JPS6093964A - Over current detecting circuit of electronic switch - Google Patents

Abstract

PURPOSE:To reduce residual voltage at the time of turn-ON as an electronic switch by reducing the over current detecting resistor of the electronic switch, by judging an over current detecting signal by using a current mirror circuit. CONSTITUTION:When a current switching element 26 is turned ON by the state of the controller 17 in a switch 10, a current is flowed to load 9, the element 26 and an over current detecting resistor R1 from a power source 19. When this current exceeds a predetermined value, the voltage of a node 46 comes to ''H'' while the output of the controller 17 comes to ''L'' and, therefore, a current flowing to the element 26 is reduced and the element 26 substantially brought to an OFF-state. Therefore a current flowing to the resistor R1 is reduced and flowed out from a node 41 to the resistor R1 through a registor 35 to drop the emitter voltage of a transistor (Tr) 25 while the balance of Tr24, 25 for constituting a current mirror circuit along with Tr21, 22, 23 and a current source 20 is lost to drop the potential of the node 46. Subsequently, when the potential of the node 46 is reversed to ''L'', the output of the controller 17 comes to ''H'' and the element 26 is turned ON.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an overcurrent detection circuit for electronic switches, such as proximity switches.

Conventionally, this type of overcurrent detection circuit inserts an emitter resistor R1 into the emitter of the output transistor Trl, as shown in FIGS. This is the simplest method for detecting overcurrent, and is used in many applications. Although this method can be easily implemented, it has the disadvantage that the residual voltage at the output terminal when the circuit is turned on becomes extremely large. That is, the remaining voltage VOn of the transistor Tr at 08:00 depends on the output current value and the output current capacity of the transistor Trl, but if
An is Von = 0.2 CV:), output current I
When t=150 (mA) and a current of 200 (mA) or more flows including the overcurrent detection circuit, the overcurrent is tossed. When the base-emitter voltage Vbe of the transistor Tr2 is detected to be 0.7 (V) or more, the value of the emitter resistance R1 becomes R7=Ushi Fen=35 [Ω]. When the output current I+=150 CmA], the voltage VrI across the emitter resistor is Vrl-35×
0.15"q 0.525 CV , 1, so the voltage Vx of the series circuit of transistor Tr and emitter resistor R3 is Vx = Von + Vr, : 0.2 + 0.52
5 = 0.725 (V). By inserting the overcurrent detection circuit in this way, the output voltage when ON/OFF as an electronic switch is more than tripled, and as is clear from the calculation formula, the output power capacity of the output transistor Trl is increased, No matter how small the output voltage Yon is, the ON/N output voltage including the overcurrent detection circuit hardly decreases. Since the voltage was the overcurrent detection voltage, it had a large negative temperature coefficient.

This invention attempts to eliminate such conventional drawbacks, and the first purpose of this invention is to
Compared to those that detect overcurrent using the emitter voltage, the detection voltage is lowered, thereby reducing the resistance of the overcurrent detection 11 of the electronic switch, thereby reducing the remaining voltage at 08:00 as a vital electronic switch. It is something.

An embodiment of the present invention will be described below with reference to the drawings.

Figure 3 is a circuit diagram when the overcurrent detection circuit according to the present invention is applied to a proximity switch, and this proximity switch 0 consists of a proximity sensor IC circuit 1 and an output transistor to supplement the output current capacity of this IC circuit. It is configured by a current switching purple sweet potato 26. And inside this IO circuit, there is an oscillation circuit 2, a oscillator circuit 2, a oscillator circuit 4, and an oscillator circuit 4.
．． It has a comparator 5, an output circuit 6, a constant voltage circuit 7, a power supply reset circuit 8, an output controller 14, and an overcurrent detection circuit 16. configured. Further, a detection coil L, a resonant capacitor C4, a sensitivity adjustment variable resistor R22, a bypass capacitor C18, an integrating capacitor C74, a power supply reset capacitor Cta, a load 9, etc. are externally attached.

Therefore, the detection coil I4. When the metal body approaches or separates from the metal body, the oscillation circuit 2 starts or stops oscillation, and the output circuit 6 outputs a logic high or H level.

The overcurrent detection circuit 16 includes a current switching element 26.
and the power supply reset circuit 8.

