hybridfree/eevblog-posts huggingface dataset:
Understanding inner current control loop compensation in boost PFC converter. - Page 1
Forum section: electronics / projects

author: Jose_Peeterson
author_rank: Newbie
timestamp: February 19, 2018, 09:25:57 am
content: Hello EEVBLOG,I am a NEW hire in our company and I am trying to understand the Analog PFC in our current design using L4981A PFC controller IC.I need to fully understand the feedback control portion in this circuit because we are having some input current oscillation problems (Dancing waveform that is non-sinusoidal).I am referring to the L4981A's application note for help. You can access it in this link:http://www.st.com/content/ccc/resource/technical/document/application_note/94/6e/ec/8c/4c/3e/40/a9/CD00003936.pdf/files/CD00003936.pdf/jcr:content/translations/en.CD00003936.pdfWe have plans to move into TI products especially the UCD3138A IC family of digital PFC solutions.My questions below are related to how to select compensation network values for the inner current loop of Boost PFC.Doubts from pages 7,8 & 9The equation below is trying to say that the inductor down slope must be smaller than the ramp up slope of the PWM ramp that sets the switching frequency.Inductor ramp down slope (we are seeing form negative side of sense resistor, before GND) is during Boost MOSFET turn ON so the voltage across inductor should be Vin and NOT VO like it is shown in the equation below right?What is the value of the current amplifier gain? Is it made up of low frequency gain and high frequency gain referring to figure 9.Actually the multiplication, ( VO/L . Rs . Gca ) is the quantity of gradient that is output from C/A right?From page 9,How is the voltage Vrs equal to below? I do not understand how Vrs is found by taking the input voltage (gradient), Vrs of +ve terminal of C/A and multiplying it to 1/S ?What is the meaning of worst condition here? where did this integrator with DC pole come from?What is the quantity Gavg ?How did Gavg come to be as shown below? What is its physical meaning?Why is Gavg multiplied to Gca? Are they combining two transfer functions? Is Gca the high frequency transfer function or Gavg? What is the reason to split them?The crossover frequency comes to the above after I equated Gca . Gavg = 0'Where did the zero come from in the below equation? Gca is not frequency dependent and Gavg only has an integrator with DC pole so where did the zero come from?Also why is there a zero in Gca around 6000 Hz in the below graph? Where did it come from?Please also give the closed loop final transfer function of the compensation network shown in Figure 9Please help to answer my questions as I try to understand the current loop compensation portion of this PFC boost converter.Thank you for your help.Regards,Peeterson.

author: fourtytwo42
author_rank: Super Contributor
timestamp: February 19, 2018, 10:03:57 am
content: Likely to many questions in one post but part of it sounds like you maybe don't understand slope compansation to prevent sub-harmonic oscillation. Have you posted these questions to ST ?
Understanding LTSpice 'Transformers' page - Page 1
Forum section: electronics / projects

author: Etesla
author_rank: Regular Contributor
timestamp: February 26, 2024, 04:14:06 am
content: Hi all,I'm on a mission to model a transformer with parasitics as well as saturation.I'm trying to use the LTSpice wiki transformers page here:https://ltwiki.org/index.php?title=Transformersbut I'm having trouble understanding some of the material. I thought it would be good to model up a totally equivalent transformer using each of the outlined methods, but I only got through two before I got confused.The first two options for models make sense to me. I'm basically just modeling 'K' in a different way between the two of them. I then got to the third concept where they talk about 'the core' and use a voltage dependent voltage source, and current dependent current source, to try to model a 'single coil', but I'm not sure how to make a transformer equivalent to my first two using this method. This was my attempt:I can see that the output voltage simulated by the third option does not match the first two, which match each other perfectly.Can someone help me understand what the 'core' node is all about? What does the voltage at 'C' represent? How is the information about the primary and secondary winding inductance preserved in the third model? Why does the third model result not match the first two?Thanks in advance!

author: moffy
author_rank: Super Contributor
timestamp: February 26, 2024, 05:01:26 am
content: The 'core' is where the magnetic fluxes of the primary and secondary basically cancel one another out, hence the two current sources that work to cancel one another, the flux in a transformer core is due to the magnetising current (this current is not implemented in this model) and Np*Ip = Ns*Is, this is because of the flux cancellation effect between primary and secondary currents.

author: Etesla
author_rank: Regular Contributor
timestamp: February 26, 2024, 05:22:51 am
content: Ok interesting, so it seems like I lost the ability to model the magnetising current in model #3. Is this the best way to add that effect back in? Just added L12 which I think you would call the mutual inductance referenced to the primary? In this updated version the output voltage again matches the other two versions perfectly so mission accomplished there.

author: Etesla
author_rank: Regular Contributor
timestamp: February 26, 2024, 05:25:49 am
content: I guess now I'm confused about the fourth model presented in the transformers page. What is the purpose of 'Lc'? Is it supposed to have an effect similar to me adding L12 in the previous post?
Understanding my own design -  moisture detection circuit - Page 1
Forum section: electronics / projects

author: Tonkabot
author_rank: Contributor
timestamp: August 08, 2022, 04:01:16 am
content: I have this circuit I desiged that tells how much resistance there is between the connector (both contacts are connected to one sense wire) and ground.Then, if the test point (a brass elbow in a co2 gas stream) gets wet (blood, most likely), we know the machine has had a biological contamination.So normally the ADC pin (A1_Fluid_Sense) reads about 32000 When J5 sensor is hooked up and open. it reads 38000 or so when J5 is open.it will read 0 if you dead short it to ground.My problem is that D34 is getting blown. it is just a sod-323 shottky. I had thought that some transorb or something would be more appropriate there, but I never did figure out something that worked. The intention of D34 was to be like a 5v transorb, but I couldn't get that to work. We need to keep the ADC pin safe from any crap that might blow the processor.D34 has not blown much (I think about 3, over a year of 200 machines running), but that is too much.Oh, Vusb is 5.2volts.Not sure I am getting the schematic png attached...

author: ConKbot
author_rank: Super Contributor
timestamp: August 08, 2022, 08:27:29 am
content: Is ESD building up from a dry gas flowing? The diode should be sufficient for charge on the wire itself, but is a nearby sections of plastic tube charging up and then discharging into the sense wire?

