External constant current circuit based on dc-dc converter

Abstract

This disclosure provides an external constant current circuit based on a DC-DC converter. The external constant current circuit includes a signal conversion operational amplifier circuit, a comparator circuit, a current regulation circuit, and a buffer. Specifically, the signal conversion operational amplifier circuit acquires the output current of the DC-DC converter, converts and amplifies the output current into a first voltage signal. The comparator circuit then compares the first voltage signal with an external reference voltage signal to output a second voltage signal. When the output current exceeds the constant current threshold, the current regulation circuit adjusts the current injected into the voltage feedback pin using the second voltage signal, thereby regulating the output current and maintaining it constant at the constant current threshold. This solves the problem of how to more efficiently implement constant current functionality in chips based on existing DC-DC converters.

Description

Technical Field

[0001] Embodiments of this disclosure relate to the field of integrated circuit technology, and more specifically, to an external constant current circuit based on a DC-DC converter. Background Technology

[0002] A DC-DC converter is a voltage converter that transforms an input voltage to effectively output a fixed voltage, and its applications are very wide. Typical DC-DC converters collect output voltage information through voltage divider resistors and send it to a voltage feedback pin, then compare it with an internal reference voltage to control the chip's operation. Generally, a basic DC-DC converter has only one voltage loop, outputting a fixed voltage, i.e., only a constant voltage effect. However, in practical applications, users may need to implement constant current functionality after achieving the main functions based on a basic DC-DC converter. To save materials, users will look for an external chip that can implement constant current for the existing basic DC-DC converter. However, often a suitable external constant current chip cannot be found (e.g., it may have unnecessary functions), thus affecting the implementation of system functions. Summary of the Invention

[0003] The embodiments described herein provide an external constant current circuit based on a DC-DC converter, in order to address the problem of how to more efficiently implement constant current functionality using existing DC-DC converter chips.

[0004] According to a first aspect of this disclosure, an external constant current circuit based on a DC-DC converter is provided. The DC-DC converter acquires an output voltage signal via a voltage divider resistor and feeds it to a voltage feedback pin. Then, it controls the operation of a chip based on a comparison with a reference voltage internal to the DC-DC converter chip. The external constant current circuit includes: a signal conversion operational amplifier circuit, a comparator circuit, a current regulation circuit, and a buffer. The signal conversion operational amplifier circuit is configured to acquire the output current of the DC-DC converter, convert and amplify the output current into a first voltage signal. The comparator circuit is configured to compare the first voltage signal with an external reference voltage signal and output a second voltage signal. The voltage signal is set according to the preset constant current threshold of the constant current circuit; the current regulation circuit is configured to adjust the current injected into the voltage feedback pin by the second voltage signal when the output current is greater than the constant current threshold, thereby adjusting the output current and keeping the output current constant at the constant current threshold; when the output current is not greater than the constant current threshold, no external current is injected into the voltage feedback pin, and the external current is the external current generated by the second voltage signal; the buffer is coupled between the comparator circuit and the current regulation circuit to isolate the comparator circuit and the current regulation circuit, or to increase the output driving force of the comparator circuit.

[0005] Optionally, the comparison circuit includes: a first operational amplifier, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, and a first capacitor. The inverting input terminal of the first operational amplifier is coupled to one end of the first resistor and one end of the third resistor, respectively. The non-inverting input terminal of the first operational amplifier is coupled to one end of the second resistor and one end of the fourth resistor, respectively. The output terminal of the first operational amplifier is coupled to the other end of the third resistor and one end of the fifth resistor, respectively. The other end of the first resistor receives the external reference voltage signal. The other end of the second resistor is coupled to the signal conversion operational amplifier circuit. The other end of the fourth resistor is grounded. The other end of the fifth resistor is coupled to one end of the first capacitor and the buffer, respectively. The other end of the first capacitor is grounded.

[0006] Optionally, the comparison circuit includes: a second operational amplifier and a second capacitor, wherein the inverting input terminal of the second operational amplifier receives the external reference voltage signal, the non-inverting input terminal of the second operational amplifier is coupled to the signal conversion operational amplifier circuit, the output terminal of the second operational amplifier is coupled to one end of the second capacitor and the buffer respectively; the other end of the second capacitor is grounded.

