Check the circuit of the pump frequency converter this week, finalize the use, find the control transistor of the digital tube, the base does not even have series resistance, this will cause the IO of the one-chip computer to burn out, although there is no problem before the frequency converter out of test, it is because The internal IO of the selected microcontroller has a certain internal resistance, and the resistance is approximately 60 to 120 ohms. If it is replaced by STM32, the internal resistance of IO is much smaller, and it may burn out. After discovering this problem, I asked my colleagues how the matter was and whether the inverter we referenced was the same. They responded because the warehouse did not refer to the triode used by the inverter and used our own commonly used 8550 triode and found no problems. Has been in use, and told me to refer to the number of the frequency converter used, I checked, with the ordinary triode is different, turned out to be a blocking transistor, as shown below: Although the band-block transistor was contacted in 2002, it was used on mobile phones at that time. In order to save PCB layout and devices, the traditional design was rarely seen. I did not expect it to be used in the past few years. Compared with triodes, I prefer to use low-power MOS tubes such as SI2301 and SI2302 in recent years. However, they are not very ideal in practical use. They are mainly micropower MOS tubes, they are prone to burnout, and their impact resistance is too weak. After the mos tube is turned on, the internal resistance is too low, and it is easily damaged by an instantaneous high-current shock. Last year understood the idea of ​​flexible hardware design, and also saw many mature designs still use triodes, so to see this band-fault transistor, think of replacing MOS transistors with band-block transistors in other circuits. And compared to the MOS tube, in addition to strong impact resistance, the external does not require two resistors, and easy to use. This band-block transistor, the commonly used model is: KRA106S PNPKRC106S NPN SOT23 package, recommend everyone to use. Different base voltages correspond to different output currents. Under the single-chip microcomputer 3.3V, it is not recommended to output collector current greater than 50mA for 106.
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