AC line detection and X capacitor discharge using a single terminal

Patent metadata

Field	Value
Publication number	US-10170975-B1
Application number	US-201815906959-A
Country	US
Kind code	B1
Filing date	Feb 27, 2018
Priority date	Feb 27, 2018
Publication date	Jan 1, 2019
Grant date	Jan 1, 2019

Abstract

A controller for a switching power converter is provided with a single detection pin through which the controller monitors whether the switching power converter is connected to an AC mains. Should a voltage for the detection pin indicate that the switching power converter is disconnected from the AC mains, the controller asserts the detection pin voltage to trigger a bleeder circuit to discharge an X class capacitor.

First claim

We claim:

1. A switching power converter controller for a switching power converter, comprising:
a detection pin for receiving a clamped and divided version of an AC mains terminal voltage from an AC mains terminal;
a comparator configured to compare a detection pin voltage of the detection pin to a reference voltage to drive a comparator output signal into a binary high state or a binary low state responsive to whether the detection pin voltage is greater or lower than the reference voltage;
a detection circuit configured to detect whether the AC mains terminal is disconnected from an AC mains through a determination of whether the comparator output signal is in the binary high state for a threshold period and of whether the comparator output signal is in the binary low state for the threshold period, wherein the threshold period is greater than one-half of a period for an oscillation of the AC mains terminal voltage; and
a driver configured to increase the detection pin voltage to switch on a bleeder circuit to discharge an X class capacitor responsive to a detection by the detection circuit that the AC mains terminal is disconnected from the AC mains.

2. The switching power converter controller of claim 1 , wherein the detection circuit comprises a counter configured to measure whether the comparator output signal is in the binary high state or in the binary low state for a time that exceeds the threshold period.

3. The switching power converter controller of claim 1 , wherein the threshold period is approximately one hundred milliseconds.

4. The switching power converter controller of claim 1 , further comprising a voltage divider coupled to the detection pin and configured to divide the AC mains terminal voltage into a divided voltage.

5. The switching power converter controller of claim 4 , wherein the bleeder circuit comprises a metal-oxide semiconductor field-effect transistor coupled across the X class capacitor.

6. The switching power converter controller of claim 4 , further comprising a Zener diode coupled to the detection pin, wherein the voltage clamp circuit clamps the divided voltage to produce the clamped and divided version of the AC mains terminal voltage.

7. The switching power converter controller of claim 1 , wherein the reference voltage is approximately 0.5 V.

8. A method for a switching power converter, comprising:
while an AC mains terminal is connected to an AC mains, clamping a divided version of an AC mains voltage to produce a detection voltage;
determining whether the detection voltage does not oscillate responsive to an oscillation of the AC mains voltage for the AC mains to detect whether the AC mains terminal is disconnected from the AC mains;
responsive to a determination that the AC mains terminal is disconnected from the AC mains, increasing the detection voltage to activate a bleeder circuit to discharge an X class capacitor connected to the AC mains terminal;
comparing the detection voltage in a comparator to a reference voltage to provide a comparator output signal; and
determining whether the comparator output signal is maintained in a binary one state for a time that is greater than a threshold period, wherein the threshold period is greater than an oscillation period for the oscillation of the AC mains voltage.

9. The method of claim 8 , wherein determining whether the detection voltage does not oscillate responsive to the oscillation of the AC mains voltage further comprises determining whether the comparator output signal is maintained in a binary zero state for the time that is greater than the threshold period.

10. The method of claim 9 , wherein determining whether the comparator output signal is maintained in the binary zero state for the time that is greater than the threshold period comprises determining whether the comparator output signal equals ground for the time that is greater than the threshold period.

11. The method of claim 10 , wherein activating the bleeder circuit comprises switching on a metal-oxide semiconductor field-effect transistor responsive to the increase of the detection voltage.

12. The method of claim 8 , wherein determining whether the comparator output signal is maintained in the binary one state for the time that is greater than the threshold period comprises determining whether the comparator output signal equals a power supply voltage for the time that is greater than the threshold period.

13. The method of claim 12 , wherein determining whether the comparator output signal equals the power supply voltage for the time that is greater than the threshold period comprises:
counting a time period the comparator output signal equals the power supply voltage; and
determining whether the time period exceeds the threshold period.

14. A switching power converter, comprising:
an X class capacitor connected between an AC line terminal and an AC neutral terminal;
a voltage divider connected to the AC line terminal and configured to divide a voltage of the AC line terminal into a divided voltage;
a Zener diode configured to clamp the divided voltage into a detection pin voltage;
a bleeder circuit configured to discharge the X class X capacitor responsive to an increase of the detection pin voltage; and
a controller including:
a detection pin for receiving the detection pin voltage;
a comparator configured to compare the detection pin voltage to a reference voltage to produce a comparator output signal,
a detection circuit configured to determine whether the comparator output signal is in a binary high state for a threshold period or in a binary low state for the threshold period to detect whether the switching power converter is disconnected from an AC mains; and
a driver configured to increase the detection pin voltage responsive to a detection by the detection circuit that the switching power converter is disconnected from the AC mains.

15. The switching power converter of claim 14 , wherein the bleeder circuit includes a switch transistor coupled across the X class capacitor and also includes a diode coupled between a gate of the switch transistor and the detection pin.

16. The switching power converter of claim 15 , wherein the switch transistor comprises a metal-oxide semiconductor field-effect transistor.

17. The switching power converter of claim 15 , wherein the bleeder circuit further comprises a pair of resistors for coupling the switch transistor across the X class capacitor.

18. The switching power converter of claim 14 , wherein the switching power converter comprises a flyback converter.

19. The switching power converter of claim 14 , wherein the voltage divider comprises a serial arrangement of at least three resistors.

Assignees

• Dialog Semiconductor Inc

Inventors

• Feng Guang
• Shi Qifeng
• Yu Jiang
• Sha Qiu
• Lin Yong Xiong

Classifications

• H02M1/00

  Details of apparatus for conversion · CPC title

• H02M5/293

  using semiconductor devices only · CPC title

• H02M1/126 Primary

  using passive filters · CPC title

• H02M5/12

  for conversion of voltage or current amplitude only · CPC title

• H02J3/24

  Electricity · mapped topic