WO1993010588A1

WO1993010588A1 - Reverse-supply protection device for power output stage transistors

Info

Publication number: WO1993010588A1
Application number: PCT/DE1992/000929
Authority: WO
Inventors: Bernhard Mattes; Siegfried Malicki
Original assignee: Robert Bosch Gmbh
Priority date: 1991-11-14
Filing date: 1992-11-09
Publication date: 1993-05-27
Also published as: DE4137452A1

Abstract

Proposed is a reverse-supply protection device for power output stage transistors, the device having, connected in series with the output-stage transistor (10), a reverse-poled FET (12) intended as a reverse-supply protection element. The gate terminal of the reverse-supply protection FET (12) is acted on by a control voltage which is derived from the supply voltage and which controls the FET (12) when the supply voltage is applied correctly. The use of two power transistors (10, 12) therefore gives an output stage which is protected against reversed supply, the FET (12) used as the protection element causing only small voltage losses and having only a low turn-on resistance.

Description

Reverse polarity protection arrangement for power stage transistors

STATE OF THE ART

The invention relates to a polarity reversal protection arrangement for power output stage transistors with a polarity reversal protection element connected in series with the output stage transistor, which blocks when the supply voltage is reversed.

In the production of power FET, a diode arises due to the process, parallel to the drain-source channel, which is blocked in normal operation. Reverse polarity of the supply voltage it ^is' However, conductive and bridged in a disturbing manner Drai the n-channel source. As a result, a consumer located in the load circuit is undesirably controlled. In the case of output stage transistors or consumers which are not designed for continuous operation, this can, in addition to malfunctions, lead to the destruction of these components. Even with bipolar or Darlington transistors as power transistors there is such a normally blocked diode that conducts polarity reversal, so that corresponding effects can occur.

In order to ensure reverse polarity protection, it is known to connect a diode in series with a power FET which blocks in the event of reverse polarity of the supply voltage. In normal operation, however, this diode brings with it a voltage drop by which the voltage available to the consumer is reduced, which is particularly the case

MARINE LEAF Lower supply voltages, such as the voltage supply in a motor vehicle, can be a significant disadvantage.

From DE-OS 39 30 896 the use of an FET as a polarity reversal protection element is known in general, but not the application for power amplifiers.

ADVANTAGES OF THE INVENTION

The polarity reversal protection arrangement according to the invention with the characterizing features of the main claim has the advantage that with safe polarity reversal protection in the power output stage, only slight voltage losses occur during operation with no polarity reversal. A very low switch-on resistance can be achieved. This reverse polarity protection arrangement is particularly suitable for fully integrated output stages.

The measures listed in the subclaims permit advantageous developments and improvements of the polarity reversal protection arrangement specified in the main claim.

If the output stage transistor is designed as an FET, it and the reverse polarity protection FET can advantageously be of identical design in order to simplify the manufacture of the output stage as a whole. This is also an advantage with full integration.

In the case of a circuit design with an FET as an output stage transistor, the source connections of the two FETs are expediently connected to one another, while in the case of a circuit design with a bipolar or Darling tone transistor, the emitter of this transistor is connected to the source connection of the polarity reversal protection FET. It is in particular the drain terminal of the polarity reversal protection FET is connected to ground and the collector or drain terminal of the output stage transistor is connected via a consumer controlled by this to the positive pole of the supply voltage.

To protect against overvoltages, a voltage limiting device to which at least part of the supply voltage is applied is connected to at least one gate connection of the polarity reversal protection FET to limit the gate voltage to a value below the critical value. This not only ensures protection of the FET, but it is also kept safely in the current-carrying state even when the supply voltage is not reversed. A Z diode is particularly suitable as such a voltage limiting device.

In order to protect both FETs in a circuit configuration with two FETs with a single voltage limiting device, in particular as a Z diode, the voltage limiting device is connected to the gate connections of all FETs via decoupling diodes.

In order to open the reverse polarity protection FET when the supply voltage is not reversed and to block it in the reverse polarity, the positive pole of the supply voltage is expediently connected to the gate connection of this reverse polarity protection FET via at least one resistor (inverse operation is possible with FETs) .

