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From our parts list we will add a capacitor to our heater circuit and get the schematic shown in Figure 3-3.
Figure 3-3: Switched Capacitor Converter
One might erroneously argue that the only dissipative element in this circuit is the load and all energy from the source goes to the load. Therefore if we control the switch to maintain 5 Vdc on the capacitor we have a 100% efficient converter. This is not the case since charging a capacitor directly from a voltage source or capacitor dissipates as much energy as is transferred to the capacitor. This problem, Energy Loss in Charging a Capacitor, is discussed in the problem section of the SMPS Technology Knowledge Base. Since you will see this circuit in many variations throughout your design career, it is well to recognize it and understand it. This circuit has it uses, but high efficiency power conversion from a source that is significantly different from the output is not one of them. In order to keep the voltages near each other and increase efficiency, many applications switch topologies during operation (e.g. from a voltage doubler to a tripler) to improve the efficiency of this circuit.
