JP2002258920A - Switching power circuit for programmable controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the switching power circuit for a programmable controller, capable of quickly generating and supplying a DC power for control to each part, and reducing power consumption in a normal state. SOLUTION: In a power source part 32 of a programmable controller 31, a positive characteristic thermistor 33 is connected between an output terminal 11d of a rectifier circuit 11 and the power input terminal of an IC 18. Then, when an AC power 12 is applied to the rectifier circuit 11, a capacitor 19 is charged through the thermistor 33, and an initial power for start is supplied to an IC 18 for controlling a transistor 14 for switching a primary side coil 13P of a switching transistor 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply circuit for generating and supplying a DC power supply to each section of a programmable controller when an AC power supply is input.

[0002]

2. Description of the Related Art As shown in FIG. 3, a programmable controller 1 is provided with functional blocks such as a power supply unit 2, a processor unit 3, an input unit 4 and an output unit 5.
The processor unit 3 includes an arithmetic unit 6 and a storage unit 7, and a personal computer (PC) 8 is connected to the processor unit 3 as a programming terminal. By uploading to the CPU 7, the processor unit 3 controls each unit.

[0005] The input unit 4 includes switches, such as a digital switch, a selector switch, a push button switch, a proximity switch, and a limit switch, which are arranged on a machine side (for example, a production line or the like) to be controlled. The operation / detection unit 9 is connected, and an operation signal or a detection signal from the operation / detection unit 9 is input.

[0004] The output unit 5 is connected to a display / drive unit 10 including a pilot lamp, a numeric display, a solenoid valve, a motor, and the like, which are arranged on the machine side. The processor unit 3 controls the display / drive unit 10 via the output unit 5 according to a program, based on the state of the signal input to the input unit 4.

FIG. 4 shows a detailed electrical configuration of the power supply unit 2 configured as a switching power supply circuit.
An AC power supply 12 is applied to the AC input terminals 11a and 11b of the rectifier circuit 11. Rectifier circuit 11
Although not specifically shown, the device includes a noise removing filter including a capacitor and an inductor, a full-wave rectifier circuit including a diode bridge, and the like.

[0006] DC output terminals 11c, 11 of the rectifier circuit 11
between the primary coil 1 of the switching transformer 13
A series circuit of a 3P, PNP transistor 14 and a resistor 15 is connected. The DC output terminal 11c is connected to the positive bus 17a of the control circuit 17 via a resistor 16.
Is connected to the DC output terminal 11d, and the negative bus 17b of the control circuit 17 is connected to the DC output terminal 11d.

The control circuit section 17 includes an IC 18 for PWM control (switching control), a capacitor 19, a coil 13 Sa which is a part of the secondary coil 13 S of the switching transformer 13, and a diode 20. The power input terminal of the IC 18 is connected to the positive bus 17a, and the ground terminal is connected to the negative bus 17b. The capacitor 18 is connected between the buses 17a and 17b. The coil 13Sa has one end connected to the negative bus 17b and the other end via the diode 20 to the positive bus 17
a.

The AC input terminal 21 of the rectifier circuit 21 on the output side
a, 21b are connected to the secondary side coil 13Sb of the switching transformer 13, and from the DC output terminals 21c, 21d of the rectifier circuit 21, the processor unit 3, the input unit 4, and the output unit 5, which are the respective units of the programmable controller 1.
DC power supply Vcc for control supplied to each functional block such as
(For example, 5 V).

Although not specifically shown, the rectifier circuit 21 is composed of a diode, a capacitor, and the like.
The AC voltage appearing in the secondary coil 13Sb is half-wave rectified. The safety monitoring unit 22 monitors the voltage and / or current of the DC power supply Vcc generated and output from the rectifier circuit 21. If the voltage and / or current exceeds the upper limit, the safety monitoring unit 22 stops the operation. A signal is output to stop the switching control.

The IC 18 separately monitors the voltage of the DC power supply Vcc, and performs feedback control by adjusting the switching on / off interval so that the voltage is maintained at a constant level. FIG. 5 is an equivalent circuit diagram showing a state in which the power supply unit 2 supplies DC power Vcc to each unit of the programmable controller 1.

