CN115118150A

CN115118150A - Method and circuit for automatically recognizing and adapting discharge function of X capacitor in switch circuit

Info

Publication number: CN115118150A
Application number: CN202210783618.4A
Authority: CN
Inventors: 程兆辉; 于玮; 蒋金星
Original assignee: Dongke Semiconductor Anhui Co ltd
Current assignee: Dongke Semiconductor Anhui Co ltd
Priority date: 2022-07-05
Filing date: 2022-07-05
Publication date: 2022-09-27
Anticipated expiration: 2042-07-05
Also published as: CN115118150B

Abstract

The embodiment of the invention relates to a method and a circuit for automatically identifying and adapting the discharge function of an X capacitor in a switch circuit, wherein the method comprises the following steps: when the voltage of the starting capacitor is greater than the reset voltage set in the starting circuit, the starting circuit outputs a power-on reset signal POR to start the identification circuit; the identification circuit starts a first timing, during a first timing period, the identification circuit detects a voltage Vhv from an input end HV of a high-voltage starting circuit connected with the switching power supply circuit and provides a pull-down current to the ground, the voltage Vhv is compared with a reference voltage Vref set inside the identification circuit, when Vhv is larger than Vref, a voltage state indicating signal GHV output by the identification circuit is 1, otherwise, the GHV is 0; the identification circuit counts whether the duration time of the voltage state indication signal GHV being 0 in the first timing period is greater than a set time threshold, if so, the identification result indicates that the switching power supply circuit needs the X capacitor discharge function, otherwise, the identification result indicates that the switching power supply circuit does not need the X capacitor discharge function.

Description

Method and circuit for automatically recognizing and adapting discharge function of X capacitor in switch circuit

Technical Field

The invention relates to the technical field of switching power supply circuits, in particular to a method and a circuit for automatically identifying and adapting the discharge function of an X capacitor in a switching circuit.

Background

The safety X capacitor is a capacitor bridged between a live wire and a zero line, is generally used for filtering in an anti-interference circuit and mainly plays a role in filtering differential mode interference. When the power line is required to be prevented from being pulled out when the X capacitor is used, the power line plug is electrified for a long time, so that the voltage is required to be reduced to a specified voltage within a specified time after the plug is pulled out according to relevant safety certification standards.

Taking a flyback switching power supply as an example, the existing control chips are divided into two categories:

one type does not have the discharge function of the X capacitor, and as shown in FIG. 1, the discharge function needs to be performed by connecting a bleeder resistor Rx in parallel with the X capacitor Cx. The chip is simple in design and application, but energy is always consumed by the bleeder resistor, so that the light load efficiency and the standby power consumption of the switching power supply are influenced, and the chip is suitable for application with lower requirements on the efficiency and the standby power consumption.

The other type of chip with the X capacitor discharge function, as shown in FIG. 2, does not need to be connected with Rx in parallel, needs two rectifier diodes D1 and D2 to be connected with an HV pin, and does X capacitor discharge work when the chip detects that a power line is pulled out.

For different application environments, the two types of chips with the X capacitor discharge function and the chips without the X capacitor discharge function are selected differently. From the perspective of a chip application, a chip needs to be selected according to application during product development, but when an application environment or an application scene changes, for example, when a product needs to be upgraded, the chip selected before may no longer be suitable for a new application environment, and at this time, the chip must be replaced, which causes difficulty in updating the product, and the time and technical difficulty brought by re-debugging the product after replacing the chip are not negligible. For chip designers and manufacturers, the problems of long design period, long production period, high research and development cost and the like exist when two chips are researched and manufactured simultaneously.

Disclosure of Invention

The invention aims to provide a method and a circuit for automatically identifying and adapting the discharge function of an X capacitor in a switch circuit, wherein the method enables the switch circuit to be simultaneously suitable for application occasions needing to discharge with the X capacitor and also can be applied to application occasions needing no discharge of the X capacitor, and can realize automatic identification and adaptation of discharge of the X capacitor, thereby not only simplifying the complexity of chip design and production, but also enabling the product to obtain better applicability and compatibility, and simultaneously reducing the cost. The identification circuit can be automatically turned off under the application environment without discharging of the X capacitor, so that power consumption is reduced.

