Power converter and control circuit therefor

Abstract

This application provides a control circuit for a power converter, the power converter including a switching transistor and an output inductor, one end of the output inductor being an output node and the other end being a switching node. The control circuit is used to generate a control signal to control the switching transistor in the power converter. The control circuit includes: a resistor-capacitor oscillation network connected to both ends of the output inductor, used to generate an oscillation signal containing a feedback ramp compensation component based on the voltage change across the output inductor. When the power converter operates in discontinuous current mode, the resistor-capacitor oscillation network is disconnected from the output inductor during the period when the inductor current is zero, so that the voltage across the output inductor does not affect the oscillation signal; a comparator; a conduction time generation circuit; and a control signal generation circuit to generate a control signal for controlling the switching transistor in the power converter.

Description

Technical Field

[0001] This application relates primarily to power electronics technology, and more particularly to a power converter and its control circuit. Background Technology

[0002] Power converters employ various control methods, such as voltage control, current control, hysteresis control, and constant-time on-time control. Among these, constant-time on-time control is widely used in power converters due to its excellent dynamic response speed and high light-load efficiency. Furthermore, to ensure stable operation of the power converter in both continuous current mode (CCM) and discontinuous current mode (DCM), further requirements are placed on the design and implementation of the power converter.

[0003] Application content

[0004] The technical problem to be solved by this application is to provide a power converter and its control circuit and control method, so as to realize steady-state operation of the power converter in both continuous inductor current mode and discontinuous inductor current mode.

[0005] To address the aforementioned technical problems, this application provides a control circuit for a power converter. The power converter includes a switching transistor and an output inductor. One end of the output inductor is an output node, and the other end is a switching node. The control circuit generates a control signal to control the switching transistor in the power converter. The control circuit includes:

[0006] A resistor-capacitor oscillation network is connected to both ends of the output inductor to generate an oscillation signal containing a feedback ramp compensation component based on the voltage change across the output inductor. When the power converter operates in discontinuous inductor current mode, the resistor-capacitor oscillation network is disconnected from the output inductor during the period when the inductor current is zero, so that the voltage across the output inductor does not affect the oscillation signal.

[0007] A comparator has a first input terminal, a second input terminal, and an output terminal. The first input terminal of the comparator is used to input a reference signal, the second input terminal of the comparator is used to input a feedback signal, and the output terminal of the comparator is used to output a comparison signal. The oscillation signal is incorporated into the reference signal or the input feedback signal.

[0008] The conduction time generation circuit starts timing according to the comparison signal or the control signal, and generates a conduction timing signal.

[0009] The control signal generation circuit generates a control signal based on the comparison signal and the turn-on timing signal, which is used to control the switching transistor in the power converter.

[0010] In one embodiment of this application, the oscillation signal is equal to the feedback signal.

[0011] In one embodiment of this application, the resistor-capacitor oscillation network includes a first switch, a first resistor, and a first capacitor. The first resistor, the first switch, and the first capacitor are connected in series and then connected to the two ends of the output inductor. The common terminal of the first switch and the first capacitor outputs the oscillation signal.

[0012] In one embodiment of this application, the resistor-capacitor oscillation network includes a first switch, a first resistor, and a first capacitor. The first switch, the first resistor, and the first capacitor are connected in series and then connected to the two ends of the output inductor. The common terminal of the first resistor and the first capacitor outputs the oscillation signal.

[0013] In one embodiment of this application, the feedback signal is generated by superimposing the oscillation signal with a signal characterizing the output voltage.

[0014] In one embodiment of this application, the resistor-capacitor oscillation network includes a second switch, a single-stage or multi-stage RC circuit, and a differential amplifier. The second switch and the single-stage or multi-stage RC circuit are connected in series to the two ends of the output inductor. The differential amplifier has a first input terminal, a second input terminal, and an output terminal. The first input terminal and the second input terminal of the differential amplifier are connected to the two ends of a capacitor or resistor in the single-stage or multi-stage RC circuit. The output terminal of the differential amplifier outputs an oscillation signal.

[0015] In one embodiment of this application, when the resistor-capacitor oscillation network includes a single-stage RC circuit, the second switch and the resistor and capacitor in the single-stage RC circuit are connected in series to the two ends of the output inductor, and the first input terminal and the second input terminal of the differential amplifier are respectively connected to the two ends of the resistor or capacitor in the single-stage RC circuit.

[0016] In one embodiment of this application, when the resistor-capacitor oscillation network includes a multi-stage RC circuit, the resistor and capacitor in the first stage of the multi-stage RC circuit are connected in series with the second switch and then connected to the two ends of the output inductor. The first input terminal and the second input terminal of the differential amplifier are respectively connected to the two ends of the highest-level resistor or capacitor in the multi-stage RC circuit.

[0017] In one embodiment of this application, a zero-crossing detection circuit is further included, the zero-crossing detection circuit comprising:

[0018] A first comparator has a first terminal, a second terminal, and an output terminal, wherein the first terminal receives a sensing signal characterizing the inductor current of the power converter, the second terminal receives a zero-crossing detection threshold, and the output terminal outputs a zero-crossing indication signal.

[0019] The RS trigger module outputs a zero-crossing detection result signal. The RS trigger module updates the zero-crossing detection result signal based on the zero-crossing prompt signal at the end of the current working cycle and before the next working cycle.

[0020] In one embodiment of this application, the zero-crossing detection circuit further includes a timer, wherein the duration for which the first switch is turned off by the zero-crossing detection result signal is greater than or equal to the oscillation duration of the switch node within one operating cycle in the discontinuous inductor current mode.