[0007] Optionally, the signal conversion operational amplifier circuit includes: a third operational amplifier, a sixth resistor, a seventh resistor, an eighth resistor, and a ninth resistor, wherein the inverting input terminal of the third operational amplifier is coupled to one end of the sixth resistor and one end of the eighth resistor, respectively; the non-inverting input terminal of the third operational amplifier is coupled to one end of the seventh resistor and one end of the ninth resistor, respectively; the output terminal of the third operational amplifier is coupled to the other end of the eighth resistor and the comparator circuit, respectively; the other end of the sixth resistor is coupled to one end of the sampling resistor, the other end of the seventh resistor is coupled to the other end of the sampling resistor, and the sampling resistor is connected in series in the path from the output voltage of the DC-DC converter to the load; the other end of the ninth resistor is grounded.

[0008] Optionally, the current regulation circuit includes: a tenth resistor and a diode; wherein the tenth resistor and the diode are connected in series between the voltage feedback pin and the buffer, the positive terminal of the diode is coupled to the buffer, and the negative terminal of the diode is coupled to the tenth resistor.

[0009] Optionally, the buffer is a buffer buffer. When the comparison circuit includes a first operational amplifier, the buffer buffer is used to increase the output driving force of the comparison circuit; when the comparison circuit includes a second operational amplifier, the buffer buffer is used to isolate the comparison circuit from the current regulation circuit.

[0010] Optionally, the external constant current circuit further includes a voltage regulation circuit, configured to regulate the output voltage of the DC-DC converter through an external pulse width modulation signal, and cooperate with the external constant current circuit to provide constant current control under different output voltage values.

[0011] Optionally, the voltage regulation circuit includes: an eleventh resistor, a twelfth resistor, and a third capacitor; wherein, one end of the eleventh resistor is coupled to the voltage feedback pin, and the other end of the eleventh resistor is coupled to one end of the twelfth resistor and one end of the third capacitor; the other end of the twelfth resistor receives the external pulse width modulation signal; and the other end of the third capacitor is grounded.

[0012] Optionally, the first resistor and the second resistor have the same resistance value, and the third resistor and the fourth resistor have the same resistance value.

[0013] Optionally, the resistance values ​​of the sixth resistor and the seventh resistor are equal, and the resistance values ​​of the eighth resistor and the ninth resistor are equal.

[0014] Optionally, the constant current threshold is less than the upper limit current value of the DC-DC converter chip.

[0015] The external constant current circuit based on a DC-DC converter in this disclosure is a circuit designed externally to implement the constant current function of an existing DC-DC converter. Specifically, the external constant current circuit includes: a signal conversion operational amplifier circuit, a comparator circuit, a current regulation circuit, and a buffer. The signal conversion operational amplifier circuit is configured to acquire the output current of the DC-DC converter, convert and amplify the output current into a first voltage signal. The comparator circuit is configured to compare the first voltage signal with an external reference voltage signal and output a second voltage signal. The external reference voltage signal is set according to a preset constant current threshold of the constant current circuit. The current regulation circuit is configured to adjust the current injected into the voltage feedback pin through the second voltage signal when the output current is greater than the constant current threshold, thereby regulating the output current and keeping it constant at the constant current threshold. When the output current is not greater than the constant current threshold, no external current is injected into the voltage feedback pin; the external current is the external current generated by the second voltage signal. The buffer is coupled between the comparator circuit and the current regulation circuit to isolate the comparator circuit from the current regulation circuit or to increase the output driving force of the comparator circuit. The external constant current circuit of this embodiment converts the output current into a first voltage signal, and then uses the second voltage signal obtained by comparing it with an external reference voltage signal to adjust the current injected into the voltage feedback pin, thereby adjusting the output voltage and then the output current. This simple and effective implementation of the constant current function of the DC-DC converter is achieved. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings of the embodiments will be briefly described below. It should be understood that the drawings described below only relate to some embodiments of this disclosure and are not intended to limit this disclosure, wherein:

[0017] Figure 1 This is a schematic block diagram of an external constant current circuit based on a DC-DC converter according to an embodiment of the present disclosure.

[0018] Figure 2 This is a schematic block diagram of another external constant current circuit based on a DC-DC converter according to an embodiment of the present disclosure;

[0019] Figure 3 , Figure 4 According to embodiments of this disclosure Figure 1 An exemplary circuit diagram of an external constant current circuit based on a DC-DC converter;

[0020] Figure 5 , Figure 6 According to embodiments of this disclosure Figure 2 An exemplary circuit diagram of an external constant current circuit based on a DC-DC converter.