FIG. 4 is a circuit diagram showing the main part of the present invention, which basically consists of four transistors, namely a first transistor 22, a second transistor 22, and a second transistor.
transistor 23, third transistor 24, and fourth transistor 25, resistors 31 and 32, and current source 2
The overcurrent detection circuit 16 is constituted by a block including the transistor 21 and the transistor 21. and transistor 22
．． A transistor 29 is provided to reduce the influence of the base current of 24. An overvoltage protection circuit 18 is configured by the diode 27 and the resistor 35, and protects the overcurrent detection circuit 16 when a large voltage is applied to the node 41. This overvoltage protection circuit is for current sinking. 19 is a power source. Note that the current switching element 26
may be configured by a transistor, for example, as long as it controls the current flowing through the load 9. Each transistor 2
Connection terminal a is connected to the connection point between 3.25 and each resistor 31.32.
tb is drawn out, and a signal output terminal G is provided at the connection point between the transistors 24 and 25, and this output terminal is further connected to the input terminal of the controller 17 that controls the current switching element 26, so that the output of the controller 17 The state is being controlled. Further, in the voltage shown in FIG. 4, the overvoltage protection circuit 18 is connected to the terminal. In FIG. 4, the overcurrent detection circuit 16 and the overvoltage protection circuit 18 are integrated into ICs.

Now, in FIG. 4, the current from the current source 2o is ■. ■o-
5 [μA], resistance value of resistor 31.32 R111' R3
! When Rst = n'u210 [KΩ], the voltage V41 at node 41 becomes the overcurrent detection voltage and its value is "4".
1 = In xR31= ro x n, St” 5 X
10:50 (m V ). This is because when node 41 is an oven, transistors 24 and 25 are balanced and output node 46 is in a critical state.

Now, when the node 41 is read directly to the output current detection resistor R3, the voltage generated across this resistor is 50 [mV].
If it is smaller, the resistor R1 is connected from the node 41 through the resistor 35.
A current starts to flow toward the resistor 32, so the current flowing through the resistor 32 decreases, and the emitter voltage of the transistor 25 decreases.
Transistors 24 and 25 become unbalanced, and node 4
The potential of 6 becomes L. At this time, the output of the electronic switch controller 17 becomes, for example, H, and the current switching element 26 is in the on state.

Further, if the current flowing through the current switching element 26 exceeds a predetermined value for some reason, the voltage generated across the resistor RI drops to 50 (mV), and the voltage at the node 46 becomes H.

Konoto II! The output of the slave switch controller 17 becomes, for example, low, and the current flowing through the current switching element 26 decreases by 12, substantially turning it off. Therefore, the resistance R
The current flowing through node 1 decreases, the potential of node 41 decreases, and the potential of node 46 also decreases. When the potential of the node 46 eventually reverses to L, the output of the electronic switch controller 17 becomes H, and the current switching element 26 is turned on.

Furthermore, when the voltage of the resistance ratio is 50 (mV), the resistance is 35
No current flows through , and this becomes the threshold voltage.

In this way, the voltage generated across the resistor R1 is 50 [mV]
When the voltage is exceeded, the overcurrent detection circuit 16 detects that point.

FIG. 5 shows an overvoltage protection circuit 18 connected to connection terminal a, and since its operation is substantially the same as that shown in FIG. 4, its explanation will be omitted.

The above explanation is an example of the current sink output format, but
In the case of the current source output format as well, the node 46 becomes H when an overcurrent is detected. FIG. 6 shows an example of the output format of the current source.

The circuit shown in FIG. 6 is a current source circuit opposite to that shown in FIGS. 4 and 5, and the emitter of the first transistor 22 is connected to one terminal of the power supply 19 via a resistor 33. , and the emitters of the third transistors 24 are each connected to one terminal of the power supply 19 via a resistor 34.

Further, the collector of the transistor 21 is connected to one terminal of the power supply 19 via the current source 20, and its emitter is connected to one terminal of the power supply 19 through the current source 20.
9, respectively. Further, the diode 28 and the resistor 36 constitute an overvoltage protection circuit 18, and this circuit is connected to a terminal d provided at the connection point between the emitter of the third transistor 24 and the resistor 34. The overvoltage protection circuit may be connected to the ninth terminal C at the connection point between the emitter of the first transistor 22 and the resistor 33. Further, a PNP type transistor is used as the current switching element 26.

