Monitoring smps power switch voltage
AssigneeTexas Instruments Incorporated
InventorsSalvatore GIOMBANCO, Filippo MARINO
Life of this patent
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Abstract
A switch-mode power supply includes a power transistor, a transformer, and detection circuitry. The transformer includes a primary winding that is coupled to a drain terminal of the power transistor. The detection circuitry is coupled to a source terminal of the power transistor. The detection circuitry is operable to monitor signal present on the drain terminal via parasitic drain-source capacitance of the power transistor while the power transistor is switched off, and to detect demagnetization of a secondary winding of the transformer via the monitored signal.
Claims20
A switch-mode power supply, comprising:
- a power transistor with a drain-source capacitance (Cds);
- a transformer comprising a primary winding coupled to a drain terminal of the power transistor;
- and
- conversion circuitry coupled to a source terminal of the power transistor, operable when the power transistor is switched off:
- to convert a Cds current signal from the Cds to a first derivative voltage signal corresponding to a first order derivative of a voltage on the drain terminal, and
- to convert the first derivative voltage signal to a second derivative voltage signal corresponding to a second order derivative of the voltage on the drain terminal;
- window comparison circuitry including first and second comparators coupled to receive the second derivative voltage signal, and to generate respective first and second comparison signals;
- and
- detection circuitry to detect demagnetization of a secondary winding of the transformer via the first and second comparison signals.
A method for controlling a switch-mode power supply, comprising:
- driving a primary winding of a transformer coupled to a drain terminal of a power transistor with a drain-source capacitance (Cds);
- when the power transistor is switched off:
- converting a Cds current signal from the Cds to a first derivative voltage signal corresponding to a first order derivative of a voltage on the drain terminal;
- converting the first derivative voltage signal to a second derivative voltage signal corresponding to a second order derivative of the voltage on the drain terminal;
- using first and second comparators to provide a window comparison based in part on the second derivative voltage signal, generating respective first and second comparison signals
- detecting demagnetization of a secondary winding of the transformer via the first and second comparison signals;
- generating a demagnetization signal indicative of an end of demagnetization time based on the detected demagnetization;
- and
- providing the demagnetization signal indicative of the end of demagnetization time to a controller to control activation of the power transistor.
A switch-mode power supply converter for use in a switch-mode power supply including an energy storage transformer, comprising:
- a power transistor to drive a primary winding of the transformer coupled to a drain terminal of the power transistor, the power transistor having a drain-source capacitance (Cds);
- and
- conversion circuitry coupled to a source terminal of the power transistor, operable when the power transistor is switched off:
- to convert a Cds current signal from the Cds to a first derivative voltage signal corresponding to a first order derivative of a voltage on the drain terminal, and
- to convert the first derivative voltage signal to a second derivative voltage signal corresponding to a second order derivative of the voltage on the drain terminal;
- window comparison circuitry including first and second comparators coupled to receive the second derivative voltage signal, and to generate respective first and second comparison signals;
- and
- detection circuitry to detect, via the first and second comparison signals
- demagnetization of a secondary winding of the transformer;
- and
- a minimum voltage on the drain terminal.
Dependencies are inferred from the claim text.