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 08, 2022, 12:39:01 pm
content: Try a larger diode and add a 1k resistor in series with pin 1?

author: Tonkabot
author_rank: Contributor
timestamp: August 08, 2022, 02:44:19 pm
content: I didn't think there could be a static build-up because there is only 75k to the 3.3v rail and 100k to the 5.1v supply. I'm thinking that that should eliminate a static potential build up.Brynn

author: Tonkabot
author_rank: Contributor
timestamp: August 08, 2022, 02:57:28 pm
content: The client is pretty resistant to making board changes... However it would be pretty simple to incorperate a series resistor in the sense wire harness, and I don't see any drawback to making such a change permanently. I'll be trying that out, and it seems like it will help protect the diode on the board.Brynn
Understanding of Thermal metrics of PCB, heatsinks, How heat flow - Books - Page 1
Forum section: electronics / projects

author: malli_1729
author_rank: Newbie
timestamp: August 04, 2021, 07:25:58 am
content: I want to understand more about Thermal metrics of PCB (Like how traces, Vias, planes etc interact thermally how they will get cooled), Heat sinks designing (like Fin structure, spacing, materials how they will affect cooling efficiency etc)How thermals flow ( i am an electrical & electronics engineer, so, If i get books which have similarities to explain thermals in electrical point of view also like heat waves to Electro magnetic waves it will be good).I need any books which can help in understanding these flows. I will take lot of time understanding basics because i am beginner.

author: trobbins
author_rank: Frequent Contributor
timestamp: August 04, 2021, 07:52:41 am
content: Thermal Analysis and Control of Electronic Equipment by Kraus & Bar-Cohen (McGraw-Hill 1983) is vintage but covers what you likely need for basic understanding before drilling in to commercial product data.

author: malli_1729
author_rank: Newbie
timestamp: August 05, 2021, 04:34:55 am
content: Any other book recommendations will be helpful sir

author: trobbins
author_rank: Frequent Contributor
timestamp: August 05, 2021, 05:04:36 am
content: Are you just after general theory, or product specific performance, or application specific, or ?What do you mean by "heat waves to Electro magnetic waves" - perhaps thermal radiation from one object/surface to another, or transmission through media that have transmission that varies with wavelength (like different glass acting as a vacuum interface)?

author: malli_1729
author_rank: Newbie
timestamp: August 18, 2021, 08:32:47 am
content: Hi Trobbins,I want to understand general theory specific to Heat transfer in PCB's & Application specific details again for Thermals on PCB,heat transfer mechanism on PCB.What do you mean by "heat waves to Electro magnetic waves" --> As i am electronics person if some analogy between EMI phenomina to heat transfer, electric analogies (like R,L,C, u,epsilon etc) to Thermal constants will helpful in faster learning of Thermals in PCB

author: trobbins
author_rank: Frequent Contributor
timestamp: August 18, 2021, 08:49:13 am
content: Any engineering assessment of a particular configuration starts with a representation of the pcb by thermal resistances, such as conductive through the pcb mass, convective away from the pcb surfaces, and radiative away from the pcb surfaces. Kraus and Bar-Cohen go through practical examples (as I recall), and of course other examples of other devices provide similar assessments (eg. the 1962 RCA Electron Tube Design book is on-line and has thermal assessment of tubes including a detailed one on the 6L6).
Understanding primary side regulation in this Flyback converter - Page 1
Forum section: electronics / projects

author: Red_Micro
author_rank: Regular Contributor
timestamp: August 10, 2020, 03:14:33 am
content: I'm going throughthis Reference Designand there is something I don't get. The controller LM5020MM-2 was not designed for primary side regulation, how does this power supply regulate through the primary side? How precise it is? Does it require certain minimum load to regulate?

author: ahbushnell
author_rank: Frequent Contributor
timestamp: August 10, 2020, 03:21:12 am
content: Quote from: Red_Micro on August 10, 2020, 03:14:33 amIt is regulating on the 5/6 secondary of the transformer. This feeds the voltage divider made of R17 and R30. I'm sure it's not tight regulation. It's simple and provides isolation.

author: eblc1388
author_rank: Frequent Contributor
timestamp: August 10, 2020, 05:54:30 am
content: I also has trouble understand how two MOSFET Q1 & Q2 rated at only 800V can share the high voltage when the supply voltage is 1260V.Would OP or others shed some lights on the mechanism of this voltage sharing?

