PPTC resettable fuse applied to over-current and over-voltage protection circuit of wrist-worn equipment

Abstract

The utility model belongs to the technical field of circuits, and particularly relates to an over-current and over-voltage protection circuit with a PPTC resettable fuse applied to wrist-worn equipment. A protection circuit is designed to be installed in a plastic shell of a magnetic attraction charging head containing an outwards-protruding spring ejector pin or installed in a plastic shell of a USB connector, and the protection circuit is a combination of a PPTC resettable fuse and a TVS tube. Due to the adoption of the PPTC device and the compact design, the number of used components is small, the safety and reliability of related products can be greatly improved, the cost is greatly reduced, the occupied PCB area and space are greatly reduced, and the design of engineers is further facilitated.

Description

Technical Field

[0001] The utility model belongs to the technical field of circuits, and in particular relates to an overcurrent and overvoltage protection circuit of a wrist-worn device using a PPTC resettable fuse. Background Art

[0002] Existing wrist-worn device products, such as wrist-worn smart phones, wrist-worn student-specific mobile phones, wrist-worn pulse meter products, wrist-worn disabled elderly positioning and tracking products, wrist-worn blood pressure monitors, wrist-worn blood glucose monitors, wrist-worn heart monitors and future related wrist-worn digital products, are all worn on the user's wrist. The devices are small in size and contain lithium batteries, so the lithium batteries need to be charged regularly to ensure the normal operation of the devices. Due to their small size, there is no space and it is impossible to design and install protection circuit devices inside them. Their chargers are all universal mobile phone chargers or high-voltage and high-current fast chargers. Therefore, for the sake of wide application, charger manufacturers will not design current and voltage limiting circuits at their charging output ends, let alone protection circuits. Therefore, they can only design protection circuits on the charging lines of the above-mentioned product devices to achieve the functional purpose of protecting the charger devices. Utility Model Content

[0003] The purpose of the utility model is to provide a PPTC resettable fuse for use in an overcurrent and overvoltage protection circuit of a wrist-worn device. By designing a PPTC resettable fuse overcurrent and overvoltage protection circuit inside the magnetic charging head or inside the USB head at the other end of the charging cable, the above-mentioned problems can be avoided and the entire system circuit can be protected from damage, thereby ensuring the safety of the charger.

[0004] In order to achieve the above-mentioned purpose, the utility model adopts the following technical solutions: a PPTC resettable fuse and a magnetic charging head and circuit for a wrist-worn device product, including a charging cable, a USB connector connected to one end of the charging cable, and a magnetic charging head connected to the other end of the charging cable, the magnetic charging head is connected to the wrist-worn device, and a PPTC resettable fuse overcurrent and overvoltage protection circuit is provided in the magnetic charging head, and the PPTC resettable fuse overcurrent and overvoltage protection circuit includes a PPTC resettable fuse and a TVS tube, the PPTC resettable fuse is connected in series to the positive line of the charging cable, and the other end is divided into two paths, one is connected to the positive electrode of the TVS tube, and the other is connected to the first spring pin, and the negative electrode of the TVS tube is divided into two paths, one is connected to the negative electrode of the charging cable, and the other is connected to the second spring pin. Because small-volume watches or watch-like devices and charger products cannot be equipped with additional protection devices, the relevant protection circuit can only be designed inside the magnetic charging head connection line.

[0005] Furthermore, the TVS tube adopts a medium-power unidirectional TVS tube or a bidirectional TVS tube with a trigger voltage of 7.0V.

[0006] Furthermore, the PPTC resettable fuse is a PPTC resettable fuse of special model WHSMD0603-050.

[0007] Furthermore, the magnetic charging head is also provided with two strong magnetic blocks with opposite polarities, and the magnetic blocks are made of φ3 NdFeB strong magnetic sheets. The strong magnetic charging head is used as the charging contact connector of the watch, which is simple and convenient to use, because two reverse strong magnetic attraction methods are used to avoid reverse connection. The strong attraction force of the magnet is used to make the pin electrode of the electrical connection reliably connected to achieve the charging purpose.

