A non-isolated buck-type switching converter

Abstract

The present invention discloses a non-isolated buck-type switching converter, which includes a first switching element, a second switching element, a first inductor, a first capacitor, a third switching element, a second inductor, a fourth switching element, a second capacitor, a first resistor, and a control module. The present invention adopts two inductor devices, and the exciting voltage of the inductor is V in / 2 - V out , which is equivalent to reducing the input voltage V in to V in / 2. The lower the input voltage, the higher the efficiency of the switching converter, thereby improving the efficiency of the buck converter.

Description

Technical Field

[0001] The present invention relates to the field of circuits, and particularly to a non-isolated buck-type switching converter. Background Art

[0002] A traditional non-isolated buck converter consists of a rectifying MOS transistor Q, a freewheeling diode D, an output inductor Lout, an output capacitor Cout, and a load resistor Rload. The positive direction is as Figure 1 shown. Among them, vin is the input voltage; vg is the driving voltage between the gate and source (GS terminal) of MOS transistor Q; vLout is the voltage across output inductor Lout; vout is the output voltage; iQ is the current flowing through MOS transistor Q; iD is the current flowing through diode D; ilout is the inductor current flowing through inductor Lout; iload is the load current flowing through load Rload.

[0003] The timing diagram of a traditional non-isolated buck converter is as Figure 2 shown. In a traditional non-isolated buck converter, when MOS transistor Q is turned on, the voltage across output inductor Lout is V in -V out , and when MOS transistor Q is turned off, the voltage across output inductor Lout is -V out . According to the volt-second balance of output inductor Lout, there is:

[0004] (V in -V out )·D = V out ·(1 - D)

[0005] Thus, after rearrangement, the relationship between voltage V out and input voltage V in satisfies:

[0006] V out = D·V in

[0007] where D is the duty cycle of MOS transistor driving voltage vg.

[0008] It can be seen from the above formula that keeping output voltage V out unchanged, as input voltage V in increases, the duty cycle D will linearly decrease. As the duty cycle D decreases, it will lead to:

[0009] the effective value (RMS value) of the current iD flowing through diode D increases, resulting in an increase in the conduction loss of diode D;

[0010] the effective value (RMS value) of the inductor current ilout flowing through inductor Lout increases, and the copper loss of output inductor Lout increases;

[0011] The peak-to-peak value (PK-PK value) of the inductor current ilout flowing through the inductor Lout increases, and the core loss of the output inductor Lout increases;

[0012] The root mean square value (RMS value) of the current iQ flowing through the MOS transistor Q decreases, and the conduction loss of the MOS transistor decreases;

[0013] As the input voltage V in increases, it will cause an increase in the turn-on and turn-off losses of the MOS transistor.

[0014] Although the root mean square value (RMS value) of the current iQ flowing through the MOS transistor Q decreases and the conduction loss of the MOS transistor decreases, since other losses are all increasing, the reduction in the conduction loss of the MOS transistor cannot offset the increasing losses, and the overall loss of the converter increases. The efficiency η of the converter decreases as the input voltage V in increases and the duty cycle D decreases.

[0015] At the same time, the breakdown voltages of the rectifying MOS transistor and the freewheeling diode of the traditional non-isolated buck converter are at least the highest input voltage. Therefore, the higher the input voltage, the higher the breakdown voltage required for the MOS transistor. And for a MOS transistor with a high breakdown voltage, its on-resistance is larger and the price is more expensive. This further reduces the efficiency η and cost of the converter. SUMMARY OF THE INVENTION

[0016] The object of the present invention is to provide a non-isolated buck switching converter.

