EP1307964A1

EP1307964A1 - Device for rapid short-circuit protection in a power semiconductor

Info

Publication number: EP1307964A1
Application number: EP01962565A
Authority: EP
Inventors: Torsten Mohr; Jörg Jehlicka; Ralf Moser; Thomas Hills; Ralf Hadeler
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2000-07-29
Filing date: 2001-07-18
Publication date: 2003-05-07
Also published as: WO2002011286A1; JP2004505599A; KR20030040377A; DE10036983A1; US20040051398A1; AU2001283775A1

Abstract

A device for rapid short-circuit protection in a power semiconductor is disclosed. Said device comprises at least one power semiconductor (10, 38), by means of which at least one electrical load (24) is supplied with a load current (IL). The current recorders (14, 18, 46) give a measure (VIS) for the load current (IL) on the electrical load (24). On the risk of an impairment of the power semiconductor (10), a semiconductor protection circuit (30, 32, 34, 36) takes the power semiconductor (10) into a protect mode. Along with the semiconductor protection circuit (30, 32, 34, 36), at least one further electronic component (62, 72, 74) is provided which compares the load current (IL), or a measure of the load current with a limiting value (60, VCC), whereby monitoring means are provided which take the power semiconductor (10) into a protection mode with regard to the electrical load (24), on said load passing above or below the limiting value (60, VCC).

Description

Device for fast short-circuit protection in a power semiconductor

State of the art

The invention is based on a device for fast short-circuit protection in a power semiconductor according to the preamble of the independent claim. A sense highside switch is described in the article "Sense highside switch performs fuse functions" by A. Blessing, A. Graf, P. Sommer in the magazine "Components 5-6 / 97", pages 32 to 35 (BTS 640S2), in which important protective functions are integrated. An overtemperature cut-off and a current limitation are provided, which are constantly active. At a so-called sense output of the power semiconductor one can

Load current proportional signal can be tapped. This sense voltage is evaluated by an A / D converter of a microcontroller and processed for example for security purposes.

In this power semiconductor, however, there is no possibility to change the value of the internal current limitation or the shutdown current from outside. Depending on the use of the power semiconductor, the maximum peak currents that occur in the connected loads very different. Most of the time, the current limit is set very high by the manufacturer of the power electronics in order to ensure the protection of the power semiconductor itself. Since a precisely adapted power semiconductor with regard to continuous current and / or maximum peak current is not available for every application, oversized power semiconductors often have to be used. This in turn has the consequence that, for example in the event of a short circuit until detection and countermeasures are initiated, unnecessarily high currents via the plug, the circuit board or the conductor track, the power semiconductor, the cable and the short circuit sink. In order not to have to dimension the components possibly affected by a short circuit to the short-circuit current of the power semiconductor, a short-circuit shutdown of the power semiconductor that can be applied in terms of value is desirable. The applicable short-circuit shutdown is particularly important in connection with a dual-voltage on-board electrical system (12 V / 42 V) in order to make a short circuit between the two voltage levels manageable.

Such a multi-voltage electrical system is described for example in the subsequently published DE-A 199 448 33. Short-circuit protection means are present between the two voltage levels of the multi-voltage electrical system, which largely reduce a short circuit and / or reduce the effects of a short circuit between the two voltages and / or protect or switch off endangered consumers in the event of a short circuit. The evaluation of a possible overcurrent is carried out under program control in a microcontroller.

It is the object of the invention to provide a device which increases the security against short circuits. This should be done in a cost-effective manner. This object is achieved by the features of the independent claim.

Advantages of the invention

The device according to the invention for fast short-circuit protection in a power semiconductor comprises at least one power semiconductor via which a load current can be applied to at least one electrical load. Current detection means are provided which provide a measure of the load current acting on the electrical load. A semiconductor protection circuit controls the power semiconductor in a protective operation in the event of impending impairment of the power semiconductor. According to the invention it is provided that in addition to the

Semiconductor protection circuit at least one further electronic component is provided which compares the load current or a measure of the load current with a limit value, monitoring means triggering the power semiconductor into a protective operation relating to the electrical load when the limit value is exceeded or fallen below. The additional load current monitoring is implemented according to the invention by a hardware circuit. Compared to a software-based evaluation, there are advantages with regard to the speed of possible overload detection. This means that countermeasures can be initiated quickly that reliably protect the electrical load. The value of the short-circuit shutdown of the power semiconductor can preferably be set by the user. The user is thus given the option of using a suitable

Dimensioning the limit value to use the power semiconductor to control any loads.

