Input voltage anomaly detection method, protection method and control circuit

Abstract

The invention provides an input voltage anomaly detection method, a protection method and a control circuit. The control circuit comprises a voltage-current conversion circuit, the input end of which is coupled with the power switch for obtaining the terminal voltage of the power switch; the first capacitor is coupled to the output end of the voltage-current conversion circuit; the comparison circuit is used for comparing the first capacitor voltage with a reference signal and providing an input voltage anomaly detection signal; and a switch control circuit which controls the power switch based on the output of the comparison circuit and starts input voltage abnormality protection when the input voltage abnormality detection signal is valid. The control circuit provided by the invention can realize the anomaly detection of the input voltage based on the terminal voltage of the power switch, can reduce the use of pins, simplifies a peripheral circuit, reduces the system cost, and accelerates the protection response speed.

Description

Technical Field

[0001] This invention relates to the field of electronics, and specifically, but not limited to, a method for detecting abnormal input voltage, a protection method, and a control circuit for a power conversion circuit. Background Technology

[0002] In applications requiring electrical isolation between input and output, such as small and medium power switching power supplies, the flyback converter is the most commonly used power conversion circuit topology. Figure 1 A flyback voltage converter circuit is illustrated. Taking discontinuous current mode as an example, when power switch Q1 is turned on, the voltage difference across it is zero, the primary current Ip rises linearly, the freewheeling diode D1 is reverse-biased and cut off, and the voltage across the primary winding Lp of the transformer is the input voltage Vin of the flyback voltage converter circuit. When power switch Q1 is turned off, the secondary diode D1 is turned on, the voltage across the secondary winding of the transformer is Vo + Vf, and the voltage difference across power switch Q1 is Vin + Nps*(Vo + Vf), where Vo is the output voltage Vo of the flyback voltage converter circuit, Vf is the forward voltage of diode D1, Nps is the turns ratio of the primary and secondary windings, the transformer releases energy to the load, and the secondary current Is of the transformer decreases linearly.

[0003] When the input voltage Vin is lower than the rated input voltage, such as 90V AC, if the power conversion circuit continues to operate, the rising slope of the current Ip will be lower due to the excessively low input voltage. If the system is operating in fixed-frequency mode, it may enter deep continuous current mode (CCM). If the system is operating in quasi-resonant mode, the operating frequency will decrease, leading to excessive peak current. All of these factors can cause the thermal and current stresses on the power supply to exceed the rated input conditions, posing a risk of damage. When the input voltage exceeds the rated threshold, such as 264V AC, if the power supply continues to operate, it may cause excessive stress on the components, also leading to a risk of damage.

[0004] To improve power supply reliability, it is necessary to sample the input voltage Vin to implement input voltage overvoltage protection and input voltage undervoltage protection, thereby improving system reliability.

[0005] Currently, commonly used bus input voltage overvoltage protection schemes employ voltage divider resistors to detect the voltage before or after the rectifier bridge. When the detected voltage exceeds a certain threshold, the control circuit triggers line voltage overvoltage protection, stopping the transmission of PWM (Pulse Width Modulation) signals to drive the power switch until the control circuit chip completes its reset sequence. This scheme has a simple circuit design, but the chip requires an additional functional pin to sample the input voltage, and external resistors are also needed. In terms of protection effectiveness, a filter circuit is typically required to remove glitches in the input voltage to prevent false triggering of the protection. However, the filter circuit introduces signal transmission delays, resulting in a slower response speed, which is unsuitable for scenarios requiring rapid protection response.

[0006] In view of this, there is a need to provide a new structure or control method in order to solve at least some of the above problems. Summary of the Invention

[0007] In response to at least one or more of the problems in the background art, the present invention proposes a control circuit for controlling power switches in a power conversion circuit, an input voltage anomaly detection method, and an input voltage anomaly protection method.

[0008] According to one aspect of the present invention, a control circuit for controlling a power switch in a power conversion circuit is provided. The control circuit includes: a voltage-to-current conversion circuit, the input terminal of which is coupled to the power switch for acquiring the terminal voltage of the power switch; a first capacitor, the first terminal of which is coupled to the output terminal of the voltage-to-current conversion circuit, and the second terminal of which is coupled to a reference ground; a comparator circuit, the first input terminal of which is coupled to the first terminal of the first capacitor, the second input terminal of which receives a reference signal, and the output terminal of which is used to provide an input voltage anomaly detection signal; and a switch control circuit, the input terminal of which is coupled to the output terminal of the comparator circuit, and the output terminal of which is coupled to the control terminal of the power switch, wherein input voltage anomaly protection is activated when the input voltage anomaly detection signal is valid.