[0021] This application also provides a power converter, including: a switching transistor; an output inductor, one end of which is an output node and the other end of which is a switching node; a control circuit, including: a resistor-capacitor oscillation network connected to both ends of the output inductor, used to generate an oscillation signal containing a feedback ramp compensation component based on the voltage change across the output inductor, wherein when the power converter operates in discontinuous current mode, the resistor-capacitor oscillation network is disconnected from the output inductor during the period when the inductor current is zero, so that the voltage across the output inductor does not affect the oscillation signal; a comparator having a first input terminal, a second input terminal, and an output terminal, the first input terminal of the comparator being used to input a reference signal, the second input terminal of the comparator being used to input a feedback signal, and the output terminal of the comparator being used to output a comparison signal, the oscillation signal being incorporated into the reference signal or the input feedback signal; a conduction time generation circuit, used to start timing based on the comparison signal or the control signal, generating a conduction timing signal; and a control signal generation circuit, used to generate a control signal based on the comparison signal and the conduction timing signal, for controlling the switching transistor in the power converter.

[0022] Compared with the prior art, this application has the following advantages: by designing the control circuit in the power converter circuit, the power converter can achieve stable operation in both continuous inductor current mode and discontinuous inductor current mode. Attached Figure Description

[0023] The accompanying drawings are included to provide a further understanding of this application. They form part of this application, illustrate embodiments of the application, and, together with this specification, serve to explain the principles of the application. In the drawings:

[0024] Figure 1 This is a schematic diagram of the circuit structure of a power converter according to an embodiment of this application.

[0025] Figure 2 This is a schematic diagram of the circuit structure of a power converter according to another embodiment of this application.

[0026] Figure 3 This is a schematic diagram of the circuit structure of a power converter according to another embodiment of this application.

[0027] Figure 4A This is a waveform diagram of a power converter according to an embodiment of this application operating in steady state in CCM mode.

[0028] Figure 4B This is a waveform diagram of a power converter according to an embodiment of this application operating in steady state in CCM mode.

[0029] Figure 5 This is a schematic diagram of the working waveform of a power converter according to an embodiment of this application when the resistor-capacitor oscillation network is in DCM mode.

[0030] Figure 6 This is a schematic diagram of the working waveform of a power converter according to an embodiment of the present application when controlling the switching on and off of the resistor-capacitor oscillation network in DCM mode.

[0031] Figure 7 This is a schematic diagram of the zero-crossing detection circuit of a power converter according to an embodiment of this application.

[0032] Figure 8 This is a schematic diagram of the zero-crossing detection circuit of a power converter according to another embodiment of this application.

[0033] Figure 9 This is a schematic diagram of the working waveform of a power converter according to an embodiment of this application when the resistor-capacitor oscillation network is in DCM mode.

[0034] Figure 10 This is a schematic diagram of the working waveform of a power converter according to an embodiment of the present application when controlling the switching on and off of the resistor-capacitor oscillation network in DCM mode. Detailed Implementation

[0035] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0036] Many specific details are set forth in the following description in order to provide a full understanding of this application. However, this application may also be implemented in other ways different from those described herein, and therefore this application is not limited to the specific embodiments disclosed below.

[0037] As indicated in this application, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" do not specifically refer to the singular and may also include the plural. Generally speaking, the terms "comprising" and "including" only indicate the inclusion of explicitly identified steps and elements, which do not constitute an exclusive list, and the method or apparatus may also include other steps or elements.

[0038] Furthermore, it should be noted that the use of terms such as "first" and "second" to define components is merely for the purpose of distinguishing the corresponding components. Unless otherwise stated, these terms have no special meaning and therefore should not be construed as limiting the scope of protection of this application. In addition, although the terminology used in this application is selected from commonly known and used terms, some terms mentioned in this application's specification may have been chosen by the applicant according to his or her judgment, and their detailed meanings are explained in the relevant sections of this description. Moreover, this application should be understood not only through the actual terms used, but also through the meaning implied by each term.

[0039] It should be understood that when a component is referred to as "on another component," "connected to another component," "coupled to another component," or "in contact with another component," it can be directly on, connected to, coupled to, or in contact with that other component, or there may be an intervening component. In contrast, when a component is referred to as "directly on another component," "directly connected to," "directly coupled to," or "directly in contact with" another component, there is no intervening component. Similarly, when a first component is referred to as "electrically contacting" or "electrically coupled to" a second component, there is an electrical path between the first and second components that allows current to flow. This electrical path may include capacitors, coupled inductors, and / or other components that allow current to flow, even if there is no direct contact between the conductive components.

[0040] The embodiments of this application describe a power converter and its control circuit.

[0041] Figure 1 This is a schematic diagram of the circuit structure of a power converter according to an embodiment of this application. Figure 1 As shown, the power converter includes a switching circuit and a control circuit. The switching circuit includes switching transistors, such as a first switching transistor M1 and a second switching transistor M2 connected in series, forming a common node N1. Specifically, the first switching transistor M1 and the second switching transistor M2 each have a source, a gate, and a drain. The first switching transistor M1 and the second switching transistor M2 are connected to the output inductor L1 and the output capacitor C1 through the common node N1. One end of the output inductor L1 is the output node, connected to the first end of the output capacitor C1, and the other end of the output inductor L1 is the switching node SW. The second end of the output capacitor C1 is grounded.

