W.M. Portnoy

High di/dt Pulse Switching of Thyristors

The fast pulse switching behavior of center-fired ring-and-dot and interdigitated thyristors was studied by switching 8 to 10 ¿s, 1000 to 1600 A peak (at 800 V) pulses. Single-shot switching was performed up to 15 400 A/¿s, and repetitive switching at 500 and 800 Hz at various di/dt levels, including 13 000 A/¿s, for up to ten hours. No damage to the devices resulted from the single-shot switching stresses.

Temperature variation effects in MCTs, IGBTs, and BMFETs

The switching characteristics of the non-complementary MOS-controlled thyristor (MCT) (i.e., an MCT that is gated with respect to the cathode as opposed to the anode) are examined over a temperature range of -180 to 195/spl deg/C. The forward conduction drop and dynamic performance of these MCTs are discussed and compared to the behavior of similar complementary MCTs, IGBTs (insulated gate bipolar transistors), and normally-off bipolar mode FETs (BMFETs) over the same temperature range.<<ETX>>

Gating Effects on Thyristor Anode Current di/dt

Triggering measurements were performed on thyristors with different gate geometries at various combinations of peak gate current, gate pulsewidth, and gate di/dt, to determine the trigger dependence of pulsed anode current di/dt. Peak gate current was varied from 4 A to 12 A, gate pulse width from 250 ns to 8 ¿s, and leading edge di/dt from 23 A/¿s to 320 A/¿s. Only the peak gate current was found to affect pulsed anode current di/dt.

Role of the amplifying gate in the turn-on process of involute structure thyristors

The switching characteristics of involute thyristors with and without the amplifying gate structure are discussed. The effects of peak gate currents (10-100 A) on the anode current di/dt, switching delay, and energy loss in both types of devices are presented. The performance of the devices without the amplifying gate was far superior than that of the devices with the amplifying gate. A model is presented to explain this difference. Thyristors without the amplifying gate successfully switched anode currents on the order of 12.6 kA, at a di/dt of 100000 A/ mu s, from an anode voltage of 2 kV on a single-shot basis. >

High di/dt switching with thyristors

Two types of involute-structured SCRs, one with the amplifying gate shorted to the pilot gate (shorted devices), and the other with a normal gate arrangement (unshortened devices), were tested as closing switches in a PFN (pulse forming network). The shorted devices were able to switch larger anode currents at higher values of di/dt of the shorted devices. All energy losses in the shorted thyristors were less than the losses in the unshorted ones. The gate current amplitude had a strong direct relationship to the anode di/dt of the shorted devices. There seemed to be a very weak, if any, correlation between the gate current amplitude and the unshorted device di/dt. The gate pulse width has no measurable effect on the switching parameters. The results indicate that for high-current, narrow-pulse switching, the amplifying gate has a detrimental effect on the thyristor performance.<<ETX>>

Development of high frequency SPICE models for ferrite core inductors and transformers

High-frequency SPICE models were developed to simulate the hysteresis and saturation effects of toroidal-ferrite-core inductors and transformers. The models include the nonlinear, multivalued B-H characteristic of the core material, leakage flux, stray capacitances, and core losses. The saturation effects were modeled using two-diode clamping arrangements in conjunction with nonlinear sources. Two possible controlling schemes were developed for the saturation switch. One of the arrangements used the current flowing through a series RC branch to control the switch, and the other used a NAND gate. The NAND-gate implementation of the switch proved to be simpler, and the parameters associated with it were easier to determine from the measurements and the B-H characteristics of the material. Lumped parameters were used to simulate the parasitic effects. Techniques for measuring these parasitics are described. The models were verified using manganese-zinc-ferrite-type toroidal cores, and they have general applicability to all circuit analysis codes provided that they contain nonlinear sources or equivalent function blocks such as multipliers, adders, and logic components.<<ETX>>

High-energy pulse-switching characteristics of thyristors

Experiments were conducted to study the high energy, high di/dt pulse-switching characteristics of silicon controlled rectifiers (SCRs) with and without the amplifying gate. High di/dt, high-energy single-shot experiments were first done. Devices without the amplifying gate performed much better than the devices with the amplifying gate. A physical model is presented to describe the role of the amplifying gate in the turn-on process, thereby explaining the differences in the switching characteristics. The turn-on area for the failure of the devices was theoretically estimated and correlated with observations. This allowed calculation of the current density required for failure. Since the failure of these devices under high di/dt conditions was thermal in nature, a simulation using a finite-element method was performed to estimate the temperature rise in the devices. The results from this simulation showed that the temperature rise was significantly higher in the devices with the amplifying gate than in the devices without the amplifying gate. From these results, the safe operating frequencies for all the devices under high di/dt conditions was estimated. These estimates were confirmed by experimentally stressing the devices under high di/dt repetitive operation. >

Temperature variation effects on the switching characteristics of bipolar mode FETs (BMFETs)

The switching performance of a bipolar mode FET (BMFET) is examined and measured over a temperature range from -184 degrees C to +197 degrees C. Data are presented which show the temperature variation of the rise and fall times, for both the current and voltage; the measured temperature dependence of the forward voltage drop is also presented. These data show that overall device switching performance is not improved for low temperature operation and is degraded at temperatures above room temperature.<<ETX>>

The low temperature switching performance of thyristors and MOSFETs

The measured switching performance of MOS-controlled thyristors (MCTs), an SCR (silicon-controlled rectifier), and a power MOSFET are discussed for operating temperatures from 25 to -180 degrees C. Current pulses of up to 340 A were conducted for a duration of 10 mu s. A comparison of the energy losses, switching times, and device behavior as a function of temperature is also presented. It is shown that under controlled situations, the MCT compares favorably when used at low ambient and junction temperatures. These devices turn on quickly enough to keep the switching losses small when conducting large currents, though at low current levels and high frequencies the MOSFET is still the superior device because of its very fast turn-on. Based on conduction losses at high current levels, the MCTs outperformed the other test devices.<<ETX>>

The low-temperature behavior of thyristors

The forward breakover voltage (V/sub BF/) and forward conduction voltage drop of a thyristor have been measured as a function of decreasing temperature between 25 degrees C and -180 degrees C. The theoretical temperature dependence of the above parameters is derived and compared to the experimental results. The predicted fall of V/sub BF/ as temperature is decreased is primarily determined by the associated decrease in the avalanche breakdown voltage. The calculated and measured forms of V/sub BF/ generally show close correspondence, although the measured data show some deviation from the initial rate of linear fall at around -140 degrees C. At room temperature, all of the donor and acceptor atoms are ionized so that the donor/acceptor concentrations and carrier concentrations can be used interchangeably. As temperature is decreased, the above becomes an approximation, and the ionized donor/acceptor concentrations should strictly be used. At lower temperatures, the effective donor concentration decreases.<<ETX>>