[0009] Optionally, the control circuit further includes: a constant current source; and a second capacitor connected in parallel with the constant current source, wherein a first terminal of the second capacitor is coupled to a second input terminal of the comparator circuit, and a second terminal of the second capacitor is coupled to a reference ground.

[0010] Optionally, the control circuit further includes: a timing circuit; a first switch connected in parallel with a first capacitor, the control terminal of the first switch being coupled to the timing circuit, the timing circuit being used to reset the voltage across the first capacitor to zero at a specific time; and a second switch connected in parallel with a second capacitor, the control terminal of the second switch being coupled to the timing circuit, the timing circuit being used to reset the voltage across the second capacitor to zero at a specific time.

[0011] Optionally, the timing circuit controls the first and second switches to reset the voltages across the first and second capacitors to zero when the power switch switches from off to on.

[0012] Optionally, the control circuit further includes a trigger circuit, wherein the first input terminal of the trigger circuit is coupled to the output terminal of the comparator circuit, the trigger input terminal of the trigger circuit is coupled to a timing circuit, the output terminal of the trigger circuit provides an input voltage abnormality detection signal, and the timing circuit controls the trigger circuit to update the output signal of the comparator circuit to the input voltage abnormality detection signal and latch it when the power switch switches from off to on, and simultaneously or subsequently controls the first switch and the second switch to be momentarily turned on.

[0013] Optionally, the power conversion circuit includes a flyback voltage converter circuit, which includes a primary winding and a power switch. The first end of the primary winding receives the input voltage, and the second end of the primary winding is coupled to the first end of the power switch. The second end of the power switch is coupled to the primary reference ground. The input end of the voltage-to-current conversion circuit is coupled to the first end of the power switch to obtain the terminal voltage of the power switch.

[0014] According to another aspect of the present invention, a control circuit for controlling a power switch in a power conversion circuit is provided. The control circuit includes: an integrator circuit, the input of which is coupled to the power switch to obtain the terminal voltage of the power switch, and the output of which provides a detection ramp signal with a slope proportional to the terminal voltage; a comparator circuit, the first input of which is coupled to the detection ramp signal, the second input of which receives a reference ramp signal, and the output of which provides an input voltage anomaly detection signal. During normal operation, the detection ramp signal and the reference ramp signal have the same period, and the period is an integer multiple of the switching period of the power switch; and a switch control circuit, the input of which is coupled to the output of the comparator circuit, and the output of which is coupled to the control terminal of the power switch. When the input voltage anomaly detection signal is valid, input voltage anomaly protection is activated.

[0015] According to one aspect of the present invention, a flyback voltage converter circuit is provided, comprising a primary winding, a power switch, and a control circuit as described in any of the above embodiments, wherein a first end of the primary winding is coupled to the input terminal of the flyback voltage converter circuit for receiving an input voltage, a second end of the primary winding is coupled to a first end of the power switch, and a second end of the power switch is coupled to a primary reference ground.

[0016] According to another aspect of the present invention, a method for detecting an abnormal input voltage in a power conversion circuit is provided, comprising: acquiring the terminal voltage of a power switch in the power conversion circuit; converting the terminal voltage into a current signal; using the current signal to charge a first capacitor to generate an integral signal; and comparing the integral signal with a reference signal to obtain an abnormal input voltage detection signal.

[0017] Optionally, the integral signal is a real-time integral signal that is instantaneously reset to zero once in each switching cycle, and the reference signal is a ramp signal with the same period as the integral signal.

[0018] Optionally, the power conversion circuit is a flyback voltage conversion circuit, where the first terminal of the power switch is coupled to the primary winding, and the terminal voltage reflects the voltage on the first terminal of the power switch.

[0019] According to one aspect of the present invention, a protection method for providing protection when the input voltage of a power conversion circuit is abnormal is proposed, comprising: integrating the terminal voltage of a power switch to calculate and outputting a real-time integrated signal; comparing the real-time integrated signal with a reference ramp signal to generate an input voltage abnormality detection signal; and protecting the power conversion circuit based on the input voltage abnormality detection signal.

[0020] Optionally, the integral calculation of the terminal voltage of the power switch includes: converting the terminal voltage into a current signal; and using the current signal to charge the first capacitor to obtain a real-time integral signal; wherein both the real-time integral signal and the reference ramp signal start to rise from zero simultaneously when the power switch changes from off to on.