[0017] The technical solution for achieving the object of the present invention is: a non-isolated buck switching converter, comprising:

[0018] A first switching element, the first end of which is coupled to a first node;

[0019] A second switching element, the first end of which is coupled to the first node, and the second end of which is coupled to a second node;

[0020] A first inductor, the first end of which is coupled to the first node, and the second end of which is coupled to a third node;

[0021] A first capacitor, the first end of which is coupled to the third node, and the second end of which is coupled to a fourth node;

[0022] A third switching element, the first end of which is coupled to the fourth node, and the second end of which is coupled to the second node;

[0023] A second inductor, the first end of which is coupled to the fourth node, and the second end of which is coupled to a fifth node;

[0024] A fourth switching element, the first end of which is coupled to the third node, and the second end of which is coupled to the fifth node;

[0025] An output module, with a first end coupled to the fifth node and a second end coupled to the second node;

[0026] A control module, configured to:

[0027] Output a first control signal to the control end of the first switching element and output a second control signal to the control end of the fourth switching element. The first control signal and the second control signal are square wave signals with the same preset switching period, and the first control signal and the second control signal are complementary;

[0028] Wherein, the second switching element and the third switching element are both diodes, and are configured to conduct when the fourth switching element conducts and disconnect when the fourth switching element disconnects.

[0029] As a preferred embodiment, the first switching element and the fourth switching element are both MOS transistors.

[0030] As a preferred embodiment, the non-isolated buck-type switching converter includes two working modes within a preset switching period, which are respectively:

[0031] The first working mode, the first switching element conducts, the second switching element, the third switching element, and the fourth switching element disconnect, and the first inductor and the second inductor are magnetized and the first capacitor is charged;

[0032] The second working mode, the first switching element disconnects, the second switching element, the third switching element, and the fourth switching element conduct, the fourth switching element passes through the demagnetization current of the first inductor and the discharge current of the first capacitor, the second switching element passes through the demagnetization current of the first inductor, and the third switching element passes through the demagnetization current of the second inductor and the discharge current of the first capacitor.

[0033] As a preferred embodiment, the duration of the first working mode is DT S , the duration of the second working mode is (1 - D)*Ts, D is the duty cycle of the non-isolated buck-type switching converter, and T s is the preset switching period.

[0034] As a preferred embodiment, the output module includes a second capacitor and a first resistor. The first ends of the second capacitor and the first resistor are both coupled to the fifth node, and the second ends are both coupled to the second node.

[0035] The present invention also provides another non-isolated buck-type switching converter, including:

[0036] A first switching element, with a first end coupled to the first node;

[0037] A second switching element, with its first terminal coupled to the first node and its second terminal coupled to the second node;

[0038] A first inductor, with its first terminal coupled to the first node and its second terminal coupled to the third node;

[0039] A first capacitor, with its first terminal coupled to the third node and its second terminal coupled to the fourth node;

[0040] A third switching element, with its first terminal coupled to the fourth node and its second terminal coupled to the second node;

[0041] A second inductor, with its first terminal coupled to the fourth node and its second terminal coupled to the fifth node;

[0042] A fourth switching element, with its first terminal coupled to the third node and its second terminal coupled to the fifth node;

[0043] An output module, with its first terminal coupled to the fifth node and its second terminal coupled to the second node;

[0044] A control module, configured to:

[0045] Output a first control signal to the control terminal of the first switching element, and output a second control signal to the control terminals of the second switching element, the third switching element, and the fourth switching element. The first control signal and the second control signal are square wave signals with the same preset switching period, and the first control signal and the second control signal are complementary.

[0046] As a preferred embodiment, the first switching element, the second switching element, the third switching element, and the fourth switching element are all MOS transistors.

[0047] As a preferred embodiment, the non-isolated buck switching converter includes two operating modes within a preset switching period, namely:

[0048] A first operating mode, in which the first switching element is turned on, the second switching element, the third switching element, and the fourth switching element are turned off, the first inductor and the second inductor are magnetized, and the first capacitor is charged;

[0049] A second operating mode, in which the first switching element is turned off, the second switching element, the third switching element, and the fourth switching element are turned on. The fourth switching element conducts the demagnetization current of the first inductor and the discharge current of the first capacitor, the second switching element conducts the demagnetization current of the first inductor, and the third switching element conducts the demagnetization current of the second inductor and the discharge current of the first capacitor.

[0050] As a preferred embodiment, the duration of the first operating mode is DT S, the duration of the second operating mode is (1 - D)*Ts, where D is the duty cycle of the non-isolated buck converter and T s is the preset switching period.

