A kind of active bidirectional current detection circuit and detection method based on magnetic isolation
By using an active bidirectional current detection circuit, which combines an active sampling switch with a current transformer, the problem of reliable operation of the current transformer in bidirectional current scenarios is solved. This enables accurate detection of bidirectional current in the power switch and is suitable for power electronic converters with synchronous rectification and bidirectional current flow.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- LUOYANG LONGSHENG SCI & TECH
- Filing Date
- 2026-03-30
- Publication Date
- 2026-06-23
AI Technical Summary
Existing current transformers cannot operate reliably in bidirectional current scenarios, resulting in distorted sampling waveforms and affecting the normal operation of power electronic converters.
An active bidirectional current detection circuit based on magnetic isolation is adopted. By cooperating with an active sampling switch and a current transformer, accurate sampling of the bidirectional current of the power switch is achieved, and a magnetic reset is performed when the power switch is turned off.
It achieves accurate detection of bidirectional current in power switching transistors, ensuring reliable operation of the current detection circuit, and is suitable for power electronic converters with synchronous rectification and bidirectional current flow.
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Figure CN122259935A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of current detection technology, specifically to an active bidirectional current detection circuit and detection method based on magnetic isolation. Background Technology
[0002] Current sensing is a key technology for realizing closed-loop current control and overcurrent protection in power electronic converters. Commonly used current sensing methods include shunt resistors, Hall effect sensors, and current transformers. Among these, current transformers are widely used in power electronic converters such as medium- and high-power switching power supplies due to their advantages of simple structure, low cost, and ability to provide electrical isolation.
[0003] Typical current transformer application circuits include Figure 1 As shown, the primary winding of current transformer T1 is connected in series in the power circuit to sample the current flowing through the drain-source of power MOSFET Q1. In this circuit, reset resistor R1 is connected in parallel with the secondary winding of transformer T1, and its resistance is much larger than that of sampling resistor R2 to ensure that the transformer can be quickly magnetically reset during the turn-off period of Q1. However, when the converter operates in synchronous rectification mode, the current may flow bidirectionally, that is, a negative current may flow through the drain-source of power switch Q1. At this time, due to the unidirectional conductivity of rectifier diode D1, the low-impedance path formed by D1 and sampling resistor R2 is blocked, causing the negative current to flow only through the larger-resistance reset resistor R1. This will generate a large negative induced voltage on R1, causing abnormal magnetic reset of the current transformer, which in turn leads to distorted sampling waveforms and seriously affects the normal operation of the converter. Summary of the Invention
[0004] In view of this, embodiments of this application provide an active bidirectional current detection circuit and detection method based on magnetic isolation to solve the problem that existing current transformer detection circuits cannot work reliably in bidirectional current scenarios, and to achieve effective and accurate sampling of the bidirectional current flowing through the power switch, thereby ensuring the reliable operation of the power electronic converter.
[0005] The embodiments of this application provide the following technical solution: an active bidirectional current detection circuit based on magnetic isolation, including: a power switch Q1, a current transformer T1, a reset resistor R1, an active sampling switch Q2, and a current sampling resistor R2;
[0006] The primary winding of the current transformer T1 is connected in series in the power circuit under test, and one end of the current transformer T1 is connected to the source of the power switch Q1; the reset resistor R1 is connected in parallel across the secondary winding of the current transformer T1; the active sampling switch Q2 is connected in series with the current sampling resistor R2 and then connected in parallel across the secondary winding of the current transformer T1 to form a low-impedance sampling branch on the secondary side. The gate of the active sampling switch Q2 receives a control signal synchronized with the switching timing of the power switch Q1, so that when the power switch Q1 is turned on, the active sampling switch Q2 is turned on synchronously, providing a low-impedance path for the secondary current of the current transformer T1 to flow through the current sampling resistor R2; when the power switch Q1 is turned off, the active sampling switch Q2 is turned off synchronously, so that the current transformer T1 is magnetically reset through the reset resistor R1.
[0007] According to one embodiment of this application, the drain of the active sampling switch Q2 is connected to the first end of the secondary winding of the current transformer T1 and the first end of the reset resistor R1; the first end of the current sampling resistor R2 is connected to the source of the active sampling switch Q2, and the second end of the current sampling resistor R2 is connected to the second end of the secondary winding of the current transformer T1 and the second end of the reset resistor R1.
