Internal-combustion engines – High tension ignition system – Electronic cylinder sequencing
Patent
1991-11-20
1993-10-26
Cross, E. Rollins
Internal-combustion engines
High tension ignition system
Electronic cylinder sequencing
307110, F02P 312
Patent
active
052556603
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a semiconductor switch, in particular as an ignition voltage switch for applying an ignition voltage to a spark plug of an internal combustion engine, having a cascade circuit formed of semiconductor components for connecting an operating voltage through to a load.
BACKGROUND
In high-voltage semiconductor switches it is known to make a cascade circuit (series circuit) of semiconductor components, to assure their electric strength. Accurate dimensioning of the semiconductor components' wiring elements, necessary for the preferably uniform voltage distribution, is important, since if the depletion voltage limit values are exceeded, destruction of the semiconductors ensues. The known wiring elements are made with relative complicated resistor-capacitor networks. This avoids uneven voltage distribution caused by deviations from one component to another and unavoidable stray capacitances. Because of the wiring elements, the circuit layout is relatively complicated and expensive.
German Patent Disclosure Document DE-OS 37 31 412 and corresponding U.S. Pat. No. 5,002,034, HERDEN, BENEDIKT & KRAUTER, discloses a high-voltage switch equipped with phototransistors, in which one resistor is connected parallel to each transistor. The thus-formed voltage divider serves to provide uniform distribution of the operating voltage to be switched. Aside from the already mentioned disadvantages of such wiring elements, the current flowing through the voltage divider also causes undesirable losses.
THE INVENTION
The device according to the invention has the advantage over the prior art that no wiring elements have to be used, yet nevertheless a maximally symmetrical voltage distribution is achieved. The circuitry expense is decisively lowered thereby, and no additional voltage control losses occur. Each of the series-connected semiconductor components of the cascade circuit has a depletion-layer capacitance, and because of the prevailing electrical field distribution, the connection existing between each two semiconductor components forms a corresponding (parasitic) capacitance to ground. These capacitances, known per se, are unavoidable and therefore have nothing in common with the wiring elements known from the prior art. The reason they are used for the symmetrical wiring distribution of the semiconductor switch according to the invention is that they bring about a displacement current, by means of an increase in the operating voltage. According to the invention, it is provided that relative to the displacement current, a breakover current flowing through the semiconductor components before the conducting state is attained is located within the range current, and a is a factor the value of which is between approximately 5 and 10. Upon successive switching of the various series-connected semiconductor components, the aforementioned capacitances of the cascade circuit accordingly vary successively as well. Various options exist for putting the teaching of the invention into practice, each of which can be used alone or in combination with others. The most important option is to predetermine the magnitude of the breakover current in such a way, by the selection of the semiconductor components, or in their manufacture, that the condition according to the invention is met. Another factor can be the setting of the depletion-layer capacitance of the semiconductors used. Moreover, the various capacitances to ground can be varied within certain limits by the layout of the cascade. Finally, the displacement current is also determined by the speed of increase in the operating voltage, so that can be a factor as well. The aforementioned magnitudes or quantities should therefore be adapted to one another in such a way that the condition according to the invention is adhered to. In practice, it can be assumed that both the depletion-layer capacitance and the ground capacitance are defined within relatively narrow limits. The speed of increase in the operating voltage is also usefully d
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patent: 5008798 (1991-04-01), Harvey
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patent: 5060623 (1991-10-01), McCoy
Marcus-Electronic Circuits Manual-1971, p. 298, "Flash-Triggered Series-SCR High-Voltage Switch".
Herden Werner
Vogel Manfred
Cross E. Rollins
Robert & Bosch GmbH
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