CN108123429B - Overvoltage protection circuit - Google Patents
Overvoltage protection circuit Download PDFInfo
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- CN108123429B CN108123429B CN201611112578.1A CN201611112578A CN108123429B CN 108123429 B CN108123429 B CN 108123429B CN 201611112578 A CN201611112578 A CN 201611112578A CN 108123429 B CN108123429 B CN 108123429B
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- 238000002955 isolation Methods 0.000 claims description 11
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
- H02H9/04—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess voltage
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- G—PHYSICS
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/165—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
- H02H3/20—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to excess voltage
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Abstract
本发明提出一种过电压保护电路,其可区别切换式电源供应装置输出电压过压状态为内部回授失效引起或是外加电源导致,可利用启动过电压保护的时间差,避免短暂且无害的外加电源影响切换式电源供应装置正常工作,但当切换式电源供应装置内部回授失效时又可实时停止切换式电源供应装置作动达成保护。
The present invention proposes an overvoltage protection circuit, which can distinguish whether the overvoltage state of the output voltage of the switchable power supply device is caused by internal feedback failure or external power supply, and can use the time difference of starting overvoltage protection to avoid short-term and harmless The external power supply affects the normal operation of the switching power supply device, but when the internal feedback of the switching power supply device fails, the switching power supply device can be stopped in real time to achieve protection.
Description
技术领域technical field
本发明是有关于一种过电压保护电路,尤其是有关于一种适用于切换式电源供应装置的过电压保护电路。The present invention relates to an overvoltage protection circuit, in particular to an overvoltage protection circuit suitable for a switching power supply device.
背景技术Background technique
一般的切换式电源供应装置(Switching power supply)都会采用过电压保护电路,以在切换式电源供应装置的输出端呈现过电压时,能够控制切换式电源供应装置中的脉宽调变(Pulse Width Modulation,PWM)控制电路停止输出脉宽调变讯号,进而降低该输出端的输出电压大小,以对切换式电源供应装置的内部线路与该输出端的外接系统的内部线路进行过电压保护,避免这二者有任何一个受到破坏。A general switching power supply device (Switching power supply) will use an overvoltage protection circuit to control the Pulse Width Modulation (PWM) in the switching power supply device when the output terminal of the switching power supply device exhibits an overvoltage. Modulation, PWM) control circuit stops outputting the pulse width modulation signal, and then reduces the output voltage of the output terminal, so as to protect the internal circuit of the switching power supply device and the internal circuit of the external system of the output terminal from overvoltage, avoiding the two Either one of them is damaged.
该输出端会因二种情况而呈现过电压,其一是由切换式电源供应装置的内部电路失效所造成,例如是回授电路失效时;其二是由外接系统所造成,例如具有马达的外接系统在减速时所引起的反电动势回馈。然而,传统的过电压保护电路并无法区别这二者,以致于使用者在正常操作外接系统而引起反电动势回馈时,传统的过电压保护电路仍会控制切换式电源供应装置立即降低其输出电压的大小来进行过电压保护,如此反倒造成外接系统关机而无法正常使用,引起使用者不小的困扰。The output end will exhibit overvoltage due to two situations. One is caused by the failure of the internal circuit of the switching power supply device, such as when the feedback circuit fails; the other is caused by an external system, such as a motor with a motor. The back EMF feedback caused by the external system during deceleration. However, the traditional overvoltage protection circuit cannot distinguish between the two, so that when the user operates the external system normally and causes back electromotive force feedback, the traditional overvoltage protection circuit will still control the switching power supply device to immediately reduce its output voltage The size of the overvoltage protection is implemented, which will cause the external system to shut down and cannot be used normally, causing users a lot of trouble.
发明内容Contents of the invention
本发明的目的在提供一种过电压保护电路,其可区别该二种情况所造成的过电压,并采取二种不同的方式来进行过电压保护。The purpose of the present invention is to provide an overvoltage protection circuit, which can distinguish the overvoltage caused by the two situations, and adopt two different methods to perform overvoltage protection.