[0021] The proposed method, protection method, and control circuit for input voltage anomaly detection in power conversion circuits can detect input voltage anomalies based on the terminal voltage of the power switch. This reduces the number of pins used, simplifies peripheral circuits, lowers system costs, eliminates the need for filter circuits, and accelerates protection response speed. Attached Figure Description

[0022] The accompanying drawings are provided to further illustrate the invention and, together with the description, serve to explain embodiments of the invention, but do not constitute a limitation thereof. In the drawings:

[0023] Figure 1 A flyback voltage converter circuit is shown;

[0024] Figure 2 A power conversion circuit with input voltage abnormality protection function according to an embodiment of the present invention is shown;

[0025] Figure 3 A waveform diagram of operation according to an embodiment of the present invention is shown;

[0026] Figure 4 A power conversion circuit with input voltage undervoltage protection according to another embodiment of the present invention is shown;

[0027] Figure 5 A power conversion circuit according to a specific embodiment of the present invention is shown. Detailed Implementation

[0028] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0029] The description in this section pertains to only a few typical embodiments, and the present invention is not limited to the scope of the embodiments described. Combinations of different embodiments, substitution of some technical features in different embodiments, and substitution of similar or identical prior art with some technical features in the embodiments are also within the scope of the description and protection of the present invention.

[0030] The terms "coupled" or "connected" in this specification include both direct and indirect connections. An indirect connection is a connection made through an intermediate medium, such as a connection through an electrically conductive medium like a conductor, which may contain parasitic inductance or capacitance. It can also be a connection through intermediate circuits or components described in the embodiments of this specification. Indirect connections may also include connections through other active or passive devices that achieve the same or similar function, such as connections through switches, signal amplification circuits, follower circuits, or other circuits or components. "Multiple" or "more" indicates two or more.

[0031] Figure 2 A power conversion circuit according to an embodiment of the present invention is shown. In this embodiment, the power conversion circuit includes a flyback voltage converter circuit, comprising a primary circuit and a secondary circuit, wherein the primary circuit and the secondary circuit are isolated by a transformer T. The transformer T includes a primary winding Lp and a secondary winding Ls magnetically coupled to each other. The primary circuit of the flyback voltage converter circuit includes the primary winding Lp, a power switch Q1, and a control circuit 20 for controlling the power switch Q1. The first terminal of the primary winding Lp receives the input voltage Vin, and the second terminal of the primary winding Lp is coupled to the first terminal of the power switch Q1, the second terminal of the power switch Q1 being grounded. The secondary circuit of the flyback voltage converter circuit includes the secondary winding Ls and a rectifier diode D. When the power switch Q1 is turned on, the primary current Ip flowing through the primary winding Lp and the power switch Q1 increases, the transformer T stores energy, and the secondary rectifier diode D is turned off. When power switch Q1 is turned off, the primary current Ip is zero, and the secondary current Is flowing through the secondary winding Ls and rectifier diode D rapidly rises to its maximum value, then gradually decreases. Transformer T releases electrical energy to the output capacitor Cout and the load. Based on the volt-second balance principle of the primary winding Lp and secondary winding Ls of transformer T, the following formula is derived:

[0032] Vin*Ton=N*Vo*Tdem (1)

[0033] Where Ton is the time for current to flow through the primary winding Lp, N is the turns ratio of the primary winding Lp to the secondary winding Ls, and Tdem is the time for current to flow through the secondary winding. During the Ton stage, power switch Q1 is turned on, the current in the primary winding rises, and the voltage at the second terminal of the primary winding Lp, i.e., the terminal voltage Vd of the first terminal of power switch Q1, is 0 (the on-resistance of power switch Q1 and the current sensing resistor Rcs are very low and can be ignored). The voltage across the primary winding Lp is approximately Vin. Tdem is the time for the secondary rectifier diode D to turn on and for current to flow through the secondary winding Ls. During this stage, the voltage across the secondary winding Ls is Vo, forming the volt-second balance formula (1) mentioned above. At this time, the terminal voltage Vd of the first terminal of power switch Q1 is Vd = Vin + N * Vo. After the secondary current drops to zero, if the primary power switch Q1 has not yet turned on, the oscillation stage Tring begins. During the oscillation stage Tring, the average value of the terminal voltage Vd is the input voltage Vin. Therefore, the average value of the terminal voltage Vd over the entire switching cycle is:

[0034]

[0035] Substituting into formula (1), we get:

[0036]

[0037] That is, the average voltage of the terminal voltage Vd of the power switch Q1 over one switching cycle is equal to the input voltage Vin of the power conversion circuit. Therefore, by detecting the average value of the terminal voltage Vd at the first terminal of the power switch Q1 over one switching cycle, the input voltage Vin at the first terminal of the primary winding can be obtained. This eliminates the need for an additional input voltage detection pin coupled to the first terminal of the primary winding Lp, reducing the number of pins and external components in the control circuit 20, simplifying the circuit, and lowering system cost.

