WO2003019779A1

WO2003019779A1 - Power communication circuit for mounting a load on the ground side

Info

Publication number: WO2003019779A1
Application number: PCT/FR2002/002971
Authority: WO
Inventors: Lionel Bitauld; Eric Rabasse; Guy Razurel
Original assignee: Dav
Priority date: 2001-08-31
Filing date: 2002-08-30
Publication date: 2003-03-06
Also published as: FR2829319A1

Abstract

The invention concerns a circuit for switching a load (4), such that a motor vehicle member, powered by a potential difference between a ground connection point (-) and a connection point (+) to a supply voltage, comprising: at least a self-protected switch (12) interposed between the connection point (+) to the supply voltage of the load (4) and a supply voltage source (6), the switch being controlled by a switching signal (Scom); and control means (20; 20N) for selectively producing said switching signal (Scom) to said self-protected switch (12). The circuit is characterised in that the self-protected switch (12) is of the low-side type, the control means (20; 20N) delivering the switching signal (Scom1-Scomn), for switching the self-protected switch in on-state, at a voltage whereof the value is higher than that of the supply voltage source (6). Said arrangement enables the load to be connected to the ground side. The switch preferably comprises a N-type MOS (QI) transistor whereof the gate receives the switching signal (Scom) via a logic signal converter for polarizing the gate.

Description

POWER SWITCHING CIRCUIT FOR MOUNTING A SIDE LOAD

MASS

The invention relates to power switching, for example for switching on-board loads in vehicles such as window actuators, air conditioners, servomechanisms and other conveniences or functional members.

It is now common in this type of application to use self-protected switches in MOS technology, which advantageously replace the conventional relay and fuse couple in the interconnection boxes.

These self-protected switches, known by the English term "smart MOS", generally consist of a power transistor of the MOS type whose source-drain channel is connected in series with the load. The gate of the transistor is connected to a switching signal input via one or more control and protection circuits integrated in the switch housing. These circuits are used to block the transistor in the open state in the event of detection of overvoltage, abnormal temperature or any other parameter under control.

There are two types of self-protected MOS switches depending on whether they are intended to be interposed between the load and the supply voltage line (generally positive) or between the load and ground.

FIG. 1 schematically and simplified illustrates the conventional mounting of a self-protected MOS switch 2 of the type intended to be interposed between the load to be switched 4 and the supply voltage line (ie the "high" voltage relative to the ground), here connected to the positive terminal of a 12V battery 6 for vehicle. Because of its planned positioning on the high voltage side with respect to load 4, this type of switch will be designated hereinafter "high side self-protected switch" (also known by the Anglo-Saxon designation "smart high side ", or" TOPFET "," PROFET ", or the like).

Switch 2 comprises a power MOS transistor Ql of type N, whose drain d is connected to the supply voltage and whose source s is connected to the positive terminal "+" of the load 4. The negative terminal "-" of the load is connected to ground 8, itself connected to the negative terminal of battery 6.

The gate g of the transistor Q1 is controlled by a set of control and protection circuits 10 which is an integral part of the self-protected MOS switch 2. This set 10 has an Ecom switching input compatible with logic signals evolving between 0 and 5 volts. In normal operation, the assembly 10 ensures that the gate g is polarized so as to put the transistor Ql in the conductive state in the presence of a logic signal at the high level (for example + 5 volts relative to the positive voltage of power supply) on the Ecom input, and to put the transistor in the off state when the logic signal is at low level (for example 0 volts).

It is therefore noted that the "high side" switches must include their own means of raising the bias voltage of the gate g beyond their supply voltage for setting the conductive state. This arrangement is typically obtained by a charge pumping circuit functionally integrated into the control and protection circuits 10.

The circuits 10 also act to force the transistor Ql in the off state when it occurs a malfunction: overheating of transistor Ql (return to normal operation then being automatically after cooling below _a. hysteresis threshold), overload at load level 4 (with limitation of supply current), or overvoltage or undervoltage of the supply. A terminal Stat of the assembly 10 makes it possible to signal an intervention during a detected anomaly.

It should be noted that the assembly which constitutes the circuits 10 is supplied directly from the voltage source, namely the battery 6, via an input Ev provided for this purpose.

An example of such a type of high-side type self-protected MOS switch 2 is sold by the company Philips Semiconductors under the product designation BUK204-50X.