In an expedient development, a locking circuit is provided which activates the Power semiconductor is prevented if the limit is fallen below in the meantime. Since the switch-on and switch-off processes particularly endanger the power semiconductor and the electrical load, the locking circuit increases the protection against destruction of the

Power semiconductor and / or the electrical load. The state of the lock can be queried for further processing. The power semiconductor can only resume normal operation with a specific unlocking signal. This targeted influencing increases the possibility for a user to influence the protective function of the power semiconductor.

Further expedient further developments result from further dependent claims and from the description.

drawing

Exemplary embodiments of the invention are shown in the drawing and are explained in more detail in the following description.

1 and 2 show typical configurations of the power semiconductor, FIG. 3 shows an additional protective function implemented in the power semiconductor, FIG. 4 shows a protective function implemented outside the power semiconductor, and FIG. 5 shows a typical dual-voltage electrical system in which the power semiconductors are preferably used.

Description of the embodiments

An integrated power semiconductor 10 has at least one load output 12, via which an electrical load 24 can be supplied with a load current IL that is connected to ground 26 flows off. To activate the power semiconductor 10, a switching means 20 is provided, when it is closed, a control input 16 of the power semiconductor 10 is connected to a logic reference potential 22. The power semiconductor 10 has a current mirror output 14, in which a current proportional to the load current IL flows through a measuring resistor 18 to the logic reference potential 22. The voltage drop VIS caused at the measuring resistor 18 is evaluated.

In the exemplary embodiment according to FIG. 2, the individual components of the power semiconductor 10 are shown in more detail. Various protection and evaluation functions are provided, such as a voltage source 30, an overvoltage protection 32, a current limitation 34, a gate protection 36, the actual circuit breaker 38, a voltage sensor 40, a charge pump 42, a protective circuit for inductive loads 44, and a current detection 46, an electrostatic discharge protection 48, a logic circuit 50 and a temperature sensor 52. Otherwise, the external components correspond to those in FIG. 1.

The exemplary embodiment according to FIG. 3 serves for an internal protective circuit which acts directly on the current limitation 34 of the power semiconductor 10. For this purpose, the current mirror output 14 is connected via the measuring resistor 18 to the control input 16 in the event that the switching means 20 is closed and the power semiconductor 10 has thus been activated. The voltage VIS dropping across the measuring resistor 18 is compared by a comparator 62 with a reference voltage 60. The output signal of the comparator 62 is fed to the current limiter 34. In the exemplary embodiment according to FIG. 4, the voltage VIS dropping across the measuring resistor 18 is smoothed by a filter 70, which consists, for example, of an RC element. The smoothed output voltage becomes a transistor stage 72 or alternatively an inverting one

Input of a comparator 74 supplied. If the smoothed voltage VIS exceeds a certain limit value VCC, both the output signal of the transistor stage 72 and that of the comparator stage 74 become logic zero. These output signals are fed to a first AND gate 76, the output signal of which serves as an input signal to a second AND gate 78. The output signal of the first AND gate 76 reaches the second input of the first AND gate 76 via a self-holding resistor 80. An unlocking signal 84 can also reach the second input of the first AND gate 76 via a diode. In addition, the state of the locking circuit or the self-holding circuit can also be queried via two resistors via the pin, via which the unlocking signal 84 can also be fed to the locking circuit. The regular control 82 of the power semiconductor 10 (and thus the load 24) is routed to the second input of the second AND gate 78. When activation is desired in normal operation, the switching means 86 is activated such that the control input 16 of the power semiconductor 10 is on

Logic reference potential 22 is set in order to apply the load current IL to the electrical load 24 (not shown in FIG. 4).

In Figure 5 are essential components of a

Two-voltage electrical system of a motor vehicle shown. Specifically, G designate the generator, for example a claw-pole alternator that is driven by the vehicle engine. The generator G supplies an output voltage UO of, for example, 42 V, which leads directly to the Charge the battery Bl with 36 V nominal voltage. The line resistance between the generator G and the battery Bl is symbolized by the resistors R1 and R2. With the generator G, the consumers that are to be supplied with the voltage UO are connected via a signal / power distributor VI. In detail, three consumers R6, R7 and R8 are shown as examples of the electrical load 24, which can be connected to the generator G, for example, via power semiconductors Hl, H2 and H3. Due to their design, these power semiconductors Hl, H2 and H3 have the inverse diodes Dl, D2 and D3 and the internal resistors R3, R4 and R5.

