Motorcycle voltage regulator chip driving circuit with hot plug and overvoltage protection

Abstract

The invention belongs to the technical field of motorcycle voltage regulator chip circuits, and particularly relates to a motorcycle voltage regulator chip driving circuit with hot plug and overvoltage protection. Comprising an overvoltage detection module which is used for detecting and processing input three-phase electric signals PH1-PH3 and then outputting signals OV1-OV3; the driving module is used for inputting the signals OV1-OV3 output by the overvoltage detection module, judging whether the signals OV1-OV3 are low levels or not, and outputting high-level signals DRV1-DRV3 when the signals OV1-OV3 are low levels so as to conduct an off-chip switch tube and cut off the three-phase voltage; and the hot plug module is used for detecting the input three-phase electric signals PH1-PH3, and when the phase voltage is too high, the output signals DRV1-DRV3 are high levels. The motorcycle voltage regulator chip driving circuit solves many problems of an existing motorcycle voltage regulator chip driving circuit in the aspects of hot plugging, overvoltage protection and electromagnetic compatibility.

Description

Technical Field

[0001] The invention belongs to the technical field of motorcycle voltage regulator chip circuits, and in particular relates to a motorcycle voltage regulator chip drive circuit with hot plug and overvoltage protection. Background Art

[0002] In a motorcycle's electrical system, the voltage regulator chip driver circuit is a critical component for ensuring stable power supply. With the continuous advancement of motorcycle technology, the performance requirements for voltage regulator chip driver circuits are becoming increasingly stringent. They must not only precisely regulate voltage but also provide reliable hot-swap and overvoltage protection. However, existing on-chip integrated voltage regulator chip power supply circuits have exposed numerous technical shortcomings in practical applications.

[0003] From a hot-swap perspective, traditional voltage regulator chip driver circuits lack effective hot-swap protection mechanisms. When hot-swap operations are performed on a motorcycle (for example, to replace a damaged lamp or connect a new electronic accessory), the instantaneous current surge can easily damage the voltage regulator chip. This is because, during the hot-swap moment, parasitic inductance and capacitance in the circuit can cause voltage spikes and current surges. Existing MOS voltage regulators, however, lack targeted hot-swap protection when dealing with complex circuit transients. This can damage the power devices within the chip due to excessive voltage and current, compromising the normal operation of the voltage regulator and even the entire electrical system. Furthermore, interference signals generated during the hot-swap process can couple through the power supply lines to the voltage regulator chip's control circuitry, causing the chip to malfunction and output abnormal voltages, potentially posing a threat to other electrical devices.

[0004] Existing voltage regulator chip power supply circuits also have shortcomings in overvoltage protection. Voltage fluctuations are common in motorcycle use scenarios. When the motorcycle engine speed fluctuates significantly, the magneto output voltage fluctuates dramatically. Furthermore, during battery charging, a malfunction in the charging system can also cause abnormal voltage increases. For example, a traditional thyristor (SCR) short-circuit voltage regulator regulates the voltage by controlling the conduction of the thyristor (SCR) when the output voltage exceeds the normal range. However, this approach is slow to respond to sudden overvoltage conditions and cannot quickly limit the voltage to a safe range. Specifically, the SCR has a delay in turning on and off, and may not activate in time at the moment of overvoltage. This allows excessive voltage to persist across the load and the voltage regulator chip, increasing the risk of chip breakdown and damage to the load. Furthermore, some existing voltage regulator chips have a single overvoltage protection threshold setting, which cannot be flexibly adjusted to suit different application scenarios and load requirements. In some motorcycle electronic devices that have extremely high requirements for voltage stability (such as high-precision fuel injection control systems, advanced on-board communication modules, etc.), fixed overvoltage protection thresholds are difficult to meet diverse operating conditions. Once the voltage exceeds the protection range, the equipment will not work properly and may even cause permanent damage.

[0005] Given that the above-mentioned situation severely restricts the performance improvement and reliability guarantee of motorcycle electrical systems, it is extremely urgent to develop a high-performance motorcycle voltage regulator chip driver circuit with hot-swap and overvoltage protection functions to solve the above-mentioned problems. Summary of the Invention

[0006] The purpose of the present invention is to provide a motorcycle voltage regulator chip driver circuit with hot-swap and overvoltage protection. It closely focuses on the high-risk scenarios of motorcycle electrical systems and the defects of traditional technologies, and can effectively solve the following core problems: 1) Resolving the risk of circuit damage during hot-swap operations; 2) Overcoming vehicle electrical system failures caused by overvoltage; 3) Implementing an overvoltage detection circuit that quickly responds to load changes.

