Electric power conversion systems – Current conversion – Using semiconductor-type converter
Reexamination Certificate
1998-09-25
2001-01-30
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
Using semiconductor-type converter
C363S052000
Reexamination Certificate
active
06181588
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to power supplies for electronic devices and particularly to circuits to maintain a constant polarity across an electrical load.
2. Description of the Related Art
Electronic devices, and particularly portable electronic devices such as portable computers, cellular phones, and personal digital assistants (PDAs) typically make use of alternating current to direct current adapters (“AC-DC adapters,” “AC adapters,” or simply “adapters”) either as a direct source of power, or as a source of power to charge on-board batteries. AC adapters can be built into such electronic devices, but given the size, weight, and cost constraints often imposed on such devices, AC adapters are more commonly provided as a separate module with a plug or cord for connecting the adapter to an AC outlet, and another cord for connecting the adapter to the electronic device through a connector.
Given the variety of electronic devices that use AC adapters, and the various output polarizations, voltage ratings, and current ratings of those adapters, an electronic device user is likely to have several, if not many, different adapters for different electronic devices. Consequently, matching the correct adapter to the intended device can be difficult because of similarity in appearance among adapters and similarity among the connectors associated with the adapters. Compounding this problem is the fact that adapters intended for different applications can be manufactured by the same company and look the same, yet have dissimilar electrical characteristics. Moreover, using the wrong adapter can damage expensive electronic equipment or even present a safety hazard.
Prior methods to prevent improper use of and/or mitigate the damage from improper use of an AC adapter generally fall into two categories: mechanical methods and electrical methods. The most common mechanical solution to the problem of improper adapter use is to provide the adapter and the electronic device using the adapter with unique connector keying such that the wrong connector cannot be inserted into the electronic device. One drawback to this method of preventing improper use of an adapter is that it prevents manufacturers from using standard connectors and adapters which allow the manufacturer to avoid the high costs of tooling, testing, and providing a custom part.
Electrical solutions typically include circuitry for clamping the improper input voltage with a dissapative device such as a zener diode, a metal oxide varistor (MOV), or a junction diode. These devices will only work if the input power source has power limiting within the capability of the dissapative device, and thus there ability to protect a device is limited. Such specialized circuits or components add cost and complexity to the electronic device. Additionally, operating conditions within the specification of the dissapative device are not always met, so damage to the electronic device can still result from using an improper adapter.
Accordingly, it is desirable to have a circuit that allows power input of various polarities, while supplying power with a constant polarity to an electrical load. Additionally, it is desirable to have such a circuit that can provide power having constant polarity given either AC or DC input power.
SUMMARY OF THE INVENTION
It has been discovered that a circuit including a bridge rectifier, switches across one or more of the diodes of the bridge rectifier, and a comparator to provide control signals to the switch or switches can be constructed to apply a constant polarity voltage to an electrical load, regardless of the polarity of the input power applied to the circuit. The comparator produces a control signal depending upon a comparison of the input power voltages, and the control signal activates one or more of the switches to allow current flow through an appropriate path in the circuit to yield the constant polarity across the electrical load. Thus, the circuit can protect the electrical load from an inappropriately applied voltage by switching the applied voltage's polarity. Because an activated switch can short a diode in the bridge rectifier, power loss associated with current flow through the diode is reduced. Additionally, the circuit can provide constant polarity across the electrical load with either AC or DC input power.
Accordingly, one aspect of the present invention provides a circuit including a first and a second input terminal, a first and a second output terminal, a bridge rectifier, a plurality of transistors, and a comparator. The bridge rectifier includes a plurality of diodes, and is coupled to the first and second input terminals and to the first and second output terminals. Ones of the plurality of transistors are coupled in parallel with ones of the plurality of diodes of the bridge rectifier. The comparator is coupled to the first and second input terminals, the first and second output terminals, and at least one of the plurality of transistors. The comparator is operable to provide a control signal to the at least one of the plurality of transistors depending upon a first signal received from the first input terminal and a second signal received from the second input terminal.
In another aspect of the invention, a computer system includes a processor, a memory coupled to the processor, and a circuit coupled to the processor and memory operable to deliver power to the processor and memory. The circuit includes a first and a second input terminal, a first and a second output terminal, a bridge rectifier, a plurality of transistors, and a comparator. The bridge rectifier includes a plurality of diodes, and is coupled to the first and second input terminals and to the first and second output terminals. Ones of the plurality of transistors are coupled in parallel with ones of the plurality of diodes of the bridge rectifier. The comparator is coupled to the first and second input terminals, the first and second output terminals, and at least one of the plurality of transistors. The comparator is operable to provide a control signal to the at least one of the plurality of transistors depending upon a first signal received from the first input terminal and a second signal received from the second input terminal.
In still another aspect of the invention, a method of maintaining a constant power supply polarity across an electrical load is disclosed. A first input voltage is compared with a second input voltage to identify which of the input voltages is more positive than the other. A first pair of switches in a circuit is activated when the first input voltage is more positive than the second input voltage. The switches are operable to receive the first and second input voltage so that activating the first pair of switches allows a voltage of a first polarity to develop across the electrical load. A second pair of switches in a circuit is activated when the second input voltage is more positive than the first input voltage. The switches are operable to receive the first and second input voltage so that activating the second pair of switches allows a voltage of the first polarity to develop across the electrical load.
In yet another aspect of the invention, a circuit includes a first and a second input terminal, a first and a second output terminal, a rectifying means, a first switching means, a second switching means, and a comparing means. The rectifying means is coupled to the first and second input terminals and coupled to the first and second output terminals for maintaining a constant polarity across an electrical load. The first switching means is for shorting a first portion of the rectifying means, and the second switching means is for shorting a second portion of the rectifying means. The comparing means is coupled to the first and second input terminals, the first and second output terminals, and at least one of the first and second switching means. The comparing means is for comparing a first voltage on the first input terminal with a secon
Cummings John A.
Kates Barry K.
Ascolese Marc R.
Berhane Adolf Deneke
Dell USA L.P.
Skjerven Morrill & MacPherson LLP
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