Discharge of an ac capacitor

Patent metadata

Field	Value
Publication number	US-2020381992-A1
Application number	US-202016885781-A
Country	US
Kind code	A1
Filing date	May 28, 2020
Priority date	May 31, 2019
Publication date	Dec 3, 2020
Grant date	—

Abstract

A circuit includes two thyristors coupled in anti-series. An AC capacitor has first and second electrodes respectively coupled to two different electrodes of the two thyristors. The first and second electrodes are coupled to receive an AC voltage. A control circuit detects discontinuance of application of the AC voltage to the AC capacitor and in response thereto simultaneously applies same gate currents to the two thyristors. A current path through the two thyristors (one passing current in forward mode and the other in reverse mode) discharges a residual voltage stored on the AC capacitor.

First claim

1 . A circuit, comprising:
a rectification circuit for rectifying an AC voltage; two thyristors coupled to the rectification circuit in anti-series; an AC capacitor having first and second electrodes respectively coupled to two different electrodes of said two thyristors and respectively coupled to two different electrodes of the rectification circuit and further configured to receive the AC voltage; and a control circuit configured to detect discontinuance of receipt of the AC voltage at the first and second electrodes of the AC capacitor and in response thereto simultaneously apply same gate currents to the two thyristors to provide a circuit path for discharge of a voltage on the AC capacitor.

2 . The circuit of claim 1 , wherein a first thyristor of said two thyristors conducts in a reverse direction in response to the simultaneous application of said gate currents.

3 . The circuit of claim 1 , wherein the control circuit detects discontinuance of receipt of the AC voltage if discontinued receipt of said AC voltage last for a time period longer than a first threshold, where said first threshold is at least one half-period of the AC voltage.

4 . The circuit of claim 3 , wherein the control circuit further stops application of said gate currents if an input voltage becomes smaller than a second threshold for a time period longer than a third threshold, where said third threshold is longer than the first threshold.

5 . The circuit of claim 1 , wherein said control circuit applies said gate currents for a time period longer than a half period of the AC voltage.

6 . The circuit of claim 5 , wherein said time period is in a range of a few tens of milliseconds to a few hundreds of milliseconds.

7 . The circuit of claim 5 , wherein said gate currents are applied continuously.

8 . The circuit of claim 5 , wherein said gate currents are applied in pulses.

9 . The circuit of claim 1 , wherein the rectification circuit comprises first and second rectifying diodes having terminals connected to terminal of the two thyristors.

10 . The circuit of claim 9 , wherein the first and second rectifying diodes form part of a bridge for rectifying the AC voltage.

11 . The circuit of claim 9 , wherein the first and second rectifying diodes connected to the two thyristors form a bridge for rectifying the AC voltage.

12 . The circuit of claim 12 , wherein said two thyristors are further controlled, in the presence of the AC voltage, with pulses to rectify the AC voltage.

13 . The circuit of claim 12 , wherein said pulses to rectify comprise a pulse applied to the thyristor corresponding to a halfwave of the AC voltage.

14 . The circuit of claim 12 , wherein each thyristor receives said pulse in only one halfwave out of two halfwaves of the AC voltage.

15 . The circuit of claim 1 , wherein an output of the rectification circuit powers a switched-mode power supply, and wherein said control circuit further operates to control the switched-mode power supply.

16 . The circuit of claim 1 , wherein the two thyristors are cathode-gate thyristors.

17 . The circuit of claim 1 , wherein the two thyristors are anode-gate thyristors.

18 . A circuit, comprising:
an inrush current limiting resistor; a rectification bridge circuit including a first diode coupled between a first input node and a first terminal of the inrush current limiting resistor, a second diode coupled between a second input node and the first terminal of the inrush current limiting resistor, a third diode coupled between the first input node and an output node, and a fourth diode coupled between the second input node and the output node, wherein the first and second input nodes are coupled to receive an AC voltage; a first thyristor coupled between the first input node and a second terminal of the inrush current limiting resistor; a second thyristor coupled between the second input node and the second terminal of the inrush current limiting resistor; an AC capacitor having first and second electrodes respectively coupled to the first and second input nodes; and a control circuit configured to detect discontinuance of receipt of the AC voltage at the first and second electrodes of the AC capacitor and in response thereto simultaneously apply same gate currents to the first and second thyristors to provide a circuit path for discharge of a voltage on the AC capacitor.

19 . The circuit of claim 18 , wherein one of the first and second thyristors conducts in a reverse direction in response to the simultaneous application of said gate currents.

20 . The circuit of claim 18 , wherein said gate currents are applied continuously.

21 . The circuit of claim 18 , wherein said gate currents are applied in pulses.

22 . The circuit of claim 18 , wherein said first and second thyristors are further controlled, in the presence of the AC voltage, with pulses to rectify the AC voltage.

23 . The circuit of claim 18 , wherein the first and second thyristors are cathode-gate thyristors.

24 . The circuit of claim 18 , wherein the first and second thyristors are anode-gate thyristors.

25 . The circuit of claim 18 , wherein the control circuit detects discontinuance of receipt of the AC voltage if discontinued receipt of said AC voltage last for a time period longer than a first threshold, where said first threshold is at least one half-period of the AC voltage.

26 . A circuit, comprising:
a rectification bridge circuit including a first thyristor coupled between a first input node and a first output node, a second thyristor coupled between a second input node and the first output node, a first diode coupled between the first input node and a second output node, and a second diode coupled between the second input node and the second output node, wherein the first and second input nodes are coupled to receive an AC voltage; an AC capacitor having first and second electrodes respectively coupled to the first and second input nodes; and a control circuit configured to detect discontinuance of receipt of the AC voltage at the first and second electrodes of the AC capacitor and in response thereto simultaneously apply same gate currents to the first and second thyristors to provide a circuit path for discharge of a voltage on the AC capacitor.

27 . The circuit of claim 26 , wherein one of the first and second thyristors conducts in a reverse direction in response to the simultaneous application of said gate currents.

28 . The circuit of claim 26 , wherein said gate currents are applied continuously.

29 . The circuit of claim 26 , wherein said gate currents are applied in pulses.

30 . The circuit of claim 26 , wherein said first and second thyristors are further controlled, in the presence of the AC voltage, with pulses to rectify the AC voltage.

31 . The circuit of claim 26 , wherein the first and second thyristors are cathode-gate thyristors.

32 . The circuit of claim 26 , wherein the first and second thyristors are anode-gate thyristors.

33 . The circuit of claim 26 , wherein the control circuit detects discontinuance of receipt of the AC voltage if discontinued receipt of said AC voltage last for a time period longer than a first threshold, where said first threshold is at least one half-perio

Assignees

• St Microelectronics Ltd

Inventors

• Gonthier Laurent

Classifications

• H02M7/1555

  with control circuit · CPC title

• H02M1/0085

  Partially controlled bridges · CPC title

• H02M1/08

  Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters · CPC title

• H02M7/155

  using semiconductor devices only · CPC title

• H02M1/322 Primary

  Means for rapidly discharging a capacitor of the converter for protecting electrical components or for preventing electrical shock · CPC title