Detection circuit for switching power supply and switching power supply

Abstract

The utility model discloses a kind of detection circuit and switching power supply for switching power supply, circuit includes: first voltage division unit, capacitor, second voltage division unit and first comparator, first voltage division unit is used to when the voltage of switching node charges capacitor, the voltage difference between the first end of first voltage division unit and the second end of first voltage division unit is divided to generate first voltage, second voltage division unit is used to divide input voltage to generate second voltage, and first comparator is based on first voltage and second voltage output for indicating whether the power tube connected with switching node in switching power supply is turned off indicating signal. According to the utility model for switching power supply of detection circuit and switching power supply for switching power supply, the unstable influence of fixed delay caused by existing detection circuit to switching frequency under different input and output can be eliminated, the utility model can also have better frequency consistency under different input and different output, simple and reliable.

Description

Technical Field

[0001] This utility model belongs to the field of integrated circuit technology, specifically relating to a detection circuit for a switching power supply and a switching power supply. Background Technology

[0002] Constant Off-Time (CFT) control mode, compared to traditional peak current mode, eliminates the need for slope compensation circuitry and offers faster dynamic response, making it widely used in switching power supplies, especially boost circuits. However, because the off-time is fixed, the duty cycle of the boost circuit continuously changes with varying input voltages (VIN) and output voltages (VOUT), leading to variations in the switching frequency and making it unsuitable for fixed-frequency applications.

[0003] Figure 1 A detection circuit for a Boost circuit is shown. The switching node SW of the Boost circuit is connected to the capacitor C0 through resistor R0. The upper plate of capacitor C0 is connected to the positive input terminal of the comparator. The input voltage VIN is divided by resistors R1 and R2 and connected to the negative input terminal of the comparator.

[0004] Its working principle is as follows: When the power transistor MG is turned off (refer to...), Figure 2 The voltage at the switching node SW reflects the output voltage VOUT, i.e., capacitor C0 is charged through resistor R0. When the voltage VP on the upper plate of capacitor C0 exceeds the voltage VN of the input voltage VIN, the comparator output signal TOFF goes high, indicating that the power transistor MG's off-time ends and it begins to conduct. Therefore, the following expression can be obtained:

[0005]

[0006]

[0007] VD is the voltage drop across the diode. Combining this with the formula above, we can obtain that when... = hour,

[0008]

[0009] Switching frequency of power transistor MG for:

[0010]

[0011] If approximated And ignoring the voltage drop VD of the output diode, then

[0012]

[0013] By properly selecting the values ​​of resistor R0, capacitor C0, and K, the switching frequency Fsw becomes independent of the input and output voltages, thus enabling fixed-frequency control with different outputs for different inputs.

[0014] The above solutions do not take into account the fixed delays present in actual circuits, such as the comparator's comparison delay and the rise and fall times of the voltage at the switching node SW. To represent these fixed delays, we have the following expression, which is approximated:

[0015]

[0016]

[0017] Switching frequency by The impact of this on the frequency range is large for different inputs and outputs, resulting in obvious drawbacks.

[0018] The information disclosed in this background section is intended only to enhance the understanding of the overall background of this utility model and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Utility Model Content

[0019] The purpose of this invention is to provide a detection circuit and a switching power supply for a switching power supply, which can ensure that the switching frequency of the switching power supply is not affected by the fixed delay of the circuit under different input and output conditions.

[0020] To achieve the above objectives, a specific embodiment of this utility model provides the following technical solution: A detection circuit for a switching power supply includes a first voltage divider unit, a capacitor, a second voltage divider unit, and a first comparator. The first terminal of the first voltage divider unit is connected to the switching node of the switching power supply. The second terminal of the first voltage divider unit is connected to the first terminal of the capacitor. The first terminal of the second voltage divider unit receives an input voltage. The second terminal of the second voltage divider unit and the second terminal of the capacitor are connected to a reference voltage. The first voltage divider unit divides the voltage difference between its first and second terminals to generate a first voltage when the voltage at the switching node charges the capacitor. The second voltage divider unit divides the input voltage to generate a second voltage. The first input terminal of the first comparator receives the first voltage. The second input terminal of the first comparator receives the second voltage. The output terminal of the first comparator outputs a characterization signal based on the first and second voltages, indicating whether the power transistor connected to the switching node in the switching power supply is turned off.

