A lot of switch-mode power supplies make use of kick-start circuits to initialize their offline process. These circuits might be simple resistors, such as International Rectifiers IRIS4015, or other complex arrangements build with bipolar transistors or MOSFETs . These transistors supply the primary current for the flyback or PFC (power-factor-correction) IC. When such a power supply starts working in a common mode, a supply voltage from a winding keeps supplying the PFC IC, hence reducing power consumption of the kick-start circuitry.

Such scheme condense but do not eliminate the power utilization of the kick-start circuitry, since the dynamic component is usually a high power bipolar transistor or high voltage enhancement mode MOSFET. These transistors base or gate needs forward biasing with respect to the emitter or the basis for usual operation. Therefore, a power failure always shown in the circuits that maintains the transistors in the off state. Unfortunately, engineers give too little attention to depletion method MOSFETs, which require no forward-biasing for usual operation and, In addition, entail gate potentials below the source. These valuable property of reduction mode MOSFETs outfit them for a position in no-loss kick-start circuit for power supply.

Refer: http://www.edn.com/article/CA6515351.html