Self-protected "high side" switches have the advantage of making it possible to connect the load 4 directly and permanently to ground 8. However, they have the drawback of being relatively expensive, in particular because they incorporate the aforementioned means voltage rise to control grid g

Figure 2 illustrates schematically and simplified the conventional mounting of a self-protected MOS switch 12, also provided with a transistor of power Ql of the type N, intended to be interposed between the load to be switched 4 and the ground 8. Because of its planned positioning on the side of the mass with respect to the load 4, this type of switch will be designated hereinafter "low side self-protected switch" (also known as "smart low side"). In addition to this mounting reversal, the self-protected low side switch

12 differs from that of FIG. 1 by the fact that it has only three terminals, which constitute direct links respectively with the drain d, the source s and the gate g of its power transistor Ql. The terminal connected to the gate g constitutes the Ecom command input, similar to that of FIG. 1. This self-protected MOS switch 12 includes protection circuits formed by:

a device for protection against overvoltages 14 of the "clamp" type, interposed between the drain d and the gate g, and

- a logic and protection block 16 which controls the grounding of the gate g (and therefore the blocking of the transistor Ql) in the event of an incident. This blocking is achieved by a control output Cb which acts on the gate of a MOS transistor Q2 connected between the gate g of the transistor Ql and the ground.

The power supply of the logic and protection block 16 is produced internally by connection respectively to the terminal connected to the source s (for ground) and to the node which connects the gate g of the transistor Ql and the overvoltage protection device 14 .

A Zener diode 18 is connected in parallel with these internal supply connections to stabilize the input voltage.

Under normal conditions, the transistor Q1 is made conductive by applying a voltage of the order of + 10 volts on the gate g, the source s being referenced to ground 8, ie at 0 volts. In this case, however, the gate voltage is referenced relative to the ground, which is ON. This voltage is therefore lower than the supply voltage (+ 10N to compare with + 12V in the example).

Therefore, a "low side" switch does not need the voltage raising means to control the gate g. This is a characteristic difference between a "high side" switch and a "low side" switch.

An example of such a low-side self-protected MOS switch

12, is marketed by Philips Semiconductors under the product designation BUK110-50GL. Lower side self-protected switches are simpler and less expensive than those of the high side type, in particular due to the fact that they do not require means for raising the voltage to control the gate g, but are not suitable for applications which require that the load 4 be connected directly and permanently-to ground 8. In fact, it can easily be seen that when the transistor Ql is blocked, either by stop command on the Ecom input, or by intervention of the logic and protection block 16, the negative terminal of the load 4 is isolated from ground 8. However, some loads 4 do not accept such isolation for functional reasons or related to safety or reliability.

In the state of the art, the document Lemme H. "Sichere Schaltungen mit TOPFET./Intelligenter Leistungs-MOSFET mit Schutzfunktionen,

Elektroni, Franzis Nerlag GmBH. Muchen, DE, vol. 42, no.4, 23 February 1993, pages 24-27, relates to a specific switching module, in this case a so-called "TOPFET" transistor incorporating thermal and overload protection, which is provided originally for mounting on the side of the high positive voltage with respect to the switched load. As such, it can be assimilated to a "high side" component described in the introductory part of this application, and therefore for mounting according to the preamble of claim 1. The switching voltage supplied to this module from the outside n 'is therefore not intended to be greater than the supply voltage of this module. The Brauschke P. document "Smart Power Switches for Industrial

Controls ", Components, Siemens Aktiengesellschaft. Munchen, DE, vol.31, no.3, May 1, 1996, pages 21-23 discloses a switching module intended for mounting between load and high voltage, and which therefore corresponds to a smart high side device as presented in the introductory part of the application. The devices described in this state of the art bear the designation PROFET, and are self-powered. When ordered, the inputs are compatible with MOS outputs, ie "signal" voltage level lower than the supply voltage.

In view of the above, the object of the invention is to provide for the use of a self-protected switch of the low side type, but in an assembly where it is, unlike a conventional assembly, between the switched load and the supply voltage.

More particularly, a first object of the invention is to provide a switching circuit for a load supplied by a potential difference between a ground connection point and a voltage connection point supply, comprising:

- at least one self-protected switch interposed between the point of connection to the load supply voltage and a source of the supply voltage, the switch being controlled by a switching signal, and - control means for selectively producing said switching signal to the self-protected switch, characterized in that the self-protected switch is of the "low side" type, the control means delivering the switching signal, for setting the self-protected switch to a conductive state, at a voltage whose magnitude is greater than that of the supply voltage source.

