1MHz bandwith optocoupler on 230VAC - Page 1
Forum section: electronics / projects

author: reyntjensm
author_rank: Regular Contributor
timestamp: October 16, 2020, 11:19:24 pm
content: Hello everyone,I'm looking for a simple optocoupler with a 1 MHz bandwith. On one side i want to use a signal generator, on the other side i have a 230VAC load and i don't have the possibility to add a voltage regulator on that side. I was wondering if there is any good optocoupler around that could work for this? Or another solution? I just need a galvanic isolation between my generator side an 230VAC load side...Thank you all!

author: TheMG
author_rank: Frequent Contributor
timestamp: October 17, 2020, 12:15:31 am
content: Are you just injecting a low-level signal on top of the 230VAC, or actually powering the load with the signal?If just injecting a small signal on top, this can be done relatively easily with a transformer. Otherwise, things get somewhat complicated...Need more specifics on what exactly your requirements are, what you're trying to achieve.

author: reyntjensm
author_rank: Regular Contributor
timestamp: October 17, 2020, 12:35:55 am
content: Quote from: TheMG on October 17, 2020, 12:15:31 amI've already tried to get some more information about my project here on the forum, with no good luck... I need to drive 2 mosfets driving an AC load with a PWM signal. I'm working on a emi/noise generator for a research project. I think i've found an optocoupler that could do the job but i can't get it to work in LTspice. Attached you can find my latest schematic. The idea is to PWM the AC load between 2kHz and 500kHz.

author: wraper
author_rank: Unknown
timestamp: October 17, 2020, 01:10:09 am
content: First of all you are naive if think you can discharge MOSFET gate at such switching frequency fast enough with 1k resistor. Secondly transistor optocouplers like TLP388 are completely incapable to work at such frequency to begin with. You need something like 6N136 or 6N137 to be this fast.QuoteWhy would you need that to begin with?

author: Marco
author_rank: Super Contributor
timestamp: October 17, 2020, 01:22:14 am
content: Quote from: wraper on October 17, 2020, 01:10:09 amInduction heating?

author: wraper
author_rank: Unknown
timestamp: October 17, 2020, 01:27:20 am
content: Quote from: Marco on October 17, 2020, 01:22:14 amThen this circuit would make no sense (not that it makes any sense even without it). You do not simply interrupt power to inductor.

author: Someone
author_rank: Super Contributor
timestamp: October 17, 2020, 01:41:00 am
content: https://www.eevblog.com/forum/beginners/ac-pwm-generator-with-mosfets-does-strange-things-in-ltspice/msg3253646/#msg3253646https://www.eevblog.com/forum/projects/ltspice-with-2-ground-doesnt-work/msg3256302/#msg3256302https://www.eevblog.com/forum/projects/pwm-noise-generator-design-advice/msg3268554/#msg3268554This is at the whip end of the tail of the project, this poster is interpreting some requirements from someone who possibly can't communicate them well.... and neither has the electronics skill to make what they need.Universities trying to cheap out on technical staff/contracts assuming its trivial work that anyone can do.

author: reyntjensm
author_rank: Regular Contributor
timestamp: October 17, 2020, 01:49:25 am
content: Quote from: Someone on October 17, 2020, 01:41:00 amI understand what they need. But i don't have experience with 230vac things. What is wrong with learning and asking questions and trying to get it to work?And it has nothing to do with cheap work since i'm still a student. I think the usage for a forum is to learn from each other, not to break other ones down. If it blows up, meh. Than i try something different. The main goal for me is to learn about EMI, this is why i'm involved in this project. But thank you for your input!

author: reyntjensm
author_rank: Regular Contributor
timestamp: October 17, 2020, 01:57:17 am
content: Quote from: wraper on October 17, 2020, 01:27:20 amIt's for a research group. They are working on a project where they want to define and measure the influence of a EMI source to other users within an industrial grid. We have a test setup with 20 electrical cabinets, each cabinet symbolizes an industrial user and are connected with each other on the same grid. We want to generate EMI in one cabinet and see how the EMI behaves within the other cabinets. For this reason they want to have a controlled EMI source. The idea is to PWM( 2kHz to 500kHz) a big resistive load( 20ohm 5kw resistor) so this would generate EMI. Other people suggested to use a motor/PV inverter. The problem with this is that we can't control the EMI emitted from these products. So we want to make our own generator so we can control the EMI. Attached you can find some pictures from the test setup.

author: uer166
author_rank: Super Contributor
timestamp: October 17, 2020, 02:00:46 am
content: You can use a transformer to inject common mode, as well as differential mode conducted EMI. Imagine a common mode choke but with an extra winding that is excited to induce CM noise on purpose. That gives inherent isolation and safety. I also concur that the current solutions seem.. weird?

