The role of capacitors in the circuit is generally summarized as: AC, DC. Capacitors typically function as filtering, bypassing, coupling, decoupling, and switching. As an energy storage component, it is also an important application field of capacitors. Compared with energy storage components such as batteries, capacitors can be charged and discharged instantaneously, and the charge and discharge current is basically unlimited, which can provide high-power transient pulse current for some devices. .
1. DC blocking: The function is to prevent DC from passing through.
2. Bypass (decoupling): Provides a low impedance path for some of the parallel components in the AC circuit.
3, coupling: as a connection between the two circuits, allowing the AC signal to pass and transmit to the next level of the circuit
4. Smoothing or filtering: Turn the pulse wave after rectification into a smooth wave close to DC, or consider ripple and interference waves.
5, temperature compensation: for the impact of other components on the temperature is not enough to compensate, to improve the temperature stability of the circuit.
6. Timing: The capacitor is used in conjunction with a resistor to determine the time constant of the circuit.
7. Tuning: System tuning of frequency-dependent circuits such as cell phones, radios, and televisions.
8. Energy storage: The energy storage capacitor collects the charge through the rectifier and transmits the stored energy to the output of the power supply through the converter lead. Aluminum electrolytic capacitors with voltage ratings between 40 and 450 VDC and capacitance values between 220 and 150 000 μF are more common specifications. Depending on the power requirements, the devices are sometimes used in series, in parallel, or a combination thereof. For power supplies with power levels above 10 kW, bulky screw-type terminal capacitors are typically used.
9. Surge voltage protection: Modern power semiconductor devices with high switching frequencies are susceptible to potentially damaging voltage spikes. Surge voltage protection capacitors across the power semiconductor device limit the peak voltage by absorbing voltage pulses, thereby protecting the semiconductor device, making the surge voltage protection capacitor an important part of the power component library.
The rated voltage and current values of the semiconductor device and its switching frequency are selected around the surge voltage protection capacitor. Because these capacitors are subject to very steep dv/dt values, film capacitors are the right choice for this application. It is not possible to select a capacitor based solely on the capacitance value / voltage value. When selecting a surge voltage protection capacitor, the required dv/dt value should also be considered.
10, EMI / RFI suppression: These capacitors are connected at the input of the power supply to mitigate electromagnetic or radio interference generated by the semiconductor. These capacitors are susceptible to damaging overvoltages and transient voltages due to their direct connection to the main input line. X-stage and Y-stage capacitors using plastic film technology offer one of the cheapest suppression methods. The impedance of the suppression capacitor decreases as the frequency increases, allowing high frequency current to pass through the capacitor. The X capacitor provides a "short circuit" to this current between the lines, and the Y capacitor "shorts" this current between the line and the grounded device.
11, control and logic circuits: all types of capacitors may be used in the power control circuit. These capacitors are generally chosen for low voltage, low loss, general purpose components, except in harsh environmental conditions.
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