[0051] As a preferred embodiment, the output module includes a second capacitor and a first resistor. The first ends of the second capacitor and the first resistor are both coupled to the fifth node, and the second ends are both coupled to the second node.

[0052] Compared with the prior art, the significant advantages of the present invention are as follows: The present invention uses two inductor devices, and the output voltage has a linear relationship with half of the input voltage. When the input voltage and the output voltage are the same, the duty cycle is twice that of the traditional buck converter, effectively improving the efficiency of the converter; when the input voltage is reduced by half in the present invention, MOS transistors and diodes with lower breakdown voltages can be selected, thereby reducing the circuit cost.

[0053] Other features and advantages of the present invention will be described in the subsequent description, and some of them will become obvious from the description, or be understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained by the structures specifically pointed out in the written description, claims, and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 Schematic diagram of a traditional buck converter.

[0055] Figure 2 Timing diagram of a traditional buck converter.

[0056] Figure 3 Schematic structural diagram of an embodiment of the present invention.

[0057] Figure 4 For Figure 3 schematic diagram of operating mode 0 (t0 - t1).

[0058] Figure 5 For Figure 3 schematic diagram of operating mode 1 (t1 - t2).

[0059] Figure 6 For Figure 3 PWM timing diagram.

[0060] Figure 7 Schematic structural diagram of another embodiment of the present invention.

[0061] Figure 8 For Figure 7 PWM timing diagram. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0062] It is easy to understand that according to the technical solution of the present invention, without changing the essence of the present invention, those of ordinary skill in the art can imagine various embodiments of the present invention. Therefore, the following specific embodiments and drawings are only exemplary descriptions of the technical solution of the present invention, and should not be regarded as all of the present invention or as a limitation or definition of the technical solution of the present invention. On the contrary, the purpose of providing these embodiments is to enable those skilled in the art to understand the present invention more thoroughly. The preferred embodiments of the present invention will be specifically described below with reference to the drawings, in which the drawings form a part of this application and are used together with the embodiments of the present invention to illustrate the innovative concept of the present invention.

[0063] Embodiment 1

[0064] As Figure 3 shown, as an embodiment, the non-isolated buck-type switching converter shown includes a first switching element, a second switching element, a first inductor, a first capacitor, a third switching element, a second inductor, a fourth switching element, a second capacitor, a first resistor, and a control module;

[0065] In this embodiment, the first switching element is a rectifying MOS transistor Q1, the second switching element is a freewheeling diode D1, the first inductor is an output inductor Lout1, the first capacitor is a DC-blocking capacitor Cc, the third switching element is a freewheeling diode D2, the second inductor is an output inductor Lout2, the fourth switching element is a freewheeling MOS transistor Q2, the second capacitor is an output capacitor Cout, and the first resistor is a load resistor Rload. Figure 3 The specific definitions of the variables are as follows: vin is the input voltage; vg1 is the driving voltage between the GS poles of the rectifying MOS transistor Q1; vg2 is the driving voltage between the GS poles of the freewheeling MOS transistor Q2; vLout1 is the voltage across the output inductor Lout1; vLout2 is the voltage across the output inductor Lout2; vCc is the voltage across the DC-blocking capacitor Cc; iQ1 is the current flowing through the rectifying MOS transistor Q1; iQ2 is the current flowing through the freewheeling MOS transistor Q2; iD1 is the current flowing through the freewheeling diode D1; iD2 is the current flowing through the freewheeling diode D2; iCc is the current flowing through the DC-blocking capacitor Cc; ilout is the inductor current flowing through the inductor Lout; and iload is the load current flowing through the load Rload.

