1
Forum section: electronics / projects

author: wilfred
author_rank: Super Contributor
timestamp: September 09, 2017, 05:29:42 am
content: /.

author: technix
author_rank: Super Contributor
timestamp: September 09, 2017, 05:36:46 am
content: Quote from: wilfred on September 09, 2017, 05:29:42 amThat triangular arrangement of three +’s means Samsung. The same Samsung that made a good portion of the world’s DRAM and NAND chips supply now, some awesome mobile processors, and some explode-y high end Android smartphones.Those may be your bog-standard 74HCT162 but you need to test it to find out.

author: Zero999
author_rank: Super Contributor
timestamp: September 09, 2017, 07:04:28 pm
content: Someone is selling them on ebay for silly money.http://www.ebay.co.uk/itm/74HCTLS162-Integrated-Circuit-/162605818941?hash=item25dc0fe43dI had another search for 74HTCLS00 but couldn't find anything other than this and someone selling them for extortionate prices on ebay..http://www.pc-caps.com/C04/composants-electroniques.nsf/docs/7TKCJNYSOI?opendocument&subcat=semiconducteurhttp://www.kynix.com/Detail/846504/74HCTLS00.htmlhttp://www.ebay.co.uk/itm/74HCTLS00-Integrated-Circuit-CASE-DIP14-MAKE-Signetics-/162605853210I don't know. I've never heard of these parts before. Perhaps it's a Soviet era copy. Please post a picture.

author: edavid
author_rank: Super Contributor
timestamp: September 09, 2017, 10:26:16 pm
content: The datasheet is right here in the Samsung databook:https://archive.org/details/bitsavers_samsungdatCTHCTLSDataBook_34259974Here's what Samsung has to say about the KS74HCTLS series:"The 54/74HCTLS high-speed CMOS family offers similar benefits as a replacement for industry-standard 54/74LS (Low-power Schottky), 54/74HCT and 54/74HC. While meeting all of the HCT electrical specifications, it also provides improved speed and drive capability, so that LS parts can be replaced with no performance degradation."

author: edavid
author_rank: Super Contributor
timestamp: September 10, 2017, 04:38:39 am
content: Quote from: wilfred on September 10, 2017, 02:27:33 amhttp://www.alldatasheet.com/datasheet-pdf/pdf/129287/MOTOROLA/MC68HC24.htmlhttps://www.nxp.com/docs/en/reference-manual/M68HC11RM.pdf

author: edavid
author_rank: Super Contributor
timestamp: September 10, 2017, 09:27:30 pm
content: Quote from: wilfred on September 10, 2017, 05:35:31 amThey didn't generally issue a separate datasheet for the XC parts, just an errata sheet if needed.

author: David Hess
author_rank: Super Contributor
timestamp: September 11, 2017, 02:05:21 am
content: Quote from: wilfred on September 10, 2017, 02:27:33 amI recognize that without even checking. It is a port replacement unit for the 68HC11. Just look up 68HC24.I had to drop the 68HC11 during development because Motorola was not interested in maintaining availability of their 68HC11 parts and especially the 68HC24. I went with the PIC instead.
Why not grounded tetrode screen grid? - Page 1
Forum section: electronics / projects

author: Circlotron
author_rank: Super Contributor
timestamp: June 09, 2020, 12:59:16 pm
content: We all know that compared with a triode, tetrode valves have an extra "screen" grid between the control grid and anode to reduce the anode/grid capacitance that causes RF feedback and instability. All of us also know that if the anode voltage dips below the screen grid voltage, secondary electrons can be drawn off the plate and onto the screen, causing a kink in the anode curves. Or something like that. Then the pentode was invented with a third, grounded grid between the anode and the screen grid that overcame this secondary emission problem.My question is - why was it necessary to have the screen grid positively charged? Could it not just be at ground potential like the third suppressor grid? Presumably it would still function as a screen grid but without secondary emission current and a kinked anode curve? Or couldn't it function as screen and suppressor at the same time by being at ground potential?The above is not rigorously accurate, but good enough to pose the question.

author: TimFox
author_rank: Super Contributor
timestamp: June 09, 2020, 01:17:50 pm
content: The cathode, control grid, and screen grid form a triode, where most of the current passes through the screen to the plate. In space-charge limited operation, the E field at the cathode determines the current. In a normal triode, the grid is much closer to the cathode than the plate, and the effect of the plate voltage is reduced (compared with a diode): this is where the amplification factor "mu" comes from. In a tetrode or pentode, the screen further shields the cathode from the plate voltage, and the cathode current is then determined by the screen and grid voltages as in a triode (relatively low mu). If you reduce the screen voltage to zero (with respect to cathode), the current would be reduced to almost zero. On page 3 of this data sheethttp://tubedata.milbert.com/sheets/093/6/6SJ7.pdfyou see the current with Ec1 = 0 (control grid, there is a typo on the graph legend) as a function of plate voltage with reduced screen voltage Ec2 down to 50 V: the current falls monotonically as you reduce the screen voltage.
Why not use two 5M resistors on the hot and comm of a DMM and do differential m? - Page 1
Forum section: electronics / projects

