I am designing a circuit to control LED drivers. The main characteristics are the following:

  1. The circuit is powered through the electrical network (230 VAC)
  2. It has three types of dimming outputs: 0-10V, PWM and DALI.
  3. In addition, the circuit has a mechanical relay to control the AC supply for the LED driver.

I have a prototype that works acceptably well but I have questions about the isolation. I have read in the forum about isolation (link1;link2) but I can not solve my question. I had thought of using two isolated GNDs and two isolated converters: one to convert 230 VAC to 12 VDC and another from 12 VDC to 12 VDC to obtain an isolated power supply for subcircuits: DALI, PWM and 0-10V. A simplified schematic is shown below.

I have many questions, but mainly these two:

  1. Is the insulation correct? If not, what should be corrected?
  2. Is isolation unnecessary or is it only necessary to isolated a part of the schematic?


simulate this circuit – Schematic created using CircuitLab



You need to isolate between the mains and the low voltage side, the LV being the 'human touchable' part. So an isolated AC:DC will do, make sure you have sufficent isolation between them (approx 2kV depending upon the application). Looking at the LV side of your scheme I don't believe you need a second isolated supply to other DC circuits.

  • \$\begingroup\$ Thanks. So, if I do not use the second isolated supply, is not it necessary to use the optocouplers, too? \$\endgroup\$
    – FranMartin
    Mar 3 '18 at 19:53
  • \$\begingroup\$ You are isolated so don't need the opto, unless they are doing level shifting ? \$\endgroup\$ Mar 3 '18 at 20:08
  • \$\begingroup\$ I use the optocouplers because I do not know how the LED driver is designed and it is powered by AC. What if the LED driver was not properly isolated? Neither would it be necessary to use an optocoupler for the mechanical relay? \$\endgroup\$
    – FranMartin
    Mar 3 '18 at 20:20

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