CN107342680B - Dcdc转换器 - Google Patents

Dcdc转换器 Download PDF

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CN107342680B
CN107342680B CN201710286392.6A CN201710286392A CN107342680B CN 107342680 B CN107342680 B CN 107342680B CN 201710286392 A CN201710286392 A CN 201710286392A CN 107342680 B CN107342680 B CN 107342680B
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circuit
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output
voltage
overcurrent protection
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CN107342680A (zh
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河野明大
后藤克也
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Ablic Inc
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    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02MAPPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00Details of apparatus for conversion
    • H02M1/32Means for protecting converters other than automatic disconnection
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02MAPPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00Conversion of dc power input into dc power output
    • H02M3/02Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02MAPPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00Conversion of dc power input into dc power output
    • H02M3/02Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • H02M3/158Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load
    • H02M3/1588Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators including plural semiconductor devices as final control devices for a single load comprising at least one synchronous rectifier element
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02HEMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/08Emergency 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 current
    • H02H3/087Emergency 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 current for dc applications
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02HEMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/10Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers
    • H02H7/12Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers
    • H02H7/1213Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers for DC-DC converters
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02MAPPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00Details of apparatus for conversion
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02MAPPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00Details of apparatus for conversion
    • H02M1/0003Details of control, feedback or regulation circuits
    • H02M1/0032Control circuits allowing low power mode operation, e.g. in standby mode
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02MAPPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00Details of apparatus for conversion
    • H02M1/08Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02MAPPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00Conversion of dc power input into dc power output
    • H02M3/02Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/10Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M3/145Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M3/155Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/156Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02MAPPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00Details of apparatus for conversion
    • H02M1/0003Details of control, feedback or regulation circuits
    • H02M1/0009Devices or circuits for detecting current in a converter
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02MAPPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00Details of apparatus for conversion
    • H02M1/0003Details of control, feedback or regulation circuits
    • H02M1/0025Arrangements for modifying reference values, feedback values or error values in the control loop of a converter
    • HELECTRICITY
    • H02GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02MAPPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00Details of apparatus for conversion
    • H02M1/0003Details of control, feedback or regulation circuits
    • H02M1/0032Control circuits allowing low power mode operation, e.g. in standby mode
    • H02M1/0035Control circuits allowing low power mode operation, e.g. in standby mode using burst mode control
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02BCLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes

Abstract

本发明提供DCDC转换器,低耗电且具有较高的安全性。DCDC转换器构成为仅在基于输出控制电路输出的接通开关元件的信号的规定期间,使过电流保护电路间歇地动作。

Description

DCDC转换器
技术领域
本发明涉及DCDC转换器,并且涉及检测输出过电流而限制流过DCDC转换器的电流的技术。
背景技术
DCDC转换器具有过电流保护电路,以防止大电流流过开关元件而损坏DCDC转换器。同步整流型DCDC转换器可采用检测输入端子侧或接地端子侧的开关元件电流而使其断开的方法。