[0011]

Here, the sequence from when the AC power supply 12 is turned on to the power supply section 2 until the power supply section 2 operates is as follows. When the AC power supply 12 (Vac1) is turned on, the rectifier circuit 1
The DC voltage Vdc rectified by 1 charges the capacitor 19 of the control circuit unit 17 via the resistor 16. When the terminal voltage of the capacitor 19 reaches the operable voltage of the IC 18, the IC 18 starts. The activated IC 18 turns on / off the transistor 14 to start the switching operation. When the switching is performed on the primary side of the switching transformer 13, an AC voltage Vac2 is induced in the secondary coil 13Sb, and the rectifier circuit 21 generates and outputs a DC power supply Vcc. Then, an AC voltage is also induced in the coil 13Sa of the control circuit section 17, and thereafter, the AC voltage Vac2 'charges the capacitor 19 via the diode 20.

That is, the resistor 16 is connected to the coil 13S
A is provided to supply initial power to the IC 18 until an AC voltage Vac2 'is induced in the capacitor a and the capacitor 19 is charged via the diode 20. The time from when the AC power supply 12 is turned on to when the IC 18 is started is determined by the charging time constant of the resistor 16 and the capacitor 19.

Here, in order to start the IC 18 faster, the resistance value of the resistor 16 may be set to a small value to reduce the charging time constant. In that case, in the subsequent steady operation state, The power consumption of the resistor 16 increases. Therefore, the resistance of the resistor 16 is
Due to a trade-off between the start-up time of No. 18 and power consumption in a steady operation state, an appropriate value had to be set.

The present invention has been made in view of the above circumstances, and an object of the present invention is to make it possible to quickly generate a control DC power supply and supply it to each unit, and to reduce power consumption in a steady state. It is an object of the present invention to provide a switching power supply circuit of a programmable controller.

[0015]

According to the switching power supply circuit of the programmable controller according to the first aspect of the present invention,
When an AC power supply is applied to the rectifier circuit to generate a switching DC voltage, the DC voltage charges a capacitor connected between power supply terminals of the switching control circuit via a variable resistance element. That is, an initial power supply for starting is supplied to the switching control circuit. In this case, since the resistance value of the variable resistance element is relatively low at the start of energization, the charging time constant for the capacitor is reduced, and the capacitor is rapidly charged and the switching control circuit starts operating.

When the switching control circuit starts operating, a DC power supply for supplying to each part of the programmable controller is generated on the secondary side of the switching transformer. Thereafter, the DC power supply is also supplied to the switching control circuit itself. By doing so, it is possible to continue operating. Since the resistance of the variable resistance element thereafter changes so as to increase with time, after the switching power supply circuit reaches a steady state of operation, the desired power is achieved by the variable resistance element. Consumption can be kept low. Therefore, it is possible to simultaneously achieve the object of rapidly generating a DC power supply and the object of reducing power consumption in a steady state, which have been contradictory in the related art.

According to the switching power supply circuit of the programmable controller, the variable resistance element is constituted by a thermistor having a positive characteristic. In other words, the thermistor having a positive characteristic has a small resistance value when the temperature of the surroundings or itself is low,
It shows a characteristic that the resistance value increases as the temperature increases. That is, the resistance value of the thermistor shows a low value at the start of energization immediately after the AC power is turned on, and when the temperature of the thermistor rises due to continuing energization thereafter, the resistance value gradually shows a low value accordingly. Become like Therefore, the function as a variable resistance element can be realized using a thermistor that is relatively easy to use.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. 3 to 5 are denoted by the same reference numerals and description thereof will be omitted, and only different portions will be described below. As shown in FIG. 1, in a power supply unit (switching power supply circuit) 32 that constitutes a part of the programmable controller 31,
Instead of 6, a thermistor (variable resistance element) 33 is provided. As shown in FIG. 2, the temperature characteristic of the thermistor 33 shows a positive characteristic in which the resistance value gradually increases as the temperature increases. Other configurations are the same as those in FIGS.

Next, the operation of the present embodiment will be described.
After the AC power supply 12 is supplied to the power supply section 32, the power supply section 3
The sequence up to the operation of 2 is basically the same as the above-mentioned processes 1 to 3, except that the thermistor 33 replaces the charging of the capacitor 19 via the resistor 16.