As explained in the introductory part, the term "low side" type self-protected switch includes in particular self-protected switches conventionally designed for mounting between earth and load, and which do not have means enabling their switching input to be polarized. a voltage whose magnitude is greater than that of the supply voltage (which corresponds to the switched voltage). These "low side" self-protected switches thus group together the family of components bearing the Anglo-Saxon designation of "smart low side" ("low side smart MOS") and the like. They are typically self-protected by internal means of protection against overvoltage and / or thermal protection.

It will be understood that the term supply voltage designates the potential which establishes the potential difference with respect to ground, the mass being defined as the point of zero potential from which the potential differences of the circuit are established. The supply voltage is generally positive, especially in automotive applications where the supply voltage comes from the positive terminal of a battery, the negative terminal of which is connected to ground. However, the supply voltage can also be negative, for example in the case of a ground connection by the positive terminal of the battery.

In one embodiment, the circuit further comprises a second source of supply voltage for supplying the control means, in order to allow the latter to produce the switching signal at the required voltage level.

This second supply voltage source can be a voltage booster, used to raise the voltage of the supply voltage source. The circuit may include a plurality of switches self-protected, with the same second source of supply voltage which supplies the control means delivering the switching signal for each self-protected switch of the plurality, so that this second voltage source serves in common for the plurality of self-protected switches. The control means in this case can comprise a plurality of independent channels, each channel delivering the respective switching signal to a respective switch.

Advantageously, the mass connection point of the load is connected to ground by a permanent link independent of the switching state of the self-protected switch of the "low side" type.

In the preferred embodiment, the switch comprises a MOS transistor whose source-drain channel is connected in series with the load, and whose gate receives the switching signal.

This MOS transistor can be of type N, the drain being connected to the supply voltage source, the source being connected to the load supply connection point, the source-drain channel being put in the conductive state by a positive bias voltage with respect to the potential at said power connection point.

The control means preferably comprise a logic level converter making it possible to control the self-protected switch of the "low side" type from a logic signal of level below the switching threshold, and compatible with logic low voltage signaling circuits.

The control means and / or the power supply can be produced in the form of an integrated circuit in a pre-broadcast network of the "ASIC" type.

A second object of the invention relates to the use of a circuit as defined above in an interconnection unit to carry out the switching and load protection functions in a vehicle.

The invention and the advantages which ensue therefrom will appear more clearly on reading the following description of a preferred embodiment, given purely by way of non-limiting example with reference to the appended drawings in which:

- Figure 1, already described, shows a conventional arrangement of a self-protected MOS switch of the high side type, installed between the load to be switched and the high supply voltage; - Figure 2, already described, shows a conventional arrangement of a self-protected MOS switch of the low side type, installed between the load to be switched and the ground;

- Figure 3 is a block diagram of the self-protected MOS switch of the low side type of Figure 2, in an assembly allowing its installation between the load to be switched and the high supply voltage, according to the invention; and

FIG. 4 is a block diagram of an assembly based on that of FIG. 3, but with several self-protected MOS switches of the low side type, the respective switching signals of which are produced by a multi-channel voltage converter supplied by a single source of voltage for obtaining all of the switching voltages.

An example of a preferred embodiment of the invention will be described with reference to FIG. 3. The elements of this figure which are common with those already described in the context of FIG. 2, in particular as regards the internal configuration of the switch Self-protected MOS of the low side type 12, the load 4 and the battery 6, are designated by the same references and will not be described again for the sake of brevity.

In this example, the low side type switch 12 and the load 4 are connected in series between earth 8 and a positive supply voltage. More particularly, the load 4 has a first connection point (designated "-") connected to ground 8 and a second connection point (designated "+") connected to the source s of the transistor Ql of the switch of the low side type 12 , the drain d of this transistor being connected to the supply voltage, in this case the positive terminal of the battery 6 12N for vehicle. As in the previous case of FIGS. 1 and 2, the negative terminal of the battery 6 is connected to the ground 8.

The mutual positioning of the load 4 and the switch of the low side type 12 with respect to the power supply is therefore reversed relative to the conventional assembly of FIG. 2. Consequently, the source s of the transistor Ql, when the latter is conductive, is at a potential level close to the supply voltage, ie 12 volts in the example, because the resistance of the load 4 is significantly higher than that of the source-drain channel of the transistor Ql in driver mode. The switching voltage Scom to be applied to the Ecom terminal of the switch 12 - and therefore at the gate g - to make the transistor Ql conductive must be higher by approximately 10 volts compared to the source s, that is to say of the order of + 22 volts compared to the mass under the conditions d '' switching to the conductive state on a grid-source polarization Ngs of + 10 volts. This switching voltage is provided by a high voltage output

O _H of a logic level converter 20, connected to the input Ecom of the self-protected switch of the low side type 12. Thus, the switching voltage Scom reproduces the states of a logic signal S _L presented on a low voltage input I _L of converter 20, with voltage rise as follows: S _L = O volt → Scom = 0 volt; S _L = + 5 volts → Scom = + 22 volts.

