What I try to build

I'm building a tiny class-d amplifier with an Arduino Nano as MCU, tiny OLED display (logo, selection info, Volume info, VU-meters), 3 buttons (input selection, volume) and a bluetooth module (and soundcard but not integrated yet because of the following problem). It all fits inside a candy case (82mm x 55mm) of throat sweets called Wybert ;-) .


The setup

The setup is pretty straightforward, there are two transistors (1020Y) controlled by the arduino that enables/disables resources, this is working fine. Only when I enable the bluetooth there is a terrible noise (data noise) because of a ground loop, everything shares the same ground. This can be solved with an isolated DC/DC converter (see this video: https://www.youtube.com/watch?v=b2Pb1KuVDS0 ). 1W is enough because the whole setup consumes only 90mA at max (arduino, screen and module when everything is switched on).

Why I need it

There is 'enough' 'room' (pretty tight actually) to implement this isolated DC/DC converter but the amplifier can run on 5VDC (2x3.5W min) to 24VDC (2x50W max). When I need a DC/DC converter, why not combine the two, a regulator like a car usb charger for example (can be very tiny also, have one, but not isolated). You can input max 24V or less to get 5V. I know normally a DC/DC step-down converter that outputs 5V needs more than 5V but the component I'm talking about is a 5VDC to 5VDC converter. It must be possible to have smart component that always outputs 5V in a range between 5V and 24V or am I wrong?

What I want to avoid

What I want to avoid is two DC/DC converters when powered on a battery (12V-24V) for example, that will be very inefficient and can introduce allot of trouble. In this case I need two powerlines that provide 5V (for the isolated DC/DC converter) and the 12-24V range for the amplifier. So when I can combine the two, I need only one powerline to power the whole device, you can input everything between 5V and 24V.

Allot of flavours

There are allot of isolated DC/DC converters but I see only with fixed input or cannot figure out if it is possible to input a lower voltage (sometimes a min range and sometimes a max range, the 'hell' of data presentation).


Can somebody tell me if it is possible what I want and point me to a component that can do what I want (in isolated form ofcourse)?

  • \$\begingroup\$ You have not defined all the measurable constraints needed to verify any solution. Please define, budget, volume, and other specs for acceptance criteria, effic, ripple vs input and load. Your assumption that adding a 1W 5V converter will be more inefficient than a wide input range shared converter is wrong since the losses in 1W are relatively small. But your question is a good story it just needs some engineering inputs. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Mar 23 '17 at 15:43
  • \$\begingroup\$ Is 12~24V the output or the input? ie. define all source power and load power specs and isolation between outputs plus other relevant specs like load regulation. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Mar 23 '17 at 15:54
  • \$\begingroup\$ @TonyStewart.EEsince'75, Thanks for the comment. Well, answers to your questions is allready in the text. For example: 5-24V input is already defined in the title of the question. The other info is specified in "the setup" alinea, a video + the spec that it uses 90mA in total so 1W will be enough. The isolated DC/DC is more ineffecient because there is a loss of 20% (more than a regular DC/DC converter) and when you have two DC/DC converters in the powerpath there is more waste of power......... \$\endgroup\$ – Codebeat Mar 23 '17 at 16:49
  • \$\begingroup\$ ...... In the past I did some experiments with two DC/DC converters in the powerpath and can introduce strange side effects, more noise for example. So if I can avoid this, it will be always better, right? \$\endgroup\$ – Codebeat Mar 23 '17 at 16:50
  • \$\begingroup\$ It depends on impedance ratios of load to source for switched currents and storage cap Zc, ESR for load regulated noise. \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Mar 23 '17 at 16:55

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