Oscillators – With device responsive to external physical condition
Patent
1994-06-15
1995-10-31
Grimm, Siegfried H.
Oscillators
With device responsive to external physical condition
331 75, 331117R, 32420716, 32420726, 324236, 324327, 307116, 361180, G01V 311, H03B 512, H03K 17945
Patent
active
054633540
DESCRIPTION:
BRIEF SUMMARY
This invention relates to proximity switches or sensors, and in particular to an oscillator/rectifier for use in inductive proximity switches.
Accordingly, a first aspect of the present invention provides a proximity switch circuit including first and second transistors connected as a long tail pair with an inductive sensing circuit connected to one leg thereof and an emitter follower circuit connected between said one leg and the base of the transistor of the other leg, whereby an oscillator circuit can be provided which is non-critically damped to enable faster speed of operation of the proximity switch.
A second aspect of the present invention provides an oscillator for use in inductive proximity switches comprising a long tail pair having first and second transistors with first and second legs extending to a first supply rail from respective collectors and a tail extending between respective emitters to a second supply rail via a First constant current source, a sense coil network associated with a coil of the proximity switch being provided between the first transistor and the first supply rail, and the base of the first transistor being held at a fixed bias by a second constant current source, further comprising an emitter follower circuit having third and fourth transistors, the emitter of the third being connected to the base of the fourth, the collectors of the third and fourth transistors being connected to a third supply rail and the first/third supply rail respectively, the emitters of the third and fourth transistors being connected to the second supply rail via third and fourth constant current sources, the base of the third transistor being connected to the collector of the first transistor, while the emitter of the fourth transistor is connected to the base of the second transistor.
The transistors may all be NPN bipolar transistors.
The second constant current source may be connected to the first supply rail via fifth, sixth and seventh diode connected NPN transistors and a first PNP diode connected transistor, and directly to the second supply rail, the base of the first transistor being connected between the emitter of the sixth transistor and the collector of the seventh transistor.
According to a third aspect of the present invention there is provided a rectifier, for use with an oscillator according to the first or second aspects, comprising an eighth NPN transistor the base and collector of which are connected to the first supply rail, the emitter of which is connected in series with a first resistor to the emitter of a second PNP transistor the collector of which is connected directly or indirectly to an integrator, further comprising a ninth NPN transistor the base of which is connected to the emitter of the fourth transistor and also to the base of the second PNP transistor, and the collector of which is connected to the first supply rail, the emitter of which is further connected in series with a second resistor to the emitter of a third PNP transistor, the collector of which is connected directly or indirectly to an integrator, and the base of which is connected to the second current source.
Regarding the oscillator, the collector of the fourth transistor may be connected to the third supply rail, and further one end of the second current source is connected to the first supply rail via the base to emitter junction of a fifth NPN transistor and a diode connected sixth NPN transistor, the collector of the fifth transistor being connected to the third supply rail, and the base of the first transistor being connected between the emitter of the sixth transistor and the one end of the second current source, the other end of the current source being connected to the second supply rail.
In this case the rectifier may comprise an eighth NPN transistor the base of which is connected to the first supply rail, the collector of which is connected to the third supply rail, and the emitter of which is connected in series with a first resistor to the emitter of a first PNP transistor the colle
REFERENCES:
patent: 4652819 (1987-03-01), Kammerer
patent: 4968953 (1990-11-01), Kanda et al.
patent: 5029300 (1991-07-01), Ishibashi et al.
Bizley Arthur J.
Calder Douglas W.
Femal Michael J.
Golden Larry I.
Grimm Siegfried H.
Shrout Larry T.
Square D Company
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