[0021] The elements in the attached diagram are schematic and not drawn to scale. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are also within the scope of protection of this disclosure.

[0023] Unless otherwise defined, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this subject matter pertains. It will be further understood that terms such as those defined in commonly used dictionaries shall be interpreted as having a meaning consistent with their meaning in the context of the specification and in the related art, and shall not be interpreted in an idealized or overly formal form unless otherwise explicitly defined herein. As used herein, statements that “connect” or “couple” two or more parts together shall mean that these parts are directly joined together or joined through one or more intermediate components. Furthermore, terms such as “first” and “second” are used only to distinguish one component (or part of a component) from another component (or another part of a component).

[0024] First, it should be noted that the external constant current circuit based on the DC-DC converter in this embodiment of the present disclosure uses a voltage divider resistor to acquire the output voltage signal and send it to the voltage feedback pin. The circuit then controls the operation of the chip based on a comparison with a reference voltage internal to the DC-DC converter chip. The DC-DC converter can be a Buck chip, a Buck controller chip, a Boost chip, etc. Figure 1 The diagram illustrates some internal structures of the DC-DC converter chip, including voltage divider resistors Ra and Rb, output capacitor Cout, voltage feedback pin FB, and external load Rload. These examples are sufficient to illustrate how the external constant current circuit of this disclosure is connected to the DC-DC converter chip. Specific structures of other DC-DC converter chips are not the focus of this disclosure and are not illustrated.

[0025] like Figure 1 The diagram illustrates a schematic block diagram of an external constant current circuit 100 based on a DC-DC converter according to an embodiment of the present disclosure. The external constant current circuit 100 based on the DC-DC converter may include: a signal conversion operational amplifier circuit 110, a comparator circuit 120, a current regulation circuit 130, and a buffer 140.

[0026] The signal conversion operational amplifier circuit 110 is coupled to the DC-DC converter via a sampling resistor Rc and is configured to acquire the output current Iout of the DC-DC converter through the sampling resistor Rc. The signal conversion operational amplifier circuit 110 is also coupled to a comparator circuit 120 and is further configured to convert and amplify the output current Iout into a first voltage signal Va. Since this embodiment aims to perform external constant current functionality for the DC-DC converter chip, the output current Iout must first be acquired, specifically by converting the current signal into a voltage signal through the sampling resistor Rc. It should be noted that to reduce losses, the resistance value of Rc should be sufficiently small, typically in the milliohm range. In practical applications, if a sampling resistor Rc is available externally to the DC-DC converter chip, it can be used directly; otherwise, a new sampling resistor can be configured. This new sampling resistor can be incorporated into an external constant current circuit, such as the signal conversion operational amplifier circuit 110, or it can be a separate unit. In addition, in order for the subsequent comparison circuit 120 to make better comparisons, the voltage signal obtained directly through the sampling resistor Rc cannot be used yet. It needs to be further amplified to obtain the first voltage signal Va that can enter the comparison circuit 120.

[0027] The comparator circuit 120 is coupled to the signal conversion operational amplifier circuit 110 and the buffer 140, respectively. It is configured to compare the first voltage signal Va output by the signal conversion operational amplifier circuit 110 with an external reference voltage signal Vref and output a second voltage signal Vb. The external reference voltage signal Vref is set according to a preset constant current threshold of the constant current circuit. Different constant current thresholds correspond to different Vref values. The comparator circuit 120 can be implemented based on a first operational amplifier (OPA) or a second operational amplifier (OTA). In practical applications, if a constant current function under a certain constant current threshold is desired, the external reference voltage signal Vref is a fixed value; if a constant current function under multiple constant current thresholds is desired, the external reference voltage signal Vref corresponds to multiple values.

