DE19737628C1 - Smart-switch open-load diagnosis method e.g. for controlled power supply in motor vehicle - Google Patents

Abstract

The method involves passing a current (IOL) into a load circuit by means of a current source (7) and evaluating a load status derived from its load driver output (1) with the smart- switch switched off. The current source is switched off i.e. deactivated during an inactive circuit environment, in which the smart-switch is functionally included. The smart-switch incorporates a logic module (2) and has a power transistor (T1) coupled to a supply voltage (Vbb).The switch drives an external load (RL) via the output with the current source being switched on and off over the module.

Description

The invention relates to a method for open-load diagnosis or load interruption diagnosis of smart switches in accordance with Preamble of claim 1 and a smart switch according to the preamble of claim 2.

Smart switches are known in the embodiment of smart highside switches or smart low-side switches. These smart switches are used for the controlled power supply of external loads, for example in motor vehicles. A conventionally constructed, internally known smart switch of the highside type is shown in Fig. 1 and is briefly explained below.

The smart high-side switch shown in FIG. 1 has an integrated design or in the form of an IC, a power switch or power transistor T1 which is connected to a supply voltage V _bb , the output of which is the driver output 1 of the smart Highside switch forms, to which an external load R _{L is} connected, and which is controlled by a switching logic 2 , which in turn is fed via an input terminal 3 of the smart highside switch with external control signals. Furthermore, the switching logic 2 is laid out, via a status input 4 , which is connected, for example, via a status resistor 5 to a 5 V voltage source 6 , and a status signal of predetermined logic L (= low or low) or H (= high or .), resulting high which is derived from the driver output 1, to detect open load and a Lastun interruption. For this purpose, a current source 7 is provided, which is connected to the supply voltage V _bb and the driver output 1 in order to impress a relatively small current I _OL into the load circuit, which also connects to the comparator with the driver output 1 and the switching logic 2 8 recognized and evaluated in the switching logic 2 for load interruption. This is called open load detection for the smart highside switch when it is switched off. The disadvantage here is that the significant quiescent current J _OL provided by the current source also flows when the circuit or inactive smart highside switch is inactive. The same applies analogously to a smart low-side switch.

A driver circuit is described in US Pat. No. 5,138,516. which is an output driver associated with a load stands, turns on and off. There is an open load the driver circuit instead of the supply voltage of the load a voltage specified by the driver circuit, which is evaluated by this and subsequently an open load displays. If the output driver is switched off, the utility is located supply voltage at the driver circuit.

An open-load diagnosis is known from US Pat. No. 5,438,286 which is an auxiliary transistor parallel to the load switch with a power source in series. Evaluating one derived from the load driver output Load status occurs there when the switch is switched on and turned on auxiliary transistor, the voltages at the Connection points load switch load and auxiliary transistor Power source can be compared. With inactive, The load source is switched off by the power switch Auxiliary transistor deactivated.

In view of this prior art, the invention lies Task based on a method for open load diagnostics in the Preamble of claim 1 and a smart switch in the Preamble of claim 2 to create the type mentioned  open-load diagnostics with low power consumption Afford.

This task is solved with regard to the procedure the features of claim 1 and with respect to the smart Switch by the features of claim 2.

Advantageous developments of the invention are in the sub claims specified.

Accordingly, the essence of the invention consists in switching off the Power source of the smart switch when the circuit is inactive exercise in which the smart switch is integrated. A ent speaking shutdown signal for the power source is invented in accordance with the status voltage source by means of a ON / OFF switch or from the logic level at the output ei micro controller.

The invention is illustrated below with reference to the drawing explained in detail. Show it:  

Fig. 1 is a circuit diagram of a conventional smart highside switch;

Fig. 2 is a circuit diagram of a first embodiment of to the invention OF INVENTION smart high-side switch;

FIG. 3 is diagram of a second embodiment of to the invention OF INVENTION smart high-side switch;

Fig. 4 is diagram of an embodiment of the smart low-side switch of the invention; and

Fig. 5 is a truth table for the smart high-side switch of FIG. 2.

The smart high-side switch according to the invention shown in FIG. 2 corresponds to the smart high-side switch shown in FIG. 1 and explained above except for the control of the current source 7 via the switching logic 2 , which is why the same parts are provided with the same reference numbers, and an explanation of this switch according to the invention is unnecessary except for the control according to the invention for switching the current source 7 on and off.

