A DC switching power supply conversion circuit capable of both stepping down and stepping up voltage

Abstract

The invention discloses a direct current switching power supply conversion circuit capable of both bucking and boosting, belonging to the technical field of switching power supplies, comprising an input positive electrode, an input negative electrode, a buck-boost control terminal, a PWM control terminal, resistors R1-R3, diodes D1, D2, D3, D4, D5, operational amplifiers N1A, N1B, an inductor L1, a capacitor C1, an N-channel field effect transistor V2, a P-channel field effect transistor V1, an output negative electrode and an output positive electrode. When a low level is input to the buck-boost control terminal, a forward input terminal of the operational amplifier N1B can be pulled down through the diode D5, so that the circuit works in a BUCK buck mode; when a high level is input to the buck-boost control terminal, a reverse input terminal of the operational amplifier N1A can be pulled up through the diode D4, so that the circuit works in a BOOST boost state. The invention realizes the functions of both bucking and boosting, and has the advantages of good practicability, high economy and high efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of switch power supply, and in particular to a DC switch power supply conversion circuit capable of both stepping down and stepping up voltage. Background Art

[0002] A switching power supply is a power supply that uses modern power electronics technology to control the time ratio of the switch on and off to maintain a stable output voltage. The switching power supply circuit has the characteristics of low power consumption, high conversion efficiency, small linear change, and stable operation. Therefore, it is widely used in various electronic devices such as industrial control, communication office, and home consumption.

[0003] The most common non-isolated switching power supply conversion methods in switching power supplies are BUCK step-down conversion and BOOST step-up conversion. The less commonly used ones are BUCK-BOOST step-down boost and SEPIC single-ended primary inductor conversion.

[0004] In the existing non-isolated switching power supply conversion mode, the simple BUCK conversion circuit can only realize step-down conversion, while the BOOST conversion circuit can only realize step-up conversion. When the output voltage fluctuation range is large or the load voltage change requirement is large, it cannot be used in some applications. For example, some multi-functional lithium-ion battery charger products require the ability to charge 1 to 6 lithium-ion batteries in series. The input power supply uses a common power supply on the market with an input voltage range of 7V to 19V. The product requires that it can charge both 1 lithium battery in series (charging voltage 4.2V) and 6 lithium-ion batteries in series with a charging voltage of 25.2V. At this time, the internal conversion circuit of the charger needs to be able to both step down and step up. Neither the single BUCK conversion circuit nor the BOOST conversion circuit can meet the requirements. If the BUCK-BOOST buck-boost topology is used, since its input voltage and output voltage are in opposite phases and the input and output do not share a common ground, the voltage and current control will become very complicated and difficult to apply; if the SEPIC single-ended primary inductor conversion circuit is used, although it can achieve the purpose of both boosting and bucking, the circuit requires two inductors and one capacitor for energy transfer, the control circuit is complex, there are many power devices, the loss is large, the conversion efficiency is not high, and the electromagnetic interference generated will also be large. Therefore, the SEPIC circuit is rarely used in practical applications. Summary of the invention

