hybridfree/eevblog-posts huggingface dataset:
Solved - Why LCD's response slower when cold? - Page 1
Forum section: electronics / beginners

author: sam1275
author_rank: Frequent Contributor
timestamp: January 19, 2017, 12:59:22 pm
content: Hello.This question is as short as the title, but I tried google hard and no answer. Could anyone explain it?Thanks.

author: PA0PBZ
author_rank: Super Contributor
timestamp: January 19, 2017, 01:07:59 pm
content: I think because the C's are less L when cold(er).

author: bktemp
author_rank: Super Contributor
timestamp: January 19, 2017, 01:13:09 pm
content: Because the liquid crystals are more viscous when cold.

author: BrianHG
author_rank: Super Contributor
timestamp: January 19, 2017, 01:14:27 pm
content: The liquid crystal is crystals suspended in an oil type fluid. Remember, when the LCD crystals align and polarize in the fluid, they are mechanically moving and aligning. As the temperature cools, the viscosity of the oily fluid changes making it difficult for the crystals to move as fast as they can. Also, since there are so many formulas out there for different voltages and response speeds to allow features like passive scanning display LCDs which wont flutter, the fluid might be designed to be slow and viscus amplifying the cool down slowing effect.You can clearly see this with LCDs where you push your finger over while operating, smearing around the fluid, disrupting the fluid and crystal alignment effect, with a freezing cold LCD, this fluid will move in a much slower smeary fashion.

author: sam1275
author_rank: Frequent Contributor
timestamp: January 19, 2017, 03:28:31 pm
content: Thank you everyone!
Why low current op amps driving headphones sound tinny? - Page 1
Forum section: electronics / beginners

author: Deactivated-1
author_rank: Frequent Contributor
timestamp: September 05, 2023, 05:38:24 pm
content: A dumb question but I don't see the reason why... Most headphone outputs have a resistor in series with the output ~100-220 ohms and sound fine.But take an op amp that has a built in 75 ohm resistor in series with the output and it just doesn't so tiny...Is it the feedback loop? because the feedback is taken from the headphone side instead of the amp side? but I would think that would instead boost the bass since that creates a high pass filter (in the negative feedback circuit)
Why many (most?) solar MPPT chargers are common positive? - Page 1
Forum section: electronics / beginners

author: fubar.gr
author_rank: Unknown
timestamp: January 31, 2018, 12:20:58 am
content: I am searching for parts to build a small (10-20Wp) solar powered system just for fun and I noticed that many of the MPPT battery chargers are common positive. Is there a reason for that?

author: Bratster
author_rank: Frequent Contributor
timestamp: January 31, 2018, 02:43:27 am
content: Can you post some links to what you have been looking at?Sent from my Nexus 6 using Tapatalk

author: mtdoc
author_rank: Super Contributor
timestamp: January 31, 2018, 02:53:12 am
content: I am familiar with most of the popular MPPT controllers in the USA - Outback Power, Midnite Solar, Morningstar and Schneider Electric. None of them are common positive.

author: fubar.gr
author_rank: Unknown
timestamp: January 31, 2018, 08:28:43 am
content: Most made by EPSolar have common positive ground, eg the Viewstar AU:http://www.epsolarpv.com/en/index.php/Technical/download

author: David Hess
author_rank: Super Contributor
timestamp: January 31, 2018, 05:15:25 pm
content: Common positive allows the use of a less expensive n-channel power switch without a level shifting stage.
why microchip removed GND details? - Page 1
Forum section: electronics / beginners

author: hsn93
author_rank: Regular Contributor
timestamp: August 02, 2018, 08:56:42 am
content: hello, im looking into ATSAM4E mcu uControllerwhy would they remove the details of which pin is which GND? did they connect them all internally and it doesnt matter anymore ?it may sound silly question, but for me i think it would make some sense

author: Daixiwen
author_rank: Frequent Contributor
timestamp: August 02, 2018, 09:30:25 am
content: Maybe not internally but they probably required all those pins externally directly connected to the GND plane anyway. Separate ground islands just create problems.

author: exe
author_rank: Unknown
timestamp: August 02, 2018, 11:29:45 am
content: I'd ask them.Here is what analog says:http://www.analog.com/en/analog-dialogue/articles/staying-well-grounded.html(see Separate Analog and Digital Grounds). They say different ground pin names doesn't mean they should be connected to different grounds. At least for their ADC they say all grounds should be connected together.

author: Rerouter
author_rank: Super Contributor
timestamp: August 02, 2018, 12:03:44 pm
content: Having clues to what grounds to keep quiet, and how you should structure your least impedance loops is important, however I suspect this was to reduce people trying to split ground planes under a BGA,to make very clear, for 99% of circuits, splitting ground planes will generally hurt you more than help you.High edge rate signals have a return current that mostly follow the path of least impedance, In general, directly under the signal trace, and it wants to stay as close to it as possible. when you break its ground plane it will detour to get back to it, but if you just provide it a way to stay near that signal, e.g. jumping the ground over the split, next to the signal, it behaves mostly as if there is no split.So for the most part, if you don't mess up the return path for the signals ground currents too badly, they are well behaved. So all that is left is keeping proper separation from analog / sensitive nets, you don't have cross talk issues if your traces are not near to one another.If you have a big DC current that flows across the board, through your analog section and you want to separate it, this is one of the few cases where creating a local ground net can benefit, but in most cases I would probably just confine those high currents to there own traces, rather than causing chaos across the plane. Technically splitting the ground, but on the problematic net rather than the victim node.