author: magic
author_rank: Super Contributor
timestamp: August 10, 2020, 06:24:55 am
content: Q2 on: Q1 source is at 0V and gate is at 15V, Q1 is onQ2 off: Q1 gate is pulled to 600V and source rises up until it reaches 600V, Q1 turns offI couldn't promise that everything here works out alright, but it's a TI reference design so they hopefully tested it.
Understanding relay specifications - Page 1
Forum section: electronics / projects

author: 741
author_rank: Frequent Contributor
timestamp: September 11, 2019, 11:05:48 am
content: I'm after an SSR with similar ratings to the OMRON G6S-2 24V. Looking the DS, I seeApproved Standards = UL, CSADielectric strength (2,000 VAC)ContactsMax. switching voltage 250 VAC, 220 VDCRated load0.5 A at 125 VAC;2 A at 30 VDCRated carry current 2AMax. switching current 2AHow do these contact specifications inter-relate?I looked at the graph "Maximum Switching Capacity" Seems I can switch absolute max of about 0.25A at about 230VAC.As for a SSR: What is a good product line? Something compact is needed.
Understanding RF transmitter measurements from FCC database ... - Page 1
Forum section: electronics / projects

author: Alexei.Polkhanov
author_rank: Frequent Contributor
timestamp: April 03, 2017, 08:21:08 pm
content: I am looking at a document provided with an application to FCC ID which I found in FCC database. It is a small remote control. I am having trouble at guessing some of the values presented in a table they have attached.I understand that emitted power is 72dBuV when adjusted to 3 meter distance from Device Under Test (DUT) as FCC requires, correct?Looks like actual measurements were made at 1 (one) meter distance from DUT.But what is AF? CL? AMP? (amplifier? Amplitude?)Speaking of radio link budget I simply took 72dBuV value at transmitter side with 0 dB losses and added 3 meters to it. I gives me about 93 meters of range with -114dB receiver sensitivity. Sounds correct, but I am still not very confident

author: hendorog
author_rank: Super Contributor
timestamp: April 03, 2017, 08:54:32 pm
content: See the bottom of the sheet, the abbreviations are listed there.
Understanding Shore durometer value. - Page 1
Forum section: electronics / projects

author: DTJ
author_rank: Super Contributor
timestamp: June 27, 2017, 08:47:23 am
content: I'm looking at some potting compound from Element14:Element14 Link:http://au.element14.com/pro-power/ppc125/encapsulant-polyurethane-resin/dp/1776513Data sheet:http://www.farnell.com/datasheets/1685361.pdf?_ga=2.137116339.2079176475.1498451642-203270231.1485772309The data sheet (Page 2) says the Shore A Durometer is "1:90 - 15:85A"What does this mean? All the Durometer charts I've seen just have a single number (0.....100) applied to a range (00, A, D)I'm looking at Durometer charts like these:http://pittsburghplastics.com/assets/images/durometer%20chart(1).JPGhttp://www.plasticsintl.com/images/hardnessScale.jpgAnyone know what Durometer "1:90 - 15:85A" means?
How to understand solenoid parameters from datasheet? - Page 1
Forum section: electronics / projects

author: Sai teja
author_rank: Regular Contributor
timestamp: April 17, 2019, 06:07:29 am
content: Hello,I am using a Solenoid in an application, but I am unable to understand specifications mentioned in the datasheet of solenoid.Below is the link of the product I am referring to. All the product specifications such as duty cycle and Force-stroke curve can be found in the link.https://www.takaha-japan.com/product/cb0730/In my application,On Time is 150 ms and Off Time is 10 sec.Voltage Available to power Solenoid - 6 VPlease answer below queries1) Can I apply 6V to Solenoid for above mentioned Off Time and On Time ?2) If yes, What is the Solenoid force if I operate Solenoid with above conditions ? Also please explain how did you find out Solenoid Force?Awaiting for reply.Thank you in advance.
Understanding STUSB4761 Stand-alone USB PD controller - Page 1
Forum section: electronics / projects

author: implor
author_rank: Regular Contributor
timestamp: June 27, 2025, 07:18:46 pm
content: I have limited experiance with USB-PD IC. I have used one by Ti before but it was very complicated and we where not impressed with it.For my current project I need something simple to negotiate PD up to 12V. I found ST STUSB4761 that looked like it will do everything I want and is bare bones.What I'm confused about is the power-path. It can do 5 PDO but it only has one power path (TI IC I used before had one for each voltage). So now i'm wondering it will act like a step-down converter?Datasheet say"Regulating voltage and current according to PD contract"on page 2.And on page 9 there is a section on Voltage regulation."Input voltage is sensed on VDD pin. Until a PD contract is negotiated, regulation is set to 5 V. In power deliverymode, the regulation aligns VBUS value on negotiated voltage value. Voltage regulation accuracy is 3% worstcase."It feels like i'm miss-interpreting the datasheet or if it can do step-down, datasheet is missing a lot of information I would expect form a dc/dc step-down datasheet.What do you think?

author: jc101
author_rank: Frequent Contributor
timestamp: June 27, 2025, 07:39:25 pm
content: I haven't used that particular IC. It looks like it adjusts the feed back of the primary side with the Opto_DRV output to adjust the primary output voltage.Check the schematic in section 5.2 of the data sheet.So when a different voltage is negotiated, it adjusts the primary side to raise the voltage. It doesn't do any DC-DC conversion itself.

