English:
[0001] The invention relates to a driving technology for a switching element adapted to the case where overcurrent is detected in the switching element.
[0003] However, in the related art described above, detection of overcurrent is followed by the rapid lowering of the gate voltage regardless of the on-state of the switching element. Therefore, the gate voltage is rapidly lowered even when overcurrent is detected during an early period in a turning-on process during which the gate voltage has not sufficiently risen. If the gate voltage is rapidly lowered when the gate voltage has not sufficiently risen, the switching element is rapidly turned off, so that the off-surge voltage increases.
[0004] The invention provides a switching element driving device and a switching element driving method that executes an appropriate protection operation against not only the overcurrent occurring during a complete-on state but also the overcurrent occurring during an early period in a turn-on.
[0005] A switching element driving device in accordance with an aspect of the invention is characterized by comprising: overcurrent detection means for detecting an overcurrent that flows through a switching element; first gate voltage decrease means for decreasing gate voltage of the switching element at a rate that is faster than the rate of decrease of the gate voltage at a time of a normal turn-off; second gate voltage decrease means for decreasing the gate voltage of the switching element at a rate that is slower than the rate of decrease of the gate voltage at the time of the normal turn-off; and gate voltage monitoring means for monitoring the gate voltage of the switching element, wherein if it is determined by the gate voltage monitoring means that the gate voltage is greater than a predetermined value when the overcurrent is detected by the overcurrent detection means, the gate voltage is decreased by the first gate voltage decrease means and then, while the switching element keeps an on-state, the gate voltage is decreased by the second gate voltage decrease means, and wherein if it is determined by the gate voltage monitoring means that the gate voltage is less than or equal to the predetermined value when the overcurrent is detected by the overcurrent detection means, the gate voltage is decreased by only the second gate voltage decrease means.
[0007] According to these aspects of the invention, an appropriate protection operation can be executed against not only the overcurrent occurring during the completely on-state of a switching element, but also the overcurrent occurring during an early period in a turn-on.
[0008] The foregoing and further objects, features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:
[0009] Hereinafter, example embodiments of the invention will be described with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a switching element driving device in accordance with the invention. The switching element driving device of this embodiment drives a voltage-driven semiconductor switching element, such as an insulated gate bipolar transistor (IGBT), a power MOSFET, etc. (hereinafter, referred to as "power element 10"). The switching element driving circuit of this embodiment includes a turning-on transistor P-Tr, for example, a p-channel FET or the like, as means for turning on a power element 10, and also includes a turning-off transistor N-Tr, for example, an n-channel FET or the like, as means for turning off the power element 10. Hereinafter, the turning-on transistor P-Tr will be referred to as the "transistor PTr", and the turning-off transistor N-Tr will be referred to as the "transistor NTr".
[0011] On the other hand, if the control circuit 30 receives a command to turn off the power element 10 from an external device, such as a microcomputer or the like, the control circuit 30 turns off the transistor PTr and turns on the transistor NTr. When the transistor PTr is turned off and the transistor NTr is turned on, the charge of the gate of the power element 10 is released via the transistor NTr and the gate resistance Rn. When the amount of charge of the gate of the power element 10 is less than or equal to a predetermined value, the power element 10 turns off.
[0012] Furthermore, the switching element driving circuit of the embodiment includes overcurrent detection means 26 for detecting overcurrent through the power element 10 in order to prevent the destruction of the power element 10 or its peripheral circuit, which may occur when overcurrent passes through the power element 10 due to a malfunction such as a load shortcircuit or the like. The overcurrent detection means 26 detects overcurrent by a sense insulated gate bipolar transistor (IGBT) system, a shunt resistance system, etc. In the sense IGBT system, a principle current flowing through the power element 10 is detected based on the voltage across a sense resistance that is connected to the emitter (or to the source) of the sense IGBT. In the shunt resistance system, a principle current flowing through the power element 10 is detected based on the voltage occurring across a shunt resistance that is inserted in series in a path through which the principle current flows. The voltage across the sense resistance or the shunt resistance is compared with a reference voltage by a comparator. If the voltage across the sense resistance or the shunt resistance is higher than the reference voltage, the detected principle current may be considered excessively high, that is, overcurrent is flowing through the power element 10.