author: hsn93
author_rank: Regular Contributor
timestamp: August 02, 2018, 01:27:38 pm
content: Quote from: Rerouter on August 02, 2018, 12:03:44 pmso on that case, you would contact them to find the pin that is related to GNDANA ?

author: Rerouter
author_rank: Super Contributor
timestamp: August 02, 2018, 08:30:11 pm
content: Ping them an email, and they should be able to send yo an older revision of the datasheet,
Why multiple capacitors in parallel? - Page 1
Forum section: electronics / beginners

author: madhu.wesly01
author_rank: Regular Contributor
timestamp: July 02, 2018, 04:27:14 am
content: Hi,Wondering why you would choose to use smaller capacitors in parallel vs one bigger one. Can I use a single 47uF capacitor at the output, or I have to place 4 X 10uF capacitors as given in datasheet?? Will there be any difference??Could you also let me know in general how to decide on capacitor package(size) used at input and output of the regulator ??Thanks in advance.

author: EEVblog
author_rank: Unknown
timestamp: July 02, 2018, 04:37:02 am
content: Quote from: madhu.wesly01 on July 02, 2018, 04:27:14 amBasically just follow the datsheet advice. They often have entire sections devoted to choosing a bypass capacitors.

author: b_force
author_rank: Super Contributor
timestamp: July 02, 2018, 08:18:33 am
content: Besides ESR it can also be cheaper or sometimes just fits better on the PCB when there are size limitations.A 100uF is a lot smaller (height) than a 470uF.In a lot of cases it's also easier to fit four smaller sized caps on a PCB than one big one (that will screw up your layout)

author: Karlo_Moharic
author_rank: Regular Contributor
timestamp: July 02, 2018, 09:43:16 am
content: Redundancy

author: Ice-Tea
author_rank: Super Contributor
timestamp: July 02, 2018, 09:50:29 am
content: Quote from: Karlo_Moharic on July 02, 2018, 09:43:16 amNot really. They tend to fail short. So adding more caps essentially increases the likeliness the entire unit fails.
Why my dc-dc buck converter is consuming 8mA of current with no load connected? - Page 1
Forum section: electronics / beginners

author: nishantnidaria
author_rank: Contributor
timestamp: September 29, 2022, 10:23:30 am
content: I am using a TPS5430 buck converter on my PCB which is converting 12V to 8V, if i shutdown the buck converter using enable pin, it consumes only a few micro amps but if i let it enabled with no load connected, it consumes about 8mA constantly.Datasheet:https://www.ti.com/lit/ds/symlink/tps5430.pdf?ts=1664439034845&ref_url=https%253A%252F%252Fwww.google.com%252FAccording to the datasheet quiescent current should be 4.4mA (max).My questions are:Is it normal?Is it consumption or power loss?How can i avoid/fix it?Thank you in advance for your help and guidance.

author: temperance
author_rank: Super Contributor
timestamp: September 29, 2022, 01:36:55 pm
content: The data sheet states:VSENSE = 2 V,Not switching,PH pin openYour device is switching.

author: nishantnidaria
author_rank: Contributor
timestamp: September 29, 2022, 01:42:54 pm
content: Thank you for your reply, when we say "Not Switching", does it means the IC is active but there is no load connected?

author: hubi
author_rank: Regular Contributor
timestamp: September 29, 2022, 02:03:39 pm
content: The 4.4mA is specified when the device is not switching. You measured 8mA while switching.

author: nishantnidaria
author_rank: Contributor
timestamp: September 29, 2022, 02:09:11 pm
content: I am confused, what is the difference between "Switching" and "Not switching" ? understanding the difference will help me a lot i think.

author: thinkfat
author_rank: Unknown
timestamp: September 29, 2022, 02:28:47 pm
content: "Switching" means the internal MOSFET is switching on and of at the set frequency (500kHz). "Not switching" means the MOSFET is gated.The "VSENS=2V" requirement means this 4.4mA figure is not achievable in reality. If you need a smaller no-load current, choose a different part.Why? Because this condition is artificial. The regulator will switch off the MOSFET when the feedback pin is at a voltage higher than the internal reference voltage of 1.221V. But in normal operation, the feedback voltage will always be equal to the reference voltage. This is how the regulation works.
why noise analysis is done in integrated circuits? - Page 1
Forum section: electronics / beginners

author: techguru
author_rank: Regular Contributor
timestamp: May 10, 2019, 05:36:47 am
content: Hi to all,can any body explain why noise analysis is done in integrated circuits?

author: brabus
author_rank: Frequent Contributor
timestamp: May 10, 2019, 07:57:52 am
content: Usually the goal is to have as little noise as possible, so the noise analysis helps you predict how much noise will your IC produce. Would you buy a very noisy OpAmp, for example? Even it if was cheap?The question is actually non trivial, let me turn it: why is noise analysis  skipped on discrete design? Well, if your discrete design happens to be noisy, you can modify it by changing some parts and pursue your SNR goal.But if an IC is noisy, there is not really much left to do than change it.

