An overcurrent protection circuit for an electronic switch

Abstract

This invention discloses an overcurrent protection circuit for an electronic switch, comprising a power supply, a load, a main switch transistor, an auxiliary switch transistor, a current sampling network for the main switch, a drive signal and a drive circuit for the main switch, a comparator, and a current reference. The power supply, load, main switch transistor, and current sampling resistor are connected in series to form the main power loop. The drains of the main switch transistor and the auxiliary switch are connected together. The auxiliary switch transistor is directly driven by the drive signal of the main switch transistor and is connected in series in the current sampling network through its source. When the current sampling network detects that the current of the main switch exceeds the current reference, the comparator output turns off the main switch transistor. Compared with the prior art, after the main switch transistor is turned off, the newly added auxiliary switch transistor operates in follower mode, withstanding the high voltage in the current sampling network, giving the overcurrent protection circuit of the electronic switch advantages such as state lockability and low power consumption.

Description

Technical Field

[0001] This invention relates to an overcurrent protection circuit for electronic switches, particularly a novel overcurrent or even short-circuit protection circuit for switches operating at relatively high voltages and employing electronic devices such as MOSFETs and IGBTs as switches. Background Technology

[0002] Compared to using circuit breakers, relays, or other mechanical switches, electronic devices for controlling load switches have the advantages of small size and controllable overcurrent.

[0003] Overcurrent protection circuits in traditional and new electronic switches, such as Figure 1 As shown, the voltage across R4 is proportional to the current flowing through the load LOAD and the switching transistor Q1. This voltage is compared with a preset reference voltage Ref through a resistor divider network. When the current flowing through Q1 exceeds a certain value, comparator U1 outputs a low level, Q1 is turned off, and the load LOAD is protected. This circuit is simple and effective. However, its drawback is that when Q1 is turned off, the current flowing through R4 becomes zero, comparator U1 reverses to a high output, and Q1 turns back on. Therefore, unless additional circuitry is added to lock the output of U1, the overcurrent protection will trigger repeatedly.

[0004] An improved circuit, such as Figure 2 As shown, the overcurrent detection resistor is connected between the drain and source terminals of the switching transistor Q1. The on-resistance Rdson of Q1 and R4 are connected in series to detect the current flowing through the load LOAD and Q1. When the current is too large, causing the comparator U1 to output a low level, Q1 is turned off. When Q1 is off, the voltage on the drain terminal of Q1 rises to the input voltage, and the negative input voltage of the comparator is even higher, so U1 locks in a low-level output, and Q1 can remain off. However, the disadvantage is that the voltage divider network R2 and R1 need to withstand the input voltage V1. When the operating voltage V1 is very high, such as the 240VDC or 380VDC commonly found in high-voltage DC (HVDC) systems, the losses of R2 and R1 increase significantly. When high resistance values ​​are chosen for R1 and R2 to reduce losses, the current flowing through R2 and R1 is too small when Q1 is on, affecting the operation of U1 and the detection accuracy of the overcurrent protection. Summary of the Invention

[0005] This invention relates to an overcurrent protection circuit for an electronic switch, particularly a protection circuit for overcurrent or even short circuit when the operating voltage is relatively high. It has the advantages of accurate and reliable overcurrent protection and low operating current.

[0006] The present invention achieves the above objective by adding a switching transistor to the sampling resistor network.

[0007] Compared with traditional control methods, this invention reduces the voltage borne by the sampling resistor network after overcurrent protection occurs by adding a switching transistor, thereby reducing the voltage borne by the overcurrent protection circuit of the electronic switch. This makes the overcurrent protection circuit of the electronic switch have advantages such as high reliability, lockability, and low power consumption. Attached Figure Description

[0008] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0009] Figure 1 An existing overcurrent protection circuit.

[0010] Figure 2 An existing overcurrent protection circuit with a locking function.

[0011] Figure 3 A new overcurrent protection circuit that adds a switching transistor.

[0012] Figure 4 A new overcurrent protection circuit that uses only the on-resistance of a switch to detect current. Detailed Implementation

[0013] In the following description, some embodiments of the present disclosure will be described in detail with reference to the accompanying illustrative drawings. When elements are indicated by reference numerals in the drawings, the same elements will be represented by the same reference numerals even if the same elements are shown in different drawings. Furthermore, in the following description of the present disclosure, detailed descriptions of known functions and configurations incorporated herein will be omitted where it may obscure the subject matter of the disclosure.

[0014] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. As used herein, the singular form is intended to include the plural form as well, unless the context otherwise indicates. It will also be understood that the terms “comprising,” “including,” and “having” as used in the specification are intended to specifically describe the presence of the stated features, entities, operations, and / or components, but do not preclude the presence or addition of one or more other features, entities, operations, and / or components.

[0015] Unless otherwise defined, all terms used herein, including technical and scientific terms, shall have the same meaning as commonly understood by one of ordinary skill in the art to which the inventive concept pertains. It will be further understood that terms such as those defined in commonly used dictionaries should be interpreted as having the same meaning as their meaning in the context of the relevant field, and should not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0016] In the following description, numerous specific details are set forth to provide a complete understanding of this disclosure. This disclosure may be practiced without some or all of these specific details. In other instances, to avoid obscuring the disclosure with unnecessary detail, only components closely related to the embodiments of this disclosure are shown in the accompanying drawings, while other details less relevant to this disclosure are omitted.

