Patent Publication Number: US-2009237849-A1

Title: Apparatus for preventing surge

Description:
RELATED APPLICATIONS 
     This application claims priority to Taiwan Application Serial Number 97109713, filed Mar. 19, 2008, which is herein incorporated by reference. 
     BACKGROUND 
     1. Field of Invention 
     The present invention relates to circuitry. More particularly, the present invention relates to apparatus for preventing surge. 
     2. Description of Related Art 
     Please refer to  FIG. 1 .  FIG. 1  illustrates a conventional circuit. In  FIG. 1 , a direct current power supply (dc power supply)  140  can be connected to the anode of the diode  120 ; an encapsulated circuit  110  and a capacitor  130  connect in parallel, where the capacitor  130  is disposed between the diode  120  and the encapsulated circuit  110 . 
     When hot plug is performed, the direct current power supply  140  makes contact at point “a” and thereby rapidly provides voltage; therefore, the encapsulated circuit  110  receives a surge with peaking voltage in a very short time. Thus, the peaking voltage may damage the encapsulated circuit  110  when the peaking voltage exceeds the rated voltage of the encapsulated circuit  110 . 
     The voltage at point “a” rises rapidly and thereby a large current flows into the capacitor  130  instantly while the direct current power supply  140  connects the anode of the diode  120 . The formula for charging the capacitor is i=C×dv/dt, in which “i” represents the current flowing into the capacitor  130 , “dv” represents variation of the voltage, “dt” represents the period during the voltage is rising. For example, the capacitance of the capacitor  130  is 1 microfarad and the voltage rises from 0V to 5V, which needs only 1 microsecond; therefore, the current instantly flowing into the capacitor  130  is 5 A. 
     Please refer to  FIG. 2 .  FIG. 2  is a timing diagram of the conventional circuit of  FIG. 1 . In the first stage  210 , the voltage at point “a” rises from 0V to the threshold voltage  212  of the diode  120  so that the diode  120  is turned on. In the second stage  220 , the voltages at point “a” and “b” rise rapidly and thereby the current “I” rises rapidly as a result of the large current flowing into the capacitor  130 . In the third stage  230 , the voltage at point “a” is steady, but IS the current “I” doesn&#39;t reduce instantly due to the parasitic inductance  152 ,  154 , 156  in the conducting wire; therefore, the unnecessary current charges the capacitor  130  too much and thereby the voltage at point “b” continues rising to form the surge  234 . In the forth stage  240 , the current “I” reduces to the normal current level, and the voltage at point “b” gradually reduces the normal  20  voltage level. At this time, the voltage at point “a” minus the threshold voltage  212  of the diode  120  leaves the voltage at point “b”. The current  242  is used for providing the encapsulated circuit  110 . It should be noted that the surge  234  usually exceeds the rated voltage of the encapsulated circuit  110 ; therefore, the encapsulated circuit  110  may be damaged. 
     Please refer to  FIG. 3 .  FIG. 3  illustrates a conventional constant voltage circuit for preventing the surge. The conventional constant voltage circuit in  FIG. 3  is similar to the conventional circuit in  FIG. 1 , except that a Zener diode  310  and the capacitor  130  connect in parallel is added. The Zener diode  310  is capable of clamping the voltage at point “b” when the voltage exceeds the breakdown voltage of the Zener diode  310 . However, for using the Zener diode  310 , the production cost is increased and the Zener diode  310  occupies large space. Alternatively, the encapsulated circuit  110  can endure the surge by means of increasing the rated voltage of the encapsulated circuit  110 . However, the area of the encapsulated circuit  110  is large and the production cost is increased. 
     For the foregoing reasons, there is a need for an apparatus for preventing surge. The present invention meets this need. 
     SUMMARY 
     The following presents a simplified summary of the disclosure in order to provide a basic understanding to the reader. This summary is not an extensive overview of the disclosure and it does not identify key/critical elements of the present invention or delineate the scope of the present invention. Its sole purpose is to present some concepts disclosed herein in a simplified form as a prelude to the more detailed description that is presented later. 
     In one aspect, the present invention is directed to an apparatus for preventing surge. 
     According to one embodiment of the present invention, the apparatus for preventing surge comprises a bypass element and a capacitor. The bypass element is disposed in an encapsulated circuit, where the encapsulated circuit has a core circuit, wherein one end of the bypass element is electrically coupled with a direct current power supply and another end of the bypass element is electrically coupled with the core circuit. The capacitor is electrically coupled with said another end of the bypass element, where the encapsulated circuit is disposed between the direct current power supply and the capacitor. 
     Many of the attendant features will be more readily appreciated as the same becomes better understood by reference to the following detailed description considered in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present description will be better understood from the following detailed description read in light of the accompanying drawings, wherein: 
         FIG. 1  illustrates a conventional circuit; 
         FIG. 2  is a timing diagram of the conventional circuit of  FIG. 1 ; 
         FIG. 3  illustrates a conventional constant voltage circuit for preventing the surge; 
         FIG. 4  shows a block diagram of an apparatus for preventing surge in accordance with one embodiment of the present invention; 
         FIG. 5A ,  FIG. 5B ,  FIG. 6A  and  FIG. 6B  illustrate the bypass element of  FIG. 4  respectively; and 
         FIG. 7  is a timing diagram of the apparatus of  FIG. 4 . 
     