[0007] To solve the above technical problems, the present invention provides a motorcycle voltage regulator chip drive circuit with hot plug and overvoltage protection, comprising: The overvoltage detection module is used to detect the input three-phase electrical signals PH1~PH3 and process them to output signals OV1~OV3; a driving module, configured to input the signals OV1-OV3 output by the overvoltage detection module, and determine whether the signals OV1-OV3 are at a low level; and when the signals OV1-OV3 are at a low level, output high level signals DRV1-DRV3 to turn on the off-chip switch tube to cut off the three-phase voltage; The hot-swap module is used to detect the input three-phase electrical signals PH1~PH3. When the phase voltage is too high, the output signals DRV1~DRV3 are high level to turn on the off-chip switch tube to cut off the three-phase voltage.

[0008] Preferably, the overvoltage detection module includes: a phase voltage sampling circuit, a comparison circuit and a trigger circuit; wherein the phase voltage sampling circuit is used to perform resistance voltage division on the input three-phase electrical signals PH1~PH3 to obtain voltage signals CMP1~CMP3; the comparison circuit is used to compare the voltage signals CMP1~CMP3 with the reference voltage VREF, and output the comparison result to the trigger circuit, and output the signals OV1~OV3 through the trigger circuit.

[0009] Preferably, the phase voltage sampling circuit includes: resistors R1~R2 and a capacitor C1; one end of the resistor R2 is connected to the three-phase electrical signals PH1~PH3, and the other end is connected to one end of the resistor R1 and one end of the capacitor C1 and outputs voltage signals CMP1~CMP3, and the other end of the resistor R1 and the other end of the capacitor C1 are grounded.

[0010] Preferably, the resistance of the resistor R2 is 8 times the resistance of the resistor R1.

[0011] Preferably, the comparison circuit includes: PMOS transistors P1 to P4, NMOS transistors N1 to N10 and a current source Ib; the sources of the PMOS transistors P1 to P4 are connected to the power supply VCC, the gate and drain of the PMOS transistor P1 are connected to the gate of the PMOS transistor P2 and the drain of the NMOS transistor N4 and are connected to the digital control signal CMBP1, and the gate of the NMOS transistor N4 is connected to the reference voltage VREF; the drain of the PMOS transistor P2 is connected to the drains of the NMOS transistors N1 and N6 and generates a signal COMP1, the gate of the NMOS transistor N1 is connected to the digital control signal D1, the source of the NMOS transistor N1 is connected to the drain of the NMOS transistor N5, and the gates of the NMOS transistors N5 and N6 are connected to the voltage signal CMP1; the gate of the PMOS transistor P3 is connected to The digital control signal CMBP1 is inputted, the drain of the PMOS transistor P3 is connected to the drains of the NMOS transistors N2 and N8 to generate the signal COMP2, the gates of the NMOS transistors N8 and N7 are connected to the voltage signal CMP2, and the drain of the NMOS transistor N7 is connected to the source of the NMOS transistor N2; the gate of the PMOS transistor P4 is connected to the digital control signal CMBP1, the drain of the PMOS transistor P4 is connected to the drains of the NMOS transistors N3 and N10 to generate the signal COMP3, the gates of the NMOS transistors N10 and N9 are connected to the voltage signal CMP3, and the drain of the NMOS transistor N9 is connected to the source of the NMOS transistor N3; and the sources of the NMOS transistors N4 to N10 are connected to one end of a current source Ib, and the other end of the current source Ib is grounded.

[0012] Preferably, the trigger circuit includes: a buffer and a Schmitt trigger; wherein the signals COMP1~COMP3 are respectively connected to the input end of the buffer, the output end of the buffer is connected to the input end of the Schmitt trigger, and the output end of the Schmitt trigger outputs signals OV1~OV3 respectively.

