Method and system for zero-crossing turn-off detection and control of mosfets in quasi-resonant bidirectional full-bridge topology

Abstract

The application provides a method for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology, comprising: sampling high-voltage side MOSFET current; comparing the high-voltage side MOSFET current with a preset threshold to generate a comparison result signal; generating a zero-crossing signal by using the comparison result signal and an enable signal and sending the zero-crossing signal to a control chip; and triggering, by the control chip, corresponding MOSFET turn-off PWM enable when the zero-crossing signal is at a high level. The application samples the high-voltage side MOSFET current, then sends the current amplitude into a comparator circuit of a preset threshold, sends the logic level generated by the comparator into an AND gate, triggers the corresponding MOSFET turn-off PWM enable after the signal generated by the AND gate is delayed and logically processed in the control chip, and realizes MOSFET zero-current turn-off. Thus, when the quasi-resonant parameters differ greatly, the MOSFET can avoid large reverse current or energy reverse flow in the turn-off process, thereby reducing the reactive loss and improving the efficiency.

Description

Technical Field

[0001] This invention relates to the field of circuit technology, and more particularly to a method and system for detecting and controlling MOSFET zero-crossing turn-off in a quasi-resonant bidirectional full-bridge topology. Background Technology

[0002] Portable mobile energy storage and home photovoltaic energy storage have developed rapidly in recent years, and with the support of national policies and the backdrop of the global energy crisis, they will have even greater room for growth. At the same time, the requirements for energy efficiency and reliability of equipment will also be higher.

[0003] Quasi-resonant push-bridge topologies and quasi-resonant full-bridge topologies are widely used in bidirectional isolated charging units. Their main resonance principle is to use the leakage inductance of the transformer (or external inductance) and external resonant capacitor to form a resonant network. Quasi-resonant soft switching can be achieved when the switching frequency is lower than the resonant frequency, thereby reducing the switching losses of power devices. However, the slight deviation of stray parameters and device tolerances can cause large errors in the resonant parameters during mass production. When the resonant frequency is lower than the switching frequency, hard switching occurs. When the resonant frequency is much higher than the switching frequency, energy flows in the opposite direction, increasing the losses of power devices or the reactive power losses of magnetic devices, affecting product performance and reducing reliability.

[0004] Therefore, existing technologies typically avoid excessive parameter differences by screening magnetic components and resonant capacitors during mass production, or by increasing the difference between the quasi-resonant frequency and the switching frequency to avoid hard switching. While screening methods solve the problem to some extent, they are costly, inefficient, and unsuitable for mass production. Increasing the difference between the quasi-resonant frequency and the switching frequency, although avoiding hard switching, may exacerbate reverse energy flow and increase reactive power loss.

[0005] Therefore, a new solution is needed. Summary of the Invention

[0006] The purpose of this invention is to provide a method for detecting and controlling the zero-crossing turn-off of MOSFETs in a quasi-resonant bidirectional full-bridge topology, so as to avoid large reverse currents or reverse energy flow in the MOSFETs during the turn-off process when the quasi-resonant parameters are significantly different, thereby reducing reactive power loss and improving efficiency.

[0007] According to one aspect of the present invention, a method for detecting and controlling the zero-crossing turn-off of a MOSFET in a quasi-resonant bidirectional full-bridge topology is provided, comprising:

[0008] Sample the high-voltage side MOSFET current;

[0009] The high-voltage side MOSFET current is compared with a preset threshold to generate a comparison result signal;

[0010] The comparison result signal and the enable signal are used to generate a zero-crossing signal, which is then sent to the control chip; and

[0011] When the zero-crossing signal is high, the control chip triggers the corresponding MOSFET to turn off the PWM enable.

[0012] In the method for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology provided by the present invention, the MOSFET current on the high-voltage side is sampled by setting a current transformer on each bridge arm on the high-voltage side, setting a current transformer at the high-voltage side bus, or setting a sampling resistor in each branch on the high-voltage side.

[0013] In the method for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology provided by the present invention, when the MOSFET current on the high-voltage side is less than a preset threshold, the comparison result signal is high level.

[0014] In the method for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology provided by the present invention, when the comparison result signal is high and the enable signal is high, the zero-crossing signal is high.

[0015] In the method for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology provided by the present invention, before the corresponding MOSFET turn-off PWM enable is triggered by the control chip, the method further includes: after the zero-crossing signal becomes high level, the control chip performs hardware circuit delay time compensation on the low-voltage side MOSFET.

