DETECTION CIRCUIT FOR AN ACTIVE DISCHARGE CIRCUIT OF AN X-CAPACITOR, RELATED ACTIVE DISCHARGE CIRCUIT, INTEGRATED CIRCUIT AND METHOD

• US 20160124029A1
• Filed: 08/27/2015
• Published: 05/05/2016
• Est. Priority Date: 11/04/2014
• Status: Active Grant

• Current Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Original Assignee: STMicroelectronics SRL (STMicroelectronics NV)
• Inventors: Gobbi, Massimiliano, Bellomo, Ignazio Salvatore, Tripodi, Domenico, Borrello, Antonio, Bianco, Alberto
• Granted Patent: US 10,345,348 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G01R 19/04 Measuring peak values or amplitude or envelope of ac or of pulses
• CPC Class Codes: G01R 19/16557 Logic probes, i.e. circuits indicating logic state (high, low, O); modifications of electronic switches or gates for indicating state of switch H03K17/18
• CPC Class Codes: H02J 7/0071 with a programmable schedule
• CPC Class Codes: H02J 7/345 using capacitors as storage or buffering devices
• CPC Class Codes: H02M 1/322 Means for rapidly discharging a capacitor of the converter for protecting electrical components or for preventing electrical shock

Abstract

An active discharge circuit discharges an X. The detection circuit includes a sensor circuit that generates a sensor signal indicative of an AC oscillation voltage at the X capacitor. The detection circuit also includes a processing unit that generates the reset signal as a function of a comparison signal. A comparator circuit generates the comparison signal by comparing the sensor signal with a threshold. A timer circuit sets a discharge enable signal to a first logic level when the timer circuit is reset via a reset signal. The timer circuit determines the time elapsed since the last reset and tests whether the time elapsed exceeds a given timeout value. If the time elapsed exceeds the given timeout value, the timer circuit sets the discharge enable signal to a second logic level. A dynamic threshold generator circuit varies the threshold of the comparator circuit as a function of the sensor signal.

Claims

1. A detection circuit, comprising:

a sensor circuit for connection to an X capacitor, said sensor circuit configured to generate a sensor signal indicative of a voltage at said X capacitor;

a comparator circuit configured to generate a comparison signal by comparing said sensor signal with a threshold;

a timer circuit configured to;

set a discharge enable signal to a first logic level in response to said timer circuit being reset via a reset signal; and

determine a time elapsed since said timer circuit has been reset via the reset signal;

test whether said time elapsed exceeds a given timeout value; and

in case said time elapsed exceeds said given timeout value, set said discharge enable signal to a second logic level to cause the active discharge circuit to discharge the X capacitor;

an elaboration circuit configured to generate said reset signal for said timer circuit as a function of said comparison signal; and

a dynamic threshold generator circuit configured to vary said threshold of said comparator circuit as a function of said sensor signal.

2. The detection circuit of claim 1, wherein said dynamic threshold generator circuit is configured to vary in a feed-forward manner said threshold of said comparator circuit as a function of said sensor signal.

3. The detection circuit of claim 2, wherein said dynamic threshold generator circuit comprises:

a peak detector circuit configured to determine an upper threshold value indicative of a peak value of said sensor signal; and

a threshold generator circuit configured to determine a lower threshold value as a function of said upper threshold value.

4. The detection circuit of claim 3, wherein said comparator circuit comprises:

a single comparator configured to generate the comparison signal indicating whether said sensor signal is greater than said lower threshold value;

or

a window comparator configured to generate the comparison signal indicating whether said sensor signal is between said lower threshold value and said upper threshold value.

5. The detection circuit of claim 4, wherein said elaboration circuit is configured to:

detect an edge of said comparison signal; and

reset said timer circuit via said reset signal in response to detecting the edge of said comparison signal.

7. The detection circuit of claim 1, wherein said dynamic threshold generator circuit is configured to vary in a feed-back manner said threshold of said comparator circuit as a function of said comparison signal.

8. The detection circuit of claim 7, wherein said comparator circuit comprises:

a first comparator configured to generate a first comparison signal indicating whether said sensor signal is greater than a first threshold value; and

a second comparator configured to generate a second comparison signal indicating whether said sensor signal is greater than a second threshold value.