Such power output stages can be used in voltage networks in which there are differently switched supply voltages, for example in the motor vehicle, where power output stages are supplied by a first supply voltage (constantly applied battery voltage), while a control signal i 1 for the power end stage is supplied by another second supply voltage (the battery voltage switched via an ignition lock). In order to achieve reliable polarity reversal protection under these conditions, the gate connection of the polarity reversal protection FET is advantageously acted upon with control voltages derived from both supply voltages, in each case this polarity reversal protection FET with correctly polarized supply voltages and with a blocking final stage transistor . This also ensures, for example, reverse polarity protection if the first supply voltage is reversed when the second supply voltage is switched off, for example if the battery is incorrectly connected. As a result of this arrangement, the connection for the control voltage obtained from the first supply voltage can be arranged between the output stage transistor and the consumer controlled by it, so it does not have to be connected, for example, to the so-called "terminal 30" in a motor vehicle his.

Another advantageous circuit arrangement consists in that the second supply voltage is applied via a diode to a resistor arrangement, via which the first supply voltage is applied to the gate connection of the polarity reversal protection FET.

DRAWING

Four exemplary embodiments of the invention are shown in the drawing and are explained in more detail in the description below. Show it:

1 shows a circuit arrangement of a first embodiment with an FET line transistor and with a supply voltage, 2 shows a circuit arrangement of a second embodiment example with a FET power transmission fault and with two supply voltages,

Fig. 3 shows a circuit arrangement of a third embodiment ^'üh- rungsbe i spi el s with a bipolar trans Leistungs¬ i fault and with a supply voltage and

Fig. A circuit arrangement of a fourth embodiment 'example with a Darling tone power transistor and with two supply voltages.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

In the exemplary embodiment shown in FIG. 1, the drain-n source channel of a power output stage Fe defective transistor 10 - hereinafter called output stage n-FET - is in series with a consumer 11 and the drain a-source channel of a second one Reverse polarity protection FET 12 serving as reverse polarity protection element. The two source connections (S) are connected to one another, while the drain connection (D) of the output stage FET 10 is connected to the load 11 and the drain connection of the second FET 12 is connected to ground. The second connection of the consumer is connected to the positive pole 13 of a supply voltage source 1 e (Ü).

The positive pole 13 is also connected via a resistor 14 to the gate connection (G) of the second FET 12 and via a resistor 15 to the gate connection (G) of the output stage FET 10. A Z diode 16 is connected to ground with its anode, while its cathode is connected via a first diode 17 to the gate connection of the second FET 12 and via a second diode 18 to the gate connection of the output stage FET 10. The diodes 17, 18 are in opposite directions switched to the Zener diode 16. Finally, a control connection 19 for the output stage FET 10 is connected via a resistor 20 to the gate connection of this output stage FET 10.

The mode of operation of the embodiment shown in FIG. 1 consists in that the FET 12 serving as reverse polarity protection is operated inversely to the output stage FET 10. The diode (inverse diode) created parallel to the drain-source channel of such FETs as a result of the process is shown symbolically in each case. In correct operation without reverse polarity, the second FET 12 is always conductive since its gate connection is acted upon by a resistor 14 with a corresponding positive potential. This is limited by the Zener diode 16 to a value below 10 volts, which is harmless for the FET 12, for example to 9.1 volts. A corresponding voltage limitation is also carried out by the same Z-diode and the diode 18 for the output stage FET 10. This can be controlled by corresponding control signal sequences at the control connection 19 via the resistors 15, 20. At the drain-source path of the second FET 12, there are slight voltage losses with a small on-resistance.

With reverse polarity operation, that is, with reversed connections of ground and positive pole of the supply voltage U1, the gate connection of the second FET 12 is connected to ground, that is to 0 volts. The source connection of this second FET 12 is also connected to 0 volts via the series connection of the inverse diode of the output stage FET 10 and the consumer 11. The second FET 12 is thus blocked and the cathode of the inverse diode of the second FET 12 is now connected to + Ub, as a result of which it is blocked. This ensures that the output stage is protected against polarity reversal.

The second exemplary embodiment shown in FIG. 2 largely corresponds to the first exemplary embodiment, so that - 7 -

Identical or equivalent components are provided with the same reference symbols and are not described again.

