JP2000236664A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To supply a required voltage accurately, when the secondary output is varied due to variation of load by making a switch from some high output to other low output, when the secondary output voltage lowers during power saving operation. SOLUTION: During normal operation of a circuit, a power supply voltage 1 is converted into an AC voltage through on/off operation of a switching circuit 2 and is supplied to the primary coil 4 of a transformer 3. Voltages induced in the secondary coils 5, 6 are rectified through diodes 7, 8, smoothed through capacitors 9, 10 and supplies, as first and second voltages V1, V2, to a load. During power save operation, the output voltage of the diode 8 is lowered, and the second voltage V2 becomes about 0V. The first voltage V1 is also lowered, and when it drops below a voltage set by a low voltage diode 13, an NPN type transistor 16 is turned off and, thereby an NPN transistor 17 is turned on by the first voltage V1 via a resistor 15. The dropped first voltage V1 is applied to a constant voltage circuit 19 and outputted as a second voltage V2.

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 and, more particularly, to a method for accurately supplying a required voltage from a high output to another low output when a secondary output voltage is reduced due to a power saving operation or the like. The present invention relates to a switching power supply.

[0002]

2. Description of the Related Art A conventional connection diagram is shown in FIG. In the prior art, a DC voltage 1 is supplied to a primary coil 4 of a transformer 3, and a switching circuit 2 is turned on and off to convert it into an alternating current. The voltages generated in a plurality of secondary coils 5, 6 are respectively rectified. And the second voltage lower than the first voltage B1 and the first voltage
Of the switching circuit 2 based on the detection signal to control the ON period of the switching circuit 2 to stabilize the output voltage. In a switching power supply device that switches to a power saving operation, a voltage detection circuit that detects a decrease in a first voltage B1 to a required voltage, and a voltage divider that divides a voltage of a first voltage line B1 based on a signal from the voltage detection circuit. And a circuit which supplies the voltage divided by the voltage dividing circuit to the second voltage line B2.

Here, in FIG. 5, 7 and 8 are diodes,
9, 10 are smoothing capacitors, 11 is a resistor, 13 is a constant voltage diode, 16 is an NPN transistor, 18 is a diode, 19 is a constant voltage circuit, 21 to 26 are resistors, 27 is a capacitor, 28 is a diode, and 29 is NPN. Reference numeral 30 denotes a PNP transistor, and 31 denotes a constant voltage diode.

[0004]

However, in this case, the voltage detection method and the constant voltage are not flexible and have little applicability. Also, the number of parts is large.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a switching power supply that supplies a necessary voltage with high accuracy when a secondary output voltage changes due to a load change such as a power saving operation. .

[0006]

In order to solve the above-mentioned problems, in the present invention, a DC voltage is supplied to a primary coil of a transformer, and a switching circuit is turned on / off to be converted into an alternating current. The voltages generated in the coils are rectified to obtain a first voltage V1 and a second voltage V lower than the first voltage.
2 to control the on-period of the switching circuit based on the detection signal to stabilize the output voltage based on the detection signal and stabilize the output voltage. In the switching power supply device, the voltage of the first voltage V1 is reduced to a required voltage, and the voltage of the first voltage V1 is supplied to the second voltage V2 based on a signal from the voltage detection circuit. It is something to do.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a switching power supply according to the present invention will be described below in detail with reference to the drawings.

(First Embodiment) FIG. 1 is a connection diagram showing a first embodiment of a switching power supply according to the present invention. In FIG. 1, 1 is a power supply, 2 is a switching circuit, 3 is a transformer, 4 is a primary coil, 5 and 6 are secondary coils, 7 and 8 are diodes, 9 and 10 are smoothing capacitors, 11 is a resistor, 13 is Constant voltage diodes, 14 and 15 are resistors,
16 and 17 are transistors, 18 is a diode, 19
Is a constant voltage circuit.

At the time of normal operation of the circuit, the power supply voltage 1 is converted into an alternating current by the on / off operation of the switching circuit 2, supplied to the primary coil 4 of the transformer 3, and the voltage induced in the secondary coils 5 and 6 is converted to a diode. Rectified by 7 and 8, respectively, smoothed by capacitors 9 and 10 and supplied to the load circuit as a first voltage V1 and a second voltage V2. The ON period of the ON / OFF of the switching circuit 2 is controlled by a detection signal that detects a change in the output voltage.

The NPN transistor 16 is turned on when a bias voltage is applied to the base thereof from the first voltage V 1 via the constant voltage diode 13 and the resistor 11, and the collector voltage becomes about 0 V. The NPN transistor 16 is biased by the resistor 15. The base voltage of the type transistor 17 becomes about 0 V and is off.

During a power saving operation or the like, the output voltage of the diode 8 decreases, and the second voltage V2 becomes about 0V. On the other hand, when the first voltage V1 also decreases and falls below the voltage set by the constant voltage diode 13, the NPN transistor 16 is turned off, whereby the NPN transistor 17 is turned on from the first voltage V1 via the resistor 15. Therefore, the reduced first voltage V1 is applied to the input of the constant voltage circuit 19, and is output as the second voltage V2. The diode 18 does not apply an excessive voltage to the diode 8 and the smoothing capacitor 10.

With such a circuit configuration, the constant voltage circuit 19 can be used effectively and the number of parts used can be reduced.

(Embodiment 2) FIG. 2 is a connection diagram showing Embodiment 2 of a switching power supply according to the present invention. The second embodiment is a circuit in which a resistor 12 is added to the connection diagram of FIG. 1 in FIG. In FIG. 2, the same reference numerals as those used in FIG. 1 indicate the same or corresponding components.