[0042] The switching circuit is used to receive the input voltage VIN and convert it into the output voltage VOUT. Figure 1 In the switching circuit, the drain of the first switching transistor M1 receives the input voltage VIN. The source of the second switching transistor is grounded. The voltage across the first terminal of the output capacitor C1 is the output voltage VOUT.

[0043] In some embodiments, the control circuit of the power converter includes a comparator, a resistor-capacitor oscillation network, an on-time generation circuit, and a control signal generation circuit. The control circuit of the power converter may also include a minimum off-time generation circuit and logic circuitry.

[0044] The minimum turn-off time generation circuit is used to overcome the influence of parasitic capacitance of components in the control circuit, such as the switching transistor itself. It can prevent the power converter circuit from turning on again before the output voltage has turned off to zero when the output is turned off, thereby avoiding circuit losses and conducted radiation interference, or damage to circuit components.

[0045] The logic circuit 102 includes a first input terminal, a second input terminal, and an output terminal. The first input terminal of the logic circuit receives the comparison signal from the output terminal of the comparator COM1. The second input terminal of the logic circuit is coupled to the minimum off-time generation circuit and receives the minimum off-time signal output by it. The output terminal of the logic circuit is coupled to the input terminal of the on-time generation circuit.

[0046] The conduction time generation circuit outputs a conduction time signal PWM. The conduction time signal PWM is then processed by a control signal generation circuit to generate a first control signal HSPWM and a second control signal LSPWM. The first control signal HSPWM and the second control signal LSPWM control the turning on and off of the first switch M1 and the second switch M2, respectively.

[0047] In one embodiment, such as Figure 1 As shown, the logic circuit 102 may include an AND gate G1 and an RS flip-flop. The first and second inputs of the AND gate G1 receive a comparison signal and a minimum off-time signal, respectively. The output of the AND gate G1 is connected to the S port of the RS flip-flop. The R terminal of the RS flip-flop receives a reset signal. The reset signal can be a synchronous or asynchronous signal. The Q output of the RS flip-flop is coupled to an on-time generation circuit to provide an excitation signal.

[0048] A resistor-capacitor oscillation network is connected across the output inductor. This network generates an oscillation signal with feedback ramp compensation based on voltage changes across the output inductor. When the power converter operates in discontinuous current mode, the oscillation network disconnects from the output inductor during periods of zero current, ensuring that the voltage across the output inductor does not affect the oscillation signal.

[0049] like Figure 1 As shown, comparator COM1 has a first input terminal, a second input terminal, and an output terminal. The first input terminal of the comparator is used to input a reference signal. The second input terminal of the comparator is used to input a feedback signal. The output terminal of the comparator is used to output a comparison signal. The value of the reference signal VREF can be set according to the actual situation.

[0050] exist Figure 1 In the circuit, the resistor-capacitor oscillation network includes a first switch S, a first resistor R, and a first capacitor C. The first switch, the first resistor, and the first capacitor are connected in series and then connected to the two ends of the output inductor. The common terminal of the first resistor R and the first capacitor C outputs the oscillation signal.

[0051] In another embodiment, the components in the resistor-capacitor oscillation network can be connected in series: the first resistor R, the first switch S, and the first capacitor C are connected to the two ends of the output inductor. The common terminal of the first switch S and the first capacitor C outputs the oscillation signal. The oscillation signal is connected to the second input terminal of comparator COM1 as a feedback signal; that is, the oscillation signal is equal to the feedback signal at this time.

[0052] When the power converter circuit operates in CCM mode, if the voltage at the first input terminal of comparator COM1 is higher than the voltage at the second input terminal, the comparator output is set high, meaning the comparison signal is high. When the output of the minimum turn-off time generation circuit is also high, the output of AND gate G1 is set high. The S terminal of the RS flip-flop receives the excitation signal and generates an output signal at the Q terminal. The Q output signal is coupled to the input terminal of the turn-on time generation circuit, enabling the turn-on time generation circuit. As mentioned above, the output terminal of the turn-on time generation circuit forms the turn-on time signal PWM. The turn-on time signal PWM then passes through the control signal generation circuit to generate the first control signal HSPWM and the second control signal LSPWM. The first control signal HSPWM and the second control signal LSPWM control the turn-on and turn-off of the first switch M1 and the second switch M2, respectively, to achieve the power conversion function.

[0053] In one embodiment, the conduction time is inversely proportional to the amplitude of the input voltage VIN and directly proportional to the amplitude of the output voltage VOUT, so that the switching frequency of the switching circuit remains basically constant under different input voltage VIN and output voltage VOUT conditions.

[0054] The second input of the comparator is connected to the feedback voltage VFB1. Figure 1 In the circuit shown, VFB1 is taken from the connection point of the first resistor R and the first capacitor C in the resistor-capacitor resonant network. The feedback signal VFB contains the VOUT component and the ramp compensation signal VRAMP component. A typical waveform of the circuit operating in CCM mode is shown below. Figure 4A exemplified.

[0055] The constant on-time control method of power converters, while having good dynamic response speed and light load efficiency, also has high requirements for the shape of output voltage ripple.