author: pwlps
author_rank: Frequent Contributor
timestamp: May 10, 2019, 08:43:39 am
content: If you deal with clean Volt-range signals then you don't care about noise analysis but for very small signals (e.g. of order of microvolt or smaller in a radio receiver front-end) the noise added by the component itself is a problem. For example the GPS signal can be 40dB below the thermal noise level, therefore selecting low-noise components for the receiver is important.
Why non zero voltage with one probe on wall outlet and other floating (NC) - Page 1
Forum section: electronics / beginners

author: perkabrod
author_rank: Contributor
timestamp: March 16, 2017, 08:39:47 am
content: I recognize this phenomina when trying to find a hum in a Marshall guitar amplifier.Even with the unit switch off, the chassis had a few volts potential if I let one of the probe not touching anything but air, of course, as long as a power cord was plugged in to the unit.Today I made a little test video but this time I used an AC-AC transformer because it's easy to access the pins and take measurementsIN VIDEO, the black probe is just touching the air, it's laying on the floor.https://youtu.be/H6eFCG_4900Note, most swedish households don't have ground connections except for kitchens or if the house was built in the 90's or later

author: Dago
author_rank: Frequent Contributor
timestamp: March 16, 2017, 09:42:32 am
content: The circuit still has capacitive coupling with the probe not connected and this is enough for a current to pass through and your meter to measure a voltage.

author: perkabrod
author_rank: Contributor
timestamp: March 16, 2017, 10:02:19 am
content: Thanks Kalle!

author: alm
author_rank: Super Contributor
timestamp: March 16, 2017, 12:31:01 pm
content: The term to search for is stray voltage or ghost voltage. For examplethis Fluke page, with, unsurprisingly, a piece of equipment they want to sell you.

author: jeroen79
author_rank: Frequent Contributor
timestamp: March 16, 2017, 12:46:13 pm
content: Quote from: alm on March 16, 2017, 12:31:01 pmWhich basically is a 3k resistor priced around $60.

author: alm
author_rank: Super Contributor
timestamp: March 16, 2017, 01:12:44 pm
content: Hey, they also give you a nicely insulated case. And possibly some overvoltage protection (PTC). While I wouldn't recommend any hobbyist to spend $60 on this, I wouldn't suggest putting a bare axial 3 kOhm resistor with some clip leads across a possibly live mains circuit either.

author: David Hess
author_rank: Super Contributor
timestamp: March 16, 2017, 06:34:46 pm
content: Quote from: Dago on March 16, 2017, 09:42:32 amYou can take advantage of this to make some difficult measurements. One unfortunately common wall socket wiring mistake is to swap hot and neutral. One lead of a high impedance voltmeter like any common multimeter will show a low voltage (close to zero) for neutral and ground and 120/240 volts for hot without relying on any other wiring to be correct. It will also reveal an isolated 120/240 volt output by reading about 60 or 120 volts for hot and neutral; this could happen if the ground bonding wire is open.Note that you get better accuracy by holding the common multimeter lead in your hand to increase the capacitive coupling but I do not really recommend this to others even though I do it myself.

author: jeroen79
author_rank: Frequent Contributor
timestamp: March 16, 2017, 06:54:00 pm
content: Quote from: alm on March 16, 2017, 01:12:44 pmNot to mention a Fluke logo.QuoteSomething similar could be constructed from a low power lightbulb and some suitable bananaplugs.
Why one pair of leads of the "octopus" type power leads have resistors in it ? - Page 1
Forum section: electronics / beginners

author: xani
author_rank: Frequent Contributor
timestamp: October 05, 2017, 10:54:20 pm
content: So I got one of those(mostly for usb tbh, got better cables for normal stuff):https://www.aliexpress.com/item/Power-Supply-Test-Lead-Cable-Kit-2-Alligator-Clips-2-Banana-Plugs-4-Hook-Clips/32698896113.htmland I've noticed that green and yellow clips have resistors connected to it. Yellow one just reads half the voltage (using 2x20k as voltage divider), green one jus just ground via resistor (so pulldown)....why ? what use that would have ?

author: ataradov
author_rank: Super Contributor
timestamp: October 05, 2017, 11:46:12 pm
content: Since this is intended for cell phone repair, those things may be for some specific phone use, like providing fake charge information, or temperature.

author: xani
author_rank: Frequent Contributor
timestamp: October 06, 2017, 01:59:07 am
content: That would explain the ground + resistor one (as AFAIK that's how thermistor on some batteries is connected) but the "shitty virtual ground" one?

author: ataradov
author_rank: Super Contributor
timestamp: October 06, 2017, 02:01:01 am
content: Possibly to pull down some digital IRQ-like input. Can't really think of any good use, but may come in handy sometime. The whole contraption is very strange.
Why P-FET does no block reverse current - Page 1
Forum section: electronics / beginners

author: Alderelrob
author_rank: Newbie
timestamp: July 07, 2023, 08:57:31 pm
content: Hi all,I am trying to understand why a P-FET is suitable for reverse polarity protection but not for reverse current blocking. See the attached image.When we reverse the polarity of the input, the Gate-Source of the P-FET are tied together to the positive side. Vin becomes GND, and the FET remains open, with no current flowing through the FET or the body diode. Reason is Vgs=0VHowever, if the input voltage is, for example, 10V, and the load is a motor that generates a back-EMF higher than Vin, how is it possible for the current to flow through the FET? the gate is always tied to the GND, the Source voltage vary making the Vgs always <0 so the PFET can conduct in both ways?Thank you.

author: wraper
author_rank: Unknown
timestamp: July 07, 2023, 09:01:17 pm
content: Because as long as there is positive voltage on the output, FET will be in ON state. And in ON state it conducts current regardless of polarity. You need more complicated gate control circuit to block reverse current.

