Switching Power Supply

Abstract

To provide a switching power supply that can suppress voltage drop of a non-voltage control type output circuit and can reduce a loss without receiving power supply from a voltage control type output circuit even if the non-voltage control type output circuit becomes a heavy-load, when the voltage control type output circuit is no-load or a light-load.SOLUTION: A switching power supply 1 is equipped with a transformer T that has a primary coil and a plurality of secondary coils, a switching element Q1 that is connected to the primary winding coil N1 of the transformer, a voltage control type output circuit 11 connected to at least one of the plurality of secondary coils N2 and N3, and a non-voltage control type output circuit 10 that is connected to the other secondary coil. The secondary coil of the transformer connected to the non-voltage control type output circuit has a plurality of coil output terminals with different generation voltage. The non-voltage control type output circuit can input induced voltage in the plurality of coil output terminals, and selectively supplies DC-converted voltage to a load on the basis of any of voltages induced in the plurality of coil output terminals according to the magnitude of the load.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a multiple-output switching power supply having a plurality of outputs, and more particularly to a switching power supply having a voltage-controlled output circuit that controls the output voltage and a non-voltage-controlled output circuit that does not control the output voltage. [Background technology]

[0002] Patent document 1 describes an invention in which a multi-output switching power supply has one output configured as a voltage-controlled output circuit and the other outputs configured as non-voltage-controlled output circuits, and in which power is supplied from the voltage-controlled output circuit to the non-voltage-controlled output circuit in order to stabilize the output voltage of the non-voltage-controlled output circuit.

[0003] Figure 6 is a circuit diagram of the conventional switching power supply described in Patent Document 1. This switching power supply includes a voltage-controlled output circuit that has a control circuit that rectifies and smoothes the voltage output from a winding P2 on the secondary side of a transformer and controls the voltage V1, and a non-voltage-controlled output circuit that rectifies and smoothes the voltage output from another secondary winding P3 and uses a constant voltage circuit IC1 to produce output voltage V3. In this switching power supply, a constant voltage adjustment circuit is connected between the voltage-controlled output circuit and the non-voltage-controlled output circuit, and when the output voltage of the non-voltage-controlled output circuit falls due to a heavy load on the output, current is passed from the voltage-controlled output circuit to the non-voltage-controlled output circuit via transistor Q2, increasing the voltage V2 of the non-voltage-controlled output circuit and stabilizing the input voltage of the constant voltage circuit IC1.

[0004] In other words, when the load connected to the voltage-controlled output circuit is unloaded or lightly loaded and does not fluctuate, the on period of the switching element Q1 controlled by the control circuit does not change. Therefore, when the output of the non-voltage-controlled output circuit is heavily loaded, the voltage of the secondary winding decreases and the output voltage V3 of the non-voltage-controlled circuit decreases. Therefore, when the voltage V2 of the non-voltage controlled output circuit falls below a value that satisfies a specified relationship, the constant voltage adjustment circuit operates to cause current to flow from the voltage controlled output circuit to the non-voltage controlled output circuit, thereby suppressing a decrease in the output voltage of the non-voltage controlled output circuit. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2002-272108 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, when power is supplied from the voltage-controlled output circuit to the non-voltage-controlled output circuit by the constant voltage adjustment circuit shown in FIG. 6, there is a problem in that the greater the difference between the voltage V1 of the voltage-controlled output circuit and the voltage V2 of the non-voltage-controlled output circuit, the greater the loss. For example, when this switching power supply is used as the power supply for a printer, the voltage V1 of the voltage-controlled output circuit is about 65 V, the voltage at which the printer operates, and the output voltage V3 of the non-voltage-controlled output circuit is about 5 V. If the current supplied from the voltage-controlled output circuit is 0.6 A, the loss in the constant voltage adjustment circuit will be the product of the voltage difference between voltages V1 and V2 and the supplied current, which is approximately 36 W, and becomes very large. [Means for solving the problem]

[0007] The present invention solves the above-mentioned problems by providing a switching power supply in which, rather than supplying power from a voltage-controlled output circuit to a non-voltage-controlled output circuit, a plurality of winding output terminals are provided on the secondary winding of a transformer, and a non-voltage-controlled output circuit is configured with the plurality of winding output terminals as inputs, and when the load on the circuit is small (light load), the non-voltage-controlled output circuit supplies power to the load using as its input a winding output terminal of the plurality of winding output terminals having a relatively low induced voltage, and when the load is large (heavy load), the non-voltage-controlled output circuit supplies power to the load using as its input a winding output terminal having a relatively high induced voltage.

