System and method for a switched-mode power supply

• US 9,991,791 B2
• Filed: 03/30/2015
• Issued: 06/05/2018
• Est. Priority Date: 03/30/2015
• Status: Active Grant

• Current Assignee: Infineon Technologies Austria Ag (Infineon Technologies AG)
• Original Assignee: Infineon Technologies Austria Ag (Infineon Technologies AG)
• Inventors: Herfurth, Michael, Gong, Xiao Wu
• Primary Examiner(s): Owens, Douglas W
• Assistant Examiner(s): Chan, Wei
• Application Number:
  US14/673,128
• Publication Number:
  US 20160294282A1
• Time in Patent Office: 1,163 Days
• Field of Search: 315119, 315224, 315297, 315291, 363 84
• CPC Class Codes: G01R 19/2503 for measuring voltage only, e.g. digital volt meters (DVM's) G01R19/2506 - G01R19/257 take precedence
• CPC Class Codes: G01R 31/40 Testing power supplies testing photovoltaic devices H02S50/10
• CPC Class Codes: H02M 1/0003 Details of control, feedback or regulation circuits
• CPC Class Codes: H02M 1/32 Means for protecting converters other than automatic disconnection
• CPC Class Codes: H02M 3/157 with digital control
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

In accordance with an embodiment, a method of operating a switched-mode power converter includes measuring an input voltage of the switched-mode power converter; determining an on-time of a switch of the switched-mode power converter; determining an off-time of the switch of the switched-mode power converter; and determining an output voltage of the switched-mode power converter based on the measured input voltage, the determined on-time and the determined off-time. The output voltage includes a voltage at a first node having a DC path to a load path of the switch.

Claims

1. A method of operating a switched-mode power converter, the method comprising:

measuring an input voltage of the switched-mode power converter;

monitoring a switch control signal of a switch of the switched-mode power converter;

measuring an on-time of a switch of the switched-mode power converter from the monitored switch control signal;

measuring an off-time of the switch of the switched-mode power converter from the monitored switch control signal;

estimating an output voltage of the switched-mode power converter based on the measured input voltage, the measured on-time and the measured off-time, wherein the output voltage comprises a voltage at a first node having a DC path to a load path of the switch;

comparing the estimated output voltage to a predetermined threshold; and

shutting down the switched-mode power converter when the estimated output voltage exceeds the predetermined threshold.

2. The method of claim 1, further comprising:

switching on the switch of the switched-mode power converter during the on-time of the switch; and

switching off the switch of the switched-mode power converter during the off-time of the switch.

3. The method of claim 1, wherein the switched-mode power converter comprises a buck converter comprising an inductor that is DC coupled between the load path of the switch and the first node.

4. The method of claim 1, wherein the output voltage of the switched-mode power converter is estimated according to:

5. The method of claim 1, wherein:

measuring the input voltage comprises performing an analog-to-digital conversion of the input voltage to produce a digitized input voltage value.

6. The method of claim 1, wherein monitoring the switch control signal comprises monitoring the switch control signal using a counter.

7. The method of claim 5, wherein estimating the output voltage of the switched-mode power converter comprises using a digital logic circuit to calculate:

8. The method of claim 1, further comprising:

operating the switched-mode power converter in a quasiresonant mode of operation; and

measuring the off-time of the switch comprises using at least one of a zero current detector and a valley detection circuit.

9. The method of claim 1, wherein measuring the input voltage of the switched-mode power converter comprises using a voltage divider.

10. The method of claim 1, wherein measuring the on-time of the switch of the switched-mode power converter comprises using a calculation circuit.

11. The method of claim 1, further comprising biasing a control node of a transistor coupled in series with the switch, biasing comprising:

coupling the control node of the transistor to a reference node via a zener diode coupled in parallel with a capacitor; and

coupling the control node to the input voltage via a resistor.

12. The method of claim 1, wherein the steps of measuring the on-time of the switch and measuring the off-time of the switch is performed using a time measurement circuit.

13. The method of claim 12, wherein the time measurement circuit comprises a counter.

14. A switched-mode power supply controller comprising:

a first input coupled to a switch control terminal;

a second input coupled to an input voltage of a switched-mode power supply; and

a calculation circuit configured to monitor a switch control signal at the switch control terminal, measure an on-time of a switch of the switched-mode power supply based on the monitored switch control signal, measure an off-time of the switch of the switched-mode power supply based on the monitored switch control signal, and estimate an output voltage of the switched-mode power supply based on the input voltage, the measured on-time and the measured off-time, wherein the output voltage comprises a voltage at a first node having a DC path to a load path of the switch, and the calculation circuit further comprises a comparator configured to compare the estimated output voltage to a predetermined threshold, and shutdown the switched-mode power supply when the estimated output voltage exceeds the predetermined threshold.