检测电流的方法有将流过开关元件的电流转换成电压而与基准值进行比较的方法、将开关元件的漏极-源极间电压与基准电压进行比较的方法(例如,参照专利文献1)。
【专利文献1】日本特开2004-364488号公报
然而,如果追加用于确保安全性的保护电路,则需要用于使该保护电路动作的电力,阻碍电子设备要求的低耗电化。例如,在具有过电流保护电路的现有的DCDC转换器中,为了监视开关元件而使电流感测放大器电路及比较器始终动作。因此,存在如下的课题:在流过DCDC转换器的电流较小而损坏的可能性较小的状态下,也会持续消耗规定的电力,导致电力效率恶化。
发明内容
本发明正是为了解决以上的课题而完成的,提供一种低耗电且具有较高的安全性的DCDC转换器。
为了解决现有的课题,本发明的DCDC转换器利用开关元件根据被输入到输入端子的电源电压向输出端子输出期望的输出电压,所述DCDC转换器具有:所述开关元件,其连接在电感器的一端与所述DCDC转换器的所述输入端子之间,所述电感器的另一端与所述输出端子连接;误差放大器,其监视所述输出电压;输出控制电路,其根据所述误差放大器的输出信号而向所述开关元件的栅极输出控制信号,以建立开关周期;过电流保护电路,其包括被与开关连接的偏置电路驱动的比较器,所述过电流保护电路在流过所述开关元件的电流为规定的电流以上时,向所述输出控制电路输出第一信号,以使所述开关元件断开;以及计时电路,其当所述开关元件导通时工作预定的计数时间,并对所述过电流保护电路输出第二信号,所述第二信号是基于所述输出控制电路的所述控制信号的信号并且对所述与开关连接的偏置电路进行控制,以使得所述过电流保护电路进行仅在所述计时电路正在进行计数的期间动作的间歇动作。
本发明的DCDC转换器使过电流保护电路间歇地动作,由此,尤其能够减少小负载时的消耗电流,从而能够提高电力效率。
附图说明
图1是示出本发明的第一实施方式的DCDC转换器的电路图。
图2是示出第一实施方式的DCDC转换器的计时电路的一例的电路图。
图3是示出第一实施方式的DCDC转换器的计时电路的动作的时序图。
图4是示出第一实施方式的DCDC转换器的过电流保护电路的一例的电路图。
图5是示出本发明的第二实施方式的DCDC转换器的电路图。
图6是示出本发明的第二实施方式的过电流保护电路的一例的电路图。
标号说明
10:误差放大器;
11:振荡电路;
12、22、62:基准电压电路;
13、21、63:比较器;
14、64:计时电路;
15、16:缓冲电路;
19:输出控制电路;
20:电流感测放大器;
23、59:过电流保护电路;
30、31、32、42、43、44、45:偏置电路;
41:脉冲生成电路;
60、61:RS-FF电路。
具体实施方式
以下,参照附图对本发明的实施方式进行说明。
图1是示出本发明的第一实施方式的DCDC转换器的电路图。DCDC转换器100是将被输入到输入端子1的电源电压Vin转换成恒电压而作为输出电压Vout输出至输出端子7的同步整流型DC-DC转换器。
本实施方式的DCDC转换器100具有作为第1开关元件的PMOS晶体管3、作为第2开关元件的NMOS晶体管4、电感器5、输出电容器6、误差放大器10、振荡电路11、基准电压电路12、比较器13、计时电路14、缓冲电路15和16、分压电阻17和18、输出控制电路19以及过电流保护电路23。
分压电阻17和18输出与输出电压Vout对应的反馈电压Vfb。误差放大器10输出与反馈电压Vfb和基准电压电路12的输出电压Vref的电压差对应的电压Verr。比较器13比较从振荡电路11输出的三角波与误差放大器10的电压Verr。输出控制电路19根据比较器13的比较结果将信号PS输出至PMOS晶体管3,将信号NS输出至NMOS晶体管4,从而控制开关动作。
过电流保护电路23监视流过PMOS晶体管3的电流,当检测到过电流时,向输出控制电路19输出用于使PMOS晶体管3截止的信号。
计时电路14与将PMOS晶体管3导通的信号对应地向过电流保护电路23输出起动信号,在经过规定时间之后向过电流保护电路23输出停止信号。
图2是示出计时电路14的一例的电路图。
脉冲生成电路41与被输入到IN端子的信号PS对应地输出单脉冲(信号OSP)。即,当由输出控制电路19输入使PMOS晶体管3导通的信号PS(低电平)时,输出规定期间的L信号。
偏置电路42、43、44、45接收RS-FF电路61输出的H信号而接通,基于施加给输入端子1的输入电压Vin而输出电流。
电容器46与偏置电路42的输出连接,利用偏置电路42的电流进行充电。电容器48与偏置电路44的输出连接,利用偏置电路44的电流进行充电。电容器48的电容大于电容器46的电容。在充电电流相同的情况下,电容器48的直到成为规定电压为止的充电时间比电容器46的直到成为规定电压为止的充电时间长。
当电容器46的电压为閾值电压以上时,NMOS晶体管50导通。反相器56与NMOS晶体管50的导通截止对应地向RS-FF电路60的设置端子S和NMOS晶体管53的栅极输出H信号或L信号。
当电容器48的电压为閾值电压以上时,NMOS晶体管51导通。反相器57与NMOS晶体管51的导通截止对应地向RS-FF电路60的重置端子R和NMOS晶体管52、54的栅极输出H信号或L信号。
NMOS晶体管52、53与电容器46并联连接,当栅极被输入H信号时导通,释放电容器46的电荷。NMOS晶体管54与电容器48并联连接,当栅极被输入H信号时导通,释放电容器48的电荷。