[0013] When the overcurrent detection means 26 detects overcurrent, greater current Ice is flowing through the power element 10 than in a normal condition, where overcurrent is not detected. In such a case, if the power element 10 is turned off in the same manner as in the normal condition, that is, by turning on the transistor NTr as described above, the greater-than-normal current Ice through the power element 10 brings about a greater rate of change of current "dlce/dt", which causes a greater surge voltage of "L*dlce/dt" as a multiplication product with the inductance L of the wiring, the drive-object load, etc., than at the time of a normal turn-off. Such an off-surge voltage may destroy the power element 10 or its peripheral circuit due to excess over the withstanding voltage thereof.
[0014] To reduce such off-surge that may destroy the power element 10 or its peripheral circuit, when overcurrent is detected by the overcurrent detection means 26, the power element 10 may be turned off by discharging the gate of the power element 10 via a gate resistance that is greater than the gate resistance Rn connected between the gate of the power element 10 and the transistor NTr. Thus, with the greater the gate resistance, the discharge duration is increased, which reduces the rate of change of current "dlce/dt". FIG. 2 is a diagram showing behaviors when the power element 10 is turned off via a gate resistance that is greater than the gate resistance Rn. However, because the greater gate resistance increases the turn-off duration as indicated in FIG. 2, the turn-off of the power element 10 via the gate resistance greater than the gate resistance Rn results in increased turn-off loss , and may damage the power element 10 by heat.
[0015] Therefore, restrain the increase of off-surge and of turn-off loss, the control of the turn-off of the power element 10 is divided into multiple stages. In the switching element driving device of this embodiment, the turn-off of the power element 10 is divided into two stages: a first step and a second step. The switching element driving device of the embodiment includes an overcurrent-time turning-off OC-TrI (overcurrent transistor), such as an n-channel FET or the like, that works in the first step, and an overcurrent transistor OC-Tr2, such as an n-channel FET or the like, that works in the second step. The overcurrent transistor OC-TrI and the overcurrent transistor OC-Tr2 release the charge of the gate of the power element 10 if overcurrent is detected by the overcurrent detection means 26. Hereinafter, the overcurrent transistor OC-TrI will be referred to as the "transistor OCTrI", and the overcurrent transistor OC- Tr2 will be referred to as the "transistor OCTr2".
[0016] If the overcurrent detection means 26 detects overcurrent, the control circuit 30 of the switching element driving circuit of this embodiment operates the transistor OCTrI as the first step so that the charge of the gate of the power element 10 is released via the gate resistance Rocl and thus the gate voltage Vge is quickly lowered to a voltage that is not below a threshold voltage at which the power element 10 becomes completely off. In order to lower the gate voltage Vge more quickly than in the case of a normal turn-off, the resistance value of the gate resistance Rocl is made smaller than the resistance value of the gate resistance Rn. Due to this, the operating point on the Ice- Vce static characteristic of the power element 10 shown in FIG. 6 shifts from a point Pl to a point P2, so that the peak current value of the current Ice flowing through the power element 10 is restrained and the turn-off loss is reduced. In order to stop the decrease of the gate voltage Vge of the power element 10 at a voltage that is not below the threshold voltage at which the power element 10 becomes completely off, various measures may be taken. For example, a timer or the like may be used so that the voltage decrease stops at the elapse of a fixed time, or the transistor PTr and the transistor OCTrI may be turned on simultaneously, so that the gate voltage Vge becomes a divided voltage value of the supply voltage 27 determined by the resistance Rp and the resistance Rocl.
