Mode switching circuit applied to buck conversion circuit

Abstract

The invention discloses a mode switching circuit applied to a step-down conversion circuit, which belongs to the field of electric energy conversion, and comprises a plurality of switches, a first amplifier, a plurality of resistors, a first diode and a plurality of current sources, the second end of the second switch is connected with the connection midpoint of the two switches in the step-down conversion circuit; the first end of the first switch is connected with the first end of the first current source through the first resistor, the first end of the second switch is connected with the first end of the second current source through the second resistor, the first input end of the first amplifier is connected with the first end of the second current source, and the second input end of the first amplifier is connected with the first end of the first current source. The first end of the third resistor is connected with the first end of the second switch, the second end of the third resistor is connected with the anode of the first diode, and the cathode of the first diode is connected with the second end of the second switch. The stability and the performance of the step-down conversion circuit can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of electric energy conversion, and in particular to a mode switching circuit applied to a step-down 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, so 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 will change from the discontinuous state to the continuous state. When the inductor current enters the critical continuous state, the converter often has the problem of uncertain working state, 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 will not only increase the output voltage ripple, but may also cause the big and small wave phenomenon, thereby affecting the stability and performance of the converter.

[0003] Although pulse frequency modulation has a high efficiency advantage under light load conditions, its dynamic response and stability when the load changes are still a technical problem that needs to be solved urgently. In particular, when the load current increases and causes the inductor current to enter 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 when the load changes without sacrificing light load efficiency has become an important direction of current research. Summary of the invention

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

[0005] To achieve the above object, the technical solution of the present invention is: A mode switching circuit applied to a buck conversion circuit comprises 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, wherein a first end of the first switch is grounded, a second end of the first switch is connected to a first end of the second switch, and a second end of the second switch is connected to a connection midpoint of two switches in the buck conversion circuit; a first end of the first switch is connected to a first end of the first current source via the first resistor, a first end of the second switch is connected to a first end of the second current source via the second resistor, a first input end of the first amplifier is connected to a first end of the second current source, a second input end of the first amplifier is connected to a first end of the first current source, a first end of the third resistor is connected to a first end of the second switch, a second end of the third resistor is connected to an anode of the first diode, and a cathode of the first diode is connected to a second end of the second switch.

[0006] Furthermore, a third terminal of the first switch and the second switch is connected to an inductor current zero-crossing signal.

[0007] 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 passes through the first NOT gate and is connected to the third end of the second switch, and the inductor current zero-crossing signal passes through the first NOT gate and the second NOT gate and is connected to the third end of the first switch.

[0008] 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 the 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.

[0009] In a specific embodiment, the second end of the first current source and the second end of the second current source are connected to a first voltage.

[0010] In a specific embodiment, when the step-down conversion circuit changes from the discontinuous state of the inductor current to the critical state of the inductor current, the first switch is closed, the second switch is opened, and the voltage expression between the first input terminal and the second input terminal of the first amplifier is 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 S1is 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 tube of the buck conversion circuit, and R3 is the third resistor.

[0011] In a specific embodiment, when the buck converter circuit enters the inductor current continuous state, the first switch is opened, the second switch is closed, and the voltage expression between the first input terminal and the second input terminal of the first amplifier is as follows: , Among them, R S2 is the on-resistance of the second switch.

[0012] In a specific embodiment, the first amplifier compares the voltages of the first input terminal and the second input terminal and outputs a first signal. The first signal is compared with a carrier and then outputs a driving signal to a switch of the buck conversion circuit.

[0013] In a specific embodiment, the step-down conversion circuit includes a third switch, a fourth switch, a first inductor and a first capacitor, the positive electrode 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 electrode 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.

[0014] In a specific embodiment, the step-down conversion circuit further includes a second capacitor, and the second capacitor is connected in parallel across the input voltage.

[0015] Beneficial effect: The present invention provides a mode switching circuit applied to a buck conversion circuit, which can enable the buck conversion circuit to smoothly switch to a continuous inductor current state, avoid causing excessive output voltage ripple and large and small waves, and can significantly improve the stability and performance of the buck conversion circuit.

[0016] In order to make the above features and advantages of the invention more obvious and easy to understand, embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The present invention is a circuit diagram of a mode switching circuit applied to a step-down conversion circuit.

[0018] Figure 2 The figure is a simulation waveform diagram of a mode switching circuit applied to a buck conversion circuit without using the present invention.

