JP3763273B2 - Switching power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a switching power supply, and more particularly to a switching power supply that realizes a sequence operation that maintains an output voltage off state for a specific time when the switching power supply is turned off from an operating state and turned on again.
[0002]
[Prior art]
For example, an RCC type switching power supply as shown in FIG. 3 is known as a switching power supply.
[0003]
In FIG. 3, when AC power is input to the input terminal 1, a DC output is obtained at both ends of the capacitor 3 via the rectifying element 2. This rectified output voltage is applied to the base of the transistor 5 via the control circuit 6, a base current flows through the transistor 5, and the transistor 5 is turned on. When the transistor 5 is turned on, a rectified output current flows through the primary winding N1 of the transformer 4, thereby causing a current to flow through the primary winding N2 of the transformer 4 to generate a voltage at both ends thereof. 5 is switched. When the transistor 5 is turned off, the energy stored in the transformer 4 is output to the output terminal 19 via the rectifier diode 9, the smoothing coil 7, and the backflow prevention diode 8 connected to the secondary winding N 3 of the transformer 4. . On the cathode side of the rectifier diode 9, a smoothing capacitor 10 is connected between the output line and the ground line.
[0004]
The constant voltage operation of this switching power supply is performed as follows. That is, 12 is a photocoupler, and its light emitting diode detects the output voltage of the transformer 4 with a voltage dividing resistor 15, and light emission is turned on / off by the shunt regulator 14, and the light receiving transistor receiving this is switched. Thus, the transistor 5 is controlled to control the output voltage at a constant voltage. Further, when the voltage of the secondary output line of the transformer 4 becomes equal to or higher than the breakdown voltage of the Zener diode 16 that sets a predetermined overvoltage detection level (breakdown voltage) due to a failure of the photocoupler 12 or for some reason. A current flows through the light emitting diode of the photocoupler 13 and the resistor 17, and the main transistor 5 is turned off by operating the light receiving transistor of the photocoupler 13.
[0005]
[Problems to be solved by the invention]
In the conventional circuit shown in FIG. 3, if a power supply is turned off and then turned on immediately after a PLC module having a DC / DC converter mounted in parallel before the input as a power supply load, On the module side, the reset operation is usually started by monitoring the input drop.
[0006]
However, if it is turned on again at 6V to 12V due to the difference in reset value due to component variations, the reset processing time of all modules cannot be secured, and products that have been reset and products that have not been reset are mixed and the system starts normally. The problem of not being able to occur.
[0007]
Accordingly, the present invention is to provide a switching power supply in which the above problems are solved.
[0008]
[Means for Solving the Problems]
According to the first aspect of the present invention, there is provided control means for controlling a switching current supplied to the primary side of the transformer, and when the voltage on the secondary side output line of the transformer exceeds a specified voltage, the transformer is turned on. First switch means that is turned off when the voltage on the secondary output line of the battery becomes equal to or lower than a specified voltage, and charging / discharging having a predetermined time constant connected to the secondary output line via backflow prevention means Charging / discharging means that performs charging when charging is performed through the backflow prevention means, and when the first switch means is off and charging current is not supplied through the backflow prevention means, and The first switch means is coupled to the first switch means and is turned off when the first switch means is turned on, and turned on in response to the discharge current of the charge / discharge means when the first switch means is turned off. 2 switch hand Coupled to the second switch means, and when the second switch means is on, an operation off means for turning off the operation of the control means in response to a discharge current of the charge / discharge means; and A third switch means connected on the secondary output line, coupled to the first switch means and responding to a discharge current of the charge / discharge means when the first switch means is off; And third switch means for turning on and discharging the secondary output line of the transformer.
[0009]
According to a second aspect of the present invention, in the first aspect, when the operation-off means is connected to the secondary output line of the transformer and detects an overvoltage on the secondary output line, an overvoltage detection current flows. It is arranged in the overvoltage detection current path of the overvoltage detection means, and when the overvoltage detection means detects an overvoltage, the operation of the control means is turned off in response to the overvoltage detection current.
[0010]
According to the present invention, according to the above configuration, (1) when the power is turned off, the secondary output line is instantaneously turned off when the voltage falls below a specified voltage value, and (2) the time constant determined by the charging / discharging means. The inside can provide a power supply that keeps the off state.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a circuit diagram showing an embodiment of the present invention. In FIG. 1, the same components as those in FIG. Since the basic operation of the switching power supply is the same as that of the conventional example, the configuration of the primary side of the transformer 4 in FIG. 1 is omitted. Further, the connection destination of the output of the light receiving transistor of the photocouplers 12 and 13 is the same as that of FIG.
[0012]
When the switching power supply is outputting a predetermined voltage to the output terminal 19, a current flows through the Zener diode 21, the diode 22, and the resistor 23 to charge the capacitor 24. Here, the Zener diode 21 (the breakdown voltage thereof) and the Zener diode 16 (the breakdown voltage thereof) together are overvoltage levels (that is, the total overvoltage level of the two is equal to the breakdown voltage of the Zener diode 16 in FIG. 3). Is determined. The diode 22 is connected to prevent backflow.
[0013]
Next, when the capacitor 24 is charged, a current flows from the middle point of the diode 22 and the resistor 23 to the transistor 27 through the resistor 25. However, at this time, it is assumed that the base current is supplied to the transistor 27 via the Zener diode 20.
[0014]
When the power supply is turned off in this state, when the voltage of the secondary output line gradually decreases and falls below a specified value (breakdown voltage) by the Zener diode 20, the transistor 27 is turned off, and from the capacitor 24 via the resistors 23 and 25. Is supplied to the bases of the transistor 26 and the transistor 29, and the transistors 26 and 29 are turned on for a time determined by the time constants of the capacitor 24, the resistor 23, and the resistor 25. When the transistor 26 is turned on, the light emitting diode of the overvoltage protection photocoupler 13 emits light, the light receiving transistor is turned on and the primary side main transistor (5) is turned off. At the same time, the transistor 29 is turned on via the resistor 28. Discharge the secondary output line instantaneously. Within the above time constant, this state, that is, the primary side main transistor (5) is turned off and the secondary side output line is discharged, and during this time, a re-on command (power-on) is issued. Even if it enters, the secondary output continues to be off.
[0015]
For reference, FIG. 2 (a) shows an example of a power supply sequence representing a state of a secondary side output from power-off to re-input according to the present invention, and FIG. 2 (b) according to the present invention. From FIG. 2, it can be seen that only by the present invention, the secondary output is turned on after a predetermined delay time after the power is turned off and then turned on again.
[0016]
【The invention's effect】
According to the present invention, for example, when a load such as a PLC module having a DC / DC converter mounted in the input unit is connected in parallel by instantaneously turning off the power supply output voltage and holding the power off state for a certain time thereafter. It is possible to secure a reset processing time for avoiding a system error at the time of off / on, which is expected to occur due to variations in parts. Thereby, it becomes possible to apply to various power supplies from general-purpose products to system equipment products.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of an embodiment of the present invention.
FIG. 2 is a diagram showing a power supply sequence.
FIG. 3 is a circuit diagram of a conventional switching power supply.
[Explanation of symbols]
4 transformer 7 smoothing coil 8 backflow prevention diode 9 rectifier diode 10 smoothing capacitor 12 photocoupler 13 photocoupler 14 shunt regulator 15 voltage dividing resistor 16 zener diode 17 resistor 19 output terminal 20 zener diode 21 zener diode 22 diode 23 resistor 24 capacitor 25 resistor 26 transistor 27 transistor 28 resistor 29 transistor