The switching of the transistor Ql to the conducting state, making it possible to supply the load 4, is then carried out by applying to the input I _L of the converter 20 a logic signal S _L in the state 1 equal to 5 volts. Conversely, the switching of the transistor Ql in the blocked state, making it possible to interrupt the supply of the load, is carried out by applying this logic signal S _L to the logic state 0 equal to 0 volts on the entry I _L.

The converter 20 thus makes it possible to switch the transistor Ql from low voltage logic signals S _L compatible with the integrated logic signaling circuits CMOS, for example. It is therefore possible to control the switching directly from outputs of microcontrollers, wired logic, or the like on the input I _L.

The design of the logic level converter 20 is known in itself, being for example a so-called "translator" circuit.

The operation of such a converter requires an operating voltage Nconv equal (or slightly higher) to the maximum of the voltage presented at the output O _H , ie + 22 volts in the example.

This voltage Nconv is supplied by an auxiliary power supply 22 with voltage rise of the DC-DC converter type with voltage rise. The auxiliary power supply 22 has two inputs 22a, 22b connected respectively to the positive terminal of + 12 volts of the battery 6 and to the ground 8, serving to supply its internal circuits, and an output 22c which presents the voltage Vconv, connected to the supply voltage input of the converter 20. The auxiliary supply 22 is of conventional design, for example being a switching power supply or the like. The invention can be implemented in a particular way advantageous in an application where several loads must be controlled by respective electronic switches. In fact, it is possible in this case to use self-protected MOS switches of the low side type according to the configuration shown in FIG. 3, with a single auxiliary power supply, the latter serving in common for all of the switches.

An example of such an assembly is represented in the form of a block diagram in FIG. 4, where the elements common with the circuit of FIG. 3 bear the same references (possibly with a suffix) and will not be described again in detail for the sake of concern. of conciseness. In the example, a plurality n of independent loads 4-1 to 4-n are each controlled by a protected switch of the "smart lowside" type 12-1 to 12-n, as described in the context of FIG. 3. Thus, each switch 12-1 to 12-n comprises a drain terminal d connected to the positive pole of a voltage source (here again a 12 N battery) and a source terminal s connected to the positive terminal + of its load. respective 4-1 to 4-n, which has its negative terminal connected to ground 8.

Each switch 12-1 to 12-n is controlled on its Ecom switching input by a common logic level converter 20Ν having a number n of independent channels. Each channel includes a switching logic control signal input (with one of the designations I _L -1 to I _L -n) and a switching voltage output (with one of the designations Scoml to Scomn) for Ecom input of its respective switch 12-1 to 12-n. As for the converter 20 of FIG. 3, the converter 20N produces for each channel i the states of a logic signal S _Li presented on its low voltage input I _Li , with voltage rise as follows: S _Li = O volt - »Scomi = 0 volts; S _Li = + 5 volts - Scom = + 22 volts, where i is index from 1 to n.

The converter 20N is supplied by a single auxiliary power supply 22 with voltage rise which supplies the voltage Nconv necessary for its operation from the voltage of the battery 6 of 12 volts. Note that the cost of the auxiliary power supply 22 is more than offset by the savings, n times multiplied, obtained by the use of a switch of the "low side" type rather than the "high side" type.

As a variant, provision may be made to replace the logic level converter 20Ν in FIG. 4 by a number n of converters as presented in the context of FIG. 3, each of the n converters receiving its voltage Nconv operation from a single auxiliary supply 22. In this case, the voltage output Nconv of the auxiliary supply 22 is simply connected in parallel to each of the supply voltage inputs of the n converters 20. Thanks to the invention, it is possible to benefit from the advantages of the low cost of a self-protected MOS switch of the low side type 12, while making it possible to connect the load 4 to ground 8. This arrangement thus authorizes the use of "low side" switches to control a very large number of loads to be switched, for example: - in cars: lamps (headlights, horns), amenities (window regulator motors, door locks, rear view mirrors, seat adjustment ), brake actuators, power steering), especially for type interconnection boxes (BSI, BSM, UPC, UCH, ...) etc. ;

- in systems control: servomechanism control, automation control,

- in IT: peripherals (printers, readers, etc.).

It is noted that many loads, in particular in the automotive field, have a body or a casing intended to be connected directly and permanently to the ground 8 (generally in common with the negative terminal of the battery 6).

