Operational amplifier circuit and switching power supply

Abstract

The application discloses an operational amplifier circuit and a switching power supply. A current generating circuit generates a bias current signal in a certain proportional relationship with an input voltage or an output voltage of the switching power supply. The bias current signal is controlled to decrease with the increase of the input voltage or the output voltage. The transconductance of the operational amplifier circuit can be adjusted. The switching power supply can have high transconductance of the operational amplifier at low output voltage, and low transconductance of the operational amplifier at high input voltage or high output voltage. The bandwidth of the system at high input voltage or high output voltage is reduced. The stability of the system under different conditions is ensured.

Description

Technical Field

[0001] This invention relates to the field of power electronics technology, specifically to an operational amplifier circuit and a switching power supply. Background Technology

[0002] In the internal compensation scheme of the power supply circuit, the same set of compensation parameters is usually used to meet the needs of different application scenarios. When the output voltage is low, it is desirable for the transconductance of the operational amplifier to be high. When the output voltage is high, if there is a feedforward capacitor, the system bandwidth will be too large when the compensation parameters are fixed. It is easy to approach or exceed half of the switching frequency, making the system unstable. It is necessary to appropriately reduce the transconductance of the operational amplifier to reduce the bandwidth and improve the system stability.

[0003] Therefore, the internal compensation scheme cannot simultaneously take into account the dynamic response at low output voltage and the stability at high output voltage, and cannot achieve optimal performance. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide an operational amplifier circuit and a switching power supply to solve the technical problem that it is difficult to simultaneously achieve dynamic response at low output voltage and stability at high output voltage in the prior art.

[0005] The technical solution of this invention is to provide an operational amplifier circuit for use in a switching power supply. The operational amplifier circuit includes a current generation circuit and an error amplifier circuit. The current generation circuit receives the input voltage or output voltage of the switching power supply to generate a bias current signal proportional to the input voltage or output voltage, wherein the bias current signal decreases as the input voltage or output voltage increases. The error amplifier circuit includes a current input terminal, a first voltage input terminal, and a second voltage input terminal. The current input terminal receives the bias current signal, and the first voltage input terminal and the second voltage input terminal respectively receive differential voltage signals to output an error amplified signal.

[0006] Preferably, the current generating circuit includes a voltage-to-current conversion circuit and a first current source.

[0007] The first current source outputs a first current signal; the voltage-to-current conversion circuit receives the input voltage or output voltage to generate a second current signal based on the input voltage or output voltage, and the difference between the first current signal and the second current signal is used as the bias current signal.

[0008] Preferably, the second current signal is proportional to the input voltage or the output voltage.

[0009] Preferably, the current generating circuit includes a second current source, the second current source outputs a third current signal, the third current signal is less than the first current signal, the difference between the first current signal and the second current signal is used as a difference current signal, and the signal obtained by adding the third current signal and the difference current signal is used as the bias current signal.

[0010] Preferably, the current generating circuit includes a first current mirror circuit, a second current mirror circuit, and a third current mirror circuit. The first current mirror circuit receives the input voltage or output voltage through a first resistor to generate the second current signal. The first current signal and the second current signal have the same current direction. The input terminal of the second current mirror circuit is connected to the current branch node of the first current signal and the second current signal. The difference current signal is input to the second current mirror circuit, and the second current mirror circuit outputs a first intermediate current signal. The third current mirror circuit receives the first intermediate current signal to output a second intermediate current signal. The second intermediate current signal and the third current signal have the same current direction, and the signal superimposed by the two signals is used as the bias current signal.

[0011] Preferably, when the operational amplifier circuit receives the input voltage, the operational amplifier circuit is connected to the input terminal of the switching power supply to sample the voltage at the input terminal of the switching power supply as the input voltage; when the operational amplifier circuit receives the output voltage, the operational amplifier circuit is connected to the output terminal of the switching power supply to sample the voltage at the output terminal of the switching power supply as the output voltage.

