The present invention claims priority to TW 102114119, filed on Apr. 22, 2013.
1. Field of Invention
The present invention relates to a protection device and a calibration method of a protection device; particularly, it relates to such protection device and calibration method, which do not require manual calibration and can be applied to, for example but not limited to, over current protection.
2. Description of Related Art
For example, according to the Advanced Technology Extended (ATX) specification, an over current protection signal OCP must be generated before the current Iout exceeds 20 A. Generally, a typical over current protection device 100 is designed to generate an over current protection signal OCP when the current Iout exceeds a magnitude of 19+/−0.5 A. However, because of the mismatch or other errors of the circuit devices resulting from the manufacturing process or other causes, the over current protection device 100 may not precisely generate the over current protection signal OCP at the above-mentioned set value. As a consequence, after the over current protection device 100 has been manufactured, it is required to adjust the resistance of the variable resistor VR included in the setting circuit 140 to calibrate the over current protection device 100, so that the over current protection device 100 complies with the requirement set forth in the ATX specification.
However, to manually adjust the resistance of the variable resistor VR is labor-consuming and the cost of the variable resistor VR is high, so the conventional over current protection device 100 is ineffective. Taiwan Patent Application No. TW 100103237 proposes a circuit capable of setting the over current protection threshold. This application, however, simply discloses an abstract idea, but does not demonstrate how the hardware should be implemented to carry out an automatic calibration for the over current protection threshold. What this application discloses is, in fact, not different from the manual calibration. In view of the above, to overcome the drawbacks in the prior art, the present invention proposes a protection device with the clear disclosure of a hardware circuit, to provide the function of automatically calibrating the protection threshold. Such protection threshold can be set for, for example but not limited to, over current protection and over voltage protection. The present invention also provides a calibration method.
From one perspective, the present invention provides a protection device, comprising: a sensing circuit for sensing a current signal or a voltage signal to generate a sensing signal; and a detection circuit coupled to the sensing circuit, for generating a protection signal according to the sensing signal, the detection circuit including: a comparing circuit coupled to the sensing circuit, for generating the protection signal according to the sensing signal and an offset setting; a setting circuit coupled to the comparing circuit, for generating the offset setting according to a calibration signal; and an automatic calibration circuit coupled between the comparing circuit and the setting circuit, for generating the calibration signal; wherein during a calibration process, the automatic calibration circuit generates and stores the calibration signal in digital form in correspondence to a protection threshold related to the current signal or the voltage signal, and under a normal operation, the comparing circuit compares the current signal or the voltage signal with the calibrated protection threshold.
In one embodiment, the automatic calibration circuit includes: a control circuit for generating a control signal according to the protection signal during the calibration process; a digital number generation circuit coupled to the control circuit, for generating a check signal and a write signal according to the control signal, wherein the check signal is used as the calibration signal during the calibration process; a memory circuit coupled to the digital number generation circuit, for storing the write signal outputted from the digital number generation circuit; and a multiplexer circuit coupled to the digital number generation circuit and the memory circuit, for selecting the check signal as the calibration signal during the calibration process and selecting a read signal outputted from the memory circuit as the calibration signal under the normal operation.
In one embodiment, the setting circuit includes: a current source circuit for generating a setting current signal; a current mirror circuit coupled to the current source circuit, for duplicating the setting current signal to a duplicated current signal which is proportional to the setting current signal; and a current to voltage circuit for converting the duplicated current signal to the offset setting; wherein the setting current signal is adjustable, or the ratio of the duplicated current signal to the setting current signal is adjustable, or a conversion ratio of the current to voltage circuit is adjustable, or two or more of the above are adjustable.
In one embodiment, the automatic calibration circuit further includes a trigger circuit for receiving a trigger signal and generating a confirmation signal in response to the trigger signal, to initiate the calibration process.
In one embodiment, the memory circuit includes a writable or a rewritable nonvolatile memory circuit.
From another perspective, the present invention provides a calibration method of a protection device, wherein the protection device is for comparing a signal to be monitored with a protection threshold to generate a judgment signal, the calibration method comprising the steps of: (1) providing a current signal or a voltage signal which corresponds to the protection threshold; (2) generating a check signal; (3) generating a calibration signal according to the check signal and generating an offset setting according to the calibration signal; (4) generating the judgment signal according to a comparison result between the offset setting and the current signal or the voltage signal; and (5) writing a digital number into a memory circuit according to a status indicated by the judgment signal.
