JP2000308338A - Switching power unit and peripheral equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce power loss of a self-exciting switching power unit provided with a starting resistor, while the power unit is in a standby or turned-off state. SOLUTION: In a switching power unit 1, a thyristor 33 is connected in series with a starting resistor which impresses a starting voltage upon a gate electrode 11G of a switching element 11, and the gate electrode 33G of the thyristor 33 is connected to an output side 3a of a rectifying circuit 3. When AC power is supplied or a switch is turned on the secondary side, the thyristor 33 is turned on which the rush current of the rectifying circuit 3. When the thyristor 33 is turned on, the power unit 1 is started, because the switching element 11 is turned on. Since the anode of the thyristor 33 is connected to the AC side, the thyristor 33 is turned off the current flowing to the starting resistor can be interrupted, when the current flowing to the thyristor becomes zero or is inverted as the AC phase advances. Therefore, the power consumption of the power unit 1 can be reduced, when the unit 1 is in a turned-off or standby state.

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 suitable for a power supply of a peripheral device such as a printer.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram showing a general configuration of a switching power supply which is frequently used as a power supply for a peripheral device such as a printer. The switching power supply device 90 includes a rectifier circuit 3 that rectifies the AC power supplied from the AC power supply 2 with the diode 5, and a rectifier circuit 3.
And a switching circuit 10 that performs switching (chopping) by the switching element 11 on the output current to control the output power and that functions as a constant voltage or constant current power supply. The switching circuit 10 of the switching power supply device 90 shown in FIG. 7 has a function as a constant voltage power supply for keeping the output voltage constant. For this reason, the output chopped by the switching element 11 is supplied to the primary side of the transformer 12 and the transformer 1
2 is detected by the voltage detection circuit 13. Then, the output of the voltage detection circuit 13 is supplied to the switching control circuit 15 via the photocoupler 14,
The switching element 11 is controlled by a method such as PWM or PFM.

[0003] A secondary voltage control circuit 20 is further connected to the secondary side of the transformer 12. The secondary side output is rectified to control electric power for controlling a predetermined voltage, for example, 42 V and 5 V, or a motor. It is output to the consumer side as drive power.

Further, the switching power supply 90 shown in FIG.
0 is a self-excited power supply that starts and functions as a constant voltage power supply. For this purpose, an activation circuit 30 for activating the switching element 11 is provided. Apparatus 90 shown in FIG.
Then, an N-channel type M is used as the switching element 11.
An OSFET is employed, and the gate electrode 11G is connected to the output side 3a of the rectifier circuit 3 via the starting resistor 31.

In the switching power supply device 90, first, when AC power is supplied to the rectifier circuit 3, a current flows through the rectifier circuit 3 to charge the smoothing capacitor 4 and the like. Therefore, by connecting the gate electrode 11G, which is the control electrode of the switching element 11, to the output side 3a of the rectifier circuit 3, a gate voltage is generated, and when the voltage exceeds a threshold, the switching element 11 is turned on. As a result,
The output of the rectifier circuit 3 is supplied to the primary side of the transformer 12,
A voltage is generated on the secondary side of the transformer. Transformer 12-2
On the secondary side, a winding 12b for supplying power to the switching control circuit 15 is provided in addition to the winding 12a for supplying power to the secondary voltage control circuit 20, and the switching control circuit 15 also starts operating. Thereafter, the switching element 1
The control of 1 is transferred to the switching control circuit 15, and the switching element 11 is controlled so that the secondary voltage control circuit 20 can supply a constant voltage power even when the power consumption fluctuates.

[0006]

As described above, the switching power supply device 90 shown in FIG. 7 starts its operation spontaneously by turning on and off the supply of an alternating current to supply electric power of a predetermined voltage to a motor or the like. Can be supplied to consumers. However, the circuit of the gate electrode 11 has a resistor 19 for overvoltage protection.
Grounded. For this reason, even after the switching power supply is activated and the control of the switching element 11 is transferred to the switching control circuit 15, the output side of the rectifier circuit 3 is connected to the gate electrode 11G of the switching element 11 via the activation resistor 31. I have. Therefore, a constant current always flows to the ground, but since this power is several mA or less, it has been almost neglected conventionally.