[0012] Preferably, the switching power supply includes a main power switching transistor and an inductor, and the common node of the main power switching transistor and the inductor is a switching node. When the operational amplifier circuit receives the output voltage, the operational amplifier circuit includes a filter circuit, which is connected to the switching node to filter the voltage of the switching node and use it as the output voltage of the switching power supply.

[0013] Preferably, the error amplifier circuit is a CMOS transconductance amplifier.

[0014] Another technical solution of the present invention is to provide a switching power supply, including a power stage circuit and a control circuit, wherein the power stage circuit receives an input voltage and converts the input voltage into a desired output voltage by switching a transistor, and the control circuit includes the above-mentioned operational amplifier circuit, and the control circuit controls the switching action of the transistor in the power stage circuit according to the error amplification signal generated by the operational amplifier circuit.

[0015] Preferably, the operational amplifier circuit receives the output voltage feedback signal and a reference voltage characterizing the desired output voltage as the differential voltage signal of the error amplifier circuit.

[0016] The operational amplifier circuit and switching power supply of this invention generate a bias current signal that is proportional to the input or output voltage of the switching power supply through a current generation circuit, thereby adjusting the transconductance of the operational amplifier circuit. The bias current signal decreases as the input or output voltage increases, resulting in a high transconductance of the operational amplifier at low output voltages and a low transconductance at high input or output voltages. This reduces the system bandwidth at high input or output voltages, ensuring good system stability under various conditions. Attached Figure Description

[0017] Figure 1 This is a circuit block diagram of a first embodiment of the operational amplifier circuit according to the present invention;

[0018] Figure 2 This is a circuit block diagram of a second embodiment of the operational amplifier circuit according to the present invention;

[0019] Figure 3 A circuit diagram of a current generation circuit according to an embodiment of the operational amplifier circuit of the present invention; Detailed Implementation

[0020] The preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitutions, modifications, equivalent methods, and solutions made within the spirit and scope of the present invention.

[0021] To provide the public with a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the invention, but those skilled in the art can fully understand the invention without these details.

[0022] The invention is described in more detail below by way of example with reference to the accompanying drawings. It should be noted that the drawings are in a simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of the invention.

[0023] refer to Figure 1 This is a circuit block diagram of a first embodiment of the operational amplifier circuit according to the present invention, with reference to... Figure 2This is a circuit block diagram of a first embodiment of the operational amplifier circuit according to the present invention. The operational amplifier circuit of this embodiment is used in a switching power supply, such as a Buck switching power supply, but is not limited thereto; it can also be used in other suitable switching power supplies. The switching power supply includes a power stage circuit and a control circuit. Taking a Buck switching power supply as an example, the power stage circuit includes an input capacitor C00, an output capacitor C01, a main power switching transistor M00, a freewheeling diode D00, and an inductor L00.

[0024] For example, the operational amplifier circuit includes a current generation circuit 10 and an error amplifier circuit 20. The current generation circuit 10 receives the input voltage or output voltage of the switching power supply to generate a bias current signal Iss proportional to the input voltage or output voltage, wherein the bias current signal decreases as the input voltage or output voltage increases. The error amplifier circuit 20 includes a current input terminal, a first voltage input terminal, and a second voltage input terminal. The current input terminal receives the bias current signal, and the first and second voltage input terminals respectively receive differential voltage signals to output an error amplified signal Vc. In one example, the operational amplifier circuit is connected to the output terminal of the switching power supply to sample the voltage at the output terminal of the switching power supply as the output voltage Vout. The operational amplifier circuit receives the output voltage feedback signal VFB and a reference voltage VREF characterizing the desired output voltage as the differential voltage signal of the error amplifier circuit.