[0038] Continue reading Figure 2The control circuit 20 includes an input voltage anomaly detection circuit and a switch control circuit 203. The input voltage anomaly detection circuit detects whether the input voltage Vin is abnormal, such as whether the input voltage is over-voltage or under-voltage. The switch control circuit 203 receives the input voltage anomaly detection signal OVP output by the voltage anomaly detection circuit and uses it to selectively control the switch control signal PWM provided by the output of the control circuit 20 to be an invalid value (such as a low-level voltage) to keep the power switch Q1 in the off state, providing protection for the flyback voltage converter circuit. Specifically, the control circuit 20 includes a voltage-to-current conversion circuit 201, a first capacitor C1, a comparator circuit 202, and a switch control circuit 203. The voltage-to-current conversion circuit 201, the first capacitor C1, and the comparator circuit 202 are part of the input voltage anomaly detection circuit, used to detect whether the input voltage is abnormal. The input terminal of the voltage-to-current conversion circuit 201 is coupled to the power switch Q1 to obtain the terminal voltage of the power switch. In the illustrated embodiment, the terminal voltage of power switch Q1 is its high-potential terminal voltage, where the high-potential terminal is coupled to the second terminal of the primary winding Lp, the first terminal of the primary winding Lp receives the input voltage Vin, and the low-potential terminal of power switch Q1 is coupled to reference ground GND. Of course, the low-potential terminal of power switch Q1 being coupled to reference ground GND includes the case where the low-potential terminal of power switch Q1 is coupled to reference ground GND through a current sensing resistor Rcs. In another embodiment, the terminal voltage of the power switch can also be the difference between the voltages across the power switch, obtained through a subtraction circuit. In the illustrated embodiment, power switch Q1 includes a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), the high-potential terminal of power switch Q1 is its drain, and the input terminal of voltage-to-current conversion circuit 201 is coupled to the drain of power switch Q1 to receive its drain voltage Vd. In other embodiments, the power switch may also include other types of transistors, such as IGBT (Insulated Gate Bipolar Transistor). Voltage-to-current conversion circuit 201 is used to convert the terminal voltage of power switch Q1 into a current signal proportional to the terminal voltage Vd. The first terminal of the first capacitor C1 is coupled to the output terminal of the voltage-to-current conversion circuit 201, and the second terminal of the first capacitor C1 is coupled to the reference ground GND. The voltage Videt at the first terminal of the first capacitor C1 forms a rising signal with a slope proportional to the voltage Vd at the power switch Q1. Videt, also known as the detection ramp signal, can be a sawtooth ramp signal with a period synchronized with the switching period of the power switch Q1 during normal operation, such as... Figure 3 As shown.

[0039] The first input terminal of the comparator circuit 202 is coupled to the first terminal of the first capacitor C1. The second input terminal of the comparator circuit 202 receives the reference signal Vref, and the output terminal of the comparator circuit 202 provides the input voltage anomaly detection signal OVP. In this embodiment, the input voltage anomaly detection signal OVP is an overvoltage protection signal. In the illustrated embodiment, the reference signal Vref is a ramp signal, which can be generated by charging the second capacitor C2 with a constant current source Iref. The constant current source Iref and the second capacitor C2 are connected in parallel. The specific working principle can be found in the following... Figure 3 This needs further explanation. Of course, the reference ramp signal can also be generated by other types of circuits, such as digital circuits. The detection ramp signal Videt and the reference ramp signal Vref can also be ramp signals with the same period during normal operation (without abnormal input voltage) and whose period is the switching period of power switch Q1 or more integer multiples of the switching period. The integrated signal over two switching periods or several integer multiples of the switching period is compared with the reference ramp signal Vref.

[0040] In another embodiment, the voltage-to-current conversion circuit 201 and the first capacitor C1 are implemented by other integrator circuits, such as digital integrator circuits, for real-time integration of the terminal voltage Vd. Anomalies in the input voltage Vin are detected by comparing the detection ramp signal Videt with the reference ramp signal Vref.

[0041] In other embodiments, the reference signal Vref can also be a fixed preset value, which is compared with the first terminal voltage Videt of the first capacitor C1 only at a specific time to provide a voltage anomaly detection signal. For example, it can be compared with the detection ramp signal Videt only at the end of each switching cycle to generate an input voltage anomaly protection signal.

