Electrolytic capacitor in switching power supply

The filter capacitor used at the output of the switching power supply is different from the filter capacitor selected in the power frequency circuit. The ordinary electrolytic capacitor used as filter in the power frequency circuit has a pulsating voltage frequency of only 100 Hz. The discharge time is on the order of milliseconds. In order to obtain a smaller pulsation coefficient, the required capacitance is as high as hundreds of thousands of microfarads. Therefore, ordinary aluminum electrolytic capacitors are generally used for low frequency.

As an electrolytic capacitor for output filtering in a switching stabilized power supply, the frequency of the sawtooth voltage is as high as tens of kilohertz or even tens of megahertz. Its requirements are different from those in low-frequency applications. The capacitance is not the main indicator, but it is good or bad. It is its impedance frequency characteristics. It must have low impedance in the working frequency band of the switching stabilized power supply. Because of the peak noise up to hundreds of kilohertz generated by the semiconductor device starting to work, it can also have a good filtering effect.

The special high-frequency aluminum electrolytic capacitor for switching power supply has four terminals. The two ends of the positive aluminum sheet are led out as the positive electrode of the capacitor, and the two ends of the negative aluminum sheet are also led out as the negative electrode. The current of the regulated power supply flows in from one positive end of the four-terminal capacitor, passes through the inside of the capacitor, and then flows from the other positive end to the load; the current returned from the load also flows in from one negative end of the capacitor, and then flows from the other negative end to the power supply Negative end. High-frequency aluminum electrolytic capacitors have good high-frequency characteristics, which provide advantages for reducing the pulsating component of the output voltage and suppressing switching spike noise.

Laminated capacitors are also called non-inductive capacitors. Generally, the cores of electrolytic capacitors are rolled into a cylindrical shape, and the equivalent series inductance is relatively large. Cancellation, and reduce the value of the inductance, has more excellent high-frequency characteristics, this kind of capacitor is generally made of square, easy to fix, but also can appropriately reduce the volume of the machine.