[0017] After a fixed time of restraining the peak current value of the current Ice in the first step, the control circuit 30 of the switching element driving circuit of this embodiment turns off the transistor OCTrI operated in the first step, and then turns on the transistor OCTr2 in the second step. By turning on the transistor OCTr2, the charge of the gate of the power element 10 is released via the transistor OCTr2 and the gate resistance Roc2 to slowly reduce the gate voltage Vge of the power element 10. In order to reduce the gate voltage Vge more slowly than in the case of a normal turn-off, the resistance value of the gate resistance Roc2 is made greater than the resistance value of the gate resistance Rn. Due to this, the power element 10 undergoes a slow-off operation as shown in FIG. 3, so that the increase in the off-surge voltage is restrained without causing a great rate of change of current "dlce/dt".
[0018] However, when overcurrent is detected by the overcurrent detection means 26 before the gate voltage Vge of the power element 10 sufficiently rises in a turning-on process, the first step of operating the transistor OCTrI, which releases the charge of the gate of the power element 10 via the gate resistance Rocl more rapidly than normal, will result in a situation where the gate voltage Vge that has not sufficiently risen is reduced to a voltage below the threshold voltage for the complete turn-off of the power element 10, that is, the operation of the transistor OCTrI will turn off the power element 10 instead of the restraining of the peak current value. Hence, the off-surge voltage will be increased as shown in FIG. 4, so that the intended protection of the power element 10 is not possible.
[0019] To avoid this, the switching element driving circuit of this embodiment monitors the gate voltage Vge, and performs only the second step operation without performing the first step operation if the gate voltage Vge is less than or equal to a predetermined monitor voltage. Therefore, when overcurrent is detected by the overcurrent detection means 26 before the gate voltage Vge of the power element 10 sufficiently rises in a turning-on process as shown in FIG. 5, the power element 10 is not caused to undergo a rapid-off operation but is caused to undergo a slow-off operation, so that the increase of the off-surge voltage can be restrained. At this time, because the current Ice through the power element 10 is still small, the turn-off loss is sufficiently smaller than in the case where overcurrent is detected during the completely on-state. Thus, the intended protection of the power element 10 is reliably achieved.
[0020] Incidentally, the magnitude of the off-surge voltage and of the turn-off loss change in accordance with the inductance of the load or the like driven by the power element 10 and the resistance constants and parasitic capacitances of various circuit elements. Therefore, the predetermined monitor voltage for determining whether to carry out the first step operation and the second step operation should be determined by simulation in accordance with a switching drive circuit that is a protection object. The monitor voltage is, as a minimum requirement thereof, a value that is greater than the gate voltage at which the power element 10 begins to turn on, and that is smaller than the gate voltage at which the power element 10 begins to be completely on. For example, where the gate voltage at which the power element 10 begins to turn on is 5 V and the gate voltage at which the power element 10 begins to be completely on is 15 V, the monitor voltage may be appropriately set at 8 to 12 V.
[0021] FIG.7 shows an embodiment of a switching element driving method in accordance with the invention. If overcurrent is detected by the overcurrent detection means 26 (step 10), the control circuit 30 changes the method of decreasing the gate voltage depending on whether or not the gate voltage is less than or equal to a predetermined value (step 20). If the gate voltage is not less than or equal to the predetermined value, it is assumed that the power element 10 is completely on, and the control circuit 30 carries out the first step operation followed by the second step operation (steps 30 and 40). On the other hand, if the gate voltage is less than or equal to the predetermined value, it is assumed that the power element 10 is not completely on, and the control circuit 30 carries out only the second step operation (step 50).
[0022] Thus, according to the foregoing embodiments, in order to turn off the power element when an overcurrent malfunction of the power element has occurred without damaging the power element or the like due to increased off-surge voltage or increased turn-off loss, the first step operation and the second step operation are carried out. However, when overcurrent is detected during a turning-on process of the power element, the operation of the first step is not carried out, instead only the operation of the second step is carried out. Thus, both the increase of the off-surge voltage and increase of the turn-off loss are restrained, and the protecting operation against overcurrent is stably executed regardless of whether it is during an early period in a turning-on process, or the completely on-state of the power element, or the like.