A second battery B2 is charged by the generator G via a direct voltage converter W1. The

Direct voltage converter (DC / DC converter) Wl converts the voltage UO = 42 V into a voltage Ul = 14 V, which is suitable for charging the battery B2 with a nominal voltage of 12 V. The voltage Ul is supplied from the voltage converter Wl to the battery B2 via the

Switch S1 and the line with the line resistance R9. The resistance denoted by R9 also includes the internal resistance of the battery B2.

The battery B2 is used to supply consumers who require a lower voltage, for example 12 V or 14 V. The connection is made via the signal power distributor V2. These consumers are designated R13, R14 and R15, they can be connected via the power semiconductors H4, H5 and H6, which each have the inverse diodes D4, D5 and D6. The line resistances between the consumers, R13, R14 and R15 are labeled RIO, Rll and R12. Among the consumers that are to be supplied with 12 V or 14 V via the SLV2, this decision also includes a Zener diode ZI and a further diode D7, which together form an overvoltage protection. The Zener diode ZI and the further diode D7 are only examples as possible

Called voltage limiting means. It is also possible to use other limiter circuits.

The consumers are selected for one or the other voltage level depending on the

Voltage requirements for their optimal operation. For example, the starter can be connected to either the 12V battery or the 36 V battery. When using power semiconductors on the 14 V side, the switch with the short-circuited 14 V load becomes conductive over the inverse diode of the power semiconductor in question and thus applies all 14 V consumers to 42 V, which means that the consumers that are not designed for it are at risk. Such a short circuit is shown in FIG. A resistor RK, which is on the voltage side between the resistors R8 and R13, represents a short circuit ■, the effects of which are reduced according to the invention. How a short circuit symbolized by the resistor R16 can be limited in its effects is explained in more detail below.

In the exemplary embodiments according to FIGS. 1 and 2, the measuring resistor 18 converts the output current IS of the current mirror output 14 into a voltage signal VIS, which is proportional to the load current IL, generally directly proportional. The measuring resistor 18 is dimensioned in such a way that the current range of interest for the application, which is located between the value zero and the peak current, reaches a voltage range which is customary for an A / D converter, for example 0 to 5 V. is mapped. As soon as the voltage VIS falling across the measuring resistor 18 becomes greater than 5 V, one is outside the desired current range. This usually signals an error, such as a short circuit in the overall system. In this case, the power semiconductor 10 is to be controlled in a protective operation. Protective operation is understood to mean, for example, operation with a current limitation or the complete shutdown of the power semiconductor 10.

As a rule, power semiconductors 10 have no possibility of tapping the logic reference potential 22 in order to detect the voltage drop across the measuring resistor 18 in relation to this logic reference potential 22. To solve this problem, it is now proposed to measure the voltage VIS falling across the measuring resistor 18 with respect to the potential tapped at the control input 16. This is because when the power semiconductor 10 is activated, the switching means 20 is closed and the control input 16 is thus connected to the logic reference potential 22. However, since monitoring is only of interest when the power semiconductor 10 is activated, the control input 16 is suitable for the application mentioned.

According to FIG. 3, as an electronic component, the comparator 62 compares the voltage VIS dropping across the measuring resistor 18 with the reference voltage 60. For the reasons already mentioned above, this is located at 5.5 V, for example, in order to reliably detect that the working range of the load current IL has been exceeded. If the voltage VIS falling across the measuring resistor 18 exceeds the reference voltage 60, the output signal of the comparator 62 activates the current limitation 34 already integrated in the power semiconductor 10. The current limiting circuit either effects the immediate one Switching off the power semiconductor 10, 38 or regulating the voltage drop across the measuring resistor 18 to a maximum of 5.5 V. This would limit the load current IL to a value proportional to the reference voltage 60. The user can adapt the reference voltage 60 as desired to the respective application or to the electrical load 24 to be controlled. This additional circuit is relatively small in comparison to the already existing circuit of the power semiconductor 10 and thus increases the additional costs only slightly. However, the functionality of the power semiconductor 10 is greatly upgraded without having to intervene in the semiconductor switch itself. This means that the user's previous interconnection can remain the same.