In recent years, power saving has become an even more important issue in peripheral devices such as printers. In a peripheral device such as a printer, the standby time in which the power is on but the job is not performed is much longer than the time in which the job is actually executed. For this reason, a power saving mode in which power supply to unnecessary sections is stopped during standby is generally performed. However, although the power consumption at the starting resistance of the switching power supply device as described above has not been studied, the inventors of the present application also consider that the power loss due to the starting resistance is very important for reducing the power consumption. We paid attention to that.

[0008] For this reason, the inventors of the present application first, FIG.
As shown in the figure, the starting resistor 31 is connected to the input side 3 of the rectifier circuit 3.
b, that is, connection to the AC side was considered. As a result, the period during which the switching element 11 is turned on is halved, so that the loss in the starting resistor 31 is １ ／ of that when the rectifier circuit 3 is connected to the output side 3 a. However, the loss still occurs in the starting resistor 31, and it is necessary to further reduce the loss in the starting resistor 31. In particular, when the switching power supply is a universal power supply, an alternating current whose maximum value is close to 400 V is applied, so that the loss in the starting resistor 31 is about 1 W. Therefore, suppressing the loss of the starting resistor 31 is very effective in reducing power consumption in the standby state.

Further, there is a peripheral device that switches off on the secondary side of the switching power supply device 90. In such a device, when the loss in the starting resistor 31 is in a standby state, the device is connected to an AC power supply. During this period, the alarm is permanently generated regardless of the on / off state of the secondary switch.

As described above, the inventors of the present application have found that the power loss due to the starting resistor, which has been neglected in the past, is a very large problem in peripheral devices. Therefore,
An object of the present invention is to provide a switching power supply that can further reduce the loss in the starting resistance of the switching power supply.

[0011]

Therefore, in the present invention, after a starting voltage is applied to a starting circuit of a switching element, a current flowing through a starting resistor is positively limited. That is, the switching power supply device of the present invention includes a rectifier circuit for rectifying AC, a switching circuit capable of controlling output power by chopping a current output from the rectifier circuit by a switching element, and rectifying a control electrode of the switching element. A starting circuit connected to an input side or an output side of the circuit via a starting resistor and capable of applying a starting voltage, wherein the starting circuit, after applying the starting voltage,
It is characterized by comprising a power limiting means capable of limiting a current flowing through the starting resistor. If the current flowing through the starting resistor is positively limited, not only power consumption in the standby state can be reduced, but also power consumption at the time of switch-off can be reduced in a device that is turned off by the switch on the secondary side.

As the power limiting means, it is most desirable to use a switch which can be turned on / off at an appropriate timing and which can cut off the current flowing through the starting resistor after starting. However, if a function or a circuit that constantly monitors appropriate timing for operating the switch is mounted, there is a problem that the cost is increased and power is consumed for operating the function for monitoring and operating the switch.

Therefore, it is desirable to connect the starting resistor to the input side of the rectifier circuit, that is, to the AC side, and to use a thyristor as the power limiting means. Although several thyristor control methods have been proposed, first, the gate electrode of the thyristor can be connected to the output side of the rectifier circuit. When an alternating current is supplied or a switch is turned on on the secondary side, an inrush current is generated because the smoothing capacitor and the like of the rectifier circuit 3 are charged. If the voltage generated at the gate electrode of the thyristor by this inrush current exceeds the threshold value, the thyristor is turned on, so that a current flows through the starting resistor and the switching element is turned on. On the other hand, since the thyristor is connected to the AC side, when the AC voltage becomes zero or inverted, conduction between the anode and the cathode of the thyristor ends. As a result, the thyristor turns off, and no current flows through the starting resistor.

