DE102007046488B4 - Method and device for diagnosis in integrated power bridge circuits - Google Patents

Abstract

Method for fault detection in integrated power bridge circuits having a high-side arm and a low-side arm and a load (L) arranged therebetween, a high-side power switch (B) between the load (L) and supply voltage (Vsupply) and one Low-side circuit breaker (G) between load (L) and ground (M), as well as with over-current measuring devices for measuring the overcurrent through the circuit breaker (B, G), characterized in that the currents (IB) in the high-side branch and (IG) are detected in the low-side branch during operation, that the detected values for the currents are subtracted from each other and that the difference thus formed is compared with an upper limit value (RO) and a lower limit value (RU) • Exceeding of the upper limit value (RO) as a short circuit (SCG1) via the low-side circuit breaker (G) is interpreted, if at the same time no overcurrent in the circuit is measured, • an exceeding of the upper size value (RO) is interpreted as a short circuit (SCG2) via the series connection of low-side circuit breaker (G) and load (L), if an overcurrent in the circuit is measured at the same time, • a shortfall below the lower limit value (RU) (SCB1) is interpreted via the high-side circuit-breaker (B), if at the same time no overcurrent in the circuit is measured, • a shortfall of the lower limit value (RU) as short circuit (SCB2) via the series circuit of high-side circuit breaker ( B) and the load (L) is interpreted as an overcurrent in the circuit is measured simultaneously, and • the measurement of an overcurrent in the circuit with simultaneous measurement of a current difference (ID), which is greater than the lower limit (RU) and smaller when the upper limit (RO) is interpreted as a short circuit (SCL) across the load (L).

Description

The invention relates to a method and a device for fault detection in integrated power bridge circuits having a high-side branch and a low-side branch and a load L, a high-side power switch B between load L and supply voltage V _Supply and a low-side branch. Side circuit breaker G between load L and ground M, and with over-current measuring devices for measuring the overcurrent through the circuit breakers B and G.

Such switching arrangements are known. Especially in the automotive industry, the detection and differentiation of different error cases, namely short circuits on individual elements, as well as the protection of the circuit against destructive overload is particularly important, especially for cost reasons, the diagnosis must be solved with the least possible circuit complexity. A factor here is that the environmental requirements for circuits in the automotive industry are extremely high, so that components are more complicated and expensive to manufacture, which in turn increases the pressure on the reduction of the circuit complexity.

In a described circuit arrangement, short circuits can occur via the high-side power switch (SCB ₁ ), via the series connection of the high-side power switch and the load L (SCB ₂ ), via the low-side power switch (SCG ₁ ) Series connection of low-side circuit breaker and load L (SCG ₂ ) and a short circuit across the load (SCL) occur. As a result of a short circuit, excessively high currents may occur. Too low currents can be the result of interrupts.

These errors can occur before the load is switched on, but also during the operation of the load.

In the prior art, in such integrated circuit breakers, the diagnosis is carried out by current measurements in both circuit breakers with the aid of shunt resistors or current-sense transistors. A highly tolerant diagnosis can also be realized by monitoring the voltage across an activated circuit breaker.

There are a number of control circuits, usually with comparators, known that are able to distinguish the various error cases in the prior art. However, in particular on the high side, a considerably greater circuit complexity arises since all circuit parts have to be designed for higher voltages. The error cases are diagnosed in the prior art by diagnosing the error SCB ₁ in the off state, stamping a voltage on the high-side output and measuring the current. Alternatively, it is also known in the state of the art to apply a current to the high-side output in the switched-off state and to measure the voltage. Furthermore, the low-side power switch can be turned on separately and the current in the diagnostic mode can be determined.

The fault SCB ₂ , which consists of a short circuit across the series circuit of high-side circuit breaker and load, is determined by overcurrent measurement in the low-side circuit breaker. Accordingly, the fault SCG ₂ leads to an overcurrent in the high-side circuit breaker. The fault SCG ₁ , ie the short-circuit through the low-side circuit-breaker, is determined, similar to the error SCB ₁ , by impressing a voltage in the switched-off state on the low-side output and measuring the current (or vice versa). It is also possible to individually switch on the low-side circuit breaker and to carry out the current measurement in the diagnostic mode.

The error SCL, ie the short circuit across the load, is monitored by the current increase in one of the two circuit breakers.

