M5 inductance type proximity switch

Abstract

The utility model relates to the technical field of proximity switches, in particular to an M5 inductance type proximity switch, which comprises a shell, an induction inductance contact, a sensor main body circuit board and a power supply signal line, the induction inductance contact, the sensor main body circuit board and the power supply signal line are sequentially and electrically connected in the shell, and an inductor is arranged in the induction inductance contact and is electrically connected with a capacitor at the top end of the sensor main body circuit board. And meanwhile, the sensor is connected to one end of a shell sleeved on the sensor main body circuit board, and a power supply signal line is led out from the other end of the shell for intelligent calibration detection. According to the M5 inductance type proximity switch, the performance is remarkably improved by optimizing circuit design and integrating intelligent functions in the aspects of detection precision, environmental adaptability, intelligent level and the like.

Description

Technical Field

[0001] This utility model relates to the field of proximity switch technology, and in particular to an M5 inductive proximity switch. Background Technology

[0002] A proximity switch is an electronic device that detects the presence or location of an object without physical contact, and is widely used in industrial automation, security, and other fields. Traditional inductive proximity switches generate an alternating electromagnetic field using an LC oscillator. When a metal object approaches, eddy currents are generated on its surface, causing the energy of the oscillation circuit to attenuate or stop oscillating, thus triggering a switching signal. However, existing inductive proximity switches have the following problems:

[0003] Insufficient detection accuracy: Traditional peak detection circuits are affected by diode voltage drop and operational amplifier bias current, resulting in low signal acquisition accuracy, especially in rapidly changing signal scenarios where the response speed is insufficient.

[0004] Temperature drift affects stability: Changes in ambient temperature will cause changes in the Q value of the oscillation circuit, which in turn affects the stability of the detection distance. Traditional designs lack an effective temperature compensation mechanism.

[0005] The calibration process is complex: existing switches require frequent manual calibration at the factory or during use, have low intelligence, and increase maintenance costs and time. Summary of the Invention

[0006] The main objective of this invention is to overcome the shortcomings of existing technologies and provide an M5 inductive proximity switch. This M5 inductive proximity switch significantly improves performance in terms of detection accuracy, environmental adaptability, and intelligence level through optimized circuit design and integrated intelligent functions.

[0007] The technical solution adopted by this utility model to achieve its technical purpose is: an M5 inductive proximity switch, including a housing and an inductive contact, a sensor main circuit board and a power signal line connected in sequence in the housing;

[0008] The inductive contact has an inductance and is electrically connected to the capacitor at the top of the main circuit board of the sensor. It is also connected to one end of the housing sleeved on the main circuit board of the sensor. One end of the inductive contact is fixedly installed in the housing, and the other end of the housing leads out a power signal line for intelligent calibration detection.

[0009] Preferably, the other end of the housing and the power signal line are encapsulated by an inverted cone, and the power signal line is further shielded by an insulating enameled wire.

[0010] Preferably, the main circuit board of the sensor circuit includes an LC oscillator, a peak detector, a differential amplifier, a microcontroller, an NTC temperature acquisition section, and an intelligent calibration and detection section.

[0011] The sensor's main circuit board consists of multiple functional modules, including an LC oscillator, a peak detector, a differential amplifier, a microcontroller, an NTC temperature acquisition unit, and an intelligent calibration and detection unit. The LC oscillator generates an alternating electromagnetic field for detecting metallic objects; the peak detector detects signal peaks to improve accuracy; the differential amplifier amplifies signal differences to enhance detection sensitivity; the microcontroller controls the entire system and processes signals; the NTC temperature acquisition unit monitors ambient temperature and compensates for temperature drift; and the intelligent calibration and detection unit automatically calibrates the detection distance, reducing manual intervention.

[0012] Preferably, the LC oscillator includes a current-limiting resistor R1 with a resistance of 220Ω, an inductor L1 with an inductance of 16µH connected to the current-limiting resistor R1, a capacitor C3 with a capacitance of 2.2nF connected in parallel with the inductor L1, and a capacitor C4 with a capacitance of 10nF connected to one end of the LC circuit.

