Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific current responsive fault sensor
Reexamination Certificate
1999-04-26
2001-08-21
Sherry, Michael J. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific current responsive fault sensor
C361S093100, C361S084000, C307S125000
Reexamination Certificate
active
06278598
ABSTRACT:
RELATED PATENT FILING
This patent document has been filed concurrently with and is cross referenced to assignee's related patent specifications Ser. No. 09/299,935
DETAILED DESCRIPTION OF THE INVENTION
Field of the Invention
The present invention relates to a control switch circuit for controlling reduction of relatively small power generations. More particularly, the present invention relates to a switch circuit for a personal computer system which immediately decreases a residual voltage generated at an output circuit of the switch with a high reliability when the switch circuit is turned off.
Description of the Prior Art
A system load constituting a personal computer contains a capacitance in their power source, so that a voltage does not immediately decrease at the turn-off of the power source. For example, when a power source voltage of 5 V is turned off, the decrease of the residual voltage to 0.4 V takes about 20 seconds. It has been well known in the art that if the power source is turned on again, before that the residual voltage in the power source circuit decreases to a predetermined voltage, the system causes an operational error. Particularly, in the case that both software and user can control the turn on/off of the switch circuit, the user possibly turns the switch on immediately after the turn off of the switch circuit by the software, whereby the operational error due to the residual voltage tends to occur. To prevent such operational error, the switch circuit includes a circuit for removing the residual voltage.
FIG. 1
shows a prior switch circuit
10
including the circuit for removing the residual voltage. As an example, an input terminal of the switch circuit, to which a main power source of 5 V is connected, is connected to a drain of a power source line switching FET
11
, and a source of the FET
11
is connected to an output terminal of the switch circuit. A gate of the FET
11
is connected to a gate drive power source of 12 V through a resistor
19
of 100 K &OHgr;, and is connected to a collector of a gate drive transistor
13
. A base of the transistor
13
is connected to a control signal
1
through a resistor
21
, and an emitter is connected to a reference potential. One terminal of a resistor
15
of 100 &OHgr; for limiting a discharge current is connected to the output terminal, and the other terminal of the resistor
15
is connected to a drain of a switching FET
17
of a discharge circuit. A gate of the FET
17
is connected to a control signal
2
, and a source is connected to the reference potential.
In order to supply the voltage 5 V from the main power source to the output terminal, the control signal
1
is applied to the base of the transistor
13
to turn it off, whereby the FET
11
is turned on. At the same time as the application of the control signal
1
, the control signal
2
is applied to the gate of the FET
17
to turn it off. In order to stop the supply of the voltage 5 V to the output terminal, the transistor
13
is turned on by the control signal
1
to turn the FET
11
off, and at the same time, the FET
17
is turned on by the control signal
2
. If this control operation is performed without a time delay and the transistors
13
and
17
are adequately turned on, the residual charges are discharged to the reference potential through the resistor
15
during a short time after the turn off of the FET
11
, whereby the residual voltage rapidly decreases.
However, if the FET
17
is in a fault condition and is in an open mode condition, the residual charges at the output terminal can not be discharged through the resistor
15
and the FET
17
. In this case, the residual charges are discharged through only parallel impedance connected to the output terminal, and the decrease of the residual voltage takes a long time period, such as about 20 seconds, so that the probability of occurrence of the operational error due to the possible reactivation of the switch circuit during this time period becomes high. Further, if the FET
17
is in a fault condition and is in a short mode condition, the current continuously flows to the reference potential through the resistor
15
and the FET
17
, so that a wasteful power is consumed. And, in this case, it is required to increase a power rating of the resistor
15
in view of a safety. Also, it is difficult to detect the fault condition of the FET
17
before the shipment of the product, which may be a personal computer system.
In general, the personal computer includes the switch circuit as shown in the
FIG. 1
for each of a plurality of power sources and operational modes of the personal computer. To prevent a large current from flowing at the simultaneous turn on of these switch circuits, a delay circuit is applied between the control signal
1
and the base of the transistor
13
of each switch circuit, and a sequential operation timing is established. In this case, when the switch circuit is turned off to stop the supply of the voltage 5 V to the output terminal, the FET
17
can be turned on during the turn on condition of the FET
11
, in other words, a period during which both the FETs
11
and
17
are turned on exists, so that the wasteful power has been consumed. It is especially required in the personal computer to prevent such wasteful power from being consumed.
SUMMARY OF THE INVENTION
The present invention works to solve the problem and seeks as one object of the present invention to provide a simple switch circuit which performs a function for expeditiously removing the residual voltage with a high reliability. Another object of the present invention is to provide a unique and more efficient switch circuit useful for the notebook type personal computer.
The concept of the present invention is the constitution of the switch circuit in which a first switch for controlling a supply of a main power source to a load component and a second switch for controlling a first switch is provided, and the second switch is used both as the switch for controlling the first switch and the switch in a discharge circuit, so that a fault condition of the second switch is easily detected and the operation of the discharge circuit is started after the turn off of the first switch.
The switch circuit of the present invention is connected to a first power source, a load component and a second power source. The switch circuit includes, a first switch having a first terminal connected to the first power source, a second terminal connected to the load component and a control terminal to which a first control signal for controlling the first switch is supplied; a second switch having a first terminal connected to the control terminal of the first switch, a second terminal connected to the second power source and a control terminal to which a second control signal for controlling the second switch is supplied; and a reverse current preventing element connected between the load component and the first terminal of the second switch. The first control signal supplies a drive voltage to the control terminal of the first switch. The second control signal controls the operation of the switch circuit.
It is preferable to use an FET or a bipolar transistor as the switch of the present invention. But, the concept of the present invention includes the use of any switch which has the control terminal for electrically controlling the operation of the switch. The load component may be any component constituting an electronic apparatus and including a capacitance. The switch circuit of the present invention can immediately discharge or remove the residual voltage in the load component for a short period. The reverse current preventing element prevents the first control signal from being supplied to the load component during the turn off condition of the second switch.
The switch circuit of the present invention can be used in the electronic apparatus or the personal computer which includes a power source, a power source controller and a system load. Any circuit supplying the control signal to the swit
Suzuki Keiji
Yamazaki Satoshi
Bogdon Bernard D
Bracewell & Patterson LLP
Huynh Kim
International Business Machines - Corporation
Schelkopf J Bruce
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