SPMS | Page 16 of 32 |
Figure:
In the
zInterval 1: t0 < t < t1primary stroke At the beginning of the first interval,the MOSFET is switched ‘on’ and energy is storedin the primary inductance (magnetization). At the end, the MOSFETis switched ‘off’ and the second interval starts.
zInterval 2:t1 < t < t2 commutation time In thesecond interval, the drain voltage will rise from almost zero to V IN +n•(V OUT +V F ). V F is the forward voltagedrop of de diode that will be omitted from the equations from nowon. The current will change its positive derivative, correspondingto V IN /L P , to a negative derivative, correspondingto
OUT /L P .
zInterval 3:t2 < t < t3 secondary stroke In thethird interval, the stored energy is transferred to the output,so the diode starts to conduct and the inductive current I L will decrease. In otherwords, the transformer will be demagnetized. When the inductivecurrent has become zero the next interval begins.
7/8/2004
