Isolation and safety: when handling high voltage
Isolation separates high-voltage circuits from the low-voltage circuits people touch. Isolation distances, isolated gate drivers and safe working.
Why isolate
- Protecting people: so mains or a high-voltage battery never reaches USB, the debugger or a hand
- Separating noise and grounds: so the large currents of an inverter do not disturb signal ground
- Potential difference: driving places whose reference potential keeps changing, such as a high-side gate
Isolation devices
| Device | Use |
|---|---|
| Optocoupler | Digital signals, slow |
| Digital isolator (capacitive / magnetic coupling) | Fast SPI, UART, CAN |
| Isolated gate driver | MOSFETs/IGBTs in high-voltage inverters |
| Isolated DC-DC | Power for the isolated side |
| Isolation amplifier, isolated ADC | Measuring current and voltage on the high-voltage side |
PCB isolation distances
- Creepage: distance measured along the surface. Important because dust and moisture cause surface leakage
- Clearance: straight-line distance through air
They are set by standards (IEC 62368, IEC 60664) according to voltage and pollution degree. If they fall short, cut a slot in the PCB to lengthen the creepage.
Safe working
- Voltage remains on the DC-link capacitor after power is off. Confirm discharge before working
- Do not clip an oscilloscope ground to a high-voltage node → use a differential probe
- Isolation transformer, one-handed working, protective equipment