The toggle switch is almost used in the circuit, and its components have semiconductor diodes, which play a very important role in the components. Semiconductor diode is one of the earliest semiconductor components and has a wide range of applications. The diode is a p-n junction formed by a p-type semiconductor and an n-type semiconductor body. A space charge layer is formed on both sides of the interface, and it has the ability to build its own electric field. . When the fluctuating switch is not energized, the diode is in the state of electrical equilibrium because the diffusion current caused by the difference in carrier concentration on both sides of the p-n junction is equal to the drift current caused by the self-built electric field.
Diodes are used in the diode switching circuit of the toggle switch. Since the switching speed of ordinary diodes is not high enough, the diodes used in this switching circuit are special switching diodes. The equivalent circuit of the switching diode is shown in the figure. It can be seen that the switch diode is equivalent to a switch Sl at the same time, and there are also two resistors. The switch Sl in the equivalent circuit can be considered as an ideal switch, that is, its on-resistance is as small as zero, and its off-resistance is as large as infinity.
If the port is normally high level, when C is connected to the ground through a resistor, the resistor is called a pull-down resistor, so that the port is usually low level, what is the function: for example: when a pull-up resistor is connected When the port is set to the input state, its normal state is high level, which is used to detect the low level input.
The color ring of different colors is painted on the resistor to indicate the resistance value and error of the resistor. This is the color ring marking method of the resistance value, referred to as the color code method. Generally suitable for pin resistance, cylindrical resistance, metal film color ring resistance. Generally speaking, there are four-ring notation method and five-ring notation method. The common point is that the last ring represents the error, the penultimate ring represents the multiplier, and the preceding ring represents the significant number. The pull-up resistor is used to provide current when the bus drive capability is insufficient. frequency characteristics.
Take the pull-up resistor as an example. The capacitance between the pull-up resistor and the drain-source stage of the switch tube and the input capacitance between the lower-level circuit will form an RC delay. The greater the resistance, the greater the delay. The setting of the pull-up resistor should consider the needs of the circuit in this regard. Low level setting. The threshold levels of high and low levels of different circuits will be different, and the resistance should be properly set to ensure that the correct level can be output.