JP2009112134A - Switching power supply unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply unit for remarkably reducing loss of an input voltage detecting circuit. <P>SOLUTION: The switching power supply unit includes two coils L<SB>1</SB>and L<SB>2</SB>whose connection states can be switched in series or parallel and which suppresses harmonic current. A power supply part 3 includes output wiring T<SB>2</SB>and input voltage detection wiring T<SB>3</SB>as secondary side wiring wound around the core which is the same as primary side winding T<SB>1</SB>. Output DC voltage V<SB>DOUT</SB>obtained on an output wiring T<SB>2</SB>side is supplied to a circuit 4 to be driven. The connection state of the coils L<SB>1</SB>and L<SB>2</SB>is switched in accordance with an amount of detection DC voltage obtained on an input voltage detection wiring T<SB>3</SB>side. The number n<SB>3</SB>of input voltage detection wiring T<SB>3</SB>is smaller than the number n<SB>1</SB>of primary side windings T<SB>1</SB>. It is desirable that a switching operation of a relay RL is compulsorily stopped by a standby signal inputted from outside the unit. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a switching power supply device, and more particularly to a switching power supply device in which a choke coil for harmonics is inserted in an AC power supply line.

As shown in FIG. 4, the switching power supply device converts an input AC voltage V _AIN supplied from an AC power source 2 such as a commercial power source into an appropriate output DC voltage V _DOUT required by the driven circuit 4. .
A conventional switching power supply device 1 shown in FIG. 4 includes a rectifier diode D that rectifies an input AC voltage V _AIN , a smoothing capacitor C that smoothes a voltage rectified by the rectifier diode D, and a switching element and a transformer. The power supply unit 3 switches the DC voltage obtained by the smoothing capacitor C and converts the AC voltage obtained by the switching into a desired output DC voltage V _DOUT . The output DC voltage V _DOUT is output to the driven circuit 4 supplied with power by the switching power supply device 1.

  A choke coil L for high frequency countermeasures is inserted in series in the AC power supply line of the switching power supply device 1. Accordingly, to satisfy the standards related to harmonic currents defined for each input AC voltage (Japan: AC100V system, “JIS C 61000-3-2”, Europe: AC200V system, “EN61000-3-2”). The harmonic current of the AC power line is suppressed.

FIG. 5 shows a switching power supply apparatus that can handle both AC100V system and 200V system, and that is provided with the above harmonic countermeasures (see, for example, Patent Document 1).
The switching power supply unit 1, the connection state by the relay RL is switchable comprises two choke coils L ₁ and L ₂ wound on the same core. Further, the relay RL is the voltage dividing resistors R ₁ and R ₂ which are connected in parallel to the smoothing capacitor C, a Zener diode ZD having a cathode side connected to the midpoint, the anode side of the Zener diode ZD It is controlled by an input voltage detection circuit comprising a transistor Q to which the base is connected.

As an example, voltage dividing resistors _{R 1} is 400 [kΩ], _{R 2} is 44 [kW], when the breakdown voltage of the constant voltage diode ZD is 20 [V], the operation of the relay RL.
When the input AC voltage V _AIN is an AC 100V system (peak voltage = √2 × 100 [V]), the DC voltage generated at both ends of the smoothing capacitor C is √2 × 100 [V], and the voltage dividing resistors R ₁ and R ₂ The midpoint voltage is 14 [V]. In this case, since the midpoint voltage is lower than the breakdown voltage (20 [V]) of the constant voltage diode ZD, the transistor Q is in the OFF state, no exciting current flows through the control coil of the relay RL, and the choke coil L ₁ and L ₂ is connected in parallel (see FIG. 5A).

On the other hand, when the input AC voltage V _AIN is an AC 200 V system (peak voltage = √2 × 200 [V]), the DC voltage generated at both ends of the smoothing capacitor C is √2 × 200 [V], the voltage dividing resistor R ₁ and midpoint voltage of R ₂ becomes 28 [V]. In this case, since the midpoint voltage exceeds the breakdown voltage (20 [V]) of the constant voltage diode ZD, the transistor Q is turned on when the base current is supplied from the constant voltage diode ZD side, and the control coil of the relay RL is turned on. An exciting current flows through the choke coils L ₁ and L ₂ (see FIG. 5B).

Generally, a choke coil for an AC 200V system requires an inductance four times that for an AC 100V system, and a choke coil for an AC 100V system requires a current capacity twice that for an AC 200V system. . In this regard, according to the switching power supply device 1 shown in FIG. 5A, the choke coil is switched by switching the connection state of the same choke coils L ₁ and L ₂ in series or in parallel according to the input AC voltage V _AIN. Harmonic countermeasures can be taken without increasing the size.

