Method and apparatus of low current startup circuit for switching mode power supplies

A switching-mode controller, comprising:

• an input terminal for receiving a feedback signal;
• an output terminal for outputting a control signal;
• a power supply terminal for receiving a supply voltage;
• and
• a startup circuit coupled to the power supply terminal and including:
• a first voltage detector configured to trigger the switching-mode power supply from a startup mode to a normal operation mode when an input supply voltage exceeds a first threshold voltage, a current consumption in the first voltage detector in the startup mode being determined by a reverse leakage current of a diode;
• a feedback circuit coupled to the first voltage detector and being capable of maintaining a positive feedback loop with a current consumption of no more than a microampere;
• and
• a second voltage detector coupled to the first voltage detector and the feedback circuit, and configured to trigger the switching-mode power supply to switch from the normal operation mode to the startup mode when the input supply voltage is below a second threshold voltage.

A switching-mode power supply (SMPS) comprising:

• a controller for controlling the switching-mode power supply, the controller having a startup circuit, the startup circuit including:
• a first voltage detector configured to trigger the switching-mode power supply from a startup mode to a normal operation mode when an input supply voltage exceeds a first threshold voltage, a current consumption in the first voltage detector in the startup mode being determined by a reverse leakage current of a diode;
• a feedback circuit coupled to the first voltage detector and being capable of maintaining a positive feedback loop with a current consumption of no more than a microampere;
• and
• a second voltage detector coupled to the first voltage detector and the feedback circuit, and configured to trigger the switching-mode power supply to switch from the normal operation mode to the startup mode when the input supply voltage is below a second threshold voltage.