A current monitoring circuit and monitoring method

Abstract

The application discloses a current monitoring circuit and a monitoring method. The current monitoring circuit comprises a Zener diode, an operational amplifier, a first MOSFET, a second MOSFET and a current mirror circuit. The current monitoring circuit and the monitoring method do not need to use a single-chip integrated or customized power tube, and accurately provide a current proportional to a current flowing through a required monitoring power switch for system monitoring.

Description

Technical Field

[0001] This invention relates to electronic circuits, and more specifically to a current monitoring circuit and monitoring method. Background Technology

[0002] A smart power switch is an integrated circuit that integrates power devices, internal drive and protection circuits, etc., onto a single chip. It has important applications in industrial control, automotive electronics, and avionics, and is significant for the miniaturization and intelligentization of related equipment. In some applications of smart power switches, there is a need to monitor the current flowing through the switch to understand the overall operating status of the device; therefore, current monitoring is an important function of smart power switches in certain applications.

[0003] Figure 1 This is a schematic diagram of the circuit structure of a common current monitoring circuit 50. Figure 1 As shown, the prior art uses a small portion of the cells 52 of the main power transistor 51 to be detected as a sampling transistor. A certain gate voltage is applied to the sampling transistor through the negative feedback clamping effect of the amplification unit (such as an operational amplifier) ​​53, so that its drain voltage is equal to the drain voltage of the main power transistor 51, thereby outputting a monitoring current Imon that is proportional to the main power transistor.

[0004] This current monitoring circuit boasts advantages such as high output accuracy, good linearity, and simple circuit structure. However, it is only suitable for applications requiring monolithic integration or custom power transistors. Monolithic integration refers to integrating the main power transistor, sampling transistor, and operational amplifier control circuitry onto a single chip, where current monitoring functionality is implemented from the chip design stage. This current monitoring method requires stringent conditions to achieve its function and has limitations for high-side power switches that lack monolithic integration or custom power transistors. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes an improved current monitoring circuit and monitoring method.

[0006] A current monitoring circuit for monitoring current flowing through a power switch, the power switch having a first terminal coupled to a power rail and a second terminal coupled to a load, the current monitoring circuit comprising: a Zener diode having an anode terminal and a cathode terminal, the cathode terminal coupled to the power rail, the anode terminal coupled to a reference ground through a first resistor; an operational amplifier having a non-inverting input terminal, an inverting input terminal and an output terminal, the non-inverting input terminal coupled to the second terminal of the power switch, the inverting input terminal coupled to the power rail through a second resistor; a first MOSFET having a gate terminal, a source terminal and a drain terminal, the gate terminal coupled to the anode terminal of the Zener diode, the drain terminal coupled to the reference ground, the source terminal providing a bias voltage; a second MOSFET having a gate terminal, a source terminal and a drain terminal, the source terminal coupled to the inverting input terminal of the operational amplifier, the gate terminal coupled to the output terminal of the operational amplifier; a current mirror circuit having a current in portion and a current out portion, the current in portion coupled between the source terminal of the first MOSFET and the drain terminal of the second MOSFET to receive current flowing through the second MOSFET and the second resistor, the current out portion coupled between the power rail and an output terminal of the current monitoring circuit to provide a monitoring current.

[0007] A current monitoring method for monitoring current flowing through a power switch, the power switch coupled to a power rail; the method comprising: providing a bias voltage through a Zener diode, a first resistor and a first MOSFET, the cathode terminal of the Zener diode coupled to the power rail, the first MOSFET having a gate terminal, a source terminal and a drain terminal, the gate terminal coupled to the anode terminal of the Zener diode, the drain terminal coupled to a reference ground, the source terminal providing the bias voltage; applying a voltage across the second resistor through an operational amplifier to make the current flowing through the second resistor proportional to the current flowing through the power switch; coupling a second MOSFET and a current in portion of a current mirror circuit in series between the second resistor and the bias voltage to obtain a monitoring current at a current out portion of the current mirror circuit.

[0008] The current monitoring circuit and the monitoring method according to the aspects of the present application can accurately provide a current proportional to the current flowing through a power switch to be monitored for system monitoring without using a single-chip integrated or customized power tube; meanwhile, the current monitoring circuit and the monitoring method use a bias voltage generated based on the power rail as a direct current working point of the operational amplifier and the current mirror circuit, so that the current monitoring circuit has high independence and ensures that the current monitoring circuit and a control circuit of the power switch to be monitored do not affect each other. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 FIG. 1 is a circuit structure schematic diagram of an existing current monitoring circuit 50;

[0010] Figure 2A schematic diagram of the circuit structure of a first current monitoring circuit 200 according to an embodiment of the present invention is shown;

[0011] Figure 3 A schematic diagram of the circuit structure of the second current monitoring circuit 300 according to an embodiment of the present invention is shown;

[0012] Figure 4 A flowchart of a method 400 for monitoring the current flowing through a power switch according to an embodiment of the present invention is shown. Detailed Implementation

[0013] Specific embodiments of the present invention will now be described in detail. It should be noted that the embodiments described herein are for illustrative purposes only and are not intended to limit the invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that these specific details are not necessary to practice the invention. In other instances, well-known circuits, materials, or methods have not been specifically described to avoid obscuring the invention.