[0013] Preferably, the hot-swap module includes: PMOS tubes P5~P8, NMOS tubes N11~N12 and resistors R3~R6; the source electrodes of the PMOS tubes P5 and PMOS tubes P7 are connected to one end of the resistor R3 and the resistor R35 and input the three-phase electrical signals PH1~PH3, the gate and drain electrodes of the PMOS tube P5 are connected to the source electrode of the PMOS tube P6, the gate and drain electrodes of the PMOS tube P6 are connected to the gate electrode of the PMOS tube P7, one end of the resistor R4, and the other end of the resistor R5, and the other end of the resistor R4 is connected to the gate electrode of the PMOS tube P7. The drain of the NMOS transistor N12 is connected to the gate and drain of the NMOS transistor N11, and one end of a diode string. The other end of the diode string is connected to the other end of the resistor R3. The sources of the NMOS transistors N11 and N12 are grounded. The drain of the PMOS transistor P7 is connected to the source of the PMOS transistor P8 and a grounded diode. The gate and drain of the PMOS transistor P8 are connected to one end of a resistor R6. The other end of the resistor R6 outputs signals DRV1 to DRV3.

[0014] Preferably, the diode string consists of five diodes connected in series.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. Regarding hot-swap protection, the present invention addresses the issue of current surges during hot-swap operations. Existing technologies lack effective mechanisms, and the resulting current surges during hot-swap operations often lead to chip damage and circuit malfunction. However, the present invention, through innovative design, constructs a complete hot-swap protection module. This module monitors current and voltage changes in the circuit in real time. At the moment of a hot-swap operation, it rapidly responds and initiates protective measures such as current limiting and clamping, effectively suppressing voltage spikes and current surges. This invention controls transient abnormal currents within a safe range, preventing them from damaging the voltage regulator chip and other electrical equipment, significantly improving circuit reliability during hot-swap operations.

[0016] 2. Regarding overvoltage protection, the present invention addresses issues such as slow response and fixed protection thresholds in conventional voltage regulator chip power circuits. This invention utilizes high-precision voltage detection and a fast-response overvoltage detection module, enabling rapid detection of overvoltage conditions and prompt triggering of protection actions, limiting voltage to within a safe threshold. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the overall structural block diagram of the motorcycle voltage regulator chip drive circuit provided by the present invention.

[0018] Figure 2 It is a circuit diagram of the phase voltage sampling circuit provided by the present invention.

[0019] Figure 3It is a circuit diagram of the comparison circuit and trigger circuit provided by the present invention.

[0020] Figure 4 This is a circuit diagram of the hot-swap module provided by the present invention. DETAILED DESCRIPTION

[0021] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description. It should be noted that the drawings are greatly simplified and not to exact scale, and are only used to facilitate and clearly illustrate the embodiments of the present invention.

[0022] like Figure 1 As shown, an embodiment of the present invention specifically provides a motorcycle voltage regulator chip driving circuit with hot plug and overvoltage protection, including: The overvoltage detection module is used to detect the input three-phase electrical signals PH1~PH3, filter them, and compare them with the on-chip reference voltage to output signals OV1~OV3. This overvoltage detection module circuit can realize real-time detection of the input signal; The driving module is used to input the signals OV1-OV3 output by the overvoltage detection module, and the output end of the driving module outputs signals DRV1-DRV3. When OV1-OV3 output a low level, the driving module outputs a high level signal DRV1-DRV3 to turn on the corresponding off-chip NMOS switch tube, thereby cutting off the three-phase voltage and stopping charging the subsequent battery.

[0023] The hot-swap module is used to detect the input three-phase electrical signals PH1~PH3. When the phase voltage is too high, the output signals DRV1~DRV3 are high level to turn on the off-chip switch tube to cut off the three-phase voltage.

[0024] like Figure 2 and Figure 3 As shown, the overvoltage detection module includes: a phase voltage sampling circuit, a comparison circuit and a trigger circuit; wherein the phase voltage sampling circuit is used to perform resistance voltage division on the input three-phase electrical signals PH1~PH3 to obtain voltage signals CMP1~CMP3; the comparison circuit is used to compare the voltage signals CMP1~CMP3 with the reference voltage VREF, and output the comparison result to the trigger circuit, and output signals OV1~OV3 through the trigger circuit.

