A novel high voltage start-up current source for SMPS

A novel high voltage start-up current source to provide start-up current for integrated circuits in a switched mode power supply (SMPS) is presented. The current source contains a VDMOS transistor to sustain high voltage. The gate of the VDMOS transistor is biased at a certain voltage by a floating p-island, to provide start-up current. A NMOS transistor is used to turn on and off the current source. Experimental results indicate the high voltage start-up current source is able to start and restart as designed. The current source draws no current from the line after turned off. The proposed structure is believed to be more energy saving and cost-effective compared with other solutions.