[0008] That is, the present invention provides a multi-output switching power supply comprising a transformer having a primary winding and multiple secondary windings, a switching element connected to the primary winding of the transformer, a voltage-controlled output circuit connected to at least one of the multiple secondary windings, and a non-voltage-controlled output circuit connected to the other secondary windings, in which a switching voltage obtained by turning a DC voltage on and off with the switching element is applied to the primary winding of the transformer, and a voltage induced in the multiple secondary windings is output to a first load connected to the voltage-controlled output circuit and a second load connected to the non-voltage-controlled output circuit. a secondary winding of a transformer connected to a non-voltage controlled output circuit has a plurality of winding output terminals generating different voltages; the voltage controlled output circuit converts a voltage induced in the secondary winding of the transformer into a direct current, stabilizes it by a predetermined control circuit, and supplies it to a first load; and the non-voltage controlled output circuit is capable of inputting the voltages induced in the plurality of winding output terminals, and selectively supplies the DC voltage to the second load based on one of the voltages induced in the plurality of winding output terminals depending on the size of the second load.

[0009] With this configuration, even if the load on the non-voltage controlled output circuit increases, it is possible to suppress voltage drops by selecting the voltage induced at the winding output terminal without receiving power from the voltage controlled output circuit, and also to reduce circuit losses.

[0010] In addition, the non-voltage controlled output circuit is characterized in that, when the output voltage output to the second load is higher than a predetermined value, it connects to the terminal among the multiple winding output terminals with the lower induced voltage to supply it to the second load, and when the voltage of the second load drops below the predetermined value, it connects to the terminal with the higher induced voltage to suppress the voltage drop of the second load. With this configuration, even if the voltage of the non-voltage controlled output circuit drops, the voltage at the winding output terminal of the secondary winding can be switched to suppress a drop in the output voltage.

[0011] Furthermore, the non-voltage controlled output circuit is a circuit in which the output voltage for the second load is divided by a resistor and input to a voltage detection element, one end of the voltage detection element is connected to the control terminal of a voltage switching element, one terminal of a current path of the voltage switching element is connected to the winding output terminal having a higher induced voltage among the multiple winding output terminals, and the other terminal of the current path of the voltage switching element is connected to the terminal having a lower induced voltage among the multiple winding output terminals, wherein when the output voltage for the second load is higher than a predetermined value, a current flows through the voltage detection element and the voltage switching element is turned off, and a voltage is output to the second load based on the voltage from the winding output terminal having the lower induced voltage, and when the output voltage for the second load falls below the predetermined value, the current flowing through the voltage detection element is cut off and the voltage switching element is turned on, and a voltage is output to the second load based on the voltage from the winding output terminal having the higher induced voltage. In this way, by switching the voltages of the multiple winding output terminals using the voltage switching element, the non-voltage controlled output circuit can be configured as a circuit with little loss.

[0012] The voltage detection element is a shunt regulator, and the voltage switching element is an NPN transistor. This allows the induced voltage in the secondary winding to be switched in response to a voltage drop in the load. Effect of the Invention

[0013] By configuring as described above, the switching power supply of the present invention can automatically switch the voltage at the winding output terminal of the secondary winding when the load on the non-voltage controlled output circuit increases and the output voltage drops, thereby suppressing the drop in output voltage and reducing power loss. [Brief description of the drawings]

[0014] [Figure 1] 1 is a circuit diagram of a switching power supply according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a circuit diagram of a non-voltage controlled output circuit. [Diagram 3] 1A and 1B are diagrams illustrating the operation of a non-voltage controlled output circuit. [Figure 4] FIG. 13 is a diagram for explaining, for comparison, the output voltage switching operation of the prior art. [Diagram 5] FIG. 11 is a circuit diagram of another embodiment of a non-voltage controlled output circuit. [Figure 6] FIG. 1 is a circuit diagram of a conventional switching power supply described in Patent Document 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] A switching power supply according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of a switching power supply according to an embodiment of the present invention. This switching power supply 1 includes a switching element Q1 that switches a DC voltage Vin to convert the voltage, a transformer T having a primary winding N1 to which the converted switching voltage is supplied and two secondary windings, a first secondary winding N2 and a second secondary winding N3, a voltage-controlled output circuit 11 that converts the switching voltage induced in the first secondary winding N2 to a DC voltage using a DC conversion circuit (rectifier / smoothing circuit) consisting of a diode D1 and a smoothing capacitor C1, a control circuit 12 such as a control IC that controls the switching element Q1 so that the output voltage of the voltage-controlled output circuit 11 becomes a predetermined voltage, and a non-voltage-controlled output circuit 10 to which a plurality of voltages induced in the second secondary winding N3 are input.

