CAPACITANCEDC CircuitsExample 3: Find the total capacitance of three capacitors in parallel, if the values are15 µF-50 V, 10 µF-100 V, and 3 µF-150 V (Figure 17). What would be theworking voltage?Figure 17 Example 3 - Capacitors Connected in ParallelCTC1C2C315µ F10µ F3µ FCT28µ FThe working voltage of a group ofcapacitors in parallel is only as high asthe lowest working voltage of anindividual capacitor. Therefore, theworking voltage of this combination isonly 50 volts.CapacitiveTimeConstantWhen a capacitor is connected to a DC voltage source, it charges very rapidly. If no resistancewas present in the charging circuit, the capacitor would become charged almost instantaneously.Resistance in a circuit will cause a delay in the time for charging a capacitor. The exact timerequired to charge a capacitor depends on the resistance (R) and the capacitance (C) in thecharging circuit. Equation (3-13) illustrates this relationship.TC = RC (3-13)whereTC = capacitive time constant (sec)R = resistance (ohms)C = capacitance (farad)The capacitive time constant is the time required for the capacitor to charge to 63.2 percent ofits fully charged voltage. In the following time constants, the capacitor will charge an additional63.2 percent of the remaining voltage. The capacitor is considered fully charged after a periodof five time constants (Figure 18).ES-03 Page 16 Rev. 0
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