The time from when the AC power supply 12 (Vac1) is turned on to when the IC 18 starts up is as follows:
It is determined by the charging time constants of the thermistor 33 and the capacitor 19, and since the resistance value of the thermistor 33 is relatively low at the start of energization, the charging time constant for the capacitor 19 becomes small, and the capacitor 1
9 is a rapidly charged IC (switching control circuit) 1
8 starts to operate.

The IC 18 starts operating, turning on / off the transistor (switching element) 14 to start the switching operation. Thereafter, an AC voltage Vac2 'is induced in the coil 13Sa, and the capacitor 19 is charged via the diode 20. Then, the purpose of providing the thermistor 33 for turning on the initial power supply for starting the IC 18 is achieved. Thereafter, the rectifier circuit 1 is connected to the thermistor 33.
Although the switching DC power supply Vdc generated by step 1 is continuously applied, the temperature of the thermistor 33 gradually increases as the energization is continued.

Then, the resistance value of the thermistor 33 increases accordingly, so that the power consumed by the thermistor 33 gradually decreases as the resistance value increases. Therefore, in the steady state, power consumption by the thermistor 33 after achieving the initial purpose can be suppressed as much as possible.

As described above, according to the present embodiment, in the power supply unit 32 of the programmable controller 31, the thermistor 33 having a positive characteristic is connected between the output terminal 11d of the rectifier circuit 11 and the power supply input terminal of the IC 18. AC power supply 12
Is applied to the rectifier circuit 11, the capacitor 19 is charged via the thermistor 33, and the initial power for startup is supplied to the IC 18 for switching control.

At the start of energization immediately after the AC power supply 12 is turned on, the resistance value of the thermistor 33 shows a low value. When the temperature of the thermistor 33 rises as the temperature of the thermistor 33 increases, the resistance value gradually increases accordingly. Consumption can be kept low. Therefore, it is possible to simultaneously achieve the object of rapidly generating a DC power supply and the object of reducing power consumption in a steady state, which have been contradictory in the related art.

The present invention is not limited to the embodiment described above and shown in the drawings, and the following modifications or extensions are possible. The variable resistance element is not limited to the thermistor 33, and may be any element exhibiting similar characteristics (not only temperature characteristics but also resistance characteristics over time). Further, a circuit equivalent to an element having such characteristics may be formed.

[Brief description of the drawings]

FIG. 1 is an embodiment of the present invention, and is a diagram showing an electrical configuration of a power supply unit constituting a programmable controller;

FIG. 2 is a diagram showing temperature characteristics of a thermistor;

FIG. 3 is an overall configuration diagram of a programmable controller showing a conventional technique.

FIG. 4 is a diagram corresponding to FIG. 1;

FIG. 5 is an equivalent circuit diagram showing a state in which the power supply unit supplies DC power Vcc to each unit of the programmable controller;

[Explanation of symbols]

11 is a rectifier circuit, 11 is an AC power supply, 13 is a switching transformer, 13P is a primary coil, 14 is a transistor (switching element), 18 is an IC (switching control circuit), 19 is a capacitor, 31 is a programmable controller, and 32 is a power supply. Part (switching power supply circuit), 3
Reference numeral 3 denotes a thermistor (variable resistance element).

Claims (2)

[Claims] 1. A switching power supply circuit for generating and supplying a DC power supply to each part of a programmable controller when an AC power supply is input, wherein the AC power supply is generated by being rectified by a rectifier circuit. DC voltage for switching is applied to the primary side,
A switching transformer in which the DC power is generated on a secondary side; a switching element connected in series to a primary coil of the switching transformer; a power input terminal and a ground terminal connected to an output side of the rectifier circuit; A switching control circuit for performing on / off control of a switching element; a capacitor connected between a power input terminal and a ground terminal of the switching control circuit; a positive output terminal of the rectifier circuit and a power input terminal of the switching control circuit And a variable resistance element that changes so that the resistance value increases with time based on the start of energization. 2. The switching power supply circuit according to claim 1, wherein said variable resistance element is a thermistor having a positive characteristic.