Japanese Patent Laid-Open No. 10-191638

However, in the conventional switching power supply device 1 shown in FIG. 5, both ends of the voltage dividing resistors R ₁ and R _2, the DC voltage supplied to the power supply unit 3 '(the peak voltage of √2 × the input AC voltage V _AIN) is Since it was applied as it was, the loss in the input voltage detection circuit was very large.

  Accordingly, an object of the present invention is to provide a switching power supply device that can reduce loss in an input voltage detection circuit.

In order to solve the above problems, a switching power supply device according to the present invention provides:
The input side is connected to the AC power line, the rectifying and smoothing means for rectifying and smoothing the input AC voltage to convert it into a DC voltage, two choke coils inserted in the AC power line, and the magnitude of the input AC voltage An input voltage detection circuit to detect, a switching means for switching the connection state of two choke coils in series or in parallel according to the magnitude of the input AC voltage detected in the input voltage detection circuit, and an output of the rectifying and smoothing means The DC voltage is switched by a switching element connected to the primary winding of the transformer, and the induced AC voltage induced in the secondary winding of the transformer by the switching is rectified and smoothed. A switching power supply unit including a power supply unit that converts the output DC voltage to be supplied to the driven circuit, The input voltage detection circuit is connected to the secondary side winding of the transformer, and uses the DC voltage obtained by rectifying and smoothing the induced AC voltage induced in the secondary side winding. It is characterized by detecting the magnitude of the AC voltage.

  Preferably, in the switching power supply device, the secondary side winding of the transformer includes an output winding and an input voltage detection winding, and the power supply unit is induced in the output winding. Obtained by supplying the output DC voltage obtained by rectifying and smoothing the induced AC voltage to the driven circuit and rectifying and smoothing the induced AC voltage induced in the input voltage detection winding. A detection DC voltage is supplied to the input voltage detection circuit, and the input voltage detection circuit detects the magnitude of the input AC voltage based on the amount of the detection DC voltage.

  Preferably, in the switching power supply device, the number of turns of the input voltage detection winding is smaller than the number of turns of the primary side winding.

  Preferably, the switching power supply device is characterized in that the switching operation of the switching means is forcibly stopped by a signal input to the input voltage detection circuit from the outside of the device.

More preferably, in the switching power supply device, the signal indicates that the driven circuit is in a low power consumption state.
Note that in this specification, the term “low power consumption state” means a state where the power consumption of the driven circuit is low to the extent that it is not necessary to take measures against harmonics. The “low power consumption state” includes a standby state, a power saving mode state, and the like, as well as a state where the power of the driven circuit is not turned on and the power consumption is zero.

  According to the switching power supply device of the present invention, loss in the input voltage detection circuit can be reduced.

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

FIG. 1 is a circuit diagram of the switching power supply device according to the first embodiment.
Similar to the conventional one shown in FIG. 4, the switching power supply device 1 according to the present embodiment includes a rectifier diode D ₁ that rectifies an input AC voltage V _AIN that is input via an AC power line, and a rectifier diode D _1. A smoothing capacitor C ₁ for smoothing the voltage rectified in step ( _1), and a power supply unit 3 for switching the DC voltage obtained by the smoothing capacitor C ₁ to convert it to a desired output DC voltage V _DOUT . Thus, in the present invention, the rectifier diode D ₁ and the smoothing capacitor C ₁ function as “rectification smoothing means”. The output DC voltage V _DOUT is output to the driven circuit 4 supplied with power by the switching power supply device 1.

Further, the switching power supply device 1 includes two choke coils L ₁ and L ₂ wound around the same core, the connection state of which can be switched in series or in parallel by a relay RL (corresponding to “switching means” of the present invention). The harmonic measures are taken in both the AC100V system and the 200V system.
Specifically, when an AC 100V system power source is connected as the AC power source 2, two choke coils are connected in parallel by switching the relay RL, and when an AC 200V system power source is connected as the AC power source 2, Two choke coils are connected in series by switching the relay RL.

As shown in FIG. 1, the power supply unit 3 according to this embodiment mainly includes a switching element Q _1, consists of a transformer T, transformer T is wound on the same core primary winding T ₁ and secondary windings T ₂ and T ₃ . The DC voltage obtained by the smoothing capacitor C ₁ is switched by the switching element Q ₁ connected to the primary side winding T ₁ of the transformer T, and the secondary side windings T ₂ , T of the transformer T are switched by the switching. _An AC voltage is induced at ₃ .

