Electricity: electrical systems and devices – Safety and protection of systems and devices – High voltage dissipation
Reexamination Certificate
1999-05-27
2001-07-10
Leja, Ronald W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
High voltage dissipation
C361S103000
Reexamination Certificate
active
06259589
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to a circuit protection apparatus. More particularly, to a protection apparatus applied to a telephone line.
2. Description of the Related Art
As the science technology becomes more and more advanced, the mutual relationship between each individual becomes more and more frequent and relative. Telephones, fax machines, modems and other appliances for telephones are necessary for daily life. Under the circumstances such as erroneously plugging a telephone connector into an integrated service digital network (ISDN) socket, malfunction of the private branch exchanger (PBX) and telephone line failure of the telephone office would cause an abnormal high voltage or current. Any appliance connected to the telephone line is very likely to be damaged by the abnormal high voltage or current. Referring to
FIG. 1
, a conventional protection device for a telephone line is shown. The telephone line is connected from a socket
40
. The connection status of the telephone line is determined by a signal sent from a fax/modem controller
12
to hook switch
14
. The protection device is implemented by connecting a fuse or poly switch
10
to the telephone line in series. When an abnormal over voltage or over current occurs, the fuse or poly switch
10
is blown out. A new fuse or poly switch has to be installed to replace the blown one to retrieve a normal operation of the fax/modem machine. It is thus very inconvenient to practical application. In European standard, a current limit circuit
20
has to be included in the circuit of the modem/fax machine. As a consequence, while an over current occurs, a current flowing though is restricted within a certain magnitude to cause a blowout of a transistor set
30
due to an over voltage, high temperature, or even high temperature of the enclosure. The protection performance is thus very limited.
SUMMARY OF THE INVENTION
Accordingly, the invention provides a protection apparatus applied to a telephone line. The protection apparatus is applied to a direct access arrangement (DAA) circuit. When an abnormal over voltage or over current occurs, an overload detecting means can detect the over voltage or current and send an overload signal to the enforcing on-hook means. Or when the temperature of the telephone line raises abnormally high, it is detected by the high temperature detecting means and a high temperature signal is output to the enforcing on-hook means. While receiving the overload signal or high temperature signal, the telephone line is hooked on by the hook switch. As the driver of the fax/modem machine detects that there is no carrier on the telephone line, the DAA is enforced to be on-hook. The phenomenon of device blowout due to over voltage or high temperature is thus prevented.
In an embodiment of the invention, a protection apparatus applied and coupled to a telephone line is provided. The protection apparatus comprises a bridge rectifier, an overload detecting means, an enforcing on-hook means, and a hook switch. The bridge rectifier has an input terminal coupled with the telephone line. The telephone line voltage is input to the bridge rectifier. The input telephone line voltage is rectified as a rectified voltage output to an overload detecting means which is coupled to the output terminal of the bridge rectifier. When the rectified voltage exceeds a predetermined magnitude, an overload signal is output by the overload detecting means. The enforcing on-hook means is coupled to the overload detecting means which connected to the telephone line in series. When the overload signal is input to the enforcing on-hook means, an on-hook operation is performed.
In another embodiment of the invention, a protection circuit applied to a fax/modem machine is provided to avoid an abnormal high temperature. The detecting circuit is used to detect the temperature of the fax/modem machine. When the temperature exceeds a predetermined value, an overload signal is output. An enforcing on-hook means is coupled to the detecting circuit to generate an on-hook signal according to the overload signal. The enforcing on-hook means is further connected to the telephone line in series, so as to perform an on-hook operation of the telephone line.
Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
REFERENCES:
patent: 5812658 (1998-09-01), Cotreau et al.
patent: 03235455 (1991-10-01), None
patent: 10023108 (1998-01-01), None
Huang Jiawei
Leja Ronald W.
Twinhead International Corp.
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