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Current Limiting Elements & MOV for SMPS

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SACHIN C

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Hi All,

Can any one share the design selection , calculation for current limiting element like Resistor or NTC & MOV required for SMPS?

Which current limiting element to be selected as SMPS input current is low approximately 200mA for 16W?

Thanks & Regards,
Sachin C:thinker:
 

There is a type of LC filter which smooths the supply current waveform, creating a steady flow. Ordinarily it would be sawtooth-like, with greater ripple.

This type of LC filter does not reduce DC during normal running conditions, but it could have the effect of reducing surge on power-up.
 

Re: Current Limiting Elements & MOV for SMPS

NTC is selected based on the energy to be charged i.e. bulk cap to be charged say 0.5*C*Vdc*Vdc. and the minimum resistance of the NTC can be decided as Vpeak/Ilimit. Here I limit is the inrush current expected in SMPS.
Rminimum thus found is the resistance of the NTC at 25 deg C with calculated Joules.

Based on the input energy of the leakage inductance W = 0.5*L*I*I, the rated Energy of the MOV is selected more than the calculated and the voltage rating being equal or more than the operating but yes less then the short term rating for the device to be protected.

- - - Updated - - -

First select your inrush current to be limited i.e. 200mA is rated current, say 3 times more is surge current, 600mA , then your input volts/surge current will provide you with the minimum resistance of the NTC to be selected. Next select the energy based on the capacitance to be charged in the input,so select NTC of the appropriate diameter which is more then the energy calculated as shown in the previous post. I am sure this will work.

Mukesh
 
Re: Current Limiting Elements & MOV for SMPS

How to decide whether to go with NTC or Resistor (If SMPS is low wattage <20W)?

As NTC is more costly then Resistor.If Resistor to be selected what shall be the material?

Thanks,
Sachin C:thinker:

- - - Updated - - -

How to decide whether to go with NTC or Resistor (If SMPS is low wattage <20W)?

As NTC is more costly then Resistor.If Resistor to be selected what shall be the material?

Thanks,
Sachin C:thinker:
 

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