Mosfet drive using  fibre optic cable link - Page 1
Forum section: electronics / beginners

author: nikolatesla
author_rank: Contributor
timestamp: June 12, 2025, 12:10:31 am
content: Hi all,I have a project that needs switching isolation via fibre optic cable .I have tried to use 3120 driver chips but the switching noise and the drive coax cable is creating problems .My attempt to use spdif audio protocols was limiting due to the 38Khz carrier that is built into the connectors.I need to switch pwm at up to 100khz with a dds ..The power supply is 500voltsThis seems simple but of course nothing is simple in a high noise environment .There must be a way to do this but I have not found any examples that use this approach which would be very useful for many thingsIf I could drive the 3120 mosfet drivers with light , it would do what I want . I even tried to grind the 3120 to access the optical receiver which was a failure and a mess and was unpredictable .Any length of coax picks up noise no matter what I have done so far . The mosfet needs to be very close to the driven coil.I feel that there must be an application that uses this but so far no joy.Thanks for any help with this .

author: Whales
author_rank: Super Contributor
timestamp: June 12, 2025, 01:18:56 am
content: It would be good to know what your application is, we'll be able to help better.QuoteDo you absolutely need to send the raw gate signal over the fibre, or can you send some other (more tolerant) signal over the fibre and generate the PWM gate drive in a circuit that's next to the mosfet?QuoteDifferential signalling & a shielded twisted pair, perhaps? Ie a shielded CAT6a/similar cable and a small pulse transformer at each end.

author: AlexRG
author_rank: Regular Contributor
timestamp: June 12, 2025, 01:58:57 am
content: Quote from: nikolatesla on June 12, 2025, 12:10:31 am1. Optical receiver – any SPDIF2. Resistor R1 limits the current through the optodriver LED3. Resistor R2 for guaranteed discharge of the Q1 gate4. Transformer T1 – any common-mode transformer with a winding inductance higher than 50 mH, for example this one:https://aliexpress.ru/item/1005006187634917.html. This transformer will dampen high-frequency interference coming from the inductive load.5. I recommend the 3120 optodriver from AOTE, very high quality, can operate up to 7 MHz (up to 2MHz for 3150 version), and much cheaper than the others. I tested them personally.https://lcsc.com/product-detail/Gate-Drive-Optocoupler_AOTE-AT3120-CuH-D_C41367997.html6. Resistor R3 to reduce high-frequency pulsations on the drain of transistor Q2. Select experimentally.7. Resistor R4 for guaranteed discharge of the Q2 gate.8. If your power transistor Q2 is silicon, apply +12V to the optodriver. If silicon carbide, then +15..18V.

author: Andy Chee
author_rank: Super Contributor
timestamp: June 12, 2025, 11:58:23 am
content: Quote from: nikolatesla on June 12, 2025, 12:10:31 amIs this project an audio modulated Tesla coil?

author: MariuszD
author_rank: Regular Contributor
timestamp: June 12, 2025, 12:22:18 pm
content: I have been using afbr-1529z and afbr-2529zhttps://www.broadcom.com/products/fiber-optic-modules-components/industrial/industrial-control-general-purpose/650nm/afbr-1529zhttps://www.broadcom.com/products/fiber-optic-modules-components/industrial/industrial-control-general-purpose/650nm/afbr-2529zhttps://docs.broadcom.com/docs/AV02-0730EN

author: Hr_Satch
author_rank: Contributor
timestamp: June 12, 2025, 07:35:16 pm
content: Hi Nikola-Tesla,I have also been playing with such idea,for fast opto galvanic isolated drive of MOSFETS.You need Fast Schmitt trigger actions as to filter out some static.In my job for MassSpectroMeters they use ultra fast opt links:HFBR-1528 & 2528 Fiber opto Links , you can lookup the datasheet.The fastest "standard" opto isolators I found in the FOD-0721,have them bought, but not yet usedHope this helps a bit your selection in what to use, regards, Harry.

author: mtwieg
author_rank: Frequent Contributor
timestamp: June 13, 2025, 12:39:19 am
content: Quote from: nikolatesla on June 12, 2025, 12:10:31 amIt's difficult to conceive of a scenario in which carrying PWM signals over fiber would necessary or even helpful, unless the devise being driven has to float to extremely high voltages (like +/-2kV). Keep in mind you would still need some circuitry on the isolated side, along with its own power supply, and that will need to withstand whatever noise/transients occur at the switch.Maybe you could explain more clearly what you're trying to achieve, and what specifically you've tried already.

author: nikolatesla
author_rank: Contributor
timestamp: June 13, 2025, 05:44:15 am
content: The device is a type of tesla coil using multiple frequency drives , Have used a schmit trigger arrangement but I was hoping that this topology has or is used somewhere like inverters or motor drives to name a few.The 3120 solution is what I have used but I need to be well away from it for safety reasons about 6 feet minimum and with these lengths of coax there are many problems .I am able to name this device as it is nothing untill it gives me results ,so its just an experimental thing.