JPH11262262A - Power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify the structure of a transformer. SOLUTION: A plurality of secondary windings 34 and 35 are provided to a transformer, and at the same time, a dropper circuit 45 having a current source 47 is provided to stabilize the output of a rectifying and smoothing circuit 42 of the winding 35, and a voltage monitoring circuit 52 which monitors the voltage at the current input section to which the electric current supplied to the dropper circuit 45 is supplied by a circuit B, which supplies the electric current to the dropper circuit 45 and outputs an input voltage monitor signal upon detecting the drop in the input voltage.

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 for generating a plurality of DC voltages from an input DC voltage.

[0002]

2. Description of the Related Art Conventionally, a power supply device shown in FIG. 4 is used for a motor, an IC logic circuit and the like. In FIG. 4, a DC voltage is applied to the primary winding 1, the DC voltage of the primary winding 1 is converted into an AC voltage by a switching circuit 2, and an induced electromotive force is applied to the secondary windings 3, 4, 5. Occurs. The switching circuit 2 includes the FET 6 and the FE
And a controller 7 for controlling T6.

The secondary windings 3, 5 are wound so as to generate an electromotive force out of phase with the secondary winding 4, and the secondary windings 3, 4, 5 are respectively provided with diodes. 8, 9,
10 and smoothing capacitors 11, 12, 13 are connected. The voltage smoothed by the capacitors 11 and 13 is
The voltage is converted into a predetermined voltage by the output terminal 14 and the constant voltage control element 17 and output from the output terminal 18. The voltage smoothed by the capacitor 12 is input to the voltage monitoring circuit 15. The ground terminal 19 of the secondary winding 3 includes a ground wire 20 of the voltage monitoring circuit 15, a ground terminal 21 of the secondary winding 4,
The ground terminal 22 of the secondary winding 5 is connected.

The secondary winding 4 is wound so that the rectifying element 9 conducts when the FET 6 is turned on.
The voltage of the capacitor 12 is a voltage that is twice the turns ratio of the input voltage Vin of the power supply device. Therefore, by monitoring the voltage of the capacitor 12 by the voltage monitoring circuit 15,
An input voltage monitoring signal for notifying a drop in the input voltage Vin or a power failure can be output from the voltage monitoring circuit 15.

[0005]

However, in this switching power supply device, it is necessary to provide the secondary winding 4 that conducts when the FET 6 is on in order to monitor the fluctuation of the input voltage of the power supply device. Therefore, there is a problem that the transformer structure is complicated and circuit components for generating the detection voltage are increased.

The power supply device of the present invention focuses on such a problem. When a plurality of outputs are provided on the secondary winding side, a secondary winding dedicated to monitoring the input voltage of the power supply device is provided. An object of the present invention is to prevent the transformer structure from becoming complicated and increasing the number of circuit components without providing them.

[0007]

According to a first aspect of the present invention, there is provided a power supply apparatus comprising: a power supply device configured to perform switching control of power supplied to a primary winding of a transformer; In the power supply device, which generates an induced electromotive force in the winding and feeds back the fluctuation of the output of the secondary winding to the switching control of the primary winding, thereby stabilizing the fluctuation of the output of the secondary winding. The transformer is provided with a plurality of secondary windings, and another secondary winding is connected to a rectified and smoothed output terminal of one of the plurality of secondary windings. A dropper circuit is provided which is supplied with a current from a rectified and smoothed output terminal of the wire and stabilizes an output of the one secondary winding, and an output terminal of the other secondary winding is connected to the dropper circuit. In the circuit that supplies the current,
A voltage monitoring circuit for monitoring a voltage of a current input section supplied to the dropper circuit and outputting an input voltage monitoring signal is provided.

[0008] The power supply according to claim 2 of the present invention is based on claim 1.
Wherein the output terminal of the one secondary winding is constituted by a regulator IC having a function similar to that of the dropper circuit.

[0009]

Next, a power supply according to a preferred embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a circuit of a switching power supply according to a first embodiment. A primary winding 30 includes a smoothing capacitor 31 and an FET 3.
2. The controller 33 is connected. Secondary windings 34 and 35 are provided on the secondary side of the transformer.

A rectifying / smoothing circuit 38 is formed in the secondary winding 34 by a diode 36 and a smoothing capacitor 37, and power is supplied from an output terminal 39 of the rectifying / smoothing circuit 38 to a load such as a microcomputer or a motor interface. It has become.

A rectifying and smoothing circuit 42 is formed in the secondary winding 35 by a diode 40 and a smoothing capacitor 41.
A dropper circuit 4 is provided between the rectifying and smoothing circuit 42 and the output terminal 43.
5 are provided.

