How do we calculate the value of fusible resistor used in the input side of a capacitive power supply. The supply produces an output voltage of 5V DC. I want to add the fusible resistor (RT1) to protect the diode (1N4007) in the circuit from surge current . The data sheet of 1N4007 specifies that the diode can withstand a peak forward surge current of 30A for a period of 8.3 ms . How do I calculate the value of fusible resistor from this data.Circuit of Capacitive power supply


put on hold as too broad by Marcus Müller, Sparky256, Bimpelrekkie, StainlessSteelRat, John Birckhead Feb 19 at 20:55

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  • \$\begingroup\$ Without being way more specific, this is far too broad to be answered here, I'd say. Can you add more specific requirements? \$\endgroup\$ – Marcus Müller Feb 10 at 13:58
  • \$\begingroup\$ we have zero knowledge of what circuit you protect, but at least we now know against what! That's a great improvement, so please edit your question to include this info, along with a schematic of the circuit – we really have no idea what you're talking about, otherwise. \$\endgroup\$ – Marcus Müller Feb 10 at 15:14
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    \$\begingroup\$ Edited the question and included schematic \$\endgroup\$ – CS Thakur Feb 11 at 7:36
  • \$\begingroup\$ It is a known principle of electronics that a transistor (or diode) will always blow to protect its fuse. You design fuses to protect against a fire or electrocution hazard and additional damage, the fuse should be dimensioned to your expected operation range, not the maximum range of a specific component. \$\endgroup\$ – Edgar Brown Feb 13 at 16:41
  • \$\begingroup\$ Maximum current of the diode is meaningless. You need to specify your requirements. Specifically, current required by load and type of load. Follow the instructions at: Everything for capacitive power supplies from a single source . \$\endgroup\$ – StainlessSteelRat Feb 18 at 16:21