A resistor is a device in a substance that has the ability to hinder the flow of electrons, that is, it has a certain resistance to the flow of current. The unit is Ω. For convenience of expression, resistors are usually referred to simply as resistors.
Lichuang EDA simulation mode provides commonly used resistor models, including fixed resistors placed normally, resistors placed at a 45° oblique angle, and adjustable resistors. Each type provides American standards, European standards, and 3D physical drawings. User use.
There are many types of resistors, including wirewound resistors, carbon film resistors, metal film resistors, etc. Readers can learn about them by themselves. Resistors are widely used in electronic design. Here are some common functions of resistors:
1. Resistor voltage division
Resistor voltage dividing is the most basic function. The voltage dividing circuit is involved in the circuit's voltage reduction, ADC voltage collection, and transistor static operating point setting. Among them, the 555 timer that we are very familiar with is named after the presence of three precise 5K resistor voltage dividers inside. Currently, our common NE555, TLC555, AiP555, etc. are all 555 timers produced by different manufacturers using this structure.
Excerpt from AiP555 datasheet
When the current flowing through a certain device in the circuit is too large, a resistor can be connected in parallel to share the current, protect the circuit, and increase the output power of the circuit.
In the above circuit, the R1 and R2 resistors are connected in parallel, and R1 is a shunt resistor, which plays a shunt role in the circuit to protect the R2 resistor (protection circuit) from damage, where I=I1+I2. The larger the resistor shunt is, the better. The impact of the current on the original circuit needs to be considered.
Resistor voltage division is also used in triode circuits. In the picture above, there is an NPN transistor. A resistor is connected in parallel between the collector and emitter. It can be seen as the internal resistance of the transistor is connected in parallel with the R1 resistor, and R1 is a shunt resistor. In the circuit, the total current remains unchanged and the error is I, but the current flowing through the transistor decreases, and part of the current is distributed to the branch of the R1 resistor. It plays the role of protecting the triode and increasing the power.
3. Resistor current limiting
We should be exposed to more resistive current-limiting circuits. The most common ones are the protective resistors of light-emitting diodes that play the role of current limiting. For example, by searching the data sheet of Taiwan Everlight's three-mm red light-emitting diode, there is the following table. From the table, we can see that the minimum forward voltage of the diode is 1.7V, which means that there must be 1.7V. The pressure drop light will light up;
In the following table, we can also get the following information: The maximum forward current of the diode is 30mA, which means that the current cannot exceed 30mA when lighting the diode, otherwise the diode will be burned.
Based on the above information, we can design a resistor current limiting circuit for a light-emitting diode. Since the internal resistance of the diode is very small, if it is directly connected to a 5V power supply, the current flowing through the diode will be too large and it will be easily burned. Take the LED conduction voltage as 2V, set the operating current as 10mA, and calculate it through Ohm's theorem: R=(VCC-VF)/IF=(5-2)/10mA=300Ω
4. Pull-up and pull-down resistors
The pull-up resistor and the pull-down resistor play a role in the circuit to avoid instability in the floating state and achieve the purpose of anti-interference.
A pull-up resistor is generally connected to the required pin in parallel with a resistor connected to VCC to keep the pin at a high level by default. When the VCC power supply is 5V, the pull-up resistor generally has a value between 4.7~10K ohms.
The pull-down resistor connects a resistor in parallel to the GND ground on the required pin, so that the default state of the pin remains low. When the VCC power supply is 5V, the pull-down resistor generally has a value between 100 and 470 ohms.
The picture below shows the pull-up resistor in the three-person voting machine. When no one votes and all three switches are turned off, the pin is pulled high; when the switch is pressed, the pin is directly connected to ground, and the corresponding input pin is low. flat.
In some high-power circuits, it is often necessary to absorb some excess power. Our common cement resistors are called load resistors. During the simulation process, we can also replace the speaker and other devices with a resistor.
There are many uses for resistors. Readers can search by themselves or analyze them on different occasions during use. Among them, resistors also have great uses in impedance matching, anti-interference, and current sampling. Resistors can also be combined with capacitors to form an RC circuit, which has functions such as integration, filtering, delay, and decoupling.
- During the simulation process, the variable resistor settings cannot be 0% and 100%.
- Modify the resistance value. Double-click to modify the resistance value or click on the resistor to modify it in the property bar on the right.
- When using some resistive sensors for simulation, you can replace it with a resistor and modify the resistance value under different circumstances to simulate the response of the sensor under different circumstances. For example, the resistance of a photoresistor can be as small as less than 1KΩ under light conditions; under no light conditions, it is in a high resistance state, and the dark resistance can generally reach 1.5MΩ or more.
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