The application of resistors on a Printed Circuit Board (PCB) is an important aspect of circuit design. A resistor is a component used to limit the flow of current. Its main function is to convert electrical energy into heat energy and control the voltage and current in the circuit by blocking the flow of current. Choosing the right resistors on a PCB can have a critical impact on circuit performance and functionality.
1. Types of resistors on PCB
In PCB design, there are many different types of resistors. Common ones include metal film resistors, carbon film resistors, thin film resistors, power resistors, etc. Each resistor has different properties and characteristics and can be selected based on specific needs.
1. Metal film resistor: Metal film resistor is a resistor formed by depositing a metal film on a ceramic substrate. It has stable resistance value, low temperature coefficient and low noise level. Metal film resistors are suitable for general low-power applications, including mobile devices, consumer electronics, and communications equipment.
2. Carbon film resistor: A carbon film resistor is a resistor formed by depositing a carbon film on a ceramic substrate. Its resistance value is higher than that of metal film resistance, and its temperature coefficient is also larger. Carbon film resistors are suitable for applications that do not require high resistance values, such as switching circuits, signal processing circuits, etc.
3. Thin film resistor: Thin film resistor is a resistor formed by depositing a thin film on a metal substrate. Thin film resistors have higher resistance values and smaller sizes, making them suitable for applications requiring high precision and stability, such as precision measuring instruments and medical equipment.
4. Power resistor: A power resistor is a type of resistor used to withstand higher power. It usually has a large size and high durability and is suitable for applications requiring high-power processing, such as power systems, motor drives, and high-power amplifiers.
2. Selection and application of resistors
When selecting a resistor, there are several factors to consider:
1. Resistance Value: Resistance value is the basic parameter of the resistor, which plays a role in limiting the flow of current in the circuit. According to different application requirements, the appropriate resistance value can be selected. The commonly used unit is ohm (Ohm).
2. Power Rating: The power of a resistor refers to the maximum power that the resistor can withstand. The power value determines whether the resistor can meet the power demand in the circuit. Excessive power may cause the resistor to overheat and be damaged.
3. Tolerance: The accuracy of a resistor refers to the difference between the resistance value and the nominal resistance value. According to specific needs, resistors with different precisions can be selected. Common precisions include ±1%, ±5%, etc.
4. Temperature Coefficient: The temperature coefficient reflects the change of resistance value with temperature. For temperature-sensitive applications, resistors with lower temperature coefficients need to be selected to ensure stable circuit performance.
5. Size: The space on the circuit board is usually limited, so it is necessary to choose a resistor of appropriate size. Smaller resistors save space and help improve the overall layout.
Depending on the above factors, different types of resistors can be applied at different locations in the PCB. For example, metal film resistors and carbon film resistors are suitable for general circuits, thin film resistors are suitable for precision measuring instruments, and power resistors are suitable for circuits requiring high power processing. In the design, factors such as the layout, connection method and circuit safety of the resistors also need to be considered.
3. Installation and soldering of resistors
The installation and soldering of resistors is a critical step in the PCB manufacturing process. In order to ensure the correct installation of the resistor and good welding quality, the following points need to be noted:
1. Installation position: The resistor should be installed correctly on the PCB according to the requirements of the circuit design to avoid misalignment or misinstallation.
2. Welding method: Commonly used welding methods include Surface Mount Technology (SMT) and Through-Hole Technology(THT). Choosing the appropriate soldering method depends on the circuit and electronic component requirements.
3. Welding process: The welding process should be set appropriately according to the type and size of the resistor. The specific welding process includes welding temperature, welding time and welding flow rate.
4. Welding equipment: To ensure welding quality and efficiency, appropriate welding equipment and tools need to be selected.
4. Troubleshooting and maintenance of resistors
When using resistors on a PCB, some faults or problems may occur that require troubleshooting and maintenance. Common problems include failed resistance values, welding problems, excessive temperatures, etc.
1. Resistor value failure: If the resistance value deviates from its nominal value, it may cause circuit performance degradation or abnormal function. You can use tools such as a multimeter to test. If the resistance value is significantly different from the nominal value, the faulty resistor may need to be replaced.
2. Welding problems: Poor welding may cause problems with the connection between the resistor and the PCB, or cause cold soldering problems at the solder joints. Insufficient welding will affect the reliability and stability of the circuit and require timely repair.
3. Temperature is too high: If the resistor operates in a temperature range exceeding its allowable temperature for a long time, the resistor may be burned or damaged. At this time, the circuit design needs to be appropriately adjusted or heat dissipation measures added to ensure the normal operation of the resistor.
Applying resistors to PCBs is an integral part of circuit design. By selecting the appropriate resistor type, and determining the appropriate resistance value, power, accuracy and temperature coefficient, the needs of different application scenarios can be met. During the installation and welding process of resistors, relevant standards and specifications should be followed to ensure the quality and reliability of the circuit. For faults or problems that occur, timely troubleshooting and maintenance are required. The application of resistors on PCB is an important and complex part of circuit design. Various factors need to be considered comprehensively to achieve the best match between the function and performance of the circuit.
FAQ - om PCB
PCB-modstand er en anordning, der omdanner elektrisk energi til varme. Den har to terminaler, hvoraf den ene er forbundet til kredsløbets positive side, og den anden er forbundet til jorden. Når du lægger en spænding over den, strømmer strømmen igennem den og forårsager, at der produceres en vis mængde varme i forhold til denne spændingsforskel.
Formålet med at bruge PCB-modstand er primært at begrænse strømmen ved at aflede varmen over deres resistive værdi i stedet for at lade den gå direkte til opvarmning af dine komponenter eller forårsage skade på dem ved overophedning.
Den vigtigste parameter, der skal tages i betragtning ved valg af en korrekt PCB-modstand, er effekt (watt) og tolerance (procent).
En modstand med lavere effekt har en lavere temperaturkoefficient for modstanden end en modstand med højere effekt. Det betyder, at den vil afgive mindre varme og derfor være mere stabil ved høje temperaturer.
For at vælge en korrekt PCB-modstand skal du kende følgende parametre:
Den nominelle effekt (watt) og tolerance (procent).
Temperaturkoefficienten for modstand.
Modstande har tre- eller firecifrede koder, der identificerer modstanden og tolerancen for modstanden. Denne metode til mærkning af modstande kaldes PCB-modstandskoden.
Trecifrede koder består af tre cifre, hvor det første ciffer angiver modstandsværdien i ohm, og det andet ciffer angiver tolerancen.
Firecifrede koder består af fire cifre - et for hvert ciffer i den trecifrede kode. De første to cifre er altid nul - de angiver, at denne modstand ikke har nogen tolerance eller specifikation. De sidste to cifre er altid et - de angiver, at denne modstand har en specifikation mellem 1% og 10%.