[0023] While the invention has been described with reference to example embodiments thereof, it is to be understood that the invention is not limited to the described embodiments or constructions. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. In addition, while the various elements of the example embodiments are shown in various combinations and configurations, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the invention.'

中文:
[0001]本发明涉及一种用于适于在开关元件中检测到过电流的情况的开关元件的驱动技术。
[0003]然而,在上述现有技术中,伴随过电流的检测的是栅极电压的快速下降,而不考虑开关元件的导通状态。因此,即使当过电流在栅极电压还没有充分上升的导通过程的初期被检测到时,栅极电压也快速下降。如果当栅极电压还没充分上升时栅极电压就快速下降,则开关元件被快速关断,以使关断浪涌电压增大。
[0004]本发明提供了执行适当的保护操作以免受在完全导通状态的过程中发生的过电流以及在导通的初期过程中发生的过电流的开关元件驱动装置以及开关元件驱动方法。
[0005]根据本发明的一个方案的开关元件驱动装置的特征在于包括:过电流检测器件,其用于检测流经开关元件的过电流;第一栅极电压降低器件,其用于以比正常关断时栅极电压的下降速率快的速率来降低开关元件的栅极电压;第二栅极电压降低器件,其用于以比正常关断时栅极电压的下降速率慢的速率来降低开关元件的栅极电压;以及栅极电压监控器件,其用于监控开关元件的栅极电压,其中如果当过电流被过电流检测器件检测到时由栅极电压监控器件判断出栅极电压大于预定值,则栅极电压通过第一栅极电压降低器件来降低,然后在开关元件保持导通状态的同时,栅极电压通过第二栅极电压降低器件来降低,其中如果当过电流被过电流检测器件检测到时由栅极电压监控器件判断出栅极电压小于或等于预定值,则栅极电压仅通过第二栅极电压降低器件来降低。
[0007]根据本发明的这些方案,能够执行适当的保护操作以免受在开关元件的完全导通状态的过程中发生的过电流以及在导通的初期过程中发生的过电流的影响。
[0008]结合附图,通过对示例性实施例的下列描述,本发明的上述以及进一步的目的、特征和优点将变得显而易见,其中,相似的附图标记用于表示相似的元件,并且其中:
[0009]以下,将结合附图来描述本发明的示例性实施例。图1为表示根据本发明的开关元件驱动装置的实施例的图。所述实施例的开关元件驱动装置驱动例如绝缘栅双极性晶体管(IGBT)、电力MOSFET等等(以下,称为“电力元件10”)的电压驱动型半导体开关元件。所述实施例的开关元件驱动电路包括导通晶体管P-Tr,例如作为用于导通电力元件10的器件的p-沟道FET等等,并且还包括关断晶体管N-Tr,例如作为用于关断电力元件10的器件的n-沟道FET等等。以下,导通晶体管P-Tr将被称为“晶体管PTr”,而关断晶体管N-Tr将被称为“晶体管NTr”。
[0011]另一方面,如果控制电路30从例如微型计算机等等的外部设备接收到关断电力元件10的指令,则控制电路30关断晶体管PTr并且导通晶体管NTr。当晶体管PTr被关断并且晶体管NTr被导通时,电力元件10的栅极的电荷经由晶体管NTr和栅极电阻Rn来释放。当电力元件10的栅极的充电量小于或等于预定值时,电力元件10关断。