author: langwadt
author_rank: Super Contributor
timestamp: July 07, 2023, 09:02:15 pm
content: once the fet is on it conducts in both directions

author: David Hess
author_rank: Super Contributor
timestamp: July 08, 2023, 12:30:14 am
content: Only the gate to source voltage matters for conduction in *either* direction. When the MOSFET is on, it will happily conduct in both directions.

author: DarkMode
author_rank: Contributor
timestamp: July 08, 2023, 02:41:27 am
content: Quote from: David Hess on July 08, 2023, 12:30:14 amDoes that you can use it as a Switch, regardless of direction?

author: xavier60
author_rank: Super Contributor
timestamp: July 08, 2023, 04:30:28 am
content: Quote from: DarkMode on July 08, 2023, 02:41:27 amNo, because the MOSFET's intrinsic body diode will always conduct in one direction.For both directions, 2 MOSFETs are needed or one MOSFET and a series diode.I often see this arrangement in laptop computers,https://electronics.stackexchange.com/questions/617878/why-does-mosfet-n-back-to-back-switch-work

author: David Hess
author_rank: Super Contributor
timestamp: July 08, 2023, 08:17:13 am
content: Quote from: xavier60 on July 08, 2023, 04:30:28 amExactly, a second MOSFET in anti-series is required to provide isolation from the body diodes. If the sources are connected together, then the same bias supply can drive both gates in parallel as shown here:https://www.bristolwatch.com/ele3/2c.htmThere are power MOSFETs which bring the substrate connection out isolating the body diode, however they are limited to lower currents and voltages:https://www.microchip.com/en-us/product/MIC94030
Why photo flash capacitors are rated at 55C ? - Page 1
Forum section: electronics / beginners

author: LinuxHata
author_rank: Frequent Contributor
timestamp: November 07, 2023, 07:02:57 pm
content: Yes, I have read the wikipedia article and I do know, what is photoflash capacitor, in fact, I'm using them for maybe 20+ yearsBut I still can't understand, why 55C?Making them 55C instead of 85C or 105C makes them cheaper? able to deliver more current? lower ESR or what?I have repaired a lot of studio flash units and usually there is no cooling of capacitors - even if cooler is present, it either blows onto power circuitry, ballast resistors or tube itself, but very rarely - onto capacitors.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 07, 2023, 07:09:16 pm
content: I'd guess to allow headroom for self-heating from the high peak current in their normal operating conditions.

author: Gyro
author_rank: Super Contributor
timestamp: November 07, 2023, 07:33:55 pm
content: Photoflash capacitors are specialised for really high energy density and discharge pulse current. I suspect that, if they were rated to 85'C, their lifetime spec would be unacceptably short.

author: bdunham7
author_rank: Super Contributor
timestamp: November 07, 2023, 07:37:20 pm
content: Quote from: LinuxHata on November 07, 2023, 07:02:57 pmWell, how hot do they get then?

author: LinuxHata
author_rank: Frequent Contributor
timestamp: November 07, 2023, 08:53:31 pm
content: Well, they usually get warm to touch, but nothing above that.In most cases, they are mostly ok, except for situations where the unit is very old, say from late 70s, and they all dried out, or say, 110V unit was plugged into 220V mains. However, there are usually 2 or 4 "normal" capacitors (100uf, 450VDC most common) inside the studio flash, used in voltage multiplier circuit and these often get both hot and "pregnant"

author: DavidAlfa
author_rank: Super Contributor
timestamp: November 07, 2023, 08:56:46 pm
content: It the entire camera heats to 85°C you'll probably have worse problems than a shortened capacitor lifespan....

author: alligatorblues
author_rank: Regular Contributor
timestamp: November 08, 2023, 07:04:41 am
content: Lower max temp caps can hold more charge, and flashes have temp protection circuitry to shut themselves down if necessary. That type of cap also charges up quickly.
Why place resistor in the ground? - Page 1
Forum section: electronics / beginners

author: chancs
author_rank: Contributor
timestamp: February 19, 2020, 10:25:44 am
content: I came across this circuit today, which is a USB to DMX for lighting control. Can someone help me to understand why the designer wants to place a 33ohm (R11) resistor between the system ground and the output groud? Also, shouldn't there be a 120ohm resistor between dmx_a and dmx_b since a DMX cable has characteristic impedance of 120ohm.Thanks a lot.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 19, 2020, 10:44:24 am
content: Presumably only signal currents flow through that resistor, and not even much at that, because RS-485 is differential. RS-485 still requires a ground reference; it is not an isolated interface, the receiver can only read signals within 7V or so of local ground.The point then, would be to provide a weak kind of isolation, allowing ground loop voltages to drop across the resistor, rather than draw larger currents through a lower resistance path, and without leaving it fully open which would all but guarantee the receivers see trash.It should be bypassed with a capacitor, so that shielded cable can be used if available, preventing RF interference from getting into the cable. As shown, the resistor simply drops some voltage (at some current), regardless of frequency, which in turn allows RFI into the cable. It does however act to terminate the cable/shield, so it won't be as prone to resonances as it would be otherwise. (If bypassed or direct-grounded, a ferrite bead might be desirable on the cable, to reduce possible resonances.)Enterprise-grade improvements would include:- Differential and common mode filtering- ESD/surge protection (the RS-485 transceiver has excellent ESD ratings, but other interference sources may be a concern, up to and including induced lightning surge on long enough runs)- A TVS on VCC would be alright, too- Isolation (very easy to do, a couple optoisolators and a DC-DC converter, adds maybe five bucks to the BOM cost)Tim

author: Rerouter
author_rank: Super Contributor
timestamp: February 19, 2020, 12:07:45 pm
content: It is to reduce fault current if someone hooks things up wrong, still wont save it for voltages higher than 5V, e.g. your connecting up your computer, is there any paths that could cause your DMX bus to sit significantly higher than mains ground voltage? as that voltage will then force a current through that resistor.Agree with the above recommendations, this is more of a hobby adapter, not really something I would trust for field work.

