Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Utilizing three or more electrode solid-state device
Reexamination Certificate
2000-08-22
2001-06-05
Riley, Shawn (Department: 2838)
Miscellaneous active electrical nonlinear devices, circuits, and
Gating
Utilizing three or more electrode solid-state device
C327S427000
Reexamination Certificate
active
06242968
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor power converting apparatus with employment of a semiconductor element and the like. More specifically, the present invention relates to a semiconductor power converting apparatus capable of suppressing a peak voltage during a switching operation without requiring a snubber circuit.
2. Description of the Related Art
IGBTs (Insulated-Gate Bipolar Transistor) known as a typical insulated-gate transistor own low gate power consumption and can be switched in high speeds with a small switching loss. Accordingly, these IGBTs are employed in semiconductor power converting apparatuses having relatively medium and small capacities. Furthermore, these IGBTs are desirably applied to semiconductor power converting apparatuses having large capacities. In general, a jump-up voltage “&Dgr;V” of an IGBT having a snubber circuit is expressed by the following formula (1—1) based upon a capacitance “C” of a snubber capacitor:
&Dgr;
V=
1
{square root over (L/C)}
(1—1)
In other words, this jump-up voltage &Dgr;V is direct proportional to both a switching current I and a root-mean-squared value of a wiring inductance L. Therefore, in the case that a wiring inductance L can be minimized and a switching current I is low in a semiconductor power converting apparatus having a medium/small capacity, since a switching loss E
off
of an IGBT is present, this power converting apparatus can be made in a snubberless form, namely a snubber capacitor C is omitted. However, a semiconductor power converting apparatus having a large capacity requires such a snubber circuit for suppressing a peak voltage produced when a large switching current is turned OFF, and furthermore, another snubber circuit for equally sharing a high DC voltage to series-connected semiconductor elements. Thus, switching losses of these snubber circuits would reduce the converter efficiency, namely could not be neglected. Moreover, since the snubber circuits are connected to such a semiconductor power converting apparatus, the cost thereof is increased and this semiconductor power converting apparatus becomes bulky. Also, when a large number of IGBTs are connected in series to each other, both ON timing and OFF timing of all of these IGBTs must be adjusted in high precision in order to equally sharing the voltages to these IGBTs. This requires time and high cost. As a result, very recently, various circuit systems have been proposed. In these circuit systems, the peak voltages are suppressed when the IGBTs are turned OFF. Alternatively, the stational voltage sharing operation for the series-connected IGBTs is uniformly carried out on that any snubber circuit. This recently proposed circuit system corresponds to, as described in Japanese laiid-open patent application No. 11-178318, the gate driving circuit with the basic circuit arrangement such that the zener diode is connected between the collector of the IGBT and the gate thereof, or the series circuit made of the zener diode and the resistor is connected between the collector and the gate of the IGBT.
In this known gate control circuit, the avalanche current will flow when the collector voltage of the IGBT becomes higher than, or equal to the avalanche voltage of the zener diode, and thus, since the voltage of the gate resistor is increased, the peak value of the collector voltage of this IGBT is suppressed. However, in connection with a high withstanding voltage of an IGBT itself, an avalanche voltage of a zener diode would also require several Kilovolts. Further, in order to rise up the gate voltage of the IGBT by an avalanche current, such avalanche currents having values of several to several tens of Amperes are required. In addition, a resistance value of a gate resistor would also require approximately several tens of Ohms, so that the switching loss of this IGBT would be increased.
Conventionally, when the peak voltage of the IGBT is suppressed, since the withstanding voltage of the IGBT is increased, the avalanche voltage of the zener diode connected to the collector of the IGBT must be high. Furthermore, the avalanche current of the zener diode must be increased, or the gate resistance value must be increased instead of increasing of the switching loss. As a result, there are such problems that the higher withstanding voltage of the IGBT cannot be realized, but also the switching loss is increased.
Also, in the case that a plurality of IGBTs which are simultaneously switched are connected in series to each other by employing the conventional circuit system capable of suppressing the peak voltage produced when the IGBT is turned OFF, if the characteristic fluctuations as to the respective circuit elements are not strictly selected and are not made coincident with each other, then the peak voltages produced when the plural IGBTs are turned OFF are fluctuated, and also the stationary voltage sharing conditions are fluctuated. These circuit elements are the IGBTs, the resistor, the zener diodes, and the transistors, which constitute this conventional circuit system. As a consequence, the switching frequency could not be made high.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above-explained problems, and therefore, has an object to provide a semiconductor power converting apparatus capable of making an electric power converting apparatus compact and in low cost, and capable of operating the electric power converting apparatus in a high efficiency.
To solve the above-explained problems, a semiconductor power converting apparatus, according to the present invention, is featured by comprising: a semiconductor element for controlling a current flowing between a collector and an emitter in response to a gate condition; driving device connected to the gate, for driving the gate in response to a drive signal entered thereinto; voltage applying device for applying both a forward bias and a reverse bias to the gate so as to set the emitter of the semiconductor element to a neutral potential; and voltage dividing device for dividing a voltage appearing between the collector and the emitter of the semiconductor element; wherein: when the drive signal is under OFF state, a voltage produced based upon the divided voltage by the voltage dividing device is applied to the gate; and the gate voltage is controlled in response to the voltage appearing between the collector and the emitter of the semiconductor element.
Also, a semiconductor power converting device, according to the present invention, is featured by that as the voltage dividing device for dividing the voltage appearing between the collector and the emitter of the semiconductor element, this voltage dividing device includes the collector and a minus-polarity terminal for applying the reverse bias voltage.
Also, a semiconductor power converting apparatus, according to the present invention, is featured by comprising; selecting device made by a switching element connected to a gate of a semiconductor element typically known as an insulating gate transistor, capable of selecting a drive signal in response to either an ON command or an OFF command issued by a control device; a voltage source for applying both a forward bias and a reverse bias to the gate while setting the emitter for driving the semiconductor element as a neutral potential; and voltage dividing device for dividing a voltage appearing between the collector of the semiconductor element and a minus-sided electrode of the voltage source by employing a resistor, in which when the drive signal is an OFF command, a gate voltage of the semiconductor element becomes such a voltage value corresponding to the voltage division; in which when the voltage appearing between the collector of the semiconductor element and the emitter thereof is higher than, or equal to a predetermined voltage, the voltage dividing device can suppress this peak voltage. With employment of this circuit arrangement, the reverse bias voltage can be applied just a
Aizawa Hidetoshi
Iyotani Ryuji
Katoh Shuji
Nagasu Masahiro
Sakai Hiromitsu
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Riley Shawn
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