The present invention relates to a power supply system arranged to supply electric power to an apparatus, said system including a power supply unit comprising primary control circuitry arranged to control power flow to the apparatus via a two-lead cable. Furthermore, the invention relates to a power supply unit and an apparatus arranged to supply and receive power respectively.
Present-day switch-mode power-supply units (SMPS) for battery-enabled electronic equipment, such as tools, shavers, portable computers and mobile communication terminals, usually comprise a number of components, including vital parts such as a connection to a mains outlet, a control circuit for controlling the electric current output to the equipment connected, a transformer and a connection to the electronic equipment.
In most electronic equipment a number of provisions, realized in more or less specific electronic circuitry, are necessary to guarantee functionality for a variety of environmental conditions as well as the safety and protection of electronic components in the equipment. However, these provisions are at least in part a duplication of the control circuitry already present in the power-supply unit.
In order to secure the function of the equipment while providing power from a power-supply unit according to the prior art under varying conditions, it is necessary to provide information relating to the function of the equipment to the power-supply control circuitry. Such information may, e.g., relate to the charging level of a battery in the equipment or any other parameter, representing a condition in the equipment, which requires a change in, e.g., the level of current supplied by the power-supply unit. This feedback information is usually provided from the equipment to the power-supply unit via electronic circuitry inside the equipment as well as a dedicated information communication lead in the form of a galvanic or non-galvanic connection. Processing of the information fed back from the equipment is taken care of in the control circuitry of the power-supply unit. Needless to say, this entails adding to the complexity of the control circuitry.
In some cases, such as in the case of the apparatus disclosed in U.S. Pat. No. 5,859,524, the information relating to conditions in the equipment is fed back to the power-supply unit via the two-lead connection used for supplying the power. However, the information feedback is performed during temporary breaks in the supply of power. That is, the power supply from the power-supply unit of U.S. Pat. No. 5,859,524 to the equipment is regularly interrupted, during which breaks information is fed back to the control circuitry of the power-supply unit.
Drawbacks related to prior art power-supply systems hence include the high complexity of the control circuitry in the power-supply unit as well as the necessity of interrupting the flow of current, and thus reducing the efficiency, when information is to be fed back from the equipment to the power-supply unit.
An object of the invention is to overcome the drawbacks related to prior art power supplies as discussed above. This object is achieved in an inventive manner in the appended claims.
According to a first aspect, the invention relates to a power supply system arranged to supply electric power to an apparatus. The system includes a power supply unit comprising primary control circuitry arranged to control the power flow to the apparatus via a two-lead cable. The system further comprises secondary control circuitry located in the apparatus, said secondary control circuitry being arranged to monitor usage of power received from the power supply unit and feedback excess energy to the power supply unit via the two-lead cable.
In other words, the invention according to the first aspect provides a system describing a bi-directional flyback topology comprising two flyback converters working in opposite directions. Energy packets, i.e. current, flowing from the power supply unit to the apparatus is converted from a mains input in the power supply unit to a rectified output current fed to the apparatus via the two-lead cable. In the opposite direction, the secondary control circuit in the apparatus causes excess current to be fed back to the power-supply unit, where the primary control circuitry reacts in order to stabilize the current fed to the apparatus. In fact, the primary control circuitry serves to minimize the amount of energy received from the feedback. The excess current in the apparatus is determined by monitoring the voltage across, and current through, the apparatus is load. If the measured parameters are too high, transfer of more energy back to the power-supply unit will be performed.
The invention is based on the recognition that it is particularly advantageous to locate the secondary control circuitry in the apparatus and in fact combine it with circuity already present in the apparatus. A system according to the invention can hence be described in terms of a split topology system. Unnecessary duplication of control circuitry related to supply of power from a power-supply unit is avoided, thereby reducing the complexity and cost of the manufacturing process.
Another advantage is that the feedback from the apparatus to the power-supply is simplified since a third information lead, e.g. an optocoupler, can be avoided.
In a preferred embodiment, the secondary control circuitry comprises a switch connected in series with the two-lead connection. The switch is controlled to open and close in dependence upon the measured values of voltage and current in the apparatus. For the switch use is preferably made of a reverse-biased field effect transistor, i.e. utilized by applying a reverse bias voltage across the body diode of the transistor.
By working continuously in a bi-directional flyback manner, the power-supply unit sends energy packets to the apparatus and the apparatus returns excess energy to the power-supply. This occurs during each cycle of the flyback conversion. In view of this, another advantage of the invention resides in that it allows a continuous supply of power from the power supply, without any interruptions for signaling, as is the case in prior art devices.
According to a second aspect of the invention, a power supply unit is provided, which is arranged to supply electric power to an apparatus. The power supply unit comprises primary control circuitry arranged to control the power flow to the apparatus via a two-lead cable, receive feedback current via the two-lead cable from the apparatus and control the power flow to the apparatus in response to the feedback current.
Advantages obtained by providing a power-supply unit according to the second aspect of the invention are apparent from the discussion above in connection with a power supply system.
According to a third aspect of the invention, an apparatus is provided, which is arranged to receive power from a power supply via a two-lead cable. The apparatus comprises secondary control circuitry, which is arranged to monitor usage of power received from the power supply unit and feedback excess energy to the power supply unit via the two-lead cable.
Advantages obtained by providing a power-supply unit according to the second aspect of the invention are apparent from the discussion above in connection with a power supply system.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter
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