[0021] In one or more embodiments of the present invention, the first voltage divider unit includes a first resistor unit and a second resistor unit. The first end of the first resistor unit is connected to a switching node. The first end of the second resistor unit is connected to the second end of the first resistor unit and the first input terminal of the first comparator. The second end of the second resistor unit is connected to the first end of a capacitor.

[0022] In one or more embodiments of the present invention, the second voltage divider unit includes a third resistor unit and a fourth resistor unit. The first end of the third resistor unit is connected to the input voltage, the first end of the fourth resistor unit is connected to the second end of the third resistor unit and the second input terminal of the first comparator, and the second end of the fourth resistor unit is connected to the reference voltage.

[0023] This utility model also discloses a switching power supply, including an inductor, a power transistor, a filter capacitor, a sampling and detection unit, a control unit, and the aforementioned detection circuit. The first end of the inductor is used to receive the input voltage, and the second end of the inductor is connected to the second end of the power transistor and the first end of the filter capacitor to form an output terminal and a switching node. The first end of the power transistor and the second end of the filter capacitor are connected to a reference voltage. The sampling and detection unit is used to detect the output voltage of the switching power supply and the current on the power transistor to generate a result signal. The control unit is connected to the detection circuit, the sampling and detection unit, and the control terminal of the power transistor to control the switching on and off of the power transistor based on the characterization signal and the result signal.

[0024] In one or more embodiments of this utility model, the sampling and detection unit includes a voltage detection unit, a current sampling unit, and a second comparator. The voltage detection unit is used to detect the output voltage of the switching power supply to generate a voltage detection signal. The current sampling unit is used to sample the current on the power transistor to generate a current sampling signal. The second comparator is used to compare the voltage detection signal and the current sampling signal to generate a result signal.

[0025] In one or more embodiments of this utility model, the voltage detection unit includes a voltage sampling unit and an error amplifier. The voltage sampling unit samples the output voltage of the switching power supply to generate a voltage sampling signal. The first input terminal of the error amplifier is used to receive a reference signal, and the second input terminal of the error amplifier is used to receive the voltage sampling signal. The error amplifier is used to amplify the reference signal and the voltage sampling signal to generate a voltage detection signal.

[0026] In one or more embodiments of the present invention, the sampling unit includes a first resistor and a second resistor. The first end of the first resistor is connected to the output terminal of the switching power supply, and the second end of the first resistor is connected to the first end of the second resistor to generate a voltage sampling signal. The second end of the second resistor is connected to a reference voltage.

[0027] In one or more embodiments of this utility model, the control unit includes an RS flip-flop, the S terminal of the RS flip-flop is used to receive a characterization signal, the R terminal of the RS flip-flop is used to receive a result signal, and the Q output terminal of the RS flip-flop is connected to the control terminal of the power transistor.

[0028] In one or more embodiments of the present invention, the control unit further includes a buffer, the input terminal of which is connected to the Q output terminal of the RS flip-flop, and the output terminal of which is connected to the control terminal of the power transistor.

[0029] In one or more embodiments of this utility model, the switching power supply further includes a diode, the anode of the diode is connected to the second terminal of the inductor and the second terminal of the power transistor to form a switching node, and the cathode of the diode is connected to the first terminal of the filter capacitor to form the output terminal of the switching power supply.

[0030] Compared with the prior art, the detection circuit and switching power supply of this invention provide an initial value when the voltage at the switching node charges the capacitor through the first voltage divider unit. This eliminates the unstable influence of the fixed delay caused by the existing detection circuit on the switching frequency under different input and output conditions. This invention can also achieve good frequency consistency under different input and output conditions, and is simple and reliable. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of this utility model or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a circuit diagram of a detection circuit for a switching power supply in the prior art.

[0033] Figure 2 This is a circuit diagram of a switching power supply according to one embodiment of the present invention.

