I. How to select a suitable capacitor in a power supply
1. Energy storage
Depending on the power requirements, components may be connected in series, parallel, or a combination thereof. For power supplies exceeding 10kW, larger can-type screw-terminal capacitors are typically used. To select an appropriate capacitance value, its rated DC voltage, permissible voltage ripple, and charge/discharge cycles must be considered.
In a typical power supply, the capacitor ripple current is a combination of ripple currents at various frequencies. The RMS (root mean square) value of the ripple current determines the temperature rise of the capacitor.
A common mistake is calculating the RMS current load by summing the squares of the ripple current at various frequencies. In reality, the ESR of the capacitor must be accounted for as the ripple frequency increases. The correct approach is to estimate the ripple current at high frequencies (up to 100Hz) based on the frequency diagram of the ripple factor. Use the square of the estimated current to determine the ripple current. This is the true current load.
Since ambient temperature determines the lifespan of a capacitor under load conditions, reputable manufacturers have precisely defined the relationship between ripple current load, ambient temperature, and probabilistic life. Under actual operating conditions, the probabilistic life is determined using ripple current load and ambient temperature, while the published probabilistic life is taken as an absolute value.
2. Surge voltage protection
Modern power semiconductor devices with high switching frequencies are susceptible to potentially damaging voltage spikes. Surge voltage protection capacitors (such as EPCOS B32620-J or B32651..56) connected across these devices absorb voltage pulses and limit peak voltages, thus protecting the semiconductor device and making them an important component in the power device library. The rated voltage and current of the semiconductor device, as well as its switching frequency, influence the selection of the surge voltage protection capacitor. Because these capacitors withstand very steep DV/DT values, film capacitors are the appropriate choice for this application.
II. How to select suitable inductors in a power supply
Power inductors play a crucial role in electronic devices, storing and releasing electrical energy and stabilizing current and voltage output to ensure normal device operation. When selecting a suitable power inductor, several factors need to be considered, including inductance value, current handling capability, and quality factors. This article will introduce how to choose a suitable power inductor and provide some suggestions.
1. Selection of inductance value
Inductance is a crucial parameter of a power supply inductor, determining the amount of energy it can store. When selecting an inductor value, we need to consider the power supply's input and output current and voltage. Generally, high-power applications require larger inductance values to store more energy, thereby stabilizing current and voltage. For low-power applications, smaller inductance values can be chosen to meet the device's requirements.
2. Considerations for current withstand capability
Current withstand capability is another important parameter of a power supply inductor. It determines the maximum current the inductor can withstand. When selecting a power supply inductor, we need to determine the current withstand capability based on the power supply's maximum output current. Generally, the current withstand capability should be greater than the power supply's maximum output current to ensure the inductor can operate normally without damage.
3. Emphasis on quality factors
Quality is one of the most important factors to consider when selecting a power supply inductor. Good quality inductors ensure stable performance and extend their lifespan. When choosing a power supply inductor, we can refer to some quality assurance indicators, such as manufacturer reputation and product certifications. In addition, understanding other users' reviews can also provide valuable reference.
4. Size and Packaging Options
In practical applications, the size and packaging of the power inductor also need to be considered. The size should be chosen based on the space constraints of the equipment to ensure proper installation. The packaging should be chosen based on the equipment requirements and environmental conditions to ensure the reliability of the inductor.
5. Evaluation of temperature characteristics
Power supply inductors generate heat during operation. Therefore, evaluating temperature characteristics is one of the factors to consider when selecting a power supply inductor. When choosing an inductor, we need to understand its temperature characteristic parameters, such as maximum operating temperature and temperature rise. These parameters can help us determine whether the inductor's performance meets requirements under different temperature conditions.
