A solenoid valve driving circuit based on intelligent MOS and its working method

Abstract

The present invention discloses an intelligent solenoid valve driving circuit and a working method thereof, which belongs to the field of automotive electronic control, and includes an MCU for outputting square wave signals, a driving module, an intelligent device, and a controlled solenoid valve, wherein the driving module is electrically connected to the intelligent device, the intelligent device is connected between one end of the electromagnetic coil of the controlled solenoid valve and the ground terminal, and the other end of the electromagnetic coil is electrically connected to the 12V power supply terminal, and is used to realize the output of high and low level signals based on the driving module to control the on and off of the intelligent device, so as to control the opening and closing of the controlled solenoid valve. The above-mentioned intelligent solenoid valve driving circuit and its working method are adopted, and the on and off of the intelligent device is controlled by outputting square waves, thereby controlling the opening and closing of the controlled solenoid valve, and taking into account both low cost and high performance, thereby meeting the needs of the market.

Description

Technical Field

[0001] The present invention relates to the technical field of automobile electronic control, and in particular to a solenoid valve driving circuit based on intelligent MOS and a working method thereof. Background Art

[0002] With the continuous innovation and technological progress of the automotive industry, solenoid valves, as key components for achieving precise control, play an increasingly important role in various complex control systems of automobiles.

[0003] The mainstream implementation schemes of solenoid valve control systems on the current market mostly rely on high-performance imported application-specific integrated circuits (ASICs) to ensure efficient and accurate control. However, this commonly used solution has limitations when facing some specific application scenarios - especially those that only require precise control of a few solenoid valves. In these cases, the use of full-featured, high-performance ASICs not only results in excess resources, such as idle computing power and additional functions, but also brings cost dissipation. Summary of the invention

[0004] The purpose of the present invention is to provide a solenoid valve driving circuit based on intelligent MOS and a working method thereof to solve the above technical problems.

[0005] To achieve the above-mentioned purpose, the present invention provides a solenoid valve driving circuit based on intelligent MOS, including an MCU for outputting PWM square wave signals, a MOS driving module, an intelligent MOS and a controlled solenoid valve, the MCU is electrically connected to the intelligent MOS via the MOS driving module, the intelligent MOS is connected between one end of the electromagnetic coil of the controlled solenoid valve and the ground terminal, and the other end of the electromagnetic coil is electrically connected to the 12V power supply terminal, so as to realize the output high and low level signals based on the MCU to control the on and off of the intelligent MOS via the MOS driving module, so as to control the opening and closing of the controlled solenoid valve.

[0006] Preferably, the MOS driving module includes an interlocked conduction transistor group and an interlocked shutoff transistor group, the interlocked conduction transistor group includes a first conduction transistor and a second conduction transistor, the interlocked shutoff transistor group includes a first shutoff transistor and a second shutoff transistor, and the first conduction transistor, the second conduction transistor, the first shutoff transistor and the second shutoff transistor are all NPN transistors;

[0007] The base of the first conducting transistor is connected to the PWM square wave signal output pin of the MCU, the emitter of the first conducting transistor is grounded, the collector of the first conducting transistor is connected to the base of the first shut-off transistor, the emitter of the first shut-off transistor is grounded, the collector of the first shut-off transistor is connected to the base of the second conducting transistor, the collector of the second conducting transistor is connected to the 5V power supply terminal, the emitter of the second conducting transistor is connected to the collector of the second shut-off transistor, the emitter of the second shut-off transistor is grounded, the base of the second shut-off transistor is connected to the base of the first shut-off transistor via a clamping diode, and the base of the first shut-off transistor and the collector of the first conducting transistor are both connected to the 5V power supply terminal;

[0008] The gate of the smart MOS is connected between the emitter of the second on transistor and the collector of the second off transistor, the drain of the smart MOS is connected in series with the electromagnetic coil and then electrically connected to the 12V power supply terminal, and the source of the smart MOS is grounded.

