JPS61128625A - Contactless switch - Google Patents

Abstract

PURPOSE:To reduce current consumption by providing a mirror transistor (TR) provided with a current limit resistor and an input TR provided with a mirror circuit. CONSTITUTION:Since a base current IBi of the input TR10 does not flow with an input voltage V not normally, an output TR3 is not conductive. On the other hand, when the voltage V gest higher, a current starts flowing to the output TR3 and a collector current flows to the mirror TR7, then a base current IB flows to the output TR3 via TRs 8, 9 of the current mirror circuit to flow the collector current (load current I0) of the TR3 until it is saturated sufficiently. Thus, only when the current flowing to the circuit is 0 normally and the input voltage V exists, the input current IBi and the current of the mirror circuit flow. Further, since the current of the TR9 is limited by the current limit resistor 6, it is very small.

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to a non-contact switch as an output circuit of a device such as a proximity switch or a photoelectric switch ◇ [Prior art and its problems] A pace current is controlled according to the detection state of a non-contact switch part detection circuit of such a device, and an output transistor that opens and closes a load is controlled by this pace current. A conventional example of such a non-contact switch is shown in FIG. In FIG. 3, a series circuit of a load 2 and an output transistor 3 is connected to a power supply 1, and the output terminal of a detector (not shown) and a constant current circuit 4 are connected to the base of the output transistor 3. When the output voltage of the device, that is, the input voltage V of the non-contact switch is 00
At this time, the constant current circuit 40 current IB is flowing to the detector side. On the other hand, when the input voltage V increases, the current of the constant current circuit 4 is 1.
The current flows through the transistor 30 pace current. Therefore, the collector of transistor 3, in other words, the current ■ in load 2. flow.

In this way, this non-contact switch operates using the output voltage of the detector as the input voltage V, but even when the input voltage is 0, a current Is flows through the constant current circuit. Moreover, in order to make the transistor conductive as a switch, it is necessary to flow a pace current I greater than or equal to 1/hfe of the maximum load factor 0 (where hfe is the amplification factor of the transistor).

Therefore, this constant current circuit has the disadvantage that a current Is corresponding to the pace current IBic is constantly flowing, and that current consumption is large. Therefore, a circuit as shown in FIG. 4 is also known. In FIG. 4, a transistor 5 is connected to the output transistor 3 in a Darlington connection, and the other connections and operations are exactly the same as in FIG. 3, so a description thereof will be omitted. 8 flows from the transistor 5, and the base current of the transistor 5 Bi is r, i = IB x 1/hfe, so it can be very small, and the current I% of the constant current circuit 4 can also be small, so the total current consumption becomes smaller. However, the disadvantage is that the residual voltage of the two Darlington-connected transistors is high.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a non-contact switch that constantly consumes low current and prevents overcurrent of an output transistor in some cases.

[Key points of the invention]

The present invention provides a non-contact switch equipped with an output transistor whose base current is controlled according to the detection state of a detection circuit, in which a pace is connected to the pace of the output transistor, a current limiting resistor is connected to the emitter, and the output transistor is connected to the pace of the output transistor. A mirror transistor constituting a first current mirror circuit, and a second transistor whose paces are connected in common, one of which is connected to the pace of the output transistor via an input transistor, and the other is connected to the coxister of the mirror transistor. When the output transistor is made conductive by the base current that flows according to the detection state of the detection circuit and begins to flow a load current, current also flows to the mirror transistor, and a second current mirror circuit is formed. As the current increases, this current is supplied to the output transistor's control circuit, and the current that constantly flows through the output transistor's control circuit becomes almost O, and only when the output transistor begins to conduct, the second A relatively large base current is caused to flow from the current mirror circuit to the output transistor so that a saturation current flows to the output transistor, thereby reducing the current consumption of the control circuit at all times. Note that if a constant voltage circuit is connected between the input transistor on the pace side of the output transistor and one side of the output transistor, the sum of the pace emitter voltage of the output transistor and the base emitter voltage of the input transistor becomes the voltage of the constant voltage circuit. When approaching , the base current and collector current of the input transistor are limited, and accordingly the base current of the output transistor is also limited, so that no excessive load current flows to the output transistor.

[Embodiments of the invention]

Hereinafter, the embodiments of the present invention will be described with reference to FIGS. 1 and 2, in which parts serving as connections are given the same reference numerals to avoid duplication of detailed description. In FIG. 1, the output transistor 3 is connected to a power source via a load (not shown) as in the conventional case. The difference between this circuit and the conventional one is that the pin of the mirror transistor 7 whose emitter is connected to the current limiting resistor 6 is connected to the pin of the output transistor 3 to form a first current mirror circuit with the output transistor 3. , the collector of one transistor 9 of the two transistors 8 and 9 constituting the second current mirror circuit whose paces are commonly connected is connected to the collector of the mirror transistor.