本发明提出一种过电压保护电路,其适用于切换式电源供应装置。其可利用启动过电压保护的时间差,区别切换式电源供应装置输出电压过压状态为内部回授失效引起或是外加电源导致,避免短暂且无害的外加电源影响切换式电源供应装置正常工作,但当切换式电源供应装置内部回授失效时又可实时停止切换式电源供应装置作动达成保护。The invention proposes an overvoltage protection circuit, which is suitable for a switching power supply device. It can use the time difference of starting overvoltage protection to distinguish whether the output voltage overvoltage state of the switching power supply device is caused by internal feedback failure or external power supply, so as to avoid the short-term and harmless external power supply from affecting the normal operation of the switching power supply device. However, when the internal feedback of the switching power supply device fails, the operation of the switching power supply device can be stopped in real time to achieve protection.
为让本发明的上述和其它目的、特征和优点能更明显易懂,下文特举较佳实施例并配合所附图式做详细说明如下。In order to make the above and other objects, features and advantages of the present invention more comprehensible, preferred embodiments are described below in detail with accompanying drawings.
附图说明Description of drawings
图1为过电压保护电路的耦接关系示意图。FIG. 1 is a schematic diagram of a coupling relationship of an overvoltage protection circuit.
具体实施方式Detailed ways
图1为过电压保护电路的耦接关系示意图。在图1中,切换式电源供应装置100包含有噪声滤波器110、交流-直流转换电路120、功率级(Power stage)130、变压器140、整流电路150、储能单元160、回授电路170与讯号隔离单元180。变压器140的一次侧线圈可依序透过功率级130、交流-直流转换电路120与噪声滤波器110来耦接输入电压VIN。噪声滤波器110可为电磁干扰滤波器,且用户可决定是否采用噪声滤波器110。FIG. 1 is a schematic diagram of a coupling relationship of an overvoltage protection circuit. In FIG. 1, the switching power supply device 100 includes a noise filter 110, an AC-DC conversion circuit 120, a power stage (Power stage) 130, a transformer 140, a rectifier circuit 150, an energy storage unit 160, a feedback circuit 170 and A signal isolation unit 180 . The primary coil of the transformer 140 can be coupled to the input voltage VIN through the power stage 130 , the AC-DC conversion circuit 120 and the noise filter 110 in sequence. The noise filter 110 can be an electromagnetic interference filter, and users can decide whether to use the noise filter 110 or not.
此外,交流-直流转换电路120可为桥式整流器。至于功率级130,其内部具有PWM控制电路132与用来当作开关的功率晶体管134。此功率晶体管134可与变压器140的一次侧线圈串联,藉由控制功率晶体管134的启闭状态(On/off state)便可决定是否允许电流通过一次侧线圈。而PWM控制电路132则用以产生PWM讯号,并输出PWM讯号至功率晶体管134的控制端,藉以控制功率晶体管134在启闭状态之间的切换频率。In addition, the AC-DC conversion circuit 120 can be a bridge rectifier. As for the power stage 130, it has a PWM control circuit 132 and a power transistor 134 used as a switch. The power transistor 134 can be connected in series with the primary side coil of the transformer 140 , and whether to allow current to pass through the primary side coil can be determined by controlling the on/off state of the power transistor 134 . The PWM control circuit 132 is used to generate a PWM signal and output the PWM signal to the control terminal of the power transistor 134 to control the switching frequency of the power transistor 134 between on and off states.
变压器140的二次侧线圈的输出在经过整流电路150与储能单元160分别进行整流与滤波后,便可作为切换式电源供应装置100的输出电压VOUT而自其输出端190提供给外接系统(未绘示)。再者,整流电路150与储能单元160亦可依设计需求而决定是否采用。另外,讯号隔离单元180可为光耦合器(Photo coupler),其可将回授电路170所产生的回授讯号传送给PWM控制电路132,以便让PWM控制电路132可据以调整PWM讯号的责任周期(Dutycycle)。因此,当切换式电源供应装置100的输出端190呈现过电压时,PWM控制电路132便可依据讯号隔离单元180传来的回授讯号来降低输出电压VOUT,以进行过电压保护。After the output of the secondary side coil of the transformer 140 is rectified and filtered by the rectifier circuit 150 and the energy storage unit 160, it can be used as the output voltage VOUT of the switching power supply device 100 and provided to the external system ( not shown). Furthermore, whether to use the rectifier circuit 150 and the energy storage unit 160 can also be determined according to design requirements. In addition, the signal isolation unit 180 can be an optocoupler (Photo coupler), which can transmit the feedback signal generated by the feedback circuit 170 to the PWM control circuit 132, so that the PWM control circuit 132 can adjust the PWM signal accordingly. Cycle (Dutycycle). Therefore, when the output terminal 190 of the switching power supply device 100 has an overvoltage, the PWM control circuit 132 can reduce the output voltage VOUT according to the feedback signal from the signal isolation unit 180 for overvoltage protection.
