Miscellaneous active electrical nonlinear devices – circuits – and – Gating – Compensation for variations in external physical values
Patent
1997-10-14
2000-02-22
Callahan, Timothy P.
Miscellaneous active electrical nonlinear devices, circuits, and
Gating
Compensation for variations in external physical values
327362, 327513, 361 57, 361106, H03K 1714, H02H 720
Patent
active
060284706
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
It is known to dimension semiconductor components, in particular power transistors, in such a way that their activatable power greatly exceeds the ordinarily permissible continuous demands and the continuous losses which thereby occur. The semiconductor elements can thus be produced more economically, since they do not need to be designed for continuous operation at the activatable power. It is known to associate with the semiconductor components protective circuits which can be activated as a function of a component temperature of the component, so that damage to the components due to extended continuous load--for which they are not designed--can be prevented.
Known for this purpose are circuit arrangements in which the semiconductor component is switched off when a limit temperature is exceeded. The power transistor is switched off, in this context, by means of a measurement of forward voltage or off-state current at integrated sensor elements which correspondingly trigger the semiconductor component. Reference is made here to Tietze and Schenk, 9th edition, page 523.
DD Patent 228 835 discloses an integrated overtemperature protection circuit arrangement in which bipolar transistors are connected together in such a way that a base-emitter voltage of one transistor is acted upon by a hysteresis, such that with the transistor in the "on" state, a working current is modified by the use of a current level in such a way as to dissipate a current which is less than the working current and is always at a constant ratio to it. This causes the power transistor to be switched on or off as a function of temperature. It is not possible to modulate the power dissipation without switching off. Another disadvantage is that this circuit can be used only in temperature ranges up to approx. 150 degrees C. A semiconductor switch having an overtemperature protector which has a temperature-sensitive element is known from GB-A 2 234 112. The temperature-sensitive element is configured in the form of a diode switched into the off-state direction, and allows the driver current of the semiconductor switch to be shunted if the latter becomes too hot.
SUMMARY OF THE INVENTION
The present invention is advantageous in that temperature-dependent modulation of the power dissipation of a power transistor can be accomplished even for very high temperatures, which may be, for example, approximately 200 degrees C. Because a transistor is provided whose off-state current, which changes as a function of temperature, initiates a change in the base current of the power transistor, it is advantageously possible to effect tolerance-stable regulation of the power transistor at very high temperatures. As a result of the temperature-dependent regulation of the base current of the power transistor, the entire circuit arrangement can be of very simple and therefore economical construction. It is especially advantageous that because the off-state current is used to initiate regulation of the power transistor, controlled modulation of the base current and thus of the power transistor is possible.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a circuit arrangement of an integrated circuit according to the present invention.
FIG. 1a shows an npn transistor block in place of the pnp transistor block of FIG. 1.
FIG. 2 shows, in a diagram, the behavior of an off-state current as a function of temperature.
FIG. 3 shows a further embodiment of the circuit arrangement according to the present invention.
FIG. 3a shows an npn transistor block in place of the pnp transistor block in place of the pnp transistor block of FIG. 3.
FIG. 4a shows a first diagram of the regulating current of the circuit arrangement as a function of temperature.
FIG. 4b shows a second diagram of the regulating current of the circuit arrangement as a function of temperature.
DETAILED DESCRIPTION
FIG. 1 shows an integrated circuit designated globally as 10. Integrated circuit 10 has a power transistor 12 and a circuit arrangement 14 which are indivi
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Tietze & Schenk, Electronic Circuits Design and Applications, pp. 520-524, 1991 (9.sup.th Edition).
Michel Hartmut
Pluntke Christian
Callahan Timothy P.
Englund Terry L.
Robert & Bosch GmbH
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