Power transistors should be used in the power adapter

Source:AdminAuthor:WPOWER Addtime:2019-06-05 Click:
 Power transistors should be used in the power adapter
   Power transistor applications
   The power transistor component is used not only for industrial machines such as industrial electromechanical servo amplifiers or AC motor controlled VVVF inverters, but also for household appliances such as inverter air conditioners and induction cookers. Or for OA equipment, chargers. The basic circuit structure of the AC motor control, the general-purpose inverter, the industrial inverter, the servo or the general industrial machine, and the inverter of the air conditioner, etc., almost all adopt this basic circuit. The transistor component is thus developed toward a high-powered three-terminal power adapter, and it is possible to achieve inverter control of 500 kVA.
   First: prevent branch short circuit
    In a bridge circuit such as an inverter, it is necessary to pay attention to a short-circuit accident of the upper and lower branches due to a delay in response time of the power transistor. Especially in Darlington transistors, the delay is very long, so it is necessary to set a tens of seconds of rest time between the base-level signals of the transistors of the upper and lower branches according to the rating of the power transistor.
    Second: base drive circuit
    The idea of ​​providing an optimum base driving condition when using a power transistor as a switch is as follows. The base forward current of the power transistor must be determined based on saturation voltage characteristics, switching time, and short circuit resistance. The base reverse current has an effect on the turn-off time. Increasing the base reverse current can reduce the turn-off time required for high frequency switching. However, it should be noted that the safe working area of ​​the reverse bias is narrowed, and the driving circuit of the power transistor is designed according to various uses, but recently these base driving circuits have been mixed and integrated, and the installation is very convenient.
   Third: resistance to dv / dt amount
    In the inverter analog circuit, when the current flows in the direction indicated by the broken line, if Td is turned on, dv/dt with a steep slope is added to T. If the reverse base bias is insufficient, the displacement current caused by dv/dt becomes large, and the switching loss at the time of disconnection increases. On the other hand, even if the reverse base bias of T1 is sufficiently large, if the reverse recovery current of the feedback diode of T1 is large, the turn-off loss is increased, so the feedback diode should be a high-speed tube.
   Fourth: buffer circuit
    In order to suppress the surge voltage applied to the power transistor, a snubber circuit is employed. Unlike the application of bipolar transistors in the power supply industry, the effect of this circuit is to suppress the operating point of the power transistor during the disconnection operation in the reverse bias safe working area, while reducing the loss of the disconnection.  

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