[0008] Furthermore, the first spring pin and the second spring pin are round-headed convex spring pins, which are φ1.5×6mm dome-top gold-plated embedded spring pins, with 3-5mm exposed and 2mm buried. Because the edge of a watch or a watch-like device is arc-shaped, the spring pin of the magnetic charging head needs to be long enough and must be exposed to ensure reliable and effective electrical connection.

[0009] A PPTC resettable fuse is applied to an overcurrent and overvoltage protection circuit of a wrist-worn device, including a charging cable, a USB connector connected to one end of the charging cable, and a magnetic charging head connected to the other end of the charging cable, wherein the magnetic charging head is connected to the wrist-worn device, and a PPTC resettable fuse overcurrent and overvoltage protection circuit is provided in the USB connector, and the PPTC resettable fuse overcurrent and overvoltage protection circuit includes a PPTC resettable fuse and a TVS tube, wherein one end of the PPTC resettable fuse is connected to the positive pole of the charging input terminal, and the other end is divided into two paths, one connected to the positive pole of the TVS tube, and the other connected to the positive pole of the charging cable, and the negative pole of the TVS tube is divided into two paths, one connected to the negative pole of the charging input terminal, and the other connected to the negative pole of the charging cable. Since additional protection devices cannot be installed inside small-sized watches or watch-like devices and charger products, the relevant protection circuit can only be designed inside the USB connector.

[0010] The utility model is a protection circuit with few components, high reliability, not easy to damage, anti-fool or anti-reverse connection function, anti-high voltage, and can effectively extend the life of the small equipment system. It can control the current limiting in advance, so that the system circuit can be timely limited and protected. Due to the use of PPTC devices and compact design, not only the number of components used is small, but also the safety and reliability of related products can be greatly improved, the cost can be greatly reduced, the occupied PCB area and space can be greatly reduced, and it is more conducive to the design of engineers, and it can be produced automatically and on a large scale. The utility model is small in size, low in cost, high in reliability, and makes repair and maintenance simpler, and the market competitive advantage will be significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is a schematic diagram of the first embodiment of the utility model;

[0012] Figure 2 This is a schematic diagram of the second embodiment of the utility model;

[0013] In the picture: 1. USB connector; 2. Magnetic charging head; 3. PPTC resettable fuse; 4. TVS tube; 5. First spring pin; 6. Second spring pin; 7. Magnetic block. DETAILED DESCRIPTION

[0014] In order to facilitate the understanding of the present invention, the present invention will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present invention are given in the drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0015] It should be noted that when an element is referred to as being "fixed to" another element, it may be directly on the other element or there may be an intermediate element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate element at the same time.

[0016] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0017] Because watches or watch-like devices can only be universally charged with 5V input, and chargers have 5V output, as well as 6V, 9V, 12V, 15V, 19V and other high-voltage fast-charging chargers. These high-voltage chargers have no obvious or special differences in appearance and size, and are easily used incorrectly. When applied to high-voltage chargers, watches or watch-like devices will be burned by high voltage and high current, so an overcurrent and overvoltage protection circuit must be designed. This circuit must also be designed inside the magnetic charging head to achieve the protection purpose.

[0018] The over-current and over-voltage protection circuit is a combination of a PPTC self-resettable fuse 3 and a TVS tube 4. Through a clever and compact design, it is combined into a unit circuit and can be made into a modular device. It can simultaneously complete short-circuit and over-voltage protection, with a simple circuit, few components, accurate control, high safety, high reliability, and can effectively extend the service life of the product. It does not require maintenance and takes up a small space. With this special combination, it can prevent foolishness and reverse connection, and can also prevent damage from overvoltage. It can be automated and mass-produced, and the design and production efficiency of engineers can be improved year-on-year.

[0019] The protection circuit design of the utility model is installed inside the plastic shell of the magnetic charging head 2 containing the external convex spring ejector pin or inside the plastic shell of the USB connector 1.