[0012]此外,本实施例的开关元件驱动电路包括过电流检测器件26,其用于通过电力元件10来检测过电流以便防止可能在过电流流经电力元件10时由于例如负载短路等等的故障而发生的电力元件10或其外围电路的损坏。过电流检测器件26通过灵敏绝缘栅双极性晶体管(IGBT)系统、分流电阻系统等等来检测过电流。在灵敏IGBT系统中,流经电力元件10的主电流基于通过连接到灵敏IGBT的发射器(或连接到源极)的灵敏电阻的电压来检测。在分流电阻系统中,流经电力元件10的主电流基于通过串联插入主电流流经的路径的分流电阻产生的电压来检测。灵敏电阻或分流电阻的电压通过比较器与参考电压进行比较。如果灵敏电阻或分流电阻的电压高于参考电压,则可以认为检测到的主电流过高,也就是说,过电流正在流经电力元件10。
[0013]当过电流检测器件26检测到过电流时,流经电力元件10的电流Ice比没有检测到过电流的正常情况大。在这种情况中,如果电力元件10以与正常情况相同的方式,即如上所述通过导通晶体管NTr来被关断,则通过电力元件10的比正常大的电流Ice带来较大的电流变化率“dIce/dt”,电流变化率“dIce/dt”引起了比正常关断时大的作为与导线、驱动对象负载等等的电感L的乘积的“L*dIce/dt”的浪涌电压。这种关断浪涌电压由于超过其耐电压而可能损坏电力元件10或其外围电路。
[0014]为了减小可能损坏电力元件10或其外围电路的这种关断浪涌,当过电流被过电流检测器件26检测到时,可以通过经由比连接在电力元件10的栅极与晶体管NTr之间的栅极电阻Rn大的栅极电阻而使电力元件10的栅极放电来关断电力元件10。因此,由于更大的栅极电阻,放电时间被增加,这减小了电流的变化率“dIce/dt”。图2为表示当经由比栅极电阻Rn大的栅极电阻来关断电力元件10时的运行情况的图。然而,如图2所示,由于较大的栅极电阻增加了关断时间,所以经由比栅极电阻Rn大的栅极电阻来关断电力元件10导致增加的关断损耗,并且可能通过热而使电力元件10损坏。
[0015]因此,为了抑制关断浪涌以及关断损耗的增加,电力元件10的关断的控制分为多个阶段。在所述实施例的开关元件驱动装置中,电力元件10的关断分为两个阶段:第一步和第二步。本实施例的开关元件驱动装置包括在第一步中工作的例如n-沟道FET等等的过电流时关断用OC-Tr1(过电流晶体管),以及在第二步中工作的例如n-沟道FET等等的过电流晶体管OC-Tr2。如果过电流被过电流检测器件26检测到,则过电流晶体管OC-Tr1和过电流晶体管OC-Tr2释放电力元件10的栅极的电荷。以下,过电流晶体管OC-Tr1将称为“晶体管OCTr1”,而过电流晶体管OC-Tr2将称为“晶体管OCTr2”。
[0016]如果过电流检测器件26检测到过电流,则所述实施例的开关元件驱动电路的控制电路30操作晶体管OCTr1作为第一步,以使电力元件10的栅极的电荷经由栅极电阻Roc1来释放,并且因此栅极电压Vge快速地下降到不低于电力元件10变得完全关断时的阈值电压的电压。为了使栅极电压Vge的下降比正常关断的情况更快,使得栅极电阻Roc1的电阻值小于栅极电阻Rn的电阻值。这样,图6中示出的电力元件10的Ice-Vce静态特性上的工作点从P1点移动至P2点,以使流经电力元件10的电流Ice的峰值电流被抑制并且关断损耗被减小。为了使电力元件10的栅极电压Vge的下降停止在不低于电力元件10变得完全关断时的阈值电压,可以采取多种措施。例如,可以使用定时器等等以使电压的下降在经过固定时间后停止,或可以同时导通晶体管PTr和晶体管OCTr1,以使栅极电压Vge变为由电阻Rp和电阻Roc1确定的电源电压27的分压值。