[0025] like Figure 2As shown, the phase voltage sampling circuit includes: resistors R1~R2 and capacitor C1; one end of the resistor R2 is connected to the three-phase electrical signals PH1~PH3, and the other end is connected to one end of the resistor R1 and one end of the capacitor C1 and outputs voltage signals CMP1~CMP3, and the other end of the resistor R1 and the other end of the capacitor C1 are grounded.

[0026] like Figure 3 As shown, the comparison circuit includes: PMOS transistors P1 to P4, NMOS transistors N1 to N10 and a current source Ib; the sources of the PMOS transistors P1 to P4 are connected to the power supply VCC, the gate and drain of the PMOS transistor P1 are connected to the gate of the PMOS transistor P2 and the drain of the NMOS transistor N4 and are connected to the digital control signal CMBP1, and the gate of the NMOS transistor N4 is connected to the reference voltage VREF; the drain of the PMOS transistor P2 is connected to the drains of the NMOS transistors N1 and N6 and generates a signal COMP1, the gate of the NMOS transistor N1 is connected to the digital control signal D1, the source of the NMOS transistor N1 is connected to the drain of the NMOS transistor N5, and the gates of the NMOS transistors N5 and N6 are connected to the voltage signal CMP1; the gate of the PMOS transistor P3 is connected to The digital control signal CMBP1 is input, the drain of the PMOS transistor P3 is connected to the drains of the NMOS transistors N2 and N8 to generate the signal COMP2, the gates of the NMOS transistors N8 and N7 are connected to the voltage signal CMP2, and the drain of the NMOS transistor N7 is connected to the source of the NMOS transistor N2; the gate of the PMOS transistor P4 is connected to the digital control signal CMBP1, the drain of the PMOS transistor P4 is connected to the drains of the NMOS transistors N3 and N10 to generate the signal COMP3, the gates of the NMOS transistors N10 and N9 are connected to the voltage signal CMP3, and the drain of the NMOS transistor N9 is connected to the source of the NMOS transistor N3; and the sources of the NMOS transistors N4 to N10 are connected to one end of a current source Ib, and the other end of the current source Ib is grounded.

[0027] like Figure 3 As shown, the trigger circuit includes: a buffer and a Schmitt trigger; wherein the signals COMP1~COMP3 are respectively connected to the input end of the buffer, the output end of the buffer is connected to the input end of the Schmitt trigger, and the output end of the Schmitt trigger outputs signals OV1~OV3 respectively.

[0028] like Figure 4As shown, the hot-swap module includes: PMOS tubes P5~P8, NMOS tubes N11~N12 and resistors R3~R6; the source electrodes of the PMOS tubes P5 and PMOS tubes P7 are connected to one end of the resistor R3 and the resistor R35 and input the three-phase electrical signals PH1~PH3, the gate and drain electrodes of the PMOS tube P5 are connected to the source electrode of the PMOS tube P6, the gate and drain electrodes of the PMOS tube P6 are connected to the gate electrode of the PMOS tube P7, one end of the resistor R4, and the other end of the resistor R5, and the other end of the resistor R4 is connected to the The gate of the NMOS transistor N12 is connected to the gate and drain of the NMOS transistor N11 and one end of a diode string. The other end of the diode string is connected to the other end of the resistor R3. The sources of the NMOS transistors N11 and N12 are grounded. The drain of the PMOS transistor P7 is connected to the source of the PMOS transistor P8 and a grounded diode. The gate and drain of the PMOS transistor P8 are connected to one end of a resistor R6. The other end of the resistor R6 outputs signals DRV1 to DRV3. The diode string consists of five diodes connected in series.

[0029] It also includes the following working principles: When in use, the hot-swap module circuit detects phase voltage levels to protect the chip. If the phase voltage is too high during a sudden connection or disconnection of the magneto, DRV (i=1,2,3) outputs a high level, driving the off-chip switch to conduct, shutting off the three-phase power and stopping the charging of the power supply. This prevents damage to the voltage regulator caused by hot-swap operation and ensures a safe and reliable circuit system. Specifically, when the hot-swap module circuit is in operation, PHi (i=1,2,3) represents the three-phase power input signal. When the PHi (i=1,2,3) signal exceeds the hot-swap threshold voltage of 30V (the voltage of the diode string, which is five times the 6V Zener diode voltage), transistors N11 and N12 conduct, pulling the gate of transistor P7 low. This turns on transistor P7, and outputs DRVi (i=1,2,3) high.

