A mode switching circuit applied to a buck conversion circuit

Abstract

The present invention discloses a mode switching circuit applied to a buck conversion circuit, belonging to the field of power conversion. It includes multiple switches, a first amplifier, multiple resistors, a first diode, and multiple current sources. The first end of the first switch is grounded, the second end of the first switch is connected to the first end of the second switch, and the second end of the second switch is connected to the connection midpoint of two switches in the buck conversion circuit; the first end of the first switch is connected to the first end of the first current source through the first resistor, the first end of the second switch is connected to the first end of the second current source through the second resistor, the first input terminal of the first amplifier is connected to the first end of the second current source, the second input terminal of the first amplifier is connected to the first end of the first current source, the first end of the third resistor is connected to the first end of the second switch, the second end of the third resistor is connected to the anode of the first diode, and the cathode of the first diode is connected to the second end of the second switch. The present invention can improve the stability and performance of the buck conversion circuit.

Description

Technical Field

[0001] The present invention relates to the technical field of power conversion, and particularly to a mode switching circuit applied to a buck conversion circuit. Background Art

[0002] Pulse Frequency Modulation (PFM) is a modulation method widely used in buck DC-DC converters. Its main advantage is that it can significantly improve the working efficiency of the converter under light load conditions. The basic feature of pulse frequency modulation is that the inductor current cannot be negative. Therefore, under no-load or light load conditions, the inductor current is usually in a discontinuous state. However, as the load current increases, the inductor current changes from a discontinuous state to a continuous state. When the inductor current enters the critical continuous state, the converter often has problems with uncertain working states and may switch back and forth between the discontinuous state of the inductor current and the continuous state of the inductor current. This back-and-forth switching not only increases the output voltage ripple but may also cause the phenomenon of large and small waves, thus affecting the stability and performance of the converter.

[0003] Although pulse frequency modulation has high efficiency advantages under light load conditions, its dynamic response and stability problems during load changes are still a technical problem to be solved urgently. Especially when the load current increases and the inductor current enters the critical continuous state, the uncertainty of the converter's working state will significantly affect the overall performance of the system. Therefore, how to improve the dynamic response and stability of pulse frequency modulation during load changes without sacrificing the light load efficiency has become an important research direction. Summary of the Invention

[0004] The present invention aims to provide a mode switching circuit applied to a buck conversion circuit.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] A mode switching circuit applied to a buck conversion circuit, comprising a first switch, a second switch, a first amplifier, a first resistor, a second resistor, a third resistor, a first diode, a first current source, and a second current source. The first end of the first switch is grounded, the second end of the first switch is connected to the first end of the second switch, and the second end of the second switch is connected to the connection midpoint of two switches in the buck conversion circuit. The first end of the first switch is connected to the first end of the first current source through the first resistor, the first end of the second switch is connected to the first end of the second current source through the second resistor, the first input terminal of the first amplifier is connected to the first end of the second current source, the second input terminal of the first amplifier is connected to the first end of the first current source, the first end of the third resistor is connected to the first end of the second switch, the second end of the third resistor is connected to the anode of the first diode, and the cathode of the first diode is connected to the second end of the second switch.

[0007] Further, the third ends of the first switch and the second switch are connected to an inductor current zero-crossing signal.

[0008] In a specific embodiment, the mode switching circuit applied to the buck conversion circuit further includes a first NOT gate and a second NOT gate. The inductor current zero-crossing signal is connected to the third end of the second switch through the first NOT gate, and the inductor current zero-crossing signal is connected to the third end of the first switch through the first NOT gate and the second NOT gate.

[0009] In a specific embodiment, the mode switching circuit applied to the buck conversion circuit further includes a second amplifier. The first input terminal of the second amplifier is connected to zero, the second input terminal of the second amplifier is connected to the inductor current in the buck conversion circuit, and the output terminal of the second amplifier outputs an inductor current zero-crossing signal.

[0010] In a specific embodiment, the second ends of the first current source and the second current source are connected to a first voltage.

[0011] In a specific embodiment, when the buck conversion circuit changes from an inductor current discontinuous state to an inductor current critical state, the first switch is closed, the second switch is opened, and the voltage expressions of the first input terminal and the second input terminal of the first amplifier are as follows:

[0012] ,

[0013] where, V R is the voltage of the second input terminal of the first amplifier, I b is the current of the first current source, R1 is the first resistor, V X is the voltage of the first input terminal of the first amplifier, I cis the current of the second current source, R2 is the second resistor, R S1 is the on-resistance of the first switch, V D1 is the voltage of the first diode, I L is the inductor current, R on_LSFET is the on-resistance of the lower switch of the buck conversion circuit, R3 is the third resistor.