[0005] The object of the present invention is to provide a DC switching power supply conversion circuit that can both step down and step up the voltage, so as to overcome the above problems.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a DC switching power supply conversion circuit that can both step down and step up, including an input positive electrode, an input negative electrode, a step-up and step-down control terminal, a PWM control terminal, resistors R1-R3, diodes D1, D2, D3, D4, D5, operational amplifiers N1A, N1B, an inductor L1, a capacitor C1, an N-channel field effect transistor V2, a P-channel field effect transistor V1, an output positive electrode, and an output negative electrode. The diode D3 is a voltage-stabilizing diode, and the input positive electrode is connected to one end of the resistor R1, the positive power supply terminal of the operational amplifier N1A, and the S pole of the field effect transistor V1; the other end of the resistor R1 is connected to the negative electrode of the voltage-stabilizing diode D3 and the operational amplifier N1 The positive input terminal of A is connected to the reverse input terminal of the operational amplifier N1B; the output terminal of the operational amplifier N1A is connected to the gate of the field effect tube V1; the drain of the field effect tube V1 is connected to one end of the inductor L1 and the cathode of the diode D1; the other end of the inductor L1 is connected to the drain of the field effect tube V2 and the anode of the diode D2; the cathode of the diode D2 is connected to the anode of the capacitor C1 and the output anode; the buck-boost control terminal is connected to the anode of the diode D4 and the cathode of the diode D5; the cathode of the diode D4 is connected to one end of the resistor R2 and the reverse input terminal of the operational amplifier N1A; the anode of the diode D5 is connected to one end of the resistor R3 and the anode of the operational amplifier N1B. The PWM control terminal is connected to the other end of the resistor R2 and the other end of the resistor R3; the output end of the operational amplifier N1B is connected to the gate of the field effect tube V2; the negative input electrode is connected to the positive electrode of the voltage-stabilizing diode D3, the negative power supply end of the operational amplifier N1, the positive electrode of the diode D1, the source of the field effect tube V2 and the negative electrode of the capacitor C1 to form a common ground connection. The resistor R1 and the voltage-stabilizing diode D3 in the circuit generate a stable reference voltage Vref and provide it to the input ends of the two operational amplifiers. When the buck-boost control terminal inputs a low level, the positive input end of the operational amplifier N1B can be pulled down through the diode D5, so that the circuit works in the BUCK buck mode; the buck-boost control terminal When the input is high level, the reverse input terminal of the operational amplifier N1A can be pulled high through the diode D4, so that the circuit works in the BOOST boost state; when working in the buck state, the PWM control end drives the field effect tube V1 in the PWM switch working state through the resistor R2 and the operational amplifier N1A, and the BUCK buck output circuit is formed by the field effect tube V1, the diode D1, the inductor L1, the diode D2 and the capacitor C1; when working in the boost state, the PWM control end drives the field effect tube V2 in the PWM switch working state through the resistor R3 and the operational amplifier N1B, and the BOOST boost output circuit is formed by the field effect tube V2, the inductor L1, the diode D2 and the capacitor C1.

[0007] Furthermore, the reference voltage Vref has a value of 1-4V and is generated by voltage division of the resistor R1 and the voltage zener diode D3, or by voltage division of a resistor or a potentiometer.

[0008] Furthermore, the P-channel field effect transistor V1 can be replaced by a PNP transistor, and the N-channel field effect transistor V2 can be replaced by an NPN transistor.

[0009] Furthermore, the operational amplifiers N1A and N1B may be replaced by comparators.

[0010] Furthermore, the voltage of the input positive electrode is 7V-18V.

[0011] Furthermore, the buck-boost control terminal is connected to a single chip microcomputer or an FPGA.

[0012] Furthermore, the amplitude of the PWM control terminal is 5V.

[0013] The beneficial effects of the present invention are:

[0014] (1) The present invention has the advantages of simple structure, reasonable design, and quick installation and maintenance;

[0015] (2) In the technical solution of the present invention, the circuit can output either a step-down voltage or a step-up voltage. The input and output have the same polarity and are connected to a common ground, which makes the control method easy to implement.

[0016] (3) In the technical solution of the present invention, the energy transfer device in the circuit has only one inductor, and the power conversion efficiency is high. In some applications requiring a wide input voltage or a wide output voltage range, it has good practicality and economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a circuit schematic diagram of the present invention; DETAILED DESCRIPTION

[0018] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific implementation disclosed below.

[0019] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may be a central element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be a central element at the same time. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only and do not represent the only implementation method.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0021] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] Embodiment 1, Figure 1 It is a schematic diagram of the circuit structure of the present invention.