In one embodiment, the calibration method further comprises: generating a flag signal to indicate that the calibration is finished.
In one embodiment, the calibration method further comprises: confirming whether the memory circuit is blank before generating the check signal; and when the memory circuit is not blank, erasing the data stored in the memory circuit.
In one embodiment, the calibration method further comprises: repeating the steps (2) to (5) to write multiple digital numbers into the memory circuit, wherein each digital number is one bit of a multi-bit data.
In one embodiment, the multi-bit data is written into the memory circuit from a most significant bit (MSB) to a least significant bit (LSB).
In one embodiment, the calibration method further comprises: before generating the check signal, confirming that a calibration process is initiated according to a trigger signal.
In one embodiment, the step of confirming that a calibration process is initiated according to the trigger signal includes: confirming whether the calibration process is initiated according to a level of the trigger signal or according to whether the trigger signal lasts for a predetermined time period.
The objectives, technical details, features, and effects of the present invention will be better understood with regard to the detailed description of the embodiments below, with reference to the attached drawings.
The present invention can be applied to all types of protection devices and is adapted for automatically setting the protection threshold in these protection devices. The present invention will be explained in detail by taking an application in over current protection as an example, but certainly, the present invention can also be applied in over voltage protection, under voltage protection or any other types of protection. Please refer to
In the above-mentioned embodiment, preferably, the automatic calibration circuit 250 initiates a calibration process according to a trigger signal. During the calibration process, first, a current Iout is provided to flow through the current sensing circuit 210. The provided current Iout has a magnitude which corresponds to a desired over current protection threshold, for example but not limited to, 19 A or 19.5 A according to the ATX specification. Next, the automatic calibration circuit 250 and the setting circuit 240 perform automatic calibration. That is, in response to the over current protection signal OCP outputted by the comparing circuit 230, and according to the information whether the over current protection signal OCP is indicative of or not indicative of an over current status, the internal setting of the setting circuit 240 is correspondingly adjusted until the over current protection signal OCP outputted by the comparing circuit 230 exactly indicates an over current status. Thus, the offset setting generated by the setting circuit 240 will be an accurate value, so that in normal operation of the application circuit, the comparing circuit 230 can correctly generate the over current protection signal OCP when the current Iout exceeds a predetermined current level.
The above explains the basic concept of the present invention; more details as to the hardware circuitry and the method steps of the present invention will be explained by embodiments later. The calibration process of the present invention does not require manual calibration. Besides, the calibration signal generated in the present invention can be stored in an internal memory circuit of the application circuit, so that, during normal operation of the application circuit, the protection device 200 can read out the data stored in the memory circuit to obtain the calibration signal. In addition, the accuracy of the calibration is determined by the circuit, so the calibration result of the present invention is far more accurate than the manual calibration of the prior art (manual calibration tends to be less accurate). Furthermore, the calibration process of the present invention can be performed during a full load condition of the application circuit; therefore, the bandgap temperature coefficient and other factors of the application circuit have been taken into consideration in the calibration process, so that the over current protection device of the present invention will operate more accurately in actual operation of the application circuit. Moreover, as compared with the manual calibration of the prior art, it takes much shorter time in the present invention to perform the calibration process. All of the above are the advantages of the present invention over the prior art.
In this embodiment, the automatic calibration circuit 350 initiates the calibration process according to a trigger signal. The calibration process writes and stores an appropriate number into a memory circuit 354 through a comparison-and-writing process, whose details will be discussed later. The automatic calibration circuit 350 comprises a trigger circuit 351, a control circuit 352, a digital number generation circuit 353, a memory circuit 354 and a multiplexer circuit 355. The trigger circuit 351 generates a confirmation signal according to a trigger signal, to confirm that the calibration process should start. As to how the trigger circuit 351 generates the confirmation signal, two examples are shown by the wave forms of the trigger signal in
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More specifically, the over current protection threshold desired to be set (e.g., 19.5 A according to the ATX specification) is an analog number. The offset setting generated by the setting circuit 340 can be adjusted within a certain range of this analog number. The calibration signal is a digital signal having a number of bits, and the number of the bits (i.e., the length or size of the digital signal) can be determined according to the desired accuracy. The value of the calibration signal expressed by a digital number of plural bits determines an adjustment amount of the offset setting. The offset setting corresponding to the current Iout can be obtained during the calibration process; for example, if the current Iout given during the calibration process is 19.5 A, the offset setting corresponding to 19.5 A can be obtained. And, the digital number of the calibration signal corresponding to this offset setting is written into the memory circuit 354 to be stored. Because the number is stored in a form of digital data, it can be preserved accurately, for generating an accurate over current protection threshold under normal operation.