[0020] See also Figure 1 A PPTC resettable fuse is applied to the overcurrent and overvoltage protection circuit of a wrist-worn device, comprising a charging cable, a USB connector 1 connected to one end of the charging cable, and a magnetic charging head 2 connected to the other end of the charging cable, wherein the magnetic charging head 2 is connected to the wrist-worn device, and a PPTC resettable fuse 3 protection circuit is arranged in the magnetic charging head 2, and the PPTC resettable fuse 3 protection circuit comprises a PPTC resettable fuse 3 and a TVS tube 4, wherein the PPTC resettable fuse 3 is connected in series to the positive electrode line of the charging cable, and the TVS tube 4 is installed at the position after the current passes through the PPTC, and the other end is divided into two paths, one of which is connected to the positive electrode of the TVS tube 4, and the other is connected to the first spring pin 5, and the negative electrode of the TVS tube 4 is divided into two paths, one of which is connected to the negative electrode line of the charging cable, and the other is connected to the second spring pin 6. PPTC can complete the overcurrent protection and overtemperature protection functions. When a 6V charger is used to charge the above digital products, a large current will be generated (relative to the ordinary 5V), and the PPTC will gradually heat up, and the resistance value of the PPTC will increase to limit the damage of the large current to the lithium battery. This achieves the purpose of protection. This protection not only protects the charging process of the lithium battery by current limiting, but also protects the charger equipment, so it is a protection for the entire system.

[0021] The TVS tube 4 uses a medium-power unidirectional TVS tube 4 or a bidirectional TVS tube 4 with a trigger voltage of 7.0V. Therefore, there will be no reaction at 6V; when the user mistakenly inserts a high-voltage (such as 9V, 12V, 15V, 19V) charger or a 20V fast charger, the TVS tube 4 will be turned on in about 1nS (close to a short-circuit state) after the voltage exceeds 7V, and a large current will be generated. This large current is invisible to the user, so the charger will generally be left after the charger is inserted. The continuous existence of this large current will cause the TVS tube 4 to heat up and burn quickly. At this time, because this large current passes through the PPTC first, the PPTC will quickly protect when this large current passes (mutated to a high resistance to greatly limit the current). In this case, the overcurrent protection of the PPTC achieves the purpose of protecting the TVS, and also protects the charger equipment from being burned by the large current. In addition, due to the application design of the TVS, the wristband instrument equipment being charged will not be damaged by external high voltage and large current. In this state, the protection of the PPTC protects the charger and the entire system equipment at the same time through the protection of the TVS.

[0022] The PPTC resettable fuse 3 is a special model WHSMD0603-050 PPTC resettable fuse 3. A special SMD nonlinear thermistor or a plug-in PPTC thermistor installed close to the PCB board: the resistance value can be selected to be slightly heated during normal operation, and the special model WHSMD0603-050 is selected.

[0023] The magnetic charging head is also provided with two strong magnetic blocks 7 with opposite polarities, and the magnetic block 7 adopts a φ3 NdFeB strong magnetic sheet. The first spring pin and the second spring pin are round-headed convex spring pins, and the convex spring pin adopts a φ1.5×6mm dome-top gold-plated embedded spring pin, which is exposed 3-5mm and buried 2mm. Because the outer edge of the watch product is arc-shaped, the exposed charging contact electrode thin copper sheet is on its outer arc line, and two reverse-connected strong magnetic sheets are embedded between the two electrical connecting sheets to ensure that the electrodes of the charging head are not connected in reverse. The end of the charging cable also has two strong magnetic blocks 7 with opposite polarities, and two φ1.5 round-headed spring pins with a length of 3-5mm exposed on the positive and negative poles are installed at the positions of the watch electrode sheets at both ends. This connector is the magnetic charging head 2 mentioned above. Two reverse-polarity magnets are used to ensure that the positive and negative poles of the charging cable head are not connected in reverse. The magnetic charging head 2 has exposed spring pins, and due to the effect of the magnet, its spring pins can easily touch other conductive metals and short-circuit, causing the charger to burn out due to the short circuit of the charging head. Therefore, a circuit protection circuit can only be designed inside the magnetic charging head 2 or inside the USB head at the other end of the charging cable. To ensure the safety of the charger. If the protection circuit is not designed, when a short circuit occurs, the wires or charger components may be burned, and a fire may also occur. However, with the timely protection of the PPTC resettable fuse 3, the above losses or fires can be avoided. Because PPTC can provide timely or advance current limiting protection, the above problems can be avoided, and the entire system circuit is protected from damage.