[0013] A current-limiting resistor R1 is connected in series with an inductor L1, and an inductor L1 is connected in parallel with a capacitor C3. The current-limiting resistor R1 limits the current and protects the circuit. The inductor L1 and capacitor C3 form a resonant circuit, generating an alternating magnetic field. Capacitor C4 is connected to an LC oscillator, and capacitor C4 adjusts the oscillation frequency to optimize detection performance.

[0014] Preferably, the peak detector includes an operational amplifier U6 of model CBM8091AST5, a capacitor C5 with a capacitance of 100nF connected to pin 5 of operational amplifier U6, a Schottky diode D1 of model WSB5524D-2 / TR connected between pins 1 and 4 of operational amplifier U6, a Schottky diode D2 directly connected to pin 1 of operational amplifier U6, a capacitor C6 with a capacitance of 5pF and a resistor R3 with a resistance of 1K connected in parallel with Schottky diodes D1 and D2, a resistor R4 with a resistance of 0 connected to Schottky diode D2, and a capacitor C7 with a capacitance of 100nF connected to resistor R4.

[0015] Operational amplifier U6 is connected to components such as capacitor C5, Schottky diodes D1 and D2, capacitor C6, resistor R3, resistor R4, and capacitor C7. Operational amplifier U6 amplifies the signal and cancels the effect of diode voltage drop; Schottky diodes D1 and D2 clamp the signal and improve the response speed; capacitor C7 stores the peak voltage and improves detection accuracy.

[0016] Preferably, the differential amplifier includes a precision operational amplifier U3 (model COS1333TRC), a resistor R12 (510KΩ) and a resistor R5 (51KΩ) connected to pin 3 of the precision operational amplifier U3, a capacitor C8 (100nF) connected to pin 5 of the precision operational amplifier U3, a resistor R11 (1KΩ) connected to pin 1 of the precision operational amplifier U3 in series with a capacitor C10 (47nF), a resistor R6 (510KΩ) connected between pins 1 and 4 of the precision operational amplifier U3, a resistor R7 (51KΩ) directly connected to pin 4 of the precision operational amplifier U3, a resistor R7 in series with a resistor R8 (0KΩ), a resistor R9 (3.1KΩ), a resistor R10 (3.2KΩ), and a capacitor C9 (10nF) in parallel.

[0017] The precision operational amplifier U3 is connected to components such as resistors R12 and R5, and capacitor C8. The precision operational amplifier U3 amplifies the differential signal and improves the detection sensitivity. The resistor and capacitor network adjusts the amplification factor and filtering to optimize signal processing.

[0018] Preferably, the microcontroller includes a 32-bit MCU microcontroller U1 with model number CW32F030F8V7, a crystal oscillator X1 with a frequency of 8MHz, and capacitors C1 and C2 with a capacitance of 12pF connected in parallel across the crystal oscillator X1.

[0019] The microcontroller U1 is connected to the crystal oscillator X1, capacitors C1 and C2. The microcontroller U1 controls the entire system and processes signals, while the crystal oscillator X1 and capacitors C1 and C2 provide a stable clock signal.

[0020] Preferably, the NTC temperature acquisition section includes a resistor R14 with a resistance of 10kΩ, and the resistor R14 is connected in parallel with a thermistor R15 and a capacitor C13 with a capacitance of 100nF.

[0021] Resistor R14 and thermistor R15 are connected in parallel, and capacitor C13 and thermistor R15 are connected in parallel. Thermistor R15 monitors changes in ambient temperature, and capacitor C13 filters and stabilizes the temperature signal.

[0022] Preferably, the intelligent calibration and detection section includes a bipolar transistor Q1 of model EMX1T2R, a resistor R19 with a resistance of 5.1kΩ connecting pins 2 and 3 of bipolar transistor Q1, a resistor R18 with a resistance of 5.1kΩ between pins 1 and 5 of bipolar transistor Q1, a resistor R15 with a resistance of 20kΩ connected to pin 6 of bipolar transistor Q1, a resistor R17 with a resistance of 6.8kΩ connected to pin 1 of bipolar transistor Q1, a comparator U5 of model GS331-TR, a capacitor C16 with a capacitance of 100nF connected to pin 5 of comparator U5, and pin 3 of comparator U5 is connected to pin 6 of bipolar transistor Q1.

