Voltage Multiplier Rectifier Research Articles

Series resonant ZCS–PFM DC–DC converter with multistage rectified voltage multiplier and dual-mode PFM control scheme for medical-use high-voltage X-ray power generator

In general, high-voltage DC power supplies employing a variety of high-frequency inverters are implemented for constant value control schemes. In particular, their good transient and steady state performances cannot be achieved under wide load variations for a medical-use high-voltage X-ray generator, ranging from 20 kV to 150 kV in the output voltage and from 0.5 mA to 1250 mA, respectively. A high-voltage DC power supply designed for X-ray power generator applications is considered, which uses a series resonant inverter-linked multistage DC voltage multiplier instead of a conventional high-voltage diode module rectifier connected to the secondary side of a high-voltage transformer. A constant on-time/variable frequency control scheme of this converter operating at zero-current soft switching mode is described. Introducing the capacitor–diode cascaded multistage voltage multiplier, the secondary turn numbers and secondary-side stray capacitance of the high-voltage, high-frequency transformer, as well as the rectifier diode voltage ratings, can be greatly reduced. It is shown that the proposed converter control scheme of the two-step selective changed frequency selection switching is more effective for improving the output voltage responses. The series resonant high-frequency transformer-linked voltage-multiplying rectifier is evaluated for an X-ray high-voltage generator on the basis of simulation analysis and observed data in experiment.

A High-Voltage, Cold-Cathode Rectifier

A new cold-cathode, high-voltage rectifier is described. Both theory and extensive experimental data are included. The operation of the tube is based upon an improved type of electron trapping similar to that occurring in a cylindrical magnetron in the cutoff condition, but augmented because of the use of end plates on the cathode. Mercury vapor is used, which at normal operating temperatures, provides a gas at a pressure of from 10-3 to 10-2 mm of Hg. Because of this low pressure and the small dimensions of the tube, ionization is inhibited when the cathode is positive, and highpeak inverse voltages are possible. However, when the anode is positive, the improved electron trapping results in conduction in spite of the low pressure and small dimensions. Experimentally, this rectifier has been operated up to 40-kv peak inverse voltage. Life tests at 30-kv peak inverse voltage and a current of 0.4 ma, at 60 cps, have run to 3,000 hours. Satisfactory operation has been obtained over a temperature range from 20 to 80 degrees C. The upper frequency limit lies between 120 and 240 kcps. This tube appears to offer, for the first time, a practical cold-cathode rectifier for output voltages up to 14 kv and currents up to one ma. Its advantages are particularly valuable in the case of voltage-multiplier rectifier circuits, since high-voltage insulated cathode-heater transformer windings are not necessary.

A Cyclotron at the Science Museum

PROF. E. O. LAWRENCE, of the University of California, has very kindly lent to the Science Museum the cyclotron, built by himself and Livingston in 1931, with which his first nuclear transmutation work was carried out in 1932. With an applied oscillating potential of only 4,000 volts peak, this instrument was capable of accelerating protons to a speed equal to that produced by a fall through 1,200,000 volts. The instrument was slightly modified afterwards by M. G. White for experiments on the scattering of protons in hydrogen, and in this modified form it has now been placed on exhibition in the Science Museum in close proximity to Cockcroft and Walton's original apparatus, which accelerated protons through 600–700 kilovolts by means of a D.C. voltage of this amount derived from a transformer through a special voltage-multiplying rectifier circuit. Prof. Lawrence has also lent to the Museum a small collection of photographs illustrating the development of the cyclotron. One of these shows the two preliminary cyclotron models built by Lawrence and Edlefsenin 1930, which, though relatively crude, gave encouragement for further development because they showed resonance effects; a further photograph shows the original cyclotron of Lawrence and Livingston, which accelerated hydrogen molecular ions through 80,000 volts with an applied high-frequency potential of less than 2,000 volts ; and a series of views illustrates the latest cyclotron of Lawrence and Cooksey, which delivers currents of the order of 100 micro-amperes of deuterons with energies in the neighbourhood of 8 million volts, or a beam of alpha-particles of about one micro-ampere at 16 million volts.