So I have the following circuit with two capacitors and a resistor in series. Shouldn't the sum of the voltage drops be equal to the voltage of the battery? Am I doing the time domain simulation wrong? I am new to this and see that the voltage on the first capacitor reaches 4.5 volts but the second one only reaches half of the value. why is this? |
by dan001
November 23, 2020 |

Your simulation does seem to be operating correctly. Voltages in the sim are relative to ground. The voltage for C2 is the voltage across C2 alone - 2.25v. However, the voltage for C1 is also relative to ground, thus it equals the voltage across C1 and C2 together - 2.25+2.25=4.5v. To see this, you can run my mod to your circuit with C1's voltage explicitly being measured. I used a negative expression for C1 to give a nice clean view. Otherwise, C1's would show up on top of C2's. https://www.circuitlab.com/circuit/u3948saww9ph/seriescaps/ It is helpful to view caps in series as voltages dividers, and the voltages across each will be calculated the same as two resistors using each caps' impedance. So, for 2 caps of equal value as you have, the 4.5volts should be divided equally. High power amplifier tubes in radio frequency amplifier circuits use voltages of 1000+ volts to produce the 1500W limit hams are allowed by license. We were always cautioned to recognize that while resistors could be +/-1 or 5%, caps were often +/- 20%, especially electrolytics. Thus to minimize the chance that you get a very unequal voltage division, we always included a high value resistor in parallel to each cap. the resistors "forced" the correct voltage division given the variability in value of the caps. |
+1 vote by jaf2009 November 23, 2020 |

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