Proactively operational over-voltage protection circuit
Systems and methods are disclosed for providing over-voltage protection for power converters. An over-voltage protection loop includes an error amplifier that maintains an external reference voltage within a highly precise range that can be used to provide a highly precise output voltage from the over-voltage protection loop. The over-voltage protection loop may also include feedback impedance that delays the output of the over-voltage protection loop. The delay may prevent the over-voltage protection loop from being engaged due to voltage transients output from a main servo loop circuit that provides a nominal output voltage under normal operation, thus allowing the threshold voltage and output voltage of the over-voltage protection loop to be set close to the nominal output voltage of the main servo loop circuit.
1. An over-voltage protection loop for a transformer, the transformer to include a primary clock and feedback control circuit, a main servo loop circuit, and the over-voltage protection loop, the over-voltage protection loop comprising:
an over-voltage winding magnetically coupled to a magnetic core, the over-voltage winding which, in response to a voltage on a primary winding in the primary clock and feedback control circuit, is activated to provide a secondary side voltage supply;
an error amplifier electrically coupled to a first node and a second node, wherein the error amplifier uses the secondary side voltage supply to maintain a voltage on the second node according to an internal reference voltage;
a feedback impedance electrically coupled between the first node and the second node, the feedback impedance which introduces a time delay to provide feedback from the first node to the second node; and
an output voltage sensing circuit electrically coupled to at least the second node and a output node, the output voltage sensing circuit which controls an output voltage at the output node based on the voltage at the second node,
wherein the over-voltage protection loop provides the output voltage for the transformer under an error condition.
2. The over-voltage protection loop of claim 1 wherein the feedback impedance prevents the over-voltage protection loop from interfering with an output from the main servo loop circuit for a period of time, wherein the period of time is larger than a dynamic response time when the main servo loop circuit outputs a voltage transient.
3. The over-voltage protection loop of claim 2 wherein the output voltage provided by the over-voltage protection loop is within 5% of a nominal voltage output by the main servo loop circuit.
4. The over-voltage protection loop of claim 1 wherein a start-up time for the over-voltage protection loop is faster relative to a start-up time for the main servo loop.
5. The over-voltage protection loop of claim 1 wherein the error amplifier comprises a shunt regulator.
6. The over-voltage protection loop of claim 5 wherein the output voltage sensing circuit comprises a first resistor and a second resistor, the first resistor having a first resistance and coupled to the second node and the output node, and the second resistor having a second resistance and coupled to the second node and ground, wherein the first resistance and the second resistance are based at least in part on a value at which the error amplifier maintains the voltage of the second node.
7. The over-voltage protection loop of claim 1 wherein the error amplifier comprises an op amp.
8. The over-voltage protection loop of claim 1 wherein the feedback impedance comprises a capacitor.
9. The over-voltage protection loop of claim 1 wherein the magnetic core is magnetically coupled to the main servo loop circuit.
10. The over-voltage protection loop of claim 1 , wherein the magnetic core is a first magnetic core that is magnetically coupled to the over-voltage protection loop and the primary clock and feedback control circuit, and wherein the main servo loop is magnetically coupled to a second magnetic core.