author: AVGresponding
author_rank: Super Contributor
timestamp: February 19, 2020, 05:35:36 pm
content: I seem to remember bigclivedotcom having something to say on this subject, you might try searching his channel for "DMX".
Why put two N MOSfets source to source? - Page 1
Forum section: electronics / beginners

author: cbc02009
author_rank: Regular Contributor
timestamp: October 04, 2018, 05:59:11 pm
content: I'm looking at the datasheet for the LTC4359 (http://www.analog.com/media/en/technical-documentation/data-sheets/ltc4359.pdf). It's an ideal diode, which is what I'm looking for, to protect a battery charger from possible reverse current from the battery it's charging.In the datasheet they have two variations, the first just takes a normal N mosfet in series from the source to the battery (the first attached picture) which I understand the concept behind.The second one is confusing to me, and the explanation they give isn't very helpful. (second attached picture) It's got two N mosfets connected source to source instead of just one. What does that change in the function of the circuit?After simulating both circuits, all I can see is that the two mosfet one seems to take several mS longer to react than the first one.Actually, after taking the screenshots, I see that the two mosfet one is also called a load switch in the description. How is that different than an ideal diode?

author: madires
author_rank: Super Contributor
timestamp: October 04, 2018, 06:13:10 pm
content: Please take a closer look at the intrinsic body diodes of the MOSFETs

author: cbc02009
author_rank: Regular Contributor
timestamp: October 04, 2018, 06:30:44 pm
content: Quote from: madires on October 04, 2018, 06:13:10 pmOkay, I think I get it now, but I just want to run it by you to make sure.With only one mosfet, the charger can still pass current to the battery, even if the mosfet is off, through the body diode. Which is okay, because it's only meant to prevent current from the battery to the charger.With two mosfets, the body diodes oppose (and sort of cancel each other out) which means that it's almost like physically disconnecting the battery from the charger If it's off, no current is passing in either direction.Is that close?

author: madires
author_rank: Super Contributor
timestamp: October 04, 2018, 07:28:10 pm
content: Yep, you got it! And be aware that the body diodes will pass a low leakage current in reverse direction.
Why rectifier diode fails but capacitor is ok? - Page 1
Forum section: electronics / beginners

author: Mp3
author_rank: Frequent Contributor
timestamp: August 03, 2021, 08:15:05 am
content: This is not related to my past thread about rectifier diodes.Diagnosing a power supply with some old electrolytics, which i desoldered then discharged and tested. Surprisingly low ESR and a bit above stated capacitance, no sign of leakage, so I think they're ok.This power supply has rectifier diodes coming from the AC transformer, into regulators and capacitors, and then all capacitors thru rectifier diodes, to the main board of the computer.I have had it hooked up for a while after replacing the bad rectifier diode, and nothing is pulling too much current, but i didn't measure any sort of ripple on the power supply. Would excessive ripple possibly cause a rectifier diode to fail?

author: fordem
author_rank: Regular Contributor
timestamp: August 06, 2021, 06:39:10 pm
content: Quote from: Mp3 on August 03, 2021, 08:15:05 amNo, but a failed diode could possibly cause excessive ripple.
Why - rectifier polarity reversed by resistor? - Page 1
Forum section: electronics / beginners

author: FriedMule
author_rank: Frequent Contributor
timestamp: June 01, 2019, 08:06:14 pm
content: I am playing with this alternative rectifier and all seem to work, until I put the right most 10K resistor, do anyone know why?http://tinyurl.com/yxe2d7zj

author: oPossum
author_rank: Super Contributor
timestamp: June 01, 2019, 08:12:47 pm
content: Note the warning "4 bad connections"And you have 24200 uF on the output of an op-amp.

author: FriedMule
author_rank: Frequent Contributor
timestamp: June 02, 2019, 12:48:11 am
content: Quote from: oPossum on June 01, 2019, 08:12:47 pmThanks I am trying to use the capacitor multiplyer that Dave talked about. But it does not look like the DC is getting smooth. Therefore did I try to add som extra capacitors and it sort of work now, but if i add the disconnected cap, the circuit stops working.The 15K is just a random load.http://tinyurl.com/yxbgt34a
Why reference control voltage to ground for waveform generator? - Page 1
Forum section: electronics / beginners

author: Mp3
author_rank: Frequent Contributor
timestamp: October 13, 2019, 07:21:24 pm
content: I am reading about the ICL8038 waveform generator. The data sheet says you can reference control voltage to +V. Howver it apparently can accept +V, ground or -V. Is this a quirk of the 8038 specifically?