To this end, in a first aspect, an embodiment of the present invention provides a method for automatically identifying and adapting an X capacitor discharge function in a switch circuit, where the method includes:

after a switching power supply circuit is powered on, a starting capacitor is charged, and when the voltage of the starting capacitor is greater than the reset voltage set in a starting circuit, the starting circuit outputs a power-on reset signal POR to start an identification circuit;

the identification circuit starts a first timing, detects a voltage Vhv from an input end HV of a high-voltage starting circuit connected with a switching power supply circuit and provides a pull-down current to the ground in a first timing period, compares the voltage Vhv with a reference voltage Vref set inside the identification circuit, and outputs a voltage state indicating signal GHV which is 1 when Vhv is larger than Vref and is 0 otherwise;

the identification circuit counts whether the duration time of the voltage state indication signal GHV being 0 in the first timing period is greater than a set time threshold, if so, the identification result indicates that the switching power supply circuit needs the X capacitor discharge function, otherwise, the identification result indicates that the switching power supply circuit does not need the X capacitor discharge function.

Preferably, the identification circuit is connected to the input end HV of the high-voltage starting circuit through an NMOS transistor;

and the input end HV of the high-voltage starting circuit is connected in front of or behind a rectifier bridge of the switching power supply circuit.

Preferably, the method further comprises an automatic adaptation process;

the automatic adaptation processing specifically comprises: when the duration time of the voltage state indicating signal GHV being 0 in the timing period is greater than a set time threshold value, the identification circuit generates an identification result signal with a first level to enable the discharge function of the X capacitor of the switching power supply circuit, otherwise, generates an identification result signal with a second level to disconnect the identification circuit from the switching power supply circuit.

Further preferably, after the identification circuit generates the identification result signal of the first level to enable the discharge function of the X capacitor of the switching power supply circuit, the method further includes:

and discharging the X capacitor of the switching power supply circuit through the identification circuit.

Preferably, after the start circuit outputs a power-on reset signal to start the identification circuit, the identification circuit outputs a start circuit control signal PS to control the start circuit to be turned off.

In a second aspect, an embodiment of the present invention provides a circuit for automatically identifying and adapting an X capacitor discharge function in a switch circuit, including: the starting capacitor, the starting circuit, the identification circuit and an NMOS transistor M2;

the starting capacitor is connected with a comparison signal input end of the starting circuit;

the drain electrode of the NMOS transistor M2 is connected with the input end HV of a high-voltage starting circuit connected with the switching power supply circuit, and the input end HV of the high-voltage starting circuit is connected in front of or behind a rectifier bridge of the switching power supply circuit; the grid electrode and the source electrode of the NMOS transistor M2 are respectively connected with the starting circuit and the identification circuit;

after the switching power supply circuit is powered on, the NMOS transistor M2 is conducted, the starting capacitor is charged through the input end HV of the high-voltage starting circuit, the NMOS transistor M2 and the starting circuit, and when the voltage of the starting capacitor is larger than the reset voltage set in the starting circuit, the starting circuit outputs a power-on reset signal POR to the identification circuit;

the identification circuit starts a first timing according to the power-on reset signal and provides a source-to-ground pull-down current of an NMOS transistor M2 to the high-voltage starting circuit input end HV through the NMOS transistor M2 and the identification circuit;

the identification circuit detects the voltage Vhv of an input end HV of the high-voltage starting circuit in a first timing period and compares the voltage Vhv with a reference voltage Vref set inside the identification circuit, and when Vhv is larger than Vref, a voltage state indicating signal GHV output by the identification circuit is 1, otherwise, the voltage state indicating signal GHV is 0;

and the identification circuit counts whether the duration time of the voltage state indication signal GHV (0) in the timing period is greater than a set time threshold value, if so, an identification result signal of a first level is generated to enable the X capacitor discharge function of the switching power supply circuit, otherwise, an identification result signal of a second level is generated to control an NMOS (N-channel metal oxide semiconductor) transistor M2 to disconnect the identification circuit from the switching power supply circuit.

