National Semiconductor Corporation

Exar Corporation

Other

Silvo Stanojevic

Bernard D Miller

A delay for short power interruptions by using a first comparator to compare the power supply voltage to a voltage reference. A second comparator has a first input coupled to the same voltage reference, and an output which generates the reset signal. A capacitor coupled to the second input of the second comparator determines when a reset signal is issued. The capacitor is normally charged by a current source. When the power supply falls below a set point indexed to the reference voltage, as indicated by the first comparator, a discharging circuit discharges the capacitor. The rate at which the capacitor is discharged and the threshold of the second comparator determines how long of a power interrupt is required to issue a reset signal. In the preferred embodiment, the discharging circuit is a latching current source. The current source is latched into the on position by the output of the comparator, and is reset when the comparator indicates that the voltage supply is returned to normal. When reset, the discharging current source is turned off.

Power-up/interrupt delay timer

A shunting regulator which is configured to act as a switch. The regulator includes an enabling input which can be used to turn it on and off when the switch is desired to be closed and opened. Preferably, the regulator includes a switching transistor connected to the enabling input which activates a drive transistor circuit. A current mirror is connected to the regulator output and provides current to both the drive circuit and a differential amplifier used for error correction. The two transistors of the differential amplifier are connected to first and second resistor divider circuits to provide the appropriate reference voltages. The invention thus provides what is essentially an adaptive current drive with a high dynamic range.

Switching shunt regulator

An improved voltage regulator which can operate in a two-lead environment with a widely varying power supply is provided. The voltage regulator of the invention has an output circuit stage connected between a supply voltage and a reference voltage. A pass transistor, as one leg of a differential current steering stage, provides drive current to the output stage. A bandgap error amplifier is coupled between the reference voltage output and the pass transistor to shunt current from the pass transistor when the reference voltage varies from the desired voltage value.

Voltage regulator with differential current steering stage

A low dropout voltage regulator with quiescent current reduction has a pass transistor coupled for conduction from a positive supply terminal to a regulated output terminal. A first switch is coupled to conduct the base current of the pass transistor to the regulated output terminal. A second switch is coupled to conduct the base current of the pass transistor to ground. A control circuit selects the action of the switches to select the conduction path for base current.

Low dropout voltage regulator with quiescent current reduction

A threshold detector circuit and method for providing an output signal indicative of the relative magnitude of an input signal and a predetermined threshold value. The circuit, which is powered by the input signal and does not require a separate power source, includes a reference stage which switches from one state to another state when the input to the reference exceeds a predetermined reference voltage. The reference voltage is equal to the sum of two voltages having positive and negative temperature coefficients, respectively so that the total coefficient is small. A pair of transistors operating at different emitter current densities provide a difference in base-to-emitter voltages used to derive the first voltage and an absolute base-to-emitter voltage is used for the second voltage. An input stage is included which has a transistor for coupling the detector input to the reference stage input. The input transistor is saturated when the detector input approaches the threshold voltage so that the overall temperature coefficient remains low. An output stage produces an output signal which changes when the input signal causes the reference stage to change states.

Threshold detector circuit and method

A bipolar switch is disclosed having a near zero standby current characteristic, low output impedance in the 'on' state, and near infinite impedance in the 'off' state. The switch is responsive to a control signal to apply regulated power to a load. The switch includes a turn-on detect circuit which is powered solely from the control signal, and switching circuitry which is powered from a power source but which normally draws no standby current when the switch is in its 'off' state. The switching circuitry includes speed-up circuitry to permit rapid turn-on, circuitry which employs positive feedback to achieve high current gain, and circuitry for rapidly turning off the switch.

Zero standby current switch method and apparatus

An IC thermal shutdown circuit is based upon the thermal characteristics of a reverse biased PN junction diode. The leakage current, at bias levels below breakdown, is closely related to the high temperature IC performance limit. A hysteresis introducing circuit produces reliable switching at predetermined levels to shut down the IC when the maximum temperature limit is reached.

Adaptive thermal shutdown circuit

A pair of ratioed emitter size transistors is operated to produce a .DELTA.V.sub.BE. A second pair of transistors is coupled in series with the first pair and matched therewith so as to produce 2.DELTA.V.sub.BE. This differential voltage appears across a resistor coupled in series with the low current density transistors. This circuit combination produces a current that is proportional to absolute temperature (PTAT) and which is passed through a suitable value resistor to develop a PTAT voltage. This voltage is combined with a negative temperature coefficient voltage produced by forward biased series connected diodes so as to produce a combined voltage that is a multiple of the semiconductor bandgap extrapolated to absolute zero. The diodes are operated at very low current levels so that the circuit requires a very low operating current.

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Milpitas, CA, United States of America

Silvo Stanojevic