In contrast to the first exemplary embodiment, the resistor 14 is not connected to the positive pole 13, but to the D ain connection of the output stage FET 10 via a further resistor 21. The voltage supply of the resistor 15 does not take place via the positive pole 13, but via a ^' voltage supply part 22. This is supplied on the supply side via a terminal 23 which is connected to a further supply voltage U1'. In a motor vehicle, the positive pole 13 corresponds, for example, to the so-called “terminal 30”, which is permanently connected to the positive pole of the motor vehicle battery. In contrast, the terminal 23 corresponds to the so-called "terminal 25" in the motor vehicle, which depending on the switching position of an ignition switch (not shown here) is either connected to the terminal 30 or separated from it.

Terminal 23 is connected via a series connection of a diode 24 with a resistor 25 to resistor 15, the connection point between resistors 25, 15 being connected to ground via a Zener diode 26 for voltage stabilization. Furthermore, the terminal 23 is connected via a diode 27 to the connection point between the resistors 14, 21. The diodes 24, 27 are used for voltage decoupling.

In this exemplary embodiment, the consumer 11 is supplied by the supply voltage U1 and the gate control of the output stage FET 10 by another supply voltage, namely by the supply voltage U1 '. Both supply voltages, however, control the second FET 12 via the resistor 14, namely the supply voltage U1 via the resistor 21 and the load 11 and the supply Supply voltage U ¹ via the diode 27. With the supply voltage U ^{1 switched on} , that is to say in the case of an ignition switched on when used in a motor vehicle, the second FET 12 becomes electrically conductive via the diode 27 and the resistor 14. When the supply voltage U1 is switched off, that is to say, for example, when the ignition in the motor vehicle is switched off, the second FET 12, on the other hand, becomes electrically conductive via the consumer 11 and the resistors 21, 14. To supply the circuit or the second FET 12, therefore, only a connection to the terminal 23 is required, but no longer to the positive pole 13, since the connection to the consumer 11 is sufficient here. The final stage is verpolgesichert in any case, for example, when the supply voltage Ub ¹ and reverse polarity supply voltage Ub.

The illustrated in Fig. 3 ent third embodiment speaks in large and ^'all the first embodiment shown in Fig. 1, as an essential difference Unter¬ now instead of the final-stage FET 10, a bipolar, NPN transistor 30 configured as a power stage transistor is provided, whose emitter is connected to the source terminal (S) of the reverse polarity protection FET 12. The Zener diode 16 is now connected in series with a diode 35 between the gate connection (G) and the source connection (S) of the polarity reversal protection FET 12 in order, as in the first embodiment, to set the gate potential limit a non-hazardous value when the reverse polarity protection FET 12 conducts. Since this is not absolutely necessary in the case of the bipolar transistor 30, the diodes 17 and 18 are dispensed with. The diode 35 replaces the diode 17 and enables the reverse-polarity reversal protection FET 12 to be driven on without the Z diode 16 causing the source gate Can limit tension in this case. The mode of operation corresponds essentially to that of the first exemplary embodiment, so that reference is made to this. Instead of the process-related diode (inverse diode) which arises parallel to the drain-source channel of the output stage FET 10 in FIG. 1, the diode formed by the base-emitter path, which is operated in the reverse direction if the polarity is reversed, is used here and break through ^" .

The illustrated in Fig. 4 fourth embodiment corresponds ^• speaks to the second embodiment shown in Fig. 2 largely, again the same or gleich¬ acting components and assemblies provided with the same reference numerals and are not described again. In this embodiment, instead of the power FET 10, an npn Darlington-Tr ans i disturbance 31. Here too - as in the third embodiment - the Z diode 16 is in series with the Z diode 35 for voltage limitation between the The gate connection (G) and the source connection (S) of the reverse polarity protection FET 12 are connected, the two diodes 17 and 18 also being omitted here accordingly. In addition, a decoupling diode 32 is connected between the control connection 19 and the resistor 20 and a further diode 33 is connected between this resistor 20 and the base of the Darlington transistor 31. A bleeder resistor 34 is additionally switched between the base and emitter of the Darlington signal transistor 31.