[0023] Figure 1The structural block diagram of an embodiment of the present invention is shown. It can be seen from the figure that a DC switching power supply conversion circuit that can step down or step up voltage includes an input positive electrode, an input negative electrode, a step-up / step-down control terminal, a PWM control terminal, resistors R1-R3, diodes D1, D2, D3, D4, D5, operational amplifiers N1A, N1B, an inductor L1, a capacitor C1, an N-channel field effect transistor V2, a P-channel field effect transistor V1, an output positive electrode, and an output negative electrode. The diode D3 is a voltage-stabilizing diode. The input positive electrode is connected to one end of the resistor R1, the positive power supply terminal of the operational amplifier N1A, and the S pole of the field effect transistor V1; the other end of the resistor R1 is connected to the negative electrode of the voltage-stabilizing diode D3, the positive input terminal of the operational amplifier N1A, and the reverse input terminal of the operational amplifier N1B; the output terminal of the operational amplifier N1A is connected to the gate of the field effect transistor V1; the drain of the field effect transistor V1 It is connected to one end of the inductor L1 and the cathode of the diode D1; the other end of the inductor L1 is connected to the drain of the field effect tube V2 and the anode of the diode D2; the cathode of the diode D2 is connected to the anode of the capacitor C1 and the output anode; the buck-boost control end is connected to the anode of the diode D4 and the cathode of the diode D5; the cathode of the diode D4 is connected to one end of the resistor R2 and the reverse input end of the operational amplifier N1A; the anode of the diode D5 is connected to one end of the resistor R3 and the forward input end of the operational amplifier N1B; the PWM control end is connected to the other end of the resistor R2 and the other end of the resistor R3; the output end of the operational amplifier N1B is connected to the gate of the field effect tube V2; the input cathode is connected to the anode of the voltage-stabilizing diode D3, the negative power supply end of the operational amplifier N1, the anode of the diode D1, the source of the field effect tube V2 and the cathode of the capacitor C1, forming a common ground connection. The resistor R1 and the voltage zener diode D3 in the circuit generate a stable reference voltage Vref and provide it to the input terminals of the two operational amplifiers. When the buck-boost control terminal inputs a low level, the forward input terminal of the operational amplifier N1B can be pulled down through the diode D5, so that the circuit works in the BUCK buck mode; when the buck-boost control terminal inputs a high level, the reverse input terminal of the operational amplifier N1A can be pulled up through the diode D4, so that the circuit works in the BOOST boost state; when working in the buck state, the PWM control terminal drives the field effect tube V1 in the PWM switch working state through the resistor R2 and the operational amplifier N1A, and the BUCK buck output circuit is formed by the field effect tube V1, the diode D1, the inductor L1, the diode D2 and the capacitor C1; when working in the boost state, the PWM control terminal drives the field effect tube V2 in the PWM switch working state through the resistor R3 and the operational amplifier N1B, and the BOOST boost output circuit is formed by the field effect tube V2, the inductor L1, the diode D2 and the capacitor C1.

[0024] The reference voltage Vref has a value of 1-4V and is generated by voltage division by the resistor R1 and the voltage stabilizing diode D3, or by voltage division by a resistor or a potentiometer.

[0025] The P-channel field effect transistor V1 can be replaced by a PNP transistor, and the N-channel field effect transistor V2 can be replaced by an NPN transistor.

[0026] The operational amplifiers N1A and N1B may be replaced by comparators.

[0027] The voltage of the input positive electrode is 7V-18V.

[0028] The buck-boost control terminal is connected to a single chip microcomputer or an FPGA.

[0029] The amplitude of the PWM control terminal is 5V.

[0030] Working principle: The working process of the voltage-stabilized power supply circuit is analyzed as follows:

[0031] 1. When the positive and negative input terminals of the circuit are connected to the input power supply, the input power supply passes through the resistor R1 and generates a stable reference voltage Vref on the voltage stabilizing diode D3. Vref can be a value between 1V and 4V, typically 2.4V. The Vref voltage is provided to the positive input terminal of the operational amplifier N1A and the negative input terminal of the operational amplifier N1B as a comparison voltage.