[0028] The current regulation circuit 130 is coupled to the buffer 140 and the voltage feedback pin FB of the DC-DC converter. The current regulation circuit 130 is configured to adjust the current injected into the voltage feedback pin via the second voltage signal Vb when the output current Iout is greater than the constant current threshold, thereby regulating the output current Iout and keeping it constant at the constant current threshold. Specifically, adjusting the current injected into the voltage feedback pin via the second voltage signal Vb adjusts the current across the voltage divider resistor Ra. When the current across Ra decreases, it affects the output voltage Vout, thus affecting the decrease in the output current Iout, allowing it to be maintained at the constant current threshold. This constant current threshold is less than the upper limit current value of the DC-DC converter chip. Furthermore, when the output current Iout is not greater than the constant current threshold, no external current is injected into the voltage feedback pin FB; this external current is the external current generated by the second voltage signal Vb. Without external current injection into the voltage feedback pin FB (i.e., the second voltage signal Vb), the output voltage Vout remains unchanged; that is, the output voltage Vout is maintained at a constant voltage by the DC-DC converter chip. However, during this phase, although the output voltage Vout remains constant, the output current Iout changes with the load until it reaches the constant current threshold, at which point it enters a constant current state. In this embodiment, constant current and constant voltage can be freely switched according to different loads.

[0029] A buffer 140 is coupled between the comparator circuit 120 and the current regulation circuit 130 to isolate them or to increase the output drive force of the comparator circuit 120. Specifically, in this embodiment, the buffer 140 is called a buffer. When the comparator circuit 120 is implemented using a second operational amplifier OTA, the high output impedance of the OTA, coupled with the low impedance of the subsequent current regulation circuit 130, can affect the performance of the OTA, thus requiring a buffer for isolation. When the comparator circuit 120 is implemented using a first operational amplifier OPA, the buffer does not serve an isolation function but rather to increase the output drive force, ensuring that the output signal of the comparator circuit 120 allows the subsequent current regulation circuit 130 to respond more effectively.

[0030] According to embodiments of this disclosure, the external constant current circuit based on a DC-DC converter converts the output current Iout into a first voltage signal Va. Then, by comparing this first voltage signal with an external reference voltage signal Vref to obtain a second voltage signal Vb, the current injected into the voltage feedback pin FB is adjusted, thereby regulating the output voltage Vout and consequently the output current Iout. This simple and effective implementation of the constant current function of the DC-DC converter is achieved. In practical applications, the constant current function can be easily implemented based on an existing basic DC-DC converter, significantly saving resources. Moreover, compared to using unsuitable external constant current chips, it can better realize the system function.

[0031] In the above Figure 1 In the embodiment, it can be seen that the external constant current circuit can achieve constant current control under different constant current thresholds. However, during the constant voltage stage, with the voltage divider resistors Ra and Rb fixed, the output voltage Vout is a fixed value. In practical applications where the constant voltage threshold does not need to be adjusted, Figure 1 The values ​​of the voltage divider components Ra and Rb can be set to a fixed value according to the actual constant voltage threshold required. However, for cases where the constant voltage threshold needs to be adjusted, Figure 1 It is not possible to achieve this more conveniently. Based on this situation, this disclosure further provides a solution that can achieve both constant current threshold adjustment and constant voltage threshold adjustment. For example... Figure 2 A schematic block diagram of another external constant current circuit 100 based on a DC-DC converter according to an embodiment of the present disclosure is shown. Figure 1 Based on this, the external constant current circuit 100 of the DC-DC converter also includes a voltage regulation circuit 150, which is coupled to an external microcontroller and the voltage feedback pin FB of the DC-DC converter. The voltage regulation circuit 150 is configured to regulate the output voltage Vout of the DC-DC converter via an external pulse width modulation signal (PWM signal provided by an external microcontroller), in conjunction with... Figure 1The external constant current circuit 100 provides constant current control for different output voltage Vout values. The specific adjustment principle is as follows: by adjusting the duty cycle of the external pulse width modulation signal PWM, the current in the injected voltage feedback pin FB is adjusted, which in turn adjusts the current in the voltage divider resistor Ra, thereby adjusting the output voltage Vout. Different duty cycles correspond to different output voltages Vout.