[0023] Bipolar transistor Q1 is connected to resistors R18, R19, R15, R17, comparator U5, and other components. Bipolar transistor Q1 controls the output of the calibration signal, and comparator U5 determines the proximity of metal and triggers the calibration program.

[0024] Compared with the prior art, the beneficial effects of this utility model are:

[0025] The M5 inductive proximity switch employs an improved peak detector (such as a buffer structure and Schottky diode clamping technology) to offset the effect of diode voltage drop, thereby improving signal acquisition accuracy and response speed, and achieving high-precision detection and dynamic balance.

[0026] The M5 inductive proximity switch features enhanced temperature stability. It integrates an NTC temperature acquisition unit to monitor the ambient temperature in real time and dynamically adjusts the threshold through a microcontroller, effectively compensating for temperature drift and ensuring the stability of the detection distance.

[0027] The M5 inductive proximity switch features intelligent calibration. Through the collaborative work of a comparator and a microcontroller, it automatically determines the proximity of metal and triggers the calibration program, reducing manual intervention and improving factory efficiency and ease of use.

[0028] The M5 inductive proximity switch features an optimized structure, with an inverted conical housing and insulated enameled wire shielding design, enhancing its sealing and anti-interference capabilities, making it suitable for complex industrial environments. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this utility model, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a front view schematic diagram of the overall structure of the M5 inductive proximity switch.

[0031] Figure 2 This is a circuit diagram of the LC oscillator, peak detector, and differential amplifier in the main circuit board of the sensor circuit.

[0032] Figure 3 This is the circuit schematic of the microcontroller in the main circuit board of the sensor circuit.

[0033] Figure 4 This is a circuit diagram of the NTC temperature acquisition section in the main circuit board of the sensor circuit.

[0034] Figure 5 This is a circuit diagram of the intelligent calibration and detection section in the main circuit board of the sensor circuit.

[0035] The components include: 1. Inductive contact; 2. Housing; 3. Inverted cone; 4. Power signal line; 5. Insulated enameled wire. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments. However, it should be understood that the specific embodiments described herein are merely illustrative of the present utility model and are not intended to limit its scope. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the present utility model.

[0037] In the description of this utility model, it should be noted that when an element is referred to as being "fixed to" or "set on" another element, it can be directly on or indirectly on the other element. When an element is referred to as being "connected to" another element, it can be directly connected to or indirectly connected to the other element.

[0038] In the description of this utility model, it should be noted that the terms "center," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating the orientation or positional relationship, are based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the utility model product is in use. They are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this utility model. Furthermore, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this utility model, "multiple" means two or more, unless otherwise explicitly specified. "Several" means one or more, unless otherwise explicitly specified.

[0039] In the description of this utility model, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances. Example:

[0040] Please see Figures 1-5 An M5 inductive proximity switch includes a housing 2 and an inductive contact 1, a sensor main circuit board, and a power signal line 4, which are electrically connected sequentially within the housing 2. The inductive contact 1 has an inductance and is electrically connected to a capacitor at the top of the sensor main circuit board. It is also connected to one end of the housing 2, which is sleeved on the sensor main circuit board. One end of the inductive contact 1 is fixedly installed inside the housing 2. The other end of the housing 2 is encapsulated by an inverted cone 3 and a power signal line 4 is led out for intelligent calibration detection. The power signal line 4 is also shielded by an insulating enameled wire 5.

[0041] The main circuit board of the sensor circuit includes an LC oscillator, a peak detector, a differential amplifier, a microcontroller, an NTC temperature acquisition section, and an intelligent calibration and detection section.

