I. Key Design Considerations for Power Modules
Key considerations for power module design:
1. Component Selection
The application of different components will result in different module performance. For example, ceramic or electrolytic capacitors are commonly used for capacitor selection, while tantalum capacitors have a long lifespan, high temperature resistance, and good performance, but are prone to circuit failure. Tongcheng Chuangpin reminds everyone that different products are used in different ways.
2. Surge protection circuit
How to design surge protection circuits? Depending on the application, the positions of inductors and TVS diodes may need to be adjusted. This can allow the system to be used more effectively and correctly, thereby improving EMC performance. Note that the design of a two-stage surge protection circuit can be counterproductive if used improperly.
3. Reduce design workload
Properly controlling components to specified values and reducing the number of components can delay degradation, improve component reliability, and enhance power supply reliability.
4. Dual power supply module design
The output of the bidirectional power supply module should be balanced under load. During the design process, attention should be paid to ensuring even output adjustment between the main and auxiliary circuits.
II. Troubleshooting Power Module Faults
1. Input voltage is too high
The issue is an abnormal input parameter in the power supply module—specifically, an excessively high input voltage. This abnormality can cause the system to malfunction, or even burn out the circuitry. So, what are the common causes of excessively high input voltage?
**Output terminal is floating or unloaded;** Output terminal load is too light, less than 10% of the rated load; Input voltage is too high or there is interference voltage.
To address this type of problem, you can adjust the output load or the input voltage range, as shown below:
Ensure that the output is at least 10% of the rated load. If there is no load in the actual circuit operation, connect a dummy load with 10% of the rated power in parallel at the output. Replace the input voltage with a reasonable range. If there is interference voltage, consider connecting a TVS diode or Zener diode in parallel at the input.
2. Output voltage is too low
The issue of abnormal power supply output parameters—specifically, excessively low output voltage—can cause the entire system to malfunction. For example, in a microcontroller system, a sudden increase in load can pull down the microcontroller's supply voltage, potentially causing a reset. Furthermore, prolonged operation of the power supply under low input voltage conditions will significantly shorten the circuit's lifespan. Therefore, the problem of low output voltage cannot be ignored. So, what are the common causes of excessively low output voltage?
The input voltage is too low or the power is insufficient; the output line is too long or too thin, resulting in excessive line loss; the voltage drop of the reverse connection protection diode at the input terminal is too large; the input filter inductor is too large.
This type of problem can be improved by adjusting the power supply or replacing the corresponding peripheral circuitry, as detailed below:
Increase the voltage or use a higher power input power supply;
Adjust the wiring by increasing the cross-sectional area of the conductors or shortening their length to reduce internal resistance;
Replace with a diode with a smaller forward voltage drop;
Reduce the value of the filter inductor or lower the internal resistance of the inductor.
3. Excessive output noise
The issue concerns abnormal power supply module output parameters, specifically excessive output ripple noise. As is well known, noise is a key indicator of a power supply module's quality. In application circuits, the module's design and layout also affect output noise. So, what are the common causes of excessive output ripple noise?
The power supply module is too close to the noise-sensitive components of the main circuit; no decoupling capacitor is connected at the power input terminal of the noise-sensitive components of the main circuit; differential frequency interference occurs between the power supply modules of each single output in a multi-channel system; and the grounding is not handled properly.
This type of problem can be improved by isolating the module from noisy devices or using decoupling capacitors in the main circuit, as detailed below:
**Keep the power supply module as far away as possible from noise-sensitive components in the main circuit, or isolate the module from noise-sensitive components in the main circuit;** Connect a 0.1μF decoupling capacitor at the power input terminal of noise-sensitive components in the main circuit (such as A/D, D/A, or MCU);** Use a multi-output power supply module instead of multiple single-output modules to eliminate differential frequency interference;** Use a remote point grounding to reduce the ground loop area.
4. Poor power supply withstand voltage
The issue concerns abnormal power module performance parameters—specifically, poor voltage withstand capability. While isolated power modules typically have withstand voltages of several kilovolts, situations may arise during application or testing where this specification cannot be met. What factors can significantly reduce their voltage withstand capability?
The withstand voltage tester has an overshoot issue upon startup; the isolation voltage of the selected module is insufficient; and reflow soldering and hot air guns were used multiple times during repairs.
This type of problem can be improved through two aspects: standardized testing and standardized usage, as detailed below:
**Increase the voltage gradually during the withstand voltage test;** Select a power module with a higher withstand voltage value; When soldering the power module, select an appropriate temperature and avoid repeated soldering to prevent damage to the power module.
