EviSun 5V DC to DC isolator

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RogerClark
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EviSun 5V DC to DC isolator

Post by RogerClark » Fri Mar 10, 2017 7:16 am

I bought some of these low small 5V DC to DC converters as I need an isolated supply to power a bluetooth audio receiver to avoid noise generated in the receiver being injected via the supply (earth loop) into the audio signal.

http://www.ebay.com/itm/291795738855
Evisun_B05005S-1W.jpg
Evisun_B05005S-1W.jpg (243.91 KiB) Viewed 518 times
I've not tested them in the application I bought them for, as I ended up running a separate 5V mains SM PSU inside my HiFi amp, but I have now tested one of these on the bench. I put a 1k load on the output, (as they need a load), and looked at the output voltage on my scope, and I didnt see any especially nasty noise.

Although the device is the 5V version, it seemed to output voltage as soon as the input was around 0.5V.

One thing to note is that the output is unregulated, and for my 1k load ended up being 5.5V when the input was 5V, but this may be because the 1k load was too low, as the spec reads
To ensure this module can operate efficiently and reliably, During operation, the minimum
output load is not less than 10% of the full load, and that this product should never be
operated under no load!
Its rated at 1W (@5V) so the max operating current is 200mA, so 10% is 20mA, so should have used something like 250 Ohm as the load.
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BennehBoy
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Re: EviSun 5V DC to DC isolator

Post by BennehBoy » Fri Mar 10, 2017 9:03 am

Are these essentially a buck converter in a nice package?

I'm using these -> http://www.ebay.com/itm/10pcs-Mini-360- ... Swx6pYrl5R

Mainly because I can vary the output (but also size and price). They seem to cope reasonably well with in vehicle voltages (12-14v input). No idea regarding isolation.

I'd looked at items similar to yours but prices were relatively high , in in the order of pounds per piece.
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RogerClark
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Re: EviSun 5V DC to DC isolator

Post by RogerClark » Fri Mar 10, 2017 9:24 am

No, they aren't buck converts. I think they contain a tiny transformer with the same number of windings on each side.

I have a load of buck converters but they all have common ground between the input and output voltage.

These are fully isolated and are supposed to provide 1kV isolation between input and output.

I tested them with my multimeter, and they basically measure as infinite resistance between GND and the V0 output, and the same applies to the Vin and Vout pins.

Edit.
The ones you linked to have this in their description

Module Properties: non-isolated buck

So I suspect the GND is common to input and output

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Re: EviSun 5V DC to DC isolator

Post by BennehBoy » Fri Mar 10, 2017 9:58 am

Gotcha.

For my project purposes the common ground makes sense but I can imagine many scenarios where it would not.
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Re: EviSun 5V DC to DC isolator

Post by Pito » Fri Mar 10, 2017 7:04 pm

DC to DC isolating converters are switchers.
So it may happen the noise from switching could be much higher than the one you want to isolate.
From the pdf:

Code: Select all

switching freq 100kHz
ripple typ 75mVpp, max 100mVpp in 20Mhz bandwith
Those ripples to filter is not easy. You need a good low pass LC filter designed for 0-20MHz.
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RogerClark
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Re: EviSun 5V DC to DC isolator

Post by RogerClark » Fri Mar 10, 2017 8:49 pm

@pito

I looked at the output on my scope and although there was noise, it wasnt that bad.

However the only way to really know if it is a problem, is to connect the output voltage via a small capacitor to the input of an audio amplifier and see if I can hear the noise.

If its higher than 20kHz, hopefully it would not be audible.

PS. My previous solution to the audio noise problem, was a RC low pass filter on the supply, using a 1000uF capacitor, and it still didnt remove all the noise being generated on the supply by the Bluetooth receiver

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Re: EviSun 5V DC to DC isolator

Post by RogerClark » Fri Mar 10, 2017 8:57 pm

BTW.

These devices are similar to isolating amplifiers, but cheaper and also far less accurate in voltage tracking.

I can also see a use for them to replace a relay in some instances.

Anyway, I have another old mini Hifi system (cd, cassette and radio), that I want to upgrade to bluetooth, so I will probably need to use one of them when doing the upgrade as I often need an isolated supply so save the whole thing going up in smoke.

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Re: EviSun 5V DC to DC isolator

Post by Pito » Fri Mar 10, 2017 9:21 pm

PS. My previous solution to the audio noise problem, was a RC low pass filter on the supply, using a 1000uF capacitor, and it still didnt remove all the noise being generated on the supply by the Bluetooth receiver
Mind there are a lot of myths re RC, LC and C filters.
Large capacitors do not filter/pass higher frequencies. 1000uF capacitor is good to filter maybe up to 1000Hz.
There are tables how the specific capacitors (value, construction, material) are effective for decoupling purposes. The same for inductors.
The value itself means nothing.
A good filter for such purposes could be a Pi network C-L-C, where C is a parallel combination of several values (types), as each of the caps "works" only within a limited frequency range.
Also a 100kHz ripple may introduce a lot of noise in audible spectra, as it may interfere inside the chips and create various mixing products.
So for quality audio and radio apps the switching power supplies are NoGo.
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RogerClark
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Re: EviSun 5V DC to DC isolator

Post by RogerClark » Fri Mar 10, 2017 9:35 pm

@pito

The noise was a hiss that was generated by the CPU in the bluetooth receiver.

LC filtering helped a little, but I didnt have suitable values of L that were low enough resistance to pass 20mA and not drop too much voltage.

Hopefully these devices will do the job in one small package.

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Re: EviSun 5V DC to DC isolator

Post by RogerClark » Fri Mar 10, 2017 10:19 pm

BTW.

I didn't mention that some of these Bluetooth receivers do not have common ground from the supply to the audio output.

And when I tried to connect the power ground to audio ground it draws a lot of current though the ground path and stops working.

Hence its another reason I need an isolated supply.

Note.

I think only the older Bluetooth receiver modules use separate gnds. But its hard to know what you are going to receive as they are in identical housings.

Actually the older one, is possibly better, as not only does it have separate audio Gnd, but also for hacking purposes it has an external SPI flash chip, which must contain settings and possibly other interesting things.

But I've not had time to hook up the SPI flash to see what is read out of it.

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