In the exemplary embodiment according to FIG. 4, external monitoring means are now provided, which at the same time also cause the power semiconductor 10 to be switched off quickly. Contrary to the exemplary embodiment in FIG. 3, the internal current limitation 34 of the power semiconductor 10 is no longer used to implement the protective function. Instead, the power semiconductor 10 is switched off via the control input 16, as will be explained below. In normal operation, the load current IL is within the permissible range. Therefore, the output signal of the first AND gate 76 has the logic 1 state, so that the control 82 reaches the control input of the switching means 86 unhindered. If the control 82 signals an activation request of the load 24, the switching means 86 connects the control input 16

Logic reference potential 22. As a result, the load 24 is acted upon by the load current IL. The signal proportional to the load current IL is available at the current mirror output 14. The voltage VIS falling across the measuring resistor 18 is smoothed by the (optional) RC element 70. That so smoothed output signal is fed to either the transistor stage 72 or the comparator stage 74 in order to carry out a monitoring for a predetermined limit value being exceeded. In the exemplary embodiment, the limit value is selected as the VCC signal, that is to say approximately 5 V.

If the smoothed voltage VIS falling across the measuring resistor 18 exceeds the reference voltage VCC of 5 V, either the transistor stage 72 or the comparator stage 74 output an output signal of logic zero. This logic zero output signal is fed to the first AND gate 76, the output signal of which therefore also assumes the logic zero value. Since the output signal of the first AND gate 76 is also used as an input signal of the second AND gate 78, the output signal of the second AND gate 78 also changes its logic state to logic zero. Thus, the switching means 86 is also no longer activated, so that the control input 16 is no longer set to logic reference potential 22. As a result, the power semiconductor 10 is switched off. The current flow IL through the load 24 is omitted. To prevent the power semiconductor 10 from being reactivated immediately, a locking circuit is provided. For this purpose, the output signal of the first AND gate 76 arrives at the second input of the first AND gate 76 via the self-holding resistor 80. Thus, the logic zero signal is also present when the monitoring function is activated at the second input of the AND gate 76, so that the output signals of the two AND gates 76, 78 always remain at logic zero. The status of the locking circuit can be queried via signal 84. It can be used for further evaluation purposes. A locking signal with the logic zero status indicates that the protective function has been activated. In order to be able to put the power semiconductors 10 back into operation, the user must send a signal 84 with the state logic one to the second input of the first and Lay gate 76. Since normally the load current IL will no longer have exceeded the limit value VCC, the first AND gate 76 has two logic one signals applied to it, so that its output signal also assumes the value logic one. In this way, the control signal 82 is switched through to the output of the second AND gate 78 in order to permit a desired activation of the switching means 86 with an associated application of the control input 16. The semiconductor 10 can thus be controlled again such that the load current IL can flow through the electrical load 24.

In the exemplary embodiment according to FIG. 5, the power semiconductors 10 can be used as power semiconductors Hl-H6 in the manner already described. Especially in the event of a short circuit between the different voltage levels U1 and UO of the multi-voltage subnet, the electronic components help to detect an impermissible load current IL at an early stage and to initiate countermeasures.

Claims

Expectations

1. Device for fast short-circuit protection in a power semiconductor, - with at least one power semiconductor (10, 38), via which at least one electrical load (24) can be loaded with a load current (IL),

- With current detection means (46, 14, 18), which provide a measure (VIS) for the electrical load (24) acting on the load current (IL), with a semiconductor protection circuit (30, 32, 34, 36) which is in the event of impending impairment of the power semiconductor (10, 38) controls the power semiconductor (10, 38) in a protective operation, characterized in that in addition to the

Semiconductor protection circuit (30, 32, 34, 36) at least one further electronic component (62, 72, 74) is provided, which compares the load current (IL) or a measure (VIS) of the load current with a limit value (60, VCC), wherein Monitoring means (34, 76, 78, 86) are provided which control the power semiconductor (10, 38) in a protective operation relating to the electrical load (24) when the limit value (60, VCC) is exceeded or not reached.

2. Device according to claim 1, characterized in that a comparator (62, 74) and / or a transistor stage (72) are provided as the electronic component.

3. Device according to one of the preceding claims, characterized in that a locking circuit is provided which prevents a renewed initiation of the protective operation relating to the electrical load (24).

4. Device according to one of the preceding claims, characterized in that the semiconductor circuit (30, 32, 34, 36) is activated when the limit value (60, VCC) is exceeded or undershot in a protective operation relating to the electrical load (24).

5. Device according to one of the preceding claims, characterized in that the control input (16) of the power semiconductor (10, 38) is used for current detection.

6. Device according to one of the preceding claims, characterized in that the state of the locking circuit is detected.

7. Device according to one of the preceding claims, characterized in that in a protective operation relating to the electrical load (24), the electrical load

(24) is loaded with no or a maximum permissible load current (IL).

8. Device according to one of the preceding claims, characterized by use in a dual-voltage electrical system of a motor vehicle.