[0024] Regarding the short-circuit protection of the outer convex spring pin of the magnetic charging head 2, it is a common problem that the outer convex spring pin touches metal and short-circuits due to improper placement or children playing (users usually unplug the magnetic charging head 2 after charging is completed and leave, and the charger and the magnetic charging head 2 wires may be powered on in the socket all the time). When this short-circuit problem occurs, a large short-circuit current will be generated. At this time, due to the overcurrent protection function of PPTC, the charger is well protected; for the reverse connection protection problem, when the charging line is connected in reverse, or the magnet of the magnetic charging head 2 is installed in reverse, or the USB interface wire is connected in reverse, the negative pole of the charging line is connected to the positive terminal of the lithium battery, and the negative pole of the charging line is connected to the positive terminal of the lithium battery. At this time, it is equivalent to a series relationship with the charger power supply, which is equivalent to a short circuit after the two power supplies are connected in series. At this time, the current of the circuit will be very large. This extremely large current passes through the PPTC. Under this extremely large current, the PPTC will quickly mutate into a high resistance and limit the current, so that the circuit system can achieve timely and effective current limiting protection. In this reverse connection state, the PPTC not only protects the lithium battery, but also protects the charger. This is also a protection for the entire system.

[0025] See also Figure 2A PPTC resettable fuse is applied to the overcurrent and overvoltage protection circuit of a wrist-worn device, including a charging cable, a USB connector 1 connected to one end of the charging cable, and a magnetic charging head 2 connected to the other end of the charging cable. The magnetic charging head 2 is connected to the wrist-worn device, and a PPTC resettable fuse 3 protection circuit is arranged in the USB connector 1. The PPTC resettable fuse 3 protection circuit includes a PPTC resettable fuse 3 and a TVS tube 4. One end of the PPTC resettable fuse 3 is connected to the positive pole of the charging input terminal, and the other end is divided into two paths, one is connected to the positive pole of the TVS tube 4, and the other is connected to the positive pole of the charging cable. The negative pole of the TVS tube 4 is divided into two paths, one is connected to the negative pole of the charging input terminal, and the other is connected to the negative pole of the charging cable. With a charging cable with PPTC and TVS, the protection of the short circuit of the external convex spring ejector pin, the overcurrent protection of high voltage and high current, the protection against reverse connection, and the overvoltage protection against high voltage input can be solved. The TVS here is an overvoltage protection component, also called a transient voltage suppressor. When the voltage applied to both ends of the TVS exceeds its design voltage, the TVS will be triggered to conduct within 1nS, and the high voltage sent from the previous stage will be discharged by the TVS so that the high voltage will not reach the charged lithium battery and related circuits, so the lithium battery and related circuits are protected by the conduction of the TVS; the above-mentioned PPTC plays an overcurrent protection role, and its working principle is: when an abnormally large current passes through, its resistance value will suddenly change to a high resistance, thereby achieving a current limiting effect. Through the above analysis and discussion, it is not difficult to find that the core of the above-mentioned role is the PPTC component and TVS The ingenious application of PPTC, and PPTC is a nonlinear thermistor, also called a resettable fuse, which can play a protective role in overcurrent, overtemperature, and short circuit in the circuit loop, and cooperate with TVS to complete the overvoltage protection. When a large current passes through PPTC, the internal temperature of PPTC rises. Within the set temperature range, its resistance value will change within a range. When PPTC is heated internally and the external temperature is superimposed, PPTC produces thermal expansion, which disconnects most of the conductive links inside PPTC, and the resistance value suddenly increases. After the power is disconnected, the temperature of PPTC decreases, and it shrinks when it is cold, and the conductive link is reconnected and restored to the initial state. Therefore, PPTC is also called a resettable fuse. However, compared with the TVS trigger conduction (similar to short circuit), its resistance value is several times or dozens of times, or even hundreds of times, when TVS is turned on, and as the large current passes, the PPTC resistance value increases and limits the current, so that the continuous large current will not burn or explode the TVS, thereby protecting the TVS. At the same time, the purpose of system protection is achieved through the protection of TVS, and ultimately the service life of the above-mentioned series of watch products and equipment is greatly extended. There will be no serious fire or personal injury. This ingenious design can not only solve the above problems.At the same time, it also solves the difficult problems encountered by manufacturers and engineers in their design work, uses the least components, occupies less space, has low cost, high reliability, makes the product safer, does not change the overall appearance of related equipment, makes related equipment truly safe, and directly enhances the market competitiveness of manufacturers.