author: Kleinstein
author_rank: Super Contributor
timestamp: October 14, 2019, 10:54:09 am
content: AFAIR the ICL8038 and similar chips use a current source to set the frequency. This current source seem to start at the positive supply. So the control voltage to set the current is (not optional as in can) relative to the positive supply. If the external circuit want's it relative to GND the choose to have V+ at ground and use a negative supply for the chip.Other oscillators can have different controls. The XR2206 has the control relative to the negative supply (= GND).
Why resistor affect voltage curve from Zener diode? - Page 1
Forum section: electronics / beginners

author: hurricanehenry
author_rank: Regular Contributor
timestamp: March 24, 2017, 10:19:09 am
content: Hi - from one of Dave's videos (on Zener diodes) I don't understand why substituting a 1K ohm resistor for a smaller, 100 ohm resistor, changes the curve?Actually I am not sure why the curve is not as sharp in the first place.It looks to me like a phase shift with the larger resistor, and less of a phase shift with the smaller resistor?

author: Gyro
author_rank: Super Contributor
timestamp: March 24, 2017, 10:29:19 am
content: I would think it's a thermal effect. The lower the resistor value, the higher the current, so the faster the Zener reaches its final temperature.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: March 24, 2017, 10:37:10 am
content: I don't really know what timescales those are, but a diode junction has a capacitance. With the resistor, you are making an R-C filter circuit. Bigger resistor in series means larger timeconstant, and thus more time to charge.There is also the fact that the current through the zener changes (a zener does not have a perfect knee, it's voltage is still dependent on the current through it. It's just a far sharper curve than a resistor. That's why in circuits with zeners as references, you will almost always see a constant-current source driving it)

author: lordvader88
author_rank: Frequent Contributor
timestamp: March 24, 2017, 10:39:43 am
content: they have a lot of equations for how and what changes as temperature also changesSo far I have not needed any of those types equations for stuff I've made/modeled

author: danadak
author_rank: Super Contributor
timestamp: March 24, 2017, 10:59:36 am
content: Probe has 10 pF of C, diode has reverse biased junction C, so change of source Z(lower)causes increased I to charge caps causing the reduced risetime.Q = C x VI = C x dV/dT or dV/dT = I / CRegards, Dana.

author: MrAl
author_rank: Super Contributor
timestamp: March 26, 2017, 11:17:24 am
content: Quote from: hurricanehenry on March 24, 2017, 10:19:09 amHi there,One thing you dont show is the TIME scale, so we dont have all the information we need to make a good guess.I tend to agree with the equivalent capacitance ideas posted elsewhere in this thread, but seeing the time scale for both waves would help a lot.The equation for a resistor charging a capacitor when the capacitor has zero volts across it to begin with is:Vc=Vcc*(1-e^(-t/RC))where RC=R*C.Using that equation you could try different capacitances and try to mimic the waves you are seeing by changing only the resistor by 10 fold.If you do that you will see the waves look like in the attachment. Note you need to keep the time scale set the same for both waves on the scope to see them compared like this. This is what you get when you change the resistor value 10 fold. Ignore the axis scales as this is a normalized comparison. You will see slightly different waves because there is a limiting zener too, but the comparison should be about the same.
why RF transistors cant amplify low freqency? - Page 1
Forum section: electronics / beginners

author: fonograph
author_rank: Frequent Contributor
timestamp: May 14, 2017, 10:54:28 pm
content: I used word "low" just to simplify title,its like their gain vs freqency curve looks like bandpass filter,maximum gain at 2.4GHz and then it fall off rapidly in both directions,a transistor that have full gain at 2GHz have 0 gain at 2MHz,that isnt even really a low freqency! Every transistor have have limited slew rate and their gain eventualy starts to roll off at higher freqencies but all normal transistors I saw had no problem with lower freqencies.Why is that many RF transistors have decreased gain the lower in freqency you go away from their peak gain freqency? It all looks like bandpass filter while the response of normal transistor is like lowpass filter,where does that high pass like curve come from? Is there some internal high pass filter build into them? I saw this in Doherty silicon ldmos,I saw it in galium arsenide hemt,why,why is the gain curve like peak at 2GHz and then roll off lower you go?

author: amspire
author_rank: Super Contributor
timestamp: May 14, 2017, 11:58:42 pm
content: RF transistors have gain down to DC. It is probably the circuit that has no gain at low frequencies. For example, an inductor on the collector going to the power rail acts like a short circuit for low frequencies but can appear as a high impedance constant current source for RF. A circuit like this can only amplify high frequencies thanks to the inductor.Can you give an example of a transistor that you think has no gain at low frequencies?

author: fonograph
author_rank: Frequent Contributor
timestamp: May 15, 2017, 01:05:45 am
content: I cant find them again,its that case of when you doesnt need it its everywhere but when you need it ,suddenly its nowhere.As I tried to find it,looking at datasheets of various transistors I noticed one thing,every time I open a datasheet I mostly ignore the first pages,I only briefly fly over them with my eyes as I scroll down to look at graphs.This time I noticed they arent measuring the transistors alone but all the measurements are listed as comming from the transistor being in specific test circuit.Now since I am noob,any circuit schematic with more than 3 or 4 elements is beyond my capability to understand what it is and what it does,but I think,in that test circuit schematic from datasheet,there is probably high pass or bandpass/resonator hidden somewhere to pass 2.4GHz and reject anythint else.
Why RMS power consumption is different than the average power consumption?  - Page 1
Forum section: electronics / beginners

author: steamedhams
author_rank: Regular Contributor
timestamp: June 29, 2021, 09:19:21 am
content: Why RMS power consumption is different than the average power consumption?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 29, 2021, 09:32:14 am
content: On what?FYI, "RMS power" is meaningless; there's no reason to take RMS of power, only the peak or average (or whatever other statistics might be relevant, but you'd need a weird circumstance to use RMS with it). The term often comes up in audio, I think typically meaning either the peak or average power at rated output for a sine or square wave signal, based on its measured voltage RMS or something like that. Used more to distinguish from peak power, or other even less honest measures (like "PMPO", which is, as far as I know, wholly devoid of meaning).Tim

author: gcewing
author_rank: Regular Contributor
timestamp: June 29, 2021, 10:01:46 am
content: I think PMPO stands for "power, marketing purposes, optomistic".