[0034] Figure 3 This is a circuit diagram of a detection circuit for a switching power supply according to one embodiment of the present invention. Detailed Implementation

[0035] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0036] The terms "coupled," "connected," or "linked" in this specification include both direct and indirect connections. An indirect connection is a connection made through an intermediate medium, such as an electrical conduction medium, which may have parasitic inductance or capacitance. Indirect connections may also include connections made through other active or passive devices to achieve the same or similar functional purpose, such as connections through switches, follower circuits, or other circuits or components. Furthermore, in utility models, terms such as "first" and "second" are primarily used to distinguish one technical feature from another, and do not necessarily require or imply any actual relationship, quantity, or order between these technical features.

[0037] In the detailed description of this specification, reference is made to the accompanying drawings, which form a part thereof, wherein like reference numerals always denote like parts, and wherein exemplary embodiments are shown by way of example that may be implemented. It should be understood that other embodiments may be utilized, and structural or logical changes may be made, without departing from the scope of this disclosure. Therefore, the following detailed description should not be considered limiting.

[0038] The various operations in the specification may be described sequentially as multiple discrete actions or operations in a manner most conducive to understanding the claimed subject matter. However, the order of description should not be construed as implying that these operations must be sequentially related. Specifically, these operations may not be performed in the order presented. The described operations may be performed in a different order than in the described embodiments. Various additional operations may be performed in additional embodiments and / or the described operations may be omitted.

[0039] For the purposes of this disclosure, the phrase “A and / or B” means (A), (B), or (A and B). For the purposes of this disclosure, the phrase “A, B and / or C” means (A), (B), (C), (A and B), (A and C), (B and C), or (A, B and C).

[0040] Various components and devices may be referred to or shown in the singular (e.g., “transistor”, “transistor”, “switch”, etc.) in this document, but only for the convenience of discussion, and any element referred to in the singular may include multiple such elements as taught herein.

[0041] The description uses the phrases "in one embodiment," "in other embodiments," or "in some embodiments," each of which may refer to one or more of the same or different embodiments. Furthermore, the terms "comprising," "including," "having," etc., used with respect to embodiments of this disclosure are synonymous.

[0042] like Figure 2 As shown, a switching power supply in one embodiment of the present invention includes an inductor L, a power transistor MG, a diode D, a filter capacitor Cp, a sampling and detection unit, a control unit, and a detection circuit.

[0043] The first terminal of inductor L receives the input voltage VIN. The second terminal of inductor L is connected to the second terminal of power transistor MG and the anode of diode D to form a switching node SW. The cathode of diode D is connected to the first terminal of filter capacitor Cp to form the output terminal of the switching power supply. The first terminal of power transistor MG and the second terminal of filter capacitor Cp are connected to a reference voltage. In one embodiment, the reference voltage is ground voltage.

[0044] The detection circuit is connected to the switching node SW. The detection circuit is used to detect the voltage on the switching node SW to generate a characterization signal TOFF that characterizes whether the power transistor MG connected to the switching node SW in the switching power supply is turned off. The sampling detection unit is used to detect the output voltage VOUT of the switching power supply and the current on the power transistor MG to generate a result signal CO. The control unit is connected to the detection circuit, the sampling detection unit, and the control terminal of the power transistor MG to control the on / off of the power transistor MG based on the characterization signal TOFF and the result signal CO.

[0045] like Figure 2 As shown, the sampling and detection unit includes a voltage detection unit, a current sampling unit, and a second comparator T2. The voltage detection unit is used to detect the output voltage VOUT of the switching power supply and generate a voltage detection signal G1. The current sampling unit is connected to the first terminal of the power transistor MG to sample the current on the power transistor MG and generate a current sampling signal G2. The second comparator T2 is used to compare the voltage detection signal G1 and the current sampling signal G2 to generate a result signal CO.

[0046] In one embodiment, the voltage detection unit includes a voltage sampling unit and an error amplifier EA. The voltage sampling unit samples the output voltage VOUT of the switching power supply to generate a voltage sampling signal RB. The first input terminal of the error amplifier EA is used to receive a reference signal VREF, and the second input terminal of the error amplifier EA is used to receive the voltage sampling signal. The error amplifier EA is used to amplify the reference signal VREF and the voltage sampling signal to generate a voltage detection signal G1.

