PRIMARY SIDE CONTROL FOR SWITCH MODE POWER SUPPLIES

Techniques are disclosed for providing a stable output voltage in switching mode power supplies (SMPS). An SMPS includes a switching converter for powering a load, a passive startup circuit for initially providing an internal voltage supply for powering switching electronics when the mains is turned on, and a feedback circuit providing the internal voltage supply once the switching converter starts switching. The SMPS also includes a decoupling circuit that decouples or otherwise isolates the gain of the passive startup circuit from the feedback circuit, so as to prevent false dynamic overvoltage protection triggers. The decoupling circuit is implemented, for instance, with the addition of two or three passive components, such as a diode and a capacitor, or a diode, a capacitor, and a resistor. Preventing false triggering of the dynamic overvoltage protection in turn provides a more stable output voltage from the SMPS.