[0026] During installation, the unit is mounted inside the plastic shell of the USB connector 1 or the magnetic charging head 2 without affecting the appearance. There are no other special requirements. It can make wristband instrument-related products and equipment in various application fields safer, more reliable, lower cost, simpler to use, and can be mass-produced and put on the market.

[0027] The above-mentioned embodiments only express several implementation methods of the utility model, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the utility model patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the utility model, which all belong to the protection scope of the utility model. Therefore, the protection scope of the utility model patent shall be based on the attached claims.

Claims

1. A PPTC resettable fuse is applied to an overcurrent and overvoltage protection circuit of a wrist-worn device, comprising a charging cable, a USB connector connected to one end of the charging cable, and a magnetic charging head connected to the other end of the charging cable, wherein the magnetic charging head is connected to the wrist-worn device, and is characterized in that: A PPTC resettable fuse over-current and over-voltage protection circuit is provided in the magnetic charging head. The PPTC resettable fuse over-current and over-voltage protection circuit includes a PPTC resettable fuse and a TVS tube. The PPTC resettable fuse is connected in series to the positive electrode line of the charging cable, and the other end is divided into two paths, one is connected to the positive electrode of the TVS tube, and the other is connected to the first spring pin. The negative electrode of the TVS tube is divided into two paths, one is connected to the negative electrode line of the charging cable, and the other is connected to the second spring pin.

2. The PPTC resettable fuse according to claim 1 is applied to an overcurrent and overvoltage protection circuit of a wrist-worn device, characterized in that: The TVS tube adopts a medium-power unidirectional TVS tube or a bidirectional TVS tube with a trigger voltage of 7.0V.

3. The PPTC resettable fuse according to claim 1 is applied to an overcurrent and overvoltage protection circuit of a wrist-worn device, characterized in that: The PPTC resettable fuse is a special PPTC resettable fuse of model WHSMD0603-050.

4. The PPTC resettable fuse according to claim 1 is applied to an overcurrent and overvoltage protection circuit of a wrist-worn device, characterized in that: The magnetic charging head is also provided with two strong magnetic blocks with opposite polarities, and the magnetic blocks are made of φ3 neodymium iron boron strong magnetic sheets.

5. The PPTC resettable fuse according to claim 1 is applied to an overcurrent and overvoltage protection circuit of a wrist-worn device, characterized in that: The first spring pin and the second spring pin are round-headed convex spring pins, which are φ1.5×6mm dome-top gold-plated embedded spring pins. The convex spring pins are exposed 3-5mm and buried 2mm.

6. A PPTC resettable fuse is applied to an overcurrent and overvoltage protection circuit of a wrist-worn device, comprising a charging cable, a USB connector connected to one end of the charging cable, and a magnetic charging head connected to the other end of the charging cable, wherein the magnetic charging head is connected to the wrist-worn device, and is characterized in that: A PPTC resettable fuse overcurrent and overvoltage protection circuit is provided in the USB connector. The PPTC resettable fuse overcurrent and overvoltage protection circuit includes a PPTC resettable fuse and a TVS tube. One end of the PPTC resettable fuse is connected to the positive electrode of the charging input terminal, and the other end is divided into two paths, one path is connected to the positive electrode of the TVS tube, and the other path is connected to the positive electrode line of the charging line. The negative electrode of the TVS tube is divided into two paths, one path is connected to the negative electrode of the charging input terminal, and the other path is connected to the negative electrode line of the charging line.

Images