author: implor
author_rank: Regular Contributor
timestamp: June 27, 2025, 07:43:48 pm
content: Quote from: jc101 on June 27, 2025, 07:39:25 pmTotally missed that optocoupler. Then it makes sense. It's then not suitable for my use case. Back to drawing board
understanding the 4D systems programmer  - Page 1
Forum section: electronics / projects

author: BiOzZ
author_rank: Regular Contributor
timestamp: September 10, 2013, 03:27:03 pm
content: OK so i have a project on the list that involves a 4D systems PICASSO display driverso i made a few prototypes and i only have one of there little USB programming dongles ... its awkward to use and when i send protos around im stuck without a programmer so i wanted to put on PCB the differences between a normal FTDI dongle and this one as im already getting NXP parts adding in a single transistor wont add any real cost to the PCB protosso i took a look at it and to no surprise its an FTDI FT232RQ with 5V power and running at 3.3v UART with an PMSS3904 to make an open collector output on the DTR lineBUT looking at it there is a cap and a resistor ... the resistor clamps the base to the emitter but it appears as if the DTR line is AC COUPLED ... what?!i probed it all around, looked at high quality scans and thought there was some sort of trickery but nope its a simple 2 sided PCB and it appears as if thats what its really likemy BEST guess is that there using this to create a really fast pulse from a longer input pulsehave any of you seen this before?im not close to a breadboard currently to test it out and wont be for a few days (out of the state) but here are the scans and what it appears to beSIDE NOTE: yes the pads on the bottom have the RTS and GND lines swapped im guessing for another model or backwards compatibility or something ...

author: senso
author_rank: Frequent Contributor
timestamp: September 10, 2013, 11:07:06 pm
content: AC coupled DTR line is sort of common, the Arduinos also use that trick, so you get a fast pulse to reset your device, but not to long that the bootloader misses the first chars coming along the serial lines.
Understanding the reference design layout of the BQ29700 Battery protector - Page 1
Forum section: electronics / projects

author: Nikos A.
author_rank: Regular Contributor
timestamp: April 22, 2021, 10:49:48 am
content: Hi everyone,I believe this is a trivial designing question but I do not have the experience to understand it.. I design a PCB using the BQ29700 battery protector and I am advising the sluuaz3 reference design. I have a question regarding the VSS pin of the protector and the battery negative terminal.BQ29700 Battery protector datasheethttps://www.ti.com/lit/ds/symlink/bq2970.pdf?ts=1619080532853&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FBQ2970%253FkeyMatch%253DBQ2970%2526tisearch%253Dsearch-everything%2526usecase%253DGPNsluuaz3 reference designhttps://www.ti.com/lit/ug/sluuaz3/sluuaz3.pdf?ts=1618864542494&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FBQ2970Looking the reference design I cannot understand why there is a net tie from Cell- to the ground... What's the purpose? This is like two grounding systems connected to a single point (like the AGND and DGND), but I do not understand the reason for that here.. Why they don't just connect Cell- to VSS?The following screenshot is the top layer layout provided from the reference design and I have denoted for your convenience the ground, the VSS pin, the negative and positive battery terminalsThanks in advanceNick

author: Nikos A.
author_rank: Regular Contributor
timestamp: April 23, 2021, 05:29:46 am
content: After talking with Texas Instruments they gave me the following answer:" The net tie It does connect Cell- to VSS, with this simple circuit there was likely not needed. In more complex designs it can be useful to keep multiple capacitors connected to VSS referencing the same potential of a high current trace such as Cell-. In this design the net tie could have been omitted."I cannot understand why itcould be usefull to keep multiple capacitors to VSS referencing the same potential of a high current trace such as Cell-Could anyone explain this to me?
Understanding the routing requirements for SRAM - Page 1
Forum section: electronics / projects

author: AndrewHodgson
author_rank: Contributor
timestamp: January 31, 2022, 11:02:53 am
content: Hi,Can someone explain the routing/skew requirements for this synchronous SRAM to me? I’ve not done it before and I’m not sure how you derive the requirements from the datasheet so it would be great someone could tell me if I’ve understood this correctly.My understanding of a standard read cycle:1) Clock goes low and the address is outputted on the address bus.2) The address is latched by the SRAM on the rising edged of the clock3) The minimum low time for the clock is 1.7nS so if the setup time is 1.2ns there is an allowance for 0.5nS of skew between the clock and the address lines. That is to say the propagation delay of the address lines can be 0.5nS longer than clock line.4) In terms of the skew requirements, it is acceptable to have a mismatch of 0.075m (7.5cm) assuming a very rough propagation time of 1.5*10^8ms.5) The same style calculation is valid for the data lines.The result seems lenient. I was under the impression the skew budget would be lower. I’ve gone wrong here but I’m not sure where.Also, for the read cycle, presumably the data is latched to the processor on the rising edge of the clock too so we need to account for the propagation delay of the data from the SRAM to the processor. If the setup time was 1.2ns again, then would the max length of the trace be 7.5cm?Thanks

author: BillW69
author_rank: Newbie
timestamp: February 02, 2022, 05:24:30 am
content: This is a synchronous system. Typically the address and control signals like write_ would be output on therisingedge of the clock.Their clock-to-Q + output delay should to be larger than the clock delay, so that they arrive after the clock's rising edge at the SRAM. This is required to meet hold time requirement. Then, you have closer to a full cycle to meet the setup time at the SRAM.Outputting at falling edge is possible but has disadvantage of being more sensitive to clock duty cycle, and tighter setup time window. An advance may be less hold time problems, depending on the relative skew.
Understanding the transformers connections for Power inside a MAGJACk - Page 1
Forum section: electronics / projects

author: Arsh ahmad
author_rank: Regular Contributor
timestamp: October 21, 2024, 10:32:32 am
content: Hi while searching for Magjack for one of my designs, Observing few with PoE and non PoE I need to understand the use of PoE pins:eg.This is one, 1840437-1 has one VCC common pin that is connected to the center tap of the transformer.and the other one, 2250508-1, there are separate pins for VCC, I know this one is PoE but then what is the role of VCC pin on the above one.I have attached both datasheets for reference.