[0009] Preferably, the intelligent MOS includes a MOS tube, a gate driving unit, an over-temperature protection unit, an over-voltage protection unit, an over-current protection unit and a temperature sensor for monitoring the temperature of the MOS tube, the input end of the gate driving unit is connected to the MOS driving module, and the output end of the gate driving unit is connected to the gate of the MOS tube;

[0010] The gate drive unit is also connected to the over-temperature protection unit and the over-current protection unit respectively. The over-voltage protection unit is connected between the gate and the drain of the MOS tube. The over-current protection unit is connected between the source of the MOS tube and the gate drive unit.

[0011] Preferably, the overcurrent protection unit is a linear current limiter for reading the voltage difference between the source and the drain of the MOS tube to obtain the current of the MOS tube, and for adjusting the duty cycle of the driving waveform of the gate driving unit according to the comparison result between the obtained MOS tube current and the typical value;

[0012] The overvoltage protection unit is the parasitic diode of the MOS tube;

[0013] The gate drive unit is the interface of the MCU.

[0014] Preferably, the MCU is also connected to the gate and drain of the MOS tube respectively, for collecting the input frequency and output frequency of the MOS tube, and for combining with the output frequency of the MCU to realize fault diagnosis.

[0015] Preferably, the frequency range of the PWM square wave signal output by the MCU is 2KHz-16KHz.

[0016] The working method of the solenoid valve driving circuit based on the intelligent MOS includes cyclically alternating high-level driving on and low-level driving off;

[0017] The high-level driving conduction step is as follows: the MCU outputs a high-level signal to the base of the first conduction transistor, the first conduction transistor is turned on, the collector of the first conduction transistor is grounded, the first turn-off transistor is driven to be turned off, and the second turn-off transistor is turned off through the clamping diode. At this time, the 5V power supply end loads voltage to the base of the second conduction transistor, the second conduction transistor is turned on, and then the voltage is loaded to the gate of the MOS tube, the MOS tube is turned on, the electromagnetic coil is energized to form a path, and the controlled electromagnetic valve is opened;

[0018] The low-level drive shutdown steps are as follows: the MCU outputs a low-level signal to the base of the first conduction transistor, the first conduction transistor is turned off, the collector of the first conduction transistor stops being grounded, the 5V power supply end loads voltage to the base of the first turn-off transistor, the first turn-off transistor is turned on, and the second turn-off transistor is driven to be turned on through the clamping diode. At this time, the base of the second conduction transistor is grounded through the first turn-off transistor, the second conduction transistor is turned off, the gate of the MOS tube is grounded through the second turn-off transistor, the MOS tube is turned off, the electromagnetic coil is powered off, and the controlled solenoid valve is closed.

[0019] Preferably, during the operation of cyclically alternating high-level driving on and low-level driving off, fault diagnosis and fault action protection are performed based on the collected frequencies of the gate and drain of the MOS tube.

[0020] Preferably, the MCU collects the drain and gate frequencies of the MOS tube by double-edge capture counting, reads the register of the MCU to obtain the output frequency of the MCU, and performs the following fault diagnosis and fault action protection:

[0021] When the collected MOS tube gate frequency is the same as the MCU output frequency, and the MOS tube drain frequency and gate frequency are within the set error range, it is determined that the MOS tube is in a normal working state;

[0022] When the collected MOS tube gate frequency is the same as the MCU output frequency, and the proportion of the MOS tube drain frequency in the MOS tube gate frequency is within the set range, the MOS tube is determined to be in an overcurrent state. At this time, the MCU adjusts the high level time in the output waveform through the gate drive unit to limit the MOS tube within the typical value range;

[0023] When the voltage difference between the source and drain of the MOS tube is greater than the set value, the parasitic diode undergoes reverse avalanche breakdown, and the MOS tube is determined to be in an overvoltage state;

[0024] When the collected MOS tube gate frequency is the same as the output frequency of the MCU, and the drain of the MOS tube does not monitor the frequency, it is determined that the MOS tube is in an over-temperature state, and the over-temperature protection unit turns off the gate drive unit to turn off the MOS tube. At this time, the temperature sensor is used to collect the temperature of the MOS tube in real time, and the MOS tube is reopened when the collected temperature is lower than the threshold.