反相器55将使从RS-FF电路61的输出端子Q输出的信号TOUT反相后的信号输出至开关47、49。开关47与电容器46并联连接,经由反相器55接收RS-FF电路61输出的L信号而导通,释放电容器46的电荷。开关49与电容器48并联连接,经由反相器55接收RS-FF电路61输出的L信号而导通,释放电容器48的电荷。
RS-FF电路60根据被输入到设置端子S和重置端子R的信号而由Q端子输出信号CLK。RS-FF电路61的设置端子S被输入脉冲生成电路41的信号OSP,重置端子R被输入从RS-FF电路60输出的信号CLK,从输出端子Q输出信号TOUT。
这样构成的计时电路14接收使PMOS晶体管3导通的信号PS,输出使过电流保护电路23接通规定时间的信号。
并且,计时电路14不限于该电路例,只要是被输入触发信号时开始动作,当计时器经过设定时间时结束动作的电路即可。此外,这样的计时电路在动作中途有触发信号进入时会重新从初始值起开始再次计数。
接下来,基于图3的时序图对计时电路14的动作进行说明。
在时刻t0,当输出控制电路19的输出信号被输入到计时电路14的IN端子时,脉冲生成电路41输出L信号脉冲。这时,电容器46,48放电,充电电压成为L。
在时刻t1,从脉冲生成电路41输出H信号而输入到RS-FF电路61的设置端子S。由此,从RS-FF电路61输出的H信号将偏置电路42、43、44、45接通而开始供给电流,对电容器46、48进行充电。同时,RS-FF电路61的输出H信号被反相器55反相,利用该L信号将开关47、49断开。
在时刻t2,当利用由偏置电路42供给的电流使电容器46的充电电压达到NMOS晶体管50的閾值电压Vtn1时,NMOS晶体管50导通而输出L信号。该L信号由反相器56转换成H信号而输入到RS-FF电路60的设置端子S。由此,从RS-FF电路60的输出端子Q输出H信号。该输出信号由反相器58反相后被输入到RS-FF电路61的重置端子R。然后,继续从OUT端子输出H信号。同时,从反相器56输出的H信号将NMOS晶体管53导通而使电容器46放电。电容值大于电容器46的电容器48的充电电压没有达到NMOS晶体管51的閾值电压Vtn2,从而继续充电。
在时刻t3,当电容器48的充电电压达到NMOS晶体管51的閾值电压Vtn2时,NMOS晶体管51导通而输出L信号。该L信号由反相器57转换成H信号而输入到RS-FF电路60的重置端子R。另一方面,反相器57输出的H信号将NMOS晶体管52、54导通而使电容器46、48放电。这时,NMOS晶体管50截止,因此输出H信号,经由反相器56将L信号输入到RS-FF电路60的设置端子S。设置端子S被输入L信号、重置端子R被输入H信号的RS-FF电路60从输出端子Q输出L信号。该L信号经由反相器58作为H信号被输入到重置端子R,RS-FF电路61输出L信号。
在时刻t4,输出控制电路19的输出信号被输入到计时电路14的IN端子,脉冲生成电路41输出L信号脉冲。RS-FF电路61在该L信号脉冲上升时输出H信号。
如上所述,当PMOS晶体管3导通时,计时电路14输出H信号,开始时间计数,在计数时间后,输出输出L信号的周期的间歇信号。可以利用电容器48的电容值、偏置电路44的电流值、NMOS晶体管51的閾值电压来设定该计数时间。
此外,在该例中,将计数时间设定成比PMOS晶体管3的开关周期短。如果使计数时间比开关周期长,则在达到计数时间之前输入用于将PMOS晶体管3导通的信号,重新开始时间计数,因此,计时电路14持续输出H信号。
这样,通过调整计数时间与开关周期的关系,能够根据情况来选择间歇输出或恒定输出。
图4是示出本发明的第一实施方式的过电流保护电路的电路例的图。过电流保护电路23具有:电流感测放大器20,其将流过PMOS晶体管3的电流转换成电压;比较器21,其锁存输出信号;偏置电路30、31;以及基准电压电路22。此外,过电流保护电路23还具有:开关35,其控制由偏置电路30向电流感测放大器20的电流供给;以及开关36,其控制由偏置电路31向比较器21的电流供给。
当由计时电路14将H信号输入到IN_T端子时,开关35、36接通,向电流感测放大器20和比较器21供给电流。电流感测放大器20利用IN1、IN2端子接收流过PMOS晶体管3的电流,输出与流过PMOS晶体管3的电流对应的电压。比较器21通过比较电流感测放大器20的输出与基准电压电路22输出的基准电压,判定流过PMOS晶体管3的电流。
当电流感测放大器20的输出电压为基准电压值以上时,比较器21判定为处于过电流状态而从OUT端子输出H信号。然后,在其开关周期中使PMOS晶体管3成为截止状态,由此防止DCDC转换器100损坏。然后,开关35、36基于被输入到IN_T端子的信号进行接通/断开动作。电流感测放大器20和比较器21在开关35、36断开时将接通时的信号锁存,以避免成为不稳定状态。用于判断PMOS晶体管3的电流是否是过电流的判定标准是根据基准电压电路22的基准电压值任意确定的。
以上的采用计时电路14和过电流保护电路23的本发明的DCDC转换器能够通过改变计数时间与开关周期的关系,控制间歇动作。
例如,在将计数时间设定成比开关周期长的情况下,利用与输出端子7连接的负载对过电流保护电路23的间歇动作与始终动作进行切换。
在负载较大的情况下,取PMOS晶体管3以规定的开关周期进行振荡动作的连续模式动作状态。因此,即使计时电路14接收输出控制电路19的信号而开始时间计数,也会在达到规定的计数时间之前再次从输出控制电路19接收信号。其结果是,计时电路14持续输出接通信号,使得过电流保护电路23不会进行间歇动作。
