National Semiconductor Corporation

John J Gough

Shengming Huang

Robin Shields

A regulator system includes a power device and a sense device. During a normal operating mode, the power device is arranged to deliver current to a load, while the sense device is arranged to monitor the load current. An over-current mode is activated when the sensed load current exceeds a short-circuit current-limit. During the over-current mode, the power device is switched off such that the energy loss is minimized. Once the short-circuit condition is removed, the regulator system returns to the normal operating mode. The sense device is coupled to the load in such a way that the quiescent current of the regulator system does not rise with increasing load current. The regulator system is further arranged such that the short-circuit current-limit decreases automatically with increased operating temperature. The described regulator system has significantly reduced energy losses while also minimizing risks of thermal induced device failures during the short-circuit condition.

Over-current protection circuit

An amplifier circuit which includes a differential amplifier, drive circuitry for driving an output of the amplifier circuit in response to an output of the differential amplifier and frequency compensation circuitry switchable between a low current mode and a high current mode of operation. Control circuitry is provided configured to switch the frequency response circuitry between the low and high current modes in response to a magnitude of current provided to a load connected to the amplifier circuit output. In the low current mode, the frequency compensation circuitry produces a frequency response having a first pole located at a first frequency. In the high current mode, the frequency compensation circuitry produces a zero at a second frequency sufficiently close to the first frequency so as to stabilize the amplifier circuit, with the first zero being absent for the frequency response in the low current mode.

Compensation technique and method for transconductance amplifier

A signal conditioning apparatus useful in applications, such as automotive applications, having a signal conditioning circuit capable of conditioning a sensor input signal and providing an output useful, for example, to a fuel-air mixture control system. The signal conditioning circuit employs an amplifier with a feedback impedance, NMOS and PMOS transistors, an input impedance, a detection impedance, input terminals coupled to a sensor. The sensor, such as an oxygen sensor, has a sensor output referenced to sensor ground and input terminals coupled to a power supply and power supply ground. The signal conditioning circuit utilizes switched impedances to provide an output voltage proportional to the differential voltage between the sensor output voltage and the sensor ground when an impedance between the signal conditioning circuit input terminals is low relative to the detection impedance. Otherwise the signal conditioning circuit utilizing switched impedances provides an output voltage proportional to the power supply voltage. The signal conditioning circuit samples the sensor differential voltage and the power supply voltage at a frequency derived from a clock generator. The signal conditioning circuit controls the NMOS transistors coupled to the sensor with a negative bias voltage derived from a single power supply, thus allowing operation when the sensor ground and power supply ground are at different potentials. Additionally, fabricating the signal conditioning circuit impedances as capacitors using linear complimentary metal oxide semiconductor technology produces very accurate gain and input impedance characteristics.

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Beith Ayrshire, United Kingdom

John J Gough