The secondary winding T _2, T ₃ has the primary winding T ₁ of the primary winding T ₁ same core wound output winding T ₂ and the transformer T of the transformer T and an input voltage detection winding T ₃ Metropolitan wound on the same core. The output winding T _2, is connected rectifier diode D ₂ and a smoothing capacitor C _2, the induced AC voltage induced in the output winding T ₂ is rectified and smoothed is outputted to the driven circuit 4 It is converted to output DC voltage V _DOUT . The output DC voltage V _DOUT is fed back to the control unit 6 via the detection unit 5, and the control unit 6 controls the switching element Q ₁ based on this, so that the output DC voltage V _DOUT is stabilized.

On the other hand, the input voltage detection winding T ₃ of the transformer T, a rectifier diode D ₃ and a smoothing capacitor C ₃ is connected, the induced AC voltage induced in the input voltage detection winding T ₃ is rectified and smoothed Converted to DC voltage. This DC voltage is divided into voltage dividing resistors R ₁ and R ₂ connected in parallel to the smoothing capacitor C ₃ , a constant voltage diode ZD whose cathode is connected to the midpoint thereof, and an anode of the constant voltage diode ZD is input to the input voltage detection circuit comprising transistors Q ₂ Metropolitan which base side is connected. The input voltage detection circuit detects the magnitude of the input AC voltage V _AIN and controls the relay RL according to the detection result.
Thus, in this embodiment, the induced connected input voltage detecting circuit to an input voltage detection winding T ₃ is a secondary winding of the transformer T, which is induced in the input voltage detection winding T ₃ The magnitude of the input AC voltage V _AIN is detected using a DC voltage (DC voltage for detection) obtained by rectifying and smoothing the AC voltage.

In the present embodiment, the voltage dividing resistor R ₁ is 120 [kΩ], R ₂ is 68 [kΩ], the breakdown voltage of the constant voltage diode ZD is 8.2 [V], and the primary winding T ₁ and the input voltage detection. turns ratio of use winding _{T 3 n} 1: _{n 3} is 9: 1.
The primary winding T ₁ and the output winding T _2, the polarity of the winding, as shown in a black circle display of FIG. 1 has a reverse polarity, with respect to the opposite polarity of the winding control section 6 Thus, the output voltage is controlled to be a constant voltage. That is, the induced AC voltage be varied input AC voltage V _AIN is induced in the output winding T ₂ are constant.
On the other hand, the primary winding T ₁ and the input voltage detection winding T _3, the polarity of the winding, as shown in a black circle display of Fig. 1 has a same polarity, and the output winding T ₂ different, is not carried out the control by the control unit 6 to the AC voltage induced in the input voltage detection winding T _3. Therefore, the detection DC voltage obtained an induced AC voltage induced in the input voltage detection winding T ₃ by rectifying and smoothing changes in proportion to the voltage applied to the primary winding T _1.

When the input AC voltage _{V AIN} is AC100V system (peak voltage = √2 × 100 [V]) , the DC voltage generated across the smoothing capacitor _{C 3} is √2 × 100/9 [V] , the voltage dividing resistors _{R 1} And the midpoint voltage of R ₂ is 5.7 [V]. In this case, since the midpoint voltage is below the breakdown voltage of the constant voltage diode ZD (8.2 [V]), the transistor Q ₂ is in OFF state, the exciting current to the control coil of the relay RL does not flow, the choke coil L ₁ and L ₂ are connected in parallel (see FIG. 1).

On the other hand, when the input AC voltage _{V AIN} is AC200V system (peak voltage = √2 × 200 [V]) , the DC voltage generated across the smoothing capacitor _{C 3} is √2 × 200/9 [V] , the voltage dividing resistors midpoint voltage of R ₁ and _{R 2} becomes 11.4 [V]. In this case, the midpoint voltage so exceeds the breakdown voltage of the constant voltage diode ZD (8.2 [V]), the transistor Q ₂ is be supplied base current from the constant voltage diode ZD side ON state, the relay RL Excitation current flows through the control coils of the choke coils L ₁ and L ₂ are connected in series.

