# An Overview of Non-Isolated Hybrid Switched-Capacitor Step-Up DC-DC Converters
## 1 Introduction
### SC Voltage Multipliers with Digital Input Signals  
The single-phase rectifiers mentioned in the last section were mainly used to obtain a large dc voltage from the utility grid, especially for generating a large electric field in particle accelerators. Still, their main applications were to obtain a relatively large voltage in electronic circuits, for example, digital circuits [17; 18]. An example of these multiple inputs, which are usually digital signals, is shown in Figure 4 (as shown in [18]).  
Figure 4: A multiple auxiliary input SC voltage multiplier [18].  
Figure 3: Several topologies of ac-to-dc switched-capacitor voltage multiplier (\(\times 6\) multiplier) (**a**) both side series capacitor topology, (**b**) combination of grounded (**left**) and series (**right**) topology, (**c**) combination of series (**left**) and grounded (**right**) topology, and (**d**) both sides (**left** and **right**) grounded topology.  
Figure 2: Ac-to-dc switched-capacitor voltage doubler (**a**) topology, (**b**) equivalent circuit when the input voltage is the negative half cycle, (**c**) equivalent circuit when the input voltage is in the positive half cycle.  
The input voltage in Figure 4 is a dc signal; the converter does not contain transistors, but two additional input pulsating signals drive the converter. Those additional pulsating signals are digital, and they take values of high and low that can, instead, be 5 V for high and 0 V for low. They are square signals with a phase shift of 180\({}^{\circ}\) between them; this produces only two equivalent circuits because when one signal is high, the other is low. The additional input signals are called \(v_{1}\) and \(v_{2}\). Figure 5 shows the two equivalent circuits.  
Input signals \(v_{1}\) and \(v_{2}\) in Figure 5 act as one firing signal with their complement, \(v_{1}\), being a square signal (50% of duty cycle), and \(v_{2}\) being their complementary signal; \(v_{2}\) is high when \(v_{1}\) is low and vice versa. This produces two equivalent circuits shown in Figure 5.  
In Figure 5, capacitor \(C_{1}\) is charged with the input voltage \(v_{g}\), at the second semi-cycle (Figure 5a). The capacitor \(C_{1}\), in series with the input voltage source, charges \(C_{2}\) with twice the input voltage in the next semi-cycle (Figure 5b), the capacitor \(C_{2}\), in series with the input voltage source, charges \(C_{3}\) with three times the input voltage. In the next semi-cycle (Figure 5a), the capacitor \(C_{3}\), in series with the input voltage source, charges \(C_{4}\) with four times the input voltage, and so on. The circuit in Figure 5 produces an output equal to seven times the input voltage.  
Other topologies can work with the same principle; for example, Figure 6 shows a simplification of the circuit in Figure 4, in which one of the digital signals is always low, and only one digital signal is required, but in this case, the voltage gain is smaller than in Figure 4.  
There are other topologies with multiple digital (or AC) inputs and a dc power source, and a voltage multiplier can be fed only with digital signals (without the dc source); as an example, see Figure 7, as shown in [17].  
Figure 5: Equivalent circuits of the multiplier in Figure 4. (**a**) First equivalent circuit when \(v_{1}\) is high and \(v_{2}\) is low, and (**b**) second equivalent circuit when \(v_{2}\) is high and \(v_{1}\) is low.  
Figure 6: A reduced version of the converter shown in Figure 4[18].