15. The switched-mode power supply controller of claim 14, further comprising a pulse modulator configured to generate the switch control signal, wherein the pulse modulator is configured to switch on the switch of the switched-mode power supply during the on-time of the switch, and to switch off the switch of the switched-mode power supply during the off-time of the switch.

16. The switched-mode power supply controller of claim 14, wherein the calculation circuit is configured to estimate the output voltage of the switched-mode power supply according to:

17. The switched-mode power supply controller of claim 14, further comprising an analog-to-digital converter coupled between the second input and the calculation circuit.

18. The switched-mode power supply controller of claim 14, wherein the calculation circuit comprises:

a first counter circuit coupled to the first input, the first counter circuit configured to measure the on-time of the switch; and

a second counter circuit coupled to the second input, the second counter circuit configured to measure at least one of the off-time of the switch and a sum of the on-time of the switch and the off-time of the switch.

19. The switched-mode power supply controller of claim 18, further comprising a digital logic circuit having a first input coupled to an output of the analog-to-digital converter, a second input coupled to an output of the first counter circuit, and a third input coupled to an output of the second counter circuit, the digital logic circuit configured to estimate the output voltage of the switched-mode power supply according to:

20. The switched-mode power supply controller of claim 18, wherein the analog-to-digital converter and the calculation circuit are disposed on a semiconductor substrate.

21. The switched-mode power supply controller of claim 14, wherein the switched-mode power supply controller is configured to operate a switched-mode buck converter comprising an inductor that is DC coupled between the load path of the switch and the first node.

22. The switched-mode power supply controller of claim 14, further comprising a biasing circuit, the biasing circuit comprising:

a resistor coupled between the second input and a biasing node configured to be coupled to a control node of a transistor coupled in series with the load path of the switch;

a capacitor coupled between the biasing node and a reference node; and

a zener diode coupled between the biasing node and the reference node.

23. The switched-mode power supply controller of claim 22, further comprising the switch and the transistor.

24. The switched-mode power supply controller of claim 14, wherein the calculation circuit comprises at least one time measurement circuit configured to measure the on-time of the switch and the off-time of the switch.

25. The switched-mode power supply controller of claim 24, wherein the at least one time measurement circuit comprises a counter.

26. A light emitting diode (LED) power supply comprising:

a first integrated circuit comprising;

a first switch,

a controller configured to control a first current through the first switch by modulating a first switching signal provided to a control node of the first switch, and

a calculation circuit comprising a first input coupled to a power input node of the LED power supply and a second input coupled to the first switching signal, the calculation circuit configured to monitor the first switching signal, wherein;

the calculation circuit is further configured to;

measure an on-time of the first switch based on monitoring the first switching signal,

measure an off-time of the first switch based on monitoring the first switching signal, and

estimate an output voltage of the LED power supply based on a voltage at the first input, the measured on-time and the measured off-time, wherein the output voltage of the LED power supply comprises a voltage at an output port having a DC path to a load path of the first switch, wherein

the calculation circuit is further configured to compare the estimated output voltage to a predetermined threshold, and

the controller is further configured to shut-down the LED power supply when the estimated output voltage exceeds the predetermined threshold.

27. The LED power supply of claim 26, further comprising:

an inductor that is DC coupled between an output node of the first switch and the output port of the LED power supply; and

a freewheeling diode coupled between the output node of the first switch and the power input node.

28. The LED power supply of claim 27, further comprising a rectifier coupled between an AC input port and the power input node.

29. The LED power supply of claim 26, further comprising an LED coupled to an output port of the of the LED power supply.

30. The LED power supply of claim 26, further comprising a resistive voltage divider coupled to the power input node and the first input of the calculation circuit.

31. The LED power supply of claim 26, further comprising:

a transistor coupled in series with the first switch;

a resistor coupled between the power input node of the LED power supply and a control node of the transistor;

a capacitor coupled between the control node of the transistor and a reference node; and

a zener diode coupled between control node of the transistor and the reference node.

32. The LED power supply of claim 26, wherein the calculation circuit comprises at least one time measurement circuit configured to measure the on-time of the first switch and the off-time of the first switch.

33. The LED power supply of claim 32, wherein the at least one time measurement circuit comprises a counter.