Electricity: electrical systems and devices – Safety and protection of systems and devices – With specific circuit breaker or control structure
Utility Patent
1999-07-16
2001-01-02
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
With specific circuit breaker or control structure
C361S058000, C361S104000
Utility Patent
active
06169649
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to power electronics and, more specifically, to a detection circuit for circuit protection devices of a power supply, a method of monitoring the protection devices and a power supply employing the circuit or the method.
BACKGROUND OF THE INVENTION
Circuit protection devices (such as fuses) are widely employed in various industrial and commercial apparatus to protect against over-current and short circuit conditions. The circuit protection devices are also employed to comply with the requirements of safety agencies. At least two input-line circuit protection devices are generally required for a single-phase three-wire input power conversion system.
As a result of the important functions performed by the circuit protection devices, it is necessary to reliably monitor the operation thereof. In many applications wherein fuses are employed as the circuit protection devices, the fuses are equipped with blown fuse indicators. Generally, the underlying systems that monitor the fuses employ thermal-mechanical apparatuses to indicate the existence of a blown fuse. Many fuse manufacturers, for instance, use trigger devices or trigger actuators wired in parallel with the fuses being monitored. The trigger devices include a mechanical actuator (e.g., a strike pin) that exerts a static force of approximately one pound to activate an add-on switch when the fuse is blown. The trigger devices, however, may only be employed in parallel with a fuse that is rated at
70
A or higher. A minimum voltage drop of 5-10 volts is also required across an open fuse to assure a reliable blown fuse indication. Further, the trigger devices add about 2-5 amps to the long term current carrying capability of the fuse.
Obviously, employing multiple mechanical devices per fuse leads to questions regarding the reliability of such a detection system including the susceptibility of such devices to detrimental environmental conditions such as dust, temperature and vibration. Additionally, the trigger devices and the associated equipment, are bulky and quite expensive. As a result, a detection system employing the mechanical components (such as the components described above) may not be optimal for many applications.
Other commonly employed detection circuits include multiple circuits, often one circuit per circuit protection device, to monitor the operation of the circuit protection devices. For instance,
FIG. 1
illustrates a schematic diagram of a power supply system
100
employing a conventional fuse detection circuit
120
. The power supply system
100
includes a AC power source
110
coupled to power conversion equipment
115
(e.g., a power converter). First and second fuses
105
a
,
105
b
are interposed between the AC power source
110
and power conversion equipment
115
to provide short-circuit, ground fault and overcurrent protection to the power conversion equipment
115
.
The conventional fuse detection circuit
120
consists of a first stage
130
that is coupled between the AC power source
110
and the first and second fuses
105
a
,
105
b
and a second stage
130
′ that is coupled between the first and second fuses
105
a
,
105
b
and the power conversion equipment
115
. The first and second stages
130
,
130
′ each consist of identical components. Each of the first and second stages includes a safety fuse
131
,
131
′ coupled to the first fuse
105
a
and to a metal-oxide-varistor (MOV)
132
,
132
′, which is further coupled to the second fuse
105
b
. The MOV
132
,
132
′ is used for input power surge protection. A first current limiting resistor
133
,
133
′, an opto-coupler
135
,
135
′ and a second current limiting resistor
134
,
134
′ are coupled across the MOV
132
,
132
′. Furthermore, a capacitor
136
,
136
′ is coupled across the output terminal of the opto-coupler
135
,
135
′ and to a pull-up resistor
137
,
137
′. The first and second stages
130
,
130
′ are powered from an isolated 5 V source.
The conventional fuse detection circuit
120
senses first and second voltages across the first and second fuses
105
a
,
105
b
, respectively. The opto-couplers
135
,
135
′ (which are bi-directional in nature) draw current from the AC lines via the current limiting resistors
133
,
134
,
133
′,
134
′. When both the first and second voltages are sensed across the current limiting resistors
133
,
134
,
133
′,
134
′, the opto-couplers
135
,
135
′ turn on the transistors of the opto-couplers
135
,
135
′ and transmit logic low signals to a controller (not shown). The logic low signal indicates that the first and second fuses
105
a
,
105
b
are operational. Otherwise, if one of the first and second voltages is not sensed across the current limiting resistors
133
′,
134
′, the opto-coupler
135
′ turns off and transmits a logic high signal to the controller, indicating that at least one of the first and second fuses
105
a
,
105
b
or the safety fuse
131
′ is blown.
While the conventional fuse detection circuit
120
does monitor the status of the first and second fuses
105
a
,
105
b
, it suffers from the following limitations. In addition to the obvious drawback of size and cost associated with multiple circuits to accomplish the intended purpose, the opto-couplers
135
,
135
′ suffer from finite current transfer ratio restrictions that limit their use in many applications. Due to the limited current transfer ratio, the opto-couplers
135
,
135
′ require a certain amount of current to operate properly. Thus, the resistance of the current limiting resistors
133
,
134
,
133
′,
134
′ is limited to a lesser value and, consequently, the current limiting resistors
133
,
134
,
133
′,
134
′ may dissipate a fair amount of energy. For instance, if the power converter
115
has a wide input voltage range (e.g., 85-270 Vrms), the total power dissipation of the current limiting resistors (e.g., 25 k&OHgr;each)
133
,
134
,
133
′,
134
′ can be as high as 5.6 watts, which represents about a 1.4% efficiency reduction for a 400 watt power converter and about a 0.56% reduction for a 1000 watt power converter.
To counteract some of the problems described above, the current limiting resistors
133
,
134
,
133
′,
134
′ should have high wattage and voltage ratings. The higher rated components, however, add cost and size to the conventional fuse detection circuit
120
. Additionally, since the conventional fuse detection circuit
120
samples the voltages across the first and second fuses
105
a
,
105
b
, it drains power from the overall system and is susceptible to high AC line voltages and surges. As a result, other protection devices (such as metal-oxide varistors) should be included with the conventional fuse detection circuit
120
to protect the components thereof.
Accordingly, what is needed in the art is a system and method for monitoring the operability of the circuit protection devices that overcomes the deficiencies of the prior art.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, the present invention provides, for use with a power supply having first and second circuit protection devices, a detection circuit, a method of monitoring the protection devices and a power supply employing the circuit or the method. In one embodiment, the detection circuit includes (1) a bridge circuit coupled to the first and second circuit protection devices, (2) a resistor parallel-coupled across one of the first and second circuit protection devices and (3) a sensing circuit, coupled to the bridge circuit and the resistor, that senses an imbalance in the bridge circuit and develops therefrom a failure signal when at least one of the first and second circuit protection devices becomes inoperable.
The present invention, in one aspect, introduces the concept
Fasullo Greg H.
He Jin
Herrmann John A.
Jorgenson Greg P.
Jackson Stephen W.
Lucent Technologies - Inc.
LandOfFree
Detection circuit for circuit protection devices of a power... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Detection circuit for circuit protection devices of a power..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Detection circuit for circuit protection devices of a power... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2496506