[0032] The external constant current circuit based on a DC-DC converter according to embodiments of this disclosure not only conveniently implements the constant current function, but also further adds a voltage regulation circuit 150, realizing a constant voltage stage under different output voltages Vout, and a constant current stage under different output voltages Vout. Additionally, Figure 2 In this circuit, when the output current Iout is not greater than the constant current threshold, no external current (the external current generated by the second voltage signal Vb) is injected into the voltage feedback pin FB. At this time, the circuit operates in a constant voltage state, and the output voltage Vout is determined by the voltage regulation circuit 150. When the output current Iout is greater than the constant current threshold, the same applies. Figure 1 The principle is the same. An external current (the external current generated by the second voltage signal Vb) is injected into the voltage feedback pin. The current injected into the voltage feedback pin can be adjusted by adjusting the second voltage signal Vb. The current on the voltage divider resistor Ra can be adjusted. When the current on Ra decreases, it will affect the output voltage Vout to decrease, thereby affecting the decrease of the output current Iout, so that the output current Iout can be maintained at the constant current threshold. Figure 2 In the middle, constant current and constant voltage can still be freely switched according to different loads.

[0033] Furthermore, Figure 3 It shows Figure 1 An exemplary circuit diagram of the external constant current circuit 100 based on the DC-DC converter is shown. Figure 3 As shown, the signal conversion operational amplifier circuit 110 includes: a third operational amplifier 111, a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, and a ninth resistor R9. The inverting input of the third operational amplifier 111 is coupled to one end of the sixth resistor R6 and one end of the eighth resistor R8, respectively; the non-inverting input of the third operational amplifier 111 is coupled to one end of the seventh resistor R7 and one end of the ninth resistor R9, respectively; the output of the third operational amplifier 111 is coupled to the other end of the eighth resistor R8 and the comparator circuit 120, respectively. The other end of the sixth resistor R6 is coupled to one end of the sampling resistor Rc, and the other end of the seventh resistor R7 is coupled to the other end of the sampling resistor Rc. The sampling resistor Rc is connected in series on the path from the output voltage Vout of the DC-DC converter to the load Rload. The other end of the ninth resistor R9 is grounded. It should be noted that the resistance values ​​of the sixth resistor R6 and the seventh resistor R7 are equal, and the resistance values ​​of the eighth resistor R8 and the ninth resistor R9 are equal.

[0034] like Figure 3 As shown, the comparator circuit 120 includes: a first operational amplifier OPA, a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, and a first capacitor C1. The inverting input of the first operational amplifier OPA is coupled to one end of the first resistor R1 and one end of the third resistor R3, respectively; the non-inverting input of the first operational amplifier OPA is coupled to one end of the second resistor R2 and one end of the fourth resistor R4, respectively; and the output of the first operational amplifier OPA is coupled to the other end of the third resistor R3 and one end of the fifth resistor R5, respectively. The other end of the first resistor R1 receives an external reference voltage signal Vref; the other end of the second resistor R2 is coupled to a signal conversion operational amplifier circuit 110; and the other end of the fourth resistor R4 is grounded. The other end of the fifth resistor R5 is coupled to one end of the first capacitor C1 and a buffer 140, respectively; and the other end of the first capacitor C1 is grounded. It should be noted that the resistance values ​​of the first resistor R1 and the second resistor R2 are equal, and the resistance values ​​of the third resistor R3 and the fourth resistor R4 are equal.

[0035] like Figure 3 As shown, the current regulation circuit 130 includes a tenth resistor R10 and a diode D1; wherein, the tenth resistor R10 and the diode D1 are connected in series between the voltage feedback pin and the buffer 140, the positive terminal of the diode D1 is coupled to the buffer 140, and the negative terminal of the diode D1 is coupled to the tenth resistor R10. In the current regulation circuit 130, the diode D1 functions as a unidirectional blocking element.

[0036] Furthermore, Figure 4 It shows Figure 1 Another exemplary circuit diagram of the external constant current circuit 100 based on the DC-DC converter is shown. Figure 4 As shown, the comparator circuit 120 includes a second operational amplifier OTA and a second capacitor C2. The inverting input of the second operational amplifier OTA receives an external reference voltage signal Vref, the non-inverting input of the second operational amplifier OTA is coupled to a signal conversion operational amplifier circuit 110, and the output of the second operational amplifier OTA is coupled to one end of the second capacitor C2 and a buffer 140. The other end of the second capacitor C2 is grounded. Figure 3 and Figure 4 Except for the comparison circuit 120, everything else is the same. Figure 3 and Figure 4 Although the two different comparator circuits 120 have different structures, they serve the same purpose.

[0037] The following will use specific examples to illustrate this. Figure 3 , 4 The example diagram illustrates the operation of the external constant current circuit 100 based on a DC-DC converter according to an embodiment of the present disclosure.

