Circuits and methods for constant output current in a flyback converter

摘要

Flyback converters are disclosed herein. An embodiment of a flyback converter includes a transformer having a primary side and a secondary side. A switch is connected to the primary side of the transformer, wherein the switch controls the current in the primary side of the transformer. A resistance is connected between the switch and a common node. The converter also includes a comparator having a first input and a second, the first input being connected between the switch and the resistor. Driver logic controls the state of the switch, wherein the output of the comparator is coupled to the driver logic. A voltage source is connected to the second input of the comparator. An error amplifier compares the voltage at the second input of the comparator to an adjustment voltage, the output of the error amplifier is coupled to the driver logic.

主权项

1. A flyback converter comprising:
a transformer having a primary side and a secondary side, wherein the primary side is connectable to a voltage source; a first switch connected to the primary side of the transformer, the first switch controlling the current in the primary side of the transformer; a current sensor resistance connected between the first switch and a common node; a comparator having a first input and a second, the first input being connected between the switch and the current sensor; driver logic that controls the state of the first switch, wherein the output of the comparator is coupled to the driver logic; a first voltage source being connected to the second input of the comparator; an error amplifier that is coupled to the voltage at the inverting input of the comparator to an adjustment voltage, the output of the error amplifier being coupled to the driver logic, wherein the adjustment voltage compensates for a propagation delay time between the time the controller generates a control signal for the switch and the time in which current in the primary side of the transformer ceases to flow, wherein output from the converter is regulated to achieve high current accuracy, wherein an open loop adjustment voltage is generated by a circuit comprising: a voltage source referenced to the common node; a second switch connected between the voltage source and a node; and a third switch connected between the node and the common node; wherein the node is coupled to the error amplifier.