Simulation of parallel resistor-capacitor voltage divider based on Multisim

Author： GOZ Electric Time：2024-11-05 09:24:43 Read：14

Voltage divider is the main equipment for measuring AC high voltage and DC high voltage on site. Generally, voltage divider can use capacitor voltage divider or resistor voltage divider, or combined resistance and capacitance voltage divider. RC voltage divider combines the advantages of resistor voltage divider and capacitor voltage divider, and improves and develops on the basis of the two, greatly improving the response performance, and is a voltage divider with better performance. Voltage divider using mixed resistance and capacitance voltage divider is generally divided into series resistance and capacitance voltage divider and parallel resistance and capacitance voltage divider according to the circuit structure. In pulse high voltage and high current test device, RC voltage divider is generally used, and its response performance has been greatly improved, which is a more superior voltage divider. Series resistance and capacitance voltage divider circuit can reduce the inductance of capacitor loop, so as to suppress the oscillation of voltage divider. Therefore, series resistance and capacitance voltage divider is also called damped capacitance voltage divider, and its dynamic response characteristics are better than those of general pure capacitance voltage divider circuit. However, due to the series connection of resistor, the response speed of resistance and capacitance voltage divider is not as fast as that of capacitance voltage divider. Too large a damping resistor reduces the response speed. When the series RC voltage divider is connected to the pulse signal loop, the formation of the output pulse voltage will also be affected. On the contrary, if the connected damping resistor is too small, the oscillation cannot be completely eliminated. In addition, if the low-voltage arm of the voltage divider circuit only has a capacitor, the corresponding initial rise time will increase, so the dynamic response characteristics of the voltage divider are not very good, which will be clearly manifested when measuring the edge characteristics of the pulse signal.

The parallel RC voltage divider circuit is improved by adding a parallel capacitor to the resistor of the resistor voltage divider. Its characteristics are that the longitudinal capacitance of the voltage divider is increased, so that the potential distribution on the voltage divider is improved, the influence of the stray capacitance to the ground of the high-voltage resistor of the resistor voltage divider on the voltage divider is reduced, and the response characteristics of the voltage divider are greatly improved. The RC parallel voltage divider has good amplitude-frequency characteristics and higher linearity than the resistor voltage divider. Since the RC parallel voltage divider has a relatively large operating frequency band, it covers almost all test voltage ranges, whether DC, power frequency or even impulse voltage. This paper uses the circuit simulation and analysis software Multisim to study the transient performance of the RC parallel voltage divider. The switch with the delayed closing function is used to simulate the dynamic circuit, and the software is used to study the change of circuit voltage at the moment of switching and the influence of different component parameters on the corresponding output voltage. The transient response characteristics of the RC parallel voltage divider are verified.

1 Analysis of simulation results

It can be seen from the simulation results that the RC parallel voltage divider circuit does not meet the switching rule: the voltage across the capacitor cannot change suddenly. The reason is that to determine the initial value of the capacitor after switching, first determine whether ic is finite. When ic is finite, the switching rule is used, and when ic is infinite, the charge conservation law combined with Kirchhoff's law is used. The so-called charge conservation law means that if the charge in a certain area increases or decreases, then there must be an equal amount of charge entering or leaving the area; if a certain charge is generated or disappeared in a physical process, then there must be an equal amount of opposite-sign charges generated or disappeared at the same time. Because of this, Kirchhoff's first law is obtained. The charging process of the capacitor of the RC parallel voltage divider must satisfy the law of conservation of charge and Kirchhoff's law.

2 Significance of simulation

The voltage divider is the main device for voltage measurement. For fast-front high-voltage pulse signals, the voltage divider is required to have good response characteristics and stability. From the simulation results, it can be seen that in the case of a complex electromagnetic environment, due to the existence of stray capacitance and distributed capacitance, the voltage divider resistor network of the voltage divider can often be regarded as a RC parallel network. If the RC values of the high-voltage arm and the low-voltage arm are not properly selected, the output voltage waveform will be distorted. When designing a voltage divider, it is necessary to set reasonable RC parameters so that the output is as shown in the figure, that is, the resistance of the high-voltage arm of the voltage divider is required to be large enough compared to the resistance on the low-voltage arm of the voltage divider, and the capacitance of the high-voltage arm of the voltage divider is required to be small enough compared to the capacitance of the low-voltage arm of the voltage divider. This paper simulates the parallel RC voltage divider circuit by using Multisim. When the input is a pulse voltage (modeled as a circuit switching), the change of the output voltage of the circuit at the switching moment is studied, as well as the influence of different low-voltage arm capacitance C2 values on the voltage divided at the output end at the switching moment. Three different resistor-capacitor combinations were used to simulate the output voltage, and the changing rules of the output waveforms of different resistor-capacitor combinations were analyzed, which has reference value in the application of Multisim to study dynamic circuits and pulse high-voltage measurement.