在负载较小的情况下,输出电压Vout的变动变小,转移至PMOS晶体管3的动作不是规定周期的振荡动作的不连续模式动作状态,从而频率下降。然后,当开关周期超过计数时间时,计时电路14输出接通/断开信号,过电流保护电路23进行间歇动作。因此,能够减少过电流保护电路23的耗电。
此外,在将计时电路14的计数时间设定成比开关周期短的情况下,过电流保护电路23与连接于输出端子7的负载无关地进行间歇动作。因此能够进一步减少耗电。
在以上的说明中,与PMOS晶体管3导通同时地开始计时电路14的时间计数,但是,也可以与PMOS晶体管3截止同时地开始计时电路14的时间计数。
过电流保护电路23是如下的电路:利用电流感测放大器20将流过PMOS晶体管3的电流转换成与电流值对应的电压,通过比较器21将所述电压与基准电压电路22的输出电压进行比较,从而判定过电流状态,但是,过电流保护电路23也可以是如下的电路:监视PMOS晶体管3的漏极-源极间电压,通过比较器将所述电压与基准电压进行比较,从而判定过电流状态。
图5是示出第二实施方式的DCDC转换器的电路图。DCDC转换器200具有过电流保护电路59和计时电路64。过电流保护电路59监视NMOS晶体管4的电流。
计时电路64与将NMOS晶体管4导通的信号对应地向过电流保护电路59输出起动信号,在经过规定时间之后向过电流保护电路59输出停止信号。
图6是示出过电流保护电路59的一例的电路图。过电流保护电路59具有:比较器63,其锁存输出信号;偏置电路32;开关37,其控制从偏置电路32向比较器63的电流供给;以及基准电压电路62。
当由计时电路64将H信号输入到IN_T端子时,开关37接通,向比较器63供给电流。比较器63利用IN1端子接收NMOS晶体管4的漏极电压,将其与基准电压电路62输出的基准电位进行比较,输出二者之差的信号。比较器63通过比较NMOS晶体管4的漏极电压与基准电压电路62输出的基准电压,判定流过NMOS晶体管4的电流。
当IN1端子的输入电压为基准电压值以上时,比较器63判定为处于过电流状态而从OUT端子输出H信号。当IN1端子的输入电压不足基准电压值时,比较器63从OUT端子输出L信号。然后,开关37基于被输入到IN_T端子的信号进行接通/断开动作。比较器63在开关37断开时将接通时的信号锁存,以避免成为不稳定状态。用于判断NMOS晶体管4的电流是否是过电流的判定标准是根据基准电压电路62的基准电压值任意确定的。
以上的采用计时电路64和过电流保护电路59的本发明的DCDC转换器能够通过改变计数时间与开关周期的关系,控制间歇动作。
例如,在将计数时间设定成比开关周期长的情况下,利用与输出端子7连接的负载对过电流保护电路59的间歇动作与始终动作进行切换。
在负载较大的情况下,取NMOS晶体管4以规定的开关周期进行振荡动作的连续模式动作状态。因此,即使计时电路64接收输出控制电路19的信号而开始时间计数,也会在达到规定的计数时间之前再次从输出控制电路19接收信号。其结果是,计时电路64持续输出接通信号,使得过电流保护电路59不会进行间歇动作。
在负载较小的情况下,输出电压Vout的变动变小,转移至NMOS晶体管4的动作不是规定周期的振荡动作的不连续模式动作状态,从而频率下降。然后,当开关周期超过计数时间时,计时电路64输出接通/断开信号,过电流保护电路59进行间歇动作。因此,能够减少过电流保护电路59的耗电。
当判定为过电流保护电路59处于过电流状态时,直到计时电路64计数结束为止,过电流保护电路59持续动作以保护DCDC转换器免受过电流之害。因此,需要使计时电路64的计数时间足够长,以使电流值下降至一定值以下。
也可以是,不使用计时电路64,使过电流保护电路59的动作与NMOS晶体管4导通的定时同步。该情况下,过电流保护电路59仅在NMOS晶体管4处于导通状态时进行电流检测,从而间歇地进行动作。该情况下,过电流保护电路59的动作期间也不会受到计时电路64的计数时间制约。
过电流保护电路59的动作期间也可以不是从NMOS晶体管4导通起的一定期间,设为从PMOS晶体管3导通起的一定期间也能够得到同等的效果。

Claims (2)

1.一种DCDC转换器,该DCDC转换器利用开关元件根据被输入到输入端子的电源电压向输出端子输出期望的输出电压,其特征在于,所述DCDC转换器具有:
所述开关元件,其连接在电感器的一端与所述DCDC转换器的所述输入端子之间,所述电感器的另一端与所述输出端子连接;
误差放大器,其监视所述输出电压;
输出控制电路,其根据所述误差放大器的输出信号而向所述开关元件的栅极输出控制信号,以建立开关周期;
过电流保护电路,其包括被与开关连接的偏置电路驱动的比较器,所述过电流保护电路在流过所述开关元件的电流为规定的电流以上时,向所述输出控制电路输出第一信号,以使所述开关元件断开;以及
计时电路,其当所述开关元件导通时工作预定的计数时间,并对所述过电流保护电路输出第二信号,
所述第二信号是基于所述输出控制电路的所述控制信号的信号并且对所述与开关连接的偏置电路进行控制,以使得所述过电流保护电路进行仅在所述计时电路正在进行计数的期间动作的间歇动作。
2.根据权利要求1所述的DCDC转换器,其特征在于,
所述计时电路根据所述输出控制电路的所述控制信号输出用于使所述过电流保护电路间歇动作的第三信号。
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