Patent Application
20060227481
1. Field of the Invention
The present invention relates to a power supply for a bus, and particularly to a power supply used for an Institute of Electrical and Electronics Engineers Standard 1394 (IEEE1394) bus.
2. General Background
The Institute of Electrical and Electronics Engineers Computer Society published the IEEE STD 1394-1995 entitled, “IEEE Standard for a High Performance Serial Bus.” This standard and its following supplements define a serial data bus with a cable and backplane environment, non-cyclic topology, scalable data rates starting at 100 Megabits per second, and a cable arbitration system that uses a self-configuring hierarchical request/grant protocol that supports hot plugging and widely varying physical topologies.
According to the IEEE1394 STD, voltage of equipment connected to the IEEE1394 bus ranges between 8V and 40V, and the current flowing through the equipment must not be more than 1.5 A. However, an operational voltage of the diode 2 may reach 40V due to a transient over loading of voltage and current, that is, the operational voltage of the diode 2 may be over the reverse breakdown voltage of the diode 2. When the operational voltage of the diode 2 is over the reverse breakdown voltage of the diode 2, the diode 2 will break down. Consequently the electronic circuit and equipment are damaged. Thus it can be seen that the diode 2 having a 20V reverse breakdown voltage cannot provide effective over-voltage protection to the circuit and equipment. In addition, the rated current of the fuse 4 is 2.6 A, well over the IEEE1394 standard and does not provide over-current protection to the circuit and equipment when the current through the equipment ranges between 1.5 A and 2.6 A. Operation voltage of the capacitors C1, C2, C3 and C4 may reach 40V, clearly over their rating, thus the capacitors C1, C2, C3 and C4 may break down as well. However, if capacitors having a higher voltage rating are employed, a cost of making the circuit will increase.
What is needed, therefore, is a power supply for interfaces of bus both able to provide an effective over voltage protection and to the circuit and equipment, and have a low cost.
A power supply for a bus interface is provided. In a preferred embodiment, the power supply comprises: an input terminal; an output terminal; a fuse providing over-current protection; a diode providing over-voltage protection, a reverse breakdown voltage of the diode being not less than a maximal voltage difference of the output terminal and the input terminal, the diode is connected to the fuse in series between an input terminal and an output terminal; and a plurality of capacitors filtering noise, one end of each of the capacitors connected to a node between the fuse and an anode of the diode, and another end of each of the capacitors grounded.
The capacitors are located between the input terminal and the anode of the diode. Thus the power supply can employ capacitors, which have a low voltage rating. Thereby, cost of the power supply will decrease. In addition, a reverse breakdown voltage of the diode is not less than a maximal voltage difference of the output terminal and the input terminal. Therefore, the power supply can provide effective over-voltage protection.
Other advantages and novel features will become more apparent from the following detailed description of preferred embodiments when taken in conjunction with the accompanying drawings, in which:
As shown in
An input terminal 10 is connected to an anode of the diode 20 via the fuse 40. An output terminal 50 is connected to a cathode of the diode 20. Nodes A, B, C between the fuse 40 and the anode of the diode are grounded via the capacitors C10, C20, C30 respectively. A node D between the cathode of the diode 20 and the output terminal 50 is grounded via the high rated capacitor C40. A rated current of the fuse 40 is 1.5 A. A reverse breakdown voltage of the diode 20 is 40V. Rated voltage of the capacitors C10, C20, C30 are all 16V. A rated voltage of the high rated capacitor C40 is 50V. Alternately, the fuse 40 can be connected between the cathode of the diode 20 and the output terminal 50.
The input terminal 10 receives a 12V voltage. The 12V voltage is sent to equipment connected to the output terminal 50 via the power supply. When the current through the fuse 40 is over 1.5 A, the fuse 40 cuts off. Thus the power supply can provide over-current protection. When a voltage of the output terminal 50 is over 12V, the diode 20 is cutoff. Thus the power supply can provide over-voltage protection.
In the illustrated embodiment, if the voltage of the output terminal 50 is as high as 40V and a voltage of the input terminal 10 is as low as 0V in some transient state, that is, the reverse voltage of the diode 20 is 40V (40V-0V), the diode 20 will not break down because the reverse breakdown voltage of the diode 20 is 40V. Thus the power supply can provide effective over-voltage protection. Considering that an operational power of an element is about 70% of the rated power, the rated voltage of the high rated capacitor C40 is 50V because an operation voltage of the high rated capacitor C40 is not more than 40V. Furthermore, when the voltage of the cathode of the diode 20 reaches 12V, the diode 20 cuts off. Therefore, operational voltages of the capacitors C10, C20, C30 are not more than 12V. So the rated voltage of the capacitors C10, C20, C30 is 16V. Thus capacitors having a lower rated voltage are employed, ensuring that a cost of manufacturing the circuit will decrease.
As shown in
It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200510034112.X | Apr 2005 | CN | national |
