Method and apparatus of providing over-temperature protection for power converters
View Patent ↗The present invention provides a power converter. The power converter includes a transformer, a power switch and a controller. The transformer has a primary winding, a secondary winding and an auxiliary winding. The power switch is coupled to the primary winding of the transformer to regulate the power converter. The controller has an output terminal for generating a driving signal to switch the power switch in response to a switching signal. A thermal resistor is coupled to the output terminal of the controller. The driving signal is adjusted across the thermal resistor during an off-period of the switching signal.
1. A controller for a power converter, comprising:
a switching circuit generating a switching signal;
a driving circuit formed by a high-side transistor and a low-side transistor to generate a driving signal, wherein said driving signal is utilized to regulate said power converter;
an over-temperature protection circuit coupled to said driving circuit, wherein a thermal resistor is coupled to said driving circuit, and said driving signal is adjusted across said thermal resistor during an off-period of said switching signal; and
a signal generator coupled to control said over-temperature protection circuit,
wherein said signal generator is further coupled to said driving circuit for driving said high-side transistor and said low-side transistor.
2. The controller as claimed in claim 1 , wherein said over-temperature protection circuit comprises:
a current-source circuit enabled to provide a current to said thermal resistor for adjusting said driving signal across said thermal resistor in response to a first signal generated by said signal generator during said off-period of said switching signal; and
a comparator comparing a threshold voltage with said driving signal during said off-period of said switching signal to generate an over-temperature signal, wherein when said over-temperature signal is enabled for longer than a delay time, said driving signal will be disabled to turn off said power converter.
3. The controller as claimed in claim 2 , wherein said signal generator comprises:
a saw-tooth circuit, generating a first driving signal and a saw-tooth signal in response to said switching signal, wherein said first driving signal is utilized to drive said high-side transistor;
a first comparison circuit, comparing said saw-tooth signal with a first reference voltage for disabling a second driving signal, wherein said second driving signal is enabled to drive said low-side transistor in response to a falling-edge of said first driving signal;
an enabling circuit, generating said first signal in response to a falling-edge of said second driving signal, wherein said first signal is utilized to enable said over-temperature protection circuit; and
a second comparison circuit, comparing said saw-tooth signal with a second reference voltage for enabling a second signal, wherein said second signal is utilized to disable said over-temperature protection circuit.
4. The controller as claimed in claim 1 , wherein said thermal resistor is a negative temperature coefficient resistor, and a level of said driving signal decreases as an environmental temperature of said power converter increases during said off-period of said switching signal.
5. The controller as claimed in claim 1 further comprising a clamping circuit enabled to couple to said thermal resistor for clamping a maximum magnitude of said driving signal during said off-period of said switching signal.
6. A method of providing over-temperature protection for a power converter, comprising steps of:
providing a switching signal;
generating a driving signal to switch a power switch in response to said switching signal for regulating said power converter;
generating a saw-tooth signal during an off-period of said switching signal;
enabling an over-temperature protection circuit as said saw-tooth signal exceeds a first reference voltage;
adjusting said driving signal in response to an environmental temperature of said power converter;
comparing said driving signal with a threshold voltage to enable a delay signal for generating an over-temperature signal after a delay time; and
disabling said over-temperature protection circuit as said saw-tooth signal exceeds a second reference voltage.
7. The method as claimed in claim 6 , wherein said driving signal is adjusted under a maximum magnitude during said off-period of said switching signal.
8. The method as claimed in claim 7 , wherein said maximum magnitude is used to avoid said power switch being turned on during said off-period of said switching signal.
9. The method as claimed in claim 6 , wherein said over-temperature signal is used for turning off said power converter.
10. The method as claimed in claim 6 , wherein said second reference voltage is greater than said first reference voltage.