JP2000059197A - Semiconductor contact output circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the circuit constitution simple and to enable high-speed pulse output by providing a pulse output circuit with a photocoupler for insulating a primary- and a secondary-side circuit and a saturation preventing circuit which prevents a transistor for pulse signal output from being saturated. SOLUTION: The output pulse signal 61 from an electromagnetic flowmeter main body after being amplified by a transistor(TR) 21 makes the light emitting diode of the photocoupler 10 emit light and is outputted as a secondary-side pulse output signal by a secondary-side photodiode 12 and an output transistor 13 to an output transistor 81. Here, a resistance 33 is added so as to prevent the saturation phenomenon that the switching speed of the output transistor 81 becomes slow. A resistance 13 operates as a feedback line for balancing the collector current IC and base current IB of the output transistor 81 to prevent the collector current IC and base current IB from becoming overcurrents.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a pulse output circuit used for an electromagnetic flow meter or the like.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram showing an example of a semiconductor contact output circuit used in a conventional electromagnetic flow meter. In the figure, reference numeral 50 denotes a pulse transformer that insulates the primary side and the secondary side of the pulse output circuit. The terminal 52 at the end of the winding of the coil is connected to an output signal of an AND gate 63 that outputs an AND signal of an output pulse signal 61 generated by the electromagnetic flowmeter main body and an internal clock signal 62.

An anode of a diode 71 is connected to a terminal 53 at the start of winding of a secondary coil of the pulse transformer 50, and one end of a capacitor 72 and one end of a resistor 73 are connected to a cathode of the diode 71. The other end of the resistor 73 is connected to the base of the output transistor 81 and one end of the resistor 74. A pulse output terminal 82 is connected to the collector of the output transistor 81.

Further, the terminal 54 at the end of winding of the secondary coil of the pulse transformer 50, the other end of the capacitor 72, the other end of the resistor 74, and the emitter of the output transistor 81 are all connected to the pulse output terminal 83. .

[0005] The operation of the pulse output in the circuit having such a configuration will be described with reference to a time chart shown in FIG.

In FIG. 1, an output pulse signal 61 generated by the electromagnetic flowmeter main body is obtained by converting an internal clock signal 62 to an internal clock signal AN.
By gating by the D gate 63, the signal is modulated into the pulse transformer primary input signal 64.

The primary input signal 64 of the pulse transformer, which is input to the primary side of the pulse transformer 50, is adjusted so as to have a pass band sufficient to pass through the pulse transformer 50. It is output as a pulse transformer secondary output signal 65 to the secondary side.

The secondary output signal 65 of the pulse transformer generated on the secondary side of the pulse transformer 50 is converted into a secondary-side demodulated signal 66 by a demodulation circuit composed of a diode 71 and a capacitor 72.

The converted secondary-side demodulated signal 66 is
The resistor 73 and the resistor 74 for protecting the base of the transistor and stabilizing the operation are adjusted to an appropriate size and input to the base of the output transistor 81.

Thus, the output pulse signal 61 generated by the electromagnetic flowmeter main body can be obtained from the pulse output terminal 82 and the pulse output terminal 83 as a pulse signal of a semiconductor contact output insulated by the pulse transformer 50. Become.

[0011]

However, in the conventional semiconductor contact output circuit, not only a pulse transformer occupying a large space on a printed circuit board is required to insulate signals on the primary side and the secondary side, but also, Since a primary-side modulation circuit and a secondary-side demodulation circuit are required, there has been a problem that the circuit configuration is complicated and expensive.

When a conventional semiconductor contact output circuit attempts to output a high-speed pulse, an input signal is lost in a process in which a pulse transformer primary input signal 64 passes through a pulse transformer 50 and is demodulated by a demodulation circuit. Therefore, a sufficient amplitude cannot be obtained for the secondary-side demodulated signal 66. Therefore, the conventional circuit configuration has a problem that it is impossible to output a high-speed pulse signal.

An object of the present invention is to provide a semiconductor contact output circuit which is constituted by a simple circuit and capable of outputting a high-speed pulse.

[0014]

According to the first aspect of the present invention, there is provided a pulse output circuit, comprising: a photocoupler for insulating a primary side circuit from a secondary side circuit; It is characterized by including a saturation prevention circuit for preventing a saturation state of the pulse signal output transistor.

As a result, it is possible to perform a high-speed pulse output composed of a simple circuit realizing space saving.

According to a second aspect of the present invention, in the first aspect, the saturation prevention circuit controls the base current by feeding back the magnitude of the collector current of the pulse signal output transistor to the base current. It is characterized by having such a configuration.

This makes it possible to prevent the transistor for pulse signal output from falling into a saturated state with a circuit having a simple configuration.

According to a third aspect of the present invention, in the first aspect of the present invention, the pulse signal output transistor is configured to be driven using a pulse detection power supply externally connected. It is characterized by having.

As a result, it is not necessary to supply power from the primary side to the photodiode on the secondary side, so that the primary side and the secondary side of the pulse output circuit can be completely insulated.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a configuration diagram showing one embodiment of a semiconductor contact output circuit according to the present invention.

In FIG. 1, reference numeral 10 denotes one of the pulse output circuits.
This is a photocoupler that insulates the secondary side from the secondary side. The driving voltage VDD is connected to the anode of the light emitting diode on the primary side of the photocoupler 10, and the output pulse signal 61 generated by the electromagnetic flowmeter main body is connected to the cathode. Is connected to the emitter of the transistor 21 that amplifies the current. The transistor 21
Are connected to the common potential of the electromagnetic flowmeter.

One end of a capacitor 32 and one end of a resistor 31 are connected to the cathode of the photodiode on the secondary side of the photocoupler 10. The other end of the resistor 31 is connected to the collector of the output transistor 81 and the pulse output terminal 82.