author: Tobias89
author_rank: Contributor
timestamp: October 22, 2024, 07:31:45 am
content: VCC pin on 1840437-1 is used for connection to a digital VCC locatedon-board(not on the cable side). It's used to pull the data signals to a digital VCC level (while not driven).You can know the other side of the transformer is cable side since it has Bob-Smith terminations (R1-R5 and C3).On the other side (on 2250508-1), center taps on acable sideof the transformer are used to get the common mode voltage out (for PoE) - VC12, VC36, VC45, VC78.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 22, 2024, 08:53:17 am
content: The second one is not PoE - the centre taps on the RJ45 side are not brought out.The centre taps on the PHY side are commoned, presumably to save pins - PHYs typically common these anyway.

author: Arsh ahmad
author_rank: Regular Contributor
timestamp: October 24, 2024, 01:56:17 pm
content: Quote from: Tobias89 on October 22, 2024, 07:31:45 amSo, What should be the default connection for this pin, this has to be left connected or it has to be connected to the supply.

author: ejeffrey
author_rank: Super Contributor
timestamp: October 24, 2024, 02:38:55 pm
content: That depends on your phy. You need to check the datasheet for the PHY you are using.
Understanding this circuit - Page 1
Forum section: electronics / projects

author: Red_Micro
author_rank: Regular Contributor
timestamp: February 16, 2020, 03:00:18 am
content: Hi,I can't wrap my head around the circuit attached. U2 comparator is acting as multivibrator, right? It's weird that U2 is powered from GND and -12V. All I know about this circuit is that it is used to inject an AC signal to the test coil when PB1 is pressed. But how does it exactly work?

author: graybeard
author_rank: Frequent Contributor
timestamp: February 16, 2020, 03:43:04 am
content: Yes it is a relaxation oscillator turning the fet it is driving on and off. Ground is arbitrary, it can be any rail.I recently designed a circuit where I ran my 5V logic from GND on the high side to -5V on the low side because it made sense for the rest of the circuit.The switch turns on M1 and its load. M1 is shut off when M2 is on.
Understanding this op amp circuit - Page 1
Forum section: electronics / projects

author: XaviPacheco
author_rank: Regular Contributor
timestamp: August 15, 2019, 01:36:16 am
content: Looking into the circuit attached:When the input signal is negative, D1 is forward biased, and D2 reverse biased. In this case the circuit is an inverting low pass filter with unity gain R3/R1 and cutoff frequency defined by R3 and C1.When the input signal is positive, D1 is reverse-biased and D2 is forward-biased. The op amp becomes a non-inverting low pass filter, right? My question is: If D1 is reversed-biased, the op amp doesn't see R1. How does the amplifier keep unity gain?

author: Ian.M
author_rank: Super Contributor
timestamp: August 15, 2019, 02:30:13 am
content: It doesn't need to see R1. Although a unit gain buffer usually has in- directly connected to out, neglecting input bias current and stray capacitance to ground, it can have any resistance for feedback and will still be unit gain, as long as there are no other connections to in- (except other two terminal components in parallel to the feedback resistor).If in doubt have a play with the attached LTspice sim!

author: SiliconWizard
author_rank: Super Contributor
timestamp: August 15, 2019, 01:52:55 pm
content: Quote from: XaviPacheco on August 15, 2019, 01:36:16 amAs Ian said.Note that the cut-off frequency of the low-pass filter will be much higher when the input signal is positive than when it's negative.
Understanding this sensing approach - Page 1
Forum section: electronics / projects

author: Red_Micro
author_rank: Regular Contributor
timestamp: April 26, 2020, 04:03:58 am
content: In the circuit attached, what could be the intent of the designer who made this? As far as I understand, if Vcc = 35V, when MOSFET is ON, actuator_sense pin goes to ~GND?. When the MOSFET is OFF, the resistance L1 and R25 are in parallel. So by resistor divider formula, we get a voltage across R27, or actuator_sense pin. I think the designer only wants to know if L1 is present or not? Am I right?

author: floobydust
author_rank: Super Contributor
timestamp: April 26, 2020, 04:30:43 am
content: The circuit is for fault detection, it can detect an open L1 or mosfet on or mosfet off, by looking at three permutations for voltage to the A/D.

author: Red_Micro
author_rank: Regular Contributor
timestamp: April 26, 2020, 04:38:33 am
content: Quote from: floobydust on April 26, 2020, 04:30:43 amOK. I want to understand the behavior.When MOSFET is OFF, and L1 is ok, the voltage at the sense pin is determined by L1//R25 + R26 + R27.When MOSFET is OFF, and L1 is open, sense pin = R25 + R26 + R27.When MOSFET is ON, sense pin = ~0V.Is this analysis OK?

author: Rerouter
author_rank: Super Contributor
timestamp: April 26, 2020, 05:00:33 am
content: L1 Good, Q1 Off = VCC * R27 / (R26+R27) (L1 is assumed to be a very low resistance)L1 Good, Q1 On = 0VL1 Bad, Q1 Off = VCC * R27 / (R25+R26+R27)so for a 35V VCCCase 1 = 1.95VCase 2 = 0VCase 3 = 1VYou can technically also see if Q1 has failed open or short,The capacitor C16 would make it difficult, but technically you can also see if D3 has failed, as on switching off the transistor the voltage seen by R26 would exceed 35.7V, meaning you would measure more than 1.95V for some timeEdit: I should note, the D3 would be failing open, if it fails short, well your hopefully going to blow a fuse,
Understanding this TRIAC circuit - Page 1
Forum section: electronics / projects

author: XaviPacheco
author_rank: Regular Contributor
timestamp: August 01, 2018, 03:19:08 pm
content: I have an inquiry about the circuit attached: When a high signal is continuously given to the transistor, it enables the optotriac with zero crossing. The optotriac enables the power triac, and the AC signal goes to the rectifier, and gets rectified. As I'm not doing phase control, the DC voltage rectified would be 120X1.41 = 170 VDC? Right?