9. The detection circuit of claim 8, wherein said dynamic threshold generator circuit is configured to:

determine which of said first and second threshold values is greater;

test whether said first and said second comparison signals indicate that said sensor signal is greater than both of said first and second threshold values;

test whether said first and second comparison signals indicate that said sensor signal is smaller than both of said first and second threshold values;

in case said first and said second comparison signals indicate that said sensor signal is greater than both of said first and second threshold values, increase the smaller one of said first or said second threshold values; and

in case said first and said second comparison signals indicate that said sensor signal is smaller than both of said first and second threshold values, decrease the greater one of said first and said second threshold values.

10. The detection circuit of claim 8, wherein said elaboration circuit is configured to:

test whether said first and said second comparison signals indicate that said sensor signal is greater than both of said first and second threshold values; and

reset said timer circuit via said reset signal in response to said first and said second comparison signals indicating that said sensor signal is greater than both of said first and second threshold values.

6. The detection circuit of 4, wherein said elaboration circuit is configured to:

test whether said comparison signal comprises both a leading and a falling edge; and

in case said comparison signal comprises both said leading edge and said falling edge, determining a time elapsed between said leading edge and said falling edge;

test whether said time elapsed between said leading edge and said falling edge is smaller than a given time threshold value; and

reset said timer circuit via said reset signal in response to detecting that said time elapsed between said leading and said falling edge is smaller than said given time threshold value.

11. An active discharge circuit, comprising:

a detection circuit configured to generate a discharge enable signal signaling whether an AC oscillation is applied to an X capacitor of a device, wherein said detection circuit comprises;

a sensor circuit for connection to said X capacitor, said sensor circuit configured to generate a sensor signal indicative of the voltage at said X capacitor;

a comparator circuit configured to generate at least one comparison signal by comparing said sensor signal with at least one threshold;

a timer circuit configured to;

set said discharge enable signal to a first logic level responsive to said timer circuit being reset via a reset signal;

determine the time elapsed since said timer circuit has been reset via a reset signal;

test whether said time elapsed exceeds a given timeout value; and

in case said time elapsed exceeds said given timeout value, set said discharge enable signal to a second logic level;

an elaboration circuit configured to generate said reset signal for said timer circuit as a function of said at least one comparison signal; and

a dynamic threshold generator circuit configured to vary said at least one threshold of said comparator circuit as a function of said sensor signal; and

a discharge circuit adapted to be coupled to said X-capacitor and configured to discharge said X-capacitor as a function of said discharge enable signal generated by said detection circuit.

12. The active discharge circuit of claim 11, wherein said discharge circuit comprises at least one electronic switch connected to a resistive element and/or a current generator.

13. The active discharge circuit of claim 12, wherein the resistive element comprises a resistor and the current generator comprises a constant current generator, or either a linear or non-linear current generator.

14. A method, comprising:

detecting whether an AC oscillation is applied to an X capacitor of a device, the detecting including;

monitoring a voltage at said X capacitor;

generating at least one comparison signal by comparing said voltage at said X capacitor with at least one threshold;

determining the presence or absence of said AC oscillation applied to an X capacitor as a function of said at least one comparison signal; and

varying said at least one threshold as a function of said monitored voltage at said X capacitor.

15. The method of claim 14, wherein monitoring the voltage at said X capacitor comprises:

generating a sensor signal responsive to the voltage at said X capacitor;

determining an upper threshold value indicative of a peak value of said sensor signal; and

determining a lower threshold value as a function of said upper threshold value.

16. The method of claim 15, wherein generating at least one comparison signal comprises generating a comparison signal indicating whether said sensor signal is contained in a voltage window defined by said lower threshold value and said upper threshold value.

17. The method of claim 14, further comprising:

detecting at least one of leading and falling edges of the comparison signal;

incrementing a count value over time starting from an initial value for the count value;

resetting the count value to the initial value as a function of the detected at least one of leaving and falling edges of the comparison signal;

determining whether the count value has reached a time threshold value; and

discharging the X capacitor responsive to the time count reaching the time threshold value.

18. The method of claim 17, wherein the count value indicates a time between leading and falling edges of the comparison signal.

19. The method of claim 14, wherein varying said at least one threshold as a function of said monitored voltage at said X capacitor comprises varying the at least one threshold value as a function the comparison signal.

20. The method of claim 19, wherein the comparison signal comprises first and second comparison signals and wherein the method further comprises:

generating a first comparison signal indicating whether said monitored voltage at said X capacitor is greater than a first threshold value; and

generating a second comparison signal indicating whether said monitored voltage at said X capacitor is greater than a second threshold value.