[0066] The source of the rectifying MOS transistor Q1 is coupled to the first end of the output inductor Lout1 and the cathode of the freewheeling diode D1 at a first node. The second end of the output inductor Lout1 is coupled to the first end of the DC-blocking capacitor Cc and the drain of the freewheeling MOS transistor Q2 at a third node. The second end of the DC-blocking capacitor Cc is coupled to the cathode of the freewheeling diode D2 and the first end of the output inductor Lout2 at a fourth node. The first end of the output capacitor Cout, the first end of the load resistor Rload are coupled to the second end of the output inductor Lout2 and the source of the freewheeling MOS transistor Q2 at a fifth node. The second end of the output capacitor Cout, the second end of the load resistor Rload, the anode of the freewheeling diode D1, and the anode of the freewheeling diode D2 are coupled to a second node.

[0067] Within one switching period Ts, the present invention has two operating modes (dead time is not considered for convenience of analysis), as Figure 4 shown in Mode 0 (t0 - t1) and as Figure 5 shown in Mode 1 (t1 - t2). The pulse width modulation (PWM) timing diagram of the non-isolated buck-type switching converter in this embodiment is as Figure 6 shown. The control module outputs a first control signal to the control terminal of the first switching element and a second control signal to the control terminal of the fourth switching element. The control terminals of the first switching element and the fourth switching element are both the gates of MOS transistors. The first control signal and the second control signal are square wave signals with the same preset switching period, and the first control signal and the second control signal are complementary. Among them, the first control signal is the driving voltage vg1 between the GS poles of the rectifying MOS transistor Q1, and the second control signal is the driving voltage vg2 between the GS poles of the freewheeling MOS transistor Q2.

[0068] The specific working processes of each operating mode in this embodiment are as follows:

[0069] 1. Operating Mode 0 (t0 - t1) of this embodiment

[0070] At time t0, the rectifying MOS transistor Q1 conducts, and the freewheeling MOS transistor Q2 and the freewheeling diodes D1, D2 turn off. During the time period t0 - t1, the output inductors Lout1 and Lout2 are magnetized, and the DC-blocking capacitor Cc is charged. During this period, the currents flowing through the rectifying MOS transistor Q1, the output inductors Lout1 and Lout2, and the DC-blocking capacitor Cc are the same.

[0071] Because within the time of (1 - D)*Ts in the previous cycle, the capacitor is directly connected in parallel to the output voltage Vout through the freewheeling MOS transistor Q2 and the freewheeling diode D2, the voltage across the capacitor is approximately the output voltage Vout (neglecting the influence of the on-resistance of the freewheeling MOS transistor Q2 and the forward voltage drop of the freewheeling diode D2). The inductances of the output inductors Lout1 and Lout2 are equal, so the magnetizing voltages on Lout1 and Lout2 are the same.

[0072] The magnetizing voltage of Lout1 or Lout2 is:

[0073]

[0074] Then, within the time period from t0 to t1, the volt-second value of Lout1 or Lout2 is as shown in Equation (2):

[0075]

[0076] Thus, it can be obtained that:

[0077]

[0078] 2. Working mode 1 (t1 - t2) of this embodiment

[0079] At the moment t1, the rectifying MOS transistor Q1 is turned off, and the freewheeling MOS transistor Q2 and the freewheeling diodes D1 and D2 are turned on. Within the time period from t1 to t2, the output inductors Lout1 and Lout2 demagnetize, and the DC-blocking capacitor Cc releases energy through Q2 and D2.

[0080] During this period, the freewheeling MOS transistor Q2 conducts the demagnetizing current of the output inductor Lout1 and the discharging current of the DC-blocking capacitor Cc; the freewheeling diode D1 conducts the demagnetizing current of the output inductor Lout1; the freewheeling diode D2 conducts the demagnetizing current of the output inductor Lout2 and the discharging current of the DC-blocking capacitor Cc.

[0081] Within the time period from t1 to t2, the output inductor Lout1 is connected to Vout through Q2 and D1, and the output inductor Lout2 is connected to Vout through D2. Then, the magnetizing voltages on Lout1 and Lout2 are the same, approximately Vout (neglecting the influence of the on-resistance of the freewheeling MOS transistor Q2 and the forward voltage drop of the freewheeling diode D2).

[0082] The demagnetizing voltage of Lout1 or Lout2 is Vout.