author: schmitt trigger
author_rank: Super Contributor
timestamp: August 01, 2018, 03:32:37 pm
content: Correct, minus the losses in the bridge rectifier and the Triac itself. About 3 to 4 volts.

author: XaviPacheco
author_rank: Regular Contributor
timestamp: August 01, 2018, 03:35:30 pm
content: Would it be a good idea to do AC phase control to lower the DC rectified voltage?

author: Zero999
author_rank: Super Contributor
timestamp: August 02, 2018, 07:50:44 am
content: Quote from: XaviPacheco on August 01, 2018, 03:35:30 pmIt depends on what you're doing.

author: schmitt trigger
author_rank: Super Contributor
timestamp: August 02, 2018, 03:55:32 pm
content: To lower voltage in a phase-control circuit, you would have to trigger the Triac after 90 degrees. The problem with this is the primary current is pulsating and with a high THD.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 02, 2018, 04:26:06 pm
content: Use a SCR instead of a triac, perhaps two replacing the top diodes of the bridge. What exactly is the load?
Undervoltage cutoff with inrush current limit - Page 1
Forum section: electronics / projects

author: ambrozy
author_rank: Contributor
timestamp: February 03, 2023, 11:49:25 pm
content: I've designed undervoltage cutoff with cutoff voltage of 52.8v and 57.8v on voltage, TL431 doesn't like such high voltages so I put a 30v zener diode D1 in series with it, R6 resistor is drawing some current through that diode so it keeps voltage drop when TL431 is off, I'm not really sure how much current I should set here to be safe.This needs to turn on a load with 10mF input capacitance, so when TL431 turns on Q1 BC640, four IRF740 Mosfets driven by R7-R8 divider are charging that capacitance through R10-R13 resistors, then 30-40ms later when capacitors are mostly charged, Q2 IRF2807Z driven by R9-C1 starts turning on, (D2 is to make it turn off faster), I chosed IRF740 because they can take quite large single pulse for the price, maybe IRF540 would make here more sense but I can't buy it, everywhere are IRF540Nwhich as it turns out are garbage in terms of single pulse capability (for 10ms at 20v only 4.5A, "old" IRF540 can take 20A), maybe there is some other mosfet of similar price that is good at this, maybe something that can replace all 4 IRF740?What do you think of this circuit, do you have any ideas for improving it?

author: Benta
author_rank: Super Contributor
timestamp: February 04, 2023, 12:03:49 am
content: I fail to see the point of Q2. Are you certain you've drawn that correctly? Shouldn't it go to the gates of the power transistors?

author: ambrozy
author_rank: Contributor
timestamp: February 04, 2023, 12:24:33 am
content: Quote from: Benta on February 04, 2023, 12:03:49 amit's connected through R9-C1 RC filter which is delaying it's turn on for 30-40ms until capacitors are mostly charged.

author: Benta
author_rank: Super Contributor
timestamp: February 04, 2023, 12:27:18 am
content: That's not what I mean. Look at its D-S connections.

author: ambrozy
author_rank: Contributor
timestamp: February 04, 2023, 12:32:49 am
content: Quote from: Benta on February 04, 2023, 12:27:18 amQ2 is the main switch for the load, it is suppose to short all other transitor-resistor pairs after they do their job of charging C2 capacitance.

author: Benta
author_rank: Super Contributor
timestamp: February 04, 2023, 12:34:15 pm
content: Ah. Sorry, I misunderstood the intention of your circuit.
Underwater acoustic communications breakthrough! - Page 1
Forum section: electronics / projects

author: JimRemington
author_rank: Regular Contributor
timestamp: May 15, 2018, 01:36:26 am
content: For a couple of decades, several research groups and startups have gotten nowhere with the idea of cheap underwater acoustic communications. However, there has recently been a real breakthrough. Jeff Neasham and colleagues at Newcastle University in the U.K. have developed spread spectrum acoustic modems (called "nanomodems"): very cheap ($70 instead of $7000), very low power, small and yet long range (km). Data rates are low, but fine for sensor networks.https://www.economist.com/news/science-and-technology/21741965-tiny-acoustic-modems-will-do-job-better-way-transmit-messages-underwaterhttps://www.york.ac.uk/electronic-engineering/research/communication-technologies/projects/smart-dust-underwater-wireless-sensing/I would hope that commercial versions of these might appear in the next couple of years.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: May 15, 2018, 01:49:21 am
content: Hedy Lamarr strikes again!

author: thermistor-guy
author_rank: Frequent Contributor
timestamp: May 15, 2018, 02:19:40 am
content: According to the Economist:QuoteQuoteAre the researchers taking advantage of the Deep Sound Channel? Fromhttps://en.wikipedia.org/wiki/SOFAR_channelQuoteIt's possible to get close to the Shannon limit with good coding e.g.https://en.wikipedia.org/wiki/Turbo_codehttps://en.wikipedia.org/wiki/Low-density_parity-check_codeBut more processing means more power consumption. It would be interesting to know how close to the limit these modems get.

author: JimRemington
author_rank: Regular Contributor
timestamp: May 15, 2018, 02:54:41 pm
content: Technical details on how the spread spectrum modem actually works are here:https://udrc.eng.ed.ac.uk/sites/udrc.eng.ed.ac.uk/files/attachments/Towards%20large%20scale%20underwater%20communication%20networks.pdf(PDF slide show by Jeff Neasham).

