Current detection circuit of switching device and switching power supply using the same

Abstract

The present application discloses a current detection circuit of a switching device and a switching power supply using the same. Through the control of a first sampling tube connected to a power switch tube, a voltage conversion circuit and a first current generating circuit, the current at the node where the first power end of the first sampling tube is located is in direct proportion to the current information of the power switch tube, so that the current information of the power switch tube can be obtained through the current information at the node where the first power end of the first sampling tube is located. The current detection circuit of the present invention does not require a sampling resistor, but only requires a sampling tube to obtain circuit information characterizing the power switch tube, and the circuit is simple and efficient.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and more specifically, to a current detection circuit of a switching device and a switching power supply using the same. Background Art

[0002] In conventional switching power supply circuits, switching devices are an indispensable component. Transistors, field effect transistors, insulated gate bipolar transistors, etc. can all be used as switching devices in switching power supplies.

[0003] As a semiconductor device, the switching device needs to monitor the current flowing through it to ensure more accurate and safe operation. The existing technology usually samples the current information flowing through the switching device through a resistor connected in series with the switching device, but the resistor itself brings large losses, affecting the efficiency of the overall switching power supply. Summary of the invention

[0004] In view of this, an object of the present invention is to provide a current detection circuit of a switching device and a switching power supply using the same, so as to solve the technical problem of affecting efficiency caused by current detection of switching devices existing in the prior art.

[0005] The technical solution of the present invention is to provide a current detection circuit of a switching device, which is used to detect the current of a power switch tube, including a first sampling tube, a voltage conversion circuit, a first current generating circuit and a mirror circuit. The first sampling tube has a first power end coupled to the mirror circuit, and a second power end connected to the first power end of the power switch tube. The common connection point of the first sampling tube and the power switch tube is recorded as a first node; the input end of the voltage conversion circuit is coupled to the first node and receives a first power supply voltage to obtain a second voltage associated with the voltage of the first node; the first input end of the first current generating circuit receives the second voltage, and the second input end is coupled to the first power end of the first sampling tube to obtain a first current signal according to the second voltage and the node voltage of the first power end of the first sampling tube; the mirror circuit receives the first current signal and the current of the node where the first power end of the first sampling tube is located, so that the two are in a mirror proportional relationship; the current of the node where the first power end of the first sampling tube is located represents the current information of the power switch tube.

[0006] Preferably, the ratio of the current value of the node where the first power terminal of the first sampling tube is located to the current value of the power switch tube is proportional to the ratio of the on-resistance of the power switch tube to the on-resistance of the first sampling tube.

[0007] Preferably, the switching state of the first sampling tube is the same as that of the power switching tube.

[0008] Preferably, the second power terminal of the power switch tube is connected to the reference ground terminal. When the voltage of the first node is greater than the voltage of the reference ground terminal, the second voltage is K times the voltage of the first node, K is a positive number greater than 1, and when the voltage of the first node is less than the voltage of the reference ground terminal, the second voltage is zero.

[0009] Preferably, the voltage conversion circuit includes a first operational amplifier circuit and a voltage divider circuit, the first input terminal of the first operational amplifier circuit is coupled to the first node, and the second input terminal is coupled to the first connection point in the voltage divider circuit; the voltage divider circuit receives the first power supply voltage through a follower, the input terminal of the follower is coupled to the output terminal of the first operational amplifier circuit, the voltage of the second connection point in the voltage divider circuit is used as the second voltage, and the voltage of the second connection point is K times the voltage of the first connection point.

[0010] Preferably, the first current generating circuit includes a second operational amplifier circuit and a first voltage-controlled current source, the first input terminal of the second operational amplifier circuit receives the second voltage, the second input terminal is coupled to the first power terminal of the first sampling tube, and the first voltage-controlled current source receives the output signal of the output terminal of the second operational amplifier circuit to obtain the first current signal.

[0011] Preferably, the mirror circuit includes two symmetrically mirrored switch tubes, the first ends of the two switch tubes both receive a second power supply voltage, the second end of one of the two switch tubes is coupled to the output end of the first current generating circuit, and the second end of the other switch tube is coupled to the first power end of the first sampling tube.

[0012] In a second aspect, a switching power supply is provided, comprising a power switch tube, wherein the switching power supply comprises a control circuit, the control circuit comprises the above-mentioned current detection circuit, and the current detection circuit is used to detect the operating current of the power switch tube.

[0013] Preferably, the first sampling tube and the power switch tube are integrated into one chip.

[0014] Preferably, the control circuit further comprises a current direction determination circuit, wherein the current direction determination circuit determines the direction of the current flowing through the power switch tube according to the voltage of the first node and the voltage of the second power terminal of the power switch tube.