[0056] In power converter circuits that do not include a resistor-capacitor resonant network and operate in CCM mode, the equivalent series resistance (ESR) of the output capacitor is very small in some cases. This is due to the ripple on the output capacitor C1 and the current I of the output inductor L1. L In comparison, it lags behind by 90 degrees in phase, therefore the output voltage cannot reflect the inductor current I in a timely manner. L The change. When the first control signal HSPWM is high (assuming the conduction time signal PWM is also high at this time), the inductor current I... L The phase lag is increased. However, due to the aforementioned 90° phase lag, the output voltage VOUT cannot be established in time, causing the feedback voltage VFB1, which is only associated with the output voltage VOUT, to also fail to rise. Therefore, it is possible that after the current on-time of the HSPWM signal has elapsed, VFB1 is still lower than VREF. At this time, an unnecessary additional PWM will be activated, resulting in an unbalanced PWM signal interval and instability.

[0057] In the technical solution of the aforementioned embodiments of this application, since the feedback signal VFB1 is taken from the connection point of the first resistor R and the first capacitor C in the resistor-capacitor oscillation network, the feedback signal VFB1 not only includes the output voltage VOUT component, but also the slope compensation signal VRAMP component, thereby improving the stability of circuit operation.

[0058] Figure 4A This is a waveform diagram of a power converter operating in steady state in CCM mode according to an embodiment of this application. The waveform of the equivalent ramp compensation signal VRAMP is, for example, a periodic sawtooth wave. The equivalent VRAMP signal is as follows: Figure 4A As shown in Figure (a). Figure 4AFigure (b) is the waveform diagram of the feedback signal VFB1. Figure 4A Figure (c) is the waveform diagram of the conduction time signal PWM. From Figure 4A Figure (d), the inductor current I L and the output current I OUT can be seen. I OUT is the load current. The waveform of I OUT is related to the load characteristics.

[0059] In some other embodiments, the power converter of the present application includes a switching circuit and a control circuit. The structure of the switching circuit and the connection of the output inductor and output capacitor are similar to those in Figure 1 the shown embodiment and will not be repeated. The control circuit of the power converter includes a first comparator COM1, a resistor-capacitor oscillation network, a conduction time generation circuit, a control signal generation circuit, a minimum off-time generation circuit, and a logic circuit. Among them, the ramp compensation circuit includes a resistor-capacitor oscillation network and a differential amplifier AMP1.

[0060] Referring to Figure 2 and Figure 3 , the resistor-capacitor oscillation network may include a second switch, a single-stage or multi-stage RC circuit, and a differential amplifier. The second switch S2 and the single-stage or multi-stage RC circuit are connected in series and then connected to both ends of the output inductor L. The differential amplifier has a first input terminal, a second input terminal, and an output terminal. The first input terminal and the second input terminal of the differential amplifier are connected to both ends of the capacitor or resistor in the single-stage or multi-stage RC circuit, and the output terminal of the differential amplifier outputs an oscillation signal. At this time, the oscillation signal is superimposed with a signal Kv representing the output voltage to generate the feedback signal. The relationship between Kv and VOUT is Kv = k * VOUT, where 0 < k < 1. The specific implementation form is, for example, VOUT is adjusted by the ratio of voltage-dividing resistors to obtain Kv.

[0061] In Figure 2 , when the resistor-capacitor oscillation network includes a single-stage RC circuit, the second switch S2, the resistor, and the capacitor in the single-stage RC circuit are connected in series in sequence and then connected to both ends of the output inductor, and the first input terminal and the second input terminal of the differential amplifier are respectively connected to both ends of the resistor or capacitor in the single-stage RC circuit.

[0062] In Figure 3 , when the resistor-capacitor oscillation network includes a multi-stage RC circuit, the resistor and capacitor in the first-stage RC circuit of the multi-stage RC circuit and the second switch are connected in series in sequence and then connected to both ends of the output inductor, and the first input terminal and the second input terminal of the differential amplifier are respectively connected to both ends of the resistor or capacitor of the highest stage in the multi-stage RC circuit.

[0063] In the power converter circuits of these embodiments, the structures of the minimum off-time generation circuit, the on-time generation circuit, and the logic circuit are similar to those of the previous embodiment, and will not be repeated here.

[0064] Compared to a single-stage RC circuit, a multi-stage RC circuit (or second-order and higher-order RC circuit) considers not only the current input state but also the output values ​​from the previous two time points. Introducing the output values ​​from the previous few time points better reflects the gradient of the output voltage VOUT, allowing the control signal to better track the trend of VOUT changes and resulting in a faster dynamic response.

[0065] The power converter circuits of these embodiments of this application, for example Figure 2 or Figure 3 In the power converter circuit, when operating in CCM mode, if the voltage at the first input terminal of comparator COM1 is higher than the voltage at the second input terminal, the comparator output is set high, meaning the comparison signal is high. When the output of the minimum turn-off time generation circuit is also high, the output of AND gate G1 is set high. The S terminal of the RS flip-flop receives the excitation signal and generates an output signal at the Q terminal. The Q output signal is coupled to the input terminal of the turn-on time generation circuit, enabling the turn-on time generation circuit. As mentioned above, the output terminal of the turn-on time generation circuit forms the turn-on time signal PWM. The turn-on time signal PWM then passes through the control signal generation circuit to generate the first control signal HSPWM and the second control signal LSPWM. The first control signal HSPWM and the second control signal LSPWM control the turn-on and turn-off of the first switch M1 and the second switch M2, respectively, to achieve the power conversion function.

[0066] In one embodiment, the conduction time is inversely proportional to the amplitude of the input voltage VIN and directly proportional to the amplitude of the output voltage VOUT, so that the switching frequency of the switching circuit remains basically constant under different input voltage VIN and output voltage VOUT conditions.