[0042] In the illustrated embodiment, the first terminal of the first capacitor C1 is coupled to the non-inverting input of the comparator circuit 202, and the reference ramp signal Vref is input to the inverting input of the comparator circuit 202. When the voltage Videot is greater than the reference signal Vref, it indicates that the input voltage Vin of the flyback voltage converter circuit is higher than the normal value. The input voltage anomaly detection signal OVP output by the comparator circuit 202 characterizes the input voltage overvoltage and is used to trigger input voltage overvoltage protection. One input terminal of the switch control circuit 203 is coupled to the output terminal of the comparator circuit 202 to receive the input voltage anomaly detection signal OVP. The output terminal of the switch control circuit 202 is coupled to the control terminal of the power switch Q1 to provide the switch control signal PWM for controlling the turn-on and turn-off of the power switch Q1. When the input voltage anomaly detection signal is invalid (e.g., low level), the control circuit 203 can control the power switch Q1 to work normally, and the system provides the output voltage Vo normally. When the input voltage anomaly detection signal OVP is valid, the switch control circuit 203 activates the input voltage anomaly protection. In one embodiment, when the input voltage abnormality protection is activated, the control switch control signal PWM is continuously low, stopping the driving of power switch Q1 until the control circuit completes a reset. The control circuit 20 further includes other circuitry for controlling the power switch Q1 to turn on and off during normal operation, which will not be described in detail here.

[0043] Figure 3 The diagram below shows the working waveform according to an embodiment of the present invention. Figure 2 The working principle of this invention is explained below. At time t0, the starting point of a switching cycle, the switching control signal PWM is high, the power switch Q1 is turned on, and the primary current Ip gradually increases. At this time, the terminal voltage Vd is approximately zero, the voltage of the detection ramp signal Videt on the first capacitor C1 is zero, and the reference ramp signal Vref begins to rise linearly. At time t1, the switching control signal PWM is low, the power switch Q1 is turned off, the secondary current Is gradually decreases from its peak value, and the terminal voltage Vd = Vin + N*Vo. At this time, Vd is converted into current to charge the first capacitor C1, and the voltage Videt gradually increases. The time t0-t1 is the conduction time Ton. At time t2, the secondary current Is drops to zero, and the time t1-t2 is the demagnetization time Tdem. From time t2, the terminal voltage Vd begins to oscillate. During the oscillation period t2-t3, the average value of Vd is equal to the input voltage Vin. At time t3, the power switch Q1 turns on again, completing one switching cycle. During one switching cycle t0-t3, the current Id output by the voltage-to-current conversion circuit 201 is k*Vd, and its integral value is:

[0044]

[0045] By comparing the integral value of the current Id with the integral value of the reference current Iref in one switching cycle, the input voltage Vin can be compared with the threshold voltage. By reasonably setting Iref and the coefficient k, overvoltage detection or undervoltage detection can be achieved to protect against abnormal input voltage.

[0046] exist Figure 2 In the embodiment shown, the value of Videot at the end of a switching cycle is proportional to the input voltage Vin.

[0047]

[0048] As can be derived from formulas (6) and (7), by using the comparison results of Videt and Vref, the comparison between the input voltage Vin and a reference voltage can be obtained. The reference voltage is C1 / C2*Iref*1 / k, thereby realizing the abnormal detection of the input voltage Vin and providing overvoltage protection or undervoltage protection.

[0049] Based on the rising patterns of the detection ramp signal Videt and the reference ramp signal Vref, even if a full switching cycle has not been reached, if Videt is greater than Vref within a switching cycle, it indicates that the input voltage Vin is overvoltage, without having to wait for the end of the switching cycle.

[0050] continue Figure 3 The explanation is as follows: During the first switching cycle t0-t3, the detection ramp signal Videot remains lower than the reference ramp signal Vref, indicating that the input voltage Vin is lower than the overvoltage reference voltage. The overvoltage protection signal OVP remains low and inactive, and the system does not activate protection. During the second switching cycle t3-t5, the input voltage Vin is higher than the overvoltage reference voltage. Therefore, when power switch Q1 is turned off, its terminal voltage Vd is higher, and the slope of voltage Videot is higher. At time t4, voltage Videot is higher than the reference signal Vref, indicating that the input voltage Vin is higher than the overvoltage reference voltage. At time t4, the input voltage anomaly detection signal OVP shows a valid value, providing protection action and suspending the switching action of power switch Q1. Therefore, by inputting the output current of the voltage-to-current conversion circuit into the first capacitor C1 to generate the detection ramp waveform Videt, and comparing the detection ramp signal Videt with the reference ramp signal Vref, overvoltage can be detected before a normal switching cycle is completed when the input voltage is overvoltaged. This allows for timely overvoltage protection, providing a faster response compared to calculating the average value over the entire switching cycle. In another embodiment, the detection ramp signal Videt and the reference ramp signal Vref can be compared at the end of the switching cycle, t5. That is, at t5, the input voltage anomaly detection signal OVP is switched to an effective value to provide protection.