[0016] The second secondary winding N3 has a plurality of winding output terminals which generate different voltages, and the plurality of winding output terminals are connected to the input of a non-voltage controlled output circuit 10. A first load is connected to the output of the voltage controlled output circuit 11, and a second load is connected to the output of the non-voltage controlled output circuit 10. The control circuit 12 is a well-known circuit that controls the on / off cycle of the switching element Q1 so that the output voltage V1 of the voltage controlled output circuit 11 becomes a predetermined voltage value. The DC voltage Vin may be a DC voltage obtained by rectifying and smoothing a commercial AC power supply voltage, or may be a DC voltage based on power generated by a power generating means such as a solar cell.

[0017] FIG. 2 is a circuit diagram of the non-voltage controlled output circuit 10. As shown in FIG. The winding output terminal at the end of the secondary winding N3 of the transformer T (hereinafter referred to as the "end terminal") is connected to the anode of the diode D2, the winding output terminal from the middle of the secondary winding N3 (hereinafter referred to as the "center tap") is connected to the anode of the diode D3, and the start of the secondary winding is connected to GND. In other words, the voltage V2 at the end terminal is higher than the voltage V3 at the center tap.

[0018] The cathode of diode D2 is connected to the collector (one terminal of the current path) of transistor Q1 (corresponding to the "voltage switching element" of the present application) and one end of resistor R1. The voltage on the cathode side of diode D2 (collector voltage of transistor Q1) is V2. The cathode of diode D3 is connected to the emitter (the other terminal of the current path) of transistor Q1 and is output to a second load. In this case, the voltage on the cathode side of diode D3 (emitter voltage of transistor Q1) V3 and the output voltage of non-voltage controlled output circuit 10 (output voltage output to the second load) Vo are the same.

[0019] The base (control terminal) of transistor Q1 is connected to the other end of resistor R1 and one end of resistor R2. The other end of resistor R2 is connected to the cathode of shunt regulator U1 (corresponding to the "voltage detection element" of this application). The reference terminal of shunt regulator U1 is connected to the connection point of resistors R3 and R4 that are connected in series between the output terminal of non-voltage controlled output circuit 10 and GND. The anode of shunt regulator U1 is connected to GND. The voltage V2 on the cathode side of diode D2 and the voltage V3 on the cathode side of diode D3 are the induced voltages output to the winding end terminal and center tap minus the voltage drops of diodes D2 and D3. In addition, a capacitor C2 is connected between the cathode of diode D3 and GND.

[0020] The operation of the non-voltage controlled output circuit 10 configured as above will be described. In the shunt regulator U1, the voltage at the connection point between resistors R3 and R4 (the voltage obtained by dividing the output voltage Vo by resistors R3 and R4) is input to the reference terminal of the shunt regulator U1, the input voltage to the reference terminal is compared with a reference voltage inside the shunt regulator U1, and when the input voltage to the reference terminal is high, current flows through the shunt regulator U1 and its function as a switch is turned on (the shunt regulator U1 is conductive).

[0021] When the output voltage Vo output to the second load is higher than a predetermined value, the shunt regulator U1 turns on, and a current flows from the winding output terminal where the induced voltage of the secondary winding N3 of the transformer T is relatively high, via the diode D2, resistor R1, and resistor R2. When a current flows, the base voltage of the transistor Q1 falls below the emitter voltage V3 due to the voltage drop caused by resistor R1, and the transistor Q1 turns off. At this time, no current flows from the cathode (voltage V2) of the diode D2 to the cathode (voltage V3) of the diode D3, so the voltage V3 becomes the output voltage Vo as it is and is output to the load (second load).