[0017]在第一步中抑制电流Ice的峰值电流达一定时间以后,所述实施例的开关元件驱动电路的控制电路30关断在第一步中工作的晶体管OCTr1,然后在第二步中导通晶体管OCTr2。通过导通晶体管OCTr2,电力元件10的栅极的电荷经由晶体管OCTr2和栅极电阻Roc2释放以缓慢地减小电力元件10的栅极电压。为了比正常关断的情况更缓慢地减小栅极电压Vge,使得栅极电阻Roc2的阻值大于栅极电阻Rn的阻值。这样,如图3所示,电力元件10经受慢关断操作,以便关断浪涌电压的增加被抑制而不引起大的电流变化率“dIce/dt”。
[0018]然而,当过电流在电力元件10的栅极电压Vge在导通过程中充分上升之前被过电流检测器件26检测到时,经由栅极电阻Roc1比正常快地释放电力元件10的栅极的电荷的操作晶体管OCTr1的第一步将导致还没有充分上升的栅极电压Vge由于电力元件10的完全关断而减小到阈值电压以下的电压的情况,也就是说,晶体管OCTr1的工作将关断电力元件10而不是抑制峰值电流。因此,如图4所示,关断浪涌电压将增加,所以电力元件10的预期保护是不可能的。
[0019]为了避免这点,如果栅极电压Vge小于或等于预定的监控电压,则所述实施例的开关元件驱动电路监控栅极电压Vge,并且仅执行第二步操作而不执行第一步操作。因此,如图5所示,当过电流在电力元件10的栅极电压Vge在导通的过程中充分上升之前被过电流检测器件26检测到时,不会使电力元件10经受快速关断操作而是使其经受慢关断操作,以使关断浪涌电压的增加能够被抑制。这时,因为通过电力元件10的电流Ice仍然小,关断损耗充分小于过电流在完全导通状态的过程中被检测到的情况。因此,可靠地实现了电力元件10的预期保护。
[0020]附带地,关断浪涌电压的幅值和关断损耗变化的幅值根据由电力元件10驱动的负载等等的电感以及各种电路元件的电阻常数和寄生电容而变化。因此,用于判断是否执行第一步操作以及第二步操作的预定监控电压应该通过根据作为保护对象的开关驱动电路的仿真来判断。作为其最低要求,监控电压为大于电力元件10开始导通的栅极电压,并且小于电力元件10开始完全导通的栅极电压的值。例如,在电力元件10开始导通的栅极电压为5V而电力元件10开始完全导通的栅极电压为15V的情况中,监控电压可以被适当地设定为8至12V。
[0021]图7示出了根据本发明的开关元件驱动方法的实施例。如果过电流被过电流检测器件26检测到(步骤10),则控制电路30基于栅极电压是否小于或等于预定值来改变降低栅极电压的方法(步骤S20)。如果栅极电压没有小于或等于预定值,则假定电力元件10完全导通,并且控制电路30执行第一步操作,然后是第二步操作(步骤S30和步骤S40)。另一方面,如果栅极电压小于或等于预定值,则假定电力元件没有完全导通,控制电路30仅执行第二步操作(S50)。
[0022]因此,根据上述实施例,当已经发生了电力元件的过电流故障而由于增大的关断浪涌电压或增大的关断损耗没有损坏电力元件等等时,为了关断电力元件而执行第一步操作和第二步操作。然而,当过电流在电力元件的导通过程中被检测到时,不执行第一步的操作,而仅执行第二步的操作。因此,关断浪涌电压的增大以及关断损耗的增大都被抑制,并且不管是在电力元件的导通过程的初期还是在完全导通状态等等的过程中都稳定地执行免受过电流影响的保护操作。
[0023]虽然已经结合示例性实施例对本发明进行了描述,但应该理解的是,本发明不局限于所描述的实施例或构造。与此相反,本发明旨在覆盖各种改进以及等同结构。另外,虽然在多种组合和结构中示出了示例性实施例的多种元件,但是包括更多、更少或仅有单个元件的其它组合和结构也在本发明的精神和范围内。