The collector of the output transistor 13 on the secondary side of the photocoupler 10 is connected to one end of a resistor 33, and the other end of the resistor 33 is connected to the collector of the output transistor 81.

The emitter of the output transistor 13 on the secondary side of the photocoupler 10 is connected to the base of the output transistor 81 and one end of the resistor 34, and the other end of the resistor 34, the other end of the capacitor 32, and the output transistor 81 The emitter is connected to the pulse output terminal 83.

The pulse output terminal 82 and the pulse output terminal 83 are connected to a pulse detector 40 provided in an external central monitoring system or the like. The power supply E for pulse detection provided therein is applied via a load resistance RL for pulse detection.

In the pulse signal output circuit having such a configuration, the output pulse signal 61 generated by the electromagnetic flowmeter main body is used.
After being amplified by the transistor 21, the light emitting diode 11 of the photocoupler 10 emits light, and is output as a secondary side pulse output signal between the collector and the emitter of the output transistor 13 by the secondary side photodiode 12.

The base side current IB is applied to the base of the output transistor 81 by the secondary side pulse output signal generated here.
Flows, a collector current IC flows between the emitter and the collector of the output transistor 81.

The pulse detector 40 uses the collector current IC
By detecting the current flowing through the load resistance RL for pulse detection, a pulse signal insulated by the internal circuit of the electromagnetic flowmeter and the photocoupler can be obtained.

However, when the output pulse signal 61 generated by the electromagnetic flowmeter main body is relatively slow, there is not much problem. However, when an attempt is made to output a high-speed pulse, the output transistor 81 stores the minority carriers. The saturation phenomenon due to the effect becomes a problem.

This is a phenomenon in which minority carriers are accumulated in the base region due to excessive flow of the base current and the collector current of the transistor, and the switching speed of the transistor is reduced.

A resistor 33 is added for the purpose of preventing the transistor from being saturated. This operates as a feedback line for balancing the collector current IC and the base current IB of the output transistor 81 in FIG. 1, and prevents both from becoming overcurrent. The operation will be described below.

The magnitude of the output transistor current IT can be represented by the sum of the collector current IC and the feedback current IF. That is, the magnitude of the output transistor current IT is: IT = IF + IC (1)

As is apparent from the equation (1), when the collector current IC increases, the feedback current IF decreases. In other words, the collector current IC depends on some factors.
When working in an increasing trend, the magnitude of the feedback current IF works in a decreasing direction. Therefore, the base current IB acts in a decreasing direction, and as a result, the collector current IC also acts in a decreasing direction.

Conversely, when the collector current IC tends to decrease due to some factor, the magnitude of the feedback current IF acts in an increasing direction. Therefore, the base current IB acts in the increasing direction, and as a result, the collector current IC also acts in the increasing direction.

That is, by feeding back the magnitude of the output transistor current IT of the output transistor 81 to the base current IB, the collector current IC is kept at an optimum level, and the output transistor 81 is prevented from being saturated. . By this operation, the switching speed of the transistor is always kept in a state where a high-speed pulse can be output, so that high-speed pulse output is always possible.

The foregoing description has been directed to specific preferred embodiments for the purpose of describing and illustrating the invention. Therefore, the present invention is not limited to the above-described embodiment, and includes many more modifications without departing from the spirit thereof.
This includes deformation.

[0037]

As is apparent from the above description,
According to the present invention, the following effects can be obtained. According to the first aspect of the present invention, in the pulse output circuit used for the electromagnetic flow type or the like, a space-saving and low-cost pulse output is provided by providing a photocoupler for insulating the primary and secondary circuits. In addition to being able to implement the circuit,
By providing the saturation prevention circuit for preventing the saturation state of the pulse signal output transistor, a high-speed pulse output operation which has been impossible in the related art can be always performed in a stable state.

According to a second aspect of the present invention, in the first aspect, the saturation prevention circuit controls the base current by feeding back the magnitude of the collector current of the pulse signal output transistor to the base current. With this configuration, a high-speed pulse output operation can always be performed in a stable state with a simple circuit configuration.

According to a third aspect of the present invention, in the first aspect of the present invention, the pulse signal output transistor is configured to be driven using an externally connected pulse detection power supply. This eliminates the need to supply power from the primary side to the secondary side circuit, so that the primary side and the secondary side can be completely insulated.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of a semiconductor contact output circuit according to the present invention.

FIG. 2 is a configuration diagram illustrating an example of a conventional semiconductor contact output circuit.

FIG. 3 is a time chart for explaining a pulse output operation of a conventional semiconductor contact output circuit.

[Explanation of symbols]

 Reference Signs List 10 photocoupler 11 primary side light emitting diode 12 secondary side photodiode 13 secondary side output transistor 21 transistor 31 resistor 32 capacitor 33 resistor 34 resistor 50 pulse transformer 61 output pulse signal 62 internal clock signal 62 AND gate circuit 71 Diode 72 Capacitor 73 Resistance 74 Resistance 81 Output transistor

Claims (3)

[Claims] 1. A pulse output circuit used for an electromagnetic flow type or the like, wherein a photocoupler for insulating a primary side circuit from a secondary side circuit and a pulse signal output from a secondary side of the photocoupler are supplied to an external device A semiconductor contact output circuit comprising a saturation prevention circuit for preventing a saturation state of a pulse signal output transistor for outputting to a semiconductor contact output circuit. 2. The circuit according to claim 1, wherein the saturation prevention circuit is configured to control the base current by feeding back the magnitude of the collector current of the pulse signal output transistor to the base current. Semiconductor contact output circuit. 3. The semiconductor contact output circuit according to claim 1, wherein said pulse signal output transistor is configured to be driven by using a pulse detection power supply connected externally.