author: CopperCone
author_rank: Super Contributor
timestamp: May 15, 2018, 03:56:25 pm
content: I wonder if its more or less annoying to fish and whales

author: SiliconWizard
author_rank: Super Contributor
timestamp: May 15, 2018, 04:10:51 pm
content: Quote from: CopperCone on May 15, 2018, 03:56:25 pmScience and ethics... still a long way to go.

author: tggzzz
author_rank: Super Contributor
timestamp: May 15, 2018, 04:52:58 pm
content: Quote from: CopperCone on May 15, 2018, 03:56:25 pmMuch less annoying, I presume. There is an awful lot of white noise in the ocean for all sorts of natural sources, and they cope with that.Indeed the text says it is (as I would expect) almost inaudible; and at any given frequency there is probably anegativesignal-to-noise ratio. See, in particular, p15 of that pdf slideshow - the "constellation before despreading".Correlation has to be seen to be believed.
unexpected gain loss in tone circuit - PROBLEM SOLVED - Page 1
Forum section: electronics / projects

author: hummusdude
author_rank: Regular Contributor
timestamp: October 02, 2021, 10:34:43 pm
content: I'm testing a preamp design I hacked together from various sources and mostly its working quite well. But I'm seeing an unexpected (for me at least) drop in signal in my tone circuit. I borrowed this design for a Baxandall 2-band active tone circuit from Elliott Sound Products. It has a center frequency at about 640 Hz, and in theory it should not exhibit any boost/cut at the center frequency. My LTSpice simulation supports that expectation.But when I supply the circuit with a 640 Hz sine wave at 1.0 volts (measured at TP3 & TP4), I'm getting 760 mV on the output of both channels. The treble and bass pots are centered but it seems like that shouldn't matter either way. Since the signal loss is the same for both I assume it's a design-related issue that I don't about. I have enough head room in the input to compensate for the loss in gain but I would really like to know if this is typical for this kind of circuit.

author: Andy Watson
author_rank: Super Contributor
timestamp: October 03, 2021, 12:31:48 am
content: Can you confirm that pins 3 and 4 of the bass control are not connected together.

author: hummusdude
author_rank: Regular Contributor
timestamp: October 03, 2021, 01:41:08 am
content: Yes, continuity test confirms they are not connected.But I have to apologize for overlooking the obvious...the preamp was connected to my power amp input when I made the measurement. When I disconnect the power amp there is no signal loss so the power amp is obviously loading down the preamp. I didn't think that would happen because it's an LM3886 op amp and so I assumed a very high impedance input but obviously something else is going on.Below is the schematic of the LM3886 circuit for reference. It works very well although my scope measurements suggest the gain is closer to 23 than 21 (the designer says R4 and R3 set the gain for the circuit) so perhaps a clue there. The input low pass filter (R1 & C2) cutoff is 234 kHz and the input high pass filter (C1 & R2) cutoff is 1.7 Hz.For the low pass filter calculated reduction in gain, my calculation is Log10(234k/640) = 2.56 decades. At 20 dB/dec that gives 51.26 dB. So the reduction in gain would be a factor of 10^(-51.26/20) = 0.00274. That gives about 999 mV.For the high pass filter the math works out to almost exactly the same result. So on the face the input filtering doesn't appear to be the issue. I'm stumped.

author: hummusdude
author_rank: Regular Contributor
timestamp: October 04, 2021, 05:39:00 am
content: Problem solved.The issue turned out to be an unreliable connection from one of the pot leads to the board.Thanks to all for your input!
Unexpected output from OPAMP - Page 1
Forum section: electronics / projects

author: fc3000
author_rank: Regular Contributor
timestamp: November 23, 2023, 07:52:38 pm
content: Hi all.The circuit below is very similar to the old uPSU project from Dave.A Micro-controller set the +V voltage for the OPAMP.VSet is applied to a Regulator.ILimit is connected to a current sensing circuit.When ILimit goes high Q3 conducts and VSet becomes 0V (almost).What I do not understand is why the OPAMP output goes up-to the power rail. (29V).This makes the OPAMP too hot !Could you tell me if this is normal behavior?Thank you.Regards

author: mawyatt
author_rank: Super Contributor
timestamp: November 23, 2023, 08:25:24 pm
content: The 2N3904 when active effectively removes the negative feedback to the op amp.Best,

author: fc3000
author_rank: Regular Contributor
timestamp: November 23, 2023, 08:40:24 pm
content: Quote from: mawyatt on November 23, 2023, 08:25:24 pmThank you for your answer.So in effect it becomes like a comparator?How can I modify the circuit to avoid this?Regards

author: SuzyC
author_rank: Frequent Contributor
timestamp: November 23, 2023, 09:02:25 pm
content: Connect the collector to the +input of the op-amp to achieve current limiting.Check that the 1K resistor on the output of the op-amp is really 1K.

author: fc3000
author_rank: Regular Contributor
timestamp: November 23, 2023, 09:08:45 pm
content: Quote from: SuzyC on November 23, 2023, 09:02:25 pmThank you for your reply.That seems a good idea. I will try!Regards

author: fc3000
author_rank: Regular Contributor
timestamp: November 24, 2023, 04:38:58 pm
content: Quote from: SuzyC on November 23, 2023, 09:02:25 pmHi SuzyC.I have implemented your suggestion and the circuit works OK now.As usual this forum is great.Thank you for your help.Regards

author: Terry Bites
author_rank: Super Contributor
timestamp: November 25, 2023, 05:57:46 pm
content: The amplifier ouput voltage is dragged towards ground by the npn. When fully turned on it will sink 30mA from the output which is pretty close to the limit for this opamp.Its probably also forcing a lot of current through the opamp input protection diodes.It is indeed forced to behave a comparator, not a good design. A zero drift amp won't help this circuit perform better.
Unexpectedly large standby current on LM2735 DC-DC boost converter - Page 1
Forum section: electronics / projects