Preferably, the start-up circuit specifically includes: the power supply comprises an NMOS transistor N1, a first resistor R1, a voltage regulator tube VR1 and a starting module;

the drain electrode of the NMOS transistor M2 is connected with the input end HV of the high-voltage starting circuit;

the voltage regulator VR1 is reversely connected between the gate of the NMOS transistor M2 and the ground;

the first resistor R1 is connected between the gate of the NMOS transistor M2 and the input end HV of the high-voltage starting circuit;

the drain of the NMOS transistor N1 is connected to the gate of the NMOS transistor M2, and the source of the NMOS transistor N1 is grounded.

The identification circuit specifically includes: the device comprises a control module, an analog-to-digital conversion module, a bleeding module and an identification output module;

the control module is connected with the starting circuit, receives the power-on reset signal and a clock signal of the switching power supply circuit, starts first timing, and outputs a preset digital voltage parameter for controlling the magnitude of the leakage current in the leakage module and a leakage control signal of a first level;

the analog-to-digital conversion module is connected with the control module and converts the preset digital voltage parameters into analog voltage values;

the drain module is respectively connected with a source electrode of the NMOS transistor M2, the analog-to-digital conversion module and the control module, and is controlled to start the drain module according to the drain control signal of the first level, and the drain module is converted into a current value on a drain resistor according to the analog voltage value to form ground drain of the input end HV of the high-voltage starting circuit;

the identification output module is connected with the source electrode of the NMOS transistor M2, compares Vhv with Vref, and outputs a voltage state indicating signal GHV which is 1 when Vhv is larger than Vref, otherwise, outputs a voltage state indicating signal GHV which is 0;

the control module is further connected with the identification output module, receives the voltage state indication signal GHV output by the identification output module, and counts whether the duration of the voltage state indication signal GHV being 0 is greater than a set time threshold value in a first timing period, if so, generates an identification result signal of the first level, otherwise, generates an identification result signal of the second level.

Preferably, the control module is further connected to the gate of the NMOS transistor N1, and controls the NMOS transistor N1 to be turned on according to the recognition result signal of the second level, so as to pull down the gate potential of the NMOS transistor M2 to turn off the NMOS transistor M2, thereby disconnecting the recognition circuit from the switching power supply circuit.

In a third aspect, an embodiment of the present invention provides a switch circuit, including the circuit for automatically identifying and adapting the discharge function of the X capacitor in the switch circuit according to the second aspect.

The method for automatically identifying and adapting the discharge function of the X capacitor in the switch circuit provided by the embodiment of the invention enables the switch circuit to be simultaneously suitable for application occasions needing to discharge with the X capacitor and application occasions needing no discharge of the X capacitor. The identification circuit can be automatically turned off under the application environment without discharging of the X capacitor, so that power consumption is reduced.

Drawings

Fig. 1 is a schematic diagram of a prior art discharging-flyback switching power supply circuit without an X capacitor;

fig. 2 is a schematic diagram of a discharge-flyback switching power supply circuit with an X capacitor provided in the prior art;

fig. 3 is a schematic diagram of a switching power supply circuit according to an embodiment of the invention;

FIG. 4 is a flowchart of a method for automatically identifying and adapting the discharge function of an X capacitor in a switch circuit according to an embodiment of the present invention;

FIG. 5 is a circuit diagram of the discharge function of the X capacitor in the automatic identification and adaptation switch circuit provided by the embodiment of the present invention;

fig. 6 is a schematic waveform diagram of a circuit in which an input terminal HV of a high-voltage start circuit in a switching power supply circuit is connected to a front end of a rectifier bridge according to an embodiment of the present invention;

fig. 7 is a schematic waveform diagram of a circuit in which an input terminal HV of a high-voltage start circuit in the switching power supply circuit is connected to a rectifier bridge according to an embodiment of the present invention;

fig. 8 is a flyback control chip integrated with a circuit for automatically recognizing and adapting the discharge function of the X capacitor in the switch circuit according to an embodiment of the present invention.

Detailed Description

The technical solution of the present invention is further described in detail by the accompanying drawings and embodiments.