[0032] 2. When the buck-boost control terminal inputs a low level, the forward input terminal of the operational amplifier N1B will be pulled down through the diode D5. At this time, the reverse input terminal voltage (2.4V) of the operational amplifier N1B is greater than the forward input terminal voltage, and the output of the operational amplifier N1B is low, so that the field effect tube V2 is in the cut-off state; at this time, if the PWM control terminal outputs a PWM waveform, the PWM signal is added to the reverse input terminal of the operational amplifier N1A through the resistor R2. At this time, since the buck-boost control terminal is at a low level, the diode D4 is in a reverse cut-off state. Since the PWM signal amplitude is 5V, which is greater than the Vref voltage value, when the PWM signal is at a high level, the reverse input terminal voltage of the operational amplifier N1A will be high. When the PWM signal is at a low level, the voltage at the reverse input of the operational amplifier N1A will be lower than the Vref voltage at the forward input of the operational amplifier N1A. At this time, the operational amplifier N1A outputs a high level, which turns off the P-channel field effect transistor V1. Therefore, the P-channel field effect transistor V1 is controlled by the PWM signal. At this time, the field effect transistor V2 is in the off state and does not work. The field effect transistor V1, the diode D1, the inductor L1, the diode D2 and the capacitor C1 form a BUCK step-down output circuit, and the power supply circuit works in the BUCK step-down mode.

[0033] 3. When the buck-boost control terminal inputs a high level (5V), the reverse input terminal of the operational amplifier N1A will be pulled to a high level through D4. At this time, the reverse input terminal voltage of the operational amplifier N1A is greater than the forward input terminal voltage (2.4V), and the output of the N1A operational amplifier is low, so that the field effect tube V1 is in a fully conductive state, which is equivalent to the input power supply being directly connected to the inductor L1; at this time, if the PWM control terminal outputs a PWM waveform, the PWM signal is added to the forward input terminal of the operational amplifier N1B through the resistor R3. At this time, since the buck-boost control terminal is at a high level, the diode D5 is in a reverse cut-off state. Since the PWM signal amplitude is 5V, which is greater than the Vref voltage value, when the PWM signal is at a high level, the forward input terminal voltage of the operational amplifier N1B will be higher than the Vref voltage of the reverse input terminal of the operational amplifier N1B. At this time, the operational amplifier N1B outputs a high level, so that the N-channel field effect tube V2 is saturated and turned on; when the PWM signal is at a low level, the operational amplifier The voltage at the positive input terminal of the amplifier N1B will be lower than the Vref voltage at the reverse input terminal of the operational amplifier N1B. At this time, the operational amplifier N1B outputs a low level, so that the N-channel field effect tube V2 is cut off; therefore, the N-channel field effect tube V2 is controlled by the PWM signal. At this time, since the field effect tube V1 is in a fully turned-on state, the field effect tube V2, the inductor L1, the diode D2 and the capacitor C1 constitute a BOOST boost output circuit, and the power supply circuit works in the BOOST boost working mode; from the above, it can be seen that when the buck-boost control terminal inputs a low level, the switching power supply circuit works in the BUCK buck working state, and the output voltage of the switching power supply circuit is controlled by the pulse width of the PWM control terminal; when the buck-boost control terminal inputs a high level, the switching power supply circuit works in the BOOST boost working state, and the output voltage of the switching power supply circuit is controlled by the pulse width of the PWM control terminal; therefore, the circuit can realize both buck conversion function and boost conversion function.

[0034] In practical applications, taking the application of a multifunctional lithium-ion battery charger as an example, the circuit can be used to form a charging circuit for 1 lithium-ion battery to 6 lithium-ion batteries in series. The input power supply voltage is 9V~15V. The voltage regulator diode D3 in the circuit adopts a voltage regulation value of 2.4V, an IO port of a single-chip microcomputer is used as the buck-boost control terminal, and the PWM output port of the single-chip microcomputer is used as the PWM control terminal. The power supply voltage of the single-chip microcomputer is 5V. When the voltage of the connected charged battery is less than the input power supply voltage, the single-chip microcomputer can control the buck-boost control terminal to a low level, so that the circuit works in the BUCK buck mode to charge the battery; when the voltage of the connected charged battery is greater than or equal to the input power supply voltage, the single-chip microcomputer can control the buck-boost control terminal to a high level, so that the circuit works in the BOOST boost mode to charge the battery. In this way, whether a single 3.6V lithium-ion battery pack or a 6-cell 22.2V lithium-ion battery pack in series is connected, the charging circuit can charge normally and has the characteristics of a wide range of applications.