In the current mirror circuit, the current value generated in one branch of the circuit block is given to the other branch exactly as it is or multiplied by a constant, and a relatively high current is applied to the emitter of the mirror transistor 7. A limiting resistor 6 is connected to set this current value to a sufficiently low value.

When the input voltage V is always 00, the base current i of the input transistor 10 does not flow, so the pace current I of the output transistor 3 also does not flow, the output transistor 3 is not conductive, and no current flows through the mirror transistor 7 either. However, when the input voltage V increases and the pace current IBi begins to flow through the input transistor 10, the base current 3 begins to flow through the output transistor 3, and the output transistor 3 begins to conduct and a collector current (load current 2) flows. At this time, a current also flows through the collector of mirror transistor 7 at the same time.

This means that a current flows through the transistor 9, and naturally a current Ic also flows through the transistor 8 via the input transistor 10. In this way, when a current starts to flow to the output transistor 3 and a collector current flows to the mirror transistor 7, the transistors 8 and 9 of the second current mirror circuit
The base current flows into the output transistor 3 through the collector current of the output transistor 3 (load current IO
) until sufficiently saturated. Therefore, the current flowing through the circuit at all times is O, and only when the input voltage V is present, the current of i and the second current mirror circuit flows from the input current.

Moreover, since the current on the transistor 9 side of this current mirror circuit is limited by the current limiting resistor 6, it is very small.

FIG. 2 shows an embodiment different from FIG. 1, in which an output transistor 3, a mirror transistor 7 forming a first current mirror circuit together with the output transistor 3, both transistors 8°9 forming a second current mirror circuit, input transistor 10
is the same as the conventional one, but three transistors 11, 12, and 13 are Darlington connected between the connection point of transistor 8 and input transistor 1o and one side of output transistor 3, and the residual voltage is used to create a constant voltage. The difference is that the circuit 14 is connected. Furthermore, diodes 14 and 15 are connected to the input side to prevent reverse current flow.

The operation Fi of this circuit is almost the same as that shown in FIG. 1, and the constant current consumption is almost 0, so a description thereof will be omitted. When an input voltage V is applied, a pace current flows through the input transistor 10, and as explained with reference to FIG. When the current increases and the sum of the base-emitter voltage of the input transistor E0 and the base-emitter voltage of the output transistor 3 approaches the voltage of the constant voltage circuit 14, the input transistor 100
Since the pace current IBi and the collector current IC are limited and the pace current of the output transistor 3 is limited, the collector current (load current Io) of the output transistor 3 is limited and overcurrent is prevented.

〔Effect of the invention〕

As described above, according to the present invention, no unnecessary current flows through the non-contact switch at all times. Then, only when the input voltage is given, in addition to the input current, the output transistor and the first
Either a pace current flows from the second current mirror circuit to the output transistor through the mirror transistor that constitutes the current mirror circuit t, or a current limiting resistor is connected in series to the mirror transistor to make this collector current as small as possible. Since the overall control current is small, the current consumption is very small even when the output transistor is in operation.The output transistor can also be connected to protect it from overcurrent, making it suitable for IC implementation.

[Brief explanation of drawings]

FIGS. 1 and 2 are connection diagrams showing different embodiments of non-contact switches according to the present invention, and FIGS. 3 and 4 are connection diagrams showing different conventional examples of non-contact switches. 3... Output 2 transistor, 6... Current limiting resistor, 7... Mirror transistor, 8, 9
...Two transistors, lO...Input transistor, 14... Constant voltage circuit. Ya, y+'j2 Niyamaguchi 8

Claims (1)

[Claims] 1) A non-contact switch equipped with an output transistor whose base current is controlled according to the detection state of a detection circuit,
a mirror transistor whose base is connected to the base of the output transistor and whose emitter is connected to a current limiting resistor to form a first current mirror circuit with the output transistor;
and a second current mirror circuit in which one of two transistors whose bases are commonly connected is connected to the base of the output transistor via an input transistor, and the other is connected to the collector of the mirror transistor. Non-contact switch. 2) In the non-contact switch according to claim 1, one transistor of the second current mirror circuit connected to the base side of the output transistor via the input transistor and one side of the output transistor A non-contact switch characterized by having a constant voltage circuit connected between them.