The implementation of the logic level converter 20 or 20Ν and of the auxiliary power supply 22 is easy and adds only little cost, so that the assembly based on the self-protected MOS switch of the low side type 12, even taking account of these additional elements 20 or 20N and 22, remains very advantageous from the economic point of view compared to the use of a self-protected MOS switch of the high side type 2 as described with reference to FIG. 1, especially if several switches low side depend on the same converter and / or the same auxiliary power supply.

For greater economy and simplicity of implementation, the logic level converter 20 or 20N and or the auxiliary power supply 22 can / can be produced in the form of a specific integrated circuit from a pre-distributed network (known also by the Anglo-Saxon term of ASIC

("application specifies integrated circuit").

The specific integrated circuit can also incorporate other functional elements, for example the control logic producing the switching signals at input I _L.

Furthermore, the same auxiliary power supply 22 can be used to power several converters 20. Similarly, a logic level converter. 20 can be used to control several self-protected switches of the "low side" type 12, depending on the applications envisaged.

Of course, it is possible to dispense with the specific auxiliary supply 22 if an adequate voltage source (ie + 22 volts in the example) is available from an existing source to operate the converter 20. Many variants can be envisaged in the context of the invention, in particular by providing a resistance between the output O _H of the converter 20 and the input Ecom of the switch 12, and / or between the ground 8 and the load 4.

Finally, it will be understood that by simple reversal of means, the teachings of the invention can also apply to circuits with positive mass.

Claims

1. Switching circuit for a load (4) supplied by a potential difference between a ground connection point (-) and a connection point (+) to a supply voltage, comprising:

- at least one self-protected switch (12) interposed between the point (+) of connection to the supply voltage of the load (4) and a source of the supply voltage (6), the switch being controlled by a signal switching (Scom), and

- control means (20; 20N) for selectively producing said switching signal (Scom) at said self-protected switch (12), characterized in that the self-protected switch (12) is of the "low side" type, the control means ( 20; 20N) delivering the switching signal

(Scom; Scoml-Scomn), for putting the self-protected switch into a conductive state, at a voltage whose magnitude is greater than that of the supply voltage source (6).

2. Circuit according to claim 1, characterized in that it further comprises a second supply voltage source (22) for supplying the control means (20; 20N), in order to allow the latter to produce the signal switching (Scom; Scoml - Scomn) at the required voltage level.

3. Circuit according to claim 2, characterized in that said second supply voltage source (22) is a voltage booster, serving to raise the voltage of said supply voltage source (6).

4. Circuit according to claim 2 or 3, characterized in that it comprises a plurality of self-protected switches (12-1 -12n), and in that the same second supply voltage source (22) supplies the means control (20N) providing the switching signal (Scoml-Scomn) for each self-protected switch of said plurality, so that said second voltage source serves in common for said plurality of self-protected switches.

5. Circuit according to claim 4, characterized in that the control means (20N) comprise a plurality of independent channels, each channel delivering to a respective switch (12-1 - 12n) said switching signal (Scoml - Scomn).

6. Circuit according to any one of claims 1 to 5, characterized in that the point (-) of mass connection of the load (4) is connected to ground (8) by a permanent link independent of the state of the self-protected "low side" switch (12).

7. Circuit according to any one of claims 1 to 6, characterized in that the switch comprises a MOS transistor (Ql) whose source-drain channel is connected in series with the load (4), and whose gate g receives the switching signal (Scom).

8. Circuit according to claim 7, characterized in that the MOS transistor is of type N, the drain (d) being connected to the supply voltage source (6), the source (s) being connected to the point (+ ) for connecting the supply voltage to the load (4), the source-drain channel being put into the conductive state by a positive bias voltage with respect to the potential at said supply point.

9. Circuit according to any one of claims 1 to 8, characterized in that the control means comprise a logic level converter (20; 20N) making it possible to control the self-protected switch of the "low side" type (12) from a logic signal (S _L ) with a level below the switching threshold, and compatible with logic circuits for low voltage signaling.

10. Circuit according to any one of claims 1 to 9, characterized in that the control means (20; 20N) are produced in the form of an integrated circuit in a pre-broadcast network of the "ASIC" type.

11. Circuit according to any one of claims 2 to 10, characterized in that the second supply voltage source (22) is produced in the form of an integrated circuit in a pre-distributed network of the "ASIC" type.

12. Use of a circuit according to any one of claims 1 to 11 in an interconnection unit to perform the switching and load protection functions (4) in a vehicle.