As capacitors, safety capacitors are well known to us, including safety x capacitors and safety Y capacitors, which play the role of protecting users at all times. X capacitor is the capacitor that is bridged between two lines of power line (L-N), generally metal film capacitor; y capacitor is the capacitor that is respectively bridged between two lines of power line and ground (l-e, N-E), generally in pairs. Based on the limitation of leakage current, the value of Y capacitor should not be too large. Generally, the value of X capacitor is UF and that of Y capacitor is NF. The X capacitor suppresses the differential mode interference and the Y capacitor suppresses the common mode interference.
What are the specific uses of safety capacitors used in various power circuit boards?
1: safety capacitor for filtering
Filtering is a very important part of the role of safety capacitors. It is used in almost all power circuits. In theory, the larger the capacitance, the smaller the impedance, and the higher the passing frequency. But in fact, most of the capacitors over 1uF are electrolytic capacitors, which have a large inductance component, so the impedance will increase when the frequency is high. Sometimes you will see a large electrolytic capacitor with a small capacitor connected in parallel. At this time, the large capacitor is connected to the low frequency and the small capacitor is connected to the high frequency. The function of the capacitor is to pass high impedance and low impedance, and pass high frequency to block low frequency. The larger the capacitance, the easier it is to pass low frequencies, and the larger the capacitance, the easier it is to pass high frequencies. Specifically used in filtering, a large capacitor (1000uF) filters low frequencies, and a small capacitor (20pF) filters high frequencies.
Safety capacitors are used as filter capacitors and can be compared to "water ponds". Since the voltage at both ends of the capacitor does not change suddenly, it can be seen that the higher the signal frequency, the greater the attenuation. It can be said that the capacitor is like a pond and will not change the amount of water due to the addition or evaporation of a few drops of water. It converts changes in voltage into changes in current. The higher the frequency, the greater the peak current, thus buffering the voltage. Filtering is the process of charging and discharging.
2: safety capacitor for bypass
The bypass capacitor is an energy storage device provided for local devices. It can uniformize the output of the regulator and reduce the load demand. Just like a small rechargeable battery, the bypass capacitor can be charged and discharged to the device. In order to minimize the impedance, the bypass capacitor should be as close as possible to the power supply pin and ground pin of the load device. This can well prevent the ground potential rise and noise caused by the input value being too large. The ground bounce is the voltage drop at the ground connection when a large current glitch passes through it.