[0025] In one example, the current generating circuit 10 includes a voltage-to-current conversion circuit and a first current source, the first current source outputting a first current signal I01; the voltage-to-current conversion circuit receives the input voltage or output voltage to generate a second current signal I02 based on the input voltage or output voltage, and the difference between the first current signal and the second current signal is used as the bias current signal Iss. For example, the second current signal I02 is proportional to the input voltage or output voltage. Based on the above description of the bias current signal, when the second current signal I02 is proportional to the input voltage or output voltage, since the first current signal is a fixed value, the bias current signal decreases as the input voltage or output voltage increases. Here, the first current signal is generally set to a relatively large value so that, under normal circumstances, the bias current signal, representing the difference, can drive the error amplifier circuit to operate normally.

[0026] For example, the error amplifier circuit 20 is a CMOS transconductance amplifier. The specific circuit structure of the CMOS transconductance amplifier can be a common circuit structure in the prior art, such as a differential pair of transistors composed of field-effect transistors and a current mirror. In a transconductance amplifier composed of CMOS transistors, the transconductance of the CMOS transconductance under small-signal conditions is proportional to the square root of the bias current, and also proportional to the square root of the channel width-to-length ratio of the differential pair. Since the transconductance of the operational amplifier remains unchanged under high input voltage or high output voltage, the system bandwidth will be too high, affecting system stability. Therefore, the inventors of this application dynamically adjust the transconductance according to the magnitude of the input voltage or output voltage. For example, the second current signal I02 is proportional to the input voltage or output voltage. In this way, under higher input voltage or output voltage, the bias current signal will decrease, the transconductance will decrease, thereby reducing the system bandwidth and maintaining system stability.

[0027] In another example, the current generating circuit includes a second current source that outputs a third current signal I03. The third current signal I03 is less than the first current signal I01. The difference between the first and second current signals is used as a difference current signal. The sum of the third current signal and the difference current signal is used as the bias current signal. The third current signal I03 is a set minimum current value that enables the error amplifier circuit to operate. This prevents the error amplifier circuit from malfunctioning if the second current signal is too large when the input or output voltage is too high, as this could result in the difference between the first and second current signals being zero.

[0028] like Figure 3 The diagram shows the structure of a specific current generation circuit. This circuit includes a first current mirror circuit (e.g., composed of M1 and M2), a second current mirror circuit (e.g., composed of M3 and M4), and a third current mirror circuit (e.g., composed of M5 and M6). The mirror relationship between the three current mirrors can be proportional or proportional to a certain value. The first current mirror circuit receives the input voltage or output voltage through a first resistor R1, such as... Figure 3The first current signal and the second current signal have the same current direction. The input terminal of the second current mirror circuit is connected to the current branch node of the first current signal and the second current signal, such as point A. The difference current signal is input to the second current mirror circuit, and the second current mirror circuit outputs a first intermediate current signal I02'. The third current mirror circuit receives the first intermediate current signal to generate a second intermediate current signal I02'". The second intermediate current signal I02' has the same current direction as the third current signal. The second intermediate current signal and the third current signal are superimposed, and the superimposed signal is used as the bias current signal Iss.

[0029] refer to Figure 2 ,and Figure 1 The embodiments shown are different. Figure 2 The embodiment discloses a switching power supply including a main power switching transistor and an inductor. The common node of the main power switching transistor and the inductor is a switching node B. The operational amplifier circuit includes a filter circuit, such as a filter circuit composed of R03 and C03. The filter circuit is connected to the switching node B to filter the voltage of the switching node and use it as the output voltage of the switching power supply, such as V1. This embodiment can be applied to situations where there is no output voltage connection point, allowing the calculation of a voltage value that characterizes the output voltage using existing nodes.

[0030] For example, when the operational amplifier circuit receives the input voltage, the operational amplifier circuit is connected to the input terminal of the switching power supply to sample the voltage at the input terminal of the switching power supply as the input voltage. Figure 2 Not shown in the image.