另外,在图1中,过电压保护电路200包括有阻抗210、阻抗220、储能单元230、开关单元240、过电压侦测单元250、电压取样单元270与讯号隔离单元280。阻抗210具有第一阻值,阻抗220具有第二阻值,而第二阻值大于第一阻值。储能单元230的一端耦接阻抗210的其中一端与阻抗220的其中一端,而储能单元230的另一端耦接参考电位SGND。其中,参考电位SGND为接地电位。In addition, in FIG. 1 , the overvoltage protection circuit 200 includes an impedance 210 , an impedance 220 , an energy storage unit 230 , a switch unit 240 , an overvoltage detection unit 250 , a voltage sampling unit 270 and a signal isolation unit 280 . The impedance 210 has a first resistance, the impedance 220 has a second resistance, and the second resistance is greater than the first resistance. One end of the energy storage unit 230 is coupled to one end of the impedance 210 and one end of the impedance 220 , and the other end of the energy storage unit 230 is coupled to the reference potential SGND. Wherein, the reference potential SGND is the ground potential.
开关单元240具有第一端241、第二端242与第三端243,第二端242耦接阻抗210的另一端,第一端241耦接阻抗220的其中一端。过电压侦测单元250耦接切换式电源供应装置100的输出端190、开关单元240的第一端241与阻抗220的另一端,用以接收输出端190上的输出电压VOUT,并判断输出电压VOUT是否超过第一默认值。The switch unit 240 has a first end 241 , a second end 242 and a third end 243 , the second end 242 is coupled to the other end of the impedance 210 , and the first end 241 is coupled to one end of the impedance 220 . The overvoltage detection unit 250 is coupled to the output terminal 190 of the switching power supply device 100, the first terminal 241 of the switch unit 240, and the other end of the impedance 220 to receive the output voltage VOUT on the output terminal 190 and determine the output voltage Whether VOUT exceeds the first default value.
电压取样单元270,具有第四端271与第五端278-5,第五端278-5耦接开关单元240的第三端243,第四端271耦接切换式电源供应装置100的变压器的二次侧线圈的其中一端,用以侦测二次侧线圈所输出的电压是否达第二默认值,且当判断为是时便导通第五端278-5与参考电位SGND,且若过电压侦测单元250输出为正电压则可控制开关单元240导通第一端241与第二端242之间的电性路径。The voltage sampling unit 270 has a fourth terminal 271 and a fifth terminal 278-5, the fifth terminal 278-5 is coupled to the third terminal 243 of the switch unit 240, and the fourth terminal 271 is coupled to the transformer of the switching power supply device 100. One end of the secondary side coil is used to detect whether the output voltage of the secondary side coil reaches the second default value, and when it is judged to be yes, it will conduct the fifth end 278-5 and the reference potential SGND, and if it exceeds When the output of the voltage detection unit 250 is a positive voltage, the switch unit 240 can be controlled to conduct the electrical path between the first terminal 241 and the second terminal 242 .
讯号隔离单元280,耦接第一储能单元230、阻抗210、阻抗220与切换式电源供应装置100的PWM控制电路132,并依据储能单元230所储存的电压大小来决定是否产生过电压保护触发讯号TRI,以利用过电压保护触发讯号TRI来控制PWM控制电路132停止输出脉宽调变讯号给功率晶体管134。The signal isolation unit 280 is coupled to the first energy storage unit 230 , the impedance 210 , the impedance 220 and the PWM control circuit 132 of the switching power supply device 100 , and determines whether to generate overvoltage protection according to the voltage stored in the energy storage unit 230 The trigger signal TRI is used to control the PWM control circuit 132 to stop outputting the PWM signal to the power transistor 134 by using the overvoltage protection trigger signal TRI.
