# Cancer Treatment: An Overview of Pulsed Electric Field Utilization and Generation
## 9 Pulse Generators
### Non-Modular PGs  
1. SMPS-Based PGs  
Generally speaking, SMPS is used as an isolated and non-isolated DC-DC converter to step voltage levels up/down. The normal output of SMPS is pulsed voltage and current, then filters are added to smooth the output based on the ripples accepted by the load. In the application of PG, filters are not required as the load requirements are pulsed waves.  
In [80], the flyback topology shown in Figure 15a was utilized to generate HV pulses, with a modification in output stage by removing the capacitor filter and utilizing a resistor, capacitor, and diode (snubber circuit) in the primary side to reset the transformer core and reduce the overvoltage spike stress on the switching device. When the switching device \(Q\) is  
Figure 14: Direct capacitor discharge circuit for capacitive and resistive loads.  
on, the energy is stored in the transformer magnetic circuit, and after turning off the switch the power is transferred to the secondary side and the diode directs the current flow. The secondary voltage is reflected onto the primary during the diode conduction period; thus, the switch should withstand the supply voltage added to the reflected secondary voltage.  
In [81], the buck-boost circuit supplies a low-voltage switch-diode-capacitor stack, as shown in Figure 15b. Capacitors are charged and pulses are shaped by controlling the switches. This topology requires complicated control to charge and shape the pulse, and can generate only unipolar pulses. In [82], two boost converters sharing the same ground were utilized, and the load was connected differentially between the positive ports. This configuration can generate bipolar pulses, while the operation depends mainly on the parameters of the passive components [29]. In [83], a single boost converter was utilized and the load was differentially connected between the output- and input-positive ports, as shown in Figure 15d. This topology can only generate unipolar pulses, and does not require HV switches.  
II. CDVM-Based PGs  
The CDVM, shown in Figure 16, is the simplest module utilized to build an HV output from an LV source by using two capacitors and two diodes. Usually, CDVM is supplied from an AC source, not a DC source, and the output of CDVM is smooth HV DC, not a pulsed shape. Therefore, it can be followed with a stack of series-connected switches to generate unipolar pulses. An H-Bridge circuit is another simple converter used to generate bipolar pulses. In [84], CDVM was utilized to build an HV PG by utilizing two semiconductor switches to switch from the charging state to the pulse generation state. This circuit is simple and utilizes a moderate number of semiconductor devices, and shares a similar concept with the Marx PG. In [85], the authors presented an HV PG based on a two-stage converter and fed from an AC source. The first stage was a rectifier followed by a buck-boost converter, the second consisted of two CDVM branches with a stack of HV switches, and the load was connected differentially in between. In [86; 87], CDVM  
Figure 15: SMPS-based PGs: (**a**) flyback, (**b**) buck-boost, (**c**) front-to-front boost, and (**d**) boost converter.  
was utilized as a basic building block with the switches in a different configuration and cascaded modules used to reach HV.