The embodiment of the invention provides a method for automatically identifying and adapting the discharge function of an X capacitor in a switch circuit, which is applied to the switch circuit shown in FIG. 3.

The circuit shown in fig. 3 is a switching power supply circuit provided in an embodiment of the present invention, and the circuit provided in the dashed line frame is a circuit for implementing the method for automatically identifying and adapting the discharge function of the X capacitor in the switching circuit according to the present invention, and includes: a starting capacitor Cvcc, a starting circuit 1, an identification circuit 2 and an NMOS transistor M2. Since the start-up capacitor Cvcc is also a peripheral circuit of the control chip, it is not enclosed in a dashed box. The circuit may be integrated in the control chip shown in fig. 1 and 2, or may be a separate chip externally connected to the control chip shown in fig. 1 and 2. Fig. 3 mainly illustrates the connection position of the circuit for automatically detecting and adapting the discharge function of the X capacitor in the switching circuit in the switching power supply circuit, so that the control chip is not shown here.

Fig. 4 is a flowchart of main steps of a method for automatically identifying and adapting the discharge function of the X capacitor in the switch circuit according to the embodiment of the present invention. The description will be made with reference to fig. 3 and 4.

Step 110, after the switching power supply circuit is powered on, charging a starting capacitor, and when the voltage of the starting capacitor is greater than the reset voltage set in the starting circuit, outputting a power-on reset signal POR by the starting circuit to start the identification circuit;

the starting circuit and the identification circuit are connected to the input end HV of the high-voltage starting circuit through an NMOS (N-channel metal oxide semiconductor) transistor M2; the high-voltage starting circuit input terminal HV may be connected before or after a rectifier bridge of the switching power supply circuit as shown in fig. 3, i.e., connected to one of the terminals Vac _ abs (before the rectifier bridge), Vsw (after the rectifier bridge), or Vdc (after the rectifier bridge).

Further, after the power-on reset signal is output to start the identification circuit, the identification circuit outputs a start circuit control signal PS to control the start circuit to be turned off.

Step 120, the identification circuit starts a first timing, during a first timing period, the identification circuit detects a voltage Vhv from an input end HV of a high-voltage starting circuit connected with the switching power supply circuit, provides a pull-down current to the ground, compares the voltage Vhv with a reference voltage Vref set inside the identification circuit, and when Vhv is greater than Vref, a voltage state indicating signal GHV output by the identification circuit is 1, otherwise, GHV is 0;

in the process of the above step 120, when the identification circuit starts the first timer T1, since the HV pin does not reach the voltage close to the ground even if the HV pin is connected to the ac input terminal in front of the rectifier bridge when the ac crosses zero, considering the influence of the leakage current of the rectifier diodes D1 and D2, if the pull-down current is not applied to the HV pin, in order to correctly measure whether the ac signal is connected, the identification circuit needs to generate the pull-down current from the source of M2 to the ground, and it is ensured that the voltage Vhv of the HV can be pulled down to the ground when the input ac voltage Vac crosses zero when the HV is connected to the rectifier bridge.

The identification circuit detects Vhv, which is compared with an internally set reference voltage Vref. During the first timing T1, if GHV ≦ 0 is detected, that is, Vhv ≦ Vref, it indicates that the switching power supply circuit may have a need for discharging the X capacitor.

Step 130, the identification circuit counts whether the duration of the voltage state indication signal GHV being 0 in the first timing period is greater than a set time threshold, if so, the identification result is that the switching power supply circuit needs the X capacitor discharge function, otherwise, the identification result is that the switching power supply circuit does not need the X capacitor discharge function.

The judgment is carried out by the set time threshold, so that the misjudgment caused by signal interference or accidental abnormal jump can be avoided.

When the duration of the voltage state indicating signal GHV being 0 in the timer period is longer than the set time threshold value by the time when the first timer T1 expires, it can be determined that HV is connected to the Vac _ abs terminal of the switching power supply circuit, and the discrimination circuit generates the discrimination result signal of the first level to enable the discharge function of the X capacitor of the switching power supply circuit. In this case, the X capacitor may be further discharged to the switching power supply circuit through the identification circuit when the switching power supply circuit is turned off.