[0017] The core idea of ​​this disclosed technology is to add a switching transistor to the current detection network of the electronic switch. When overcurrent protection occurs, this added switching transistor is used to withstand the high voltage applied to the detection network, so that the overcurrent protection of the electronic switch has the advantages of state lockability and low power consumption.

[0018] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. The switch is described using MOSFET, but other types of electronic switching devices, such as IGBT, can be used to achieve the same circuit function.

[0019] like Figure 3 As shown, the overcurrent protection circuit upon which this invention is based includes a power supply (V1), a load (LOAD), a main switch (Q1), a current sampling resistor (R4), a drive signal (DRIVER) and a drive network (R1) for the main switch, an auxiliary switch (Q2), a voltage divider network (R2, R3), a comparator (U1), and a reference signal (REF). The power supply (V1), load (LOAD), main switch (Q1), and current sampling resistor (R4) are connected in series to form the main power circuit. The drive (DRIVER) controls the main switch (Q1) through the drive resistor R1. The drain of the auxiliary switch is connected to the drain of the main switch. The source of the auxiliary switch is connected in series with the voltage divider network. The midpoint of the voltage divider network is connected to the negative input of the comparator (U1), and the positive input of the comparator (U1) is connected to the reference (REF).

[0020] Assuming the negative terminal of the power supply is referenced to zero potential, both Q1 and Q2 are initially on. When the current flowing through Q1 is small, the voltage generated by R4 and the on-resistance of Q1 is low. After passing through the voltage divider network, the voltage at the negative input of U1 is lower than the reference voltage, the comparator continues to output a high level, and Q1 remains on. When the current flowing through Q1 increases, the voltage generated by R4 and the on-resistance of Q1, after passing through the voltage divider network, becomes higher than the reference voltage at the negative input of U1. The comparator flips to output a low impedance, and Q1 quickly turns off. After Q1 turns off, the voltage at the drain of Q1 rises to the input voltage of the power supply. Because there is a resistance between the source of Q2 and ground, Q2 operates in follower mode. The source voltage of Q2 is approximately the drive voltage minus the turn-on threshold voltage of Q2. Assuming the drive voltage is 12V and the turn-on threshold voltage of Q2 is about 4V, then the source voltage of Q2 is approximately 8V, which is still higher than the reference voltage, and Q1 remains off. In the sampling network, Q2 bears most of the input voltage, while the voltage across the sampling voltage divider network R2 / R3 is relatively low, totaling about 8V.

[0021] Figure 4 This describes another implementation scheme. Compared to the previous scheme, the sampling resistor R4 is removed, and the current flowing through Q1 is directly sampled using the on-resistance of Q1. All other components remain the same. Although the sampling accuracy will be reduced, the circuit is relatively simplified and can still be used for overcurrent or short-circuit protection. Furthermore, the on-resistance of the MOSFET has a positive temperature coefficient; at high temperatures, the sampling resistor increases, and the trigger point for overcurrent protection decreases, which is precisely the control method we desire in most cases.

[0022] Although this disclosure has been described above through a specific embodiment, it should be understood that those skilled in the art can devise various modifications, improvements, or equivalents to this disclosure within the spirit and scope of the appended claims. Such modifications, improvements, or equivalents should also be considered to be included within the scope of this disclosure.

Claims

1. An overcurrent protection circuit for an electronic switch, comprising a power supply, a load, a main switching transistor, a current sampling device, a voltage divider network, a drive signal, a drive circuit for the main switch, a comparator and a current reference, and an auxiliary switching transistor composed of MOSFETs; wherein the power supply, load, main switching transistor, and current sampling device are connected in series and form a closed loop to constitute a main power circuit; the drive signal is connected to the control electrode of the main switch through the drive circuit; the drain of the auxiliary switching transistor is connected to the current input terminal of the main switching transistor; the gate is connected to the drive signal of the main switching transistor; the source of the auxiliary switching transistor is connected in series with the sampling voltage divider network; the midpoint of the voltage divider network is connected to the negative input of the comparator; the current reference is connected to the positive input of the comparator; and the output of the comparator is connected to the control electrode of the main switching transistor; wherein... When the current flowing through the main switch increases, the negative input voltage of the comparator is higher than the reference voltage. The comparator flips and outputs a low impedance, turning off the main switch. The voltage at the drain of the main switch rises to the input voltage of the power supply. The source of the auxiliary switch has a resistance to ground, so the auxiliary switch operates in follower mode. The source voltage of the auxiliary switch is the drive voltage minus the turn-on threshold of Q2.

2. The overcurrent protection circuit for an electronic switch according to claim 1, characterized in that, The current sampling device can be short-circuited.

3. The overcurrent protection circuit for an electronic switch according to claim 1, characterized in that, The comparator output and the control electrode of the switching transistor are connected via an additional drive resistor.

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