author: wraper
author_rank: Unknown
timestamp: October 17, 2020, 02:13:17 am
content: IMHO use 12-15V isolated power supply (for example small module like thishttps://eu.mouser.com/ProductDetail/MEAN-WELL/SPU03L-15?qs=WtedIhRlNpvPHrObktptiQ%3D%3D), fast optocoupler and proper gate driver IC. What you are trying to do simply will not work without a good gate driver and beefy enough power source.

author: reyntjensm
author_rank: Regular Contributor
timestamp: October 17, 2020, 02:15:41 am
content: Quote from: uer166 on October 17, 2020, 02:00:46 amThat would also be an option. I didn't think about that. Since they were asking me to switch a big load. The first schematic i attached was just the one i was working on right now. Attached you can find a working simulation. But this simulation can't go up to 500kHz because the opto's are too small. I know this is not a good circuit and needs to be fine tuned. But for now, i'm just trying to get the simulation to work. And i know, a simulated schematic is not the same as a real life project. But they first want me to have a working simulation....

author: reyntjensm
author_rank: Regular Contributor
timestamp: October 17, 2020, 02:17:51 am
content: Quote from: wraper on October 17, 2020, 02:13:17 amI know... I would also like to use a gate driver IC. But since they want to calculate the influence from the EMI generator to the grid. They want to have the circuit as easy as possible with the least amount of components. If i could use whatever i want i could definitely come up with a better circuit.

author: uer166
author_rank: Super Contributor
timestamp: October 17, 2020, 02:19:57 am
content: In that case, instead of using an opto, search for "isolated gate drivers". You can use a gate driver combined with a special isolated DCDC to provide power to the gate driver output. Note the DC/DC needs to have great common mode transient immunity and low input/output capacitance.Your current circuit has only 1k resistance pulling the gate of the FETs down. You need to sink manyampsto properly drive that FET at those frequencies. Find a fast, isolated, half-bridge gate driver with integrated deadtime generation, and you're probably halfway there to where you need to be.

author: uer166
author_rank: Super Contributor
timestamp: October 17, 2020, 02:21:37 am
content: Jeez: "least amount of components" does not necessarily make simpler circuit. Your requirements ask for a high-performace, finely tuned solution, where the layout and parasitics can make or break the whole concept. Not some random components stringed together.

author: reyntjensm
author_rank: Regular Contributor
timestamp: October 17, 2020, 02:24:24 am
content: Quote from: uer166 on October 17, 2020, 02:19:57 amCorrect, i've also looked at such IC's. But as soon as i use IC's, they can't calculate the influence of that component to the grid. For this reason they want to use "simple" components. I know this would be the best solution but they don't want it. So i was hoping there might be more simple solution... I think i will have to convince them to use such components. Otherwise it wouldn't work... Thank you for your feedback!Quote from: uer166 on October 17, 2020, 02:21:37 amYes i know... But if they ask me to do so i can only try. The people i'm working with have 0 experience with PCB design etc. That's the reason why i'm working on the project. Although i'm not an expert. I usually work with low voltage DC circuits

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 17, 2020, 06:41:29 am
content: Do they have astrong motivating reasonfor doing it differently?Are they familiar with the traditional method of injecting interference? Why do they want a different method?Do they know in what ways their method might fail, or be inconsistent or non-repeatable?The traditional method is a coupling-decoupling network (CDN) or line impedance stabilization network (LISN), paired with a pulse generator or RF amplifier. Mains passes through the network unchanged (impedance is increased slightly, series inductance), noise is superimposed upon it.This gives a consistent, repeatable environment to inject noise through, and also reciprocally, to measure noise from the EUT.Tim

author: BrianHG
author_rank: Super Contributor
timestamp: October 17, 2020, 06:55:46 am
content: >2 MHz opto-coupler 2.5amp gate driver:https://www.vishay.com/product?docid=849212 channel isolated (cap-coupled) 4 AMP gate driver IC, >10 MHz:https://www.ti.com/product/UCC21220A?keyMatch=UCC21220ADR&tisearch=Search-EN-everything&usecase=OPN#product-details

author: Someone
author_rank: Super Contributor
timestamp: October 17, 2020, 09:29:36 am
content: Quote from: T3sl4co1l on October 17, 2020, 06:41:29 amIts a popular methodology in academia right now to build these little island grids and do odd things with control schemes and compensation. But that still doesn't explain the impractical topologies this poster is insisting on pushing ahead with.The researchers probably want a load that can simulate a range of different current waveforms, with some challengingly high bandwidth+power combination.