To control the smart high-side switch a Mikrocon troller 9 is provided which is connected to the input terminal 3 of the switching logic 2 and the status terminal ST of the smart high-side switch. At the status terminal ST, similar to the conventional smart highside switch of FIG. 1, via the status resistor 5 is a DC voltage of z. B. +5 volts connected, which is also present at the Mikrocontrol ler 9 . According to the invention, the DC voltage source 6 is connected to the resistor 5 via a switch S1. A comparator 10 is connected between the status connection ST of the smart highside switch and the status input 4 of the switching logic 2 . Furthermore, a transistor T2 is connected to the status terminal ST of the high side switch, which is controlled internally by the switching logic 2 and is also connected to ground. This transistor T2 with its load path between ground potential GND and the status connection ST and is connected to the control logic 2 with its control connection.

If a 5 V signal is present at the status input ST when the switch S1 is closed, ie when the circuit environment in which the smart highside switch is integrated is activated, the current source 7 is switched on via the switching logic 2 with the aid of the comparator 10 and a load interruption can be detected at a low logic level of the control signal present at switching logic input 3 (ie the transistor T1 is switched off).

If, on the other hand, the switch S1 is switched off in accordance with an inactive circuit environment, a low-level signal is present at the status connection ST, as a result of which the current source 7 is switched off or on. If an error is reported at status terminal ST at a low logic level with transistor T2 switched on, control logic 2 recognizes this state and switches current source 7 on .

An exemplary truth table for controlling the current source x of this smart highside switch is shown in FIG. 4.

Fig. 3 shows an alternative embodiment of the inventive smart high-side switch, which differs from the smart high-side switch shown in Fig. 2 in that no switch S1 is provided. In this example, the function of the switch is taken over by an ON output 11 of the microcontroller 9 in order to apply a high logic level signal to the status resistor 5 and so to switch off the current source 7 directly from the microcontroller 9 .

An embodiment for a smart low-side switch according to the invention corresponding to the embodiment of the smart high-side switch of FIG. 2 is shown in FIG. 4, the same parts being provided with the same reference numbers. The function of the current source control of this switch is analogous to that of FIG. 2.

Reference list

1

Driver output

2nd

Switching logic

3rd

Input connector

4th

Status input

5

Status resistance

6

Voltage source

7

Power source

8th

Comparator

9

Microcontroller

10th

Comparator

11

ON output
GND ground potential
INexternal control signal
I _OL

Quiescent current
R _L

load
S1 switch
ST status connection
T1 power transistor
T2 transistor
V _bb

Supply voltage

Claims (7)

1. Method for open-load diagnosis or load interruption diagnosis of a smart switch in a circuit arrangement, to the output ( 1 ) of which a load (R _L ) is connected, by impressing a current (I _OL ) into the load circuit by means of a current source ( 7 ) and evaluating a load status derived from its load driver output ( 1 ) when the smart switch ( 1 ) is switched off, characterized in that the current source ( 7 ) is switched off or deactivated when the circuit arrangement is inactive. 2. Smart switch with an input-side switching logic ( 2 ), a power transistor (T1) controlled by this and connected to a supply voltage (V _bb ) for driving an external load (RL) via a driver output ( 1 ), a current source ( 7 ) for impressing a current (I _OL ) and a voltage comparator ( 8 ) for evaluating a load interruption and outputting a corresponding status signal, characterized in that a circuit device for detecting the activation / deactivation of the circuit arrangement and for providing a corresponding signal is provided is that the power source switches on or off via the switching logic ( 4 ). 3. Smart switch according to claim 2, characterized in that the output signal from the detection circuit via a further voltage voltage comparator ( 10 ) is applied to the switching logic ( 2 ). 4. Smart switch according to claim 3, characterized in that the detection circuit at a given voltage potential (5 V) and an input of the comparator ( 10 ) via an opposing ( 5 ) connected ON / OFF switch (S1) . 5. Smart switch according to claim 3, characterized in that the detection circuit comprises a resistor ( 5 ) which is connected to the ON output of a microcontroller ( 9 ) and an input of the comparator ( 10 ). 6. Smart switch according to claim 3, 4 or 5, characterized in that it as Smart highside switch is designed. 7. Smart switch according to claim 3, 4 or 5, characterized in that it as Smart low side switch is designed.