And if the time that GHV is always equal to 1 or GHV is equal to 0 in the timing period is less than or equal to the time threshold Tref, the HV is judged to be connected to the end of Vdc or Vsw, and a second level identification result signal is generated for disconnecting the identification circuit from the switching power supply circuit.

Therefore, whether the X capacitor discharging function is needed by the switching circuit or not can be realized, and the X capacitor discharging function is automatically adapted to execute X capacitor discharging on the switching power supply circuit when the switching power supply circuit is powered off under the condition that the X capacitor discharging function is needed.

The principle of the invention is explained above, and the method and circuit for automatically recognizing and adapting the discharge function of the X capacitor in the switch circuit are described in detail below with reference to the circuit diagrams and waveform diagrams of FIGS. 5-7. FIG. 5 is a circuit diagram of the discharge function of the X capacitor in the automatic identification and adaptation switch circuit provided by the embodiment of the present invention; fig. 6 is a schematic waveform diagram of a circuit in which an input terminal HV of a high-voltage start circuit in a switching power supply circuit is connected to a front end of a rectifier bridge according to an embodiment of the present invention; fig. 7 is a schematic waveform diagram of a circuit in which an input terminal HV of a high voltage start circuit in the switching power supply circuit is connected to a rectifier bridge according to an embodiment of the present invention.

One specific circuit form of the present invention for implementing the method can be shown in fig. 5, and includes: a starting capacitor Cvcc, a starting circuit 1, an identification circuit 2 and an NMOS transistor M2;

the starting capacitor Cvcc is connected with a comparison signal input end of the starting circuit 1; the drain electrode of the NMOS transistor M2 is connected with the input end HV of a high-voltage starting circuit of the switch power supply circuit, and the input end HV of the high-voltage starting circuit is connected in front of or behind a rectifier bridge of the switch power supply circuit; the gate and the source of the NMOS transistor M2 are connected to the start circuit 1 and the identification circuit 2, respectively;

the starting circuit 1 specifically includes: the power supply comprises an NMOS transistor N1, a first resistor R1, a voltage regulator tube VR1 and a starting module 10; the drain electrode of the NMOS transistor M2 is connected with the input end HV of the high-voltage starting circuit; the voltage regulator VR1 is reversely connected between the gate of the NMOS transistor M2 and the ground; the first resistor R1 is connected between the gate of the NMOS transistor M2 and the input end HV of the high-voltage starting circuit; the drain of the NMOS transistor N1 is connected to the gate of the NMOS transistor M2, and the source of the NMOS transistor N1 is grounded. .

The identification circuit 2 specifically includes: a control module 21, an analog-to-digital conversion module (D/a)22, a bleeding module 23, and an identification output module 24;

the control module 21 is connected with the output end of the power-on reset signal POR of the starting module 10, and the analog-to-digital conversion module 22 is connected with the digital voltage parameter signal output end of the control module 21; the bleeding module 23 is composed of an operational amplifier OP, an NMOS transistor N2 and a resistor R2 in fig. 4, and the bleeding module 23 is connected to the source of the NMOS transistor M2, the analog-to-digital conversion module 22 and the control module 21, respectively; the identification output block 24 Is composed of a PMOS transistor P3, an NMOS transistor N3, a current source Is, and a schmitt trigger 20 in fig. 4, and the identification output block 24 Is connected to the source of the NMOS transistor M2 and Is connected to the power-on reset signal POR output from the start block 10. Meanwhile, the voltage status indication signal GHV output by the output terminal of the identification output module 24 is fed back to the control module 21, the control module 21 is further connected to the gate of the NMOS transistor N1, and outputs a circuit access control signal GN1 for controlling the gate voltage of the NMOS transistor N1 according to the received voltage status indication signal GHV, so as to control the on or off of the NMOS transistor N1, further control the on or off of the NMOS transistor M2, and thus enable the unit 1 and the control unit 2 to be kept connected or disconnected.