author: ballsystemlord
author_rank: Frequent Contributor
timestamp: August 29, 2025, 01:11:21 pm
content: Hello,So you'll see various people, such as Dave, winding the DMM leads together to try and cancel out any picked up noise.I'm curious, why not place one 5Mohm resistor on the comm, one on the hot, and do differential measurements with the DMM's ADC? Wouldn't that solve the picked-up noise problem? (As opposed to one 10Mohm resistor across the hot.)Thanks!

author: Berni
author_rank: Super Contributor
timestamp: August 29, 2025, 01:17:33 pm
content: Nope it would not.Problem is that one of the multimeter leads takes a different route to the multimeter, so the voltage induced in it by stray magnetic fields could be different.Tho this is not that much of an issue with DMMs as they don't tend to deal with high frequency. But with oscilloscope probes it really matters a lot.

author: mikerj
author_rank: Super Contributor
timestamp: August 29, 2025, 01:57:44 pm
content: Quote from: ballsystemlord on August 29, 2025, 01:11:21 pmThe noise suppression capabilities of differential measurement relies on the noise in each wire being of equal, or very simmilar phase and amplitude. To help make this happen twisted pairs are used.

author: coromonadalix
author_rank: Super Contributor
timestamp: August 29, 2025, 02:22:12 pm
content: unlees im wrong do you talk about 10Meg of input impedance of a dmm ?a 10Meg impedance is made by many resistors in serial to do the dmm ranges ... they all sum's up at 10-11 meg ohms, with 1 value to the ground, to end the divider stages ?

author: David Hess
author_rank: Super Contributor
timestamp: August 30, 2025, 01:03:44 pm
content: Wrapping the leads together still works to lower noise pickup with a single ended measurement.Common also attaches to the multimeter's shielding, so the common lead is shielding the input lead, and capacitance to ground is greater on the common lead than on the input lead.Differential voltmeters exist for special applications.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: August 30, 2025, 04:22:44 pm
content: Twisting the wires has a different effect then taking a differential measurement, although they can augment each other.But there is another reason too. Resistance and current measurement don't work anymore if you put a high impedance on the "GND" bus of the DMM.
Why SHUNT DC Regulators are not popular? - Page 1
Forum section: electronics / projects

author: 001
author_rank: Super Contributor
timestamp: November 12, 2018, 08:32:58 am
content: Hi!I see that all of commercial linear power supplies use power transistor in series with loadWhy parellel wiring aka shunt regulator is not so popular?I see many benefits like low output impedance, shorting stability etcAny opinions?

author: brabus
author_rank: Frequent Contributor
timestamp: November 12, 2018, 09:45:58 am
content: I would say the main issue is the inverted logic in comparison with a series regulator: in a parallel regulation scheme, you need to burn all the power you don't need, both in the regulation element and in the series resistor. On full power, you reach the same efficiency as the equivalent series regulator, but in all other cases you are wasting more heat.Given the fact that power supplies are seldom used continuously at full power, you would end up with a nice stove for winter times. Heat causes then quicker aging of the system.Output impedance in a power supply is basically never considered by the traditional designer (plenty of filtering on the DUT); in case of need he/she will buy a 4-quadrant supply.Short circuit protection as well: old problem, solved in many ways since the early days of electronics. Basically every power supply is short circuit tolerant nowadays.

author: glarsson
author_rank: Frequent Contributor
timestamp: November 12, 2018, 09:59:46 am
content: Be clearer. Parallel pass elements (using several transistors to increase current capability) is not the same as connecting a regulator in parallel with the load. The question seems to be about the second case, usually called a shunt regulator.

author: 001
author_rank: Super Contributor
timestamp: November 12, 2018, 10:12:30 am
content: Quote from: glarsson on November 12, 2018, 09:59:46 amYeaI mean shunt regulator sorry for my english

author: Zero999
author_rank: Super Contributor
timestamp: November 13, 2018, 11:27:12 am
content: Shunt regulators are regularly used, but only for very low current power supplies, such as voltage references. Look at many power supply schematics and you'll commonly see the voltage reference is generated by a zener diode or shunt voltage regulator IC and resistor. They are not used for high power regulators because the power draw is the same, irrespective of the load, as mentioned above.
Why PCB holes are linked with thin branches? - Page 1
Forum section: electronics / projects

author: Kokoriantz
author_rank: Frequent Contributor
timestamp: November 21, 2022, 05:11:46 am
content: I see sometimes through hole component leads are linked with thin branches, why?