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: April 21, 2012, 05:32:35 pm
content: Hello gentlemen,I have usedLM2735XDC-DC boost converter in a battery powered design that has no power-off switch. The LM2735 is used in its bog standard configuration as on the front page of the datasheet. Vin supply is 5V. Load does not consume any current below 6V.After going through prototype verification I have found that LM2735 consumes 2.2mA of current in shutdown mode (Ven grounded) instead of 1uA as planned. In standby mode this drains battery in a matter of hours instead of weeks.After going through possible leakage paths around the design I have found that the 2.2mA is flowing from the Vin, through the inductor, and into the LM2735 switch pin. Datasheet states that switch leakage current is 1uA @ 24V.This does not look like a latch-up and is repeatable at each power-on and across LM2735 samples.Can anybody suggest what might be going on there?ThanksLeo

author: cybergibbons
author_rank: Frequent Contributor
timestamp: April 21, 2012, 06:44:19 pm
content: Sounds very strange.When you say:"After going through possible leakage paths around the design I have found that the 2.2mA is flowing from the Vin, through the inductor, and into the LM2735 switch pin"Is this measured experimentally?The NMOS switch transistor shouldn't be letting that much current flow in that situation.

author: Leo Bodnar
author_rank: Frequent Contributor
timestamp: April 21, 2012, 06:49:00 pm
content: Quote from: cybergibbons on April 21, 2012, 06:44:19 pmYes, measured in situ.Just tried another batch of ICs and they behave as expected.Not sure what happened there originally. IC still worked fine, so I am a bit confused.Anyway, new batch of ICs works fine.Leo
Unfamiliar Board Interface - Page 1
Forum section: electronics / projects

author: kbarnette
author_rank: Contributor
timestamp: October 02, 2017, 03:48:07 am
content: Hi all,I have small memory boards that I need to be able to easily plug in to retrieve the data off of them. The boards have 37 0.9mm pitch pads and the board itself is 1.5mm thick. These seem like odd dimensions but I'm not surprised since it was probably a custom design when they were first made (30 some-odd years ago).I was initially assuming I could use a card edge connector but I can't find any with 0.9mm pitch and 1.5mm thickness.Does anyone have any ideas on ways to interface with this board?

author: kbarnette
author_rank: Contributor
timestamp: October 02, 2017, 03:51:02 am
content: My fault, coworker posted about this for me some time ago athttps://www.eevblog.com/forum/eda/interface-to-unknown-edge-connector/msg1176915/#msg1176915.Please delete this topic.
Unfamiliar IC logo - Page 1
Forum section: electronics / projects

author: KE5FX
author_rank: Super Contributor
timestamp: November 22, 2016, 06:25:31 am
content: Trying to figure out what this part might be. It drives a SAW filter in a Tek RSA306:

author: KE5FX
author_rank: Super Contributor
timestamp: November 23, 2016, 01:50:45 am
content: Thanks, that does make sense given its place in the circuit. It doesn't look like any Intersil logo I've ever seen, though.
Unfamiliar with this SMPS topology - Page 1
Forum section: electronics / projects

author: GelatinCapacitor
author_rank: Contributor
timestamp: August 15, 2023, 04:58:05 am
content: I was dissasembling a SONY CRT TV, model KV-21R22/5Before so, I was dumbfounded by the power supply section in the schematic; how the heck do you drive a transistor-driver-transformer with nothing but a TL431?Of course, this looks to me like a half bridge forward, but where the half bridge is exactly isn't very apparent to me.I'm also not sure how do Q603 and Q604 not quickly kill each other. Of course I assume that is prevented somehow at T604.I remade the circuit in Falstad just for the sake of more clarity (also attached here the falstad file just in case).I'm aware of transistor driving transformers thanks to ATX power supplies, but I'm yet to study the details.However, this transformer (T604) doesn't look like a typical transformer:It's tiny, looks like a common mode choke, and has a weird shaped core, with weirdly wounded coils.Also, it has a separator between the core pieces, so it could also be a flyback somehow?Does this arrangement have a name? Or could you link me to other examples of this, or explanations?

author: ArdWar
author_rank: Frequent Contributor
timestamp: August 15, 2023, 06:38:40 am
content: Self oscillating push-pull?Just instead of tapping off the drive pulses from main transformer (T603) it have its own pulse transformer. Bottom half of L3 is the "primary", L2 and top half of L3 is the complementary drive secondary. Regulation is achieved by "loading" the pulse transformer from L1, modifying the L3_bottom to L3_top and L3_bottom to L2 coupling.

author: dietert1
author_rank: Super Contributor
timestamp: August 15, 2023, 08:58:01 am
content: It reminds me of some ancient color TV circuitry with inductors of variable inductance, controlled by a DC current through a helper coil. Maybe the strange transformer shape wants to avoid the helper coil being a secondary of the transformer.It saves an optocoupler.Regards, Dieter

author: Wolfram
author_rank: Frequent Contributor
timestamp: August 15, 2023, 10:45:25 am
content: Our very own Tim has a note on this exact topology on his website, with a good explanation of how it works.https://seventransistorlabs.com/Monitor/index.html