[0016] In the method for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology provided by the present invention, after the high-voltage side MOSFET is driven on, the enable signal is delayed and set high; when the high-voltage side MOSFET is driven off, the enable signal is synchronously or delayed and set low.

[0017] According to another aspect of the present invention, a system for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology is also provided, comprising:

[0018] Current sampling module, used to sample the current of the high-voltage side MOSFET;

[0019] The comparison module, connected to the current sampling module, is used to compare the high-voltage side MOSFET current with a preset threshold and generate a comparison result signal.

[0020] A zero-crossing signal generation module, connected to the comparison module, is used to generate a zero-crossing signal using the comparison result signal and the enable signal; and

[0021] A control chip, connected to the zero-crossing signal generation module, is used to generate the enable signal and trigger the corresponding MOSFET to turn off the PWM enable based on the zero-crossing signal.

[0022] In the system provided by this invention for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology, the current sampling module is a current transformer respectively set on each bridge arm on the high-voltage side, a current transformer set at the high-voltage side bus, or a sampling resistor set on each branch on the high-voltage side.

[0023] In the system for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology provided by the present invention, the comparison module includes a first resistor R1, a second resistor R2, a third resistor R3, a first capacitor C1, a second capacitor C2, a third capacitor C3, and a comparator. The first end of the first resistor R1 is connected to the output terminal of the current sampling module. The fourth end of the comparator is connected to the second end of the first resistor R1 and the first end of the first capacitor C1. The third end of the comparator is connected to the first end of the third resistor R3, the second end of the second capacitor C2, and the second end of the second resistor R2. The fifth end of the comparator is connected to the second end of the third capacitor C3. The first end of the comparator is connected to the input terminal of the zero-crossing signal generation module. The second end of the comparator, the second end of the third resistor R3, the second end of the first capacitor C1, the first end of the second capacitor C2, and the first end of the third capacitor C3 are grounded.

[0024] In the system for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology provided by the present invention, the zero-crossing signal generation module includes an AND gate, a fourth resistor R4, a fifth resistor R5, and a fourth capacitor C4. The first terminal of the AND gate is connected to the first terminal of the comparator, the second terminal of the AND gate is connected to the enable signal and the second terminal of the fourth resistor R4, the fifth terminal of the AND gate is connected to the second terminal of the fourth capacitor C4, the fourth terminal of the AND gate is connected to the second terminal of the fifth resistor R5 and the control chip, and the third terminal of the AND gate, the first terminal of the fourth resistor R4, the first terminal of the fifth resistor R5, and the first terminal of the fourth capacitor R4 are grounded.

[0025] The method for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology provided by the present invention has the following beneficial effects: The method for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology provided by the present invention samples the current of the high-voltage side MOSFET, and then sends the current amplitude to a comparator circuit with a preset threshold. The logic level generated by the comparator is sent to an AND gate. The signal generated by the AND gate is delayed and logically processed inside the control chip to trigger the corresponding MOSFET turn-off PWM enable, thereby realizing zero-current turn-off of the MOSFET. Thus, it can avoid large reverse current or reverse energy flow in the MOSFET during the turn-off process when the quasi-resonant parameters are large, thereby reducing reactive power loss and improving efficiency. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort:

[0027] Figure 1 The diagram shows a flowchart of a MOSFET zero-crossing turn-off detection and control method in a quasi-resonant bidirectional full-bridge topology according to an embodiment of the present invention.

[0028] Figure 2 What is shown is Figure 1 The method shown is a timing diagram of each signal when implementing control of the transmission from the high-voltage side to the battery side;

[0029] Figure 3 The diagram shown is a schematic of a system for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology according to an embodiment of the present invention.

[0030] Figure 4 yes Figure 3 The circuit diagram of the comparison module and the zero-crossing signal generation module is shown below;

[0031] Figure 5 As shown Figure 4 The circuit diagram shown is of the current sampling module installed on the current transformer of each bridge arm on the high-voltage side.

[0032] Figure 6 As shown Figure 4 The current sampling module shown is a circuit diagram of a current transformer installed at the high-voltage side bus.

[0033] Figure 7 As shown Figure 4The circuit diagram shown is of the sampling resistors installed in each branch on the high-voltage side of the current sampling module.

[0034] Figure 8 This is a MATLAB simulation result of precise zero-crossing turn-off of a MOSFET using existing control methods.