[0038] For example, if the constant current threshold is 3A and the corresponding externally set reference voltage signal Vref = 3V, when Iout < 3A, Va < Vref, Vb = 0. Due to the presence of diode D1, there is no sink / source current on the voltage feedback pin FB, and the output voltage Vout remains unchanged, and the circuit operates in the constant voltage state; when Iout is slightly greater than 3A, Va > Vref, Vb increases, and a current is generated through R10 that injects into the voltage feedback pin FB, resulting in a decrease in the current on Ra and a decrease in Vout. Under the same load conditions, after Vout decreases, Iout also decreases, so that the output current Iout is kept constant within the set constant threshold, and the circuit enters the constant current state.

[0039] In addition, the relationship between the constant current threshold and the externally set reference voltage signal Vref in the embodiments of the present application is described as follows:

[0040] R6 = R7, R8 = R9

[0041] Va = Iout × Rc × (R8 / R6)

[0042] Vref = Icc × (Rc × (R8 / R6)), where Icc is the constant current threshold.

[0043] It can be seen from the above formula that when the resistances of Rc, R8, and R6 are determined, different Icc values can correspond to different externally set reference voltage signals Vref. In practical applications, if the required Icc is known, the value of the externally set reference voltage signal Vref can be set according to the values of Rc, R8, and R6.

[0044] According to the above Figure 3 and Figure 4 embodiments, it can be seen that the external constant current circuit based on the DCDC converter according to the embodiments of the present disclosure can convert the output current Iout into a first voltage signal Va through the third operational amplifier 111, and then adjust the current injected into the voltage feedback pin FB by comparing the first voltage signal Va with the externally set reference voltage signal Vref to obtain a second voltage signal Vb through the first operational amplifier OPA or the second operational amplifier OTA, thereby adjusting the output voltage Vout and further adjusting the output current Iout, simply and effectively implementing the constant current function of the DCDC converter. In practical applications, the constant current function can be conveniently implemented based on the original basic DCDC converter, saving resources, and better realizing the system function compared to using inappropriate external constant current chips.

[0045] Furthermore, Figure 5 and Figure 6 shows Figure 2 Exemplary circuit diagram of the external constant current circuit 100 based on a DCDC converter in Figure 5 Compared with Figure 3 a voltage regulation circuit 150 is added. Figure 6 Compared with Figure 4 a voltage regulation circuit 150 is added and the others are the same. As Figure 5 、 Figure 6 shown, the voltage regulation circuit 150 includes: the eleventh resistor R11, the twelfth resistor R12, and the third capacitor C3; wherein, one end of the eleventh resistor R11 is coupled to the voltage feedback pin FB, and the other end of the eleventh resistor R11 is respectively coupled to one end of the twelfth resistor R12 and one end of the third capacitor C3; the other end of the twelfth resistor R12 receives an external pulse width modulation signal PWM; the other end of the third capacitor C3 is grounded.

[0046] Combined with Figure 5 and Figure 6 to illustrate the working principle of the voltage regulation circuit 150: the DC voltage after the external pulse width modulation signal PWM is filtered by RC (the structure composed of R12 and C3) affects the current of sink / source (sink / pull) FB through the resistors R11 and R12, and then adjusts the current of Ra, thereby adjusting the output voltage Vout. Different PWM duty cycles can obtain different output voltages Vout.

[0047] Next, through a specific example combined with Figure 5 、 6 the example diagram to illustrate the working process of the external constant current circuit 100 based on a DCDC converter according to an embodiment of the present disclosure.

[0048] If the constant current threshold is 3A and the corresponding externally set reference voltage signal Vref = 3V, when Iout < 3A, Va < Vref, Vb = 0. Due to the presence of the diode D1, there is no sink / source current on the voltage feedback pin FB, and the circuit operates in the constant voltage state. The value of the output voltage Vout is determined by the duty cycle of the external pulse width modulation signal PWM in the voltage regulation circuit 150; when Iout is slightly greater than 3A, Va > Vref, Vb increases, and a current is generated on the resistor R10 that injects into the voltage feedback pin FB, resulting in a decrease in the current on Ra and a decrease in Vout. Under the same load conditions, after Vout decreases, Iout also decreases, so that the output current Iout is kept constant within the set constant threshold, and the circuit enters the constant current state.

