1. The base must be connected in series with a resistor to protect the base and protect the IO port of the CPU.
2. The base is based on a PNP or NPN tube plus a pull-up or pull-down resistor.
3. The collector resistance value is adjusted according to the actual situation of the drive current. The same base resistance can also be adjusted according to the actual situation.
The base and the emitter need a series resistor. The function of the resistor is to reliably turn off the transistor when the input is in a high-impedance state. The minimum value is that the transistor can be satisfied after the pre-driver saturates the transistor and the base-limit current resistor is divided. The critical saturation, the actual selection will be much higher than this minimum value, usually the smaller the external interference, the heavier the load, the higher the resistance value, usually 10K.
Prevent the triode from being affected by the noise signal and cause malfunction, so that the transistor is cut off more reliably! The base of the triode cannot be left floating. When the input signal is uncertain (such as when the input signal is high impedance), the pull-down resistor can be used to make Effective grounding.
In particular, when the GPIO is connected to the base, when the GPIO is just powered on and initialized, the GPIO is also in a power-on state. It is very unstable and is prone to noise and malfunction. Add this resistor. This effect can be eliminated (if a sharp pulse level occurs, this voltage is easily pulled low by the resistor due to the short time; if the high level is long, it cannot be pulled low, that is, at a normal high level. No effect)!
However, the resistance should not be too small, affecting the leakage current! (If it is too small, there will be a large current flowing from the resistor to the ground)
When the triode switch is activated, the ON and OFF times are as short as possible. In order to prevent the time lag caused by the residual charge in the transistor during OFF, an R is applied between B and E to discharge.
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