# Research on a Novel Nanosecond Marx Generator and Its Efficiency Analysis
## 2 The Proposed Nanosecond Pulse Generator
### The 3 \(\times\) 5 Stage Marx Generator Based on Avalanche BJTs  
Compared with the traditional Marx generators based on avalanche BJTs, each avalanche BJT in the proposed nanosecond Marx generator turns on through self-breakdown without any triggering signal. The principle of the novel Marx generator is that the capacitors \(C_{\rm 1-5}\) are charged in parallel by a constant average current as indicated by the blue arrowed lines, and discharge to the load \(R_{\text{L}}\) in series as indicated by the red arrowed line in Figure 2.  
The series-resonant source charges the capacitors during the charging period, and when the avalanche breakdown voltage \(V_{\text{break}}\) is reached, it enters the discharge period and automatically discharges to the load. The voltage over the capacitors is related to the number of BJTs in series. When M BJTs are connected in series, the avalanche breakdown voltage is M times the breakdown voltage of a single BJT. Theoretically, the maximum voltage on the storage capacitor is \(MV_{\text{break}}\), \(V_{\text{C}}=MV_{\text{break}}\). In the experiment, \(MV_{\text{break}}\) is designed to be lower than \(nV_{\text{dc}}\) so that the series-resonant source always charges the capacitors with a constant current. During the discharging period, the voltage of capacitors is higher than the C-E breakdown voltage of the avalanche BJTs \(V_{\text{break}}\), all BJTs avalanche break down, and all diodes are reverse biased. A negative nanosecond pulse is obtained over the load. When the discharge current through the avalanche BJTs is lower than the cutoff current, the BJTs turn off, and the capacitors are charged again in parallel. In this way, repetitive negative pulses are obtained over the load. Pulses with a higher voltage amplitude can be obtained by connecting the number \(M\) of avalanche BJTs in series or increasing the number \(N\) of stages of the Marx generator. The theoretical waveform of the circuit is shown in Figure 4. The pulse frequency can be adjusted by changing the average charging current. The higher the average charging current is, the higher the pulse repetition frequency.  
To further improve the energy efficiency of the generator, isolation inductors are used to replace the isolation resistors, as shown in Figure 5.  
The inductors store or release the energy as current changes, and the energy loss of the circuit can be reduced. At the same time, a BJT T16 is added to ensure the first stage of the circuit is turned on first. As shown in Figure 5, C1 is charged by the series-resonant charging power supply through R1 as shown in the red line, and the Base current \(\text{I}_{\text{b}}\) can turn on T16. The capacitors C1\(\sim\)C5 will be charged as indicated by the blue arrowed lines. Since C1 is charged first, T1\(\sim\)T3 will breakdown first as if they are turned on first. Then, the  
Figure 4: The theoretical waveforms with different average currents in the novel generator.  
other stages will rapidly break down due to the overvoltage, and the capacitors discharge to the load in series.