JPH0330881Y2 - - Google Patents

Description

[Detailed explanation of the idea] [Industrial application field]

The present invention relates to an output circuit for a programmable controller that improves control delay when opening an inductive load.

[Prior art]

Conventionally, in a programmable controller, a DC drive output circuit using a transistor output,
To protect the transistor from the surge voltage that occurs when opening an inductive load such as a solenoid,
A diode is connected to both terminals of the inductive load. FIG. 3 is a circuit diagram showing the configuration of a conventional transistor output circuit. In the figure, 12 is a photocoupler for isolating the internal circuit 10 of the programmable controller and the load. Photocoupler 12 has a phototransistor PT. Darlington-connected transistors Tr1 and Tr2 are connected to the phototransistor 12. transistor
A solenoid S, which is an output element, is connected to the collectors of Tr1 and Tr2. The solenoid S is supplied with power from the battery E by the switching action of the transistor Tr2. Also, on both ends of solenoid S,
A diode D1 is connected to absorb surges. In such a configuration, when the phototransistor PT is turned off and therefore the transistor Tr2 is turned off, the terminal voltage V of the solenoid S and the load current I change according to the characteristics shown in FIG. The magnetic energy stored in solenoid S is dissipated in a bypass circuit via diode D1. Therefore, the terminal voltage of solenoid S is equal to that of diode D1.
is limited by the forward voltage drop, _VD . Additionally, the current I flowing through the solenoid S decreases from the steady current Is by the time constant of the bypass circuit. Conventionally, a bypass circuit using a diode was provided to protect the transistor from surge voltage.

[Problem that the invention attempts to solve]

However, the surge voltage is generated by diode D1.
However, since the resistance of the diode D1 during operation is small and the power consumption in the diode is low, it is not possible to take a large time constant for current decay. For this reason, there is a problem in that the delay when controlling the opening of an inductive load such as a solenoid becomes large. The present invention solves these conventional problems. That is, the purpose of the present invention is to protect the output transistor from surge voltage, and
The goal is to reduce the opening delay of the output element.

[Means to solve the problem]

The configuration of the present invention for solving the above problems is as follows. The present invention includes a DC power supply that supplies power to a load, and one or more transistors that constitute a switching circuit that controls the conduction and interruption of current from the DC power supply to the load in accordance with a control signal. In the output circuit of a programmable controller in which a load forms a series circuit, a voltage greater than the driving DC voltage of the DC power source is applied between the base or gate and collector or drain of one transistor or at least one of two or more transistors. An operating constant voltage element is connected, and a resistance element is connected between the base or gate and emitter or source of the transistor.

[Effect]

The transistors mentioned above are of bipolar type and
It goes without saying that FET type monopolar transistors are included, and the base and gate, emitter and source, and collector and drain have the same functions and meanings, with only different names. Therefore, in the following, it is natural that the base will also substantially refer to the gate, the emitter to the source, and the collector to the drain. Loads such as solenoids are driven by a DC power source. The transistor is connected in series with the load to a drive circuit that serves as a power supply path for the DC power supply. The transistor functions as a switching element to control opening and closing of a load such as a solenoid. When the transistor is turned off, if the load is inductive, a back electromotive force is generated, and this back electromotive force is applied between the emitter and collector of the transistor. On the other hand, a constant voltage element whose operating voltage is higher than the power supply voltage is connected between the base and collector of the transistor, and a resistance element is connected between the base and emitter. For this reason, the surge voltage is divided between the resistance element and the constant voltage element, and is input as the base voltage of the transistor. When the transistor is turned off and the back electromotive force due to the inductive load increases, and the voltage between the emitter and collector of the transistor becomes slightly higher than the operating voltage of the constant voltage element, the constant voltage element operates and the voltage between the emitter and base increases. , forward biased. At this time, this transistor enters the active region, causing a large collector loss. For this reason, the surge current is rapidly reduced, so that the opening speed of a load such as a solenoid can be improved.

