What is the reverse capacitance? Do you need to use the PCB ground plane and power plane?

What is the reverse capacitance?

The line-return capacitor, the package inductor and the equivalent capacitance in the circuit together form a parallel resonant circuit. The line capacitance of the reverse path determines the length of the line scan reversal time, the capacitance capacity decreases, the scan reversal time is short, the output anode voltage rises, the deflection power is relatively small, the grating amplitude is reduced, the line reverse capacitance capacity becomes larger, and the output voltage is lowered. The grating amplitude increases. Therefore, if necessary, the magnitude of the grating amplitude can be changed by adjusting the magnitude of the reverse path capacitance (excluding the S correction capacitor capacity abnormality). The reverse capacitance is damaged, the false soldering, and the capacitance is reduced, which is the cause of damage to the line output power tube. Huawei Network China Computer Repair Network - the most in China.

The size of the capacitor in the reverse direction also determines the size of the high voltage. When the capacitance of the reverse path is small, the number of times the line tube is turned on becomes faster, and the output voltage of the line output transformer is increased, which also makes the amplitude of the image larger. Then the capacitance is made larger and the high voltage is lower.

Do you need to use the PCB ground plane and power plane?

Multilayer PCBs typically include one or more pairs of voltage and ground planes. The power plane functions as a low-inductance capacitor that constrains the RF capacitance generated on components and channels. The chassis generally has multiple grounding points connected to the ground plane, which helps to reduce the voltage gradient between the chassis and the PCB of the PCB board and between the PCB boards. The voltage gradient is the primary source of the common mode RF field and is the source of the RF power from the chassis to the ground. Like capacitors, the power and ground planes also have very small equivalent lead length inductance, but no ESR. However, in most layer PCB boards, the maximum inter-board inductance between the two components is much less than 1nH.

Where ε0=8.85pF/m is the free space dielectric constant; εr is the relative dielectric constant of the medium between the power plane and the ground plane; A is the area of the power plane and the ground plane overlap; d is the power plane and ground The distance between the planes.

The actual capacitance value is usually less than this calculated value. In general, network analysis, mathematical calculations, or simulation experiments will give the actual inductance values of the power plane, as well as the impedance values and potential self-resonant frequencies of all circuit layers.

Since discrete decoupling capacitors are typically used in multilayer PCBs, the value of the capacitor at slower edge rates at low frequencies must be considered, typically less than 25 MHz.

The impedance of the "bare PCB" is very close to the impedance of an ideal decoupling capacitor. The ideal decoupling capacitor is a capacitor with only pure capacitance and no additional inductance and resistance. The ideal impedance is calculated as

When the frequency is higher than fa, the additional n discrete decoupling capacitors do not provide additional benefits because the impedance of the bare PCB is much less than the impedance of a separate capacitor load. When approaching the pole frequency of the load PCB (parallel resonance), the value of the impedance of the load PCB is abnormally high, and the decoupling performance of the load PCB is much worse than that of no load (without additional discrete decoupling capacitors). The results of the analysis clearly show that reducing the series inductance of the decoupling capacitor wiring is the key to achieving the desired performance over a wide frequency range.

The parallel resonance corresponds to the pole and the series resonance corresponds to the zero. When multiple capacitors are provided, the poles and zeros will alternate. Therefore, there is a parallel resonance between each pair of series resonant frequencies. There is always one parallel resonance point between the two series resonances.