[0035] Figure 9 The figure shows the results of MatLab simulation of precise zero-crossing turn-off of MOSFET using the control method provided by this invention. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] The overall idea of ​​this invention is to address the problems of high cost and low production efficiency caused by screening magnetic components and resonant capacitors in mass production to avoid excessive parameter differences; and the problem of increased energy reverse flow and increased reactive power loss caused by increasing the difference between the quasi-resonant frequency and the switching frequency to avoid hard switching. This invention provides a method for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology. By sampling the MOSFET current on the high-voltage side, the current amplitude is sent to a comparator circuit with a preset threshold. The logic level generated by the comparator is sent to an AND gate. The signal generated by the AND gate is delayed and logically processed within the control chip, triggering the corresponding MOSFET turn-off PWM enable, thus achieving zero-current turn-off of the MOSFET. Therefore, it can avoid large reverse currents or energy reverse flow during the MOSFET turn-off process when the quasi-resonant parameters differ significantly, thereby reducing reactive power loss and improving efficiency.

[0038] Figure 1 The diagram shows a flowchart of a method for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology according to an embodiment of the present invention. Figure 1 As shown, the method for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology provided by the present invention includes the following steps:

[0039] Step S1: Sample the current of the high-voltage side MOSFET;

[0040] Specifically, in one embodiment of the present invention, such as Figure 5-7As shown, the high-voltage side MOSFET current can be sampled by installing a current transformer on each arm of the high-voltage side bridge, installing a current transformer at the high-voltage side bus, or installing a sampling resistor in each branch of the high-voltage side. The current magnitude obtained through any of the above methods for each switching cycle is denoted as CS_CT (e.g., ...). Figure 2 The high-voltage side MOSFET current waveform shown is fed into the comparator circuit.

[0041] Step S2: Compare the current of the high-voltage side MOSFET with a preset threshold to generate a comparison result signal;

[0042] Specifically, in one embodiment of the present invention, at the beginning of a cycle, the high-voltage side MOSFET current begins to increase continuously, and the comparison result signal is low. After the high-voltage side MOSFET current passes its peak, it gradually decreases. When it falls below the comparator's set threshold, it indicates that the MOSFET is about to cross zero. Therefore, the comparison result signal output by the zero-crossing comparator changes from low to high. This preset threshold can be obtained based on experience or actual debugging. Figure 2 As shown, when the high-voltage side MOSFET current is close to 0, the signal changes from low level to high level after the high-voltage side MOSFET current zero-crossing comparison.

[0043] Step S3: Generate a zero-crossing signal using the comparison result signal and the enable signal, and send it to the control chip;

[0044] Specifically, in one embodiment of the present invention, the enable signal ZERO_EN is generated by the control chip. After the high-voltage side MOSFET is driven on, it is delayed and set high, waiting for the next zero-crossing comparator signal, and this cycle repeats. When the high-voltage side MOSFET is driven off, the ZERO_EN signal is synchronously or delayed and set low. Specifically, the enable signal ZERO_EN is set high after the high-voltage side MOSFET current rises to its maximum value. Figure 2 As shown, after the high-voltage side MOSFET is driven on, the enable signal ZERO_EN is set high when the current of the high-voltage side MOSFET crosses its peak; when the high-voltage side MOSFET is driven off, it is set low simultaneously. This ensures that when the comparison result signal is high after the high-voltage side MOSFET is driven off, it will not affect the zero-crossing judgment of the control chip and erroneously trigger a new shutdown action.

[0045] Furthermore, in one embodiment of the present invention, the enable signal and the comparison result signal are fed into an AND gate to generate a zero-crossing signal ZERO_EN_DSP. For example... Figure 2 As shown, the zero-crossing signal ZERO_EN_DSP only outputs a high level when both the zero-crossing comparison signal (i.e., the comparison result signal) and the enable signal ZERO_EN are high, indicating that the MOSFET current is about to cross zero.

[0046] Step S4: When the zero-crossing signal is high, the control chip triggers the corresponding MOSFET to turn off the PWM enable.

[0047] Specifically, in one embodiment of the present invention, after the control chip (including but not limited to a DSP / ARM processor) detects that the zero-crossing signal ZERO_EN_DSP level goes high, it sends a PWM shutdown command to the corresponding MOSFET driver. Because Figure 2 This is explained as transmission from the high-voltage side to the battery. When ZERO_EN is enabled, the drive signals for the high-voltage side MOSFET and the low-voltage side MOSFET are issued synchronously. However, there may be a delay in the hardware circuitry. Therefore, as... Figure 2 As shown, when the control chip detects the zero-crossing signal and the ZERO_EN_DSP level goes high, if there is a delay, the delay time of the hardware circuit is compensated by software, and then the PWM shutdown command of the low-voltage side MOSFET is executed, so that the low-voltage side MOSFET achieves zero-current shutdown; at the same time, no more waves are allowed to be generated within this cycle to avoid multiple power-on and power-off malfunctions.