author: bdunham7
author_rank: Super Contributor
timestamp: November 21, 2022, 05:17:26 am
content: Usually to make it easier to solder the component without losing too much heat to the huge copper pour surrounding the pad.

author: retiredfeline
author_rank: Frequent Contributor
timestamp: November 21, 2022, 06:06:20 am
content: They are called thermal reliefs and as bdunham7 says they are to prevent the surrounding copper from drawing away too much heat during soldering and preventing the solder from melting satisfactorily,

author: Kokoriantz
author_rank: Frequent Contributor
timestamp: November 21, 2022, 01:21:36 pm
content: Thank you for the explanation.

author: JeremyLeaf
author_rank: Newbie
timestamp: November 21, 2022, 05:24:06 pm
content: Note that these are normally enabled by default in most CAD packages. However for certain high speed designs, or where you need a good thermal connection from a component to a copper pour (heatsinking), you can choose to remove these and have a flooded connection. This can hurt the reliability of the assembly process however.
Why place a diode in parallel with the filter choke on a buck converter ? - Page 1
Forum section: electronics / projects

author: chipeater
author_rank: Contributor
timestamp: January 27, 2025, 10:02:45 am
content: Hello,I saw a design where a diode is placed in parallel with the filter choke of a buck converter.What's the point, apart from discharging the choke?Does this bring anything in terms of efficiency and/or performance?Thank you for your help

author: mtwieg
author_rank: Frequent Contributor
timestamp: January 27, 2025, 01:28:04 pm
content: Never seen something like that before...When the main switch is turned on, the circuit behaves like a normal buck, with input current flowing to the output.When the main switch is off, the freewheeling current will flow only through D8, as opposed to a normal buck where freewheeling current flows through D2 and the load.So basically D8 will destroy the power efficiency, for no apparent benefit.edit: oh and D8 will likely prevent the bootstrap cap C7 from maintaining voltage, so this circuit probably can't even function with terrible efficiency.

author: CosteC
author_rank: Regular Contributor
timestamp: January 27, 2025, 04:52:50 pm
content: D8 placement denies idea of buck converter. Reduces efficiency, rises voltage ripple on output, loads output capacitor with far higher ripple current.Where you found this abomination?

author: youngda9
author_rank: Regular Contributor
timestamp: January 27, 2025, 06:05:56 pm
content: I smell smoke...

author: Siwastaja
author_rank: Super Contributor
timestamp: January 27, 2025, 06:07:36 pm
content: Looks like some unfinished sketch / accidental placement of a random component in random place.
why so many relays!!?!?? - Page 1
Forum section: electronics / projects

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 11, 2014, 03:17:58 pm
content: I know: cost. But still, I feel like venting a bit.I have a split a/c and the wall unit has a relay in it. The constant clicking annoyed me... but I got used to it. Then I bought a motion-activated light switch for the bathroom...CLICK!!!CLICK!!!!!I thought we are in the era of the IGBT and power MOSFET? TRIACs are over half a century old!!!ARGH!!!

author: alimirjamali
author_rank: Regular Contributor
timestamp: September 11, 2014, 05:38:17 pm
content: Quote from: Alex Eisenhut on September 11, 2014, 03:17:58 pmActually it is called the era ofSolid-state relays. It hasmany disadvantages. The biggest disadvantage is higher voltage drop in closed mode * current = Wasted Energy = Heat = Higher Electricity bills = Unhappy customersThe real question is: Why those lazy mechanical designers could not create a silenced good mechanical relay after so many years!

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: September 11, 2014, 05:51:54 pm
content: Quote from: alimirjamali on September 11, 2014, 05:38:17 pmI don't know. I have speed controllers here for my RC toys that can control 120 amps and they just get warm. I can't imagine that we can't light up 3 LED lamps in my bathroom at 25W total (generously) ....

author: SeanB
author_rank: Super Contributor
timestamp: September 11, 2014, 05:55:02 pm
content: They do exist, and are made by Panasonic. Only drawback is they are expensive, and in the cost cutting world of consumer goods that is the first thing to get cut. Cheap noisy one is one tenth the cost.

author: gxti
author_rank: Frequent Contributor
timestamp: September 11, 2014, 05:57:41 pm
content: A solid-state relay that switches mains AC almost alwaysisa power TRIAC + opto-TRIAC. It's possible to do it with a MOSFET output stage but it costs a lot more and doesn't seem to gain much other than lower leakage, unless you spend even more to get the resistance down further.Besides, the efficiency of a switch that controls a 100 watt light bulb (or a 20 watt CFL/LED bulb) is comparatively irrelevant. An extra volt or two of drop is still only 1% efficiency loss.