In FIG. 1 of the first embodiment, the detected voltage value is substantially determined by the constant voltage diode 13. That is,
The upper limit of the detected voltage is determined by the rating of the constant voltage diode 13. By adding the resistor 12, the limitation due to the rating of the constant voltage diode 13 can be eliminated, and the degree of freedom in element selection can be increased.

(Embodiment 3) FIG. 3 is a connection diagram showing Embodiment 3 of a switching power supply according to the present invention. The third embodiment is a circuit in which a constant voltage diode 20 is added to the connection diagram of FIG.
In FIG. 3, the same reference numerals as those used in FIG. 1 indicate the same or corresponding components.

In FIG. 1 of the first embodiment, by adding a constant voltage diode 20 to the base of the NPN transistor 17 used as a switch, the base voltage is made constant by the constant voltage diode 20. Becomes a constant voltage. Therefore,
Even when the constant voltage circuit 19 is omitted, it is possible to supply a highly accurate voltage, and the cost is reduced.

(Embodiment 4) FIG. 4 is a connection diagram showing Embodiment 4 of the switching power supply according to the present invention. Embodiment 4 is a circuit in which a constant voltage diode 20 is added to the connection diagram of FIG. 2 in FIG. In FIG. 4, the same reference numerals as those used in FIG. 1 indicate the same or corresponding components.

In the fourth embodiment, by combining the constant voltage diode 20 with the second embodiment, there is a synergistic effect of the effects of the second and third embodiments.

[0019]

As described above, according to the present invention,
When the secondary output voltage decreases during a power saving operation or the like, the second voltage V that is lower than the first voltage V1 with high accuracy from the first voltage V1
2 can be supplied.

[Brief description of the drawings]

FIG. 1 is a main part connection diagram of a power supply circuit according to a first embodiment of the present invention.

FIG. 2 is a main part connection diagram of Embodiment 2 of the power supply circuit according to the present invention.

FIG. 3 is a connection diagram of Embodiment 3 of the power supply circuit according to the present invention.

FIG. 4 is a connection diagram of a power supply circuit according to a fourth embodiment of the present invention.

FIG. 5 is a main part connection diagram of a conventional example.

[Description of Signs] 1 Power supply 2 Switching circuit 3 Transformer 4 Primary coil 5, 6 Secondary coil 7, 8 Diode 9, 10 Smoothing capacitor 11, 12 Resistance 13 Constant voltage diode 14, 15 Resistance 16, 17 NPN transistor 18 Diode Reference Signs List 19 constant voltage circuit 20 constant voltage diode 21, 22, 23, 24, 25, 26 resistor 27 capacitor 28 diode 29 NPN transistor 30 PNP transistor 31 constant voltage diode V1 first voltage V2 second voltage B1 first voltage ( 140V) B2 Second voltage (12V)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5G065 AA00 DA07 EA01 FA02 HA01 JA02 KA02 KA05 LA01 MA01 MA10 NA01 NA02 NA04 NA07 NA09 5H410 BB04 CC05 DD02 DD05 DD09 DD10 EB04 EB37 FF03 FF24 5H730 AA04 BB21 EE02 EE07

Claims (8)

[Claims] 1. A switching power supply device for converting a DC input into a predetermined voltage by a switching means and outputting the voltage,
A DC voltage is supplied to a primary coil of a transformer, voltages generated in a plurality of secondary coils are respectively rectified, and a first voltage and a second voltage lower than the first voltage are output, and a change in the output voltage is detected. A switching power supply device that controls the switching means based on the detection signal and switches operation under load conditions, a voltage detection circuit that detects a drop to the first voltage, and a signal from the voltage detection circuit. A switching circuit for switching the first voltage to a required voltage line based on the switching power supply. 2. The switching power supply device according to claim 1, wherein said voltage detection circuit and said switch circuit comprise a first N
The emitter of the PN transistor is connected to the ground, the first resistor is connected to the base, the anode is connected to the ground, the anode of the first constant voltage diode is connected from the base, the cathode is connected in series with the second resistor, and the first voltage is connected. And a collector connected to a third resistor connected to the first voltage line, a connection point connected to a base of a second NPN transistor, and a collector connected to the second NPN transistor. A first voltage line is connected, an emitter is connected to a cathode of the first diode, and an anode of the first diode is connected to an input of a first constant voltage circuit, and an anode of the first diode and a second diode for smoothing are connected. A switching power supply device characterized by being connected to one capacitor. 3. A switching power supply according to claim 1, wherein a fourth resistor is connected to a connection point between said second resistor and said first constant voltage diode, and
A switching power supply device characterized in that the resistance of the switching power supply is connected to the ground. 4. The switching power supply according to claim 1, wherein the first power supply is connected to the first power supply.
Instead of using the constant voltage circuit, a cathode of a third constant voltage diode is connected to the base of the second NPN transistor, the anode is connected to ground, and the voltage is made constant. apparatus. 5. The switching power supply according to claim 1, wherein the voltage detection circuit includes a constant voltage diode that is turned off when the first voltage becomes equal to or lower than a predetermined voltage, and the switch circuit includes the constant voltage diode. A switching power supply device, comprising: a switch element for applying the first voltage to the required voltage line when the diode is turned off. 6. The switching power supply according to claim 5, further comprising control means for controlling said predetermined voltage at which said constant voltage diode is turned off. 7. The switching power supply device according to claim 5, wherein the switch element includes a first switch element that is turned off when the constant voltage diode is turned off, and the first switch element. A switching power supply device comprising a second switch element that is turned on when turned off and applies the first voltage to the required voltage line. 8. A switching power supply according to claim 7, wherein said second switching element controls said second switching element so as to supply a predetermined constant voltage to said required voltage line. The switching power supply device characterized by being provided.