在此例中,阻抗210、阻抗220与储能单元230可分别为电阻与电容。接下来,将先介绍过电压保护电路200其余部分的详细实施方式。如图1所示,过电压侦测单元250包括有分压电路252与比较器254。分压电路252耦接于切换式电源供应装置100的输出端190与参考电位SGND之间,并依据输出端190的电压而产生分压讯号。比较器254的正输入端用以接收分压电路252的分压讯号,负输入端用以接收参考电位Vref,而其输出则耦接开关单元240的第一端241与阻抗220。分压电路252可为阻抗252-1与252-2,其中阻抗252-1的一端耦接输出端190,而阻抗252-2的一端耦接阻抗252-1的另一端,阻抗252-2的另一端耦接参考电位SGND。阻抗252-1与252-2皆可为电阻。In this example, the impedance 210, the impedance 220, and the energy storage unit 230 may be a resistor and a capacitor, respectively. Next, the detailed implementation of the rest of the overvoltage protection circuit 200 will be introduced first. As shown in FIG. 1 , the overvoltage detection unit 250 includes a voltage dividing circuit 252 and a comparator 254 . The voltage dividing circuit 252 is coupled between the output terminal 190 of the switching power supply device 100 and the reference potential SGND, and generates a voltage dividing signal according to the voltage of the output terminal 190 . The positive input terminal of the comparator 254 is used to receive the voltage division signal of the voltage dividing circuit 252 , the negative input terminal is used to receive the reference potential Vref, and its output is coupled to the first terminal 241 of the switch unit 240 and the impedance 220 . The voltage dividing circuit 252 can be impedances 252-1 and 252-2, wherein one end of the impedance 252-1 is coupled to the output terminal 190, one end of the impedance 252-2 is coupled to the other end of the impedance 252-1, and one end of the impedance 252-2 is coupled to the other end of the impedance 252-2. The other end is coupled to the reference potential SGND. Both the impedances 252-1 and 252-2 can be resistors.
开关单元240包括有PNP型晶体管244、阻抗245与阻抗246。PNP型晶体管244具有射极、基极与集极,且其基极透过阻抗245耦接电压取样单元270的第五端278-5,并据以决定是否导通。The switch unit 240 includes a PNP transistor 244 , an impedance 245 and an impedance 246 . The PNP transistor 244 has an emitter, a base, and a collector, and its base is coupled to the fifth end 278 - 5 of the voltage sampling unit 270 through the impedance 245 to determine whether to conduct.
电压取样单元270包括有二极管273、储能单元274、分压电路276与压控开关278。二极管273的阳极耦接变压器140的二次侧线圈的一端。储能单元274耦接于二极管273的阴极与参考电位SGND之间。分压电路276耦接于二极管273的阴极与参考电位SGND之间,并依据储能单元274所储存的电压而产生分压讯号。压控开关278具有第五端278-5、第六端278-6与参考端R,且第五端278-5耦接开关单元260,第六端278-6耦接参考电位SGND,而参考端R用以接收分压电路276所产生的分压讯号。当压控开关278的参考端R的电压达到第三默认值时,压控开关278便使第五端278-5与第六端278-6形成导通状态。分压电路276可为阻抗276-1与276-2。其中阻抗276-1的一端耦接二极管273的阴极,阻抗276-2的一端耦接阻抗276-1的另一端,而阻抗276-2的另一端耦接参考电位SGND。The voltage sampling unit 270 includes a diode 273 , an energy storage unit 274 , a voltage dividing circuit 276 and a voltage control switch 278 . The anode of the diode 273 is coupled to one end of the secondary coil of the transformer 140 . The energy storage unit 274 is coupled between the cathode of the diode 273 and the reference potential SGND. The voltage dividing circuit 276 is coupled between the cathode of the diode 273 and the reference potential SGND, and generates a voltage dividing signal according to the voltage stored in the energy storage unit 274 . The voltage-controlled switch 278 has a fifth terminal 278-5, a sixth terminal 278-6 and a reference terminal R, and the fifth terminal 278-5 is coupled to the switch unit 260, the sixth terminal 278-6 is coupled to the reference potential SGND, and the reference The terminal R is used for receiving the voltage division signal generated by the voltage division circuit 276 . When the voltage of the reference terminal R of the voltage-controlled switch 278 reaches the third default value, the voltage-controlled switch 278 makes the fifth terminal 278-5 and the sixth terminal 278-6 into a conduction state. The voltage dividing circuit 276 can be impedances 276-1 and 276-2. One end of the impedance 276-1 is coupled to the cathode of the diode 273, one end of the impedance 276-2 is coupled to the other end of the impedance 276-1, and the other end of the impedance 276-2 is coupled to the reference potential SGND.