author: pqass
author_rank: Super Contributor
timestamp: June 29, 2021, 11:14:37 am
content: In the context of a power amplifier, there is no such thing as RMS power according to:https://geoffthegreygeek.com/understanding-amplifier-power/"In many specifications for amplifier power you will see this referred to as the RMS power. This is not a correct term (because technically there is no such thing). Although the power calculation uses RMS voltage (and/or RMS current if you use other formulas) the result is simply “power”, not RMS power. As shown in the graph above, it is the average continuous power. However, for most amplifier specifications, you can consider RMS power (while an incorrect term) to refer to average continuous power."

author: Gyro
author_rank: Super Contributor
timestamp: June 29, 2021, 12:05:16 pm
content: I think RMS power of an amplifier simply became a shorthand term for what you could get out of it, when driving with a continuous tone and resistive load, before clipping. It was just a handy term for the HiFi press. This is contrasted with 'Music Power' ('typical' music waveform, usually quoted at twice what you would get 'RMS' (limited by PSU rail sag). And PMPO (what you would get if you stuff a large amplitude pulse up the input for a couple of microseconds)).
Why short source and drain on a JFET transistor?  - Page 1
Forum section: electronics / beginners

author: giosif
author_rank: Frequent Contributor
timestamp: September 20, 2016, 11:35:03 am
content: I am trying to understand a board where, occasionally, I see a JFET transistor (specifically, model MMBF4393LT1) with the source and drain pins on the same trace.What would be the purpose of doing that?Thanks!Sent from my D6603 using Tapatalk

author: Andy Watson
author_rank: Super Contributor
timestamp: September 20, 2016, 11:42:33 am
content: The gate junction forms a good, low-leakage diode.

author: David Hess
author_rank: Super Contributor
timestamp: September 20, 2016, 12:13:51 pm
content: Quote from: Andy Watson on September 20, 2016, 11:42:33 amAnd at less cost and with greater availability than an actual low leakage diode.

author: giosif
author_rank: Frequent Contributor
timestamp: September 20, 2016, 01:53:06 pm
content: Ok. Thank you both for the explanation!Back to "reading" the board now...Sent from my D6603 using Tapatalk

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 20, 2016, 07:02:20 pm
content: Though to be fair, small BJTs (like BFR93) make better diodes -- less series resistance.Tim

author: danadak
author_rank: Super Contributor
timestamp: September 20, 2016, 11:52:13 pm
content: Depends on the JFET. Some cannot tolerate much I in the gate.Regards, Dana.

author: David Hess
author_rank: Super Contributor
timestamp: September 21, 2016, 05:08:03 am
content: Quote from: T3sl4co1l on September 20, 2016, 07:02:20 pmThey do but you can buy JFETs with guaranteed maximum gate leakage specifications while transistors just have to meet their maximum cutoff current specifications which are typically tested to 50 or 100 nanoamps. If you want low leakage from a transistor used as a diode, you have to qualify and test them yourself.
Why should analog ground and digital ground be separated in some instrumentation - Page 1
Forum section: electronics / beginners

author: nour
author_rank: Frequent Contributor
timestamp: May 27, 2017, 07:20:10 pm
content: I have noticed that in a lot of instrumentations, the ground of the analog part and the digital part are usually separated and also the connection between them(control and data transfer) are usually separated by optocouplers? Why?Why does the ground should be separated and why they use optocoupler also between them?

author: Ghydda
author_rank: Regular Contributor
timestamp: May 27, 2017, 07:34:17 pm
content: Quote from: nour on May 27, 2017, 07:20:10 pmThe short answer is proberbly: to ensure/control the path of each sections return current.If two subcircuits share return current path or have crossing return current paths, they will interact.Usually this is okay for most circuits, but when high precision or low noise must be achieved, then completely separating the return currents is the way to go.Sendt fra min Nexus 6 med Tapatalk

author: tablatronix
author_rank: Regular Contributor
timestamp: May 27, 2017, 10:03:39 pm
content: My understanding is I thought it was because digital is high speed and induces noise into the analog stuff, opamps filters etc. so keeping power seperate allows better filtering and isolation. I could be totally wrong.

author: Bud
author_rank: Super Contributor
timestamp: May 28, 2017, 12:06:50 am
content: Ground partitioning may be difficult to figure out when using 'hybrid' devices such as DDS ICs that have both digital and analog circuits inside. I stopped worrying about it after speaking to a engineer at Analog Devices who said they do not use separate grounds in the Lab and when characterizing their products.

author: danadak
author_rank: Super Contributor
timestamp: May 28, 2017, 10:10:58 am
content: Some application notes on this topic -http://www.cypress.com/documentation/application-notes/an57821-psocr-3-psoc-4-and-psoc-5lp-mixed-signal-circuit-boardhttp://www.semtech.com/images/datasheet/rf_design_guidelines_semtech.pdfhttp://cache.freescale.com/files/analog/doc/app_note/AN3962.pdfhttp://www.analog.com/en/analog-dialogue/articles/high-speed-printed-circuit-board-layout.htmlhttps://wiki.analog.com/resources/app-notes/an-1119Regards, Dana.

