Dc and inductor

[Manuv16589]

Hi people,
Everybody knows that there should be change of current for inductor to charge and store energy. But dc current never changes. No change of current then no magnetic flux. then how can flux linking with coil changes and inductor store energy with dc voltage?

 

[RCinFLA]

DC current will build a static field in an inductor. If it is iron based core it will move the magnetic S curve of core flux density to one side eating up part of the available non-saturated core range.

For a use like a switching power supply flyback, buck, or boost converter there will be an average DC bias on the core. This must be taken into account on sizing the core so it doesn't get into saturation with the AC current riding on top of the DC average. When you start to saturate the core the inductance value drops.

For a case like a push-pull primary switching power supply (like found in most portable AC inverters), if each side switching device (MOSFET) does not balance out there can be a DC bias developed in the core limiting its power transferring capability. If this DC bias moves the core saturation curve enough to one side the AC primary currents will drive the core into saturation causing a current spike in primary side devices making them overheat or burn out.

 

[Ratchit]

Manuv16589,

Everybody knows that there should be change of current for inductor to charge and store energy.

Everybody but me and others, that is. As long as current exists in a inductor, even constant current, a magnetic field which contains stored energy will exist. To change that amount of stored energy, one has to change the current.

But dc current never changes. No change of current then no magnetic flux.

Yes, DC current does not change by definition. But, magnetic flux exists for any current, even constant current.

then how can flux linking with coil changes and inductor store energy with dc voltage?

A changing flux induces a voltage in a coil. If the coil is open, then no current can exist and no energy is stored. The flux can be changed by moving the coil in a magnetic field, or changing the current within the coil.

Ratch