Here too, the mode of operation corresponds to that of the second exemplary embodiment shown in FIG. 2, so that reference can be made to this. The diode 33 ensures a more secure blocking of the Da lington transistor 31 and supports the blocking conditions. Since it conducts in the event of polarity reversal, the decoupling diode 32 is switched in the manner described, since otherwise an excessive current flow through the resistor, which is very small in comparison with the resistor 15, stood 20 would flow

Of course, in the third exemplary embodiment shown in FIG. 3, a Darong tone transistor can also be provided, while on the other hand, in the fourth exemplary embodiment shown in FIG. 4, a bipolar transistor according to FIG. 3 can be connected.

Claims

Expectations

1. polarity reversal protection arrangement for power stage transistors with a series-connected polarity reversal protection element which blocks in the event of a polarized supply voltage, characterized in that the polarity reversal element as to the output stage transistor (10; 30; 31) inversely polarized polarity reversal protection -FET (12) is formed, the gate connection of which is derived from the supply voltage and the FET (12) is charged to the expensive control voltage if the supply voltage is correctly polarized.

2. Reverse polarity protection arrangement according to claim 1, characterized gekenn¬ characterized in that the output stage transistor (30; 31) is designed as a bi-polar or Darling tone transistor.

3. reverse polarity protection arrangement according to claim 2, characterized gekenn¬ characterized in that the emitter of the final stage T ansisto s (30; 31) with the source connection (S) of the reverse polarity protection FET (12) i st.

4. polarity reversal protection arrangement according to claim 1, characterized gekenn¬ characterized in that the output stage transistor (10) as FET- bi 1 det i st.

5. Reverse polarity protection arrangement according to claim 4, characterized gekenn¬ characterized in that the two FETs (10, 12) are identisc in essence.

6. Reverse polarity protection arrangement according to claim 4 or 5, characterized in that the source connections (S) of the two FETs (10, 12) are connected to one another.

7. polarity reversal protection arrangement according to claim 3 or 6, characterized in that the drain connection (D) of the polarity reversal protection FET (12) with ground and the collector or drain connection (D) of the final stage trans stors (10; 30; 31) is connected via a consumer (11) controlled by this to the positive pole (13) of the supply voltage.

8. polarity reversal protection arrangement according to one of the preceding claims, characterized in that a voltage limiting device (16) acted on with at least part of the supply voltage with at least the gate terminal (G) of the polarity reversal protection FET (12) for limiting the gate voltage is linked to the value below the critical value.

9. polarity reversal protection arrangement according to claim 8, characterized gekenn¬ characterized in that the voltage limiting device (16) is designed as a Zener diode.

10. Reverse polarity protection arrangement according to claim 8 or 9, characterized in that the voltage limiting device (16) via decoupling diodes (17, 18, 35) is connected to the gate connections (G) of all FETs (10, 12).

11. Reverse polarity protection arrangement according to one of the preceding claims, characterized in that the positive pole (13) of the supply voltage is connected via at least one resistor (14, 21) to the gate connection (G) of the reverse polarity protection FET (12).

12. Reverse polarity protection arrangement according to one of claims 1 to 10 for a power output stage, which is supplied by a first supply voltage (Ü), while a control signal part for the power output stage is supplied by another, second supply voltage (Ü ¹ ), characterized in that the gate connection (G ) of the polarity reversal protection FET (12) with control voltages derived from both supply voltages (Exercise, Exercise '), this FET (12) is applied to the FET (12) with a correctly polarized supply voltage and with a blocking output stage transistor (10,31).

13. Reverse polarity protection arrangement according to claim 12, characterized gekenn¬ characterized in that the connection for the control voltage obtained from the first supply voltage (ÜB) for the reverse polarity protection FET (12) of the collector or drain connection (D) of the output stage transis disturb (10; 31).

14. Reverse polarity protection arrangement according to claim 12 or 13, characterized in that the second supply voltage (Ü ¹ ) via a diode (27) on a resistor arrangement (14, 21) lies, via which the first supply voltage (Ü) to the gate connection the reverse polarity protection FET (12).

15. Reverse polarity protection arrangement according to one of claims 12 to 14 for the arrangement in a motor vehicle, characterized gekenn¬ characterized in that the first supply voltage (Ü) the constantly applied battery voltage and the second supply voltage (Ü ¹ ) the battery connected via an ignition lock ¬ voltage.