[0014] In a specific embodiment, after the buck conversion circuit enters the continuous inductor current state, the first switch is turned off, the second switch is turned on, and the voltage expression of the first input terminal and the second input terminal of the first amplifier is as follows:

[0015] ,

[0016] wherein, R S2 is the on-resistance of the second switch.

[0017] In a specific embodiment, the first amplifier compares the voltages of the first input terminal and the second input terminal, outputs a first signal, and after comparing the first signal with a carrier wave, outputs a driving signal to the switch of the buck conversion circuit.

[0018] In a specific embodiment, the buck conversion circuit includes a third switch, a fourth switch, a first inductor and a first capacitor. The positive pole of the input voltage is connected to the first end of the third switch, the second end of the third switch is connected to the first end of the fourth switch, the second end of the fourth switch is connected to the negative pole of the input voltage, the first end of the fourth switch is connected to the first end of the first inductor, the second end of the first inductor is connected to the first end of the first capacitor, and the second end of the first capacitor is connected to the second end of the fourth switch.

[0019] In a specific embodiment, the buck conversion circuit further includes a second capacitor, and the second capacitor is connected in parallel across the input voltage.

[0020] Beneficial effects: A mode switching circuit applied to a buck conversion circuit according to the present invention can enable the buck conversion circuit to smoothly switch to the continuous inductor current state, avoid causing excessive output voltage ripple and large and small wave problems, and can significantly improve the stability and performance of the buck conversion circuit.

[0021] To make the above features and advantages of the invention more obvious and understandable, specific embodiments are hereinafter given, and detailed descriptions are made in conjunction with the accompanying drawings as follows. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a circuit schematic diagram of a mode switching circuit applied to a buck conversion circuit according to the present invention.

[0023] Figure 2The simulation waveform diagram when the buck conversion circuit does not use the mode switching circuit of the present invention applied to the buck conversion circuit.

[0024] Figure 3 The simulation waveform diagram when the buck conversion circuit uses the mode switching circuit of the present invention applied to the buck conversion circuit. Detailed implementation manners

[0025] To make the objectives and technical solutions of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0026] Figure 1 The circuit schematic diagram of a mode switching circuit of the present invention applied to a buck conversion circuit. As Figure 1 shown, a mode switching circuit 1 of the present invention applied to a buck conversion circuit is connected to a buck conversion circuit 2, and is used to switch the buck conversion circuit 2 between an inductor current discontinuous state and an inductor current continuous state.

[0027] Further, the buck conversion circuit 2 includes a switch S3, a switch S4, an inductor L1, and a capacitor C1. The positive pole of the input voltage V in is connected to the first end of the switch S3. The second end of the switch S3 is connected to the first end of the switch S4. The second end of the switch S4 is connected to the negative pole of the input voltage V in . The first end of the switch S4 is connected to the first end of the inductor L1. The second end of the inductor L1 is connected to the first end of the capacitor C1. The second end of the capacitor C1 is connected to the second end of the switch S4. The second end of the switch S4 is grounded.

[0028] Optionally, the buck conversion circuit 2 further includes a resistor R L . The resistor R L is connected in parallel across the two ends of the capacitor C1. Among them, the resistor R L is a load, and the voltage across the resistor R L is the output voltage V o .

[0029] Optionally, the buck conversion circuit 2 further includes a capacitor C2. The capacitor C2 is connected in parallel across the two ends of the input voltage V in . The capacitor C2 functions as an input filter.

[0030] Further, a mode switching circuit 1 applied to a buck conversion circuit according to the present invention includes a switch S1, a switch S2, an amplifier A1, a resistor R1, a resistor R2, a resistor R3, a diode D1, and a current source I b , the current source I c . The first end of the switch S1 is grounded, the second end of the switch S1 is connected to the first end of the switch S2, and the second end of the switch S2 is connected to the connection midpoint of two switches in the buck conversion circuit 2, that is, the connection midpoint of the switch S3 and the switch S4; the first end of the switch S1 is connected to the first end of the current source I b through the resistor R1, the first end of the switch S2 is connected to the first end of the current source I c through the resistor R2, the first input terminal of the amplifier A1 is connected to the first end of the current source I c , the second input terminal of the amplifier A1 is connected to the first end of the current source I b , and the output terminal of the amplifier A1 outputs a signal V ERR . The first end of the resistor R3 is connected to the first end of the switch S2, the second end of the resistor R3 is connected to the anode of the diode D1, and the cathode of the diode D1 is connected to the second end of the switch S2.