讯号隔离单元280包括有二极管282、讯号传送部284与讯号接收部286。二极管282的阳极耦接储能单元230与阻抗220。讯号传送部284的一端耦接二极管282的阴极,而另一端耦接参考电位SGND。此讯号传送部284用以产生耦合讯号。讯号接收部286的一端耦接PWM控制电路132,而另一端耦接参考电位PGND。此讯号接收部286用以接收耦合讯号,并据以产生过电压保护触发讯号TRI。其中,讯号传送部284包括是光耦合器的光发射部,光发射部用以产生光源来当作耦合讯号,而讯号接收部286包括是光耦合器的光接收部,光接收部用以接收光源所形成的耦合讯号。二极管282可视需求而决定是否采用。The signal isolation unit 280 includes a diode 282 , a signal transmitting part 284 and a signal receiving part 286 . The anode of the diode 282 is coupled to the energy storage unit 230 and the impedance 220 . One end of the signal transmission part 284 is coupled to the cathode of the diode 282 , and the other end is coupled to the reference potential SGND. The signal transmission part 284 is used for generating coupling signals. One end of the signal receiving part 286 is coupled to the PWM control circuit 132 , and the other end is coupled to the reference potential PGND. The signal receiving part 286 is used for receiving the coupling signal and generating the overvoltage protection trigger signal TRI accordingly. Wherein, the signal transmitting part 284 includes a light emitting part which is an optical coupler, and the light emitting part is used to generate a light source as a coupling signal, and the signal receiving part 286 includes a light receiving part which is an optical coupler, and the light receiving part is used to receive The coupling signal formed by the light source. The diode 282 can be used or not depending on requirements.
接下来,将介绍过电压保护电路200的详细操作方式。首先来说明在切换式电源供应装置100的内部电路失效而导致其输出端190呈现过电压的情况下,电压保护电路200的操作方式。请再参照图1,当输出端190上的输出电压VOUT超过第一默认值,而使得分压电路252所产生分压讯号的电压大于参考电位Vref的电压时,比较器254的输出便会呈现正饱和。Next, the detailed operation of the overvoltage protection circuit 200 will be introduced. Firstly, the operation of the voltage protection circuit 200 will be described when the internal circuit of the switching power supply device 100 fails and the output terminal 190 of the switching power supply device 100 exhibits overvoltage. Please refer to FIG. 1 again, when the output voltage VOUT on the output terminal 190 exceeds the first default value, so that the voltage of the divided signal generated by the voltage divider circuit 252 is greater than the voltage of the reference potential Vref, the output of the comparator 254 will appear. Positive saturation.
承上述,由于输出端190呈现过电压是因为切换式电源供应装置100的内部电路失效而引起的,例如是因回授电路170失效而引起的。那么回授电路170就会无法产生回授讯号,因此PWM控制电路132也会无法依据讯号隔离单元180传来的回授讯号来调整PWM讯号的责任周期,因而无法降低输出电压VOUT,且二次侧线圈(Secondary winding)所输出的电压会不断提升。Based on the above, the overvoltage at the output terminal 190 is caused by the failure of the internal circuit of the switching power supply device 100 , for example, the failure of the feedback circuit 170 . Then the feedback circuit 170 will not be able to generate the feedback signal, so the PWM control circuit 132 will not be able to adjust the duty cycle of the PWM signal according to the feedback signal from the signal isolation unit 180, so the output voltage VOUT cannot be reduced, and the secondary The output voltage of the side coil (Secondary winding) will continue to increase.
当二次侧线圈所输出的电压不断提升而达到第二默认值,进而使分压电路276所产生的分压讯号的电压达到第三默认值时,将使压控开关278的第五端278-5与第六端278-6形成导通状态。因此,开关单元240的第三端243将会电连接至参考电位SGND而被下拉至接地电位,进而使开关单元240的第一端241与第二端242形成导通状态。由于PNP型晶体管244所提供的路径的阻值会远小于阻抗220的阻值,因此比较器254输出的电流会选择走PNP型晶体管244所提供的路径来对储能单元230充电。When the voltage output by the secondary side coil continuously increases to reach the second default value, and then the voltage of the divided signal generated by the voltage divider circuit 276 reaches the third default value, the fifth terminal 278 of the voltage control switch 278 will be -5 forms a conduction state with the sixth terminal 278-6. Therefore, the third terminal 243 of the switch unit 240 is electrically connected to the reference potential SGND and is pulled down to the ground potential, so that the first terminal 241 and the second terminal 242 of the switch unit 240 are turned on. Since the resistance of the path provided by the PNP transistor 244 is much smaller than the resistance of the impedance 220 , the current output by the comparator 254 chooses the path provided by the PNP transistor 244 to charge the energy storage unit 230 .
