Patent ID: 8885361

Claim:
A low power switch mode power supply comprising a primary oscillating circuit, which primary oscillating circuit is connected to a DC power source, which primary oscillating circuit is connected to a first primary coil of a transformer, which transformer comprises at least a first secondary coil, which secondary coil is connected through a rectifier to an output circuit, which output circuit comprises at least a first capacitor for forming a DC output voltage, the switch mode power supply further comprises a feedback circuit, which feedback circuit uses the actual output voltage for control of a primary switching circuit, characterized in that the feedback circuit comprises an opto coupler, which input LED of the opto coupler is connected through a current and voltage limiting circuit to the output voltage, which low power switch mode power supply comprises a first current loop in form of a voltage divider, which voltage divider is connected to the DC power source through at least one resistor, which first resistor is connected to a first terminal of a first transistor, which voltage divider is connected to a first terminal of a second transistor, having a second terminal and a third terminal connected to ground, which low power switch mode power supply further comprises a second current loop in form of the first primary coil of the transformer which a first end is connected to the DC power source and a second end of the first primary coil is connected to a second terminal of the first transistor, which second current loop further comprises a second resistor, which second resistor is connected to ground, which a third terminal of the first transistor is further connected to a first terminal of an output transistor of the opto coupler, which first terminal of the output transistor of the opto coupler is further connected to the first terminal of the second transistor, and a second terminal of the output transistor of the opto coupler is further connected to ground.