[0025] Preferred, typical value The calculation formula is as follows:

[0026] ;

[0027] In the formula, Indicates the drain voltage of the MOS tube; Indicates the duty cycle of the PWM square wave output by the MCU; Indicates the internal resistance of the MOS tube.

[0028] Therefore, the present invention adopts the above-mentioned solenoid valve driving circuit based on intelligent MOS and its working method, which has the following beneficial effects:

[0029] 1. The MCU outputs PWM square waves to control the on and off of the intelligent MOS, which can then control the opening and closing of the controlled solenoid valve, while taking into account both low cost and high performance, thus meeting market demand;

[0030] 2. It has a fault diagnosis function, which can act quickly when overcurrent or overtemperature occurs to avoid further expansion of losses.

[0031] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a circuit schematic diagram of a solenoid valve drive circuit based on intelligent MOS of the present invention;

[0033] Figure 2 It is a structural block diagram of an intelligent MOS based on an electromagnetic valve driving circuit of the present invention;

[0034] Figure 3 This is a structural block diagram of a solenoid valve driving circuit based on intelligent MOS of the present invention;

[0035] Figure 4 The output waveform diagram of the embodiment of the present invention under normal working state;

[0036] Figure 5 This is an output waveform diagram under an overcurrent state of an embodiment of the present invention;

[0037] Figure 6 This is an output waveform diagram under an over-temperature state of an embodiment of the present invention. DETAILED DESCRIPTION

[0038] In the description of the present invention, it should be noted that the terms "upper", "lower", "inside", "outside", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the invented product is usually placed when in use. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In the description of the present invention, it should also be noted that, unless otherwise clearly specified and limited, the terms "setting", "installation", and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0039] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings.

[0040] like Figure 1-Figure 3 As shown, a solenoid valve driving circuit based on intelligent MOS includes an MCU for outputting PWM square wave signals, a MOS driving module, an intelligent MOSQ15 and a controlled solenoid valve, wherein the MCU is electrically connected to the intelligent MOSQ15 via the MOS driving module, the intelligent MOSQ15 is connected between one end of the electromagnetic coil LSD5 of the controlled solenoid valve and the ground terminal, and the other end of the electromagnetic coil LSD5 is electrically connected to the 12V power supply terminal COIL_SUP, so as to realize the output high and low level signals based on the MCU to control the on and off of the intelligent MOSQ15 via the MOS driving module, so as to control the opening and closing of the controlled solenoid valve.

[0041] Specifically, the MOS driving module includes an interlocked conduction transistor group and an interlocked shutoff transistor group, the interlocked conduction transistor group includes a first conduction transistor Q69B and a second conduction transistor Q69A, the interlocked shutoff transistor group includes a first shutoff transistor Q68B and a second shutoff transistor Q68A, the first conduction transistor Q69B, the second conduction transistor Q69A, the first shutoff transistor Q68B and the second shutoff transistor Q68A are all NPN transistors; the base of the first conduction transistor Q69B is connected to the PWM square wave signal output pin of the MCU, the emitter of the first conduction transistor Q69B is grounded, the collector of the first conduction transistor Q69B is connected to the base of the first shutoff transistor Q68B, the emitter of the first shutoff transistor Q68B is grounded, and the collector of the first shutoff transistor Q68B is connected to the second conduction transistor Q68B. The base of the second transistor Q69A is connected, the collector of the second transistor Q69A is connected to the 5V power supply terminal VCC5, the emitter of the second transistor Q69A is connected to the collector of the second transistor Q68A, the emitter of the second transistor Q68A is grounded, the base of the second transistor Q68A is connected to the base of the first transistor Q68B via a clamping diode, the base of the first transistor Q68B and the collector of the first transistor Q69B are both connected to the 5V power supply terminal VCC5; the gate of the smart MOS Q15 is connected between the emitter of the second transistor Q69A and the collector of the second transistor Q68A, the drain of the smart MOS Q15 is connected in series with the electromagnetic coil LSD5 and then electrically connected to the 12V power supply terminal COIL_SUP, and the source of the smart MOS Q15 is grounded.

