I am currently in the process of designing a Tesla Coil and am stuck at the Full Bridge Rectifier and have some reservations about what I propose to do. Currently, the circuit looks like this:FBR

I decided on adding in a 22kOhm bleed resistor for when the unit is turned off, and thought why not add in an LED to show that the circuit is on. The problem I have is when I throw it into a simulator, it shows me that the cathode on every half cycle will see -170V because it is not earth grounded.

So basically I'd like to know if am I wrong in thinking that the cathode will see this -170V and then reverse bias and blow the diode, and if not then will putting an appropriately rated diode in front of it fix the issue?


  • \$\begingroup\$ What do you have in the simulator? That diode is past the rectifier. The rectifier rectifies, so the LED only sees DC. \$\endgroup\$
    – uint128_t
    Jan 11 '16 at 0:30
  • \$\begingroup\$ Also, I don't know where you got that circuit, but keep in mind that because of the inductor, you are not going to necessarily get 170VDC out, it will be highly dependent on the load. \$\endgroup\$
    – uint128_t
    Jan 11 '16 at 0:33
  • \$\begingroup\$ I have exactly what is shown in the schematic, 120VAC 60Hz in. I think Spehro's answer helped to explain what was going on more with the SPICE ground referencing and that there should not be a problem. As for the inductor, I am just using it together with the capacitor for a cleaner output. Thanks for the input, I need to ensure that the inductor will not alter my resonant frequency \$\endgroup\$
    – Poozy101
    Jan 11 '16 at 1:11

It will not see -170V. It will have a relatively constant current from the positive bus as you probably initially expected. The problem is phantom- to do with your simulation.

Suggest you put the ground in your simulation on the minus rail (and let the incoming AC supply float- that should work- if it doesn't, then add some very high value resistors to ground). I don't see a ground in the schematic- simulations should have a reference ground specified. This is not earth ground, it's just a reference point for SPICE to use for voltages.

The LED is still effectively connected to the mains and it could lead to a shock hazard if it's not appropriately insulated. Also if the resistor or LED were to go open the light would go off, despite the capacitor being fully charged. I'll let you evaluate the safety concerns- there's no enough information to make conservative suggestions there.

  • 1
    \$\begingroup\$ Thanks. Just thought it was something nice to have but I definitely see the issue where it could give me a false sense of security. \$\endgroup\$
    – Poozy101
    Jan 11 '16 at 1:20

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