[0035] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions of the present invention, which should be included in the scope of the claims of the present invention. The techniques, shapes, and structural parts not described in detail in the present invention are all known technologies.

Claims

1. A DC switching power supply conversion circuit capable of bucking or boosting voltage, comprising an input positive electrode, an input negative electrode, a buck-boost control terminal, a PWM control terminal, resistors R1-R3, diodes D1, D2, D3, D4, D5, operational amplifiers N1A, N1B, an inductor L1, a capacitor C1, an N-channel field effect transistor V2, a P-channel field effect transistor V1, an output negative electrode and an output positive electrode, characterized in that: The diode D3 is a voltage-stabilizing diode, and the input positive electrode is connected to one end of the resistor R1, the positive power supply end of the operational amplifier N1A, and the S pole of the field effect tube V1; the other end of the resistor R1 is connected to the cathode of the voltage-stabilizing diode D3, the positive input end of the operational amplifier N1A, and the reverse input end of the operational amplifier N1B; the output end of the operational amplifier N1A is connected to the gate of the field effect tube V1; the drain of the field effect tube V1 is connected to one end of the inductor L1 and the cathode of the diode D1; the other end of the inductor L1 is connected to the drain of the field effect tube V2 and the positive electrode of the diode D2; the cathode of the diode D2 is connected to the positive electrode of the capacitor C1 and the input The positive electrode of the output is connected to the positive electrode of the buck-boost control terminal, the positive electrode of the diode D4 and the negative electrode of the diode D5; the negative electrode of the diode D4 is connected to one end of the resistor R2 and the reverse input end of the operational amplifier N1A; the positive electrode of the diode D5 is connected to one end of the resistor R3 and the positive input end of the operational amplifier N1B; the PWM control terminal is connected to the other end of the resistor R2 and the other end of the resistor R3; the output end of the operational amplifier N1B is connected to the gate of the field effect tube V2; the negative input electrode is connected to the positive electrode of the voltage stabilizing diode D3, the negative power supply end of the operational amplifier N1A, the positive electrode of the diode D1, the source of the field effect tube V2 and the negative end of the capacitor C1. The two poles are connected to form a common ground connection. The resistor R1 and the voltage zener diode D3 in the circuit generate a stable reference voltage Vref and provide it to the positive input terminal of the operational amplifier N1A and the reverse input terminal of the operational amplifier N1B. When the buck-boost control terminal inputs a low level, the DC switching power supply conversion circuit works in the BUCK buck working state, and the output voltage of the DC switching power supply conversion circuit is controlled by the pulse width of the PWM control terminal; when the buck-boost control terminal inputs a high level, the DC switching power supply conversion circuit works in the BOOST boost working state, and the output voltage of the DC switching power supply conversion circuit is controlled by the pulse width of the PWM control terminal. Control; This circuit can realize both buck conversion function and boost conversion function; When working in buck state, the PWM control end drives the field effect tube V1 in PWM switch working state through the resistor R2 and the operational amplifier N1A, and the field effect tube V1, the diode D1, the inductor L1, the diode D2 and the capacitor C1 constitute the BUCK buck output circuit, when the low level input by the buck-boost control end pulls down the positive input end of the operational amplifier N1B through the diode D5, the reverse input end voltage of the operational amplifier N1B is greater than the forward input end voltage, the output of the operational amplifier N1B is low level, and the field effect tube V2 is in the cut-off state;The PWM control terminal outputs a PWM signal, which is added to the reverse input terminal of the operational amplifier N1A through the resistor R2. The buck-boost control terminal is at a low level, and the diode D4 is in a reverse cut-off state. Since the high-level amplitude