[0014] Throughout this specification, references to “an embodiment,” “an example,” or “an example” mean that a particular feature, structure, or characteristic described in connection with that embodiment or example is included in at least one embodiment of the invention. Therefore, the phrases “in an embodiment,” “in an embodiment,” “an example,” or “an example” appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. Moreover, those skilled in the art will understand that the accompanying drawings provided herein are for illustrative purposes and are not necessarily drawn to scale. It should be understood that when an element is referred to as “coupled to” or “connected to” another element, it can be directly coupled to or coupled to the other element, or there may be intermediate elements. Conversely, when an element is referred to as “directly coupled to” or “directly connected to” another element, there are no intermediate elements. The same reference numerals indicate the same elements. The term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0015] like Figure 2 The diagram shown is a schematic representation of the circuit structure of a first current monitoring circuit 200 according to an embodiment of the present invention. Figure 2 As shown, the first current monitoring circuit 200 is used to monitor the current I flowing through the power switch 110. 110The first terminal of the power switch 110 is coupled to the power rail VDD, and the second terminal is coupled to the load 120. The first current monitoring circuit 200 includes: a Zener diode 101 having an anode and a cathode, the cathode of which is coupled to the power rail VDD, and the anode of which is coupled to a reference ground through a first resistor 102; and an operational amplifier 103 having a non-inverting input, an inverting input, and an output, the non-inverting input of which is coupled to the second terminal of the power switch 110 to receive the voltage V at the second terminal of the power switch. S Its inverting input is coupled to the power rail VDD via a second resistor 104; the first MOSFET (metal-oxide-semiconductor field-effect transistor) 105 has a gate, a source, and a drain, its gate is coupled to the anode of the Zener diode 101, its drain is coupled to a reference ground, and its source provides a bias voltage V. F The second MOSFET 106 has a gate, a source, and a drain. Its source is coupled to the inverting input of the operational amplifier 103, and its gate is coupled to the output of the operational amplifier 103. The current mirror circuit 107 has a current inflow portion 71 and a current outflow portion 72. The current inflow portion 71 is coupled between the source of the first MOSFET 105 and the drain of the second MOSFET 106 to receive the current flowing through the second MOSFET 106 and the second resistor 104. The current outflow portion 72 is coupled between the power rail VDD and the output 130 of the first current monitoring circuit 200 to provide a monitoring current Imon.

[0016] In one embodiment of the invention, the power rail VDD provides a positive reference voltage to the operational amplifier 103, and the bias voltage V F Provide a negative reference voltage to operational amplifier 103.

[0017] In one embodiment of the present invention, the first MOSFET 105 is P-type doped.

[0018] In one embodiment of the present invention, the second MOSFET 106 is a P-type laterally diffused metal-oxide semiconductor (LDMOS).

[0019] The working principle of this invention is as follows:

[0020] After the first current monitoring circuit 200 is powered on, a bias voltage V relative to the power rail VDD is provided through the Zener diode 101, the first resistor 102, and the first MOSFET 105. F The bias voltage V F The DC operating points of operational amplifier 103 and current mirror circuit 107 were determined. The non-inverting input of operational amplifier 103 receives the voltage V from the second terminal of power switch 110. SBased on the operating principle of virtual short and virtual open at the non-inverting and inverting input terminals of an operational amplifier, the voltage at the inverting input terminal of the operational amplifier 103 is also V. S That is, the voltage at one end of the second resistor 104 is V. S The voltage at the other end is the power rail VDD. Therefore, the voltage across the second resistor 104 is equal to the voltage across the power switch 110. The current I flowing through the second resistor 104 is... 104 for:

[0021] (1).

[0022] Where R104 is the resistance value of the second resistor, R dson is the on-resistance of power switch 110.

[0023] From the above expression (1), it can be seen that the current I flowing through the second resistor 104 is 104 With the current I flowing through power switch 110 110 Proportional.

[0024] Because the current I flowing through the second resistor 104 104 Simultaneously, the current flowing through the current inflow portion 71 of the current mirror circuit 107, and as can be seen from the working principle of the current mirror circuit, the current flowing out portion 72 of the current mirror circuit 107 (i.e., the monitoring current Imon) is related to I... 104 The current Imon is proportional to the current I flowing through the power switch 110. 110 It is also directly proportional. That is, the monitored current Imon reflects the current I flowing through the power switch 110. 110 The first current monitoring circuit 200 monitors the current of the power switch 110. This monitored current, Imon, can be output to an external resistor (not shown) to provide the system with a monitoring voltage characterizing the power switch current, thereby enabling the system to perform control and protection functions.

