I want to connected an LED at the output of 500V DC. This DC power supply is made by 3phase DC rectifier and is floating.

I would like to have a display on the front panel of the supply which will show the supply is healthy.

I know that it could be done by voltage divider circuit and connecting LED across the one of the resisters. I want to know whether it is safe as per the safety point of view because in this case I need to bring connection to the front panel and if a fault occurs with chassis (grounded,) it would put high voltage on the chassis.

  • 1
    \$\begingroup\$ ..chaises.. That's French for "chairs", I think you mean "chassis". Anything high voltage can be unsafe so take care. I'd start by finding an LED which can work at a current that is as low as possible. Even at 1 mA (which might be enough for some efficient LEDs) you would dissipate 1 mA * 500 V = 0.5 W already. \$\endgroup\$ Apr 2, 2019 at 12:12
  • \$\begingroup\$ yes it is chassis.... voltage can be reduced by voltage divider circuit ... but are they safe? \$\endgroup\$
    – user133896
    Apr 2, 2019 at 12:23
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    \$\begingroup\$ is this kind of practice is safe for use? It is not what you do but how it is done. I can take a safe circuit and then use it under wet conditions => unsafe. If you make sure the LED circuit is properly isolated then it can be safe. You need to learn how to work safely with high voltage. So learn about creeping distance, clearance etc... There is no "just do this and it is safe". Safety isn't that simple. Maybe you need some help from a more experienced engineer. \$\endgroup\$ Apr 2, 2019 at 12:24
  • \$\begingroup\$ Is the supply bonded to earth ground? is there any surge suppression? Do you know how to choose resistor divider power and voltage ratings? \$\endgroup\$ Apr 2, 2019 at 12:49
  • \$\begingroup\$ you can use an optocoupler \$\endgroup\$
    – yogece
    Apr 2, 2019 at 13:56

2 Answers 2


You can use an efficient LED that operates from (say) 3mA and then your series resistor would dissipate 1.5W so you could use a suitable rated resistor or resistors (rated voltage as well as power dissipation). You could consider using two (or more) resistors in series.

To get a safe circuit you can mount the resistors and LED in close proximity to the HV supply, and use a flexible light pipe (there are others made by Bivar, VCC and Industrial Fiberoptics- with fiber lengths up to at least ~12"/300mm) to bring the light to the panel (photo from Digikey):

enter image description here


You wouldn't normally feed an LED with a voltage divider. It's more efficient to just put a resistor in series with the LED, and leave out the one in parallel with it.

But that may not be what you need if you want to indicate that the voltage is approximately correct.

But with a 500V supply, you will find you get about 3V across the LED and 497V across the resistor (or one of the resistors), which could lead to a very hot resistor.

The safety all depends on how you mount the LED to the chassis. If in doubt, use a light pipe to keep them apart.


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