Bias circuit for a switching power supply
View Patent ↗A bias circuit for a switching power supply includes a rectifier that is connected to an AC power source and outputs a full wave rectified voltage Vs; a voltage divider, a diode, a first transistor, and a second transistor connected in parallel between Vs and ground; a capacitor connected between a first terminal of the second transistor and ground; and a node between the capacitor and the first terminal of the second transistor providing an output bias voltage Vcc from the bias circuit. A voltage from the voltage divider is provided to a gate of the first transistor, and the diode and a first terminal of the first transistor are connected to a gate of the second transistor.
1. A bias circuit for a switching power supply, comprising:
a rectifier that is connected to an AC power source and outputs a full wave rectified voltage Vs;
a voltage divider, a diode, a first transistor, and a second transistor connected in parallel between Vs and a ground, wherein a voltage from the voltage divider is provided to a gate of the first transistor, and wherein the diode and a first terminal of the first transistor are connected to a gate of the second transistor;
a capacitor connected between a first terminal of the second transistor and the ground; and
a node between the capacitor and the first terminal of the second transistor providing an output bias voltage Vcc from the bias circuit.
2. The circuit of claim 1 , wherein the voltage divider comprises two resistors connected in series.
3. The circuit of claim 1 , further comprising a resistor connecting both the diode and the first terminal of the first transistor to Vs.
4. A bias circuit for a switching power supply, comprising:
a rectifier that is connected to an AC power source and outputs a full wave rectified voltage Vs;
a voltage divider connected between Vs and a ground;
a diode having a first terminal connected to Vs and a second terminal connected to the ground;
a first transistor having a first terminal connected to Vs and a second terminal connected to the ground;
a second transistor having a first terminal connected to Vs and a second terminal connected to a node, wherein a divided voltage from the voltage divider is provided to a gate of the first transistor, and wherein the first terminal of the diode and the first terminal of the first transistor are connected to a gate of the second transistor; and
a capacitor connected between the node and the ground, the node outputting a voltage Vcc from the bias circuit.