Optocoupler technology - Page 1
Forum section: electronics / projects

author: IconicPCB
author_rank: Super Contributor
timestamp: January 16, 2019, 10:30:09 pm
content: I need some help in identifying optocoupler technology.Some time ago i stumbled across an opto device whihc consists of LED source and a photo cell ( of the solar panel variety ) which can be used to:a) provide isolation for the signalb) provide low level power to the isolated circuitI cant recall where or what the device is, I ask for any pointers to the device.

author: IconicPCB
author_rank: Super Contributor
timestamp: January 16, 2019, 10:42:34 pm
content: This was fast... dangerously fast...Thank YouYes this is the kind of device I was looking for.

author: digsys
author_rank: Unknown
timestamp: January 16, 2019, 11:16:34 pm
content: These were my favourite part -https://www.silabs.com/documents/public/data-sheets/Si844x.pdfdamn fast / logicNot for new designs? Need to check if there is a replacement.

author: zitt
author_rank: Regular Contributor
timestamp: January 17, 2019, 06:48:26 am
content: What I want to know is why we don't see ever increasingly smaller optocouplers in SMT packages.I don't remember now why I was looking; but I wanted something really small to work in an SMT design... sadly; I couldn't find anything really smaller than SO8.I was kind of hoping for some SC7 or hell even BGA style for the really small boards. I actually toyed with the idea of combining a photo transistor and smd right angle diode.

author: BravoV
author_rank: Super Contributor
timestamp: January 17, 2019, 07:03:32 am
content: What coincidence , just used a VOM1271T + 2 beefy high voltage N mosfets to build a DIY SSR, really handy.

author: Phoenix
author_rank: Frequent Contributor
timestamp: January 17, 2019, 08:11:04 am
content: Quote from: zitt on January 17, 2019, 06:48:26 amI would suggest that it's because they are usually used for voltage isolation and need the physical creepage and clearance. Is there a need or market for 50V isolation?

author: beduino
author_rank: Regular Contributor
timestamp: January 17, 2019, 09:38:04 am
content: Quote from: IconicPCB on January 16, 2019, 10:30:09 pmSmall ferrite core with 5 turns in primary (transformer) and 15 secondary driven by MPU pins with current limited to a few mA @ 100kHz easy switches 230VAC home LED lights by using AC mosfet switch protected by zener 12V and around 100k resistor on mosfets gate, but 1M resistor could be even better.Galvanic insulation from mains high voltages.No problem with aging processes in optocouplers.So, yes it provides low level power to AC mosfets gates - short circuit current measured was 10mA at configuration with bigger ferrite core to have better AC mains insulation.Anyway, for mass production probably not the best solution while we need small ferrite cores, but it works programmed by tiny small ATTiny85 MPU

author: TrickyNekro
author_rank: Frequent Contributor
timestamp: January 17, 2019, 01:37:49 pm
content: I know that these ain´t optocouplers but I have used Analog Devices Isolators before.I am not really sure if they are magnetic or capacitive isolators. Texas Instruments and Analog Devices use these technologies but I can´t remember which uses which.But the main thing is that if not both, at least Analog Devices offer their "isoPower" isolators. They offer both signals and power delivery to the Isolated side on a single IC.I have used only the plain isolators and isolated gate drivers and I have had no complains with their performance, although haven´t tested for high dv between sides.And these parts are probably much much more expensive than simple optocouplers, most of them I have seen being used in instruments (I think that was also from a Dave´s video).Cheers!

author: spec
author_rank: Frequent Contributor
timestamp: January 17, 2019, 11:27:15 pm
content: Hi IconicPCBThere is a bit of chat about optocoupler (coupler) technology here:https://www.eevblog.com/forum/beginners/how-do-you-select-optoisolator-current-does-it-affect-switching-speed/msg2095888/#msg2095888

author: spec
author_rank: Frequent Contributor
timestamp: January 17, 2019, 11:59:53 pm
content: By the way, this coupler looks like a nice job:https://www.silabs.com/documents/public/data-sheets/Si87xx.pdf

author: IconicPCB
author_rank: Super Contributor
timestamp: January 18, 2019, 01:34:44 am
content: Hi Spec,The reason why I started to look at the gate driver optos is as followsI am looking to drive some commercial ( Meanwell ) switchmode powersupplies in a series/parallel combination under a controlled regime.They require a variable voltage to control the output.I had seen these opto drivers in the past but could not recall details. Unfortunately they are a bit unsuitable ( too low a drive ).

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: January 18, 2019, 07:33:35 am
content: QuoteThis device looks interesting, do we have a cheaper version to build Solid state relays with MOSFETs!?

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: January 18, 2019, 09:01:39 am
content: QuoteThanks, Do we have Chinese manufacture of such devices? also I wonder what would be the turn on time of these devices with two 20N60 MOSFETs acting as a an SSR, what sort of times should I expect? Also there are lot's of cheaply P-JFETs out there

author: spec
author_rank: Frequent Contributor
timestamp: January 19, 2019, 06:19:19 am
content: Quote from: blueskull on January 16, 2019, 10:31:02 pmWow- didn't know about those.

author: spec
author_rank: Frequent Contributor
timestamp: January 19, 2019, 06:35:47 am
content: Quote from: IconicPCB on January 18, 2019, 01:34:44 amGot it.Can you define exactly what you would like to do with the Manwell PSUs?Maybe we could help with an alternative approach.

author: IconicPCB
author_rank: Super Contributor
timestamp: January 19, 2019, 08:39:09 am
content: For example Meanwell RSP-750 can be connected in series but it calls for isolated floating control voltage sources so as to be able to vary output from 20% to 110% .I can take the analog "linear " path with optocouplers or A PWM optocoupler output and convert to analog voltage but i had hoped these gate drivers would have a bit more grunt which would make the PWM path much simpler...that is no need for a power supply...

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: January 19, 2019, 08:50:17 am
content: what would be the life expectancy of these Optocouplers?

author: spec
author_rank: Frequent Contributor
timestamp: January 19, 2019, 09:19:58 am
content: Quote from: ali_asadzadeh on January 19, 2019, 08:50:17 amFor a top-tier optocoupler from the likes of Vishay: 100k hours after which the CTR will be at least 50%.https://www.vishay.com/docs/80059/80059.pdfThe two main alternatives to opto coupling are capacitive and inductive, both of which have an 'infinite' life and are very fast.

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: January 19, 2019, 12:17:47 pm
content: QuoteThanks for the tip, do we have a cheap option on them?

author: zitt
author_rank: Regular Contributor
timestamp: January 20, 2019, 08:10:01 am
content: Even these SMT optos are pretty big by today's standards. Glad they exist; but was kind hoping for something even smaller.I get that most of the apps are for physical isolation... but there are time when we are just trying to keep systems from directly connecting.