Based on the circuit structure, after the switching power supply circuit is powered on, the control module 21 outputs preset digital voltage parameters DIS [1:0] ═ 00, the ENOP is set to 0, the operational amplifier OP and the N2 discharge path are turned off, the circuit access control signal GN1 equals 0, and the control module 21 outputs a high-level start circuit control signal PS to control the start module 10 to be turned on.

At this time, the NMOS transistor N1 is turned off, and Vgs of the NMOS transistor M2 is larger than V as the HV voltage at the input end of the high-voltage starting circuit is increased _TH The NMOS transistor M2 is turned on, charging Cvcc through the NMOS transistor M2 and the start-up module 10; when VCC is charged above the reset voltage set inside the starting module 10, the starting module 10 outputs a low-level power-on reset signal POR to the identification circuit 2;

after receiving the power-on reset signal POR at a low level, the control module 21 outputs a start circuit control signal PS at a low level to control the start module 10 to be turned off, the Cvcc charging is stopped, the control module 21 starts timing, and the circuit enters an identification stage.

The control module 21 receives the power-on reset signal POR with low level and the clock signal CLK of the switching power supply circuit, starts first timing, and the timing time T1 can be 16ms to 32 ms. The control module 21 outputs a bleeding control signal ENOP having a preset digital voltage parameter DIS [1:0] 01 and a high level for controlling the magnitude of the bleeding current in the bleeding module 23.

The bleeding module 23 controls the operational amplifier OP to operate according to the high-level bleeding control signal ENOP, the digital voltage parameter DIS [1:0] ═ 01 is converted by the analog-to-digital conversion module (D/a)22 and then sent to the operational amplifier OP, the NMOS transistor N2 is turned on by the output control of the operational amplifier OP, and the voltage at the input terminal HV of the high-voltage starting circuit is bled to ground through the NMOS transistor M2, the NMOS transistor N2 and the resistor R2.

It should be noted that if the input terminal HV of the high-voltage start-up circuit is connected to the front Vac _ abs of the rectifier bridge, the waveform is as shown in fig. 6, and in order to pull Vhv to 0V at the time of Vac zero crossing, the current IR2 of R2 needs to be large enough. In the specific implementation of the present invention, the corresponding relationship and values between the digital voltage parameters and the corresponding analog-to-digital converted voltages Vrds and IR2 currents are adopted as shown in table 1 below. The IR2 corresponding to the digital voltage parameter DIS [1:0] ═ 01 is 1.6mA, so as to ensure that the current IR2 of R2 needs to be large enough to pull Vhv of the input terminal HV of the high-voltage starting circuit to 0V at the time of Vac zero crossing.

The identification output module 24 Is composed of a PMOS transistor P3, an NMOS transistor N3, and a current source Is (which may take a value of 2-4 uA), and gates of the PMOS transistor P3 and the NMOS transistor N3 are controlled by an internal reference voltage Vref1 (which may take a value of about 5V).

Thus, the sum of Vref1 and the turn-on threshold Vt of PMOS transistor P3 becomes the reference voltage for turning on the PMOS transistor, that is, the reference voltage Vref set inside the identification circuit in the above-mentioned method.

In the case where the input HV of the high-voltage starting circuit is connected in front of the rectifier bridge, there are the following situations: when Vhv is greater than Vref, the PMOS transistor P3 is turned on, the input end of the schmitt trigger 20 is a high-level signal, and the voltage state indicating signal GHV output by the identification circuit is 1; when Vhv Is equal to or less than Vref, the PMOS transistor P3 Is turned off, the level of the input terminal of the schmitt trigger 20 Is pulled to a low level signal by the current source Is, and the output GHV Is 0.

In the case where the input terminal HV of the high-voltage start-up circuit is connected to the rear of the rectifier bridge, there are only the following cases: vhv > Vref, PMOS transistor P3 is turned on, the input terminal of schmitt trigger 20 is a high level signal, and the voltage status indication signal GHV output from the identification circuit is 1.

The control module 21 receives the voltage status indication signal GHV output by the identification output module 24, and counts whether the duration of the voltage status indication signal GHV being 0 is greater than the set time threshold Tref within the first timing period T1, if so, generates the identification result signal ENCHG being 1 at the first level within the first timing period T1, otherwise, generates the identification result signal ENCHG being 0 at the second level. The recognition result signal ENCHG is an internal signal of the control module.