[0022] On the other hand, when the second load becomes large and the output voltage Vo falls below a predetermined value, the voltage divided by resistors R3 and R4 also falls, and the input voltage of the reference terminal of the shunt regulator U1 falls below the reference voltage. Then, the switch function of the shunt regulator U1 turns off (the shunt regulator U1 becomes non-conductive). As a result, no voltage drop occurs due to the shunt regulator U1 of the resistor R1, so the base voltage becomes higher than the emitter voltage V3 of the transistor Q1, and the transistor Q1 turns on. A current flows from the cathode (voltage V2) side of the diode D2 to the cathode (voltage V3) side of the diode D3 via the transistor Q1. As a result, the drop in voltage V3 is suppressed, and voltage V2 is output to the load as the output voltage Vo. In this case, the output voltage Vo is not, strictly speaking, voltage V2, but the voltage obtained by subtracting the collector-emitter voltage of transistor Q1 from voltage V2.

[0023] In other words, when the load on the non-voltage controlled output circuit 10 is small (light load), the voltage of the winding output terminal where the induced voltage of the secondary winding N3 is relatively low is output to the load, and when the load on the non-voltage controlled output circuit is large (heavy load), the voltage of the winding output terminal where the induced voltage of the secondary winding N3 is relatively high is output to the load. Here, the predetermined value of the output voltage Vo is a voltage value determined by the reference voltage value inside the shunt regulator U1 and the resistance values ​​of the resistors R3 and R4, i.e., the predetermined value = (R3 + R4) / R4 × reference voltage value.

[0024] FIG. 3 is a diagram for explaining the operation of the non-voltage controlled output circuit 10. The horizontal axis is the output current of the second load, and the vertical axis is the voltage. Voltage V1 indicated by the dashed line is the output voltage V1 of the voltage-controlled output circuit 11 shown in FIG. 1. A continuous curve in which the voltage gradually decreases as the output current increases (shown by a dotted line, but shown by a solid line in the region where the output current is large) is voltage V2, and a continuous curve in which the voltage gradually decreases as the output current increases and whose voltage value is smaller than V2 (shown by a dotted line, but shown by a solid line in the region where the output current is small) is voltage V3. The curve in which the voltage becomes constant at point A from the solid line portion of voltage V3 and then switches to the solid line portion of voltage V2, i.e., a curve consisting only of solid lines with a straight line inserted in the middle, indicates the output voltage Vo to the second load.

[0025] At point A, the output voltage Vo does not immediately switch to voltage V2 but remains constant (a predetermined value) because the shunt regulator U1 operates to keep the output voltage Vo constant. When the output current increases further and voltage V2 drops, the shunt regulator U1 turns off completely, which turns on the transistor Q1 and outputs voltage V2 as is to the second load. In both curves, the voltage decreases as the output current increases. The turns ratio of the secondary winding N3 is set so that the voltage V2 is about 10 to 15% higher than the voltage V3.

[0026] Point A in Figure 3 is the point in time when the output current becomes constant when the output voltage Vo becomes a constant value (for example, 0.1 A). Here, the output voltage Vo is maintained at a constant value from voltage V3 and then switches to voltage V2. Because transistor Q1 is not operating at the output current up to point A, there is no power loss regardless of the output current value. When the output current increases and exceeds point A, transistor Q1 operates, and after maintaining a constant value, it switches to voltage V2 and the output voltage Vo also decreases. For example, when the output current is 0.6 A (corresponding to point B of voltage Vo in Figure 3), the loss of non-voltage controlled output circuit 10 is 0.30 W if the difference between voltages V2 and V3, which are the voltages applied between the collector and emitter of transistor Q1, is 0.5 V.

[0027] The losses in the non-voltage controlled output circuit 10 of this embodiment are compared with the losses in the conventional circuit shown in FIG. Figure 4 is a diagram for explaining, for comparison, the switching operation of the output voltage of the conventional technology shown in Figure 6. The horizontal axis is the output current, and the vertical axis is the voltage, which is the same as in Figure 3. The dashed line and the dashed dotted line in Figure 4 are voltage V1 and voltage V3 shown in Figure 6, and the solid line, which becomes a constant value at point A after the voltage decreases with an increase in the output current, is voltage V2. For example, if the output currents at points A and B in Figure 4 are 0.1A and 0.6A, the same as in Figure 3, and if voltage V1 is 65V and voltage V3 is 5V, then there will be no loss in the constant voltage adjustment circuit at point A, but at point B, the loss will be the product of the difference between voltage V1 and voltage V3 (60V) and the output current of 0.6A, which is 36W. Compared to the losses in the prior art constant voltage regulator circuits, the losses in the non-voltage controlled output circuit 10 of the present invention are significantly reduced.