[0008] According to one embodiment of this application, the switching timing of the active sampling switch Q2 is the same as that of the power switch Q1.
[0009] According to one embodiment of this application, the value of the reset resistor R1 is greater than the value of the current sampling resistor R2, so as to establish a high reset voltage on the secondary side of the current transformer T1 during the turn-off period of the power switch Q1.
[0010] According to one embodiment of this application, the sampling voltage U across the current sampling resistor R2 is... R The polarity of the sampling voltage U represents the direction of the drain-source current of the power switch Q1. R The amplitude represents the magnitude of the drain-source current of the power switch Q1.
[0011] According to one embodiment of this application, the sampling voltage U R After filtering, limiting, amplification and / or analog-to-digital conversion, the output is sent to the controller for current closed-loop control, overcurrent protection or status monitoring.
[0012] This application also provides an active bidirectional current detection method based on magnetic isolation, applied to the aforementioned active bidirectional current detection circuit, comprising: synchronously turning on the active sampling switch Q2 during the conduction of the power switch Q1, so that the secondary current of the current transformer T1 flows through the sampling branch formed by the active sampling switch Q2 and the current sampling resistor R2, thereby forming a sampling voltage U across the current sampling resistor R2. R During the turn-off period of power switch Q1, active sampling switch Q2 is synchronously turned off, so that current transformer T1 is magnetically reset via reset resistor R1; according to the sampling voltage U RThe polarity and amplitude determine the direction and magnitude of the drain-source current flowing through the power switch Q1.
[0013] According to one embodiment of this application, the method is applied to a buck converter or full-bridge converter employing synchronous rectification.
[0014] Compared with the prior art, the beneficial effects that can be achieved by at least one of the above-mentioned technical solutions adopted in the embodiments of this specification include at least the following: The active bidirectional current detection circuit based on magnetic isolation proposed in the embodiments of this invention can realize accurate detection of bidirectional current of power MOSFET through active switching of active sampling MOSFET, ensuring reliable operation of current detection circuit. Moreover, the circuit structure is simple and easy to implement, and it is particularly suitable for various power electronic converters that require synchronous rectification and bidirectional current flow. Attached Figure Description
[0015] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0016] Figure 1 This is a schematic diagram of a typical existing MOSFET current sampling circuit; Figure 2 This is a schematic diagram of an active bidirectional current detection circuit based on magnetic isolation provided by the present invention; Figure 3 This is a key waveform diagram of the detection circuit of this invention; Figure 4 This is a circuit diagram of the first embodiment of the detection circuit of the present invention in a synchronous rectifier buck converter; Figure 5 This is a key waveform diagram of the first embodiment of the present invention; Figure 6 This is a circuit diagram of the second embodiment of the detection circuit of the present invention in a full-bridge converter; Figure 7 This is a key waveform diagram of the second embodiment of the present invention. Detailed Implementation
[0017] The embodiments of this application will now be described in detail with reference to the accompanying drawings.
[0018] The following specific examples illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. This application can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this application. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0019] like Figure 2 As shown, this invention provides an active bidirectional current detection circuit based on magnetic isolation, including a power switch Q1, a current transformer T1, a reset resistor R1, an active sampling switch Q2, and a current sampling resistor R2; both the power switch Q1 and the active sampling switch Q2 are MOSFETs. Specific embodiments of this invention include: The circuit consists of a power MOSFET Q1, a current transformer T1, a reset resistor R1, an active sampling MOSFET Q2, and a sampling resistor R2. The primary winding of the current transformer T1 is connected in series in the power circuit to isolate and sample the current flowing through the drain-source of the power MOSFET Q1. The reset resistor R1 is connected in parallel across the secondary winding of the current transformer T1 to perform a magnetic reset of the current transformer during turn-off.
[0020] The active sampling MOSFET Q2 is connected in series with the sampling resistor R2 and then connected in parallel across the secondary winding of the current transformer T1. The drain of the active sampling MOSFET Q2 is connected to the lower end of the reset resistor R1, the source of the active sampling MOSFET Q2 is connected to the lower end of the sampling resistor R2, and the upper end of the sampling resistor R2 is connected to the upper end of the reset resistor R1, thus forming a low-impedance sampling branch on the secondary side.
