Fast Recovery Diode Research Articles

1.2 MW DC-DC converter

A DC-DC power converter has been developed to charge power capacitors to 16 kV from a 400 V battery bank. It is designed to charge an 8.5 MJ bank nine times in 3 min. The converter is composed of six modules, each producing 12.5 A of charging current, and an enclosure which houses the modules and provides control power and a master controller. The six 200 kW modules have a combined power rating of 1.2 MW. The pulse width modulation converter system operates at 24 kHz and contains inverters with power metal-oxide-semiconductor field effect transistors (MOSFETs) as the principal inverter components, 200 kW power transformers and power inductors, and full-bridge rectifiers with fast recovery diodes. The converter modules have a volume power density of 1.0 MW/m/sup 3/ and a mass power density of 1.2 kW/kg. The converter design and test results are described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Investigations on turn-off effects in fast-recovery power diodes by modelling and simulation

A model describing the transient turnoff behaviour of a fast-recovery power diode is derived and implemented into a simulation program for analysis of electrical networks. The modelling is based on the physical processes in the low-doped middle region of the semiconductor device, using the charge control approach and approximating the excess charge distribution by sinusoidal curves. The transient behaviour of the model is verified by experimental measurements in a chopper circuit with a MOSFET as the switching element.

250V 1A three-phase monolithic inverter IC for brushless motor drives.

This paper describes a high voltage three-phase monolithic inverter IC using dielectrically isolated power IC technology. This inverter IC has the ability to drive a 50 W brushless motor, and it can be supplied voltage from a commercial voltage source using only a rectifier. This inverter IC includes six insulated gate bipolar transistors (IGBTs) and fast recovery diodes for output stages having a current capability of 1 A for continuous current. The IGBTs and fast recovery diodes realize a reduction in forward voltage drops and fast switching speeds. The IC also provides functions such as drive circuits suitable for pulse width modulation (PWM) control at a switching frequency of 20 kHz, a charge pump type power supply for each upper driver, and unique overcurrent protection circuits on one chip. The drive circuits which prevent the IGBTs from incorrect turning on under the large dV/dt condition, and the overcurrent circuits, provide easy use and enhanced reliability.

Period-doubling bifurcation in an electronic circuit with a fast-recovery diode and square-wave input.

An inductance-resistance diode circuit with square-wave input shows period-doubling and chaotic behaviors similar to a circuit with sinusoidal-wave input. These near-resonance phenomena using a fast-recovery diode agree well with our theoretical model that includes neither diffusion capacitance nor reverse recovery time but only includes the varactor characteristics of the junction capacitance. Computer solutions and experiments show only period-doubling 2T bifurcations which agree very well with each other.

New device for measuring post-arc currents in circuit breakers

This paper describes a new technique for measuring post-arc currents in circuit breakers. The measurements are performed with a specially designed current monitor. In contrast to commonly used current monitors saturation of the core of the transformer at high pulses of current is prevented by shunting the turns of the transformer by antiparallel fast-recovery diodes. This new device offers several advantages in comparison to other known techniques for post-arc measurements: there is no galvanic coupling to the network, the system is easy to handle, and the costs of the components are low. The two post-arc-current monitors (PACM) described have a sensitivity of 0.1 V/A and 10 mV/A, and are linear within 1% in the range of ±4 and ±100 A, respectively. The first PACM has an upper cutoff frequency of 18 MHz, the second one 3.8 MHz and are designed for sinusoidal fault currents of 6.3 kA and 56 kA, respectively, at a frequency of 50 Hz. Examples of applications to axially blown arcs in SF6 and to vacuum circuit breakers are presented.

CHOPPEFtED DC MOTOR DRIVE USING MOS AND BIPOLAR POWER TRANSISTORS

A four quadrant DC chopper circuit is presented applying a combination of MOS and bipolar power transistors as the main power elements. This circuit uses two MOS switches to take all required high frequency (up to 100 KHz) switching in the four quadrant operation. Two bipolar transistors are used in the return path of current as fast contactors to select the required quadrant of operation. Using of this scheme greatly reduces cost than the case of using four MOS switches. Moreover separate fast recovery diodes can be used as freewheeling diodes instead of relatively slower integral body-drain diode of the power MOSFET which cause restrictions on ON state switching speed. In the following work, the detailes of design of power circuit to feed a 20 A- 18V separately excited DC motor is given. Analytical dependence of overall efficiency on operating frequency and battery voltage is discussed. Results show that frequency has a little effect so that a 100 kHz frequency seems to be practically possible with this configuration. Under such high frequency the armature leakage reactance alone is sufficient to draw smooth continuous current to give good motor operating characteristics.

Rotator cuff tears: preliminary application of high-resolution MR imaging with counter rotating current loop-gap resonators.

A new class of radio frequency (RF) coils for magnetic resonance (MR) imaging and spectroscopy is introduced. The coils consist of two loop-gap resonators of equal diameters positioned along a common axis. They are tuned to the mode in which the current in the two loops flows in opposite directions. These coils are "decoupled" from a uniform excitation field of arbitrary orientation (including circularly polarized fields) by intrinsic decoupling and by means of back-to-back fast recovery diodes. Measurements made with the coils and a phantom saline tank indicate that the signal-to-noise ratio obtainable with these coils is almost identical to that obtained with single loops. Imaging of several anatomic areas, including knee, wrist, and shoulder, has been performed with a 1.5-T MR system that uses circularly polarized RF. A small series of patients with torn rotator cuffs underwent imaging. Difficulties in establishing the diagnosis with MR imaging because of anatomic complexity are illustrated. The value of pulse sequences with long repetition times to increase the signal intensity of fluid in the joint is shown.

Improvements In Avalanche-Transistor Sweep Circuitry For Electro-Optic Streak Cameras

We have improved the performance of the avalanche-transistor deflector-driver (sweep) circuitry used in the high-speed, electro-optic streak camera at Lawrence Livermore National Laboratory. In the previous design for the sweep circuit, trigger-to-output delay time drifted on some cameras. This delay drift is a function of a somewhat randomly unstable breakdown voltage of some avalanche transistors. Both temperature and differences in manufacturing methods for transistors affect this instability. However, a significant improvement in system performance is achieved by long-term burn in and by selection of only the most stable transistors for the sweep circuit. The peak-to-peak sweep voltage has been increased about 80% by increasing the number of avalanche transistors in the string and raising the quality factor (Q) of the resonant circuit. The result is an improvement in sweep uniformity by a factor of approximately 2. Design equations for selecting components are given. Fast-recovery diodes are used to prevent undershoot and to keep the beam out of the intensifier field of view until after the intensifier is gated off. The sweep time range has been extended to over 100 ns.