[0028] It should be noted that the non-voltage controlled output circuit 10 shown in FIG. 2 does not include the constant voltage circuit IC1 shown in FIG. 6, but may include a constant voltage circuit. Moreover, although the voltage switching element is configured with an NPN transistor, a MOSFET may also be used.

[0029] Fig. 5 is a circuit diagram of another embodiment of a non-voltage controlled output circuit. Compared to Fig. 2, the element U2 (voltage detection element) that detects a drop in the output voltage and outputs it to the transistor Q1 is different, but since the other configurations are the same, the specifications of the elements such as resistors of the non-voltage controlled output circuit 20 are the same. This element U2 can use a comparator that compares a terminal that detects a drop in the output voltage Vo with a reference voltage, and is configured so that when the voltage drops, the output of the comparator operates the transistor Q1.

[0030] In this embodiment, the secondary windings are two, the first secondary winding N2 and the second secondary winding N3, but the number of secondary windings may be three or more. In this case, a voltage-controlled output circuit is connected to one of the secondary windings, and a non-voltage-controlled output circuit is connected to the other secondary winding, and the present invention can be applied to at least one of the non-voltage-controlled output circuits connected to the other secondary windings. [Explanation of symbols]

[0031] 1...Switching power supply, 10...Non-voltage controlled output circuit, 11...Voltage controlled output circuit, 12...Control circuit, 20...Non-voltage controlled output circuit.

Claims

1. A multi-output switching power supply comprising a transformer having a primary winding and a plurality of secondary windings, a switching element connected to the primary winding of the transformer, a voltage controlled output circuit connected to at least one of the plurality of secondary windings, and a non-voltage controlled output circuit connected to another secondary winding, wherein a switching voltage obtained by turning a DC voltage on / off with the switching element is applied to the primary winding of the transformer, and a voltage induced in the plurality of secondary windings is output to a first load connected to the voltage controlled output circuit and a second load connected to the non-voltage controlled output circuit, a secondary winding of the transformer connected to the non-voltage controlled output circuit has a plurality of winding output terminals each having a different generated voltage; the voltage controlled output circuit converts a voltage induced in the secondary winding of the transformer into a direct current, stabilizes the direct current by a predetermined control circuit, and supplies the direct current to the first load; the non-voltage controlled output circuit is capable of inputting voltages induced in the plurality of winding output terminals, and selectively supplies to the second load a voltage that has been converted to DC based on one of the voltages induced in the plurality of winding output terminals depending on the magnitude of the second load; detects an output voltage to be output to the second load, and when the output voltage is higher than a predetermined value, connects to the winding output terminal having the lower induced voltage among the plurality of winding output terminals, and when the output voltage falls below the predetermined value, connects to the winding output terminal having the higher induced voltage; The non-voltage controlled output circuit is a circuit in which an output voltage to be output to the second load is divided by a resistor and input to a voltage detection element, one end of the voltage detection element is connected to a control terminal of a voltage switching element, one terminal of a current path of the voltage switching element is connected to a winding output terminal having a high induced voltage among the plurality of winding output terminals, and the other terminal of the current path of the voltage switching element is connected to a winding output terminal having a low induced voltage among the plurality of winding output terminals, a switching power supply comprising: when an output voltage output to the second load is higher than a predetermined value, a current flows through the voltage detection element, the voltage detection element is turned on and the voltage switching element is turned off, and a voltage is output to the second load based on the voltage from the winding output terminal having the low induced voltage; and when the output voltage output to the second load falls below a predetermined value, the current flowing through the voltage detection element is interrupted, the voltage detection element is turned off and the voltage switching element is turned on, and a voltage is output to the second load based on the voltage from the winding output terminal having the high induced voltage.

2. the voltage detection element is a shunt regulator, 2. The switching power supply according to claim 1, wherein the voltage switching element is an NPN transistor.

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