[0042] The intelligent MOSQ15 includes a MOS tube, a gate drive unit, an over-temperature protection unit, an over-voltage protection unit, an over-current protection unit and a temperature sensor for monitoring the temperature of the MOS tube. The input end of the gate drive unit is connected to the MOS drive module, and the output end of the gate drive unit is connected to the gate of the MOS tube; the gate drive unit is also connected to the over-temperature protection unit and the over-current protection unit respectively, the over-voltage protection unit is connected between the gate and the drain of the MOS tube, and the over-current protection unit is connected between the source of the MOS tube and the gate drive unit.

[0043] The overcurrent protection unit is a linear current limiter used to read the voltage difference between the source and drain of the MOS tube to obtain the current of the MOS tube, and is used to adjust the driving waveform duty cycle of the gate drive unit according to the comparison result between the obtained MOS tube current and the typical value; the overvoltage protection unit is the parasitic diode of the MOS tube; and the gate drive unit is the interface of the MCU.

[0044] The MCU is also connected to the gate and drain of the MOS tube respectively, and is used to collect the input frequency and output frequency of the MOS tube, and is used to combine with the output frequency of the MCU to realize fault diagnosis.

[0045] The frequency range of the PWM square wave signal output by the MCU is 2KHz-16KHz.

[0046] The working method of the solenoid valve driving circuit based on the intelligent MOSQ15 includes cyclically alternating high-level driving on and low-level driving off;

[0047] The high-level driving conduction step is as follows: the MCU outputs a high-level signal to the base of the first conduction transistor Q69B, the first conduction transistor Q69B is turned on, the collector of the first conduction transistor Q69B is grounded, the first turn-off transistor Q68B is driven to be turned off, and the second turn-off transistor Q68A is turned off through the clamping diode. At this time, the 5V power supply terminal VCC5 loads voltage to the base of the second conduction transistor Q69A, the second conduction transistor Q69A is turned on, and then the voltage is loaded to the gate of the MOS tube, the MOS tube is turned on, the electromagnetic coil LSD5 is energized to form a path, and the controlled electromagnetic valve is opened;

[0048] The low-level driving shutdown steps are as follows: the MCU outputs a low-level signal to the base of the first conduction transistor Q69B, the first conduction transistor Q69B is turned off, the collector of the first conduction transistor Q69B stops being grounded, the 5V power supply terminal VCC5 loads voltage to the base of the first turn-off transistor Q68B, the first turn-off transistor Q68B is turned on, and the second turn-off transistor Q68A is driven to be turned on through the clamping diode. At this time, the base of the second conduction transistor Q69A is grounded through the first turn-off transistor Q68B, the second conduction transistor Q69A is turned off, the gate of the MOS tube is grounded through the second turn-off transistor Q68A, the MOS tube is turned off, the electromagnetic coil LSD5 is powered off, and the controlled electromagnetic valve is closed.

[0049] like Figure 4-Figure 6 As shown, in the working process of cyclically alternating high-level drive on and low-level drive off, when the MOS tube is turned on, the drain and source of the MOS tube are turned on, and the drain voltage is 0. When the MOS tube is turned off, the drain and source of the MOS tube are not turned on, and the drain voltage is infinitely close to the MCU output voltage. Therefore, fault diagnosis and fault action protection can be performed based on the collected gate and drain frequencies of the MOS tube.

[0050] Specifically, the MCU collects the drain and gate frequencies of the MOS tube through double-edge capture counting, reads the MCU register to obtain the MCU output frequency, and performs the following fault diagnosis and fault action protection:

[0051] When the collected MOS tube gate frequency is the same as the MCU output frequency, and the MOS tube drain frequency and gate frequency are within the set error range (3%), the MOS tube is judged to be in normal working state;

[0052] When the collected MOS tube gate frequency is the same as the MCU output frequency, and the proportion of the MOS tube drain frequency in the MOS tube gate frequency is within the set range (1 / 5), the MOS tube is determined to be in an overcurrent state. At this time, the MCU adjusts the high level time in the output waveform through the gate drive unit to limit the MOS tube within the typical value range;

[0053] Typical Value The calculation formula is as follows:

[0054] ;

[0055] In the formula, Indicates the drain voltage of the MOS tube; Indicates the duty cycle of the PWM square wave output by the MCU; Indicates the internal resistance of the MOS tube.

