1. Application scope:

　　High-voltage and large-capacity energy storage capacitors are widely used in industrial products. Due to the characteristic that the voltage across the capacitor cannot change suddenly, at the moment the system is turned on, the current flowing into the capacitor from the grid energy often reaches a peak level of hundreds of amperes. Such a high The startup current seriously threatens the rectifier devices and overcurrent fuses in the circuit, and also brings great harmonic pollution to the public commercial power grid. Therefore, almost all circuits are equipped with a "start-up surge suppression circuit" to suppress the startup surge current to a reasonable level.

　　The traditional "surge suppression component" is a common fixed resistance "cement resistor". Especially in products with power above kilowatts, high-power "cement resistors" are commonly used as surge suppression components. From the original intention of designing the power-on surge suppression circuit, the fixed resistor can meet the basic function of the design - to suppress the power-on charging current.

　　However, the fixed resistor itself brings new safety hazards - due to the possibility that the relay connected in parallel with the "surge suppression component" cannot be effectively closed, such as mechanical fatigue, drive failure, load failure, etc., the continuous load current flow Passing this high-resistance fixed resistor (commonly used resistance is 10~100 ohms) will inevitably produce extremely high temperatures, causing the "cement resistor" to smoke, explode and other unsafe phenomena. In extreme cases, the PCB will be melted by the high temperature. Destroy or even ignite. This is a shortcoming of linear resistors in surge suppression applications. To solve this problem, Huaju Electronics has launched a positive temperature coefficient ceramic thermistor PTC with surge suppression function.Its unique positive temperature coefficient characteristic (that is, the resistance increases as the temperature increases) can effectively suppress the continuous increase in the temperature of the device itself. The temperature change process is as follows:

　　PTC has low temperature and low resistance => is heated by current => temperature increases => (when exceeding the PTC thermistor operating temperature) resistance increases => current decreases => thermal power decreases => PTC resistance continues to increase ( Until tens of KΩ) => heat generation and heat dissipation are balanced => PTC temperature is maintained near the operating point (about 130~150°C).

　　From the above analysis, it can be seen that the "resistance-temperature" positive correlation characteristic of Huaju Electronics' surge suppression PTC enables it to have a "self-protection" function - in the case of a fault where the relay cannot be closed, the thermal power generated by the load current It can only be heated to near the Curie temperature point, effectively avoiding the phenomenon of temperature runaway similar to "cement resistor", which means that it can safely protect itself and at the same time protect the downstream circuit located behind it, and after the relay fault is eliminated , it can also automatically restore its original functions.

　　Therefore, Huaju's surge suppression PTC thermistor provides help to improve the safety and reliability of switching power supplies. It is an ideal startup surge current suppression component. This product is gradually being widely used in air conditioners, industrial inverters, Provide safe and reliable power-on surge protection for power supply and other industries.

　　1. Application scope of soft start charging resistor:

　　High-voltage large-capacity energy storage capacitor charging protection thermistor is a thermistor specially used by Huaju Electronics to protect energy storage capacitors. It limits the initial charging current of the energy storage capacitor to prevent the energy storage capacitor from being charged during power-on. Excessive current may cause equipment damage. Prevent large surge current from damaging equipment.

　　High-voltage and large-capacity energy storage capacitors are widely used in industrial products. Due to the characteristic that the voltage across the capacitor cannot change suddenly, at the moment the system is turned on, the current flowing into the capacitor from the grid energy often reaches a peak level of hundreds of amperes. Such a high The startup current seriously threatens the rectifier devices and overcurrent fuses in the circuit, and also brings great harmonic pollution to the public commercial power grid. Therefore, almost all circuits are equipped with a "start-up surge suppression circuit" to suppress the startup surge current to a reasonable level.

　　The traditional "surge suppression component" is a common fixed resistance "cement resistor". Especially in products with power above kilowatts, high-power "cement resistors" are commonly used as surge suppression components. From the original intention of designing the power-on surge suppression circuit, the fixed resistor can meet the basic function of the design - to suppress the power-on charging current.

　　However, the fixed resistor itself brings new safety hazards - due to the possibility that the relay connected in parallel with the "surge suppression component" cannot be effectively closed, such as mechanical fatigue, drive failure, load failure, etc., the continuous load current flow Passing this high-resistance fixed resistor (commonly used resistance is 10~100 ohms) will inevitably produce extremely high temperatures, causing the "cement resistor" to smoke, explode and other unsafe phenomena. In extreme cases, the PCB will be melted by the high temperature. Destroy or even ignite. This is a shortcoming of linear resistors in surge suppression applications. To solve this problem, Huaju Electronics has launched a positive temperature coefficient ceramic thermistor PTC with surge suppression function. Its unique positive temperature coefficient characteristic (that is, the resistance increases as the temperature increases) can effectively suppress the continuous increase in the temperature of the device itself. The temperature change process is as follows:

　　PTC has low temperature and low resistance => is heated by current => temperature increases => (when exceeding the PTC operating temperature) resistance increases => current decreases => thermal power decreases => PTC resistance continues to increase (until several tens KΩ)=〉Heating and heat dissipation balance=〉PTC temperature is maintained near the operating point (about 130~150°C).