[0042] Furthermore, in this embodiment, the LC oscillator includes a current-limiting resistor R1 with a resistance of 220Ω, an inductor L1 with an inductance of 16µH connected to the current-limiting resistor R1, a capacitor C3 with a capacitance of 2.2nF connected in parallel with the inductor L1, and a capacitor C4 with a capacitance of 10nF connected to one end of the LC circuit.

[0043] Furthermore, in this embodiment, the peak detector includes an operational amplifier U6 of model CBM8091AST5, a capacitor C5 with a capacitance of 100nF connected to pin 5 of operational amplifier U6, a Schottky diode D1 of model WSB5524D-2 / TR connected between pins 1 and 4 of operational amplifier U6, a Schottky diode D2 directly connected to pin 1 of operational amplifier U6, a capacitor C6 with a capacitance of 5pF and a resistor R3 with a resistance of 1K connected in parallel with Schottky diodes D1 and D2, a resistor R4 with a resistance of 0 connected to Schottky diode D2, and a capacitor C7 with a capacitance of 100nF connected to resistor R4.

[0044] Furthermore, in this embodiment, the differential amplifier includes a precision operational amplifier U3 of model COS1333TRC, a resistor R12 with a resistance of 510K connected to pin 3 of the precision operational amplifier U3, a resistor R5 with a resistance of 51K connected to pin 3, a capacitor C8 with a capacitance of 100nF connected to pin 5 of the precision operational amplifier U3, a resistor R11 with a resistance of 1K connected to pin 1 of the precision operational amplifier U3 in series with a capacitor C10 with a capacitance of 47nF, a resistor R6 with a resistance of 510K connected between pins 1 and 4 of the precision operational amplifier U3, a resistor R7 with a resistance of 51K directly connected to pin 4 of the precision operational amplifier U3, a resistor R7 in series with a resistor R8 with a resistance of 0, and a resistor R9 with a resistance of 3.1K and a resistor R10 with a resistance of 3.2K connected in parallel with a capacitor C9 with a capacitance of 10nF.

[0045] Furthermore, in this embodiment, the microcontroller includes a 32-bit MCU microcontroller U1 with model number CW32F030F8V7, a crystal oscillator X1 with a frequency of 8MHz, and capacitors C1 and C2 with a capacitance of 12pF connected in parallel across the crystal oscillator X1.

[0046] Furthermore, in this embodiment, the NTC temperature acquisition section includes a resistor R14 with a resistance of 10kΩ, and the resistor R14 is connected in parallel with a thermistor R15 and a capacitor C13 with a capacitance of 100nF.

[0047] Furthermore, in this embodiment, the intelligent calibration and detection section includes a bipolar transistor Q1 of model EMX1T2R, a resistor R19 with a resistance of 5.1kΩ connecting pins 2 and 3 of bipolar transistor Q1, a resistor R18 with a resistance of 5.1kΩ between pins 1 and 5 of bipolar transistor Q1, a resistor R15 with a resistance of 20kΩ connected to pin 6 of bipolar transistor Q1, a resistor R17 with a resistance of 6.8kΩ connected to pin 1 of bipolar transistor Q1, a comparator U5 of model GS331-TR, and a capacitor C16 with a capacitance of 100nF connected to pin 5 of comparator U5, and pin 3 of comparator U5 is connected to pin 6 of bipolar transistor Q1.

[0048] The working principle and specific usage process of the M5 inductive proximity switch:

[0049] S1. First, a PWM wave is generated from the 32-bit MCU microcontroller U1 and output to the LC resonator;

[0050] When no metal is near, the circuit resonates, the impedance is at its maximum, and the inductor voltage is high. When metal is near the inductor of the inductor contact 1, the rising / falling edge of the square wave generates an alternating magnetic field and eddy currents, causing the equivalent inductance L1 to decrease. The circuit becomes detuned, the impedance decreases, and the corresponding inductor voltage decreases, resulting in an oscillating voltage waveform.