[0025] Figure 3 A schematic diagram of the circuit structure of a second current monitoring circuit 300 according to an embodiment of the present invention is shown. Figure 3 The second current monitoring circuit 300 shown is... Figure 2 The first current monitoring circuit 200 shown is similar to, and is... Figure 2 The difference is that, in Figure 3 In the illustrated embodiment, the second current monitoring circuit 300 further includes a high-voltage P-type MOSFET 108, having a gate, a drain, and a source, with its gate coupled to a bias voltage V. FThe source of the high-voltage P-type MOSFET 108 is coupled to the current outflow portion 72 of the current mirror circuit 107, and the drain of the high-voltage P-type MOSFET 108 is coupled to the output terminal 130 of the second current monitoring circuit 300 to provide the monitoring current Imon. The high-voltage P-type MOSFET 108 is a high-voltage resistant transistor, and the voltage resistance value can be tens of volts, hundreds of volts, or even thousands of volts. When the power supply rail VDD has a relatively high voltage value, the high-voltage P-type MOSFET 108 provides protection for the current outflow portion 72 of the current mirror circuit 107.

[0026] In an embodiment of the present application, the high-voltage P-type MOSFET 108 is a lateral diffusion metal oxide semiconductor (LDMOS).

[0027] Figure 4 A flow chart of a current monitoring method 400 according to an embodiment of the present application is shown. The method is used to monitor the current flowing through a power switch coupled to a power supply rail. The method comprises:

[0028] In step 401, a bias voltage is provided by a Zener diode, a first resistor, and a first MOSFET. The cathode of the Zener diode is coupled to the power supply rail, and the first MOSFET has a gate, a source, and a drain. The gate of the first MOSFET is coupled to the anode of the Zener diode, the drain of the first MOSFET is coupled to a reference ground, and the source of the first MOSFET provides the bias voltage.

[0029] In step 402, a voltage across a second resistor is applied by an operational amplifier to make the current flowing through the second resistor proportional to the current flowing through the power switch. The power supply rail provides a positive reference voltage to the operational amplifier, and the bias voltage provides a negative reference voltage to the operational amplifier.

[0030] In step 403, a second MOSFET and a current inflow portion of a current mirror circuit are coupled in series between the second resistor and the bias voltage to obtain a monitoring current at a current outflow portion of the current mirror circuit.

[0031] In an embodiment of the present application, the method further comprises: providing protection for the current outflow portion of the current mirror circuit by a high-voltage P-type MOSFET. The high-voltage P-type MOSFET has a gate, a drain, and a source. The gate of the high-voltage P-type MOSFET is coupled to the bias voltage, the source of the high-voltage P-type MOSFET is coupled to the current outflow portion of the current mirror circuit, and the drain of the high-voltage P-type MOSFET is coupled to the output terminal of the current monitoring circuit.

[0032] While the application has been described with reference to several exemplary embodiments, it is to be understood that the use of other words or terminologies used herein is intended to convey a practical, and conceptual meaning and not a limiting meaning as used in any particular exemplary embodiment. It is therefore submitted that the foregoing disclosure of exemplary embodiments of the application are intended for illustrative purposes only and not for limiting the scope of the application as contemplated by the appended claims and their equivalents.

Claims

1. A current monitoring circuit for monitoring the current flowing through a power switch, wherein a first terminal of the power switch is coupled to a power rail and a second terminal is coupled to a load, characterized in that, The current monitoring circuit includes: A Zener diode has an anode and a cathode, with the cathode coupled to the power rail and the anode coupled to ground via a first resistor. An operational amplifier has a non-inverting input terminal, an inverting input terminal, and an output terminal. Its non-inverting input terminal is coupled to the second terminal of a power switch, and its inverting input terminal is coupled to the power rail through a second resistor. The first MOSFET has a gate, a source, and a drain. Its gate is coupled to the anode of a Zener diode, its drain is coupled to a reference ground, and its source provides a bias voltage. The second MOSFET has a gate, a source, and a drain. Its source is coupled to the inverting input of the operational amplifier, and its gate is coupled to the output of the operational amplifier. The current mirror circuit has a current inflow section and a current outflow section. The current inflow section is coupled between the source of a first MOSFET and the drain of a second MOSFET to receive the current flowing through the second MOSFET and the second resistor. The current outflow section is coupled between the power rail and the output terminal of the current monitoring circuit to provide the monitoring current. The power rail provides a positive reference voltage to the operational amplifier, and the bias voltage provides a negative reference voltage to the operational amplifier.

2. The current monitoring circuit as described in claim 1, characterized in that, The first MOSFET is P-type doped.

3. The current monitoring circuit as described in claim 1, characterized in that, The second MOSFET is a P-type laterally diffused metal-oxide semiconductor.

4. The current monitoring circuit as described in claim 1, characterized in that, Further includes: A high-voltage P-type MOSFET has a gate, a drain, and a source. Its gate is coupled to a bias voltage, its source is coupled to the current outflow portion of a current mirror circuit, and its drain is coupled to the output of a current monitoring circuit to provide the monitoring current.

5. The current monitoring circuit as described in claim 4, characterized in that, The high-voltage P-type MOSFET mentioned above is a high-voltage resistant transistor.

6. The current monitoring circuit as described in claim 4, characterized in that, The high-voltage P-type MOSFET is a laterally diffused metal-oxide semiconductor.

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