If the identification result signal is the signal for generating the first level, the input end HV of the high-voltage starting circuit is connected to the front of the rectifier bridge, the waveform of the circuit is as shown in fig. 6, the internal signal ENCHG is set to 1, at this time, the control module 21 continues to set the circuit access control signal GN1 to 0, so that the NMOS transistor N1 is kept off, the gate voltage of the NMOS transistor M2 is kept at the high level, and the NMOS transistor M2 is kept on;

if the identification result signal of the second level is generated, the waveform in the circuit is as shown in fig. 7 after the input end HV of the high-voltage starting circuit is connected to the rectifier bridge, the internal signal ENCHG is set to 0, at this time, the control module 21 continues to connect the circuit to the control signal GN1 to be set to 1, so that the NMOS transistor N1 is turned on, the gate voltage of the NMOS transistor M2 is pulled down, and the NMOS transistor M2 is turned off, thereby disconnecting the circuit with the automatic identification and adaptive X capacitor discharge function in the switching power supply circuit, achieving the function of automatic adaptation according to the application requirements, and simultaneously reducing the power consumption.

In the case where the recognition result signal ENCHG at the first level is generated at 1, the recognition circuit 2 can also be automatically adapted to perform X capacitance discharge of the switching power supply circuit when the switching power supply circuit is powered off.

The identification result signal ENCHG is 1, the third timing is started, the timing time T3 in this embodiment is 700ms, that is, the plug pull-out is monitored after the interval of 700ms, and the second timing stage is started when the timing time T3 is reached. The third timing stage ENOP is set to 0, the discharge path of the operational amplifier OP and the NMOS transistor N2 is cut off, and the direct current loss is reduced.

The second timer is started, and the ENOP is set to 1, that is, the bleeding control signal is set to high level, so as to eliminate the influence of leakage of the rectifier diode in the switching power supply circuit, and therefore, the ground current IR2 at the input terminal HV of the high-voltage starting circuit is also started when detecting whether the switching power supply circuit is powered off (the power plug is pulled out).

DIS[1:0]Value of	Corresponding to Vrds voltage	Corresponding to IR2 current
			00	/	/
01	800mV	1.6mA
			10	2000mV	4mA

TABLE 1

In the specific implementation of the present invention, the second timing time T2 takes a value of 72ms, and DIS [1:0] is output as 01 within the timing time T2; if GHV is detected to be 0 at any time between 0 and 72ms, the timing time T2 is cleared, and the plug is considered not to be pulled out.

At this time, ENOP is set to 0 again, the third timing is started again, the process is repeated, and the second timing stage is started again when the timing time T3 is up. Therefore, the plug can be continuously monitored without being pulled out on line, and the power consumption can be reduced to a certain extent. Of course, the monitoring of the second timing phase can also be carried out continuously without providing the third timing phase.

If the second timing phase is executed, and GHV is not detected to be 0 when T2 times 72ms, then it is determined that the plug is unplugged, and then the output DIS [1:0] ═ 10 is output, and the X capacitor discharge operation is executed by the large current on R2.

The method and the circuit for automatically identifying and adapting the discharge function of the X capacitor in the switch circuit provided by the embodiment of the invention enable the switch circuit to be simultaneously suitable for application occasions needing to discharge with the X capacitor and also can be applied to application occasions needing no discharge of the X capacitor. The identification circuit can be automatically turned off under the application environment without discharging of the X capacitor, so that power consumption is reduced.

Fig. 8 is a flyback control chip integrated with a circuit for automatically recognizing and adapting the discharge function of the X capacitor in the switch circuit according to an embodiment of the present invention. Fig. 8 shows a specific application of the circuit provided by the present invention for automatically identifying and adapting the discharge function of the X capacitor in the switch circuit integrated in the switch circuit.

