[sdiy] get 5V from 12V - DC-DC converter or 7805?

[Ben Stuyts]

Hi Florian,

For my work (non audio/synth!), I have just completed a prototype with maybe a suitable DC/DC converter. It might be a bit overkill as it can supply 1 Amp though, and there is even a 3 Amp version. I used the WPMDH1102401 from Wuerth: https://www.we-online.com/catalog/datasheet/171012401.pdf <https://www.we-online.com/catalog/datasheet/171012401.pdf> I measured the output noise at about 30 mV p/p (20 MHz bw limited), so that’s pretty good. Efficiency was > 90%. I did not check the input noise as that was not a criterium. No heatsink was needed but I used plenty of via’s and copper on both sides of the pcb. There are a few others in this range, see https://www.we-online.com/katalog/en/pm/step-down-converter/magic_variable_output_voltage <https://www.we-online.com/katalog/en/pm/step-down-converter/magic_variable_output_voltage>

I followed their pcb and component guidelines from the datasheet and it worked great first time. See attachment for an idea of the pcb. You might want to add some additional input filtering though. On the other hand, most of the wall wart (or other) power supplies are switched mode from often unknown origin anyways, so I’m not sure how much a bit of additional noise on the +12V will matter. :-)

Ben





> On 27 Dec 2020, at 22:58, Florian Anwander <fanwander at mnet-online.de> wrote:
> 
> Hello,
> 
> I am at designing the pcb for a simple  MIDI-sequencer based on an arduino nano (the basic idea is derived from the JX-3P / SH-101 sequencer). I want to build it as a euro rack module, but want to have it also as standalone unit. So the pcb has the usual eurorack power connector and a socket for a wall wart. I have jumpers to select between 5V from the euro rack connector, or 5V from a regulator which is fed either by the 12V from the eurorack connector or by 9V-12V from a wall wart.
> 
> At the moment I implemented the 5V conversion with a 7805. But I think this will cause a lot of "useless" current on the 12V rail of the euro rack. I thought about one of these DC-DC converters, but I am not sure how much (switching-)noise those can insert into the euro racks supply and ground. The module also has voltage inputs (for note length and velocity) and trigger/gate inputs, so electric relations with ground to other modules or external devices are quite likely, and I fear I transfer potential supply noise this way in the external signal paths.
> 
> On the other hand the 7805 circuit is quite easy to implement, the DC-DC converter has to be bought as module or requires buying parts I won't have use for anywhere else.
> 
> Does anyone have experience with those DC-DC converters?
> 
> 
> Regards
> Florian
> 
> -- 
> http://www.florian-anwander.de/
> 
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