[0047] like Figure 2As shown, the sampling unit includes a first resistor R1 and a second resistor R2. The first end of the first resistor R1 is connected to the output terminal of the switching power supply, and the second end of the first resistor R1 is connected to the first end of the second resistor R2 to generate a voltage sampling signal RB. The second end of the second resistor R2 is connected to a reference voltage.

[0048] In one embodiment, the control unit includes an RS flip-flop and a buffer BUF. The S terminal of the RS flip-flop is used to receive the characterization signal TOFF, and the R terminal is used to receive the result signal CO. The input terminal of the buffer BUF is connected to the Q output terminal of the RS flip-flop, and the output terminal of the buffer BUF is connected to the control terminal of the power transistor MG. The buffer BUF is used to improve the driving capability of the signal on the power transistor MG and generate different switching frequencies through the RS flip-flop. The control signal is used to control the on / off state of the power transistor MG.

[0049] like Figure 3 As shown, the detection circuit for the switching power supply includes a first voltage divider unit, a capacitor C, a second voltage divider unit, and a first comparator T1. The first terminal of the first voltage divider unit is connected to the switching node SW of the switching power supply, and the second terminal of the first voltage divider unit is connected to the first terminal of the capacitor C. The first terminal of the second voltage divider unit receives the input voltage VIN, and the second terminal of the second voltage divider unit and the second terminal of the capacitor C are connected to a reference voltage. The first voltage divider unit divides the voltage difference between its first and second terminals to generate a first voltage Vp when the voltage at the switching node SW charges the capacitor C. The second voltage divider unit divides the input voltage VIN to generate a second voltage Vn. The first input terminal of the first comparator T1 receives the first voltage Vp, and the second input terminal of the first comparator T1 receives the second voltage Vn. The output terminal of the first comparator T1 outputs a characterization signal TOFF based on the first voltage Vp and the second voltage Vn, indicating whether the power transistor MG connected to the switching node SW in the switching power supply is turned off.

[0050] The first voltage divider unit includes a first resistor unit Rp1 and a second resistor unit Rp2. The first end of the first resistor unit Rp1 is connected to the switch node SW. The first end of the second resistor unit Rp2 is connected to the second end of the first resistor unit Rp1 and the first input terminal of the first comparator T1 to generate a first voltage Vp. The second end of the second resistor unit Rp2 is connected to the first end of the capacitor C.

[0051] The second voltage divider unit includes a third resistor unit Rp3 and a fourth resistor unit Rp4. The first terminal of the third resistor unit Rp3 is connected to the input voltage VIN. The first terminal of the fourth resistor unit Rp4 is connected to the second terminal of the third resistor unit Rp3 and the second input terminal of the first comparator T1 to generate a second voltage Vn. The second terminal of the fourth resistor unit Rp4 is connected to the reference voltage.

[0052] When the power transistor MG is turned off, the voltage at the switching node SW reflects the output voltage VOUT (the voltage at the switching node SW equals VOUT + VD, where VD is the forward conduction voltage of diode D). The voltage at the switching node SW charges capacitor C through the first resistor unit Rp1 and the second resistor unit Rp2. Unlike the traditional scheme, due to the presence of the second resistor unit Rp2, the first voltage Vp initially has an initial value, which is determined by the voltage at the switching node SW divided by the first resistor unit Rp1 and the second resistor unit Rp2. When the first voltage Vp exceeds the second voltage Vn, the characteristic signal TOFF output by the first comparator T1 goes high, meaning that the power transistor MG's off-time has ended and it has started to conduct. Therefore:

[0053]

[0054]

[0055] Combining the above formulas, we can obtain that when = hour,

[0056]

[0057] Switching frequency of power transistor MG for:

[0058]

[0059] This represents the signal delay time from the rise and fall time of the voltage at the switching node SW to the comparison delay of the first comparator T1. Simplifying the formula, we ignore the diode voltage drop. ,and Switching frequency Then there is

[0060]

[0061] If through design Then there is the switching frequency. expression:

[0062]

[0063] At this time, the switching frequency Only with , Since C and K are related but independent of input and output, a stable frequency can be achieved.