The dropper circuit 45 includes a transistor 46, a constant current source 47, a constant voltage IC 48, and resistors 49 and 50. The cathode of the diode 40 is connected to the collector of the transistor 46, and the emitter of the transistor 46 is connected to the output terminal 43. Transistor 46
The output terminal of the constant current source 47 and the constant voltage IC 48
Input terminals are connected. A reference voltage is applied to the constant voltage IC 48 from a voltage dividing circuit composed of resistors 49 and 50. The input side of the constant current source 47 and the output terminal 39 of the secondary winding 34 are connected by a resistor 51, and a circuit B connecting the constant current source 47 and the output terminal 39
Is a circuit for supplying a current from the output terminal 39 to the dropper circuit 45. The voltage at point A between the resistor 51 and the constant current source 47 is monitored by a voltage monitoring circuit 52.

The voltage monitoring circuit 52 monitors a drop in the input side voltage of the power supply device based on the voltage fluctuation at the input side point A of the constant current source 47. That is, when the input voltage Vin of the power supply decreases due to a power failure or the like, the input voltage of the dropper circuit 45 also decreases, and the current of the constant current source 47 increases so that the voltage of the output terminal 43 does not fall below the specified value. I do.
When the current of the constant current source 47 increases, the voltage at the point A decreases, and the voltage monitoring circuit 52 detects this voltage decrease and outputs an input voltage monitoring signal. At this time, the dropper circuit 4
5 operates so that the current of the constant current source 47 increases to a specified value accuracy. Therefore, before the output of the dropper circuit 45 falls below the specified value, the power failure detection signal is output by a simple method. Can output.

[Second Embodiment] FIG. 2 shows a circuit according to a second embodiment of the present invention. In the second embodiment, a regulator IC 60 having the same function as the dropper circuit 45 is provided at the output terminal 43 of the secondary winding 35 instead of the dropper circuit 45, and the voltage monitoring circuit 61 is connected to the resistor 6
2, 63, a transistor 64, and a resistor 65. In the voltage monitoring circuit 61, the voltage drop at the point A is output by a voltage dividing circuit composed of resistors 62 and 63, using the base voltage of the transistor 64 as a reference value to output an input voltage detection signal.

[Third Embodiment] FIG. 3 shows a circuit according to a third embodiment of the present invention. The circuit of the third embodiment is a further modification of the circuit configuration of the second embodiment. A constant voltage diode 71 is provided in place of the resistor 62 of the voltage monitoring circuit 61, and the voltage monitoring circuit 70 is connected to the constant voltage diode 71. , A resistor 63, a transistor 64, and a resistor 65.

With this configuration, when a voltage drop occurs at point A, which is a current input terminal of the regulator IC 60, due to a drop in input voltage, the constant voltage diode 71 of the voltage monitoring circuit 70 becomes non-conductive. , A voltage drop is detected, and an input voltage monitoring signal is output.

[0018]

According to the power supply device of the first and second aspects of the present invention, the decrease in the input voltage of the power supply device appears as a change in the supply current to the dropper circuit or the regulator IC having the same function. The change is a voltage change at the current input section of the dropper circuit or the regulator IC.
Voltage monitoring circuit is dropper circuit or regulator IC
The input voltage monitoring signal is output by detecting a voltage change at the current input unit to the input terminal.

Therefore, when detecting a drop in the input voltage of the power supply device or a power failure on the secondary side of the transformer, it is not necessary to provide a secondary winding dedicated to monitoring the input voltage, which complicates the structure of the transformer and reduces circuit components. Increase can be suppressed.

[Brief description of the drawings]

FIG. 1 is a switching power supply circuit showing a configuration of a first embodiment of the present invention;

FIG. 2 is a switching power supply circuit showing a configuration of a second embodiment of the present invention;

FIG. 3 is a switching power supply circuit showing a configuration of a third embodiment of the present invention;

FIG. 4 shows a conventional switching power supply circuit.

[Explanation of symbols]

 Reference Signs List 30 primary winding 32 FET 33 controller 34 secondary winding (one of plural secondary windings) 35 secondary winding (two or more secondary windings) 45 dropper circuit 51 resistance 52 voltage Monitoring circuit A Input side point of the constant current source of the dropper circuit B Circuit that supplies current from the output terminal to the dropper circuit

Claims (2)

[Claims] 1. A switching control of electric power supplied to a primary winding of a transformer to generate an induced electromotive force in a secondary winding of the transformer, and a change in output of the secondary winding is controlled by the primary side. Feedback to the winding switching control,
In the power supply device for stabilizing the output fluctuation of the secondary winding, the transformer is provided with a plurality of secondary windings, and one of the plurality of secondary windings is a secondary winding. A dropper circuit that is supplied with current from the rectified and smoothed output terminal of another secondary winding to stabilize the output of the one secondary winding is provided at the rectified and smoothed output terminal of the wire, A voltage monitoring circuit that monitors a voltage of a current input unit supplied to the dropper circuit and outputs an input voltage monitoring signal to a circuit that supplies current to the dropper circuit from an output terminal of the other secondary winding. A power supply device characterized by being provided. 2. The power supply device according to claim 1, wherein an output terminal of said one secondary winding is constituted by a regulator IC having a function similar to that of said dropper circuit. Power supply.