| Electronics > Projects, Designs, and Technical Stuff |
| Tone (audio) generator : breaking the ground loop |
| (1/2) > >> |
| ratatax:
Hi, It's me again with my ground problems. I'm designing a sound generator in a grounded/earthed metal enclosure... Everything was fine until I had my first ground issues, when connecting my device to other mains earthed devices. The easy solution would be to get rid of earth, but I can't disconnect it from my chassis since most AC adapters have (harmless but nasty) leakage, like 20V creating a buzz feeling when touching the chassis. So I tried to separate grounds by using an isolated DC/DC converter for my analog/output circuitry. However a problem shows up where the DAC send its signal to the opamp. They both have different ground references (see schematic below). I initially thought the DC blocking capacitor at the DAC output was enough... But I feel it's not. It gets rid of the absolute difference between grounds, but coudn't the DAC be damaged if the potential between the two grounds changes rapidly ? I'm searching for the proper solution to this problem |
| NiHaoMike:
Move the DAC to the other side and use a digital isolator. |
| ratatax:
Possible but costs quite a lot : needs another isolated DC/DC converter (for +3.3V) and a several digital isolator chips that are quite expensive. Is there a simpler way ? |
| MagicSmoker:
No, your scheme won't work because there is no defined return path for current from the DAC (except for parasitic capacitances). Just replace the RC network with a digital isolator to transmit the DAC information digitally. You won't need an additional isolated power supply or much in the way of expense. Silicon Labs makes a whole range of digital isolators for tasks like this and which don't cost too much - maybe $1-$3. |
| SiliconWizard:
--- Quote from: ratatax on November 16, 2019, 04:02:12 pm ---Possible but costs quite a lot : needs another isolated DC/DC converter (for +3.3V) and a several digital isolator chips that are quite expensive. --- End quote --- I would also suggest isolating at the digital level. Why would you need another DC/DC converter? Can you not generate the +3.3V voltage from the existing isolated DC/DC converter with just an additional LDO? The digital isolator ICs are not that expensive (define your budget). You can find them as 4 isolated I/Os. If your DAC is SPI, that should do it? |
| Navigation |
| Message Index |
| Next page |