A major disadvantage of the prior art is the complex interconnection and the necessary design of the measuring circuits for high loads. Another disadvantage is that the diagnosis of a short circuit via a switch alone can only be done in the off state.

The object of the present invention is therefore to avoid these disadvantages of the prior art and to provide a method and a device which, with a simple circuitry design and low load, can reliably distinguish the various error cases.

This object is achieved by a method and an apparatus according to claims 1 and 3. Disclosed is a method which detects the currents I _B and I _G in the high-side and low-side branch, subtracts the detected values of the currents and compares the difference thus formed with an upper limit R _O and a lower limit R _U ,

In this case, the currents can be detected directly, for example, with the aid of current mirror circuits and processed further as currents. However, it is also possible to measure the currents as voltages dropping across shunt resistors and processing them as voltages.

Exceeding the upper limit value R _O can be interpreted as a short circuit SCG ₁ via the low-side power switch G, if at the same time no overcurrent in the circuit is measured. If an overcurrent is measured at the same time, the exceeding of the upper limit value R _{O can be} interpreted as a short circuit SCG ₂ via the series connection of low side circuit breaker G and load L.

Conversely, falling below the lower limit value R _{U can be} interpreted as a short circuit SCB ₁ via the high-side power switch B, if at the same time no overcurrent in the circuit is measured. If, on the other hand, an overcurrent is measured at the same time, the undershooting of the lower limit value R _{U can be} interpreted as a short circuit SCB ₂ via the series connection of high-side power switch G and the load L.

Finally, it is possible to measure an overcurrent in the circuit while simultaneously measuring a current difference I _D which is greater than the lower limit R _U and less than the upper limit R _O , which therefore moves within the normal range defined by the limits, be interpreted as a short circuit SCL across the load L.

Disclosed is also an apparatus for fault detection in integrated power bridge circuits with a load L, a high-side power switch B between load L and supply voltage V _supply and a low-side power switch G between load L and ground M, and with over-current measuring devices for measurement the overcurrent via the power switches B and G, wherein the device comprises at least two ammeters, which detect the currents I _KS and I _LS in the high-side and the low-side branch, and at least one differential circuit, to which the measured currents I _B and I _{G are} guided, so that the differential current I _{D of} the currents I _B and I _{G is} formed. In addition, the device has a comparison circuit K, which compares the differential current I _D with an upper limit R _O and a lower limit R _U.

Also disclosed is a device for fault detection in integrated power bridge circuits with a load L, a high-side power switch B between load L and supply voltage V _supply and a low-side power switch G between load L and ground M, as well as over-current measuring devices for measuring the Overcurrent via the circuit breakers B and G,
in which the device has at least two current measuring devices with paired shunt resistors, which detect the currents I _B and I _G in the high-side and in the low-side branch via the voltages U _B and U _G dropping across the shunt resistors, wherein the device further comprises at least one level converter (level shifter), which shifts the voltage U _B to the low side, and at least one differential circuit, to which the measured voltages U _B and U _{G are} guided, so that the differential voltage U _D the voltages U _B and U _{G is} formed. In addition, the device has a comparison circuit K, which compares the differential voltage U _D with an upper limit R _O and a lower limit R _U.

Alternatively, the level shifter may also be implemented to directly shift a current that is proportional to the current flowing in the high-side power switch. In this case, the current measurement can be done both with shunt resistors and with current mirror circuits (sense FET). The further processing of the current signal from the high-side switch can be realized on the low-side by means of voltages or currents.

It has proved to be advantageous if the ammeters have integrated in the switch current mirror. In this case, it is also advantageous if the device has an additional circuit which ensures that the gate-source voltages of the switch transistor and its mirror transistor are kept equal.

The invention will be explained in more detail below with reference to three exemplary embodiments. Show it:

1 the possible errors involving the high-side circuit breaker B,

2 the possible errors involving the low-side circuit breaker G,

3 a circuit for carrying out the method with integrated current measuring devices,

4 a circuit with a determination of the currents by measuring voltage across a shunt resistor, as well

5 a use of current mirrors for current measurement in the switches.

1 shows, in principle, the structure of the circuit whose possible errors are to be detected and which is known as such in the prior art. In this case, a load L on the one side is applied to a supply voltage V _Supply via a high-side power switch B. On the other hand, the load L is connected to the ground M via a low-side power switch G.