[0031] Further, the second end of the current source I b is connected to the second end of the current source I c and a voltage V cc . The function of the voltage V cc is to supply power to the current source I b and the current source I c .

[0032] More specifically, the third ends of the switch S1 and the switch S2 are connected to the inductor current zero-crossing signal ZCD.

[0033] Further, a mode switching circuit 1 applied to a buck conversion circuit according to the present invention further includes a NOT gate N gate 1 and a NAND gate N gate 2. The inductor current zero-crossing signal ZCD passes through the NOT gate N gate 1 and is connected to the third end of the switch S2, and the inductor current zero-crossing signal ZCD passes through the NOT gate N gate 1 and the NAND gate N gate 2 and is connected to the third end of the switch S1.

[0034] Further, a mode switching circuit 1 applied to a buck conversion circuit according to the present invention further includes an amplifier A2. The first input terminal of the amplifier A2 is connected to zero, the second input terminal of the amplifier A2 is connected to the inductor current I L in the buck conversion circuit 2, and the output terminal of the amplifier A2 outputs the inductor current zero-crossing signal ZCD. The amplifier A2 compares the inductor current I L with zero, and when the inductor current I LWhen it is zero, the zero-crossing signal ZCD of the output inductor current is 1; otherwise, the zero-crossing signal ZCD of the inductor current is 0.

[0035] Next, the working principle of a mode switching circuit 1 applied to a buck conversion circuit of the present invention will be further introduced.

[0036] When the buck conversion circuit 2 changes from the discontinuous inductor current state to the critical inductor current state, at this time, the inductor current I L still crosses zero, the zero-crossing signal ZCD of the inductor current is 1, the switch S1 is closed, and the switch S2 is opened. At this time, the voltage expressions at the first input terminal and the second input terminal of the amplifier A1 are as follows:

[0037] ,

[0038] where, V R is the voltage at the second input terminal of the amplifier A1, V X is the voltage at the first input terminal of the amplifier A1, R S1 is the on-resistance of the switch S1, V D1 is the voltage of the diode D1; R on_LSFET is the on-resistance of the lower switch of the buck conversion circuit, that is, the on-resistance of the switch S4.

[0039] When the buck conversion circuit 2 enters the continuous inductor current state, at this time, the inductor current I L does not cross zero, the zero-crossing signal ZCD of the inductor current is 0, the switch S1 is opened, and the switch S2 is closed. At this time, the voltage expressions at the first input terminal and the second input terminal of the amplifier A1 are as follows:

[0040] ,

[0041] where, R S2 is the on-resistance of the switch S2.

[0042] Furthermore, the amplifier A1 compares the voltage V R with the voltage V X , and outputs the signal V ERR . The signal V ERR is compared with the carrier wave and then outputs a drive signal to the switches S3 and S4 of the buck conversion circuit 2. When the zero-crossing signal ZCD of the inductor current is 1, the lower switch of the buck conversion circuit 2, that is, the switch S4, should be turned off; when the zero-crossing signal ZCD of the inductor current is 0, the lower switch of the buck conversion circuit 2, that is, the switch S4, should remain conducting. If there is no branch of the diode D1 and the resistor R3, when changing from the discontinuous inductor current state to the critical inductor current state, the voltage V R basically remains unchanged, and the voltage V X changes violently, which will cause the signal V ERRWhen there is a mutation, the driving signal output after comparison with the carrier will also mutate, which causes the operating state of the buck conversion circuit 2 to be uncertain, resulting in an increase in the output voltage ripple and may also trigger the phenomenon of large and small waves, thus affecting the stability and performance of the buck conversion circuit.

[0043] In the present invention, due to the existence of the branch of diode D1 and resistor R3, the inductor current I in the buck conversion circuit 2 L information is introduced. As can be seen from the above formula, the variation range of voltage V X is greatly reduced, whereby the signal V ERR changes continuously, avoiding the mutation of the driving signal after comparison with the carrier. As a result, the buck conversion circuit can smoothly switch to the continuous inductor current state, avoiding excessive output voltage ripple and large and small wave problems.