It is also effective to connect the gate electrode of the thyristor to the input side of the rectifier circuit, that is, to the AC side. In this case, an AC voltage is applied to the gate electrode of the thyristor, and when the threshold voltage is exceeded, the thyristor turns on, a current flows through the starting resistance, and the switching element turns on. Also in this case, when the AC voltage becomes zero or inverted, conduction between the anode and the cathode of the thyristor ends, and the thyristor turns off, so that no current flows through the starting resistor. Therefore, the time during which the AC current flows through the starting resistor can be shorter than when the starting resistor is simply connected to the AC side.
Further, by connecting the gate electrode of the thyristor to the input side of the rectifier circuit with an appropriate phase shift circuit, the conduction time can be adjusted by delaying the phase of the voltage applied to the gate electrode. Therefore, the power flowing through the starting resistor can be further reduced.

Therefore, by employing the switching power supply according to the present invention as a power supply for a peripheral device such as a printer, power consumption in a standby state can be further reduced. Further, in the peripheral device of the type that is turned off by the secondary switch, the power consumed at all times can be reduced, and a great power saving effect can be obtained when the device is turned off and in the standby state.

[0016]

FIG. 1 shows an example of a switching power supply according to the present invention. The switching power supply device 1 shown in FIG. 1 includes a rectifier circuit 3 for rectifying AC power supplied from an AC power supply 2 and a switching device for switching a current output from the rectifier circuit 3, similarly to the switching power supply device shown in FIG. A switching circuit for controlling output power by chopping with the element. Since these components are the same as those of the switching power supply device shown in FIG. 7, the same reference numerals are given below, and detailed description is omitted. The switching power supply device 1 of the present embodiment is also a self-excited switching power supply device. For this reason, a starting circuit 30 having a starting resistor 31 is provided.
A start-up voltage can be applied to the gate electrode 11G.

In the starting circuit 30 of this embodiment, in addition to the starting resistor 31, a switch 32 capable of turning on and off a current flowing through the starting resistor 31 is connected in series with the starting resistor 31. Therefore, by turning on the switch 32 before activating the switching power supply 1, the switching element 11 is turned on when AC is supplied, and the switching power supply 1 starts operating. On the other hand, by turning off the switch 32 at an appropriate timing after the switching power supply device 1 is started, the current flowing from the starting resistor 31 to the ground via the resistor 19 can be cut. Therefore, once started, the loss due to the starting resistor 31 when the switching power supply device 1 is in the standby state can be eliminated.

In this embodiment, the starting resistor 31 is connected to the AC side which is the input side 3b of the rectifier circuit 3. However, even when the starting resistor 31 is connected to the output side 3a, the switch 3 is similarly connected.
2, the loss due to the starting resistor 31 can be reduced.

Further, in the switching power supply 1, the power supply can be turned on / off by a switch on the secondary side. In this case, when the switch on the secondary side is off, the switch 32 of the starting circuit 30 is also turned off. By doing
It is possible to eliminate not only the power loss in the standby state but also the power loss when the switching power supply device 1 is off. In this case, a timing for turning on the switch 32 of the starting circuit 3 is required. However, when an alternating current is supplied or the secondary side is turned on, a current for charging the smoothing capacitor 4 and the like of the rectifier circuit 3 flows. Therefore, the switch 32 can be turned on by the current. Or 2
The switch 32 of the starting circuit 30 is operated in conjunction with the switch on the next side.
May be turned on.

However, the switching power supply 1 shown in FIG. 1 requires a circuit for controlling the switch 32 of the starting circuit 30 at an appropriate timing. In contrast,
In the example of the switching power supply device 1 shown in FIG. 2, the current flowing through the starting resistor 31 of the starting circuit 30 can be automatically cut off.

In the switching power supply device 1 shown in FIG. 2, a thyristor 33 is connected in series with the starting resistor 31, and the anode side of the thyristor 33 is connected to the input side 3b of the rectifier circuit 3, that is, the AC side. I have. Further, the gate electrode 33 </ b> G of the thyristor 33 is connected to the output side 3 a of the rectifier circuit 3. In the switching power supply 1 of the present example, an alternating current is supplied,
When the next switch is turned on, a current flows through the smoothing capacitor 4 or the coil of the transformer 12 and the like, and the current is output from the rectifier circuit 3 instantaneously. Then, this rush current flows as a base current via the gate electrode 33G of the thyristor 33. As a result, when the voltage of the gate 33G exceeds the threshold value, the thyristor 33 turns on, and the starting voltage is applied to the switching element 11 via the starting resistor 31. Therefore, the switching element 11 is turned on, and the switching power supply device 1 starts automatically.