[0030] When the overvoltage detection module circuit is in use, the three-phase voltage signals PH1, PH2, and PH3 are divided by resistors R1 and R2 (the resistance value of the resistors R2=8R1) to obtain CMP1, CMP2, and CMP3 voltage signals, and the voltage signals are compared with the reference voltage signal VREF=2.3V. When the input voltage exceeds the set threshold voltage, the COMP1, COMP2, and COMP3 signals will first flip, and then a feedback signal will turn on the digital tubes N1, N2, and N3, making the flipping of COMP1, COMP2, and COMP3 more stable. The comparison result is output to the subsequent Schmitt trigger through the COMP1, COMP2, and COMP3 signals after passing through a first-level buffer, and the final output is the OV1, OV2, and OV3 signals. Since the three-phase output voltage is divided by resistors R2 and R1 with a voltage division ratio of 8:1, the on-chip detection of the three-phase output voltage is an output voltage of 1 / 9, which is compared with the on-chip reference voltage VREF = 2.3V. When the three-phase output voltage is higher than 2.3*9=20.7V, overvoltage protection is activated. Since this circuit is an overvoltage protection circuit, when the output voltage of one phase of the three-phase motor is higher than 20.7V, the overvoltage detection module circuit will output low-level OV1, OV2 and OV3 signals to the driver module accordingly. The driver module outputs high-level signals DRV1~DRV3 to turn on the corresponding off-chip switch tube and stop charging the battery.

[0031] In summary, the present invention solves many of the problems of hot-plugging, overvoltage protection, and electromagnetic compatibility in existing motorcycle voltage regulator chip driver circuits. To address the problem of current surges during hot-plugging operations that can easily damage the chip and cause circuit malfunction, the present invention constructs a hot-plug protection module that monitors current and voltage changes in real time, rapidly initiating current limiting and clamping measures at the moment of hot-plugging to prevent abnormal current from damaging the voltage regulator chip and other electrical equipment. To address the slow response and fixed threshold issues of traditional overvoltage protection, the present invention utilizes high-precision voltage detection and a fast-response overvoltage detection module circuit to rapidly detect and activate overvoltage, and supports flexible threshold adjustment to effectively address various voltage anomalies. To address situations where electromagnetic interference can disrupt the stability of the electrical system, the present invention optimizes the circuit topology to ensure the normal operation of the system in complex electromagnetic environments, comprehensively improving the performance and reliability of the motorcycle voltage regulator chip driver circuit and ensuring the safe and stable operation of the motorcycle electrical system.

[0032] The above description is only a description of the preferred embodiments of the present invention and does not limit the scope of the present invention. Any changes and modifications made by ordinary technicians in the field of the present invention based on the above disclosure shall fall within the scope of protection of the claims.

Claims

1. A motorcycle voltage regulator chip drive circuit with hot-swap and overvoltage protection, characterized in that: include: The overvoltage detection module is used to detect the input three-phase electrical signals PH1~PH3 and process them to output signals OV1~OV3; a driving module, configured to input the signals OV1-OV3 output by the overvoltage detection module and determine whether the signals OV1-OV3 are at a low level; and when the signals OV1-OV3 are at a low level, the output end of the driving module outputs high-level signals DRV1-DRV3 to turn on the off-chip switch tube to cut off the three-phase voltage; The hot-swap module is used to detect the input three-phase electrical signals PH1~PH3. When the phase voltage is too high, the output signals DRV1~DRV3 are high level to turn on the off-chip switch tube to cut off the three-phase voltage.

2. A motorcycle voltage regulator chip drive circuit with hot-swap and overvoltage protection as claimed in claim 1, characterized in that: The overvoltage detection module includes: a phase voltage sampling circuit, a comparison circuit and a trigger circuit; wherein the phase voltage sampling circuit is used to perform resistance voltage division on the input three-phase electrical signals PH1~PH3 to obtain voltage signals CMP1~CMP3; the comparison circuit is used to compare the voltage signals CMP1~CMP3 with the reference voltage VREF, and output the comparison result to the trigger circuit, and output signals OV1~OV3 through the trigger circuit.