of the PWM signal is 5V, which is greater than the reference voltage Vref, when the PWM signal is at a high level, the reverse input terminal voltage of the operational amplifier N1A is higher than the Vref voltage at the forward input terminal of the operational amplifier N1A, and the operational amplifier N1A outputs a low level, and the P-channel field effect transistor V1 is saturated and turned on; when the PWM signal is at a low level, the operational amplifier N1A The voltage at the reverse input terminal is lower than the Vref voltage at the forward input terminal of the operational amplifier N1A, and the operational amplifier N1A outputs a high level, and the P-channel field effect transistor V1 is cut off and turned off; therefore, the P-channel field effect transistor V1 is controlled by the PWM signal, and the field effect transistor V2 is in the cut-off state and does not work. The field effect transistor V1, the diode D1, the inductor L1, the diode D2 and the capacitor C1 form a BUCK step-down output circuit, and the DC switching power supply conversion circuit works in the BUCK step-down state; when working in the boost state, the PWM control end drives the field effect transistor through the resistor R3 and the operational amplifier N1B. V2 is in the PWM switch working state, and the BOOST boost output circuit is composed of the field effect tube V2, the inductor L1, the diode D2 and the capacitor C1. When the high level input to the buck-boost control terminal pulls the reverse input terminal of the operational amplifier N1A to a high level through D4, the reverse input terminal voltage of the operational amplifier N1A is greater than the forward input terminal voltage, the output of the N1A operational amplifier is low, and the field effect tube V1 is in a fully turned-on state; the PWM control terminal outputs a PWM signal, and the PWM signal is added to the forward input terminal of the operational amplifier N1B through the resistor R3, and the buck-boost control terminal is high. , the diode D5 is in the reverse cut-off state. Since the high level amplitude of the PWM signal is 5V, which is greater than the Vref voltage value, when the PWM signal is at a high level, the voltage at the positive input terminal of the operational amplifier N1B is higher than the Vref voltage at the reverse input terminal of the operational amplifier N1B, the operational amplifier N1B outputs a high level, and the N-channel field effect transistor V2 is saturated and turned on; when the PWM signal is at a low level, the voltage at the positive input terminal of the operational amplifier N1B is lower than the Vref voltage at the reverse input terminal of the operational amplifier N1B, the operational amplifier N1B outputs a low level, and the N-channel field effect transistor V2 is turned off; Therefore, the N-channel field effect transistor V2 is controlled by the PWM signal. Since the field effect transistor V1 is in a fully on state, the field effect transistor V2, the inductor L1, the diode D2 and the capacitor C1 constitute a BOOST boost output circuit, and the DC switching power supply conversion circuit works in the BOOST boost working state.

2. A DC switching power supply conversion circuit capable of both stepping down and stepping up voltage according to claim 1, characterized in that: The reference voltage Vref has a value of 1-4V and is generated by voltage division of the resistor R1 and the voltage stabilizing diode D3, or by voltage division of a resistor or a potentiometer.

3. A DC switching power supply conversion circuit capable of both stepping down and stepping up voltage according to claim 1, characterized in that: The P-channel field effect transistor V1 is replaced by a PNP transistor, and the N-channel field effect transistor V2 is replaced by an NPN transistor.

4. The DC switching power supply conversion circuit capable of both stepping down and stepping up voltage according to claim 1, characterized in that: The operational amplifiers N1A and N1B are replaced by comparators.

5. The DC switching power supply conversion circuit capable of both stepping down and stepping up voltage according to claim 1, characterized in that: The voltage of the input positive electrode is 7V-18V.

6. A DC switching power supply conversion circuit capable of both stepping down and stepping up voltage according to claim 1, characterized in that: The buck-boost control terminal is connected to a single chip microcomputer or an FPGA.

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