Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Accelerating switching
Reexamination Certificate
2000-08-22
2001-12-25
Cunningham, Terry D. (Department: 2816)
Miscellaneous active electrical nonlinear devices, circuits, and
Gating
Accelerating switching
C327S428000, C327S453000, C327S381000, C327S475000
Reexamination Certificate
active
06333664
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to telecommunications switching apparatus, and more particularly to a high voltage, high current, low operating power ringing access relay for telecommunications switching applications in remote environments.
2. Description of Related Art
A solid state switch connected between a ringing signal generator and a ring device in telecommunications systems has a known minimum breakdown voltage requirement determined by the maximum clamp voltage of the external protection device connected from the ring device to ground plus the maximum ring voltage having an opposite polarity. In certain applications, the minimum breakdown voltage of the ringing access switch is approximately 500 volts. However, when utilizing components having a 320 volt breakdown capability, the high voltage junctions must necessarily be placed in series to meet this requirement.
In addition to the breakdown requirement in the OFF state, the ringing access switch must survive fault conditions in the ON state without degradation of performance. Surge currents through this switch resulting from, for example a lightening strike, can reach over 2 amps depending upon the amplitude of the lightening pulse and the impedance in the ringing circuit path.
To minimize current flow through a ringing access switch, the switch design can include current limiting circuitry to permit a maximum level of conduction that does not interfere with peak ringing signal currents, approximately 150 mA. However, because of the breakdown voltage requirement, current limiting of two series bidirectional switches is required. This presents a very complicated and costly design problem, for each series switch must share the same voltage and power.
Previous designs consisting of ringing access switches implemented in integrated circuits have exhibited inherent limitation of inadvertent turn-on in the presence of fast voltage transients at the switch terminals. This dV/dt sensitivity can cause the switch to become latched in the wrong state, requiring a reset of the device. Designs that improve dV/dt sensitivity to eliminate the inadvertent turn-on of the switch requires relatively higher bias current and operating power. However, these designs cannot be used in applications where low operating power is of primary importance.
SUMMARY
Accordingly, it is an object of the present invention to provide an improvement in telecommunications switching apparatus.
It is another object of the invention to provide an improvement in solid state ringing access switches used to telecommunications switching apparatus.
It is another object of the invention to provide an improvement in ringing access switches for telecommunications apparatus using semiconductor devices that can withstand 2 amp surges and can be connected in series to support 500 volt isolation pole-to-pole.
These and other objects are provided by a ringing access switch circuit for an integrated circuit that provides improved dV/dt sensitivity at low operating power by using a pilot controlled rectifier such as an SCR that conducts at low ringing signal currents and operates to steer a bias current for causing a relatively larger controlled rectifier in parallel therewith to become conductive during higher load current operation.
In one aspect of the invention, the ringing access switch circuit is comprised of: a solid state switch circuit, comprising: at least one pair of parallel semiconductor devices connected together such that the conductive state of one of the semiconductor devices of said pair controls the conductive state of the other semiconductor device of said pair, and thus becoming sequentially conductive, said pair of semiconductor devices each having first and second current conducting electrodes and at least one current control electrode, a load circuit connected across the first and second current conducting electrodes of said pair of semiconductor devices via a pair of switch output terminals whereby a load current flows in the load circuit when one or both of said pair of semiconductor devices are in a conductive state, a bias supply circuit connected across said one semiconductor device of said pair of semiconductor devices for connecting a source of bias voltage to the control electrode of said one semiconductor device and rendering it conductive in response to a switch turn-on signal applied to an input terminal and causing a load current of a first value to flow therethrough via respective first and second current conducting electrodes thereof, said first value of load current being used to generate a turn-on voltage signal applied to the control electrode of said other semiconductor device so as to render it conductive and causing a load current of a second value to then flow therethrough the device via respective first and second current conducting electrodes thereof concurrently with the first value of load current through said one semiconductor device.
Further scope of applicability of the present invention will become apparent from the detailed description which follows. It should be noted, however, that the detailed description and the specific examples, while indicating the preferred embodiments of the invention, are provided by way of illustration only, since various changes, modifications, within the spirit and scope of the invention will become apparent to those skilled in the art.
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patent: 5861639 (1999-01-01), Bernier
Agere Systems Guardian Corp.
Cunningham Terry D.
Nguyen Long
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