Author Topic: How would you power 4x separate isolated RS485 transceivers?  (Read 785 times)

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Offline jneudorfTopic starter

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How would you power 4x separate isolated RS485 transceivers?
« on: December 18, 2019, 07:20:51 pm »
I am considering using 4x Recom RFMM-0505S DC-DC modules ($1.31 each at Mouser) for power, and Analog's ADUM1201ARZ-RL7 ($0.65 at LCSC) to get the signal across.

I'd rather just make some isolated converter like in http://www.ti.com/lit/ug/tidu590/tidu590.pdf but the Wurth 760390014 only has a single output and costs $1.25 on its own.

Should I consider using Coiltronics Versa-Pac or Coil-Craft Hex-Path HPH1 series, or are there other options that might work? I can't find Asian sources that seem similar to these.

The context is bi-directional DMX/RDM at 250kbps.
« Last Edit: December 18, 2019, 07:24:18 pm by jneudorf »
 

Offline David Hess

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Re: How would you power 4x separate isolated RS485 transceivers?
« Reply #1 on: December 19, 2019, 01:10:56 am »
I would use a pair of trifillar wound transformers in an inverter circuit.  This only requires one simple driver.

 

Offline T3sl4co1l

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Re: How would you power 4x separate isolated RS485 transceivers?
« Reply #2 on: December 19, 2019, 02:23:21 am »
Hex-Path is a good option, mind the isolation is only a hundred volts or whatever -- fine for signal purposes, but beware of ESD damaging it.  (You could bridge grounds with a little MOV or TVS to control this.)

If I needed more, or lower cost, I might consider planar transformers -- do it all in the PCB itself.  This is a more advanced option though, as you're doing the transformer design yourself, and you don't have many protos to iterate on.


I would use a pair of trifillar wound transformers in an inverter circuit.  This only requires one simple driver.

An interesting option would be to abuse some CMCs (data or data/power type), driven with a few logic gates or a gate driver, to make a simple chopper; FWB the secondaries and there you go.  Put a bunch of primaries in parallel -- one for each channel -- not really a need for multifilar, the dual-line kind (which are usually bifilar) should be good enough.  Downside is the lack of current limiting, which may have workarounds (e.g., use a motor-driver H-bridge chip, and use its internal current limiting, or supply it with a current limiter), and of course the cross-regulation is limited by leakage inductance.

Tim
« Last Edit: December 19, 2019, 02:27:27 am by T3sl4co1l »
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Offline rvalente

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