10-15v DC to 12v DC 1A ISOLATED output design

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Hello,

I've been installing some audio equipment into my car and every single time I put an aftermarket device into the car I seem to be getting some sort of pollution on the output. I've followed all of the best practices on grounding at a

common point, and running power and signal lines separately. Also, in the case of my 5v USB DAC and my 5v bluetooth connection i've used an ADUM3160 chip based board for isolation of the GND. These have minimized my issues, however, I

still get issues on my accessories using 12v such as my Alpine KTP-445U amplifier. It's not a huge "hum" but it's there. The point of using isolation is to eliminate ground loop path between devices.

What I'm thinking, and please correct me if I'm wrong, is that a similar device to the 5v isolated USB module to isolate the DC from the car and the DC to the unit (such as my Amplifier) would clean up the signal since a transformer is

used as part of the circuit.

I searched around and found the LT3999 chip and some "typical application" schematics. I've attached 2 of them from the LT3999 specifications sheet here. Essentially, I would like to:

Input 10-15v DC
Output 12-15v DC with .8-1 Amp

The first schematic inputs 12v DC and you get 12v DC out at 0.8A (with Coilcraft PA6384 transformer) which would be perfect, except that a car outputs 13.7-14.7 volts when on. I need the device to work with the ignition off as well as the ignition running. Now, I don't mind if the device fluctuates and provides a 1:1 no matter what you apply. Ie: 12v in 12v out OR 15v in and 15v out. I just don't think that the coilcraft transformer used in the first schematic could handle that based on the spec sheet.

The second schematic inputs 10v - 15v DC so is perfect other than it outputs 12v and .2A and -12v at .2A. This second design uses the WURTH 750314781 transformer. Looking at the datasheet I see that it states that it accepts a wide input and outputs at a 1:2 ratio.

9-15v in (1MHz) and 14-20v out at .5A (per side).

What I'm wondering is:

1) Any chance that the Coilcraft transformer and schematic would work with 10-15v DC and function similarily as with just 12v in? ie: it's a 1:1 transformer, would it not still work at 13.7 or 14.7 volts and just give me the same output as the input? If it needs modification for that then how would it be modified?

or

2) If I went with the second transformer, is it possible with the 1:2 ratio to set it to get between 12-15 volts DC when the input varies from 12-15 volts but at a higher amperage (between 0.8 and 1 A)? I imagine that combining both outputs you would get a full amp but I don't know how to do that...

3) finally, with regards to the SYNC pin - both of the schematics show a signal going to it, however, based on the datasheet, I imagine that I can just connect it to ground?

Any help is appreciated!

Thanks,

Michael
 

Attachments

  • LT3999 Applications.png
    LT3999 Applications.png
    146.3 KB · Views: 127
  • LT3999 Spec Sheet.pdf
    302.3 KB · Views: 29
  • Coilcraft PA6381.pdf
    185.9 KB · Views: 43
  • WURTH 750314781.pdf
    121.7 KB · Views: 43
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