author: ajb
author_rank: Super Contributor
timestamp: September 11, 2014, 06:04:43 pm
content: A mechanical relay easily handles any sort of lighting load you throw at it. Building a a cheap solid state switch that will handle incandescent, fluorescent (with any type of ballast), LV, etc is a bit trickier.

author: alimirjamali
author_rank: Regular Contributor
timestamp: September 11, 2014, 06:29:57 pm
content: Choosing between Mechanical Relays and Solid State Relays is really application specific. I Googled and this article clearly explains, whyEach Has It's Place.Who can guaranty that every customer is going to light up 3 LED lamps?COST plays an important rule. You can compare prices ofMechanical RelaysandSSRsof the same voltage/current to have a better idea.Oh, I should avoid controversial topics
Why some CP2102 IC's need driver installation? - Page 1
Forum section: electronics / projects

author: Sai teja
author_rank: Regular Contributor
timestamp: December 09, 2017, 07:13:24 am
content: Hello, I am using CP2102 IC in my project. When I inserted a CP2102, COM port detected directly in my desktop(windows 10 based). When I insert another CP2102 IC in the same desktop, COM port didn't detected. I had to install CP2102 drivers manually and it worked. What might be the reason for this behaviour?

author: Sai teja
author_rank: Regular Contributor
timestamp: December 09, 2017, 09:16:14 am
content: Thanks for your reply!But target CP2102 doesn't have custom PID and VID.

author: ballanux
author_rank: Contributor
timestamp: December 09, 2017, 11:05:47 am
content: I use that IC and when you change USB port or connect a different CP2102 it always has to reinstall the device and every time it generates an additional COM port, I think I have 36 or something now... anyway it usually works without user intervention on windows xp, 7 and 10 AFAIK.Of course the COM port will be different and you have to select the correct one on your application

author: JoeO
author_rank: Frequent Contributor
timestamp: December 09, 2017, 11:46:32 am
content: Lady Ada tells you how to delete the "excess" com ports.https://learn.adafruit.com/how-to-find-hidden-com-ports/overview?view=all
Why triac driver circuits use NON ISOLATED POWER supplies??? - Page 1
Forum section: electronics / projects

author: Dhanushka
author_rank: Regular Contributor
timestamp: June 03, 2020, 01:36:30 pm
content: Dear all,I am confusing whether why triac driver circuits use non isolated power supplies instead of SMPS, transformers in washing machines, remote controlled fans etc.Is it cheap or other reason?It is not safe as I think.Thanks.

author: brabus
author_rank: Frequent Contributor
timestamp: June 03, 2020, 02:44:44 pm
content: In order to trigger the TRIAC you need to be synchronous with the line phase (zero crossing), so it's convenient to tie the system to the non-isolated side of things. As long as the load does not require isolation (which is the case by any mains driven load), and as long as the user interface is isolated (e.g.: a plastic potentiometer shaft), you're good to go! :-)

author: Ian.M
author_rank: Super Contributor
timestamp: June 03, 2020, 03:10:05 pm
content: TRIACs are inherently non-isolated as their gate drive must be applied with respect to MT1 which is part of the load circuit. Adding isolation adds cost, and *IF* there is no requirement for any user-accessible low voltage interface, rather than isolate the control circuit, its cheaper and easier to simply use an enclosure and controls that prevent physical access to any live part without the use of tools and meet the requirements for reinforced insulation.
Why USB-C GND is being connected to the shield of the cable after connecting? - Page 1
Forum section: electronics / projects

author: Pinkus
author_rank: Frequent Contributor
timestamp: January 09, 2024, 05:46:00 pm
content: I need some help: I have designed a circuit board with a USB C connector. Shield and GND are separated and are not connected to each other on my PCB (there is a C and R planned for later).However, as soon as I plug in an adapter cable (e.g. USB-C->USB-A or USB-C -> USB-C) (still without a device at the other end of the cable), the shield of the cable is connected to GND. I tried several cables. Is this normal? With my older designs using Micro USB this never happend. I am a little at a loss.Thanks for your help!

author: coromonadalix
author_rank: Super Contributor
timestamp: January 09, 2024, 05:53:00 pm
content: normally the usb ground is connected to the shield .... provide better protection against noises / interferences ... all my circuits usb -c and micro-usb have their ground common with the shieldthe shield one side or the other "normally speaking" must be ended to the ground ..usb-c pin 6 vss is tied to the pin 11 shield / metal casing of the connector

author: wraper
author_rank: Unknown
timestamp: January 09, 2024, 06:12:20 pm
content: Quote from: Pinkus on January 09, 2024, 05:46:00 pmAnd that's the most stupid thing that is commonly done with zero clue why in hell you put this nonsense in.https://www.unit3compliance.co.uk/hdmi-more-like-hdm-why-thoughts-on-cable-shield-grounding/As of why they become connected, IIRC it's because USB type C standard requires connection between the shield and GND wire at the ends of the cable.