In other words, the major difference between the circuit shown in FIG. 6 and the circuits shown in FIGS. 4 and 5 is the power supply 19 of the overcurrent detection circuit 16.
The two points are that the connection direction to the current switching element 26 is reversed, and that a PNP type transistor is used as the current switching element 26.

Note that FIG. 7 shows a modification of the current mirror circuit, and the modifications shown in FIG. 7 (al) and FIG. 7 (bl and (cl) are well known.

In Figure 4, when the detection voltage is 50 (mV) and the overcurrent is 200 (mA), the resistance R2 is R1 = Σμ month - M =
= 0.25 (Ω) 0 mA, therefore the output current '[4 = 150 [m^]
The remaining voltage Vx at 08 o'clock at the output terminal is Vx
= Von + Vr, :0.2 10. 25X0.
15 = 0.2 + 0.0375 = 0.2375
(V), which is a great improvement over the conventional one.As is clear from this calculation example, in the conventional example, the voltage Vrl across the resistor R4 was quite large compared to the 8-hour residual voltage Von of the transistor Tr1. According to this invention, the voltage Vrl across the resistor R1 is considerably smaller than the 08 o'clock remaining voltage Von of the current switching element 26, and therefore a transistor with a large capacity is used to reduce the 08 o'clock remaining voltage Von. For example, it is also possible to reduce the remaining voltage Vx when the output terminal is ON.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams showing conventional overcurrent detection circuits, FIG. 3 is a block diagram when the overcurrent detection circuit according to the present invention is applied to a proximity switch, and FIG. 4 is a circuit diagram showing the overcurrent detection circuit according to the present invention. A circuit diagram showing one embodiment of the detection circuit, FIG. 5 is a circuit diagram showing another embodiment of the invention, FIG. 6 is a circuit diagram showing still another embodiment of the invention, and FIG. 7 is a current mirror. FIG. 7 is a circuit diagram showing a modified example of the circuit. ■...IC circuit, 2...Oscillation circuit, 3...Comparator, 4...Integrator circuit, 5...Comparator, 6
... Output circuit, 7... Constant voltage circuit, 8... Power supply reset circuit, 9... Load, 10... Switch, 14
...output controller, ...detection coil, R,
R2...variable resistor, cl...common capacitor, C7
4... Integrating capacitor, ctIl... Capacitor,
16... Overcurrent detection circuit, 17... Electronic switch controller, 18... Overvoltage protection circuit, 19... Power supply, 20... Current source, 21-25... Transistor, 26... Current switching element, 27... diode, 28... diode, 31, 32.33.34
...Resistance, R1...Resistance, 41.42...Node, 46...Output node. Patent applicant Yamatake Honeywell Co., Ltd. Figure 4 Figure 5 Figure 6 Figure 7 (a) Procedural amendment (method) % formula % [3 1. Indication of case Patent application No. 1983-203055 2. Title of invention Electronic switch overcurrent detection circuit 3, patent applicant name (666) Yamatake Honeywell Co., Ltd. 5 related to the case of the person making the amendment; engraving of the drawing dated the amendment order (no change in content)

Claims (1)

[Claims] A load, a current switching element for controlling the current flowing through the load, and an overcurrent detection resistor are connected in series to the power supply, and the emitter of the first transistor is connected to one terminal of the power supply. and the collector thereof is connected to the other terminal of the power supply via a current source, and the emitter of the second transistor is connected to one terminal of the power supply, and the emitter of the second transistor is connected to the other terminal of the power supply. The emitters of the transistors are connected through a resistor, and the collectors of both transistors are connected to each other.1. Further, the emitter of the fourth transistor is connected to one terminal of the power supply, and the emitter of the fifth transistor is connected to the other terminal of the power supply via a resistor, and the collectors of both transistors are connected to each other. connecting the first transistor, the second transistor and the fourth transistor,
Further, the third transistor and the fifth transistor are connected to form a current mirror circuit, and connecting terminals are drawn out from the connection points between the third and fifth transistors and the respective resistors, and the terminals are connected to each other so as to form a current mirror circuit. is selectively connected to the connection point between the current switching element and the overcurrent detection resistor, and a signal output terminal is provided at the connection point between the fourth transistor and the fifth transistor, and this output terminal is connected to the connection point between the fourth transistor and the fifth transistor. An overcurrent detection circuit for an electronic switch, characterized in that it is connected to an input terminal of a controller that controls a current switching element, and controls an output state of the controller.