[0051] The input voltage anomaly detection method provided by this invention compares the integrated signal of the power switch terminal voltage with a reference signal, achieving a filtering effect. This eliminates the need for an additional filtering circuit after sampling the input voltage to remove glitches, avoiding signal delay caused by the filtering circuit and accelerating the protection response speed. It also reduces the number of pins, simplifies peripheral components, and lowers system costs.

[0052] In one embodiment, the control circuit 20 is fabricated as a semiconductor chip on a semiconductor substrate. In another embodiment, the control circuit 20 is fabricated in a semiconductor package. In yet another embodiment, the control circuit semiconductor chip and the power switch power chip are fabricated in the same semiconductor package.

[0053] Besides the flyback voltage converter circuit shown in the figure, this invention can also be applied to other types of power conversion circuits. In one embodiment, the power conversion circuit includes a buck voltage converter circuit. By employing the input voltage anomaly detection circuit and protection method of this invention, input voltage detection can also be performed, eliminating the need for filtering circuits and improving protection response speed. In one embodiment, the power conversion circuit includes other isolated power conversion circuits besides the flyback voltage converter circuit. Using the volt-second balance formula, the input voltage of the power conversion circuit can be obtained through a correlation function of the average value of the terminal voltage, realizing input voltage anomaly detection and protection, improving protection response speed while reducing control circuit pins.

[0054] Figure 4 A flyback voltage converter circuit according to another embodiment of the present invention is shown. Compared to Figure 3 The embodiment shown, Figure 4 In the intermediate embodiment, the input voltage anomaly detection circuit 400 is used to implement input voltage undervoltage detection to provide undervoltage protection for the input voltage Vin. The inverting input terminal of the comparator circuit 401 is coupled to the first terminal of the first capacitor C1, and the non-inverting input terminal of the comparator circuit 401 receives a reference signal Vref2. At the end of the switching cycle, if the voltage at the first terminal Videt of the first capacitor C1 is lower than the reference signal Vref2, the comparator circuit 401 outputs an input voltage anomaly detection signal BOP, which indicates input voltage undervoltage, to trigger input voltage undervoltage protection and prevent the power switch from operating in an undervoltage state.

[0055] Figure 5A power conversion circuit according to a specific embodiment of the present invention is shown. The input voltage anomaly detection circuit 500 in the control circuit further includes a first switch S1, a second switch S2, a timing circuit 501, and a trigger circuit 502. The first switch S1 is connected in parallel with a first capacitor C1, and the first switch S1 is used to reset the voltage Videt on the first capacitor C1 to zero when it is turned on. The second switch S2 is connected in parallel with the second capacitor C2, and the second switch S2 is used to reset the voltage Vref on the second capacitor C2 to zero. The timing circuit 501 outputs three control signals Ctr1, Ctr2, and Ctr3 to control the first switch S1, the second switch S2, and to provide a trigger signal to the trigger circuit 502, respectively. At the end of a switching cycle, the detected ramp signal Videt is proportional to the input voltage Vin, and the timing circuit 501 controls the trigger circuit 502 to latch the output signal of the comparator circuit as the input voltage anomaly detection signal at this time. Preferably, the timing circuit 501 triggers the first switch S1 and the second switch S2 to turn on simultaneously. Preferably, the timing circuit 501 triggers the first switch S1 and the second switch S2 to momentarily turn on at corresponding time nodes in each switching cycle, such as when the power switch Q1 switches from off to on, so that voltages Videt and Vref are simultaneously reset to zero at that moment. In another embodiment, the timing circuit 501 may also trigger the first switch S1 and the second switch S2 to turn on every two switching cycles. In yet another embodiment, the timing circuit 501 may trigger the first switch S1 and the second switch S2 at different times. The first input terminal of the trigger circuit 502 is coupled to the output terminal of the comparator circuit, the trigger input terminal of the trigger circuit 502 is coupled to the timing circuit 501, and the output terminal of the trigger circuit 502 provides an input voltage anomaly detection signal OVP. Preferably, the timing circuit 501 provides a valid signal when the power switch Q1 switches from off to on. The control trigger circuit 502 outputs the output signal of the comparator circuit as the input voltage anomaly detection signal OVP and latches it, making the signal Videot proportional to the input voltage Vin. Simultaneously or subsequently, it controls the first switch S1 and the second switch S2 to momentarily turn on, resetting Videot and Vref to zero and initiating the input voltage anomaly detection for the next switching cycle. In another embodiment, the second switch S2, the constant current source Iref, and the second capacitor C2 can be replaced by a fixed reference voltage. When the power switch Q1 switches from off to on, the timing circuit controls the trigger circuit 502 to update the output signal. Since the detection ramp signal Videot is proportional to the input voltage Vin, the input voltage Vin detection signal is compared with the fixed reference voltage for overvoltage or undervoltage protection. In another embodiment, the control circuit does not include the trigger circuit 53. The timing circuit 502 outputs signals Ctr1 and Ctr2 to control the first switch S1 and the second switch S2.In another embodiment, the timing circuit controls the first switch S1 and the second switch S2 to not be turned on at the same time. For example, the second switch S2 is controlled to be turned on momentarily when the power switch Q1 switches from off to on, while the first switch S1 is controlled to be turned on momentarily when the power switch Q1 switches from on to off. Since the terminal voltage Vd is zero during the conduction period of the power switch Q1, it does not affect the waveform change of the detection ramp signal Videt and the control effect.