author: wraper
author_rank: Unknown
timestamp: January 09, 2024, 06:23:10 pm
content: https://www.usb.org/sites/default/files/USB%20Type-C%20Spec%20R2.0%20-%20August%202019.pdfQuoteThat you are violating by adding RC nonsense.QuoteMost of micro USB cables I've seen have shield and GND pin connected together with rare exceptions when they are not connected.

author: selcuk
author_rank: Frequent Contributor
timestamp: January 09, 2024, 07:13:12 pm
content: For such cables, it's better to connect circuit ground and cable shield together with minimal inductance. That high frequency shorting with capacitor method is for long transmission lines (ethernet from building to building) to prevent common mode currents from occurring due to ground voltage differences. So no worries for USB.If your device has a metal chassis and usb connector is a panel type, preferably you may connect the shield first to chassis then chassis to ground.You may refer to Figure 17 and Table 5 on the below document. It shows EMC measurements for direct ground connections vs. capacitor, resistor, varistor etc.https://www.we-online.com/catalog/media/o721297v410%20ANP116_Gigabit-Ethernet__EN.pdf

author: Miek
author_rank: Regular Contributor
timestamp: January 09, 2024, 08:26:08 pm
content: The shield should be connected to GND in the connector, it's part of the Type-C specification:https://www.usb.org/document-library/usb-type-cr-cable-and-connector-specification-release-23Quote from: USB Type-C spec, Table 3-11
Why USB Data Series Resistors? - Page 1
Forum section: electronics / projects

author: Gytis
author_rank: Contributor
timestamp: May 09, 2014, 07:17:10 am
content: Hello All,I have seen many USB-interfaced application PCBs, but one thing I never understood: why are there series resistors for the data lines: I see many At(x)mega applications use 22ohm, i've seen other applications use 33ohm, even 68ohm, or just connected into the IC with no resistors.I don't find anything explanation in Atmel datasheets, and I didn't find any thread similar to this around here.What are these resistors doing? Does it have to do with transmission line theory?I am designing a small PCB interfacing through USB, (Atxmega32A4U). Do I need 22Ohm resistors?Can I just leave them with no series resistance?Thanks!

author: Dago
author_rank: Frequent Contributor
timestamp: May 09, 2014, 07:20:44 am
content: Quote from: Gytis on May 09, 2014, 07:17:10 amThey are series termination resistors. The USB standard specifies that the signal-to-ground impedance is 30 ohms and differential impedance (between data lines) is 90 ohms. Also technically your traces should also be matched to these impedances. Matching is important to avoid problems with signal integrity (reflections and so forth).http://www.usb.org/developers/usbfaq#sig6

author: Araho
author_rank: Regular Contributor
timestamp: May 09, 2014, 07:19:04 pm
content: Read the datasheet for your part. In the USB section, it specifies 22 ohm resistors in series with the datalines. As noted above, they are termination resistors, used so that the total impedance of the line, including internal circuitry in the part, matches that of the USB specification. In addition, series resistors limit the edge-speed of pulses, which means less EMI-generation. 22 ohms probably won't have much of an effect here, though.That said, your circuit would probably work without the resistors, but you're risking problems with signal integrity. At least put the footprints for the resistors in, and then add a jumper or solder bridge if it turns out you don't need them for your required level of performance, at least while prototyping.
Why Use a Bridge Rect and Opto In This Circuit - Page 1
Forum section: electronics / projects

author: bostonman
author_rank: Super Contributor
timestamp: April 22, 2021, 02:08:14 am
content: The attached is a schematic for the add on MOSFET upgrade to an Anet A8 3D printer.The hot bed connector on the main board can melt, so this board bypasses the board by using the signal and powering the hot bed directly from the AC/DC supply.It seems this board is overly engineered. Although it shows AC on the input, the input voltage is DC (even if it were AC, the circuit doesn't have a filtering capacitor). Also, why use an opto since the entire printer is referenced to the same ground?I'm guessing the bridge rectifier eliminates wiring the DC input backwards (it also wastes voltage/power), but why an opto?

author: ledtester
author_rank: Super Contributor
timestamp: April 22, 2021, 02:35:30 am
content: Yes, the bridge makes it idiot proof from a polarity point of view.The opto provides more safety and idiot-proofing.Since this is going to be connected up by the consumer there's a much larger risk that they will screw something up. And if the MOSFET blows it's going to cost the company in terms of bad reviews, time spent troubleshooting the problem with the customer, returned orders, etc. A string of bad reviews can kill a product on ebay/amazon/aliexpress. It's probably well worth the extra cost to add those components.

author: bostonman
author_rank: Super Contributor
timestamp: April 22, 2021, 03:16:05 am
content: Thanks.It was relatively straight forward, but wanted to make sure I wasn't missing something.