author: German_EE
author_rank: Super Contributor
timestamp: May 28, 2017, 04:16:19 pm
content: A practical example.I have on my bench at the moment a phased locked loop that covers 35 MHz to 75 MHz in 0.1 Hz steps. The VCO sensitivity is 3.5 MHz/V or (and this is where it gets interesting) 3.5 Hz per microvolt. So, if I change from 40.0000001 MHz to 40.0 MHz the VCO voltage has just dropped 29 nV, not a lot. If the 3.3V control logic was sharing the same groundplane*** as the VCO the switching noise would modulate the VCO input and I would not have a very good synthesizer.*** Note that no groundplane is perfect, it has inductance and resistance and therefore has circulating currents.
why smps Tank capacitor voltage rating is high? - Page 1
Forum section: electronics / beginners

author: kgavionics
author_rank: Regular Contributor
timestamp: July 12, 2020, 07:25:06 pm
content: Hello guysI'm not an expert of smps, but I have a question: yesterday, I fixed a SMPS and I found that the capacitor for the power factor correction is rated to 450V, normally in linear power supply the voltage after the brige recifier would be 115Vacx square root of 2 which is about 163Vac.why in smps the voltage rating of the tank capacitor is so high?Thanks in advance

author: exe
author_rank: Unknown
timestamp: July 12, 2020, 07:29:19 pm
content: Can it be a "universal input" smps accepting 90-263V AC? Anyway, higher rating is better for lifetime.

author: bdunham7
author_rank: Super Contributor
timestamp: July 12, 2020, 07:33:48 pm
content: PFC boost doesn't depend on peak input voltage.https://www.infineon.com/dgdl/Infineon-ApplicationNote_PFCCCMBoostConverterDesignGuide-AN-v02_00-EN.pdf?fileId=5546d4624a56eed8014a62c75a923b05

author: kgavionics
author_rank: Regular Contributor
timestamp: July 12, 2020, 07:51:00 pm
content: Quote from: bdunham7 on July 12, 2020, 07:33:48 pmThank you for the link it's very interesting!

author: eblc1388
author_rank: Frequent Contributor
timestamp: July 13, 2020, 12:45:26 am
content: Usually, the PFC circuitry boosts the rectified voltage up to 380~400V DC for the converter that follows, regardless of the input AC voltage.However, I was puzzled when I measured only about 350V(350V, 354V) on two working units of server SMPS. The model is HP C7000 2400W power supply. The rated nameplate input ac voltage is 200~240V. The capacitors are all rated at 450V though.Before someone said the PFC is probably not working, but it did maintain the same 350V on the capacitor when I vary the input ac from 180V to 240V.
Why some cam timers have multiple motors ? - Page 1
Forum section: electronics / beginners

author: tigrou
author_rank: Regular Contributor
timestamp: February 17, 2024, 05:04:05 pm
content: I took a look at some cam timers and wondered why they have (or seems to have) multiple motors ?Is this for redundency ? Or to rotate the other way around ? Or to monitor the device ? (eg: detect current angle)

author: Gyro
author_rank: Super Contributor
timestamp: February 17, 2024, 07:08:14 pm
content: Have you checked the shaft rotation speeds? Sometimes they are used alternately for slow and fast parts of the cycle.
Why some micro switches have a small circuit board attached to them? - Page 1
Forum section: electronics / beginners

author: eeguy
author_rank: Regular Contributor
timestamp: April 06, 2024, 05:08:49 pm
content: Hello, while looking for some micro switches for micro-controller, I noticed that some are sold with three pins which we could solder the wires to at one end and attach to a micro-controller at the other end. There are also switches that are sold with a small circuit board (with condenser and resistor) attached. What do those circuit boards do?

author: kevin.gibbs
author_rank: Regular Contributor
timestamp: April 10, 2024, 01:44:21 pm
content: It may be a protection against contact rattle.

author: electr_peter
author_rank: Unknown
timestamp: April 10, 2024, 08:55:52 pm
content: Quote from: kevin.gibbs on April 10, 2024, 01:44:21 pmYes, most likely PCB is prepared with contact debouncing parts.

author: MarkT
author_rank: Frequent Contributor
timestamp: April 11, 2024, 07:35:14 pm
content: Or a snubber to reduce contact arcing?

author: tooki
author_rank: Super Contributor
timestamp: April 12, 2024, 08:54:25 am
content: Quote from: kevin.gibbs on April 10, 2024, 01:44:21 pmQuote from: electr_peter on April 10, 2024, 08:55:52 pmI think you’re both referring to contactdebouncing. (Yes, I had to override my phone’s autocorrect.)

author: Infraviolet
author_rank: Super Contributor
timestamp: April 13, 2024, 07:00:44 pm
content: Often mechanical in its nature, the small board lets one easily fit a wire-to-board connector for one-or-another 2 or 3 wire cable connector system (JST something, Molex something, 2.54mm headers...), you can plug and unplug the cables easily. That compares to trying to directly solder wires to the male pins of the microswitch, not pleasant when you're using multi-cored wire as flexing of it will be cmmon and the wire breaks at the interface between the solder joint and the insulation, and soldered wires can't be as easily attach and removed as cables with headers.