[0067] In the technical solutions of the foregoing embodiments of this application, the second input terminal of the first comparator COM1 is connected not only to the VFB signal related to the VOUT signal, but also to the slope compensation signal VRAMP. This overcomes the problem that in some cases, the equivalent series resistance (ESR) of the output capacitor is very small, and the ripple on the output capacitor C1 and the current I of the output inductor L1... L In comparison, it lags behind by 90 degrees in phase, therefore the output voltage cannot reflect the inductor current I in a timely manner. L The changes in the signal intensity may cause an unnecessary additional PWM signal to be activated during circuit operation, resulting in an uneven PWM signal interval and instability. This necessitates the stable operation of the power converter circuit in CCM mode.

[0068] Figure 4B This is a waveform diagram of a power converter in steady-state operation in CCM mode according to another embodiment of this application. The waveform of the ramp compensation signal VRAMP is, for example, a periodic sawtooth wave. The VRAMP signal is as follows: Figure 4B As shown in Figure (a). Figure 4B Figure (b) shows the waveform of the feedback signal VFB plus the slope compensation signal VRAMP. Figure 4B Figure (c) shows the waveform of the PWM conduction time signal. Figure 4B The inductor current I can be seen in diagram (d). L waveform and output current I OUT The waveform. I OUT That is the load current. I OUT The waveform is related to the load characteristics.

[0069] exist Figure 1 In the power converter circuit of one embodiment of this application shown, when the circuit is operating in DCM mode, and when the resistor-capacitor oscillation network in the circuit is a closed loop, the output inductor L1 is depleted of energy (i.e., the inductor current I). L After crossing zero, the second switch M2 is turned off. The voltage change at the switching node (SW node) causes resonance, generating a ringing wave. At this time, the inductor L1 is equivalent to zero resistance, and the switching node (SW node) oscillates with damping around VOUT, that is, the average value is equal to VOUT.

[0070] Specifically, in the current I of the output inductor L1 L Just before the zero-crossing, since the voltage VSW at the switching node (SW node) is approximately equal to ground potential, current will flow from the connection point of the first resistor R and the first capacitor C to the switching node (SW node), and the VOUT voltage will also decrease. The voltage at the R-C connection point, i.e., the VOUT and VRAMP components of the feedback voltage VFB1, will gradually decrease. However, since the voltage across the capacitor cannot change abruptly, the current in the inductor I... L At the moment after the zero crossing, the voltage value at the R / C connection point is still close to the value before the zero crossing. At this time, as mentioned above, the voltage at the switching node (SW node) suddenly changes to VOUT and begins to oscillate. In order for the feedback network to generate sawtooth waveforms such as triangular waves normally, the voltage at the R / C connection point (or RC midpoint) is usually set to be lower than the output voltage VOUT throughout a complete cycle of circuit operation, that is, the feedback voltage VOUT > VFB1.

[0071] At this point, the VOUT component in the feedback signal VFB1 continues to decrease as VOUT continues to decrease. The VRAMP component from the resistor-capacitor resonant network, when the network is a single-path, continues to charge because the voltage value VSW at node SW > VFB1, thus increasing the equivalent VRAMP component. Figure 5 The slow upward segment 501 in Figure (a) is shown. Figure 5 The horizontal dashed line in Figure (a) represents the initial value of the period, VSTART, of the equivalent VRAMP component. During steady-state operation, the equivalent VRAMP component returns to its initial value after one period T. After decreasing to the initial value VSTART in the falling segment 500, the equivalent VRAMP component continues to decrease by a specific value until the inductor current I... L The decline stops at the moment it crosses zero, reaching the low point P1 in the cycle. Figure 5 The position of P1 and the marked inductor current I L The vertical dashed line Izc, crossing zero, corresponds to this. The value of P1 is set to match the amount of change required for the equivalent VRAMP component to return to the initial value VSTART of the period in the subsequent rising segment 501. It is important to note that the initial value VSTART is not zero. Figure 5 Figure (c) is a schematic diagram of the PWM signal generated by the conduction time generation circuit. Figure 5 Figure (d) shows the inductor current I. L A waveform diagram.

[0072] Due to the decrease in the VOUT component and the increase in the VRAMP signal, the combined effect will slow down the rate of decrease of the feedback voltage VFB1 during this period in DCM mode. For example... Figure 5 As shown in Figure (b). Figure 5 In diagram (b), the horizontal dashed line represents the reference voltage VREF. A relatively gentle VFB1 means that, in order to ensure that VFB1 touches the reference voltage VREF at the desired time, VFB1 must be as follows: Figure 5 As shown in the dashed box 502, if a relatively small numerical difference is maintained with VREF over a long period of time, the oscillation or other interference of the voltage value VSW from the switching node (SW node) can easily cause VFB1 to unexpectedly touch VREF earlier than expected within the time period shown in the dashed box 502, thereby causing the comparator COM1 to be falsely triggered and the control circuit to operate prematurely.

[0073] Therefore, in this application Figure 1 In the technical solution of the embodiment shown, the first switch S in the resistor-capacitor oscillation network has a control terminal.

[0074] In some embodiments, the control circuit of the power converter further includes a current zero-crossing detection circuit, which is used to detect whether the inductor current crosses zero in the current cycle and outputs a zero-crossing detection result signal to the resistor-capacitor oscillation network.

[0075] If the zero-crossing detection circuit detects that the inductor current of the power converter has crossed zero in the current cycle, it outputs a zero-crossing detection result signal to indicate that the inductor current is in the zero current range.