[0056] As can be seen from the above embodiments, the present invention proposes a detection method for abnormal input voltage in a power conversion circuit. Preferably, the detection method includes first acquiring the terminal voltage of the power switch in the power conversion circuit, then converting the terminal voltage into a current signal, using the current signal to charge a first capacitor to generate an integral signal, and obtaining an abnormal input voltage detection signal by comparing the integral signal with a reference signal. This allows for a comparison between the input voltage and a reference value, reduces the number of pins coupled to the input voltage terminal, eliminates signal delay caused by glitches in the filtering circuit, and accelerates the protection response speed.

[0057] Preferably, the integral signal is instantaneously reset to zero once per switching cycle, and the reference signal is a ramp signal. In one embodiment, both the integral signal and the reference signal are instantaneously reset to zero simultaneously when the power switch transitions from off to on. In another embodiment, the reference signal is instantaneously reset to zero and begins to rise linearly when the power switch transitions from off to on, while the integral signal is instantaneously reset to zero when the power switch transitions from on to off. This allows for protection when the real-time integral signal exceeds the reference ramp signal, without waiting for the end of a complete switching cycle, resulting in a faster response time.

[0058] Preferably, the power conversion circuit includes a flyback voltage converter circuit, wherein the first terminal of the power switch is coupled to the primary winding, and the terminal voltage is the voltage on the first terminal of the power switch. In another embodiment, the power conversion circuit includes a Buck circuit.

[0059] In one embodiment, the integral signal is the instantaneous value of the first capacitor C1 after charging in one switching cycle, and the reference signal is a fixed preset signal. In another embodiment, the voltage-to-current conversion circuit and the first capacitor can be replaced by other integrator circuits to output a real-time integral signal.

[0060] This invention also proposes a protection method for providing protection when the input voltage of a power conversion circuit is abnormal. Preferably, the protection method includes integrating the terminal voltage of the power switch to output a real-time integrated signal; comparing the real-time integrated signal with a reference ramp signal to generate an input voltage anomaly detection signal; and protecting the power conversion circuit based on the input voltage anomaly detection signal. Preferably, integrating the terminal voltage of the power switch includes: performing current transformation on the terminal voltage to obtain a current signal; and using the current signal to charge a first capacitor to obtain a real-time integrated signal; wherein both the real-time integrated signal and the reference ramp signal can simultaneously begin to rise from zero when the power switch switches from off to on.

[0061] Those skilled in the art should know that the logic controls such as "high level" and "low level", "set" and "reset", "non-inverting input" and "inverting input" in the logic control involved in the specification or drawings can be interchanged or changed, and the same function or purpose as the above embodiment can be achieved by adjusting the subsequent logic control.

[0062] The description and application of the present invention herein are illustrative and not intended to limit the scope of the invention to the embodiments described above. The effects or advantages described in the specification may not be apparent in actual experimental cases due to uncertainties in specific conditions or other factors, and such descriptions are not intended to limit the scope of the invention. Variations and modifications to the embodiments disclosed herein are possible, and various substitutions and equivalents of the components in the embodiments are well known to those skilled in the art. It should be understood by those skilled in the art that the invention can be implemented in other forms, structures, arrangements, proportions, and with other components, materials, and parts without departing from the spirit or essential characteristics of the invention. Other variations and modifications can be made to the embodiments disclosed herein without departing from the scope and spirit of the invention.

Claims

1. A control circuit for controlling a power switch in a power conversion circuit, comprising: A voltage-to-current conversion circuit, the input terminal of which is coupled to a power switch to obtain the terminal voltage of the power switch; The first capacitor has its first terminal coupled to the output terminal of the voltage-to-current conversion circuit, and its second terminal coupled to the reference ground. The comparator circuit has a first input terminal coupled to the first terminal of the first capacitor, a second input terminal receiving a reference signal, and an output terminal used to provide an input voltage anomaly detection signal. as well as The switch control circuit has its input terminal coupled to the output terminal of the comparator circuit, and its output terminal coupled to the control terminal of the power switch. When the input voltage abnormality detection signal is valid, the input voltage abnormality protection is activated.