Possible faults include short circuits via the high-side circuit breaker alone (SCB ₁ ), via the load alone (SCL) and via a series connection of high-side circuit breaker B and load L (SCB ₂ ).

2 shows the corresponding error via the low-side power switch G. To detect and plotted are shorts on the low-side power switch G alone (SCG ₁ ), again on the load L alone (SCL) and on the series connection of low-side Power switch G and load L (SCG ₂ ).

According to the invention, as in 3 shown with a paired structure the current in the high-side and low-side branch with ammeters 20 . 30 detected. The measured currents I _B and I _G are thereby applied to the two inputs of a differential circuit 27 passed, which forms the difference of these currents, which is output as the differential current I _D.

The differential current I _D is then compared with an upper and a lower limit, for which purpose a respective comparator, such as an operational amplifier, is used, to which the differential current I _D or a signal is proportional to the differential current I _D on the one side. For comparison with the lower limit R _U is to the one comparator 25 a current (or voltage) is applied which represents the lower limit R _U , while to the other comparator 23 a current (or voltage) is applied which represents the upper limit R _O.

At the same time, in 3 not shown, as usual in such circuits, the overcurrent detected by the switches.

Now gives the comparator 25 a signal indicating an exceeding of the upper limit R _{o of} the differential current I _D , a short circuit must have occurred, in which the low-side power switch was involved, ie either a short circuit through the low-side power switch alone (SCG ₁ ) or a short circuit through the series circuit of low-side circuit breaker and load (SCG ₂ ), which in the 3 collectively referred to as SCG _X.

On the other hand, if a higher current flows across the low-side branch, the difference between I _B and I _G becomes negative. If it falls below the lower limit R _U , the comparator 23 a signal indicating an error SCB _X , in which the low-side power switch B was involved. As with the errors over the low-side power switch G, this may either be a fault SCB ₁ , ie a short circuit alone across the high-side power switch B, or an error of the type SCB ₂ , ie a short circuit via the series connection of high-side circuit breaker B and load L, act.

In the method, which is based on the circuit according to 3 In addition, shorts across a switch alone (SCB _{1 ,} SCG ₁ ) of shorts across the series combination of switch and load (SCB ₂ , SCG ₂ ) can also be distinguished by the detection of the overcurrent. This detection of the overcurrent is usually required anyway in practical and technical applications, so that this does not cause additional circuit complexity.

A special case is a short circuit over the load alone (SCL), because here the current difference between I _B and I _G will remain below the limit value. However, an overcurrent will flow, which is detected, so that the measurement of an overcurrent while simultaneously maintaining the current difference within the two limit values R _O and R _{U is} reliably interpreted as a short circuit across the load.

It is clear from the description of this device as well as the method performed that a low-tolerance comparison of the currents in high-side and low-side circuit breakers is exploited by this use of paired structures, which is possible during operation. Thus, the diagnosis over the prior art is greatly simplified, since the need for a separate diagnostic mode outside the regular operation of the circuit is dispensable.

Due to the higher accuracy that allows this circuit according to the invention and carried out with this circuit method, the oversizing for a short circuit case can be lower, which further reduces the cost of producing the circuit and the associated costs. A currentless state for diagnosis is not required, but above all, the circuit complexity compared to the solutions which are known from the prior art, less.

Another circuit simplification can be achieved when the current as a voltage drop across a shunt resistor 40 is determined as in 4 is shown. As shunt resistors, it is possible to use, for example, already existing interconnects from the connection pads (bond pads) to the integrated switches, which practically does not increase the area required on the integrated circuit, so that this measurement can be practically neutral in space.

As in a method with a circuit after 4 the currents corresponding voltages are measured, the voltages and not the corresponding currents are to be compared with each other, which in 4 not shown. In doing so, the voltage U _{B is} above the high-side shunt 40 shifted to the low-side using a level shifter and there from the voltage U _G over the low-side shunt 50 subtracted. The differential voltage U _D is then how the differential current after 3 , compared with limits.

Another embodiment shows 5 ,

According to this embodiment, for current measurement current mirror ( 60 . 70 ) used in the switches, such. B. Sense field effect transistors (sense FET). The gate-source voltages of the switch transistor and the mirror transistor can, as 5 by way of example for the high-side shows are kept the same with the aid of known from the prior art circuits. This is necessary for sufficient mirror accuracy.