[0076] In one embodiment, such as Figure 7 As shown, the zero-crossing detector includes a first comparator COMP and an RS flip-flop. The first comparator COMP has a first terminal, a second terminal, and an output terminal. The first terminal receives a sensing signal Isense characterizing the inductor current of the power converter, the second terminal receives a zero-crossing detection threshold THR, and the output terminal outputs a zero-crossing indication signal Sr. The Q output of the RS flip-flop outputs a zero-crossing detection result signal ZCD. The S terminal of the RS flip-flop is connected to the zero-crossing indication signal Sr, and the R terminal is connected to a first control signal HSPWM. The RS flip-flop module updates the zero-crossing detection result signal based on the zero-crossing indication signal Sr before the next operating cycle at the end of the current operating cycle. Specifically, for example, the ZCD signal is set when a valid signal of Sr arrives, and the ZCD signal is reset when the rising edge of HSPWM arrives. The zero-crossing detection result (ZCD signal) disconnects the first switch during the period when the power converter is operating in discontinuous current mode and is in zero current, specifically, by controlling the control terminal of the first switch S through the zero-crossing detection result signal. The first switch S is, for example, a certain type of switching transistor.

[0077] When the current I of the output inductor L1 L When the circuit crosses zero and the first switch S in the resistor-capacitor oscillation network is open, the resistor-capacitor oscillation network will no longer form a closed circuit. Before the first switch S closes again, the value of the equivalent VRAMP component will also remain at the inductor current I. L A specific value at the zero-crossing moment. The duration for which the zero-crossing detection result signal causes the first switch to open is greater than or equal to the oscillation duration of the switching node within one duty cycle in discontinuous current mode. For example... Figure 8 Therefore, the zero-crossing detection circuit also includes a timer, through which the duration for which the first switch is turned off is greater than or equal to the oscillation duration of the switching node within one operating cycle in the discontinuous current mode of the inductor. Figure 8In this configuration, the timer's timing duration is a preset oscillation duration greater than or equal to the duration itself. After the timing period ends, the timer outputs a high level to the R terminal of the RS flip-flop to reset the ZCD signal. Additionally, when the rising edge of the first control signal HSPWM arrives, the timer also immediately outputs a high level to the R terminal of the RS flip-flop to reset the ZCD signal. The other input of the timer is connected to the ZCD signal to obtain a timing reference point. In this technical solution, because VFB1 can maintain a normal decreasing speed with VOUT, rather than... Figure 5 As shown, the descent speed slows down, so the reference signal VREF can maintain a certain distance from VFB1 in terms of value, making it less likely to be falsely triggered.

[0078] exist Figure 6 In the middle, the time for the first switch S to open is equal to the time for the current I from the inductor to flow out. L From the zero-crossing point to the start of the next cycle, the value of the equivalent VRAMP component will remain at the inductor current I before the start of the next cycle. L The specific value at the zero crossing time, Figure 6 In the middle, it is also its initial value of the cycle, VSTART.

[0079] Figure 2 or Figure 3 In the power converter circuit of the illustrated embodiment, if the output inductor L1 is depleted (i.e., the inductor current I...), L When the second switch M2 is turned off (at zero crossing), and the resistor-capacitor oscillation network in the power converter circuit becomes a closed circuit, it can also cause damped oscillations around VOUT at the switching node (SW node). This will also cause the aforementioned... Figure 5 Similar to the false triggering phenomenon described in the explanation, this is detrimental to the stable operation of the power converter in DCM mode, specifically as follows: Figure 8 exemplified.

[0080] Therefore, in this application Figure 2 and Figure 3 In the technical solution of the illustrated embodiment, the second switch S2 in the resistor-capacitor oscillation network has a control terminal. Referring to the foregoing, the power converter of this application further includes a zero-crossing detection circuit, which outputs a zero-crossing detection result signal. The zero-crossing detection result signal is transmitted to the control terminal of the second switch S2 in the resistor-capacitor oscillation network, causing the second switch S2 to open when the inductor current is in the zero current range. The second switch S2 is, for example, a certain type of switching transistor. The specific structure of the zero-crossing detection circuit is described above.

[0081] When the current I of the output inductor L1 LWhen the circuit crosses zero and the second switch S2 in the resistor-capacitor resonant network is open, the resistor-capacitor resonant network will no longer form a closed circuit. Before the second switch S2 is closed, the value of VRAMP will also remain at the inductor current I. L A specific value at the zero-crossing moment. The duration for which the second switch is turned off by the zero-crossing detection result signal is greater than or equal to the oscillation duration of the switching node within one duty cycle in the discontinuous inductor current mode, specifically, for example, through... Figure 8 The illustrated zero-crossing detection circuit includes a timer. In this technical solution, VFB+VRAMP can maintain a normal decreasing rate with VOUT, rather than as... Figure 9 As shown, the descent speed slows down, so the reference signal VREF can maintain a certain distance from VFB in value, making it less likely to be falsely triggered.

[0082] exist Figure 10 In the middle, the time for the second switch S2 to open is equal to the time for the inductor current I to flow out. L The time from the zero-crossing point to the start of the next cycle. Therefore, the value of VRAMP will be positioned at the inductor current I before the start of the next cycle. L The specific value at the zero crossing time, Figure 10 In this context, VSTART is also the initial value of its cycle. The power converter and its control circuit of this application, through the setting of the control circuit, enable the power converter to achieve stable operation in both continuous inductor current mode and discontinuous inductor current mode.