    
    
     Like reference numerals are used to designate like parts in the accompanying drawings. 
     DETAILED DESCRIPTION 
     The detailed description provided below in connection with the appended drawings is intended as a description of the present examples and is not intended to represent the only forms in which the present example may be constructed or utilized. The description sets forth the functions of the example and the sequence of steps for constructing and operating the example. However, the same or equivalent functions and sequences may be accomplished by different examples. 
     Please refer to  FIG. 4 .  FIG. 4  shows a block diagram of an apparatus for preventing surge in accordance with one embodiment of the present invention. In  FIG. 4 , the apparatus comprises a bypass element  400  and a capacitor  430 . The bypass element  400  disposed in an encapsulated circuit  410 . The encapsulated circuit  400  has a core circuit  642 . One end of the bypass element  400  is electrically coupled with a direct current power supply (dc power supply)  440 , and another end of the bypass element  400  is electrically coupled with the core circuit  642 . The capacitor  430  is electrically coupled with said another end of the bypass element  400 . It should be noted that the encapsulated circuit  410  is disposed between the direct current power supply  440  and the capacitor  430 . 
     The capacitor  430  can store at least one electric charge form the direct current power supply  440  via the bypass element  400 . Additionally, the capacitor  430  can discharge the electric charge to the core circuit  642 . The core circuit  642  may be a motor driver, a switching regulator, an audio amplifier or the like. When switching output stage, the core circuit  642  may generate a reverse current, and then the capacitor  430  can absorb the reverse current from the core circuit  642 . Furthermore, a diode may be disposed at the output terminal of the direct current power supply  440  to prevent the reverse current. 
     Please refer to  FIG. 5A ,  FIG. 5B ,  FIG. 6A  and  FIG. 6B .  FIG. 5A ,  FIG. 5B ,  FIG. 6A  and  FIG. 6B  illustrate the bypass element of  FIG. 4  respectively. In  FIG. 5A ,  FIG. 5B ,  FIG. 6A  and  FIG. 6B , the bypass element  400  comprises a controller  460  and a controlled switch  470 . The controlled switch  470  is disposed in the encapsulated circuit  410 . The controlled switch  470  comprising a first end  481 , a second end  482  and a third end  483 , where the first end  481  is electrically coupled with the direct current power supply  440  and the second end  482  is electrically coupled with the capacitor  430 . The controller  460  is disposed in an encapsulated circuit  410 , where one end of the controller  460  is electrically coupled with the direct current power supply  440  and another end of the controller  460  is electrically coupled with the third end  483  of the controlled switch  470 . 
     It should be noted that the controlled switch  470  can separate the parasitic inductance  456  in the conducting wire and the capacitor  430 . For example, the controller  460  can electrically connect the first end  481  and the second end  482  of the controlled switch  470  when said one end of the controller  460  receives positive electricity from the direct current power supply  440 . On the contrary, the controller  460  can electrically disconnect the first end  481  and the second end  482  when the one end of the controller  460  doesn&#39;t receive the positive electricity from the direct current power supply  440 . Furthermore, the bypass element  400  may comprises a built-in direct current power supply  442 . The built-in direct current power supply  442  is electrically coupled with the controller  460  for providing power to the controller  460 , whereby the controller  460  can execute above-mentioned operation. 
     In  FIG. 5A , the controlled switch  470  is a p-channel metal-oxide-semiconductor, where the first end  481  of the controlled switch  470  is the source of the p-channel metal-oxide-semiconductor; the second end  482  of the controlled switch  470  is the drain of the p-channel metal-oxide-semiconductor; the third end  483  of the controlled switch  470  is the gate of the p-channel metal-oxide-semiconductor. The controller  460  can control the voltage of the gate to turn on/off the controlled switch  470 . 
     In  FIG. 5B , the controlled switch  470  is an n-channel metal-oxide-semiconductor, where the first end  481  of the controlled switch  470  is the drain of the n-channel metal-oxide-semiconductor; the second end  482  of the controlled switch  470  is the source of the n-channel metal-oxide-semiconductor; the third end  483  of the controlled switch  470  is the gate of the p-channel metal-oxide-semiconductor. The controller  460  can control the voltage of the gate to turn on/off the controlled switch  470 . 
     In  FIG. 6A , the controlled switch  470  is a PNP bipolar transistor, where the first end  481  of the controlled switch  470  is the emitter of the PNP bipolar transistor; the second end  482  of the controlled switch  470  is the collector of the PNP bipolar transistor; the third end  483  of the controlled switch  470  is the base of the PNP bipolar transistor. The controller  460  can control the voltage of the base to turn on/off the controlled switch  470 . 
     In  FIG. 6B , the controlled switch  470  is an NPN bipolar transistor, where the first end  481  of the controlled switch  470  is the collector of the NPN bipolar transistor; the second end  482  of the controlled switch  470  is the emitter of the NPN bipolar transistor; the third end  483  of the controlled switch  470  is the base of the NPN bipolar transistor. The controller  460  can control the voltage of the base to turn on/off the controlled switch  470 . 
     In other embodiment, the controlled switch  470  may be a low drop-out linear voltage regulator or the like. The bypass element  400  may be an impedance component or a conductor, such as a metal wire. One of ordinary skill in the art will appreciate that the above examples are provided for illustrative purposes only to further explain applications of the present invention and are not meant to limit the present invention in any manner. Other material of the bypass element  400  may be used as appropriate for a given application. 
     For a more complete understanding of the present invention, and the advantages thereof, please refer to  FIG. 7  and  FIG. 4 .  FIG. 7  is a timing diagram of the apparatus of  FIG. 4 . In the first stage  620 , the controlled switch  470  control the voltage output and the current output at point c′; the voltages and the current at point b′ and c′ synchronously rise to steady. In the second stage  630  and the third stage  640 , the current is steady without surge because there is no capacitor that is disposed between the direct current power supply  440  and point b′. The current  682  is used for providing the encapsulated circuit  410 . The voltage drops of the bypass element  400  plus the voltage at point c′ equals the voltage at point b′. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. The above specification, examples and data provide a complete description of the structure and use of exemplary embodiments of the invention. Although various embodiments of the invention have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those with ordinary skill in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this invention.