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

An electronic circuit, comprising:

• an input terminal for receiving a feedback signal;
• an output terminal for outputting an output signal;
• a power supply terminal for receiving a supply voltage;
• a first circuit coupled to the power supply terminal and configured to trigger the electronic circuit from a first operation mode to a second operation mode when the supply voltage exceeds a first threshold voltage;
• a feedback circuit coupled to the first circuit for maintaining a positive feedback loop;
• and
• a second circuit coupled to the first circuit and the feedback circuit, and configured to trigger the electronic circuit to switch from the second operation mode to the first operation mode when the supply voltage is below a second threshold voltage.

A switching-mode power supply (SMPS) comprising:

• a controller for controlling the switching-mode power supply, wherein a startup circuit for the controller includes:
• a first voltage detector configured to trigger the switching-mode power supply from a first operation mode to a second operation mode when an input supply voltage exceeds a first threshold voltage, a current consumption in the first voltage detector in the first operation mode being determined by a reverse leakage current of a diode;
• a feedback circuit coupled to the first voltage detector for maintaining a positive feedback loop;
• 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 second operation mode to the first operation mode when the input supply voltage is below a second threshold voltage.