[0083] This application uses specific terms to describe embodiments of the application. Terms such as "an embodiment," "one embodiment," and / or "some embodiments" refer to a particular feature, structure, or characteristic associated with at least one embodiment of the application. Therefore, it should be emphasized and noted that references to "an embodiment," "one embodiment," or "an alternative embodiment" in different locations throughout this specification do not necessarily refer to the same embodiment. Furthermore, certain features, structures, or characteristics in one or more embodiments of the application can be appropriately combined.

[0084] Similarly, it should be noted that, in order to simplify the description of the present application and thus aid in the understanding of one or more embodiments, the foregoing description of the embodiments of the present application sometimes combines multiple features into a single embodiment, drawing, or description thereof. However, this disclosure method does not imply that the subject matter of the present application requires more features than those mentioned in the claims. In fact, the embodiments contain fewer features than all the features of the single embodiments disclosed above.

[0085] Although this application has been described with reference to specific embodiments, those skilled in the art should recognize that the above embodiments are only used to illustrate this application, and various equivalent changes or substitutions can be made without departing from the spirit of this application. Therefore, any changes or modifications to the above embodiments within the essential spirit of this application will fall within the scope of the claims of this application.

Claims

1. A control circuit for a power converter, the power converter including a switching transistor and an output inductor, one end of the output inductor being an output node and the other end of the output inductor being a switching node, the control circuit being used to generate a control signal to control the switching transistor in the power converter, the control circuit comprising: A resistor-capacitor oscillation network is connected to both ends of the output inductor to generate an oscillation signal containing a feedback ramp compensation component based on the voltage change across the output inductor. When the power converter operates in discontinuous inductor current mode, the resistor-capacitor oscillation network is disconnected from the output inductor during the period when the inductor current is zero, so that the voltage across the output inductor does not affect the oscillation signal. A comparator has a first input terminal, a second input terminal, and an output terminal. The first input terminal of the comparator is used to input a reference signal, the second input terminal of the comparator is used to input a feedback signal, and the output terminal of the comparator is used to output a comparison signal. The oscillation signal is incorporated into the reference signal or the input feedback signal. The on-time generation circuit starts timing according to the comparison signal and generates an on-time signal. The control signal generation circuit generates a control signal based on the comparison signal and the conduction time signal, which is used to control the switching transistor in the power converter.

2. The control circuit according to claim 1, characterized in that, The oscillation signal is equal to the feedback signal.

3. The control circuit according to claim 2, characterized in that, The resistor-capacitor oscillation network includes a first switch, a first resistor, and a first capacitor. The first resistor, the first switch, and the first capacitor are connected in series and then connected to the two ends of the output inductor. The common terminal of the first switch and the first capacitor outputs the oscillation signal.

4. The control circuit according to claim 2, characterized in that, The resistor-capacitor oscillation network includes a first switch, a first resistor, and a first capacitor. The first switch, the first resistor, and the first capacitor are connected in series and then connected to the two ends of the output inductor. The common terminal of the first resistor and the first capacitor outputs the oscillation signal.

5. The control circuit according to claim 1, characterized in that, The feedback signal is generated by superimposing the oscillation signal with a signal characterizing the output voltage.

6. The control circuit according to claim 5, characterized in that, The resistor-capacitor oscillation network includes a second switch, a single-stage or multi-stage RC circuit, and a differential amplifier. The second switch and the single-stage or multi-stage RC circuit are connected in series to the two ends of the output inductor. The differential amplifier has a first input terminal, a second input terminal, and an output terminal. The first and second input terminals of the differential amplifier are connected to the two ends of a capacitor or resistor in the single-stage or multi-stage RC circuit. The output terminal of the differential amplifier outputs an oscillation signal.

7. The control circuit according to claim 6, characterized in that, When the resistor-capacitor oscillation network includes a single-stage RC circuit, the second switch and the resistor and capacitor in the single-stage RC circuit are connected in series to the two ends of the output inductor, and the first input terminal and the second input terminal of the differential amplifier are respectively connected to the two ends of the resistor or capacitor in the single-stage RC circuit.

8. The control circuit according to claim 6, characterized in that, When the resistor-capacitor oscillation network includes a multi-stage RC circuit, the resistor and capacitor in the first stage of the multi-stage RC circuit are connected in series with the second switch and then connected to the two ends of the output inductor. The first input terminal and the second input terminal of the differential amplifier are respectively connected to the two ends of the highest stage resistor or capacitor in the multi-stage RC circuit.

9. The control circuit according to claim 3 or 4, characterized in that, The system further includes a zero-crossing detection circuit, the zero-crossing detection circuit comprising: A first comparator has a first terminal, a second terminal, and an output terminal, wherein the first terminal receives a sensing signal characterizing the inductor current of the power converter, the second terminal receives a zero-crossing detection threshold, and the output terminal outputs a zero-crossing indication signal. The RS trigger module outputs a zero-crossing detection result signal. The RS trigger module updates the zero-crossing detection result signal based on the zero-crossing prompt signal at the end of the current working cycle and before the next working cycle.

10. The control circuit according to claim 9, characterized in that, The zero-crossing detection circuit further includes a timer, wherein the duration for which the first switch is turned off by the zero-crossing detection result signal is greater than or equal to the oscillation duration of the switch node within one operating cycle in the discontinuous inductor current mode.