[0056] Typical values ​​in this example .

[0057] The voltage difference between the source and drain of the MOS tube is read by a linear current limiter. When the voltage difference between the source and drain of the MOS tube is greater than the set value (40V), the parasitic diode undergoes reverse avalanche breakdown, and the MOS tube is determined to be in an overvoltage state.

[0058] Continuous operation with overcurrent or overvoltage will cause the MOS tube to heat up and trigger the over-temperature protection (in this embodiment, the over-temperature protection is triggered when the MOS tube reaches 170°C). When the collected gate frequency of the MOS tube is the same as the output frequency of the MCU and the drain of the MOS tube does not detect the frequency, it is determined that the MOS tube is in an over-temperature state, and the over-temperature protection unit turns off the gate drive unit to turn off the MOS tube. At this time, the temperature sensor is used to collect the temperature of the MOS tube in real time, and the MOS tube is reopened when the collected temperature is lower than the threshold (155°C).

[0059] At the same time, the control frequency can support up to 50kHZ, which is also applicable to some applications in automotive electronics that have strict requirements on noise.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A solenoid valve drive circuit based on intelligent MOS, characterized in that: It includes an MCU for outputting PWM square wave signals, a MOS driving module, an intelligent MOS, and a controlled solenoid valve. The MCU is electrically connected to the intelligent MOS via the MOS driving module. The intelligent MOS is connected between one end of the electromagnetic coil of the controlled solenoid valve and the ground terminal. The other end of the electromagnetic coil is electrically connected to the 12V power supply terminal, so as to realize the control of the on and off of the intelligent MOS via the MOS driving module based on the output high and low level signals of the MCU, so as to control the opening and closing of the controlled solenoid valve. The MOS driving module includes an interlocked conduction transistor group and an interlocked shutoff transistor group, the interlocked conduction transistor group includes a first conduction transistor and a second conduction transistor, the interlocked shutoff transistor group includes a first shutoff transistor and a second shutoff transistor, the first conduction transistor, the second conduction transistor, the first shutoff transistor and the second shutoff transistor are all NPN transistors; The base of the first conducting transistor is connected to the PWM square wave signal output pin of the MCU, the emitter of the first conducting transistor is grounded, the collector of the first conducting transistor is connected to the base of the first shut-off transistor, the emitter of the first shut-off transistor is grounded, the collector of the first shut-off transistor is connected to the base of the second conducting transistor, the collector of the second conducting transistor is connected to the 5V power supply terminal, the emitter of the second conducting transistor is connected to the collector of the second shut-off transistor, the emitter of the second shut-off transistor is grounded, the base of the second shut-off transistor is connected to the base of the first shut-off transistor via a clamping diode, and the base of the first shut-off transistor and the collector of the first conducting transistor are both connected to the 5V power supply terminal; The gate of the smart MOS is connected between the emitter of the second on transistor and the collector of the second off transistor, the drain of the smart MOS is connected in series with the electromagnetic coil and then electrically connected to the 12V power supply terminal, and the source of the smart MOS is grounded.

2. The solenoid valve driving circuit based on intelligent MOS according to claim 1, characterized in that: The intelligent MOS includes a MOS tube, a gate drive unit, an over-temperature protection unit, an over-voltage protection unit, an over-current protection unit and a temperature sensor for monitoring the temperature of the MOS tube. The input end of the gate drive unit is connected to the MOS drive module, and the output end of the gate drive unit is connected to the gate of the MOS tube. The gate drive unit is also connected to the over-temperature protection unit and the over-current protection unit respectively. The over-voltage protection unit is connected between the gate and the drain of the MOS tube. The over-current protection unit is connected between the source of the MOS tube and the gate drive unit.