[0019] Figure 3 The present invention is a simulation waveform diagram of a mode switching circuit applied to a buck conversion circuit using the present invention. DETAILED DESCRIPTION

[0020] In order to make the purpose and technical solution of the embodiment of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings of the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all of the embodiments. Based on the described embodiment 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.

[0021] Figure 1 FIG. 1 is a circuit diagram of a mode switching circuit applied to a step-down conversion circuit of the present invention. Figure 1 As shown, a mode switching circuit 1 applied to a buck conversion circuit of the present invention is connected to a buck conversion circuit 2, and is used to switch the buck conversion circuit 2 between a discontinuous state of the inductor current and a continuous state of the inductor current.

[0022] Furthermore, the step-down conversion circuit 2 includes a switch S3, a switch S4, an inductor L1 and a capacitor C1, and the input voltage V in The positive electrode of 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, and the second end of the switch S4 is connected to the input voltage V in The first end of the switch S4 is connected to the negative electrode 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, and the second end of the switch S4 is grounded.

[0023] Optionally, the step-down conversion circuit 2 further includes a resistor R L , resistor R L Connected in parallel across capacitor C1, where resistor R L is the load, the resistance R L The voltage across the terminals is the output voltage V o .

[0024] Optionally, the step-down conversion circuit 2 further includes a capacitor C2, which is connected in parallel to the input voltage V in At both ends, the capacitor C2 acts as an input filter.

[0025] Furthermore, the mode switching circuit 1 for a step-down conversion circuit of 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, a current source I b , current source I cThe 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 the two switches in the step-down 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 current source I through the resistor R1 b The first end of the switch S2 is connected to the current source I through the resistor R2. c The first input terminal of the amplifier A1 is connected to the current source I c The first end of the amplifier A1 is connected to the current source I b The first end 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.

[0026] Furthermore, the current source I b The second terminal is connected to the current source I c The second end is connected to the voltage V cc , voltage V cc The role of the current source I b With current source I c powered by.

[0027] More specifically, the third terminals of the switch S1 and the switch S2 are connected to the inductor current zero-crossing signal ZCD.

[0028] Furthermore, the mode switching circuit 1 applied to the step-down conversion circuit of the present invention further includes a NOT gate N gate 1NAND gate N gate 2. The inductor current zero-crossing signal ZCD passes through the NOT gate N gate 1 is connected to the third terminal of switch S2, and the inductor current zero-crossing signal ZCD passes through the NOT gate N gate 1NAND gate N gate 2Connect the third terminal of switch S1.

[0029] Furthermore, the mode switching circuit 1 applied to the buck conversion circuit of the present invention further includes an amplifier A2, a first input terminal of the amplifier A2 is connected to a zero value, and a second input terminal of the amplifier A2 is connected to an inductor current I in the buck conversion circuit 2 L , the output terminal of amplifier A2 outputs the inductor current zero-crossing signal ZCD. Amplifier A2 compares the inductor current I L With zero value, the inductor current I L When is zero, the output inductor current zero-crossing signal ZCD is 1; otherwise, the inductor current zero-crossing signal ZCD is 0.

[0030] The following continues to introduce the working principle of a mode switching circuit 1 applied to a buck conversion circuit of the present invention.

[0031] When the step-down conversion circuit 2 changes from the discontinuous state of the inductor current to the critical state of the inductor current, the inductor current I L Still crossing zero, the inductor current zero crossing signal ZCD is 1, switch S1 is closed, and switch S2 is open. At this time, the voltage expression between the first input terminal and the second input terminal of amplifier A1 is as follows: , Among them, V R is the voltage at the second input terminal of amplifier A1, V X is the voltage at the first input terminal of amplifier A1, R S1 is the on-resistance of switch S1, V D1 is the voltage of diode D1; R on_LSFET is the on-resistance of the lower tube of the buck converter circuit, that is, the on-resistance of switch S4.

[0032] When the step-down conversion circuit 2 enters the inductor current continuous state, the inductor current I L The inductor current 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 expression between the first input terminal and the second input terminal of the amplifier A1 is as follows: , Among them, R S2 is the on-resistance of switch S2.