[0083] Then, within the time period from t1 to t2, the volt-second value of Lout1 or Lout2 is as shown in Equation (3):

[0084] V out ×(1 - D)·T s (3) According to the volt - second balance principle of the inductor, Equation (2) is equal to Equation (3), so we have:

[0085]

[0086] According to Equation (4), the relationship between the input voltage Vin and the output voltage Vout of the present invention can be derived, as shown in Equation (5).

[0087]

[0088] The expression of the duty cycle D is Equation (6).

[0089]

[0090] According to the above - mentioned working mode, it can be seen that this embodiment uses two inductor devices, and the exciting voltage of the inductor is V in / 2 - V out , which is equivalent to reducing the input voltage V in to V in / 2. The lower the input voltage, the higher the efficiency of the switching converter, thereby improving the efficiency of the buck converter. At the same time, due to the reduction of the input voltage, MOS transistors and diodes with lower breakdown voltages can be selected, thus reducing the cost of the entire converter.

[0091] The DC - blocking capacitor in the topology shown in this embodiment is always connected in parallel with the output voltage Vout during the conduction stage of the free - wheeling diode. Whether during the startup process or in steady - state operation, the capacitor voltage always follows the change of the output voltage and will not change the volt - second balance of the inductor in the circuit, eliminating the need for the pre - charging process of the DC - blocking capacitor and simplifying the control complexity.

[0092] Embodiment 2

[0093] As another embodiment, the non - isolated buck - type switching converter shown in Embodiment 2 includes a first switching element, a second switching element, a first inductor, a first capacitor, a third switching element, a second inductor, a fourth switching element, a second capacitor, a first resistor, and a control module;

[0094] Different from Embodiment 1, the second switching element in this embodiment is a rectifying MOS transistor Q3, the third switching element is a rectifying MOS transistor Q4, the control module outputs a first control signal to the control terminal of the first switching element, and outputs a second control signal to the control terminals of the second switching element, the third switching element, and the fourth switching element. The first control signal and the second control signal are square - wave signals with the same preset switching period, and the first control signal and the second control signal are complementary.

[0095] The non - isolated buck - type switching converter of this embodiment is a synchronous rectification scheme. Its circuit diagram is as shown in Figure 7As shown, its PWM timing diagram is as Figure 8 shown. The first control signal is the driving voltage vg1 of the rectifying MOS transistor Q1, and the second control signal is divided into three paths, which are the driving voltages vg2 to vg4 of the freewheeling MOS transistor Q2, the rectifying MOS transistor Q3, and the rectifying MOS transistor Q4 respectively. The specific working processes of each working mode in this embodiment are basically the same as those in Embodiment 1. The non-isolated buck-type switching converter in this embodiment only needs two PWM waves to realize the control of the entire circuit, further simplifying the control circuit and reducing costs.

[0096] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

[0097] It should be understood that in order to streamline the present invention and help those skilled in the art understand various aspects of the present invention, in the above description of the exemplary embodiments of the present invention, various features of the present invention are sometimes described in a single embodiment or with reference to a single figure. However, the present invention should not be construed as meaning that the features included in the exemplary embodiments are all essential technical features of the claims of the present invention.

[0098] It should be understood that the modules, units, components, etc. included in the device of an embodiment of the present invention can be adaptively changed to be arranged in a device different from that of this embodiment. The different modules, units or components included in the device of the embodiment can be combined into one module, unit or component, or they can be divided into multiple sub-modules, sub-units or sub-components.

Claims

1. A non-isolated step-down switching converter, characterized in that, including: a first switching element, the first end of which is coupled to a first node; a second switching element, the first end of which is coupled to the first node and the second end of which is coupled to a second node; a first inductor, the first end of which is coupled to the first node and the second end of which is coupled to a third node; a first capacitor, the first end of which is coupled to the third node and the second end of which is coupled to a fourth node; a third switching element, the first end of which is coupled to the fourth node and the second end of which is coupled to the second node; a second inductor, the first end of which is coupled to the fourth node and the second end of which is coupled to a fifth node; a fourth switching element, the first end of which is coupled to the third node and the second end of which is coupled to the fifth node; an output module, the first end of which is coupled to the fifth node and the second end of which is coupled to the second node; a control module, configured to: output a first control signal to the control end of the first switching element, output a second control signal to the control end of the fourth switching element, the first control signal and the second control signal are square wave signals with the same preset switching period, and the first control signal and the second control signal are complementary; wherein, the second switching element and the third switching element are both diodes, and are configured to conduct when the fourth switching element conducts and disconnect when the fourth switching element disconnects.