[0051] S2, Schottky diode D2, resistor R4, and capacitor C7 form a basic peak detection circuit. When the voltage signal is in the positive half-cycle, it is greater than the initial voltage of the capacitor. Schottky diode D2 conducts, and the voltage on capacitor C7 rises accordingly to reach the peak value. After that, the voltage signal begins to drop. Since the voltage on the capacitor is still at its peak value, which is greater than the falling voltage signal, Schottky diode D2 is cut off and conducts. Capacitor C7 has no discharge circuit and maintains a certain fixed value. However, due to the leakage current backflow of the diode, the voltage signal will drop until the inductor voltage signal reaches the next peak value. Only then will the capacitor voltage rise and retain the next peak value.

[0052] To prevent the voltage signal frequency from being too fast and missing the peak during the voltage signal drop process, a load is applied to capacitor C7 to discharge it quickly. At the same time, an operational amplifier U6 is added and the Schottky diode D2 is configured as a buffer structure to keep the positive and negative input voltages consistent in order to offset the impact of diode voltage drop on the acquisition accuracy.

[0053] However, even with the addition of operational amplifier U6, the capacitor still significantly affects the bias current and output slew rate of operational amplifier U6, which in turn have a significant impact on fast signal detection. Therefore, a Schottky diode D1 is added to the feedback loop to clamp the maximum input signal of operational amplifier U6 by subtracting the diode voltage drop, thereby improving the response speed and achieving dynamic balance.

[0054] S3. After the peak signal processed by the peak detector is filtered by capacitor C7, the difference between it and the reference voltage of 5V at the other input terminal of the precision operational amplifier U3 is amplified by 10 times and acquired by the ADC of the PA2 port of the 32-bit MCU microcontroller U1. It is then compared with the set threshold in the microprocessor.

[0055] When the metal gets close enough to the detection distance, the inductor voltage drops sufficiently. After peak detection, differential amplification, and conversion, the voltage reaches the calibrated detection distance threshold, resulting in a proximity detection trigger signal.

[0056] S4. Secondly, MCU_OUT serves as the microprocessor's output port, outputting a signal indicating that metal is approaching.

[0057] If the voltage is high, metal will be near it, and the gate of the MOS transistor on the right side of the bipolar transistor Q1 will be turned on. The source and drain will be connected, which will ground the positive input terminal of the comparator U5 (pin 3), which is less than the other negative input terminal of VCC_5V, thus outputting a low level.

[0058] Similarly, if MCU_OUT is low, there is no metal nearby and the MOSFET is not conducting. Then the positive input of comparator U5 is the same as 24V of VIN, which is higher than 5V of the negative input. Therefore, the output is high. So when there is no metal nearby, the output PB5 port of comparator U5 is always high and does not need to be calibrated.

[0059] When metal approaches, the MCU_OUT outputs a judgment signal. When the output PB5 port of comparator U5 is at a low level, the microprocessor needs to run the calibration program. Calibration is the standard setting of the detection distance when the sensor is manufactured. While OUT is led out as the metal proximity signal line, the microprocessor can also know whether calibration is needed through the PB5 port.

[0060] S5. Finally, the NTC thermistor R15 is connected to the 32-bit MCU microcontroller U1 through the TEMP port to collect and monitor the ambient temperature of the proximity switch, compensate for temperature drift, and intelligently adjust the threshold. This solves the problem of the Q value of the oscillation circuit changing due to temperature changes, thus affecting the detection distance and keeping the detection distance stable.

[0061] It should be noted that although the above embodiments have been described herein, this does not limit the scope of patent protection for this utility model. Therefore, any changes and modifications made to the embodiments described herein based on the innovative concept of this utility model, or equivalent structural, procedural, or functional transformations made using the content of this utility model's specification and drawings, directly or indirectly applying the above technical solutions to other related technical fields, are all included within the scope of protection of this utility model patent.

Claims

1. An M5 inductive proximity switch characterized by: The sensor comprises a shell (2), an inductive sensing head (1), a sensor main circuit board and a power signal line (4) connected in sequence in the shell (2); The inductive sensing head (1) is provided with an inductor, which is electrically connected with a capacitor at the top of the sensor main circuit board and connected to one end of the shell (2) sleeved on the sensor main circuit board, and the other end of the shell (2) leads out the power signal line (4) for intelligent calibration detection.