[0044] The buck conversion circuit is simulated and verified without using and using a mode switching circuit for a buck conversion circuit according to the present invention, and the waveform diagram is obtained as Figure 2 shown in Figure 3 From the figure, it can be seen that after using a mode switching circuit for a buck conversion circuit according to the present invention, the ripple and large and small wave problems of the output voltage of the buck conversion circuit are significantly improved, and at the same time, the problem of the inductor current being less than zero is avoided.

[0045] Although the present invention has been disclosed as above by way of embodiments, it is not intended to limit the present invention. Any person with ordinary knowledge in the technical field to which the present invention pertains may make some modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to that defined by the appended patent application scope.

Claims

1. A mode switching circuit applied to a buck conversion circuit, characterized in that, It includes a first switch, a second switch, a first amplifier, a first resistor, a second resistor, a third resistor, a first diode, a first current source, and a second current source. The first end of the first switch is grounded, the second end of the first switch is connected to the first end of the second switch, and the second end of the second switch is connected to the connection midpoint of the two switches in the buck conversion circuit; the first end of the first switch is connected to the first end of the first current source through the first resistor, the first end of the second switch is connected to the first end of the second current source through the second resistor, the first input terminal of the first amplifier is connected to the first end of the second current source, the second input terminal of the first amplifier is connected to the first end of the first current source, the first end of the third resistor is connected to the first end of the second switch, the second end of the third resistor is connected to the anode of the first diode, and the cathode of the first diode is connected to the second end of the second switch; the third ends of the first switch and the second switch are connected to the inductor current zero-crossing signal. The mode switching circuit applied to the buck conversion circuit further includes a first NOT gate and a second NOT gate. The inductor current zero-crossing signal is connected to the third end of the second switch through the first NOT gate, and the inductor current zero-crossing signal is connected to the third end of the first switch through the first NOT gate and the second NOT gate. The mode switching circuit applied to the buck conversion circuit further includes a second amplifier. The first input terminal of the second amplifier is connected to zero value, the second input terminal of the second amplifier is connected to the inductor current in the buck conversion circuit, and the output terminal of the second amplifier outputs the inductor current zero-crossing signal.

2. The mode switching circuit applied to the buck conversion circuit according to claim 1, wherein The second ends of the first current source and the second current source are connected to a first voltage.

3. The mode switching circuit applied to the buck conversion circuit as described in claim 1, characterized in that, When the buck conversion circuit changes from the inductor current discontinuous state to the inductor current critical state, the first switch is closed, the second switch is open, and the voltage expressions of the first input terminal and the second input terminal of the first amplifier are as follows: ， Among them, V R is the voltage at the second input terminal of the first amplifier, I b is the current of the first current source, R1 is the first resistor, V X is the voltage at the first input terminal of the first amplifier, I c is the current of the second current source, R2 is the second resistor, R S1 is the on-resistance of the first switch, V D1 is the voltage of the first diode, I L is the inductor current, R on_LSFET is the on-resistance of the lower switch of the buck conversion circuit, and R3 is the third resistor.

4. The mode switching circuit applied to the buck conversion circuit according to claim 3, characterized in that, After the buck conversion circuit enters the inductor current continuous state, the first switch is open, the second switch is closed, and the voltage expressions of the first input terminal and the second input terminal of the first amplifier are as follows: ， wherein, R S2 is the on-resistance of the second switch.

5. The mode switching circuit applied to the buck conversion circuit according to any one of claims 1-4, characterized in that, The first amplifier compares the voltages of the first input terminal and the second input terminal, outputs a first signal, and after comparing the first signal with a carrier wave, outputs a driving signal to the switch of the buck conversion circuit.

6. The mode switching circuit applied to the buck conversion circuit according to claim 1, wherein The buck conversion circuit includes a third switch, a fourth switch, a first inductor, and a first capacitor. The positive pole of the input voltage is connected to the first end of the third switch, the second end of the third switch is connected to the first end of the fourth switch, the second end of the fourth switch is connected to the negative pole of the input voltage, the first end of the fourth switch is connected to the first end of the first inductor, the second end of the first inductor is connected to the first end of the first capacitor, and the second end of the first capacitor is connected to the second end of the fourth switch.

7. The mode switching circuit applied to the buck conversion circuit as described in claim 6, wherein The buck conversion circuit further includes a second capacitor, and the second capacitor is connected in parallel across the input voltage.

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