Seperate USB Data and Power

[FIX]

The GL850G is NOT an isolator. It is just a hub. A USB 2.0 Hub. Nothing wrong with using it, it is comparable to the chinese FE1.1. But it is easiest to buy an existing hub and hack it, over building one's own.

There is currently no USB 2.0 high speed capable USB isolator (there was one for a while but it was EOL'ed years ago). It looked like this:



VL811 is a USB 3.0 Hub, ICE08 is the USB 2.0 Isolator.

USB 3.0 is capacitively isolated inherently and is as such easily isolated, HOWEVER as USB 3.0 needs USB2.0 high speed working to negotiate USB3.0 capabilities, USB 3.0 isolation does not work without USB 2.0 high speed isolation.

This is a fully tested and working design to isolate USB1.1, 2.0 & 3.0. The isolated power supply is a simple flyback design, 5V in 5V out.

Thor

Geez. Relax. The isolation discussed is not for data, it's for ground loops that cause current on the shield or ground return and make data errors, and or hum in some audio interfaces. I've use this in several products and never had any problems.

 

[thor.zmt]

Geez. Relax. The isolation discussed is not for data, it's for ground loops that cause current on the shield or ground return and make data errors, and or hum in some audio interfaces. I've use this in several products and never had any problems.

I understand that 100%. It is however that potential DIY'ers understand that it is not a full isolator, but just a ground loop breaker.

I have commercialised both similar products and full isolators (including data) both USB 2.0 and 3.0.

What you show is in effect the same as the later ifi "iUSB" stand alone units, though these use USB 3.0 Hubs. They work well, but they are not the same as a "USB Isolator".

Some comments on your schematic (I understand that these have been used in commercial products). I would recommend to add back-to-back diodes across the 100R/100n RC to limit any error voltages in case of faulty equipment. It is possible to fry USB Ports without these.

It is possible to use somewhat higher voltage than single diodes, most USB Phy's tolerate up to 3.3V (more risks damage - so < 33mA peak fault current in the 100R resistor will exceed this) on their DP/DM but need the common mode range usually < 2.5V to work correctly. I tend to use 1N4148 which clamp the error voltage across 100R to 0.4V (4mA error current max).

Second, it is possible to add a switch to disconnect the RC and have only the diodes, which works often very well and completely opens the link except for a few pf of the diode Junctions (~ 10pF for 1N4148).

I commonly fit a 3-Way toggle switch that select between hard ground (short out RC), no ground and "soft ground" (RC connected). The middle position is recommended if this causes no errors.

Thor

 

[FIX]

I've never in may live every heard of a need for an isolator for USB to that extent. What would be the reason for this?

 

[Tubetec]

As I said towards the start of this thread , there seems to be a fixation with isolators ,
but that doesnt help us with the underlying grounding issue that occurs with usb/motherboard power .

 

[thor.zmt]

As I said towards the start of this thread , there seems to be a fixation with isolators ,
but that doesnt help us with the underlying grounding issue that occurs with usb/motherboard power .

I've never in may live every heard of a need for an isolator for USB to that extent. What would be the reason for this?

Most simply put, a galvanic isolation barrier (to get technical) prevents (ideally) any noise coupling. And usually such isolators are rated at "kV" isolation.

Thus, to many's thinking they must be better than "ground loop breakers". And the isolation voltage becomes figure of merit.

Another thing is the comparable ease and reliability of using such an isolator to a layman (plug, play, forget) and the fact that by principle galvanic isolation of USB also acts as repeater. So you get the added potential "repeater" benefit.

Objectively I tested both ground loop breakers and isolators in a simulated ground loop situation.

Using the ground loop breaker noise was dramatically reduced, but some components remained measurable above the noise floor.

The isolator killed all noise, at least dropping it below AP2 measurement limits.

So all else equal a USB isolator capable of high speed is the easiest universal choice as system improvement for Audio over USB.

Thor

 

[Newmarket]

Most simply put, a galvanic isolation barrier (to get technical) prevents (ideally) any noise coupling. And usually such isolators are rated at "kV" isolation.

Thus, to many's thinking they must be better than "ground loop breakers". And the isolation voltage becomes figure of merit.

For general info' - the "kV" isolation spec' is usually for a limited time eg "60 seconds @ X kV".
Basically able to reject eg the 1kV spikes it might see during EMC Immunity testing.
Continuous working differential much lower.

 

[thor.zmt]

For general info' - the "kV" isolation spec' is usually for a limited time eg "60 seconds @ X kV".
Basically able to reject eg the 1kV spikes it might see during EMC Immunity testing.
Continuous working differential much lower.

Yes. The issue is that in the mind of those not sufficiently educated technically there is a link between voltage rating and isolation, NOT actually looking at the noise coupling which is the main actual figure of merit for isolation.

A higher rated isolation voltage is not automatically lower noise coupling.

Thor

 

[FIX]

I have reached the same undetectable noise with my simple isolator…. Of course I could have made a laser isolator that was 3 feet apart and used nuclear fused ionic galvonometric reconstructive mega volt isolation, but I chose the simple path…