JPH033000Y2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to a contactless switch suitable for IC implementation.

[Prior art and its problems]

An example of a conventional non-contact switch used as a proximity switch is shown in FIG. In Figure 1,
A series circuit of a load 2 and a transistor 3 is connected to a power supply 1, and a detection circuit 5 having a detection coil 4 is connected to the base of the transistor 3. A current of a constant frequency is passed through the detection coil 4, and a constant current circuit 6 The base current supplied from the output transistor to the output transistor is always bypassed.

When a metal object approaches the detection coil 4 and the detection coil 4 detects it as an amount of electricity, the detection circuit 5 confirms this and transfers the current of the constant current circuit 6 to the transistor 3.
flow to the base of In this way, when the base current flows through the output transistor 3, the transistor 3 becomes conductive.
Apply current to load 2.

In order to miniaturize such non-contact switches, it is becoming necessary to use monolithic ICs.
However, in the circuit shown in FIG. 1, it is necessary to flow a sufficient base current in order to flow a sufficient collector current to the output transistor. Therefore, the current capacity of the constant current circuit must be sufficiently larger than the current in other parts, and since this current is constantly flowing, the current consumption is large, making it difficult to integrate into an IC. In order to reduce the base current, the output transistor may be connected to Darlington, but this has the disadvantage that the saturation voltage of the output transistor becomes high.

[Purpose of invention]

The purpose of the present invention is to provide a non-contact switch that balances and lowers the control current consumption of each part and can be implemented as an IC.

[Key points of the idea]

The present invention provides a non-contact switch having an output transistor whose base current is controlled according to the detection state of a detection circuit, the base of which is connected to the base of the output transistor supplied with the base current according to the detection state of the detection circuit. and a current limiting resistor is connected to the emitter of the output transistor, forming a first current mirror circuit with the output transistor, and one of the two transistors whose bases are connected in common is connected to the base of the output transistor, and the other is connected to the base of the output transistor. A second current mirror circuit is connected to the collector of the mirror transistor, and when the output transistor is made conductive by the base current supplied according to the detection state of the detection circuit and a load current starts flowing, the first current mirror circuit is connected to the collector of the mirror transistor. Current also flows through the mirror transistor that makes up the current mirror circuit, the current in the second current mirror circuit increases, and this current is connected to the base of the output transistor so that the current always flows through the constant current circuit. In addition to making it possible to reduce the current consumption of the control circuit at all times, it allows a large base current to flow from the second current mirror circuit only when the output transistor begins to conduct, causing a saturation current to flow to the output transistor.
The aim is to obtain a non-contact switch that is balanced and easy to convert into an IC.

[Example of idea]

Next, an embodiment of the present invention will be described in detail based on the wiring diagram shown in FIG. In FIG. 2, parts having the same role as those shown in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted. In FIG. 2, a series circuit of a load 2 and an output transistor 3 connected to a power source 1 and a constant current circuit 6 connected to the base of the output transistor 3 are completely the same as in the prior art. This circuit differs from conventional ones in that the base of the mirror transistor 8 whose emitter is connected to the current limiting resistor 7 is connected to the base of the output transistor 3 to form a first current mirror circuit, and the bases are common. Of the two transistors 9 and 10 constituting the second current mirror circuit connected to is connected to. Of course, the configuration and connection of the detection coil 4 and detection circuit 5 are the same as those of the conventional ones.

In the current mirror circuit, the current value generated in one branch of the circuit configuration block is given to the other branch exactly as is or after being multiplied by a constant, and a relatively high current is applied to the emitter of the mirror transistor 8. A limiting resistor 7 is connected and the current value is set to a sufficiently low value.

When the impedance of the detection circuit 5 increases due to the proximity of the metal body to the detection coil 4, and the current of the constant current circuit 6 begins to flow to the base of the output transistor 3, the output transistor 3 begins to conduct and a collector current flows, but at the same time, the mirror transistor 8
Since the base current flows through the mirror transistor 8, the collector current also flows through the mirror transistor 8. This means that current flows through transistor 10, and naturally current also flows through transistor 9. In this way, when a current begins to flow into the output transistor 3 and a collector current flows into the mirror transistor 8, a base current flows into the output transistor 3 via the transistors 9 and 10 of the second current mirror circuit, and the output transistor 3 Flow the collector current until it is fully saturated. Therefore, the current that always flows through the constant current circuit 6 may be small, and only when the output transistor 3 is conductive, a sufficient collector current of the transistor 9 is added to the current of the constant current circuit 6 and flows to the base of the output transistor 3. In this way, the control current of this non-contact switch increases only when the output transistor conducts, but the control currents of each part at this time are almost balanced, and there are no extreme differences, making it convenient for IC implementation.

[Effect of idea]

As described above, the present invention reduces the control current that is constantly consumed, and when the output transistor becomes conductive and the load current begins to flow, the output transistor is controlled by the first and second current mirror circuits that include this output transistor. This is a non-contact switch that increases the base current and provides sufficient switching characteristics.It is an excellent non-contact switch that can be easily integrated into an IC because its constant current consumption is low and a balanced control current flows.

[Brief explanation of drawings]

FIG. 1 is a wiring diagram showing an example of a conventional non-contact switch applied to a proximity switch, and FIG. 2 is a wiring diagram showing an example of a non-contact switch according to the present invention applied to a proximity switch. 3... Output transistor, 7... Current limiting resistor, 8... Mirror transistor, 9, 10... Two transistors forming the second mirror current circuit.

Claims (1)

[Scope of utility model registration request] In a non-contact switch having an output transistor whose base current is controlled according to the detection state of the detection circuit, the base is connected to the base of the output transistor supplied with the base current according to the detection state of the detection circuit, and the emitter current is A mirror transistor is connected to a limiting resistor and constitutes a first current mirror circuit with the output transistor, and one of two transistors whose bases are connected in common is connected to the base of the output transistor, and the other is connected to the base of the output transistor. A non-contact switch comprising a second current mirror circuit connected to a collector.