[0049] In addition, in the embodiment of the present application, the relationship between the duty cycle of the external pulse width modulation signal PWM and the output voltage Vout is described as follows:

[0050] First, the external pulse width modulation signal (PWM) is filtered by an RC filter to obtain the filtered DC signal Vpwm_DC, where Vpwm_DC = Vpwm_AMP × Duty.

[0051] Where Vpwm_AMP is the amplitude of the external pulse width modulation signal PWM, and Duty is the duty cycle;

[0052] The equivalent DC voltage Vpwm_DC is injected into FB through R11+R12, and a current I3 (the current flowing from R11 into FB) is injected into FB.

[0053] in addition,

[0054] therefore,

[0055] Where I1 is the current flowing into Ra in the direction of FB, and I2 is the current flowing out of Rb in the direction of FB.

[0056] As can be seen from the above formula, Vout is related to Vpwm_DC, and Vpwm_DC is related to the duty cycle (Duty). This relationship exists between Ra, Rb, and Vout. FB With R11 and R12 unchanged, different duty cycles (Duty) correspond to different output voltages (Vout).

[0057] Additionally, it should be noted that the capacitance value of C3 can be adjusted according to the frequency of the external pulse width modulation signal (PWM). Preferably, R12·C3 ≥ 10·(1 / f) sw ), where f sw The frequency of the external pulse width modulation signal (PWM).

[0058] According to the above Figure 5 as well as Figure 6 As can be seen from the embodiments, the external constant current circuit based on the DC-DC converter according to the embodiments of this disclosure can, in addition to achieving Figure 3 as well as Figure 4 In addition to the functions that can be achieved, a voltage regulation circuit 150 has been added to realize constant current and constant voltage under different thresholds, and can be freely switched according to different loads.

[0059] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of apparatuses and methods according to various embodiments of the present disclosure. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of an instruction containing one or more executable instructions for implementing a specified logical function. In some alternative implementations, the functions marked in the blocks may occur in a different order than those marked in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, may be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

[0060] Unless otherwise expressly indicated by the context, the singular form of words used herein and in the appended claims includes the plural form, and vice versa. Thus, when referring to the singular, the plural form of the corresponding term is generally included. Similarly, the terms “comprising” and “including” shall be interpreted as including rather than exclusively. Likewise, the terms “including” and “or” shall be interpreted as including unless such interpretation is expressly prohibited herein. Where the term “example” is used herein, particularly when it follows a set of terms, the “example” is merely exemplary and illustrative and should not be considered exclusive or extensive.

[0061] Further aspects and scope of adaptation become apparent from the description provided herein. It should be understood that various aspects of this application may be implemented individually or in combination with one or more other aspects. It should also be understood that the descriptions and specific embodiments herein are for illustrative purposes only and are not intended to limit the scope of this application.

[0062] Several embodiments of this disclosure have been described in detail above. However, it is obvious that those skilled in the art can make various modifications and variations to the embodiments of this disclosure without departing from the spirit and scope of this disclosure. The scope of protection of this disclosure is defined by the appended claims.