2. An M5 inductive proximity switch according to claim 1, characterized in that: The other end of the shell (2) and the power signal line (4) are packaged by an inverted cone (3), and the power signal line (4) is further sleeved with an insulating enamel wire (5) for shielding.

3. The M5 inductive proximity switch of claim 1, wherein: The sensor main circuit board comprises an LC oscillator, a peak detector, a differential amplifier, a microcontroller, an NTC temperature acquisition part and an intelligent calibration detection part.

4. An M5 inductive proximity switch according to claim 3, characterised in that: The LC oscillator comprises a current limiting resistor R1 with a resistance of 220, an inductor L1 with an inductance of 16uH connected with the current limiting resistor R1, a capacitor C3 with a capacitance of 2.2nF connected in parallel with the inductor L1, and a capacitor C4 with a capacitance of 10nF connected with one end of the LC.

5. An M5 inductive proximity switch according to claim 3, characterized in that: The peak detector comprises an operational amplifier U6, a capacitor C5 with a capacitance of 100nF connected with the 5th pin of the operational amplifier U6, a Schottky diode D1 connected between the 1st pin and the 4th pin of the operational amplifier U6, a Schottky diode D2 directly connected with the 1st pin of the operational amplifier U6, a capacitor C6 with a capacitance of 5pF and a resistor R3 with a resistance of 1K connected in parallel on the Schottky diode D1 and the Schottky diode D2, a resistor R4 with a resistance of 0 connected with the Schottky diode D2, and a capacitor C7 with a capacitance of 100nF connected with the resistor R4.

6. An M5 inductive proximity switch according to claim 3, characterized in that: The differential amplifier comprises a precision operational amplifier U3, a resistor R12 with a resistance of 510K and a resistor R5 with a resistance of 51K connected with the 3rd pin of the precision operational amplifier U3, a capacitor C8 with a capacitance of 100nF connected with the 5th pin of the precision operational amplifier U3, a resistor R11 with a resistance of 1K connected in series with a capacitor C10 with a capacitance of 47nF and connected with the 1st pin of the precision operational amplifier U3, a resistor R6 with a resistance of 510K connected between the 1st pin and the 4th pin of the precision operational amplifier U3, a resistor R7 with a resistance of 51K directly connected with the 4th pin of the precision operational amplifier U3, the resistor R7 connected in series with a resistor R8 with a resistance of 0, and a resistor R9 with a resistance of 3.1K and a resistor R10 with a resistance of 3.2K connected in parallel with the capacitor C9 with a capacitance of 10nF.

7. The M5 inductive proximity switch of claim 3, wherein: The microcontroller comprises a 32-bit MCU microcontroller U1, a crystal oscillator X1 with a frequency of 8MHz, a capacitor C1 with a capacitance of 12pF and a capacitor C2 with a capacitance of 12pF connected in parallel on both sides of the crystal oscillator X1.

8. The M5 inductive proximity switch of claim 3, wherein: The NTC temperature acquisition part comprises a resistor R14 with a resistance of 10k, the resistor R14 connected with a thermistor R15 and a capacitor C13 with a capacitance of 100nF connected in parallel.

9. An M5 inductive proximity switch according to claim 3, characterized in that: The intelligent calibration detection part includes a bipolar transistor Q1, a resistance R19 with a resistance value of 5.1k connected to the 2nd and 3rd pins of the bipolar transistor Q1, a resistance R18 with a resistance value of 5.1k added between the 1st and 5th pins of the bipolar transistor Q1, a resistance R15 with a resistance value of 20k connected to the 6th pin of the bipolar transistor Q1, a resistance R17 with a resistance value of 6.8k connected to the 1st pin of the bipolar transistor Q1, a comparator U5, and a capacitor C16 with a capacitance value of 100nF connected to the 5th pin of the comparator U5, and the 3rd pin of the comparator U5 is connected to the 6th pin of the bipolar transistor Q1.

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