Introduction

RC Circuit consists of resistors and capacitors. Depending on the configuration, RC circuit can be applied in various fields. For example, RC circuit can be used as a Delay circuit.

Step Response

Practical Issues

Voltage Rating

Every capacitor has a limit on the amount of voltage that it can withstand across its plates. The voltage rating specifies the maximum dc voltage that can be applied without risk of damage to the device. Below is a datasheet of a MLCC. Appropriate capacitors must be selected to avoid damage to the circuit.

Temperature Coefficient

The temperature coefficient indicates the amount and direction of a change in capacitance value with temperature. For example, a negative temperature coefficient of 150 ppm/°C for a 1 mF capacitor means that for every degree rise in temperature, the capacitance decreases by 150 pF.

Leakage

No insulating material is perfect. The dielectric of any capacitor will conduct some very small amount of current. Thus, the charge on a capacitor will eventually leak off. Some types of capacitors, such as large electrolytic types, have higher leakages than others.

Types of Capacitors

Mica Capacitor
Mica capacitors are available with capacitance values ranging from 1 pF to 0.1 mF and voltage ratings from 100 V dc to 2,500 V dc. Mica has a typical dielectric constant of 5.

Ceramic Capacitor
Ceramic dielectrics provide very high dielectric constants (1,200 is typical). As a result, comparatively high capacitance values can be achieved in a small physical size. Ceramic capacitors typically are available in capacitance values ranging from 1 pF to 100 mF with voltage ratings up to 6 kV.

Plastic-Film Capacitors
A film capacitor is a capacitor that uses a thin plastic film as the dielectric. They are relatively cheap, stable over time and have low self-inductance and ESR, while some film capacitors can withstand large reactive power values.

Electrolytic Capacitors
An electrolytic capacitor is a polarized capacitor which uses an electrolyte to achieve a larger capacitance than other capacitor types. Electrolytic capacitors have polarity. So, they must be forward biased.

Calculation of capacitance

Series

1/Ceq = 1/C1 + 1/C2 + … + 1/Cn

Parallel

Ceq = C1 + C2 + … + Cn

Applications

Delay Circuit

The larger R2, the longer it will take for the neon lamp to fully light up.

Charging State

4~5τ can be used as a settling time.

Discharging State

4~5τ can be used as a settling time.

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