Claims

1. An external constant current circuit based on a DCDC converter, the DCDC converter collects an output voltage signal through a voltage dividing resistor to a voltage feedback pin, and then controls the chip to work according to the comparison with the reference voltage inside the DCDC converter chip, characterized in that, The external constant current circuit includes: a signal conversion operational amplifier circuit, a comparator circuit, a current regulation circuit, and a buffer. The signal conversion operational amplifier circuit is configured to acquire the output current of the DC-DC converter, convert and amplify the output current into a first voltage signal; The comparison circuit is configured to compare the first voltage signal with an external reference voltage signal and output a second voltage signal. The external reference voltage signal is set according to a preset constant current threshold of the constant current circuit. If the first voltage signal is less than the external reference voltage signal, the second voltage signal is zero. If the first voltage signal is greater than the external reference voltage signal, the second voltage signal increases. The current regulation circuit is configured to, when the output current is greater than the constant current threshold, adjust the current injected into the voltage feedback pin through the second voltage signal, thereby regulating the output current and keeping the output current constant at the constant current threshold; when the output current is not greater than the constant current threshold, the second voltage signal output by the comparator circuit causes the current regulation circuit to be cut off, and no external current is injected into the voltage feedback pin, wherein the external current is the external current generated by the second voltage signal; the current regulation circuit includes: a tenth resistor and a diode; wherein the tenth resistor and the diode are connected in series between the voltage feedback pin and the buffer, the positive terminal of the diode is coupled to the buffer, and the negative terminal of the diode is coupled to the tenth resistor; The buffer is coupled between the comparator circuit and the current regulation circuit to isolate the comparator circuit and the current regulation circuit, or to increase the output driving force of the comparator circuit. The external constant current circuit further includes a voltage regulation circuit configured to adjust the output voltage of the DC-DC converter via an external pulse width modulation signal, providing constant current control for different output voltage values ​​in conjunction with the external constant current circuit. The voltage regulation circuit includes an eleventh resistor, a twelfth resistor, and a third capacitor. One end of the eleventh resistor is coupled to the voltage feedback pin, and the other end of the eleventh resistor is coupled to one end of the twelfth resistor and one end of the third capacitor. The other end of the twelfth resistor receives the external pulse width modulation signal. The other end of the third capacitor is grounded. The DC voltage of the external pulse width modulation signal, after being filtered by the structure composed of the twelfth resistor and the third capacitor, flows through the eleventh and twelfth resistors to sink / pull the current into the voltage feedback pin. When the output current is not greater than the constant current threshold, the output voltage is determined by the voltage regulation circuit. When the output current is greater than the constant current threshold, an external current is injected into the voltage feedback pin, adjusting the output current to maintain it at the constant current threshold, thus entering a constant current state.

2. The DCDC converter based external constant current circuit according to claim 1, characterized in that, The comparator circuit includes: a first operational amplifier, a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, and a first capacitor. Wherein, the inverting input terminal of the first operational amplifier is coupled to one end of the first resistor and one end of the third resistor, the non-inverting input terminal of the first operational amplifier is coupled to one end of the second resistor and one end of the fourth resistor, and the output terminal of the first operational amplifier is coupled to the other end of the third resistor and one end of the fifth resistor. The other end of the first resistor receives the external reference voltage signal, the other end of the second resistor is coupled to the signal conversion operational amplifier circuit, and the other end of the fourth resistor is grounded. The other end of the fifth resistor is coupled to one end of the first capacitor and the buffer, respectively, and the other end of the first capacitor is grounded.

3. The DCDC converter based external constant current circuit of claim 1, wherein, The comparator circuit includes: a second operational amplifier and a second capacitor. Wherein, the inverting input terminal of the second operational amplifier receives the external reference voltage signal, the non-inverting input terminal of the second operational amplifier is coupled to the signal conversion operational amplifier circuit, and the output terminal of the second operational amplifier is coupled to one end of the second capacitor and the buffer respectively; The other end of the second capacitor is grounded.

4. The external constant current circuit based on a DC-DC converter according to claim 2 or 3, characterized in that, The signal conversion operational amplifier circuit includes: a third operational amplifier, a sixth resistor, a seventh resistor, an eighth resistor, and a ninth resistor. The inverting input terminal of the third operational amplifier is coupled to one end of the sixth resistor and one end of the eighth resistor, respectively; the non-inverting input terminal of the third operational amplifier is coupled to one end of the seventh resistor and one end of the ninth resistor, respectively; and the output terminal of the third operational amplifier is coupled to the other end of the eighth resistor and the comparator circuit, respectively. The other end of the sixth resistor is coupled to one end of the sampling resistor, and the other end of the seventh resistor is coupled to the other end of the sampling resistor. The sampling resistor is connected in series in the path from the output voltage of the DC-DC converter to the load. The other end of the ninth resistor is grounded.

5. The external constant current circuit based on a DC-DC converter according to claim 1, characterized in that, The buffer is a buffer buffer. When the comparison circuit includes a first operational amplifier, the buffer buffer is used to increase the output driving force of the comparison circuit. When the comparison circuit includes a second operational amplifier, the buffer buffer is used to isolate the comparison circuit from the current regulation circuit.

6. The external constant current circuit based on a DC-DC converter according to claim 2, characterized in that, The first resistor has the same resistance value as the second resistor, and the third resistor has the same resistance value as the fourth resistor.

7. The external constant current circuit based on a DC-DC converter according to claim 4, characterized in that, The sixth resistor has the same resistance value as the seventh resistor, and the eighth resistor has the same resistance value as the ninth resistor.

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