Several types of modern equipment require an electrical power supply that is capable of producing high energy pulses at a very high pulse repetition rate. Examples of these include, but are not necessarily limited to, certain laser systems, and more modernly, extreme ultraviolet (EAV) sources for advanced photolithography techniques.
Heretofore, resonant circuits that are configured to charge a capacitor have been employed when power at a high pulse repetition rate has been required. These resonant circuits typically include an inductor in addition to the capacitor. When a power source (e.g. battery) is connected to the resonant circuit and activated, a voltage appears across the capacitor that increases from zero to a maximum value during a time period, t, defined by the LC circuit. After the voltage across the capacitor reaches the maximum value, a load (e.g. UAV laser) can be connected to the resonant circuit to discharge the capacitor and energize the load. This sequence of charging and discharging the capacitor can be repeated, as desired, to drive the load with a train of substantially constant energy pulses.
One problem associated with the above-described resonant charge circuit is the regulation of the maximum voltage across the capacitor. Specifically, any residual voltage on the capacitor (i.e. voltage remaining between pulses) will affect the maximum voltage on the capacitor at the end of a charge transfer. In attempts to overcome this difficulty, dequeing techniques have been developed and used. In general, these dequeing techniques have employed a voltage probe to monitor the voltage across the capacitor. When the desired voltage is reached, a switch is used to divert current from the resonant circuit, and as a result, stop all charge transfer to the capacitor.
By way of example, FIG. 1 shows a typical, prior art resonant circuit (generally designated 10) that uses a dequeing technique to charge a capacitor 12 at a high pulse repetition rate. As shown, the resonant circuit 10 includes an inductor 14, a power source 16, diodes 18, 19, 20 and two transistor switches 22, 24 (note: the circuit 10 also requires a voltage probe and control circuit that are not shown in FIG. 1). Operation of the resonant circuit 10 begins by closing switch 22 at time t=0. With switch 22 closed, the capacitor 12 is resonantly charged with current that passes through the diode 20 and inductor 14. Once the voltage probe indicates that a desired voltage across capacitor 12 has been reached, the control circuit quickly closes switch 24. With switch 24 closed, all remaining current in the circuit 10 is routed through the circuit branch 21 having switch 22, switch 24 and the inductor 14. With the circuit 10 in this configuration, all current flow to the capacitor 12 is stopped. Switch 22 is then opened, diverting current from branch 21 through a circuit branch 25 having the power source 16, diode 18, inductor 14 and switch 24. This allows the energy in the inductor 14 to be returned to the source 16 and recovered. The charge across the capacitor 12 can then be maintained until required by a load (not shown). Once the capacitor 12 has been discharged, switch 24 is then opened, configuring the circuit 10 to generate the next pulse.
In a typical setup of the prior art resonant circuit 10 shown in FIG. 1, the desired voltage across the capacitor 12 is selected to be less than the peak voltage generated by the resonant circuit 10, which in turn, is typically about twice the voltage of the source 16. For the circuit 10, the switches 22, 24 are preferably constructed of either MOSFET's or IGBT's, which unfortunately, have limited voltage ratings. Specifically, operational charging voltages for the circuit 10, as shown, have been generally limited to a maximum voltage that is below about 2 kV.
In light of the above, it is an object of the present invention to provide a power supply that is capable of producing pulses at a very high pulse repetition rate and that is operable at relatively high voltages (i.e. greater than about 2 kV). It is yet another object of the present invention to provide a system for charging a capacitor at a high voltage and high pulse repetition rate while accurately regulating the maximum voltage across the capacitor. Yet another object of the present invention is to provide a high pulse rate, pulsed power system which is easy to use, relatively simple to implement, and comparatively cost effective.