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Isolation amps, gate transformers 5kV or better, UL60601

Folks,

Sometimes I design medical devices and now another system is around the corner. Since quantitities will initially be low I don't want to do the usual where we build our own ferrite isolation transformers and modulate everything onto carriers. This series came up:

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Says it's just a feedback amp but looks like it can be pressed into service as a general iso-amp, especially since I only need performance DC to 20kHz. Offset can be auto-calibrated out if needed. Creepage would just scrape by, the med standard calls for 8mm. However, looking at the the recommended land pattern for such a device it would not pass, less than 8mm, would have to be slotted or we'd have to use our own non-standard land pattern and then the assemblers would complain:

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Is there anything better in the sub-$5 class? Would be nice if it had UL60601 approval but if 5kV and 8mm creepage we can also have it certified in the system.

I am also looking for ferrite transformers with split bobbins (or a thick PTFE-insulated winding) but haven't scanned all mfgs yet. If someone happens to know a series that can fulfill the 5kV, creepage and ideally UL60601 I'd appreciate a hint.

With opto couplers I'll see if the HCNW137 still comes with "the papers", else I'll use NRZ via a transformer.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg
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You could roll your own with a ADUM2201, SI8421, ISO75xx, etc?

Cheers

Klaus

Reply to
Klaus Kragelund

Dang, this is close:

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It's not really multifilar wound, looks more like scramble to me, but it's very low leakage. Maybe not enough inductance and flux and a low enough impedance for gate drive use, but good for a push-pull forward converter if you need DC isolation, or a high isolation DSL transformer.

Frequency response is good, in the 100MHz range I think, at a characteristic impedance (end-to-end) of something like 600 ohms.

Bank wound coils are basically limited to CMCs, which necessarily have shitty leakage, low bandwidth and low power handling (a watt or a few) as transformers. I don't see how you'd ever find one with patient-to-system medical certs or even the creepage, but I've hi-potted even a small one at

12kV for what it's worth.

Tim

-- Seven Transistor Labs Electrical Engineering Consultation Website:

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Reply to
Tim Williams

The creepage on the component is lowered due to high CTI material. Creepage on the PCB is normally not an issue since for some reason UL and IEC rates PCB as having good control of mechanical tolerances (even though CTI is below 175)

Analog devices icouplers has bad CTI

TI, Silabs etc has good CTI (above 400), so less creepage distance needed

Cheers

Klaus

Reply to
Klaus Kragelund

I could but this time I wanted to avoid that. It's a small series initially where we have to keep the EE effort as low as possible. But it has to fulfill UL/EN 60601.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

Thanks. It's only rated 4kV but if they truly mean RMS it might work. It's just weird that they do not state 60601 under agency compliance. But I can inquire if they'd bless it for cardiac CF-class apps.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

IME they always flag things if you don't have the minimum millimeters in the standard. If things are encapsulated that may be a different story but then the manufacturer has to state 60601 compliance.

As long as air can be there or enter the agency compliance guys typically insist on 8mm no matter what. This is a cardiac contact application, meaning some of the electrical stuff will be inside a human (non-stopped) heart for a while. That gets almost as much scrutiny as when trying to register a new spacecraft :-)

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

This is a Coilcraft PL300.

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It's rated 1500 volts isolation, but I think the planar construction would be good for a lot more if the layers were shuffled a bit.

I have one here, and it's really cool. It's about an inch square and good for 300 watts!

How about LED:air gap:photodiode? Light pipe maybe.

Fiberoptics would get you to megavolts, but may not be in your budget.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

That is cool. But the gaps seem to be a bit tight for 5kV, ferite is considered conductive in that respect.

For the opto I am set, the HCNW series is good.

The old McGyver trick is a TX, an RX, an inch or so apart and connected by a snippet of plastic tubing.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

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?

-Lasse

Reply to
Lasse Langwadt Christensen

The voltage rating is good but the creepage paths look very marginal. It also doesn't come with 60601 rating. The way it goes with that if you want to have the unit certified is that the agency test house requests "the papers" for all parts that cross the safety barrier. Ideally all info shall be in the datasheets and where not we'd have to cajole that out of the manufacturers. With HP/Avago that was never a problem but with some others it was a bureaucratic hurdle. I try to avoid it where I can.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

this maybe?

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-Lasse

Reply to
Lasse Langwadt Christensen

Almost. The one below in the gull-wing wide-body package is my favorite that I've used in many projects. We always got the papers but for this project (other company) would have to obtain them again because it's been so long ago:

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--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

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