[0015] When the voltage of the first node is greater than the voltage of the second power terminal of the power switch tube, the current direction of the power switch tube is from the first power terminal to the second power terminal.

[0016] When the voltage of the first node is less than the voltage of the second power terminal of the power switch tube, the current direction of the power switch tube is from the second power terminal to the first power terminal.

[0017] By adopting the circuit structure of the present invention, the first sampling tube connected to the power switch tube, the voltage conversion circuit and the first current generating circuit are controlled so that the current at the node where the first power end of the first sampling tube is located is associated with the current information of the power switch tube, so that the current information of the power switch tube can be obtained through the current information of the node where the first power end of the first sampling tube is located. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a circuit block diagram of a current detection circuit of a switching device according to the present invention;

[0019] Figure 2 A circuit implementation diagram of a current detection circuit of a switching device according to the present invention;

[0020] Figure 3 A circuit block diagram of a switching power supply according to the present invention; DETAILED DESCRIPTION

[0021] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, but the present invention is not limited to these embodiments. The present invention covers any substitution, modification, equivalent method and scheme made within the spirit and scope of the present invention.

[0022] In order to make the public have a thorough understanding of the present invention, specific details are described in detail in the following preferred embodiments of the present invention, but those skilled in the art can fully understand the present invention without these detailed descriptions.

[0023] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. It should be noted that the accompanying drawings are all simplified and not in exact proportion, and are only used for the purpose of conveniently and clearly assisting in explaining the embodiments of the present invention.

[0024] refer to Figure 1 A circuit block diagram of a current detection circuit of a switching device according to the present invention and Figure 2 The circuit implementation diagram of the current detection circuit of the switch device according to the present invention is shown in FIG. The switch device may be a power switch tube M0. The current detection circuit of this embodiment includes a first sampling tube M1, a voltage conversion circuit, a first current generating circuit and a mirror circuit. Figure 1As shown, the first power end (such as the source) of the first sampling tube M1 is coupled to the mirror circuit, and the second power end (such as the drain) is connected to the first power end (such as the drain) of the power switch tube. The common connection point of the first sampling tube and the power switch tube is recorded as the first node, recorded as SW. In this embodiment, the current I1 at the node where the first power end of the first sampling tube is located represents the current information I0 of the power switch tube. In this implementation, the switching state of the first sampling tube is the same as that of the power switch tube, that is, when the power switch tube is turned on, the first sampling tube is also turned on to obtain information representing the current of the power switch tube. The switching action of the first sampling tube and the power switch tube can be controlled by the control circuit of the switching power supply where the current detection circuit is located.

[0025] In one example, the input terminal of the voltage conversion circuit is coupled to the first node SW, and receives a first power supply voltage such as Vcc to obtain a second voltage associated with the voltage of the first node. Specifically, the voltage conversion circuit includes a first operational amplifier circuit and a voltage divider circuit. The voltage divider circuit receives the first power supply voltage Vcc through a follower. Here, the follower can be implemented by a MOS switch tube M2. The source voltage following function can be achieved by controlling the control terminal of the MOS switch tube M2 to make it work in the saturation region. The voltage divider circuit includes resistors R3 and R4 connected in series between the switch tube M2 and the reference ground terminal. The resistance values ​​of the resistors R3 and R4 are set to be equal, or they can be set to a certain multiple relationship. The first input terminal of the first operational amplifier circuit is coupled to the first node SW, and the second input terminal is coupled to a first connection point in the voltage divider circuit, such as the middle connection point of the resistors R3 and R4; the control terminal of the first switch is coupled to the output terminal of the first operational amplifier circuit, and the voltage of the second connection point in the voltage divider circuit is used as the second voltage, such as VA. Here, the second connection point is a node different from the first connection point, and the voltage of the second connection point is K times the voltage of the first connection point, such as Figure 1 The node of the switch tube M2 and the resistor R3 is used as the second connection point. In this embodiment, the second power terminal of the power switch tube is connected to the reference ground terminal. When the voltage of the first node is greater than the voltage of the reference ground terminal, the second voltage VA is K times the voltage of the first node, K is a positive number greater than 1, and K depends on the size ratio of the resistors R3 and R4. When the voltage of the first node is less than the voltage of the reference ground terminal, the second voltage is zero. According to the principle of the first operational amplifier circuit, its output is at least the zero voltage of the reference ground terminal.

[0026] In this embodiment, the first current generating circuit includes a second operational amplifier circuit and a first voltage-controlled current source. The first voltage-controlled current source can be implemented by a MOS switch tube M3. For example, the MOS switch tube M3 is controlled to operate in a saturation region to obtain a corresponding current according to the output of the second operational amplifier circuit. The first input terminal of the second operational amplifier circuit receives the second voltage VA, and the second input terminal is coupled to the first power terminal of the first sampling tube to obtain a voltage VB. The first voltage-controlled current source receives an output signal at the output terminal of the second operational amplifier circuit to obtain the first current signal I2.