[0021] like Figure 3 As shown in the figure, i p G1 is the bidirectional current flowing through the drain and source of the power MOSFET Q1, G2 is the gate drive signal of the power MOSFET Q1, and G2 is the gate drive signal of the active sampling MOSFET Q2. R This is the sampled voltage across the sampling resistor R2. G1 and G2 have the same switching timing.
[0022] When the power MOSFET Q1 is turned on, the active sampling MOSFET Q2 is turned on simultaneously. At this time, regardless of the measured current i... pWhether the current transformer T1 is in forward or reverse direction, its secondary side has a low-impedance path consisting of the active sampling MOSFET Q2 and the sampling resistor R2. Therefore, a corresponding bidirectional sampling voltage U can be generated across the sampling resistor R2. R According to U R The polarity of the current can be used to determine the direction of the measured current, based on U. R The amplitude can be used to determine the magnitude of the measured current.
[0023] When the power MOSFET Q1 is turned off, the active sampling MOSFET Q2 is simultaneously turned off. The secondary current of the current transformer T1 then flows through the reset resistor R1, thereby achieving magnetic reset. Since the resistance of the reset resistor R1 is much larger than that of the sampling resistor R2, a sufficiently high reset voltage can be established during the turn-off period, improving the reset speed, avoiding insufficient reset and sampling waveform distortion, and ensuring fast and reliable magnetic reset of the current transformer.
[0024] Example 1: As Figure 4 As shown, this embodiment applies the above-described active bidirectional current detection circuit to a synchronous rectified buck converter. This converter includes an input voltage source V. in The circuit consists of a power MOSFET Q1, a synchronous rectifier MOSFET Q2, a filter inductor L1, an output capacitor C1, a load resistor R3, and a bidirectional current detection circuit composed of a current transformer T1, a reset resistor R1, an active sampling MOSFET Q3, and a sampling resistor R2.
[0025] In this embodiment, the current transformer T1 samples the current flowing through the drain-source of the power MOSFET Q1. The active sampling MOSFET Q3 turns on and off synchronously with the power MOSFET Q1; the synchronous rectification MOSFET Q2 turns on complementaryly with the power MOSFET Q1. Therefore, even if the drain-source current of the power MOSFET Q1 exhibits a reverse component during the synchronous rectification phase, the secondary side of the current transformer T1 still has a low-impedance sampling path.
[0026] like Figure 5 As shown in the figure, i p G1 is the bidirectional current flowing through the drain and source of power MOSFET Q1, G2 is the gate drive signal for power MOSFET Q1, G3 is the gate drive signal for synchronous rectifier MOSFET Q2, and G3 is the gate drive signal for active sampling MOSFET Q3. U R This represents the sampling voltage across the sampling resistor R2. G1 and G2 are complementary conductions, while G1 and G3 are synchronous switches.
[0027] Example 2: Figure 6 As shown, this embodiment applies the above circuit to a full-bridge power electronic converter. It includes an input voltage source V. inPower MOSFETs Q1, Q2, Q3, and Q4; power transformer T1; current transformer T2 and T3; reset resistor R1 for current transformer T2; reset resistor R2 for current transformer T3; active sampling MOSFET Q5 for current transformer T2; active sampling MOSFET Q6 for current transformer T3; current sampling resistor R3; the gates of power MOSFET Q2 and Q5 are connected; and the gates of power MOSFET Q4 and Q6 are connected.
[0028] In this circuit, current transformer T2 samples the drain-source current flowing through power MOSFET Q2. Therefore, the switching timing of its active sampling MOSFET Q5 is synchronized with that of power MOSFET Q2. Since the voltage across the primary winding of current transformer T2 is low, active sampling MOSFET Q5 and power MOSFET Q2 can share the same gate drive signal. Similarly, current transformer T3 samples the drain-source current flowing through power MOSFET Q4. Therefore, the switching timing of its active sampling MOSFET Q6 is synchronized with that of power MOSFET Q4. Again, since the voltage across the primary winding of current transformer T3 is low, active sampling MOSFET Q6 and power MOSFET Q4 can share the same gate drive signal.
