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I have found a basic design for a SPD and I would like to simplify it. However, I have little experience designing SPD circuits.

This is my parallel type SPD circuit with embeded LED indicator:Circuit

In this case:

  • Can I remove MOV3 and TCO F3 between N and E? Will this still comply with IEC61643-11/UL 1449?
  • Do I have to add a normal fuse(5A) at the input side of parallel type ? I will add it for serial type but not sure for parallel.
  • I will make a direct contact between TCO and MOV on my PCB. This
    system will be inside in epoxy. How will this effect the thermal performace? (I know, this is an experimental question)
  • I've chosen a 10kA surge MOV for 10kA protection level. Should I overrate the MOV as you would overrate a fuse i.e. using a 5A fuse for 3A normal current?
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    \$\begingroup\$ SPD ? Is that the Social Democratic Party of Germany or Symphysis pubis dysfunction ? But looking at the schematic you probably mean some sort of surge protector. It does not hurt to write SPD in full once so that its clear what you mean. I would add a small signal diode (1N4148) in (anti-) parallel with the LED so that the LED will never suffer more than 0.6 V reverse voltage. LEDs don't like reverse voltages. Yes the 1N4007 will block it also but there will always be some leakage. \$\endgroup\$ – Bimpelrekkie Feb 6 at 8:21
  • \$\begingroup\$ Please take time to review spelling, punctuation, grammar, and conciseness. Asking a well-formatted and structured question is the key to getting a quality answer. \$\endgroup\$ – Andy West Feb 6 at 8:31
  • \$\begingroup\$ SPD is defined in the title. \$\endgroup\$ – AnalogKid Feb 6 at 13:41
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Generally surges couple well with capacitive transformers so that you don’t use resistor power dividers. This improves the protection after the 1st surge when the fuse blows for the MOV drawing excessive current. (Research Offline Power Supplies)

There are many solutions but the best design has all the specs tolerances on input voltage Power lightning transient test levels and output V,I,P, then current limiting without fused MOV’s may be avoided.

The ideal is to divide the voltage with film caps then raise the impedance (and attenuate HF surge impulses ) into a ferrite L to rectify with a full wave diode bridge to get 2f instead of 1/2 wave f flicker then into a cap shunt to reduce the ripple. This way fuses are optional using a series R as a fuse if you expect 50% overvoltage in your region but even this can be protected.

See examples of this here. E.g. 330nF film to 100uF e-cap is a 3300:1 voltage divider for AC It is not quite linear with the diode bridge effects, so simulate the link above and optimize your inputs and outputs with extra LEDs up to whatever Vdc you like.

Your 30kohm 5W +5W to LED of 15 Ohms is 2000:1 voltage divider.

One can optimize the design for 20Vdc out with a string of LEDs at 20mA by changing component values in Falstad with 350Vp 50Hz or whatever you like. This way you can avoid two 5W resistors.

I chose to offer a better design instead critiquing a worse design. If you understand something good. if you want more info ask for what you need.

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