The chip consists of a starting circuit, an identification circuit, a high-voltage MOS device M2, a PWM generating circuit and a driving circuit. The startup circuit is used to supply power to the VCC pin when power is on and supplemental power is needed. The identification circuit identifies whether an X capacitor discharge function is needed or not according to an external connection method of the HV pin, and is used for detecting whether the power plug is pulled out or not in a normal working stage and making corresponding action when the X capacitor discharge function is enabled; when the discharge function of the X capacitor is not enabled, the circuit does not work and does not consume current; the PWM generating circuit generates a control signal PWM of the main power device according to the feedback signal FB; the drive circuit generates a drive signal GT according to the PWM that can directly drive the main power device.

The application of the invention in the switch power supply is not limited to a flyback framework in the switch power supply, and the invention is suitable for any application occasion needing an X discharge function; the chip pins in fig. 8 only indicate necessary pins, and the pins may be increased or decreased according to the specific switching power supply architecture and function, which all belong to the protection scope of this patent.

Those of skill would further appreciate that the various illustrative components and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both, and that the various illustrative components and steps have been described above generally in terms of their functionality in order to clearly illustrate this interchangeability of hardware and software. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the implementation. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied in hardware, a software module executed by a processor, or a combination of the two. A software module may reside in Random Access Memory (RAM), memory, Read Only Memory (ROM), electrically programmable ROM, electrically erasable programmable ROM, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.

The above-mentioned embodiments, objects, technical solutions and advantages of the present invention are further described in detail, it should be understood that the above-mentioned embodiments are only examples of the present invention, and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. A method for automatically identifying and adapting the discharge function of an X capacitor in a switching circuit, the method comprising:

2. The method according to claim 1, characterized in that the identification circuit is connected to the high voltage starting circuit input terminal HV through an NMOS transistor;

3. The method of claim 1, further comprising an automatic adaptation process;

4. The method of claim 3, wherein after the identification circuit generates the first level of the identification result signal to enable the discharge function of the X capacitor of the switching power supply circuit, the method further comprises:

5. The method of claim 1, wherein the identification circuit outputs a start-up circuit control signal PS to control the start-up circuit to be turned off after the start-up circuit outputs a power-on reset signal to start up the identification circuit.

6. A circuit for automatically identifying and adapting the discharge function of an X capacitor in a switching circuit, the circuit comprising: the starting capacitor, the starting circuit, the identification circuit and an NMOS transistor M2;

the identification circuit counts whether the duration time that the voltage state indication signal GHV is 0 in the timing period is greater than a set time threshold value, if so, an identification result signal of a first level is generated to enable the X capacitor discharge function of the switching power supply circuit, otherwise, an identification result signal of a second level is generated to control the NMOS transistor M2 to disconnect the connection of the identification circuit to the switching power supply circuit.

7. The circuit according to claim 6, characterized in that the start-up circuit comprises in particular: the power supply comprises an NMOS transistor N1, a first resistor R1, a voltage regulator tube VR1 and a starting module;

8. The circuit according to claim 7, characterized in that the identification circuit comprises in particular: the device comprises a control module, an analog-to-digital conversion module, a bleeding module and an identification output module;

the analog-to-digital conversion module is connected with the control module and converts the preset digital voltage parameter into an analog voltage value;

the bleeder module is respectively connected with a source electrode of the NMOS transistor M2, the analog-to-digital conversion module and the control module, and is controlled to start the bleeder module according to the bleeder control signal of the first level and is converted into a current value on a bleeder resistor according to the analog voltage value to form ground bleeder of the input end HV of the high-voltage starting circuit;

the control module is further connected to the identification output module, and is configured to receive the voltage status indication signal GHV output by the identification output module, and count whether the duration of the voltage status indication signal GHV ═ 0 in the first timing period is greater than a set time threshold, if so, generate the identification result signal of the first level, otherwise, generate the identification result signal of the second level.

9. The circuit of claim 8, wherein the control module further connects the gate of the NMOS transistor N1, and controls the NMOS transistor N1 to turn on according to the recognition result signal of the second level, so as to pull down the gate potential of the NMOS transistor M2 to turn off the NMOS transistor M2, thereby disconnecting the recognition circuit from the switching power supply circuit.

10. A switching circuit comprising a circuit for automatically identifying and adapting the discharge function of an X capacitor in a switching circuit according to any one of claims 6 to 9.