As we all know, the color TVs of medium and small screens are connected in series with a current limiting rectifier filter circuit with a current limiting resistor with a resistance of several ohms. The function is to prevent the charging current of the filter capacitor from being large due to the startup. Set up due to breakdown of the rectifier bridge. However, this resistor also has its drawbacks: not only consumes energy in normal operation, but also increases the internal resistance of the power supply, which affects the voltage regulation characteristics of the power supply.
For general medium and small screen color TVs, because of the small capacity of the filter capacitor, a small resistance resistor can be selected for current limiting, but for large-screen color TVs such as 29 and 34 inches, this method is adopted. It won't work. Because the filter capacitor of this type of machine is usually as high as 570μF, if it is treated as described above, the current limiting resistor should be selected very large, which consumes energy in vain, and directly affects the power supply voltage due to voltage drop across the resistor during operation. characteristic. If there is no current limiting resistor, the charging current is too large due to the startup, and it is easy to damage the rectifier bridge and the filter capacitor itself. There is a contradiction here: there is no current limiting resistor or current limiting resistor is too small, the inrush current is large, endangering the device, but the current limiting resistor affects the voltage regulation characteristics of the power supply. In order to prevent the voltage regulation performance after the charging current is turned on, some models use a relay to short-circuit the current limiting resistor (such as Konka T2910/T2988 and other color TVs), but this method increases the cost and makes the circuit It is complicated and the reliability is further reduced.
The negative temperature coefficient thermistor NTC2.5 is qualified for this task.
The following figure shows the rectification and filtering circuit of Konka T3498/T3898 switching power supply. The HT902 and HT903 are a negative temperature coefficient (NTC) thermistor. This resistor is used as a current limiting resistor to overcome the inherent limitation of conventional current limiting resistors. Defects. This thermistor has a resistance of 2.5 Ω at normal temperature, and the resistance rapidly decreases as the temperature rises. When the temperature rises to 75 ° C, the resistance is only about 0.12 Ω. The two series of negative temperature coefficient thermistors in the circuit have a cold resistance of 5Ω, which effectively limits the impact of large currents on components such as BR901 and C907. The current generates heat while passing through it, and its own temperature rises. When the TV is in normal working state, its resistance is only about 0.25 Ω (the voltage drop across the measured voltage is almost zero), which is equal to no current limiting resistor. Reduced power consumption and guaranteed high performance of regulation. Due to the use of this new device, the contradiction between the current limiting in the large-screen color TV and the large internal resistance of the power supply and the large power consumption can be solved, and the circuit can be made simple and reliable.
AC (Alternating Current) Power cord is to transmit high voltage. It is used to drive machinery or home appliances. Since AC Power Cord is output of high voltage electric power, there is a risk of electric shock injury, therefore, All the AC power cord must comply with safety standard to produce. DC (direct Current) power cord is used to the applicance with lower voltage mostly, so safety requirement is less stringent.
Power Cable, battery cable, DC power cable, AC power cable, power cord
ETOP WIREHARNESS LIMITED , https://www.wireharnessetop.com