[0029] like Figure 7 As shown in the figure, i a and i b These are the bidirectional currents flowing through the drain and source of power MOSFETs Q2 and Q4, respectively. G1 is the gate drive for power MOSFET Q1, G2 is the gate drive for power MOSFET Q2 and active sampling MOSFET Q5, G3 is the gate drive for power MOSFET Q3, and G4 is the common gate drive signal for power MOSFET Q4 and active sampling MOSFET Q6. G1 and G4 switch synchronously, as do G2 and G3. G1 and G4 are interleaved with G2 and G3 by 180°. R This is the sampling voltage across the sampling resistor R3.
[0030] As can be seen from the above embodiments, the active bidirectional current detection circuit based on magnetic isolation proposed in this invention can reliably detect the bidirectional current of the drain and source of the power MOSFET. It retains the advantages of isolation sampling of the current transformer and solves the problem of the secondary sampling branch being blocked by unidirectional devices in the synchronous rectification scenario. Moreover, the circuit is simple, easy to implement, and has good engineering application value.
[0031] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.
Claims
1. An active bidirectional current detection circuit based on magnetic isolation, characterized in that, include: Power switch Q1, current transformer T1, reset resistor R1, active sampling switch Q2 and current sampling resistor R2; The primary winding of the current transformer T1 is connected in series in the power circuit under test, and one end of the current transformer T1 is connected to the source of the power switch Q1; the reset resistor R1 is connected in parallel across the secondary winding of the current transformer T1; the active sampling switch Q2 is connected in series with the current sampling resistor R2 and then connected in parallel across the secondary winding of the current transformer T1 to form a low-impedance sampling branch on the secondary side. The gate of the active sampling switch Q2 receives a control signal synchronized with the switching timing of the power switch Q1, so that when the power switch Q1 is turned on, the active sampling switch Q2 is turned on synchronously, providing a low-impedance path for the secondary current of the current transformer T1 to flow through the current sampling resistor R2; when the power switch Q1 is turned off, the active sampling switch Q2 is turned off synchronously, so that the current transformer T1 is magnetically reset through the reset resistor R1.
2. The active bidirectional current detection circuit based on magnetic isolation according to claim 1, characterized in that, The drain of the active sampling switch Q2 is connected to the first end of the secondary winding of the current transformer T1 and the first end of the reset resistor R1; the first end of the current sampling resistor R2 is connected to the source of the active sampling switch Q2, and the second end of the current sampling resistor R2 is connected to the second end of the secondary winding of the current transformer T1 and the second end of the reset resistor R1.
3. The active bidirectional current detection circuit based on magnetic isolation according to claim 1, characterized in that, The switching timing of the active sampling switch Q2 is the same as that of the power switch Q1.
4. The active bidirectional current detection circuit based on magnetic isolation according to claim 1, characterized in that, The value of the reset resistor R1 is greater than the value of the current sampling resistor R2, so as to establish a high reset voltage on the secondary side of the current transformer T1 during the turn-off period of the power switch Q1.
5. The active bidirectional current detection circuit based on magnetic isolation according to claim 1, characterized in that, The sampling voltage U across the current sampling resistor R2 R The polarity of the sampling voltage U represents the direction of the drain-source current of the power switch Q1. R The amplitude represents the magnitude of the drain-source current of the power switch Q1.
6. The active bidirectional current detection circuit based on magnetic isolation according to claim 5, characterized in that, The sampling voltage U R After filtering, limiting, amplification and / or analog-to-digital conversion, the output is sent to the controller for current closed-loop control, overcurrent protection or status monitoring.
7. An active bidirectional current detection method based on magnetic isolation, characterized in that, The active bidirectional current detection circuit applied to any one of claims 1 to 6 includes: During the conduction of power switch Q1, active sampling switch Q2 is simultaneously turned on, so that the secondary current of current transformer T1 flows through the sampling branch formed by active sampling switch Q2 and current sampling resistor R2, thereby forming a sampling voltage U across current sampling resistor R2. R During the turn-off period of power switch Q1, active sampling switch Q2 is synchronously turned off, so that current transformer T1 is magnetically reset via reset resistor R1; according to the sampling voltage U R The polarity and amplitude determine the direction and magnitude of the drain-source current flowing through the power switch Q1.
8. The method according to claim 7, characterized in that, The method is applied to buck converters or full-bridge converters that employ synchronous rectification.