Once activated, the thyristor 33 does not turn off unless the current flowing through the thyristor 33 becomes zero or negative. In the switching power supply device 1 of the present embodiment, since the thyristor 33 is connected to the AC side, that is, the input side 3b of the rectifier circuit 3, even if the thyristor 33 is turned on once, the AC phase advances and the thyristor 33 is applied to the thyristor 33. Since the applied voltage is 0 or inverted, conduction between the anode and the cathode of the thyristor 33 disappears, and the thyristor 33 turns off. Therefore, after the switching power supply device 1 is started, the current flowing through the starting resistor 31 can be cut off.

As described above, in the switching power supply device 1 of the present embodiment, power loss due to the starting resistor 31 can be prevented with a simple configuration without providing a timing generation circuit for operating switches. Therefore, it is possible to provide a switching power supply device that is low in cost and has little power loss in the standby state or the off state.
As described above, the power loss due to the starting resistor 31 is generally not large. However, in the case of a 220V-compatible universal power supply mounted on a peripheral device such as a printer, an AC having a maximum voltage of approximately 400V is applied, and accordingly, the power loss is in watts. Further, a peripheral device such as a printer spends much longer time in a standby state or an off state than a time period in which a job such as printing is actually performed. Therefore, a great power saving effect can be obtained by eliminating or reducing the loss of the starting resistor 31 according to the present invention described in detail in the above and the following examples.

In this embodiment, voltage dividing resistors 39a and 39b are provided so that the voltage applied to the gate electrode 33G of the thyristor 33 does not exceed 10V. Further, a transistor 39c for preventing backflow is provided.

FIG. 3 shows a different example of the switching power supply 1 according to the present invention. In the switching power supply 1 of the present example, the gate electrode 33G of the thyristor 33 connected in series with the starting resistor 31 is connected to the AC side, that is, the input side 3b of the rectifier circuit 3, similarly to the anode side of the thyristor. I have.

The gate electrode 33G of the thyristor 33 of this embodiment
4 changes with respect to the AC voltage v applied to the anode of the thyristor 33 as shown in FIG.
That is, when the AC voltage v becomes higher than a predetermined value, a current flows through the gate electrode 33G, and when the gate voltage exceeds the threshold value, the thyristor 33 is turned on. on the other hand,
When the AC voltage is 0 or inverted, the thyristor 33 is turned off. Therefore, the turn-on period T of the thyristor 33 is about 1/4 cycle. Therefore, when an AC is applied from the AC power supply 2, the thyristor 33 becomes 1
The switching element 11 is turned on by turning on for cycle, and the switching power supply device 1 is started.

In the switching power supply device 1 of this embodiment, when AC is supplied, the thyristor 33 is always turned on for 1/4 cycle, and a loss due to the starting resistor 31 occurs even when the thyristor 33 is not started. However,
As compared with the switching power supply device in which the starting resistor is simply connected to the AC side shown in FIG. 8, the loss due to the starting resistor 31 can be further reduced to 1/4 or less.

In the switching power supply device 1 shown in FIG. 5, the gate electrode 33G of the thyristor 33 and the AC side 3b are further connected by a phase shift circuit 34. The phase shift circuit 34 of this example includes a variable resistor 35a and a capacitor 35b.
As a result, as shown in FIG. 6, the phase of the current i flowing through the gate electrode 33G of the thyristor 33 can be shifted from the phase of the AC voltage v applied to the anode of the thyristor 33. Therefore, thyristor 3
3 can be turned on later than in the power supply device shown in FIG. As a result, as shown in FIG. 6, the period T during which the thyristor 33 is turned on can be further reduced, and the loss due to the starting resistor 31 can be reduced.