3. The solenoid valve driving circuit based on intelligent MOS according to claim 2, characterized in that: The overcurrent protection unit is a linear current limiter for reading the voltage difference between the source and drain of the MOS tube to obtain the current of the MOS tube, and is used to adjust the driving waveform duty cycle of the gate driving unit according to the comparison result between the obtained MOS tube current and the typical value; The overvoltage protection unit is the parasitic diode of the MOS tube; The gate drive unit is the interface of the MCU.

4. The solenoid valve driving circuit based on intelligent MOS according to claim 3, characterized in that: The MCU is also connected to the gate and drain of the MOS tube respectively, and is used to collect the input frequency and output frequency of the MOS tube, and is used to combine with the output frequency of the MCU to realize fault diagnosis.

5. The solenoid valve driving circuit based on intelligent MOS according to claim 1, characterized in that: The frequency range of the PWM square wave signal output by the MCU is 2KHz-16KHz.

6. The working method of the solenoid valve driving circuit based on intelligent MOS as claimed in claim 4, characterized in that: It includes cyclically alternating high-level driving on and low-level driving off; The high-level driving conduction step is as follows: the MCU outputs a high-level signal to the base of the first conduction transistor, the first conduction transistor is turned on, the collector of the first conduction transistor is grounded, the first turn-off transistor is driven to be turned off, and the second turn-off transistor is turned off through the clamping diode. At this time, the 5V power supply end loads voltage to the base of the second conduction transistor, the second conduction transistor is turned on, and then the voltage is loaded to the gate of the MOS tube, the MOS tube is turned on, the electromagnetic coil is energized to form a path, and the controlled electromagnetic valve is opened; The low-level drive shutdown steps are as follows: the MCU outputs a low-level signal to the base of the first conduction transistor, the first conduction transistor is turned off, the collector of the first conduction transistor stops being grounded, the 5V power supply end loads voltage to the base of the first turn-off transistor, the first turn-off transistor is turned on, and the second turn-off transistor is driven to be turned on through the clamping diode. At this time, the base of the second conduction transistor is grounded through the first turn-off transistor, the second conduction transistor is turned off, the gate of the MOS tube is grounded through the second turn-off transistor, the MOS tube is turned off, the electromagnetic coil is powered off, and the controlled solenoid valve is closed.

7. The working method of the solenoid valve driving circuit based on intelligent MOS according to claim 6, characterized in that: In the working process of cyclically alternating high-level driving on and low-level driving off, fault diagnosis and fault action protection are performed based on the collected frequencies of the gate and drain of the MOS tube.

8. The working method of the solenoid valve driving circuit based on intelligent MOS according to claim 7, characterized in that: The MCU collects the drain and gate frequencies of the MOS tube through double-edge capture counting, reads the MCU register to obtain the MCU output frequency, and performs the following fault diagnosis and fault action protection: When the collected MOS tube gate frequency is the same as the MCU output frequency, and the MOS tube drain frequency and gate frequency are within the set error range, it is determined that the MOS tube is in a normal working state; When the collected MOS tube gate frequency is the same as the MCU output frequency, and the proportion of the MOS tube drain frequency in the MOS tube gate frequency is within the set range, the MOS tube is determined to be in an overcurrent state. At this time, the MCU adjusts the high level time in the output waveform through the gate drive unit to limit the MOS tube within the typical value range; When the voltage difference between the source and drain of the MOS tube is greater than the set value, the parasitic diode undergoes reverse avalanche breakdown, and the MOS tube is determined to be in an overvoltage state; When the collected MOS tube gate frequency is the same as the output frequency of the MCU, and the drain of the MOS tube does not monitor the frequency, it is determined that the MOS tube is in an over-temperature state, and the over-temperature protection unit turns off the gate drive unit to turn off the MOS tube. At this time, the temperature sensor is used to collect the temperature of the MOS tube in real time, and the MOS tube is reopened when the collected temperature is lower than the threshold.

9. The working method of the solenoid valve driving circuit based on intelligent MOS according to claim 8, characterized in that: Typical Value The calculation formula is as follows: ； In the formula, Indicates the drain voltage of the MOS tube; Indicates the duty cycle of the PWM square wave output by the MCU; Indicates the internal resistance of the MOS tube.

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