Current limitation programmable circuit for smart power actuators

Abstract

A circuit for limitation of maximum current delivered by a power transistor comprises: a network for detection of the current delivered by the power transistor which generates a first electrical signal; a reference network for generating a reference current proportional to a resistor and self-limited, provided by means of a current generator circuit and a limiting circuit with current mirror; and an operational amplifier which compares the first electrical signal with the reference current and which tends to inhibit the power transistor if the current delivered exceeds a certain threshold value.

Description

FIELD OF THE INVENTIONThe present invention relates to a circuit for protection of the output stage of an intelligent power actuator from overloads and short circuits. The need for protecting these devices which can be switches, amplifiers and voltage or current regulators appears obvious when the power in play becomes high because an overload or an accidental short circuit could irreparably damage both the load and the device.In many applications and in particular in current regulators it is often required that the limitation current be programmable from outside the integrated circuit.PRIOR ARTThe output stage of the device which is the subject of the present invention is provided by means of a power transistor and the technique used for limiting the current is that of driving the above mentioned transistor with a negative feedback network which tends to inhibit the transistor when the current running therein exceeds a certain predefined threshold. The simplest way to detect the cu...

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Problems solved by technology

However, in the case of `low drop` applications, i.e. in which the voltage drop on the power transistor must be very low, this technique has the obvious disadvantage of increasing the voltage drop and requiring, as a sense resistor, a resistor with power structure.

The above mentioned solution however presents in principle the characteristic of having two negative feedback loops and this characteristic involves a considerable circuit complexity and nearly always the need for having compensation capacitors inserted in the feedback loop with the obvious disadvantage of waste of surface area on the integrated circuit.

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