I am using a linear regulator (MIC29302WU) to power a computer mounted inside my car; however, there is significant noise being passed along the ground of the regulator to the main computer. I verified this by connecting an inverter to the battery and using a 12v power supply which eliminated the noise.

Can anyone suggest an isolation circuit? I would like to consider cost and board area. Would this require a flyback design? Or can I get away with not using a transformer?

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    \$\begingroup\$ You could use a DC-DC boost regulator instead. 14 to 19V instead of a square wave AC inverter \$\endgroup\$ – Tony Stewart EE75 Jun 3 '19 at 13:51
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    \$\begingroup\$ I tried a SMPS after the linear reg, but no reduction in noise. Probably because input/output shares a ground. Are you talking about isolated boost circuit? Do you have a schematic you can link to? \$\endgroup\$ – physiii Jun 3 '19 at 13:57
  • \$\begingroup\$ The combo of DC to AC ( square wave) and AC to DC charger has too much common mode noise at line freq + harmonics so it interferes with audio quality to line input on car stereo. My suggestion is avoid the line freq (square wave) and go DC-DC non-isolated 50kHz to laptop for charging battery. Possibly 50~65W. This Could be a purchase item online \$\endgroup\$ – Tony Stewart EE75 Jun 3 '19 at 14:07
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    \$\begingroup\$ Okay I think there is a miscommunication. I am currently using a non-isolated DC-DC regulator on my circuit (MIC29302WU)...This is for a stereo that goes into the dash a car. However using the linear reg I get noise because ground planes are not isolated, I can stop the noise by using an inverter, to psu like I said but obviously that's not what I'm actually implementing, I was just telling you how I stopped the noise by using isolation. Now I need to figure out how to implement the isolation on my board \$\endgroup\$ – physiii Jun 3 '19 at 14:19
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    \$\begingroup\$ You could define all DC V,I ranges and AC noise characteristics better in your question with measurements and design so one can know you analyzed the EMI correctly between radiated, conducted, CM and DM noise and if speaker drivers are differential or single ended \$\endgroup\$ – Tony Stewart EE75 Jun 3 '19 at 14:45

Get a 12V DC DC converter with isolation. Make sure the input voltage can handle 12V and the output voltage is a 12V output.

There are some that can be found at digikey

With some searching some can be found with terminals.

Before you try that, try a clamp-on ferrite on the wires to see if you can increase the inductance and stop high frequency noise.

  • \$\begingroup\$ The cheapest 3A isolated DC DC converter from your digikey link cost $15 (digikey.com/product-detail/en/tamura/BPM1234SJ/MT7391-ND/…) That seems like a costly solution, I would think there is a cheaper way to get galvanic isolation with some chip/transformer combo. \$\endgroup\$ – physiii Jun 3 '19 at 18:57
  • \$\begingroup\$ Cost is relative. It was a suggestion, you are more then welcome to do your own shopping to find what you need. There are cheaper isolated DC to DC's of chinese make. Try the ferrite first. Transformers don't work with DC, they need a chopping circuit. \$\endgroup\$ – Voltage Spike Jun 3 '19 at 19:05
  • \$\begingroup\$ Will try ferrite, thank you. And yes ofcourse you need an alternating b-field to induce current in the secondary of the transformer, this is why I said chip/transformer pair where the chip controls the switching current on the primary. \$\endgroup\$ – physiii Jun 3 '19 at 22:19
  • \$\begingroup\$ You could always roll your own DC to DC, linear makes some good controllers. Just for the PCB you'd be spending 5 to 7$, the controller will be at least 2$. \$\endgroup\$ – Voltage Spike Jun 3 '19 at 22:31

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