author: ledtester
author_rank: Super Contributor
timestamp: April 22, 2021, 03:28:22 am
content: QuoteAlso consider that these extra components allow the module to be used in more situations. With fewer restrictions the module could potentially be used with other printers.
Why use an N channel MOSFET to connect GND - Page 1
Forum section: electronics / projects

author: ilium007
author_rank: Frequent Contributor
timestamp: March 10, 2019, 01:22:48 am
content: Hi - I came across this Freescale MC33926 breakout from Pololu and found this in the schematic. The numerous GND pins on the SMD package are connected to GND via an N channel MOSFET triggered by Vin. I am wondering why these pins aren't just tied direct to a GND plane on the PCB ?I am starting out with electronics design and wondered why the designer may have chosen to go this way ?

author: tsman
author_rank: Frequent Contributor
timestamp: March 10, 2019, 01:26:55 am
content: Quote

author: retrolefty
author_rank: Super Contributor
timestamp: March 10, 2019, 02:47:22 am
content: I suspect it's to properly sequence powering up to prevent glitches on the output drivers.

author: bson
author_rank: Unknown
timestamp: March 10, 2019, 03:03:56 am
content: Note that the source pin is on the top and drain on the bottom, and it connects GND to Earth/Chassis.

author: Mr.B
author_rank: Unknown
timestamp: March 10, 2019, 03:05:11 am
content: Quote from: tsman on March 10, 2019, 01:26:55 amThis...^

author: georges80
author_rank: Frequent Contributor
timestamp: March 10, 2019, 03:10:15 am
content: http://www.ti.com/lit/an/slva139/slva139.pdfBeen using these schemes for years now for reverse polarity protection. Minimal voltage drop compared to using a diode (even a schottky).The zener is needed if the gate voltage would otherwise be too high (depends on the supply rails).cheers,george.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 10, 2019, 03:14:52 am
content: The part that trips most beginners up is that MOSFETs can conduct in both directions when turned on. And in fact, will do so better than a diode - look up "synchronous rectification" as well as the poorly named "ideal diode".Here's a video explaining different options of reverse polarity protection:

author: ilium007
author_rank: Frequent Contributor
timestamp: March 10, 2019, 04:59:26 am
content: Thanks for all the replies. I have another weeks worth of reading to do !
Why use two fets for reverse voltage protection? - Page 1
Forum section: electronics / projects

author: trevwhite
author_rank: Frequent Contributor
timestamp: June 26, 2017, 09:02:51 am
content: I was looking at a TI reference design and they use 2 P channel fets in series on the input from a coin cell battery.I attached the schematic section. Why have they used two, I thought one would be good enough?Trev

author: Leon23
author_rank: Contributor
timestamp: June 26, 2017, 11:11:21 am
content: Putting the mosfets/diodes in series seems to make the reverse voltage protection to withstand twice the reverse voltage compared to just having one mosfet/diode in series.

author: bktemp
author_rank: Super Contributor
timestamp: June 26, 2017, 11:15:24 am
content: The limiting factor is often the gate voltage (I have never seen a mosfet with Vdsmax lower than Vgdsmax), so putting them in series does not increase the reverse maximum voltage.I would assume it is for safety in case one mosfet fails, or maybe to reduce the leakage current.

author: AndyC_772
author_rank: Super Contributor
timestamp: June 26, 2017, 11:25:28 am
content: In this design, though, they're in series, and pointing the same way.I've done many designs using a series pair of FETs facing opposite ways, so they can block current flow in either direction. That's not what they're doing here, though.I'd guess at minimising reverse leakage through the body diode. The thing being powered must be very high impedance if it's being powered from a coin cell, so perhaps a single reverse-biased diode isn't enough to prevent the supply voltage going negative?

author: tszaboo
author_rank: Super Contributor
timestamp: June 26, 2017, 11:35:44 am
content: Probably leakage. At a given temperature, the leakage is the (somewhat linear) function of drain source voltage, if Vds is smaller, the leakage is smaller. With two in series, Vds will be half-ish. I'm not sure, if this is an economic way to protect the device though.

author: Paul Price
author_rank: Super Contributor
timestamp: June 26, 2017, 11:43:13 am
content: Somebody has a interest in selling a big overstock of P-Chan MOSFETS, no other reason.

author: Niklas
author_rank: Frequent Contributor
timestamp: June 26, 2017, 04:01:19 pm
content: The additional MOSFET is related to the reverse current rating from the coin cell manufacturer. Check the note above Figure 3 in the user manual for the demo board.
Why wont my LED work in this circuit. - Page 1
Forum section: electronics / projects

author: Grayfox
author_rank: Regular Contributor
timestamp: May 15, 2014, 03:29:53 pm
content: I have made a homing light/follow me home light circuit which uses some capacitors to power a relay coil to keep the headlights on for about 15 seconds, but the LED wont work when the second relay is active.The second relay does make a clack sound and the LED is hooked up to the same circuit by wont work and the LED works fine.And should I add a diode to the coil of the second relay?

