Study On Short Pulse MOSFET Modulator And Its Trigger And Control Techniques

The recent development of pulse modulator is to use solid-state switches such as IGBT (Insulated Gate Bipolar Transistor ) and power MOSFET(Metal Oxide Semiconductor Field Effect Transistor)etc. as substitute for hydrogen thyratrons. Solid-state modulators have many advantages such as smaller size, more stable and higher frequency etc. At present, solid-state modulators are widely studied in many famous laboratory of the developed countries, while there are few reports about solid-state modulators in China. Power MOSFET, with its switch time lower than 20ns, can be used as switches in modulators which can generate short pulse with the width of around 100 ns. This paper studied MOSFET modulators from two aspects. First, the characters of MOSFET modulators with different circuit topologies were studied from theory and experiments. In the other hand the trigger circuit, driver circuit and control circuit of MOSFET switches were also studied.MOSFET is a rigid-tube, and the external trigger signal can turn it on and off. The energy is stored in capacitors in MOSFET modulators. When the MOSFET switches are turned on, pulse power is generated on the load. The distributed inductance of the main loop which can increase the rise time of the pulse must be reduced. When many cell modulators are paralleled, their distributed inductions are also paralleled, the effective distributed inductance of the modulator is reduced. The inductive-adder modulator which is made up of many cell modulators which drive the primary winding of a number of 1:1 pulse transformer are also studied to generate high voltage output. The secondary windings of the pulse transformers are connected in series. Both the primary and secondary winding consists of a single turn to keep the leakage inductance small. The output voltage on the secondary winding is the sum of all the voltages appearing on the primary windings. The output character of a small inductive-adder modulator which is made up of 2 cell MOSFET modulators consisted of 6 single MOSFET modulators. The pulse current with 25ns rise time, 60ns flat top time, 40A amplitude is generated on the 20Ω load with the 450V charge voltage. The trigger circuit which can generate fixed frequency and width pulse signal is...