Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-10-31
2001-12-11
Nguyen, Matthew (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S222000
Reexamination Certificate
active
06329803
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention relates generally to switching circuits. More specifically, embodiments of the present invention are directed to circuits for providing magnetic assistance to high power switching devices, such as those used in high power modulator circuits in applications such as radar, accelerators, medical accelerators, pulsed lasers and the like.
2. The Relevant Technology
A number of applications require the use of very high current pulses of extremely short and precise duration. For example, various types of pulse forming networks or capacitor loads are used to supply short duration, fast-rising, high peak-amplitude voltage and current pulses to various types of loads, such as medical linear accelerator systems, magnetrons, laser systems and the like. A typical approach for providing such pulses is to deliver energy to an intermediate pulse forming network or storage capacitor, and then utilize a high power switching device to accurately discharge the energy into a load, such as the linear accelerator, laser, etc.
It will be appreciated that the delivery of a fast-rising, short duration and high peak-amplitude voltage/current pulse is dependent largely on the operating efficiency of the switching device used. Moreover, in such applications involving high power pulses and requiring high frequency and extended operating periods, the switches used must be reliable. To improve switching efficiencies and reliability, such switches are often supplemented with a saturable reactor device, typically referred to as a magnetic assist switch. For example, in thyratron-switched circuits where large currents must be switched quickly (i.e., when large values of di/dt are present), a saturable magnetic switch is often connected in series with the tube. Use of the magnetic device provides several advantages. First, it reduces the commutation losses typically associated with a high power switch, such as a thyratron and the like. For example, the use of a magnetic switch provides magnetic pulse compression that improves switch life by reducing the amount of anode dissipation during the commutation phase of the thyratron. This also reduces cooling requirements. Second, the magnetic switch reduces switch damage. In particular, it reduces the amount of anode damage caused by high-energy electrons associated with the initial period of the commutation switch phase. This also reduces the likelihood of exposing impurities embedded in the anode to other portions of the switch tube. Also, use of a saturating magnetic switch in series with the thyratron maintains the integrity of the anode surface, and therefore maintains the voltage integrity of the switch. Consequently, use of this type of saturating magnetic device improves the primary switch life, and increases the operating efficiency of the primary switch.
However, while the overall usefulness of the magnetic switch assist has been recognized, the manner of using the device has resulted in some undesirable problems. In particular, the magnetic switch device has traditionally been connected in series with the primary switch directly to the high voltage connection of the primary switch. Interconnection of the components in this manner makes it difficult to connect a reset bias supply circuit to the magnetic material portion of the magnetic switch, and thus requires a magnetic assist switch that is significantly larger that what would otherwise be desired. This increases the number and/or size of the electronic components needed, and thus increases the overall cost and complexity of the of the switch circuit.
Consequently, there is a need for a switching circuit that is capable of receiving energy from an intermediate pulse forming network or storage capacitor, and then discharging the energy into a load, such as the linear accelerator, laser, etc. Further, it would be an improvement if the device utilized a magnetic switch assist device during the turn-on phase. Moreover, it would be an improvement if the circuit provided the ability to utilize a reset bias supply signal for use by the magnetic switch, but that does so in a manner so as to utilize a minimal number of electrical components. Further, it would be desirable if the reset bias was provided in a manner so as to reduce the amount of saturated inductance needed in the magnetic switch and thereby improve the ability to provide short pulse durations and fast pulse rise times. It would also be an improvement if the magnetic switch device would have a lower overall physical package size, thereby reducing the physical space and cost associated with the overall circuit. Embodiments of the present invention address these and other needs.
BRIEF SUMMARY OF EMBODIMENTS OF THE INVENTION
In view of these and other problems present in the prior art, it is an overall objective of the present invention to provide an improved switch circuit and method that is capable of discharging energy from a pulse forming network or capacitor load to a load, such as a linear accelerator, laser, etc., in the form of a fast-rising, short duration and high peak-amplitude voltage/current pulse. Moreover, it is an overall general objective to provide a circuit that utilizes a minimal number of circuit components, and that also provides the advantages otherwise associated with the use of a magnetic assist switch. Similarly, it is an overall objective to provide a circuit in which the magnetic assist switch is physically smaller in size due to a lower required saturated inductance requirement, by virtue of a bias reset signal. The circuit and method contemplated have ideal application in connection with high power modulator circuits, such as those that may be used in such applications and devices that include radar, accelerators, medical accelerators (e.g., klystron devices), pulsed lasers and the like.
By way of summary, embodiments of the present invention are directed to an improved switch circuit and method, that receives energy from a pulse forming network or capacitor load, and that is capable of discharging that energy to another load in the form of a fast-rising, short duration and high peak-amplitude voltage/current pulse. In a preferred embodiment, the switching circuit includes at least one high power, solid state switch device that has a first input electrically connected to a first terminal of the energy storage circuit (e.g., a pulse forming network or capacitive load). The switch is oriented so as to be capable of selectively discharging energy from the energy storage circuit to the input of a step-up pulse transformer. The output winding of the transformer is then connected to the load that requires the output pulse (e.g., the linear accelerator, laser system, etc).
Disposed between the energy storage circuit and the step-up pulse transformer is a saturable reactor device that provides a predetermined amount of saturated and unsaturated inductance. In preferred embodiments, this device is comprised of a magnetic assist switch, which has an input terminal connected to an output terminal of the energy storage circuit. An output terminal of the magnetic assist switch is then connected to the primary winding of the pulse transformer. The magnetic assist switch provides a predetermined level of unsaturated inductance so as to reduce the overall switching losses of the solid state switch, and to improve the reliability and operating life of the solid state switch.
Preferred embodiments further include a bias circuit, comprised of a DC reset bias supply and a reset bias inductor. This circuit is electrically connected directly to at least one turn of the magnetic assist switch so that the bias circuit is capable of supplying a bias reset signal to the core of the assist switch, thereby providing a larger magnetic flux swing within the switch and resulting in a lower saturated inductance. This improves the overall operating characteristics of the magnetic assist switch in a manner so that a smaller magnetic switch can be used. Moreover, the DC reset bi
Nguyen Matthew
Varian Medical Systems Inc.
Workman & Nydegger & Seeley
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