author: madires
author_rank: Super Contributor
timestamp: May 15, 2014, 03:49:40 pm
content: Please reverse the LED (NC of left relay is ground) and it's not a bad idea to add a freewheeling diode.
Why would an isolation transformer add noise to the waveform? - Page 1
Forum section: electronics / projects

author: sprok
author_rank: Contributor
timestamp: July 23, 2016, 12:18:29 am
content: /

author: ataradov
author_rank: Super Contributor
timestamp: July 23, 2016, 12:29:43 am
content: It is possible that you are reaching core saturation. Saturation usually does not look like this, it typically affects shape of the slopes, not peaks.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 23, 2016, 12:36:46 am
content: Hmm, the combination of leakage inductance and filter capacitance may be making a resonant circuit, that's being excited by your mains' flattened tops. Or put another way: your mains voltage contains a small amount of higher harmonics, which are being magnified by a resonant filter.Try a 1uF film cap in series with a resistor of 10-100 ohms, placed across the terminals. Does that dampen it?Tim

author: System Error Message
author_rank: Frequent Contributor
timestamp: July 23, 2016, 03:06:57 am
content: The circuit you measure is the secondary of the transformer. Since you connected it to ground and the oscilloscope is usually grounded as well, a loop can be formed or signals can also travel to ground. Some circuits filter noise by grounding so your oscilloscope picks out the noise from ground.

author: Delta
author_rank: Super Contributor
timestamp: July 23, 2016, 03:14:37 am
content: Are you sure that capacitor is directly across the secondary?7uF across 125VAC will allow 0.33A to flow!

author: Arjan Emm
author_rank: Regular Contributor
timestamp: July 23, 2016, 06:41:44 am
content: Maybe the isolation transformer was intended for a specific inductive load. In that case they may have added the capacitor to compensate for that and improve cosine phi with it.

author: BravoV
author_rank: Super Contributor
timestamp: July 23, 2016, 01:55:07 pm
content: Abit off topic, but I guess its still related.I can see you used old CRO to measure mains voltage, interested on how or what probe did you use to get those results ?

author: Mechatrommer
author_rank: Super Contributor
timestamp: July 23, 2016, 03:15:28 pm
content: Quote from: sprok on July 23, 2016, 02:28:39 pmwe can understand case insensitive typing out of laziness but since H is capital....mHz = milliHertzMHz = MegaHertz
Wich Sound card oscilloscope probe circuit? - Page 1
Forum section: electronics / projects

author: samsagaz
author_rank: Contributor
timestamp: June 15, 2016, 10:43:34 pm
content: Hey guys, i want to purchase an external USB Sound Card to use as simple oscilloscope to use soft like multiintruments. Want to know if can someone recommend me some circuits to have protection circuit ensures its output to be less than 2-3V at all time.

author: xtoffer
author_rank: Contributor
timestamp: June 16, 2016, 07:40:17 am
content: I seem to recall making something similar as well before I got a "proper" scope. To clip the input you can use a few diodes in series (https://en.wikipedia.org/wiki/Clipper_(electronics)). On a sound card you normally have mic or line input (or both). Line input can take the highest voltage but 2-3V still seem a bit high to me.Ok I had a look at Wikipedia, line level for "consumer audio" is listed as 0.894 Vpp and for "professional" 3.472 Vpp. Mic input will be even lower I believe.Mine was rather minimalistic, I think I put a resistive divider followed by diodes for the protection and buffered it with opamps before and after. Could maybe have used some filtering as well...Otherwise there are a lot of circuits out there if you search around.

author: tggzzz
author_rank: Super Contributor
timestamp: June 16, 2016, 08:15:14 am
content: Protection againstallovervoltage sources is non-trivial. Seehttp://in.tek.com/dl/3AW_19134_2_MR_Letter.pdfhttp://www.tek.com/dl/51W_10640_1.pdfYou might decide to specify protection against a subset of overvoltage conditions.

author: EntropyWizard
author_rank: Contributor
timestamp: June 17, 2016, 01:46:13 am
content: I built one of thesehttp://xoscope.sourceforge.net/hardware/hardware.htmland it seemed to work ok with a regular PC sound card. I only used it very briefly though since I acquired an old analog scope, and haven't had much use for the sound card one since.