　　From the above analysis, it can be seen that the "resistance-temperature" positive correlation characteristic of Huaju Electronics' surge suppression PTC enables it to have a "self-protection" function - in the case of a fault where the relay cannot be closed, the thermal power generated by the load current It can only be heated to near the Curie temperature point, effectively avoiding the phenomenon of temperature runaway similar to "cement resistor", which means that it can safely protect itself and at the same time protect the downstream circuit located behind it, and after the relay fault is eliminated , it can also automatically restore its original functions.

　　Therefore, Huaju's surge suppression PTC provides help to improve the safety and reliability of switching power supplies. It is an ideal startup surge current suppression component. This product is gradually being widely used in air conditioners, industrial inverters, power supplies and other industries. Provide safe and reliable power-on surge protection. This PTC thermistor is mainly used for overheating and overcurrent protection of welding equipment such as digital welding machines, inverter DC hand arc welding machines, and inverter DC argon arc/hand arc welding machines. The main principle is that when the welding equipment is working normally, the current flowing through the PTC thermistor does not exceed its maximum operating current, and the PTC is in a low resistance state. When an abnormal state occurs and the circuit current greatly exceeds the rated current, the PTC suddenly heats up and the resistance value Suddenly increases to a high resistance state, thereby limiting or blocking the current and protecting the circuit from damage. After the current returns to normal, the PTC also automatically returns to the low resistance state, and the circuit returns to normal operation.

　　Most of the input circuits of high-power electronic equipment use capacitor filter rectifier circuits. At the moment when the incoming power supply is turned on, since the initial voltage on the capacitor is zero, a large surge current will form at the moment when the capacitor is charged, especially for high-power applications. Electronic equipment uses filter capacitors with larger capacities to increase the surge current to more than 100A. Such a large surge current at the moment when the power is turned on will often cause the input fuse to blow out or the contacts of the closing switch to burn out, causing overcurrent damage to the rectifier bridge; in the worst case, it will also cause the air switch to fail to close. The above phenomena will cause high-power electronic equipment to fail to work properly. For this reason, almost all high-power electronic equipment is equipped with a soft-start circuit to prevent inrush current to ensure normal and reliable operation of the power supply. The figure (1) below is an anti-surge current circuit composed of relay K1 and current-limiting resistor WMZ13A series impact-resistant PTC thermistor. At the moment when the power is turned on, the input voltage is rectified (D1~D4) and the current limiting resistor RT charges the filter capacitor C1 to prevent the surge current at the moment of turn on. At the same time, the auxiliary power supply Vcc is connected to the relay K1 wire package through the resistor R2 pair. Capacitor C2 is charged. When the voltage on C2 reaches the operating voltage of relay K1, K1 acts, its contact K1.1 closes and bypasses the current limiting resistor R1, and the power supply enters normal operation. The delay time of current limiting depends on the time constant (R2C2), which is usually selected from 0.3 to 0.5s. In order to improve the accuracy of the delay time and prevent jitter and oscillation of the relay action, the delay circuit can use the circuit shown in Figure 2 instead of the RC delay circuit.

　　Inverter power supply schematic diagram

　　The RT in the red box is the MZFLY series impact-resistant PTC thermistor with good impact resistance.

　　

 

　　figure 2)

　　

 

　　1. Main technical parameters

　　Application and selection

　　l Typical application circuit:

　　ⅡSelection

　　Select the charging capacitor according to the following formula

　　C: Filter capacitor.

　　Tc: Curie temperature of PTC Ta: ambient temperature

　　V: The highest charging voltage across the capacitor, the power supply voltage is AC, and V is the peak value of AC.

　　K coefficient K = 1 for DC, K = 0.96 for three-phase AC rectifier, K = 0.76 for half-wave rectifier

　　When a single PTC surge suppression thermistor cannot meet the requirements, multiple PTC surge suppression thermistors can be used in parallel.

　　The maximum load capacitance of the PTC soft-start resistor is inversely proportional to the square of the voltage across the capacitor when the capacitor is fully charged. Therefore, under the same environmental conditions, the maximum load capacitance can be increased by 4 times with half the voltage drop.

　　PTC charged capacity calculation tool

　　EPCOS material number Huaju replacement comparison table