Balanced loss driver circuit including high-side/low-side...

Miscellaneous active electrical nonlinear devices – circuits – and – Signal converting – shaping – or generating – Current driver

Reexamination Certificate

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Details

C327S309000, C327S512000

Reexamination Certificate

active

06191625

ABSTRACT:

BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a driver circuit having series-connected high-side and low-side MOS switches (M
1
, M
2
) with MOS transistors for driving a load, a temperature-limiting circuit and a current-limiting circuit, which is assigned to one of the two MOS transistors.
The driver circuit under discussion is implemented, for example, using BICDMOS (Bipolar C- and D-MOS) technology and is in particular provided for use in automobile electronics, for example in conjunction with airbag applications. In the driver circuit under discussion, with the series-connected high-side and low-side MOS switches for driving a load, for the purpose of driving the respective MOS transistor, which is implemented, for example, using DMOS technology, it is normal to provide circuits which are equipped with specific safety measures, in particular with a temperature limiter and with a current limiter. While each drive circuit for the respective power transistor is equipped with its own temperature limiter, it is usually only one of these drive circuits which is equipped with a current limiter.
It is often demanded of MOS transistors that they have a turn-on resistance R
ON
of the order of magnitude of about 1.5 ohm. In addition, in particular in conjunction with airbag applications in automobile electronics, it is necessary for the turn-on time of the MOS transistors of greater than 2 milliseconds to be ensured during current limiting operation, the current limiter is typically activated at a current load of approximately 2 A, without the temperature limiter being activated, since within this period of time any thermally induced current “toggling” of the driver stage would prevent the controlled switching of the load. In the case of the airbag application in automobile electronics, failing to satisfy this requirement would mean that the explosion of the detonator for the airbag, and hence the controlled triggering of the latter, would be prevented. In addition, in the case of the application in automobile electronics, there is the risk that the car battery is separated from the on-board network in the event of a collision (load dump), as a result of which a voltage pulse of 40 V in the on-board network is caused, which may lead to overloading of at least one MOS switch of the driver circuit under discussion.
A significant aspect of SPT technology is to keep the chip appropriately small, the factor which determines the area primarily is the power loss which has to be coped with in the MOS transistors. This is particularly critical in the case of using DMOS transistors, which already occupy a relatively large chip area.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a balanced loss driver circuit including high-side/low-side MOS switches that overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which the power loss of the MOS transistors is reduced without impairing the functional capability of the driver circuit.
With the foregoing and other objects in view there is provided, in accordance with the invention, a driver circuit, including: a high-side MOS switch having a high-side MOS transistor with a gate for driving a load; a first temperature limiting circuit connected to the high-side MOS transistor; a low-side MOS switch having a low-side MOS transistor connected in series with the high-side MOS transistor for driving the load; a second temperature-limiting circuit connected to the low-side MOS transistor; a current-limiting circuit connected to the low-side transistor; and a voltage generator having a first side connected to the gate of the high-side MOS transistor and a second side connected to ground, the voltage generator outputting a voltage corresponding to a maximum drive voltage for the high-side MOS transistor.
In other words, the invention accordingly provides a driver circuit with a balanced distribution of the power loss to both the transistor of the high-side MOS switch and to the transistor of the low-side MOS switch. Balancing the power loss according to the invention is achieved by a surprisingly simple technical measure, specifically by providing a Zener diode or a voltage source for the gate of that MOS transistor in the driver circuit that is not provided with the current limiting circuit. In principle, the MOS transistor equipped with a Zener diode or voltage source according to the invention may be either the low-side transistor or the high-side transistor.
The optimum voltage for the Zener diode or the voltage source under discussion can be determined by computation from parameters of the driver circuit.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a balanced loss driver circuit including high-side/low-side MOS switches, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.


REFERENCES:
patent: 4384287 (1983-05-01), Sakuma
patent: 5534811 (1996-07-01), Gist et al.
patent: 5602724 (1997-02-01), Balakrishnan
patent: 5796276 (1998-08-01), Phillips et al.

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