2. The non-isolated buck-type switching converter according to claim 1, characterized in that, The first switching element and the fourth switching element are both MOS transistors.

3. The non-isolated buck-type switching converter according to claim 1, wherein The non-isolated buck switching converter includes two operating modes within a preset switching period, respectively: a first operating mode, the first switching element conducts, the second switching element, the third switching element, and the fourth switching element disconnect, the first inductor and the second inductor are magnetized, and the first capacitor is charged; a second operating mode, the first switching element disconnects, the second switching element, the third switching element, and the fourth switching element conduct, the fourth switching element conducts the demagnetization current of the first inductor and the discharge current of the first capacitor, the second switching element conducts the demagnetization current of the first inductor, and the third switching element conducts the demagnetization current of the second inductor and the discharge current of the first capacitor.

4. The non-isolated buck-type switching converter according to claim 3, characterized in that, The duration of the first operating mode is DT S , the duration of the second operating mode is (1 - D)*Ts, where D is the duty cycle of the non-isolated buck switching converter, and T s is the preset switching period.

5. The non-isolated buck-type switching converter according to claim 1, wherein The output module includes a second capacitor and a first resistor, the first ends of the second capacitor and the first resistor are both coupled to the fifth node, and the second ends are both coupled to the second node.

6. A non-isolated buck-type switching converter, characterized in that, including: a first switching element, the first end of which is coupled to a first node; a second switching element, the first end of which is coupled to the first node and the second end of which is coupled to a second node; a first inductor, the first end of which is coupled to the first node and the second end of which is coupled to a third node; a first capacitor, the first end of which is coupled to the third node and the second end of which is coupled to a fourth node; a third switching element, the first end of which is coupled to the fourth node and the second end of which is coupled to the second node; a second inductor, the first end of which is coupled to the fourth node and the second end of which is coupled to a fifth node; a fourth switching element, the first end of which is coupled to the third node and the second end of which is coupled to the fifth node; an output module, the first end of which is coupled to the fifth node and the second end of which is coupled to the second node; a control module, configured to: output a first control signal to the control end of the first switching element, output a second control signal to the control ends of the second switching element, the third switching element, and the fourth switching element, The first control signal and the second control signal are square wave signals with the same preset switching period, and the first control signal and the second control signal are complementary.

7. The non-isolated buck-type switching converter according to claim 6, wherein The first switching element, the second switching element, the third switching element, and the fourth switching element are all MOS transistors.

8. The non-isolated buck switching converter according to claim 6, characterized in that, The non-isolated buck-type switching converter includes two operating modes within a preset switching period, which are respectively: The first operating mode: the first switching element is turned on, the second switching element, the third switching element, and the fourth switching element are turned off, the first inductor and the second inductor are magnetized, and the first capacitor is charged. The second operating mode: the first switching element is turned off, the second switching element, the third switching element, and the fourth switching element are turned on, the fourth switching element conducts the demagnetizing current of the first inductor and the discharging current of the first capacitor, the second switching element conducts the demagnetizing current of the first inductor, and the third switching element conducts the demagnetizing current of the second inductor and the discharging current of the first capacitor.

9. The non-isolated buck switching converter according to claim 8, wherein, The duration of the first operating mode is DT S , the duration of the second operating mode is (1 - D)*Ts, where D is the duty cycle of the non-isolated buck switch converter, and T s is a preset switching period.

10. The non-isolated buck-type switching converter according to claim 6, characterized in that, The output module includes a second capacitor and a first resistor. The first ends of the second capacitor and the first resistor are both coupled to the fifth node, and the second ends are both coupled to the second node.

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