author: LaserSteve
author_rank: Super Contributor
timestamp: June 17, 2016, 02:47:37 pm
content: Some of the 5.1 and 7.1 19$ USB sound modules can be modified for direct coupling by adding an adjustable 1.2V offset to your signal.Just remove the electrolytic caps.The trick is adjusting the setup software to turn off the audio signal processing, echos, depth cue phasing, and "surround sound".We used them mainly for DC coupled high speed outputs, but input is also possible..CM series chipsets were the ones we had success with...While my application was control of a mechanically scanned RGB projection graphics system, this fellow uses them for DAQ work,,Reviews:http://www.daqarta.com/dw_gguu.htmMods:http://www.daqarta.com/dw_ggmm.htmYou really do need to protect your PC when you do this, a failure of the motherboard USB hub goes right in to "soft tissue" near the processor on the motherboard...Steve
Wide range discrete negative voltage regulator - Page 1
Forum section: electronics / projects

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: August 31, 2020, 08:56:20 pm
content: So I have been going arround the internet trying to find a negative voltage regulator but all that pops up is the 79xx stuff. I cant really fund a universal schematic I could use to achieve what I want. So here are the speciiffications I would like to achieveInput voltage -130VOutput voltage : Variable between -20 and -100Output current would be a few mA (10mA)The purpose of this regulator is providing bias voltage for a vacuum tube amplifier.If anyone can point me a to universal circuit I could modify to fit my needs then I would be gratefull for that too.Many thanks

author: MasterT
author_rank: Frequent Contributor
timestamp: August 31, 2020, 09:39:19 pm
content: https://www.eleccircuit.com/the-variable-high-voltage-power-supply-0-300v/https://sound-au.com/project151.htmhttps://www.homemade-circuits.com/0-300v-variable-voltage-current/andhttps://tubecad.com/2006/11/blog0087.htm

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: August 31, 2020, 09:47:18 pm
content: https://www.eleccircuit.com/the-variable-high-voltage-power-supply-0-300v/Positive voltage regulator : not what I needhttps://sound-au.com/project151.htmstill a positive voltage regulatorhttps://www.homemade-circuits.com/0-300v-variable-voltage-current/yet another positive voltage regulatorhttps://tubecad.com/2006/11/blog0087.htmdid you guess it? its a positive voltage regulator once againI need a negative voltage regulator..one that can be scaled up. None of these are really any help to me

author: aargee
author_rank: Frequent Contributor
timestamp: August 31, 2020, 10:21:39 pm
content: Not that I've looked for what you want, but is there any reason you can't use an isolated supply using one of the positive power supply circuits and reference positive to common/ground?

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: August 31, 2020, 11:05:13 pm
content: Quote from: aargee on August 31, 2020, 10:21:39 pmYes, its the way the power transformer is designed. its a 800VAC CT. On one side of the CT I have a 100VAC tap

author: MasterT
author_rank: Frequent Contributor
timestamp: August 31, 2020, 11:28:34 pm
content: Quote from: SK_Caterpilar_SK on August 31, 2020, 09:47:18 pmChanging polarity is simple, N-MOSFET & NPN BJT replace with P-MOSFET and PNP BJT. Turn over Zenner .
Wide range voltage detector - Page 1
Forum section: electronics / projects

author: foxabilo
author_rank: Newbie
timestamp: December 14, 2018, 11:04:55 pm
content: Evening all,I have a project where the input is in the form of a couple of input terminals and the potential difference between them can be from 3.3v DC to 240v AC and I need to let a micro controller know if the inputs are energised.I have shoved the inputs into a rectifier put it through a 220K and a zener diode to clamp it with a BJT to pull a 100k load down to GND and the input to the microcontroller all works great.Now I want to try and opto isolate it just to be double safe, but of course the output from the 220K+rectifier from 3.3V is nowhere near enough to drive an opto , any ideas?CheersFoxa

author: ogden
author_rank: Super Contributor
timestamp: December 14, 2018, 11:09:25 pm
content: Quote from: foxabilo on December 14, 2018, 11:04:55 pmUse isolated DC-DC 5v->5v module, add some kind of amplifier between clamp and opto.

author: unitedatoms
author_rank: Frequent Contributor
timestamp: December 14, 2018, 11:26:06 pm
content: You can try using current limiter based on lnd150 fets.https://www.eevblog.com/forum/beginners/mains-zero-crossing/

author: foxabilo
author_rank: Newbie
timestamp: December 14, 2018, 11:34:11 pm
content: Quote from: unitedatoms on December 14, 2018, 11:26:06 pmNow that is a nice starting point, let me guess though, no depleted FET models in spice , still have the issue of not enough ompf to drive an opto for the full 340 volt (dc) range though.

author: foxabilo
author_rank: Newbie
timestamp: December 15, 2018, 12:00:10 am
content: Scratch that, I getcha now, as the depletion fet starts to conduct any highvoltagescurrents it turns itself off at a point set by the feedback resistor and .... yea I get it .... Very smart that.