The mirrored high-side current is then mirrored again on the low-side and the mirrored high-side and low-side currents are subtracted from each other.

As already in the embodiment according to 3 the current difference and the occurrence of an overcurrent is used as information to determine, according to the same algorithm, which short-circuit case exists.

Claims (5)

Method for fault detection in integrated power bridge circuits having a high-side branch and a low-side branch and a load (L) arranged therebetween, a high-side circuit breaker (B) between the load (L) and supply voltage (V _supply ) and a low-side power switch (G) between the load (L) and ground (M), and with over-current measuring devices for measuring the overcurrent through the circuit breaker (B, G), characterized in that the currents (I _B ) in the high-side Branch and (I _G ) are detected in the low-side branch during operation, that the detected values for the currents are subtracted from each other and that the difference thus formed with an upper limit (R _O ) and a lower limit (R _U ), whereby • exceeding the upper limit value (R _O ) as a short circuit (SCG ₁ ) is interpreted via the low-side power switch (G), if at the same time no overcurrent in the circuit is measured, • exceeded of the upper limit value (R _O ) is interpreted as a short circuit (SCG ₂ ) via the series connection of low-side circuit breaker (G) and load (L), if an overcurrent in the circuit is measured at the same time, • an undershooting of the lower limit value ( R _U ) is interpreted as a short circuit (SCB ₁ ) via the high-side circuit breaker (B), if at the same time no overcurrent in the circuit is measured, • an undershooting of the lower limit value (R _U ) as a short circuit (SCB ₂ ) via the Series connection of high-side power switch (B) and the load (L) is interpreted when an overcurrent in the circuit is measured simultaneously, and • the measurement of an overcurrent in the circuit while measuring a current difference (I _D ), the is greater than the lower limit (R _U ) and less than the upper limit (R _O ), is interpreted as a short circuit (SCL) across the load (L). Device for error detection in integrated power bridge circuits ( 1 ) with a high-side branch and a low-side branch and a load (L), a high-side power switch (B) between load (L) and supply voltage (V _supply ) and a low-side circuit breaker ( G) between load (L) and ground (M), and with over-current measuring devices for measuring the overcurrent via the circuit breaker (B, G), characterized in that the device at least two ammeters ( 20 . 30 ), which detect the currents (I _B , I _G ) or voltages (U _B , U _G ) derived therefrom in the high-side and in the low-side branch, and at least one differential circuit ( 27 ), to which the measured currents (I _B , I _G ) or voltages derived therefrom (U _B , U _G ) are guided, so that the differential current (I _D ) of the currents (I _B , I _G ) or the differential voltage ( U _D ), wherein the device further comprises a comparison circuit ( 23 . 25 ), which compares the differential current (I _D ) or the differential voltage (U _D ) with an upper limit value (R _O ) and a lower limit value (R _U ), wherein • exceeding the upper limit value (R _O ) as a short circuit (SCG ₁ ) is interpreted via the low-side circuit breaker (G), if no overcurrent is measured in the circuit at the same time, • exceeding the upper limit value (R _O ) as a short circuit (SCG ₂ ) via the series circuit of low-side circuit breaker (G) and load (L) are interpreted, if at the same time an overcurrent in the circuit is measured, • an undershooting of the lower limit value (R _U ) is interpreted as a short circuit (SCB ₁ ) via the high-side power switch (B), if at the same time no overcurrent in the circuit is measured, • an undershooting of the lower limit value (R _U ) is interpreted as a short circuit (SCB ₂ ) via the series connection of high-side circuit breaker (B) and the load (L), if the same applies an overcurrent is measured in the circuit, and measuring the overcurrent in the circuit while measuring a current difference (I _D ) which is greater than the lower limit (R _U ) and less than the upper limit (R _O ), is interpreted as a short circuit (SCL) across the load (L). Apparatus according to claim 2, characterized in that the ammeters ( 20 . 30 ) have in the switch integrated current mirror. Apparatus according to claim 3, characterized in that it comprises an additional circuit which ensures that the gate-source voltages of the switch transistor and its mirror transistor are kept equal. Apparatus according to claim 3 or 4, characterized in that the ammeter ( 20 ), which detects the current (I _B ) in the high-side branch, has a further current mirror which mirrors the current to the level of the low-side branch.

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