[sdiy] Elektron Digitakt teardown

[rburnett at richieburnett.co.uk]

If you're using a flyback converter you can easily put extra windings on 
the flyback transformer to generate additional isolated voltage rail 
outputs.  This is one of the reasons why flyback power supplies are so 
popular.  Low cost being the other! ;-)

Usually only one of the output rails from a flyback converter is used 
for closed-loop voltage feedback.  This is often the rail with the 
highest power loading.  The other rails have poorer regulation, but it 
can still be pretty decent if the flyback transformer is designed 
properly.  Maybe the LDOs are to tighten up regulation on otherwise 
poorly regulated secondary outputs from a flyback converter.

-Richie,

On 2017-07-13 13:23, Julian Schmidt wrote:
> Am 09.07.2017 um 12:42 schrieb Julian Schmidt:
>> 
>> 
>> Am 09.07.2017 um 12:28 schrieb rsdio at audiobanshee.com:
>>> Interesting stuff, particularly the enhanced analog isolation.
>> yes! how does it actually work?
>> I see two SI8660 digital isolator ICs that are probably used to 
>> isolate the data lines for the DAC/ADC from the digital to the analog 
>> part.
>> +/-12V is only used for the analogue side.
>> But how are the GNDs isolated?
> 
> I had a closer look at the PSU.
> 
> 12V DC input from the external wallwart go in.
> https://www.elektron.se/wp-content/uploads/2016/11/PSU3b.jpg
> 
> GND isolation for the digital part seems to be achieved with a LT3575,
> an isolated 5V flyback converter.
> http://www.linear.com/product/LT3575
> 
> but the analog PSU is not completely clear to me.
> They have a VPH2-0066 fixed inductor with 6 coils with 6.6uH each
> http://www.mouser.com/ds/2/87/BUS_Elx_PM_4301_VERSA_PAC-335903.pdf
> 
> A lot of 1117 LDO regulators to the left of the coils, but how is the
> negative voltage generated from the +12V input?
> I can not spot a switching regulator IC near the coils, nor a MOSFET
> or similar to generate a PWM for a switching PSU.
> 
> Any ideas?
> 
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