[0031] In summary, the switching power supply of this invention has a large transconductance, high bandwidth, and good dynamic response at low output voltages. At high output voltages, it adaptively adjusts the transconductance to reduce bandwidth and has good stability, thus solving the technical problem of balancing different output voltage conditions.

[0032] In addition, although the embodiments are described and illustrated separately above, some common technologies are involved, and those skilled in the art can replace and integrate them between the embodiments. If there is any content not explicitly described in one embodiment, then another embodiment that is described can be referred to.

[0033] The embodiments described above do not constitute a limitation on the scope of protection of this technical solution. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the above embodiments should be included within the scope of protection of this technical solution.

Claims

1. An operational amplifier circuit for use in a switching power supply, wherein, The operational amplifier circuit includes a current generation circuit and an error amplifier circuit. The current generating circuit receives the input voltage or output voltage of the switching power supply to generate a bias current signal proportional to the input voltage or output voltage, wherein the bias current signal decreases as the input voltage or output voltage increases. The error amplifier circuit includes a current input terminal, a first voltage input terminal, and a second voltage input terminal. The current input terminal receives the bias current signal, and the first and second voltage input terminals respectively receive differential voltage signals to output an amplified error signal. The current generating circuit includes a voltage-to-current conversion circuit and a first current source. The first current source outputs a first current signal, and the voltage-to-current conversion circuit receives the input voltage or output voltage to generate a second current signal based on the input voltage or output voltage. The second current signal is proportional to the input voltage or output voltage. The current generating circuit includes a second current source, which outputs a third current signal. The third current signal is less than the first current signal. The difference between the first current signal and the second current signal is used as a difference current signal. The signal obtained by adding the third current signal and the difference current signal is used as the bias current signal.

2. The operational amplifier circuit according to claim 1, wherein, The current generating circuit includes a first current mirror circuit, a second current mirror circuit, and a third current mirror circuit. The first current mirror circuit receives the input voltage or output voltage through a first resistor to generate the second current signal; The first current signal and the second current signal have the same current direction. The input terminal of the second current mirror circuit is connected to the current branch node of the first current signal and the second current signal. The difference current signal is input to the second current mirror circuit, and the second current mirror circuit outputs the first intermediate current signal. The third current mirror circuit receives the first intermediate current signal and outputs a second intermediate current signal. The second intermediate current signal and the third current signal have the same current direction, and the signal superimposed by the two is used as the bias current signal.

3. The operational amplifier circuit according to claim 1, wherein, When the operational amplifier circuit receives the input voltage, the operational amplifier circuit is connected to the input terminal of the switching power supply to sample the voltage at the input terminal of the switching power supply as the input voltage; When the operational amplifier circuit receives the output voltage, the operational amplifier circuit is connected to the output terminal of the switching power supply to sample the voltage at the output terminal of the switching power supply as the output voltage.

4. The operational amplifier circuit according to claim 1, wherein, The switching power supply includes a main power switching transistor and an inductor, and the common node of the main power switching transistor and the inductor is a switching node. When the operational amplifier circuit receives the output voltage, the operational amplifier circuit includes a filter circuit connected to the switching node, so as to filter the voltage of the switching node and use it as the output voltage of the switching power supply.

5. The operational amplifier circuit according to claim 1, wherein, The error amplifier circuit is a CMOS transconductance amplifier.

6. A switching power supply, comprising a power stage circuit and a control circuit, wherein, The power stage circuit receives the input voltage and converts it into a desired output voltage through the switching action of the switching transistor. The control circuit includes an operational amplifier circuit as described in any one of claims 1 to 5, and the control circuit controls the switching action of the switching transistor in the power stage circuit according to the error amplification signal generated by the operational amplifier circuit.

7. The switching power supply according to claim 6, wherein, The operational amplifier circuit receives the output voltage feedback signal and the reference voltage characterizing the desired output voltage as the differential voltage signal of the error amplifier circuit.

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