3. A motorcycle voltage regulator chip drive circuit with hot-swap and overvoltage protection as claimed in claim 2, characterized in that: The phase voltage sampling circuit includes: resistors R1~R2 and capacitor C1; one end of the resistor R2 is connected to the three-phase electrical signals PH1~PH3, and the other end is connected to one end of the resistor R1 and one end of the capacitor C1 to output voltage signals CMP1~CMP3, and the other end of the resistor R1 and the other end of the capacitor C1 are grounded.

4. A motorcycle voltage regulator chip drive circuit with hot-swap and overvoltage protection as claimed in claim 3, characterized in that: The resistance of the resistor R2 is 8 times the resistance of the resistor R1.

5. A motorcycle voltage regulator chip drive circuit with hot-swap and overvoltage protection as claimed in claim 2, characterized in that: The comparison circuit includes: PMOS transistors P1-P4, NMOS transistors N1-N10 and a current source Ib; the sources of the PMOS transistors P1-P4 are connected to the power supply VCC, the gate and drain of the PMOS transistor P1 are connected to the gate of the PMOS transistor P2 and the drain of the NMOS transistor N4 and are connected to the digital control signal CMBP1, and the gate of the NMOS transistor N4 is connected to the reference voltage VREF; the drain of the PMOS transistor P2 is connected to the drains of the NMOS transistors N1 and N6 and generates a signal COMP1, the gate of the NMOS transistor N1 is connected to the digital control signal D1, the source of the NMOS transistor N1 is connected to the drain of the NMOS transistor N5, and the gates of the NMOS transistors N5 and N6 are connected to the voltage signal CMP1; the gate of the PMOS transistor P3 is connected to the digital control signal D1. The digital control signal CMBP1 is connected to the drain of the PMOS transistor P3, which is connected to the drains of the NMOS transistors N2 and N8 to generate the signal COMP2. The gates of the NMOS transistors N8 and N7 are connected to the voltage signal CMP2, and the drain of the NMOS transistor N7 is connected to the source of the NMOS transistor N2. The gate of the PMOS transistor P4 is connected to the digital control signal CMBP1, the drain of the PMOS transistor P4 is connected to the drains of the NMOS transistors N3 and N10 to generate the signal COMP3. The gates of the NMOS transistors N10 and N9 are connected to the voltage signal CMP3, and the drain of the NMOS transistor N9 is connected to the source of the NMOS transistor N3. The sources of the NMOS transistors N4 to N10 are connected to one end of the current source Ib, and the other end of the current source Ib is grounded.

6. A motorcycle voltage regulator chip drive circuit with hot-swap and overvoltage protection as claimed in claim 5, characterized in that: The trigger circuit includes: a buffer and a Schmitt trigger; wherein signals COMP1~COMP3 are respectively connected to the input end of the buffer, the output end of the buffer is connected to the input end of the Schmitt trigger, and the output end of the Schmitt trigger outputs signals OV1~OV3 respectively.

7. A motorcycle voltage regulator chip drive circuit with hot-swap and overvoltage protection as claimed in claim 1, characterized in that: The hot-swap module includes: PMOS transistors P5-P8, NMOS transistors N11-N12 and resistors R3-R6; the source electrodes of the PMOS transistors P5 and PMOS transistors P7 are connected to one end of the resistor R3 and the resistor R35 and input the three-phase electrical signals PH1-PH3, the gate and drain electrodes of the PMOS transistor P5 are connected to the source electrode of the PMOS transistor P6, the gate and drain electrodes of the PMOS transistor P6 are connected to the gate electrode of the PMOS transistor P7, one end of the resistor R4, and the other end of the resistor R5, and the other end of the resistor R4 is connected to the The drain of the NMOS transistor N12 is connected to the gate and drain of the NMOS transistor N11 and one end of the diode string. The other end of the diode string is connected to the other end of the resistor R3. The sources of the NMOS transistors N11 and N12 are grounded. The drain of the PMOS transistor P7 is connected to the source of the PMOS transistor P8 and a grounded diode. The gate and drain of the PMOS transistor P8 are connected to one end of the resistor R6. The other end of the resistor R6 outputs signals DRV1 to DRV3.

8. A motorcycle voltage regulator chip drive circuit with hot-swap and overvoltage protection as claimed in claim 7, characterized in that: The diode string comprises five diodes connected in series.

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