11. The control circuit according to any one of claims 6 to 8, characterized in that, The system further includes a zero-crossing detection circuit, the zero-crossing detection circuit comprising: A first comparator has a first terminal, a second terminal, and an output terminal, wherein the first terminal receives a sensing signal characterizing the inductor current of the power converter, the second terminal receives a zero-crossing detection threshold, and the output terminal outputs a zero-crossing indication signal. The RS trigger module outputs a zero-crossing detection result signal. The RS trigger module updates the zero-crossing detection result signal based on the zero-crossing prompt signal at the end of the current working cycle and before the next working cycle.

12. The control circuit according to claim 11, characterized in that, The zero-crossing detection circuit further includes a timer, wherein the duration for which the zero-crossing detection result signal causes the second switch to open is greater than or equal to the oscillation duration of the switch node within one operating cycle in the discontinuous inductor current mode.

13. A power converter, comprising: Switching transistor; An output inductor, one end of which is an output node and the other end of which is a switching node; Control circuit, including: A resistor-capacitor oscillation network is connected to both ends of the output inductor to generate an oscillation signal containing a feedback ramp compensation component based on the voltage change across the output inductor. When the power converter operates in discontinuous inductor current mode, the resistor-capacitor oscillation network is disconnected from the output inductor during the period when the inductor current is zero, so that the voltage across the output inductor does not affect the oscillation signal. A comparator has a first input terminal, a second input terminal, and an output terminal. The first input terminal of the comparator is used to input a reference signal, the second input terminal of the comparator is used to input a feedback signal, and the output terminal of the comparator is used to output a comparison signal. The oscillation signal is incorporated into the reference signal or the input feedback signal. The on-time generation circuit starts timing according to the comparison signal and generates an on-time signal. The control signal generation circuit generates a control signal based on the comparison signal and the conduction time signal, which is used to control the switching transistor in the power converter.

14. The power converter according to claim 13, characterized in that, The oscillation signal is equal to the feedback signal.

15. The power converter according to claim 14, characterized in that, The resistor-capacitor oscillation network includes a first switch, a first resistor, and a first capacitor. The first resistor, the first switch, and the first capacitor are connected in series and then connected to the two ends of the output inductor. The common terminal of the first switch and the first capacitor outputs the oscillation signal.

16. The power converter according to claim 14, characterized in that, The resistor-capacitor oscillation network includes a first switch, a first resistor, and a first capacitor. The first switch, the first resistor, and the first capacitor are connected in series and then connected to the two ends of the output inductor. The common terminal of the first resistor and the first capacitor outputs the oscillation signal.

17. The power converter according to claim 13, characterized in that, The feedback signal is generated by superimposing the oscillation signal with a signal characterizing the output voltage.

18. The power converter according to claim 17, characterized in that, The resistor-capacitor oscillation network includes a second switch, a single-stage or multi-stage RC circuit, and a differential amplifier. The second switch and the single-stage or multi-stage RC circuit are connected in series to the two ends of the output inductor. The differential amplifier has a first input terminal, a second input terminal, and an output terminal. The first and second input terminals of the differential amplifier are connected to the two ends of a capacitor or resistor in the single-stage or multi-stage RC circuit. The output terminal of the differential amplifier outputs an oscillation signal.

19. The power converter according to claim 18, characterized in that, When the resistor-capacitor oscillation network includes a single-stage RC circuit, the second switch and the resistor and capacitor in the single-stage RC circuit are connected in series to the two ends of the output inductor, and the first input terminal and the second input terminal of the differential amplifier are respectively connected to the two ends of the resistor or capacitor in the single-stage RC circuit.

20. The power converter according to claim 18, characterized in that, When the resistor-capacitor oscillation network includes a multi-stage RC circuit, the resistor and capacitor in the first stage of the multi-stage RC circuit are connected in series with the second switch and then connected to the two ends of the output inductor. The first input terminal and the second input terminal of the differential amplifier are respectively connected to the two ends of the highest stage resistor or capacitor in the multi-stage RC circuit.

21. The power converter according to claim 15 or 16, characterized in that, The system further includes a zero-crossing detection circuit, the zero-crossing detection circuit comprising: A first comparator has a first terminal, a second terminal, and an output terminal, wherein the first terminal receives a sensing signal characterizing the inductor current of the power converter, the second terminal receives a zero-crossing detection threshold, and the output terminal outputs a zero-crossing indication signal. The RS trigger module outputs a zero-crossing detection result signal. The RS trigger module updates the zero-crossing detection result signal based on the zero-crossing prompt signal at the end of the current working cycle and before the next working cycle.

22. The power converter according to claim 21, characterized in that, The zero-crossing detection circuit further includes a timer, wherein the duration for which the first switch is turned off by the zero-crossing detection result signal is greater than or equal to the oscillation duration of the switch node within one operating cycle in the discontinuous inductor current mode.

23. The power converter according to any one of claims 18 to 20, characterized in that, The system further includes a zero-crossing detection circuit, the zero-crossing detection circuit comprising: A first comparator has a first terminal, a second terminal, and an output terminal, wherein the first terminal receives a sensing signal characterizing the inductor current of the power converter, the second terminal receives a zero-crossing detection threshold, and the output terminal outputs a zero-crossing indication signal. The RS trigger module outputs a zero-crossing detection result signal. The RS trigger module updates the zero-crossing detection result signal based on the zero-crossing prompt signal at the end of the current working cycle and before the next working cycle.

24. The power converter according to claim 23, characterized in that, The zero-crossing detection circuit further includes a timer, wherein the duration for which the zero-crossing detection result signal causes the second switch to open is greater than or equal to the oscillation duration of the switch node within one operating cycle in the discontinuous inductor current mode.

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