根据前述说明,储能单元230可以很快地充饱而使二极管282导通,而使讯号传送部284可以很快地产生耦合讯号。而讯号接收部286在接收到耦合讯号后,便可据以产生过电压保护触发讯号TRI给PWM控制电路132,让PWM控制电路132可以透过控制功率晶体管134的操作来立即降低输出电压VOUT,以进行过电压保护。According to the above description, the energy storage unit 230 can be fully charged quickly so that the diode 282 can be turned on, so that the signal transmission part 284 can quickly generate a coupled signal. After the signal receiving part 286 receives the coupling signal, it can generate an overvoltage protection trigger signal TRI to the PWM control circuit 132, so that the PWM control circuit 132 can immediately reduce the output voltage VOUT by controlling the operation of the power transistor 134, for overvoltage protection.
接下来将说明在外接系统造成输出端190呈现过电压的情况下,电压保护电路200的操作方式。请再参照图1,当输出端190上的输出电压VOUT超过第一默认值,而使分压电路252所产生分压讯号的电压大于参考电位Vref的电压时,比较器254的输出便会呈现正饱和。Next, the operation of the voltage protection circuit 200 will be described under the condition that the external system causes the output terminal 190 to exhibit overvoltage. Please refer to FIG. 1 again, when the output voltage VOUT on the output terminal 190 exceeds the first default value, so that the voltage of the divided signal generated by the voltage divider circuit 252 is greater than the voltage of the reference potential Vref, the output of the comparator 254 will appear. Positive saturation.
承上述,由于输出端190呈现过电压是由外接系统所造成的,例如是具有马达的外接系统在减速时引起的反电动势回馈所造成的。因此回授电路170就会正常产生回授讯号,使PWM控制电路132能够依据讯号隔离单元180传来的回授讯号调整PWM讯号的责任周期,因而能够降低输出电压VOUT,且二次侧线圈(Secondary winding)所输出的电压就会下降。Based on the above, the overvoltage at the output terminal 190 is caused by the external system, for example, the back electromotive force feedback caused by the external system with a motor during deceleration. Therefore, the feedback circuit 170 will normally generate a feedback signal, so that the PWM control circuit 132 can adjust the duty cycle of the PWM signal according to the feedback signal from the signal isolation unit 180, thereby reducing the output voltage VOUT, and the secondary side coil ( Secondary winding) the output voltage will drop.
当二次侧线圈所输出的电压不断下降而无法达到第二默认值,而使分压电路276所产生的分压讯号的电压也无法达到第三默认值时,将无法使压控开关278的第五端278-5与第六端278-6形成导通状态。因此PNP型晶体管244也会跟着呈现关闭状态(Off state),进而无法使开关单元240的一端241与第二端242形成导通状态。因此比较器254输出的电流只能透过阻抗220来对储能单元230充电。When the voltage output by the secondary side coil keeps dropping and fails to reach the second default value, and the voltage of the divided signal generated by the voltage divider circuit 276 cannot reach the third default value, the voltage control switch 278 cannot be activated. The fifth terminal 278-5 and the sixth terminal 278-6 form a conduction state. Therefore, the PNP transistor 244 will also be in an off state (Off state), so that the one end 241 and the second end 242 of the switch unit 240 cannot be turned on. Therefore, the current output by the comparator 254 can only charge the energy storage unit 230 through the impedance 220 .