[0027] In this embodiment, the mirror circuit includes two symmetrical mirrored switch tubes, such as switch tube M4 and switch tube M5, the first ends of the two switch tubes both receive a second power supply voltage, such as Vcc, the first power supply voltage and the second power supply voltage may be equal or unequal, the second end of one of the two switch tubes is coupled to the output end of the first current generating circuit to obtain a first current signal I2, and the second end of the other switch tube is coupled to the first power end of the first sampling tube to obtain the current of the first power end of the first sampling tube, the current of the first power end of the first sampling tube is recorded as I1. According to the working principle of the current mirror, the mirror circuit receives the first current signal and the current of the node where the first power end of the first sampling tube is located, and the two are in a mirror proportional relationship, which may be an equal-proportional mirror relationship or a certain-proportional mirror relationship.

[0028] in accordance with Figure 3 In the circuit diagram shown, when the power switch tube M0 is turned on, the direction of the current flowing through it can be from the first power end to the second power end, such as the drain to the source, which is recorded as direction ①, or from the second power end to the first power end, such as the source to the drain, which is recorded as direction ②. When the current direction is direction ①, the voltage of the first power end is greater than the voltage of the second power end, that is, the voltage of the first node is greater than the voltage of the reference ground terminal. According to the operational amplifier principle, the voltage of the first connection point is the voltage of SW, recorded as V SW , assuming that the resistors R3 and R4 are equal, the voltage at the second connection point is 2 VSW For the second op amp circuit, according to the op amp principle, the voltage at the first power end of the first sampling tube is 2V. SW , then the current I1 passing through the first sampling tube is:

[0029] I1=(2V SW -V SW ) / R M1 =V SW / R M1 (1)

[0030] Among them, R M1 is the conduction internal resistance of the first sampling tube.

[0031] The current I0 of the power switch tube is:

[0032] I0=V SW / R M0 (2)

[0033] Among them, R M0 It is the on-state internal resistance of the power switch tube.

[0034] According to formula (1) and formula (2), we can get:

[0035] I0=I1*R M1 / R M0 (3)

[0036] According to formula (3), the current of the power switch tube is directly proportional to the current of the first sampling tube, and the proportionality coefficient is related to the on-resistance of the two.

[0037] When the current direction is direction ②, the voltage at the first power terminal is less than the voltage at the second power terminal, that is, when the voltage at the first node is less than the voltage at the reference ground terminal, according to the operational amplifier principle, the voltage at the first connection point is zero, and the voltage at the second connection point is also zero. For the second operational amplifier circuit, according to the operational amplifier principle, the voltage at the first power terminal of the first sampling tube is also zero, and the current I1 passing through the first sampling tube is:

[0038] I1=(0-V SW ) / R M1 =-V SW / R M1 (4)

[0039] The current I0 of the power switch tube is:

[0040] I0=V SW / R M0 (5)

[0041] According to formula (4) and formula (5), we can get:

[0042] I0=|I1|*R M1 / R M0 (6)

[0043] According to formula (6), the current of the power switch tube is directly proportional to the absolute value of the current of the first sampling tube, and the proportionality coefficient is related to the on-resistance of the two.

[0044] According to the above formula (3) and formula (6), the ratio of the current value of the node where the first power terminal of the first sampling tube is located to the current value of the power switch tube is proportional to the ratio of the on-resistance of the power switch tube to the on-resistance of the first sampling tube.

[0045] In this embodiment, through the above-mentioned current detection circuit, only the first sampling tube and the operational amplifier circuit are needed to realize the current detection of the power switch tube. The current information characterizing the power switch tube can be obtained by detecting the current of the first power end of the first sampling tube or sampling the current that is in a mirror relationship with the current of the first power tube of the first sampling tube. The sampling is convenient and the circuit is simple to implement. The obtained current information can be used as the information for subsequent control, such as current limiting, overcurrent protection, etc., and the direction of the current can be further detected as the information for switch control.

[0046] refer to Figure 3 The circuit block diagram of the switching power supply according to the present invention is shown. The switching power supply takes a Buck step-down circuit as an example. The power switch tube is the switch tube M0. The switching power supply includes a control circuit. The control circuit includes the above-mentioned current detection circuit. The current detection circuit is used to detect the operating current of the power switch tube.

[0047] In one embodiment, the first sampling tube and the power switch tube are integrated into one chip. Moreover, the first sampling tube and the power switch tube are switch tubes with the same parameters, so that the first sampling tube and the power switch tube have the same degradation characteristics, and the current detection is more accurate.