In the above description, an example using a switch or a thyristor has been described.
Bipolar transistor, SCR, GTO or IG
It is needless to say that the function of limiting the power flowing through the starting resistor 31 can be realized using a semiconductor element such as a BT. However, the circuit configuration using a thyristor is the simplest, and the thyristor can sufficiently fulfill the function of suppressing the power flowing through the starting resistor 31 and reducing the loss.

The switching element 11 employed in the switching circuit 30 is not limited to a MOSFET, but may be another known semiconductor element such as a bipolar transistor or an IGBT. Furthermore, in the above example, the description has been given based on the switching power supply device that performs constant voltage control. However, it is needless to say that the present invention can be applied to a switching power supply device that performs constant current control.

[0031]

As described above, in the switching power supply of the present invention, the power limiting means constituted by a switch or a thyristor is connected in series to the starting resistor for applying the starting voltage to the switching element. After the switching power supply is started, or even in an off state, the power flowing through the starting resistor is limited. Therefore, in a peripheral device such as a printer equipped with the switching power supply device according to the present invention, the loss due to the starting resistance during standby or during off can be eliminated or greatly reduced. Peripheral devices that realize the peripheral functions of personal computers have a much longer standby or off time than the actual job, and reduce the power loss during this period, resulting in a large power saving effect as a whole. Obtainable.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a schematic configuration of a switching power supply device according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an example different from the switching power supply device shown in FIG. 1;

FIG. 3 is a block diagram showing an example further different from the switching power supply device shown in FIG. 2;

4 is a graph showing an AC power supply applied to an anode of a thyristor and a current flowing through a gate of the thyristor in the switching power supply device shown in FIG.

FIG. 5 is a block diagram showing still another example different from the switching power supply device shown in FIG. 3;

6 is a graph showing an AC power supply applied to the anode of the thyristor and a current flowing through the gate of the thyristor in the switching power supply device shown in FIG.

FIG. 7 is a block diagram illustrating an example of a conventional switching power supply device.

FIG. 8 is a block diagram illustrating a schematic configuration of a switching power supply device in which a startup resistor is connected to an AC side to suppress a loss of the startup resistor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Switching power supply device 2 AC power supply 3 Rectifier circuit 4 Smoothing capacitor 5 Rectifier diode 10 Switching circuit 11 Switching element 11G Gate electrode of switching element 12 Transformer 13 Voltage detection circuit 14 Photocoupler 15 Switching control circuit 20 Secondary voltage control circuit 30 Start-up Circuit 31 Starting resistance 32 Switch 33 Thyristor 33G Thyristor gate electrode 34 Delay element 90 Switching power supply

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C061 HH11 HT13 5G065 AA00 AA01 DA06 DA07 EA06 FA02 GA04 GA06 HA04 HA08 JA01 KA02 KA05 LA01 MA10 NA02 NA08 5H730 AA14 AS01 BB43 BB52 CC01 DD04 EE61 FD01 FF19 V01 X01

Claims (7)

[Claims] A rectifier circuit for rectifying an alternating current; a switching circuit capable of chopping a current output from the rectifier circuit with a switching element to control output power; and connecting a control electrode of the switching element to an input of the rectifier circuit. A starting circuit connected to the output side or the output side via a starting resistor and capable of applying a starting voltage, wherein the starting circuit is capable of limiting a current flowing through the starting resistor after applying the starting voltage. A switching power supply device comprising limiting means. 2. The switching power supply device according to claim 1, wherein said power limiting means is an on / off switch. 3. The switching power supply device according to claim 1, wherein the starting resistor is connected to an input side of the rectifier circuit, and the power limiting unit is a thyristor. 4. The switching power supply according to claim 3, wherein a gate electrode of the thyristor is connected to an output side of the rectifier circuit. 5. The switching power supply according to claim 3, wherein a gate electrode of the thyristor is connected to an input side of the rectifier circuit. 6. The switching power supply according to claim 5, wherein a gate electrode of the thyristor is connected to an input side of the rectifier circuit via a phase shift element. 7. A peripheral device having the switching power supply device according to claim 1.