I am having a trouble with a mains rectifier. Simplified schematic:


simulate this circuit – Schematic created using CircuitLab

Only problem I have is that R1 sometime explodes during circuit power-up. It happens when C1 is discharged, and there is a 310v peak in input.

Due to resistive nature of capacitor charge, same amount of energy as stored in capacitor (~50mJ) should be dissipated somwhere else

The simple solution is to whack a giant 2W resistor, capable of withstanding high energy pulses, but I am having a limited space. Also, if I remove a resistor, then fuse will blow up

I would like to use a few 0805 in a row, but they explode sometimes.

I assume that this is due to the fact that metal film is extremely thin and not capable of holding a significant amount of energy. Carbon film should be better.

How this problem is solved in modern PSU? Is there some special resistors available?

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    \$\begingroup\$ Metal film resistor only has a VERY THIN resistive element. Use a bulk carbon-composition resistor. \$\endgroup\$ – analogsystemsrf Apr 13 '19 at 20:06
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    \$\begingroup\$ The "special resistors" you mention are called inrush current limiters, or ICLs. They're made of a material that lowers in resistivity when it heats up, so that its resistance falls after it limits the inrush current. They're also designed to be able to actually handle the inrush current, too. \$\endgroup\$ – Hearth Apr 13 '19 at 20:17

Typical solution to limit inrush current is to use NTC thermistors instead of plain resistors, See this TDK publication for example.

enter image description here

Here is an application note on how to properly select an NTC resistor for an application.

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  • \$\begingroup\$ Are NTC some big volumetric-type resistor, with all that volume to absorb the transient heat? \$\endgroup\$ – analogsystemsrf Apr 14 '19 at 2:46
  • \$\begingroup\$ Anatherm have some very small NTC surge suppressors: ametherm.com/datasheets/sl0322101 These are only 3mm, but they will (as all NTC surge suppressors) run hot at their rated current. In this application there probably isn't enough heat generated to get them down much less than 50 Ohms or so, but that may well be suitable for the OP. \$\endgroup\$ – Jack Creasey Apr 14 '19 at 22:03
  • \$\begingroup\$ @JackCreasey, there is a whole spectrum of such devices, for every power and current rating and initial resistance at 25 deg.C \$\endgroup\$ – Ale..chenski Apr 14 '19 at 22:08

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