[0033] Further, amplifier A1 compares the voltage V R With voltage V X , output signal V ERR , signal V ERR After comparing with the carrier, the drive signal is output to the switch S3 and switch S4 of the buck converter circuit 2. When the inductor current zero-crossing signal ZCD is 1, the lower tube of the buck converter circuit 2, i.e., switch S4, should be turned off; when the inductor current zero-crossing signal ZCD is 0, the lower tube of the buck converter circuit 2, i.e., switch S4, should remain turned on. If there is no branch of the diode D1 and the resistor R3, when the inductor current changes from the intermittent state to the critical state, the voltage V R Basically unchanged, voltage V X The signal V ERR The driving signal output after comparison with the carrier will also mutate, which will cause the working state of the buck conversion circuit 2 to be uncertain, resulting in an increase in the output voltage ripple and may also cause the big and small waves phenomenon, thereby affecting the stability and performance of the buck conversion circuit.

[0034] In the present invention, due to the existence of the branch of diode D1 and resistor R3, the inductor current I LThe above formula shows that the voltage V X The amplitude of the change is greatly reduced, thus making the signal V ERR Continuous changes avoid sudden changes in the driving signal after comparison with the carrier, thereby allowing the buck conversion circuit to smoothly switch to the continuous state of the inductor current, avoiding problems such as excessive output voltage ripple and large and small waves.

[0035] The buck conversion circuit is simulated and verified without and with the mode switching circuit for buck conversion circuit of the present invention, and the waveforms are as follows: Figure 2 and Figure 3 As shown, it can be seen from the figure that after using a mode switching circuit applied to a buck conversion circuit of the present invention, the ripple and large and small waves of the output voltage of the buck conversion circuit are significantly improved, and the problem of the inductor current being less than zero is avoided.

[0036] Although the present invention has been disclosed as above by way of embodiments, it is not intended to limit the present invention. Any person having ordinary knowledge in the technical field may make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be determined by the scope of the attached patent application.

Claims

1. A mode switching circuit applied to a step-down conversion circuit, characterized in that: The invention comprises 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, wherein 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 via the first resistor, the first end of the second switch is connected to the first end of the second current source via the second resistor, the first input end of the first amplifier is connected to the first end of the second current source, the second input end 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.

2. A mode switching circuit for a step-down conversion circuit as claimed in claim 1, characterized in that: The third terminals of the first switch and the second switch are connected to the inductor current zero-crossing signal.

3. A mode switching circuit for a step-down conversion circuit as claimed in claim 2, characterized in that: It also includes a first NOT gate and a second NOT gate, the inductor current zero-crossing signal passes through the first NOT gate to connect to the third end of the second switch, and the inductor current zero-crossing signal passes through the first NOT gate and the second NOT gate to connect to the third end of the first switch.

4. A mode switching circuit for a step-down conversion circuit as claimed in claim 3, characterized in that: It also includes a second amplifier, a first input end of the second amplifier is connected to a zero value, a second input end of the second amplifier is connected to the inductor current in the buck conversion circuit, and an output end of the second amplifier outputs an inductor current zero-crossing signal.

5. A mode switching circuit for a step-down conversion circuit as claimed in claim 1, characterized in that: The second end of the first current source and the second end of the second current source are connected to a first voltage.

6. A mode switching circuit for a step-down conversion circuit as claimed in claim 4, characterized in that: When the step-down conversion circuit changes from the discontinuous state of the inductor current to the critical state of the inductor current, the first switch is closed, the second switch is opened, and the voltage expression between the first input terminal and the second input terminal of the first amplifier is 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 tube of the buck conversion circuit, and R3 is the third resistor.

7. A mode switching circuit for a step-down conversion circuit as claimed in claim 6, characterized in that: When the buck converter circuit enters the inductor current continuous state, the first switch is opened, the second switch is closed, and the voltage expression between the first input terminal and the second input terminal of the first amplifier is as follows: ， Among them, R S2 is the on-resistance of the second switch.

8. A mode switching circuit applied to a step-down conversion circuit according to any one of claims 1 to 7, characterized in that: The first amplifier compares the voltages of the first input terminal and the second input terminal, and outputs a first signal. The first signal is compared with a carrier and then outputs a driving signal to a switch of the buck conversion circuit.

9. A mode switching circuit for a step-down conversion circuit as claimed in claim 1, characterized in that: The step-down conversion circuit includes a third switch, a fourth switch, a first inductor and a first capacitor, the positive electrode 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 electrode 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.

10. A mode switching circuit for a step-down conversion circuit as claimed in claim 9, characterized in that: The step-down conversion circuit also includes a second capacitor, which is connected in parallel across the input voltage.

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