Claims (2)

  Control means for controlling the switching current supplied to the primary side of the transformer, and on when the voltage on the secondary output line of the transformer exceeds the specified voltage, on the secondary output line of the transformer A first switch means that is turned off when the voltage of the battery becomes equal to or lower than a specified voltage, and a charge / discharge means having a predetermined time constant connected to the secondary output line via a backflow prevention means, Charging / discharging means for performing charging when the first switching means is off and charging current is no longer supplied via the backflow preventing means, and charging / discharging means is connected to the first switching means. The second switch means turned off in response to the discharge current of the charge / discharge means when the first switch means is on, and turned off when the first switch means is turned off; 2 Sui An operation off means for turning off the operation of the control means in response to a discharge current of the charge / discharge means when the second switch means is on, and the secondary output line A third switch means connected to the first switch means, wherein the first switch means is turned on in response to a discharge current of the charge / discharge means when the first switch means is turned off; A switching power supply comprising: third switch means for discharging a secondary output line of the transformer.   The operation off means is arranged in an overvoltage detection current path of an overvoltage detection means that is connected to the secondary output line of the transformer and causes an overvoltage detection current to flow when an overvoltage on the secondary output line is detected. 2. The switching power supply according to claim 1, wherein when the overvoltage detection means detects an overvoltage, the operation of the control means is turned off in response to the overvoltage detection current.

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