由于阻抗220的阻值远大于PNP型晶体管244所提供的路径的阻值,因此储能单元230的充电时间就会变长而使二极管282延迟了一段时间后才导通。由于讯号传送部284必须等到二极管282导通后才能产生耦合讯号,因此讯号接收部286也是在延迟了该段时间后才能接收到耦合讯号而据以产生过电压保护触发讯号TRI给PWM控制电路132。由此可知,PWM控制电路132也是在延迟了该段时间后才能透过控制功率晶体管134的操作来降低输出电压VOUT,以进行过电压保护。换句话说,在这种情况下,切换式电源供应装置100并不会立即进行过电压保护而造成外接系统无法正常操作,而是会延迟了该段时间后才会进行过电压保护。当然,本领域的通常知识者应知,延迟时间可透过改变阻抗220的阻值来调整,也可透过改变储能单元230的电容值来调整。Since the resistance value of the impedance 220 is much greater than the resistance value of the path provided by the PNP transistor 244 , the charging time of the energy storage unit 230 will be longer and the diode 282 will be turned on after a delay for a period of time. Since the signal transmitting part 284 must wait until the diode 282 is turned on to generate the coupling signal, the signal receiving part 286 can only receive the coupling signal after a delay of this period of time, so as to generate the overvoltage protection trigger signal TRI to the PWM control circuit 132 . It can be seen that the PWM control circuit 132 can reduce the output voltage VOUT by controlling the operation of the power transistor 134 after a delay of this period of time, so as to perform over-voltage protection. In other words, in this case, the switching power supply device 100 will not perform the overvoltage protection immediately to cause the external system to fail to operate normally, but will delay the overvoltage protection for a period of time. Of course, those skilled in the art should know that the delay time can be adjusted by changing the resistance value of the impedance 220 or by changing the capacitance value of the energy storage unit 230 .
在一实施态样中,阻抗210耦接于开关单元240的第一端241与PNP型晶体管244的射极之间。由于,此实施态样的电路操作方式与图1所示电路的操作方式相同,在此便不再赘述。In an embodiment, the impedance 210 is coupled between the first end 241 of the switch unit 240 and the emitter of the PNP transistor 244 . Since the operation of the circuit in this embodiment is the same as that of the circuit shown in FIG. 1 , it will not be repeated here.
综上所述,在本发明的过电压保护电路中,电压取样单元的判断结果可用来反映切换式电源供应装置的输出端若呈现过电压,是因为切换式电源供应装置的内部电路失效所造成的,还是由外接系统所造成的。藉此电压取样单元可据以决定是否控制开关单元提供并联于阻抗的路径,以进一步决定是要让电流通过阻抗来对储能单元进行充电,或是让电流通过路径来对储能单元进行充电。而由于上述路径的阻值小于该阻抗的阻值,使得储能单元在二种不同的过电压情况下能有二种不同的充电时间,促使讯号隔离单元在二种不同的过电压情况下,产生过电压保护触发讯号的时间也跟着不同。藉由这样的控制,本发明的过电压保护电路能在切换式电源供应装置的内部电路失效时立即产生过电压保护触发讯号以控制切换式电源供应装置进行过电压保护,并在外接系统造成过电压时推迟产生过电压保护触发讯号的时间,以使切换式电源供应装置不会立即进行过电压保护而造成外接系统无法正常操作。To sum up, in the overvoltage protection circuit of the present invention, the judgment result of the voltage sampling unit can be used to reflect that if the output terminal of the switching power supply device exhibits overvoltage, it is caused by the failure of the internal circuit of the switching power supply device. Yes, it is still caused by the external system. In this way, the voltage sampling unit can determine whether to control the switch unit to provide a path connected in parallel with the impedance, so as to further determine whether to let the current pass through the impedance to charge the energy storage unit, or to let the current pass through the path to charge the energy storage unit . And because the resistance value of the above-mentioned path is smaller than the resistance value of the impedance, the energy storage unit can have two different charging times under two different overvoltage conditions, so that the signal isolation unit can be charged under two different overvoltage conditions. The time to generate the overvoltage protection trigger signal is also different. With such control, the overvoltage protection circuit of the present invention can immediately generate an overvoltage protection trigger signal to control the switchover power supply device to perform overvoltage protection when the internal circuit of the switchover power supply device fails, and cause overvoltage in the external system. The timing of generating the trigger signal for over-voltage protection is delayed when the voltage is low, so that the switching power supply device will not immediately perform over-voltage protection and cause the external system to fail to operate normally.
虽然本发明已以较佳实施例揭露如上,然其并非用以限定本发明,任何熟习此技艺者,在不脱离本发明的精神和范围内,当可作些许的更动与润饰,因此本发明的保护范围当是权利要求所界定的范围为准。Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, this The protection scope of the invention shall be defined by the claims.
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