[0064] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this disclosure. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0065] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A detection circuit for a switching power supply, characterized in that, The system includes a first voltage divider unit, a capacitor, a second voltage divider unit, and a first comparator. The first terminal of the first voltage divider unit is connected to the switching node of the switching power supply. The second terminal of the first voltage divider unit is connected to the first terminal of the capacitor. The first terminal of the second voltage divider unit receives the input voltage, and the second terminal of the second voltage divider unit and the second terminal of the capacitor are connected to a reference voltage. The first voltage divider unit divides the voltage difference between its first and second terminals to generate a first voltage when the voltage at the switching node charges the capacitor. The second voltage divider unit divides the input voltage to generate a second voltage. The first input terminal of the first comparator receives the first voltage, and the second input terminal of the first comparator receives the second voltage. The output terminal of the first comparator outputs a characteristic signal based on the first and second voltages, indicating whether the power transistor connected to the switching node in the switching power supply is turned off.

2. The detection circuit for a switching power supply according to claim 1, characterized in that, The first voltage divider unit includes a first resistor unit and a second resistor unit. The first end of the first resistor unit is connected to a switching node. The first end of the second resistor unit is connected to the second end of the first resistor unit and the first input terminal of the first comparator. The second end of the second resistor unit is connected to the first end of a capacitor.

3. The detection circuit for a switching power supply according to claim 1, characterized in that, The second voltage divider unit includes a third resistor unit and a fourth resistor unit. The first end of the third resistor unit is connected to the input voltage. The first end of the fourth resistor unit is connected to the second end of the third resistor unit and the second input end of the first comparator. The second end of the fourth resistor unit is connected to the reference voltage.

4. A switching power supply, characterized in that, The device includes an inductor, a power transistor, a filter capacitor, a sampling and detection unit, a control unit, and a detection circuit as described in any one of claims 1 to 3. The first end of the inductor is used to receive the input voltage. The second end of the inductor is connected to the second end of the power transistor and the first end of the filter capacitor to form an output terminal and a switching node. The first end of the power transistor and the second end of the filter capacitor are connected to a reference voltage. The sampling and detection unit is used to detect the output voltage of the switching power supply and the current on the power transistor to generate a result signal. The control unit is connected to the detection circuit, the sampling and detection unit, and the control terminal of the power transistor to control the switching on and off of the power transistor based on the characterization signal and the result signal.

5. The switching power supply according to claim 4, characterized in that, The sampling and detection unit includes a voltage detection unit, a current sampling unit, and a second comparator. The voltage detection unit is used to detect the output voltage of the switching power supply and generate a voltage detection signal. The current sampling unit is used to sample the current on the power transistor and generate a current sampling signal. The second comparator is used to compare the voltage detection signal and the current sampling signal to generate a result signal.

6. The switching power supply according to claim 5, characterized in that, The voltage detection unit includes a voltage sampling unit and an error amplifier. The voltage sampling unit samples the output voltage of the switching power supply to generate a voltage sampling signal. The first input terminal of the error amplifier is used to receive a reference signal, and the second input terminal of the error amplifier is used to receive the voltage sampling signal. The error amplifier is used to amplify the reference signal and the voltage sampling signal to generate a voltage detection signal.

7. The switching power supply according to claim 5, characterized in that, The sampling unit includes a first resistor and a second resistor. The first end of the first resistor is connected to the output terminal of the switching power supply, and the second end of the first resistor is connected to the first end of the second resistor to generate a voltage sampling signal. The second end of the second resistor is connected to a reference voltage.

8. The switching power supply according to claim 4, characterized in that, The control unit includes an RS flip-flop, the S terminal of which is used to receive a characterization signal, the R terminal of which is used to receive a result signal, and the Q output terminal of which is connected to the control terminal of the power transistor.

9. The switching power supply according to claim 8, characterized in that, The control unit further includes a buffer, the input of which is connected to the Q output of the RS flip-flop, and the output of which is connected to the control terminal of the power transistor.

10. The switching power supply according to claim 4, characterized in that, The switching power supply also includes a diode. The anode of the diode is connected to the second terminal of the inductor and the second terminal of the power transistor to form a switching node. The cathode of the diode is connected to the first terminal of the filter capacitor to form the output terminal of the switching power supply.

Images