[0048] In one embodiment, the control circuit further includes a current direction judgment circuit, which judges the direction of the current flowing through the power switch tube according to the voltage of the first node and the voltage of the second power terminal of the power switch tube. When the voltage of the first node is greater than the voltage of the second power terminal of the power switch tube, the current direction of the power switch tube is from the first power terminal to the second power terminal. When the voltage of the first node is less than the voltage of the second power terminal of the power switch tube, the current direction of the power switch tube is from the second power terminal to the first power terminal. In this way, combined with the absolute value information of the current detected by the above-mentioned current detection circuit, comprehensive current information of the power switch tube can be obtained, which can be used by the subsequent switch control circuit.

[0049] The above-described implementation methods do not constitute a limitation on the protection scope of the technical solution. Any modification, equivalent replacement and improvement made within the spirit and principle of the above-described implementation methods shall be included in the protection scope of the technical solution.

Claims

1. A current detection circuit of a switching device, used to detect the current of a power switch tube, characterized in that: It includes a first sampling tube, a voltage conversion circuit, a first current generating circuit and a mirror circuit, A first sampling tube, a first power end of which is coupled to the mirror circuit, a second power end of which is connected to the first power end of the power switch tube, and a common connection point between the first sampling tube and the power switch tube is recorded as a first node; The input terminal of the voltage conversion circuit is coupled to the first node and receives a first power supply voltage to obtain a second voltage associated with the voltage of the first node; the second power terminal of the power switch tube is connected to a reference ground terminal, when the voltage of the first node is greater than the voltage of the reference ground terminal, the second voltage is K times the voltage of the first node, K is a positive number greater than 1, and when the voltage of the first node is less than the voltage of the reference ground terminal, the second voltage is zero; The first input terminal of the first current generating circuit receives the second voltage, and the second input terminal is coupled to the first power terminal of the first sampling tube to obtain a first current signal according to the second voltage and the node voltage of the first power terminal of the first sampling tube; The mirror circuit receives the first current signal and the current of the node where the first power end of the first sampling tube is located, so that the two are in a mirror proportional relationship; The current at the node where the first power terminal of the first sampling tube is located represents the current information of the power switch tube.

2. The current detection circuit according to claim 1, characterized in that: The ratio of the current value of the node where the first power terminal of the first sampling tube is located to the current value of the power switch tube is proportional to the ratio of the on-resistance of the power switch tube to the on-resistance of the first sampling tube.

3. The current detection circuit according to claim 1, characterized in that: The switching state of the first sampling tube is the same as that of the power switching tube.

4. The current detection circuit according to claim 1, characterized in that: The voltage conversion circuit includes a first operational amplifier circuit and a voltage divider circuit. The first input terminal of the first operational amplifier circuit is coupled to the first node, and the second input terminal is coupled to the first connection point in the voltage divider circuit; The voltage divider circuit receives a first power supply voltage through a follower, the input end of the follower is coupled to the output end of the first operational amplifier circuit, the voltage of a second connection point in the voltage divider circuit is used as a second voltage, and the voltage of the second connection point is K times the voltage of the first connection point.

5. The current detection circuit according to claim 1, characterized in that: The first current generating circuit includes a second operational amplifier circuit and a first voltage-controlled current source, The first input terminal of the second operational amplifier circuit receives the second voltage, and the second input terminal is coupled to the first power terminal of the first sampling tube. The first voltage-controlled current source receives an output signal at an output end of the second operational amplifier circuit to obtain the first current signal.

6. The current detection circuit according to claim 1, characterized in that: The mirror circuit includes two switch tubes with symmetrical mirror images. The first ends of the two switch tubes both receive the second power supply voltage, the second end of one of the two switch tubes is coupled to the output end of the first current generating circuit, and the second end of the other switch tube is coupled to the first power end of the first sampling tube.

7. A switching power supply, comprising a power switch tube, characterized in that: The switching power supply comprises a control circuit, wherein the control circuit comprises the current detection circuit according to any one of claims 1 to 6, The current detection circuit is used to detect the operating current of the power switch tube.

8. The switching power supply according to claim 7, characterized in that: The first sampling tube and the power switch tube are integrated into one chip.

9. The switching power supply according to claim 7, characterized in that: The control circuit also includes a current direction judgment circuit. The current direction determination circuit determines the direction of the current flowing through the power switch tube according to the voltage of the first node and the voltage of the second power terminal of the power switch tube. When the voltage of the first node is greater than the voltage of the second power terminal of the power switch tube, the current direction of the power switch tube is from the first power terminal to the second power terminal. When the voltage of the first node is less than the voltage of the second power terminal of the power switch tube, the current direction of the power switch tube is from the second power terminal to the first power terminal.

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