Moreover, in a preferred embodiment of the present invention, the calibration process first determines the most significant bit (MSB) of the calibration signal, then the next most significant bit (MSB-1) of the calibration signal, then the next, until the least significant bit (LSB) of the calibration signal. This method has the following advantage. For example, assuming that the calibration signal has eight bits, the calibration process can be completed by eight comparison steps. Under the same assumption that the calibration signal has eight bits, it takes longer to complete the calibration process if the calibration process starts the comparison from the greatest value in a top-down manner (i.e., 11111111→11111110→11111101→ . . . ), or from the smallest value in a bottom-up manner (i.e., 00000000→00000001→00000010→ . . . ). Besides, preferably, the calibration process should be performed in a pipeline manner; that is, the comparison for determining a next bit starts at the same time as a preceding bit is written into the memory circuit 340, to speed up the calibration process.
Although the above-mentioned method from MSB to LSB is preferred, it is also practicable and within the scope of the present invention to adopt any other comparison order (e.g., the top-down or the bottom-up manner).
In one embodiment, the memory circuit includes a writable or a rewritable nonvolatile memory circuit, such as a programmable read only memory (PROM), an erasable programmable read only memory (EPROM), an electrically erasable programmable read only memory (EEPROM), or a flash memory. These memory circuits are well known to those skilled in the art and are therefore not redundantly explained here. Certainly, it is also possible to adopt a volatile memory circuit in the present invention, but this requires to re-set the over current protection threshold in every use.
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The above-mentioned embodiments shown in
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To sum up, the applications for the present invention are not limited to the embodiments as shown above. Any application which requires to compare a current/voltage with a threshold by a comparing circuit can adopt the present invention to adjust the threshold.
The present invention has been described in considerable detail with reference to certain preferred embodiments thereof. It should be understood that the description is for illustrative purpose, not for limiting the scope of the present invention. An embodiment or a claim of the present invention does not need to achieve all the objectives or advantages of the present invention. The title and abstract are provided for assisting searches but not for limiting the scope of the present invention. Those skilled in this art can readily conceive variations and modifications within the spirit of the present invention. For example, a device which does not substantially influence the primary function of a signal, such as a switch, can be inserted between any two devices shown to be in direct connection in the embodiments. For another example, the technical meanings represented by the high level and low level of a digital signal are interchangeable, with corresponding amendments of the circuits processing these signals. For yet another example, the positive and negative input terminals of an error amplifier circuit or a comparator are interchangeable, with corresponding amendments of the circuits processing these signals. For still another example, although, in the above-mentioned embodiments, it is demonstrated that the offset setting generated by the setting circuit is inputted to the comparing circuit and compared with the current sensing signal (or the voltage sensing signal), it is equivalent to input a combination of the offset setting with the current sensing signal (e.g., by addition or subtraction) to one terminal of the comparing circuit 230, and to provide a reference signal to the other terminal of the comparing circuit 230. For still another example, the current sensing signal (or the voltage sensing signal) can be multiplied by a ratio such as by using a divider circuit, before it is inputted to the comparing circuit 230. Therefore, the term “current sensing signal (or voltage sensing signal)”, as may be used herein in the specification or claims, should not be limited to referring to a signal directly taken by sensing a current (or a voltage), but can be a signal related to such direct sensing. In view of the foregoing, the spirit of the present invention should cover all such and other modifications and variations, which should be interpreted to fall within the scope of the following claims and their equivalents.
Number | Date | Country | Kind |
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102114119 | Apr 2013 | TW | national |