[0048] Those skilled in the art will understand that the control method is implemented in the same way when transferring energy from the battery side to the high-voltage side. The above-described detection and control method is also applicable to quasi-resonant push-pull bidirectional topologies, and also to synchronous rectification schemes in unidirectional applications.

[0049] Figure 3 The diagram shown is a schematic of a system for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology, according to an embodiment of the present invention. Figure 3 As shown, the system for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology provided by the present invention includes: a current sampling module 10 for sampling the high-voltage side MOSFET current; a comparison module 20 connected to the current sampling module for comparing the high-voltage side MOSFET current with a preset threshold and generating a comparison result signal; a zero-crossing signal generation module 30 connected to the comparison module for generating a zero-crossing signal using the comparison result signal and an enable signal; and a control chip 40 connected to the zero-crossing signal generation module for generating the enable signal and triggering the corresponding MOSFET turn-off PWM enable according to the zero-crossing signal.

[0050] Specifically, in one embodiment of the present invention, such as Figure 5-7 As shown, the current sampling module is a current transformer installed on each bridge arm on the high-voltage side, a current transformer installed at the high-voltage side bus, or a sampling resistor installed in each branch on the high-voltage side.

[0051] Figure 4 yes Figure 3 The circuit diagrams for the comparison module and the zero-crossing signal generation module are shown below. Figure 4 As shown, the comparison module includes a first resistor R1, a second resistor R2, a third resistor R3, a first capacitor C1, a second capacitor C2, a third capacitor C3, and a comparator. The first end of the first resistor R1 is connected to the output terminal of the current sampling module. The fourth end of the comparator is connected to the second end of the first resistor R1 and the first end of the first capacitor C1. The third end of the comparator is connected to the first end of the third resistor R3, the second end of the second capacitor C2, and the second end of the second resistor R2. The fifth end of the comparator is connected to the second end of the third capacitor C3. The first end of the comparator is connected to the input terminal of the zero-crossing signal generation module. The second end of the comparator, the second end of the third resistor R3, the second end of the first capacitor C1, the first end of the second capacitor C2, and the first end of the third capacitor C3 are grounded. The zero-crossing signal generation module includes an AND gate, a fourth resistor R4, a fifth resistor R5, and a fourth capacitor C4. The first terminal of the AND gate is connected to the first terminal of the comparator, the second terminal of the AND gate is connected to the enable signal and the second terminal of the fourth resistor R4, the fifth terminal of the AND gate is connected to the second terminal of the fourth capacitor C4, the fourth terminal of the AND gate is connected to the second terminal of the fifth resistor R5 and the control chip, and the third terminal of the AND gate, the first terminal of the fourth resistor R4, the first terminal of the fifth resistor R5, and the first terminal of the fourth capacitor R4 are grounded.

[0052] Specifically, such as Figure 4 As shown, the current magnitude acquired by the current sampling module for each switching cycle is marked as CS_CT and sent to the comparator circuit. When the current is less than the preset value, the zero-crossing comparator level flips. The comparator output level and the enable signal ZERO_EN are ANDed by an AND gate to generate the ZERO_EN_DSP signal, which is the zero-crossing signal and is sent to the control chip for control.

[0053] This invention uses high-voltage side current detection to determine the time of current zero crossing in both bidirectional operation, and achieves precise zero-crossing turn-off of the MOSFET through the control method described above. Figure 8 and Figure 9 The following are the MATLAB simulation results (I_Q1 is the high-voltage side MOSFET current, I_Q6 is the battery-side (low-voltage example) MOSFET current): Figure 8 As shown, under the same load power conditions, when the quasi-resonant parameters deviate significantly from the design, there is a noticeably larger reverse reactive current, and the MOSFET peak current is also larger; for example... Figure 9As shown, after applying the aforementioned detection and control method, under the same resonance parameters and design deviation values, there is no significant reverse current, and the MOSFET peak current is also greatly reduced. Therefore, after applying the aforementioned detection and control method, energy efficiency is improved, reliability is enhanced, and production efficiency is significantly increased without increasing production costs.

[0054] Certain specific embodiments of the invention have been described above. Note that the terminology used herein is for the purpose of describing specific embodiments only and is not intended to be limiting. For example, unless the context clearly indicates otherwise, the singular forms “a” and “the” as used herein are intended to also include the plural forms. It will also be understood that the word “comprising”, when used in this specification, specifies the presence of the stated features, integrals, steps, operations, units, and / or components without excluding the presence or addition of one or more other features, integrals, steps, operations, units, components, and / or combinations thereof.