【Example】

The present invention will be explained below based on specific examples. FIG. 1 is an electrical circuit diagram showing the configuration of an output circuit according to a specific embodiment of the present invention. A photocoupler 12 is provided to isolate the internal circuit 10 of the programmable controller from the load side. The base of a transistor Tr1 is connected to the collector of the phototransistor PT of the photocoupler 12, and the base of a transistor Tr2 is connected to the emitter of the transistor Tr1.
The transistor Tr1 and the transistor Tr2 form a Darlington connection. A resistor R1 is connected between the emitter and base of transistor Tr1, and a resistor R1 is connected between the emitter and base of transistor Tr2.
R2 is connected. Furthermore, a Zener diode ZD with a breakdown voltage of 75V is connected between the base and collector of the transistor Tr1. A solenoid S, which is an output element, is connected to the collector circuit of the transistor, and this solenoid S is connected to a transistor, which is a switching element.
Power is supplied from a DC power supply E via Tr1 and Tr2. Next, the operation of the circuit of this embodiment will be explained with reference to the characteristic diagram shown in FIG. When the solenoid S is activated, the terminal voltage V is approximately equal to the power supply voltage E. Further, the phototransistor PT is in the on state, and therefore the transistors Tr1 and Tr2 are both in the on state. At this time, the solenoid S is supplied with a steady current Is from the power source E via the transistor Tr2. In such an on state, an off signal is output from the internal circuit 10, and the phototransistor PT
turns off, the base voltage of transistor Tr1 rises to the power supply voltage E, and the transistor
Both Tr1 and Tr2 are turned off. At this time, a back electromotive force is generated in the solenoid S, and as it grows, this back electromotive force is applied between the terminals T1 and T2 to which the emitter and collector of the transistor Tr2 are connected. When this terminal voltage is slightly higher than the operating voltage of Zener diode ZD, 75V,
Zener diode ZD is activated and current flows to terminal T1
The current flows from the resistors R1 and R2 to the Zener diode ZD. Then, due to the voltage drop across the resistors R1 and R2, a potential difference is generated between the emitter terminal T1 of the transistor Tr2 and the base terminal T3 of the transistor Tr1, and this creates a forward bias between the base and emitter of the transistors Tr1 and Tr2. ，
Tr2 enters the active region and emits,
It will operate at an operating point where the voltage between the collectors is approximately 75V. At this time, if the voltage between terminals T1 and T2 tries to rise further, the bias between the base and emitter of the transistor becomes deeper, and the emitter of the transistor,
It acts in the direction of decreasing the voltage between the collectors.
However, since the voltage between the base and collector is controlled by the Zener diode ZD, the base,
Since the bias between the emitters tends to decrease, the voltage drop between the emitters and the collectors increases. In the end, due to such a feedback effect, the transistors Tr1 and Tr2 operate stably at the operating point where the voltage between the base and the collector becomes the Zener diode operating voltage of 75V. Therefore, the current flows through the transistor Tr2 and the resistor
Flows in parallel with transistor Tr1 via R2,
Collector losses occur in those transistors.
Therefore, the surge current decreases rapidly. Surge current decreases and voltage between terminals T1 and T2 becomes 75V
When it becomes smaller, the Zener diode ZD turns off and there is no base bias for the transistor, so the transistor is completely turned off. As a result, the attenuation time constant of the current flowing through the solenoid S can be increased, and the delay in the opening operation of the output element can therefore be reduced.

[Effect of the idea]

The present invention provides an output circuit for a DC-driven programmable controller in which a load, a DC power supply, one or more transistors constituting a switching circuit, and the load are connected in series, and a switch between the base and collector of the transistor. A constant voltage element that operates at a voltage higher than the driving DC voltage is connected to the
This is an output circuit for a programmable controller, characterized in that a resistance element is connected between the base and emitter of the transistor. In order to adopt the above configuration, the surge voltage generated during the opening operation of the inductive load is applied to the series circuit of the constant voltage element and the resistance element, so the voltage between the emitter and collector of the transistor is approximately the same as that of the constant voltage element. Controlled by the voltage, the base of the transistor is
The transistor is biased to operate in the active region. Therefore, since the transistor operates transiently in the active region, the collector loss is large and the surge current can be rapidly reduced. Then,
The control delay when opening the load can be reduced.

[Brief explanation of the drawing]

Fig. 1 is an electric circuit diagram showing the configuration of an input circuit according to a specific embodiment of the present invention, and Fig. 2 shows the terminal voltage of the solenoid and the current flowing through the solenoid to explain its operation. Figure 3 is an electrical circuit diagram showing the configuration of a conventional input circuit.
FIG. 4 is a characteristic diagram showing the terminal voltage of the solenoid and the current flowing through the solenoid to explain the operation of the circuit. 12...Photocoupler, S...Solenoid,
PT...Phototransistor, ZD...Zener diode.

Claims (1)

[Claims for Utility Model Registration] A DC power supply that supplies power to a load, and one or two circuits constituting a switching circuit that controls the conduction and interruption of current from the DC power supply to the load in accordance with a control signal. In the output circuit of a programmable controller in which the above transistors and a load constitute a series circuit, the DC power source is connected between the base or game and the collector or drain of at least one of the one transistor or the two or more transistors. 1. An output circuit for a programmable controller, characterized in that a constant voltage element that operates at a voltage higher than a driving DC voltage is connected, and a resistance element is connected between the base or gate and emitter or source of the transistor.