Over-voltage protection circuit for a switched mode power supply
View Patent ↗The switched mode power supply comprises an inductor, a switching transistor, a controller circuit coupled to the switching transistor, a rectifying means and a feedback regulation loop for providing a stabilised output voltage. It comprises further a protection circuit coupled to an output or input of a comparator of the controller circuit for providing an overvoltage protection in case of a failure of the regulation loop. The protection circuit comprises in particular an integrating circuit and a comparating circuit. In a preferred embodiment, an output of the protection circuit is coupled to a sense input of the controller circuit, for switching off the controller circuit immediately in case of a failure. In another aspect of the invention, the protection circuit comprises further a second comparator coupled to the first comparating circuit for the surveillance of the input voltage of the switched mode power supply, and for the detection of a short circuit of the inductor or the rectifying means.
1. Switched mode power supply comprising:
an inductor coupled to an input voltage,
a switching transistor coupled with a current input to said inductor and coupled with a current output via a sense resistor to a reference potential,
rectifying means coupled to said inductor for providing a rectified output voltage,
an integrated controller circuit comprising,
a driver circuit being coupled to a control input of said switching transistor
a comparator with a feedback input for a regulation of said output voltage,
a voltage regulator for providing a reference voltage for said comparator,
a first over-voltage protection circuit coupled with an input intemally to said comparator for switching off said driver circuit in case of a low load condition, and
a sense input coupled to said sense resistor,
a feedback loop coupling said rectified output voltage to said feedback input, and
a second over-voltage protection circuit comprising a second comparing circuit, which comprises a first input, to which an output of a first comparing circuit and a short circuit information provided by said inductor is coupled, the output of said second comparing circuit being coupled to said sense input for switching off the controller circuit in case of an interruption of said feedback loop.
2. The switched mode power supply of claim 1 , wherein said second protection circuit comprises a first integrating circuit coupled to said comparator output and said first comparing circuit is coupled to said first integrating circuit for controlling a threshold level.
3. The switched mode power supply of claim 1 , wherein to said first input of said second comparing circuit an information signal about the average level of the input voltage is coupled.
4. The switched mode power supply of claim 1 , wherein said switching transistor is coupled with a current input to an output terminal of said inductor and with a current output to a reference potential, and wherein said rectifying means is coupled to said output terminal of said inductor for operating in a step-up converter mode.
5. The switched mode power supply of claim 1 , wherein an input of said inductor is coupled to a rectified mains voltage for operating as a power factor correction pre-converter.
6. The switched mode power supply of claim 1 , wherein said second protection circuit is integrated into said integrated controller circuit.
7. Switched mode power supply, comprising:
an inductor coupled to an input voltage,
a switching transistor coupled to said inductor,
rectifying means coupled to said inductor for providing a rectified output voltage,
an integrated controller circuit comprising a driver circuit being coupled to a control input of said switching transistor, a comparator with a feedback input for a regulation of said output voltage, and a first integrated over-voltage protection circuit coupled intemally to said comparator for switching off said driver circuit in case of a low load condition,
a feedback loop coupling said output voltage to said feedback input, and
a protection circuit having a second over-voltage protection circuit comprising,
a first comparing circuit coupled with an input to an output or input of said comparator for providing an over-voltage protection of said output voltage in case of a failure of said feedback loop, and
a second comparing circuit with a first input, to which an output of said first comparing circuit is coupled, and with an output, which is coupled to a sense input of said controller circuit for switching off said controller circuit,
wherein to said first input of said second comparing circuit in addition an information signal about an average level of said input voltage is coupled.
8. The switched mode power supply of claim 7 , wherein said first integrating circuit is coupled with an input to said comparator output and wherein said first comparing circuit is coupled with an input to said first integrating circuit for controlling a threshold level.
9. The switched mode power supply of claim 7 , wherein to said first input of said second comparing said short circuit information provided by said inductor is coupled.
10. The switched mode power supply of claim 7 , wherein said switching transistor is coupled with a current input to an output terminal of said inductor and with a current output to a reference potential, and wherein said rectifying means is coupled to said output terminal of said inductor for operating in a step-up converter mode.
11. The switched mode power supply of claim 7 , wherein an input of said inductor is coupled to a rectified mains voltage for operating as a power factor correction pre-converter.
12. The switched mode power supply of claim 7 , wherein said second protection circuit is integrated into said integrated controller circuit.
13. The switched mode power supply of claim 7 , wherein said protection circuit is coupled further with an auxiliary winding of said inductor for switching off said switched mode power supply in case of a short circuit in said inductor or said rectifying means.
14. Integrated circuit comprising a comparator for operating a switching transistor of a switched mode power supply in response to a feedback loop, the integrated circuit further comprising:
a first over-voltage protection circuit with a first comparing circuit coupled to an output or input of said comparator for controlling a threshold level,
wherein an output of said first comparing circuit and a short circuit information provided by an inductor is coupled to a second comparing circuit of a second over-voltage protection circuit, the output of said second comparing circuit being coupled to a sense input of said first over-voltage protection circuit for switching off said integrated circuit in case of an interruption of said feedback loop, and
wherein said first comparing circuit becoming active and switching off said switched mode power supply when the control voltage of said feedback loop is above said threshold level for longer than a predetermined time period.