2. The control circuit as described in claim 1, further comprising: Constant current source; as well as The second capacitor is connected in parallel with the constant current source. The first end of the second capacitor is coupled to the second input terminal of the comparator circuit, and the second end of the second capacitor is coupled to the reference ground.

3. The control circuit as described in claim 2, further comprising: Sequential circuits; The first switch is connected in parallel with the first capacitor. The control terminal of the first switch is coupled to a timing circuit, which is used to reset the voltage across the first capacitor to zero at a specific time. as well as The second switch is connected in parallel with the second capacitor. The control terminal of the second switch is coupled to a timing circuit, which is used to reset the voltage across the second capacitor to zero at a specific time.

4. The control circuit as described in claim 3, wherein the timing circuit controls the first switch and the second switch to reset the voltage across the first capacitor and the voltage across the second capacitor to zero when the power switch switches from off to on.

5. The control circuit as described in claim 3 further includes a trigger circuit, wherein the first input terminal of the trigger circuit is coupled to the output terminal of the comparator circuit, the trigger input terminal of the trigger circuit is coupled to a timing circuit, the output terminal of the trigger circuit provides an input voltage abnormality detection signal, and the timing circuit controls the trigger circuit to update the output signal of the comparator circuit to the input voltage abnormality detection signal and latch it when the power switch switches from off to on, and simultaneously or subsequently controls the first switch and the second switch to be momentarily turned on.

6. The control circuit as described in claim 1, wherein the power conversion circuit includes a flyback voltage conversion circuit, the flyback voltage conversion circuit includes a primary winding and a power switch, the first end of the primary winding receives the input voltage, the second end of the primary winding is coupled to the first end of the power switch, the second end of the power switch is coupled to the primary reference ground, and the input end of the voltage-to-current conversion circuit is coupled to the first end of the power switch for obtaining the terminal voltage of the power switch.

7. A control circuit for controlling a power switch in a power conversion circuit, comprising: An integrator circuit, whose input is coupled to a power switch to obtain the terminal voltage of the power switch, and whose output provides a detection ramp signal with a slope proportional to the terminal voltage. The comparator circuit has a first input terminal coupled to a detection ramp signal, a second input terminal receiving a reference ramp signal, and an output terminal used to provide an input voltage anomaly detection signal. During normal operation, the detection ramp signal and the reference ramp signal have the same period, and the period is an integer multiple of the switching period of the power switch. as well as The switch control circuit has its input terminal coupled to the output terminal of the comparator circuit, and its output terminal coupled to the control terminal of the power switch. When the input voltage abnormality detection signal is valid, the input voltage abnormality protection is activated.

8. A flyback voltage converter circuit, comprising a primary winding, a power switch, and a control circuit as described in any one of claims 1-7, wherein a first end of the primary winding is coupled to the input terminal of the flyback voltage converter circuit for receiving an input voltage, a second end of the primary winding is coupled to a first end of the power switch, and a second end of the power switch is coupled to a primary reference ground.

9. A method for detecting abnormal input voltage in a power conversion circuit, comprising: Obtain the terminal voltage of the power switch in the power conversion circuit; Convert the terminal voltage into a current signal; The first capacitor is charged using a current signal to generate an integral signal; as well as The input voltage anomaly detection signal is obtained by comparing the integrated signal with the reference signal.

10. The input voltage anomaly detection method as described in claim 9, wherein the integral signal is a real-time integral signal and is instantaneously set to zero once in each switching cycle, and the reference signal is a ramp signal with the same period as the integral signal.

11. The input voltage anomaly detection method as described in claim 9, wherein the power conversion circuit is a flyback voltage conversion circuit, the first terminal of the power switch is coupled to the primary winding, and the terminal voltage reflects the voltage on the first terminal of the power switch.

12. A protection method for providing protection when the input voltage of a power conversion circuit is abnormal, comprising: The terminal voltage of the power switch is integrated and calculated to output a real-time integrated signal; The real-time integral signal is compared with the reference ramp signal to generate an input voltage anomaly detection signal; as well as The power conversion circuit is protected based on the abnormal input voltage detection signal.

13. The protection method as described in claim 12, wherein integrating the terminal voltage of the power switch includes: The terminal voltage is transformed into a current signal; as well as A real-time integral signal is obtained by charging the first capacitor with a current signal. Both the real-time integral signal and the reference ramp signal begin to rise from zero simultaneously when the power switch switches from off to on.

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