[0055] Although several embodiments of the invention have been described above with reference to the accompanying drawings, it should be understood that the invention is not limited to the specific embodiments disclosed. The invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the appended claims is to be interpreted in the broadest possible sense, thus encompassing all such modifications and equivalent structures and functions.

Claims

1. A method for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology, characterized in that, include: Sample the high-voltage side MOSFET current; The high-voltage side MOSFET current is compared with a preset threshold to generate a comparison result signal; The comparison result signal and the enable signal are used to generate a zero-crossing signal, which is then sent to the control chip. as well as When the zero-crossing signal is high, the control chip triggers the corresponding MOSFET to turn off the PWM enable. Specifically, after the high-voltage side MOSFET is driven to power on, the enable signal is delayed and then set high; when the high-voltage side MOSFET is driven to power off, the enable signal is simultaneously or delayed and then set low. Before the control chip triggers the corresponding MOSFET to turn off the PWM enable, the method further includes: after the zero-crossing signal becomes high, the control chip performs hardware circuit delay time compensation on the low-voltage side MOSFET.

2. The method for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology according to claim 1, characterized in that, The high-voltage side MOSFET current is sampled by setting a current transformer on each bridge arm on the high-voltage side, setting a current transformer at the high-voltage side bus, or setting a sampling resistor in each branch on the high-voltage side.

3. The method for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology according to claim 1, characterized in that, When the current of the high-voltage side MOSFET is less than a preset threshold, the comparison result signal is at a high level.

4. The method for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology according to claim 3, characterized in that, When the comparison result signal is high and the enable signal is high, the zero-crossing signal is high.

5. A system for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology, characterized in that, include: Current sampling module, used to sample the current of the high-voltage side MOSFET; The comparison module, connected to the current sampling module, is used to compare the high-voltage side MOSFET current with a preset threshold and generate a comparison result signal. A zero-crossing signal generation module, connected to the comparison module, is used to generate a zero-crossing signal using the comparison result signal and the enable signal; as well as A control chip, connected to the zero-crossing signal generation module, is used to generate the enable signal and trigger the corresponding MOSFET to turn off the PWM enable according to the zero-crossing signal; The control chip is further configured to: after the high-voltage side MOSFET is driven on, delay and set the enable signal high; when the high-voltage side MOSFET is driven off, synchronize or delay and set the enable signal low; and after the zero-crossing signal becomes high, perform hardware circuit delay time compensation for the low-voltage side MOSFET.

6. The system for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology according to claim 5, characterized in that, The current sampling module is a current transformer installed on each arm of the high-voltage side, a current transformer installed at the high-voltage side bus, or a sampling resistor installed in each branch of the high-voltage side.

7. The system for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology according to claim 5, characterized in that, The comparison module includes a first resistor R1, a second resistor R2, a third resistor R3, a first capacitor C1, a second capacitor C2, a third capacitor C3, and a comparator. The first end of the first resistor R1 is connected to the output terminal of the current sampling module. The fourth end of the comparator is connected to the second end of the first resistor R1 and the first end of the first capacitor C1. The third end of the comparator is connected to the first end of the third resistor R3, the second end of the second capacitor C2, and the second end of the second resistor R2. The fifth end of the comparator is connected to the second end of the third capacitor C3. The first end of the comparator is connected to the input terminal of the zero-crossing signal generation module. The second end of the comparator, the second end of the third resistor R3, the second end of the first capacitor C1, the first end of the second capacitor C2, and the first end of the third capacitor C3 are grounded.

8. The system for MOSFET zero-crossing turn-off detection and control in a quasi-resonant bidirectional full-bridge topology according to claim 7, characterized in that, The zero-crossing signal generation module includes an AND gate, a fourth resistor R4, a fifth resistor R5, and a fourth capacitor C4. The first terminal of the AND gate is connected to the first terminal of the comparator, the second terminal of the AND gate is connected to the enable signal and the second terminal of the fourth resistor R4, the fifth terminal of the AND gate is connected to the second terminal of the fourth capacitor C4, the fourth terminal of the AND gate is connected to the second terminal of the fifth resistor R5 and the control chip, and the third terminal of the AND gate, the first terminal of the fourth resistor R4, the first terminal of the fifth resistor R5, and the first terminal of the fourth capacitor C4 are grounded.

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