As described above, the switching power supply device 1 shown in FIG. 1, the number of turns than the primary winding T ₁ is provided with a considerably less input voltage detection winding T _3. Since the magnitude of the input AC voltage V _AIN is determined using the detection DC voltage obtained by rectifying and smoothing the induced AC voltage induced thereby, the voltage _dividing resistor in the input voltage detection circuit is used. The loss of R ₁ and R ₂ can be greatly reduced.
The measurement result of the loss compared with the conventional switching power supply device will be described later.

Next, a switching power supply device according to a second embodiment will be described with reference to FIG.
Originally, when the power consumption of the driven circuit 4 is small, such as when the driven circuit 4 supplied with power by the switching power supply 1 is in a standby state, the harmonic current generated by the choke coil is small because the generated harmonic current is small. There is no need to take countermeasures against waves.
However, in the conventional switching power supply device 1 shown in FIG. 5, the driven circuit 4 regardless of whether the standby state, when the AC200V system, the excitation current for connecting the choke coils L ₁ and L ₂ in series Is continuously flowing through the control coil of the relay RL, and loss has also occurred in the relay RL.

In order to solve the above-described problem, the switching power supply device 1 according to the present embodiment is a standby signal input terminal for receiving a standby signal from the driven circuit 4 in the switching power supply device according to the first embodiment illustrated in FIG. 7 is additionally connected to the input voltage detection circuit. Specifically, the standby signal input terminal 7 is connected between the constant voltage diode ZD and the base of the transistor Q ₂ and also connected to the driven circuit 4.
There are various types of driven circuits 4 that can be supplied with power by the switching power supply. For example, when the driven circuit 4 is a copying machine, a low power consumption state (for example, a standby state or the like such as printing). When the processing is not performed, a signal that becomes “Low” is output from the copying machine (4) to the standby signal input terminal.

As described above, the input AC voltage _{V AIN} cases of AC100V system, the transistor _{Q 2} is an OFF state, change with the signal is input does not occur.
On the other hand, when the input AC voltage V _AIN is an AC 200V system and this signal is input, all the current supplied from the constant voltage diode ZD side to the transistor Q ₂ is driven via the standby signal input terminal 7. It flows to the circuit 4. Thus, no longer supplied with the base current to the transistor Q _2, the transistor Q ₂ is ON state will be forced OFF. When transistor Q ₂ is turned OFF, since the exciting current does not flow to the control coil of the relay RL, the choke coil L ₁ and L ₂ are switched to the parallel connection (see FIG. 2).

FIG. 3 is a diagram illustrating a relationship between the input AC voltage V _AIN and the voltages of the respective parts of the input voltage detection circuit.
The threshold value of the input AC voltage V _{AIN at which} the relay RL (connection state of the choke coils L ₁ and L ₂ ) switches is obtained as follows. When the threshold value of the input AC voltage V _AIN is x, the voltage _dividing resistor R ₁ is 120 [kΩ], R ₂ is 68 [kΩ], the breakdown voltage of the constant voltage diode ZD is 8.2 [V], and the primary side winding turns ratio _n 1 of the line _{T 1} and the input voltage detection winding _{T 3: n 3} is 9: 1 is from equation (1) is satisfied. Here, it is assumed the base-emitter voltage of the transistor Q ₂ and 0.6 [V].
(X × √2 / 9) × 68 / (68 + 120) = 8.2 + 0.6 (1)
From equation (1), the threshold value x = 154.8 [V] is derived. Therefore, when the input AC voltage _{V AIN} becomes 154.8 [V] or more, a current flows through the constant voltage diode ZD, the transistor _{Q 2} is turned ON. As a result, the relay RL operates and the connection state of the choke coils L ₁ and L ₂ is switched from parallel to series.

For this reason, if the “Low” level is applied to the standby signal input terminal 7 in a state where the input AC voltage V _AIN is 154.8 [V] or more and the power is turned on, all the voltage from the constant voltage diode ZD is applied. since the current to flow in the driving circuit 4 via the standby signal input terminal 7, the transistor Q ₂ is turned OFF, the relay RL is also OFF in association with this, the power consumed by the relay RL is zero .
On the other hand, when the input AC voltage _{V AIN} is below 154.8 [V] is, since the original is the transistor _{Q 2} is the state of OFF, regardless of the waiting signal, the relay RL is the OFF state (operation stop ). Therefore, power is not consumed in the relay RL.
When the driven circuit 4 is in a standby state, the harmonic current generated is small in the first place, so there is no need to take measures against harmonics by the choke coil, and the connection of the choke coils L ₁ and L ₂ is changed from serial to parallel. However, no problem occurs.

As described above, according to the switching power supply device 1 according to the second embodiment illustrated in FIG. 2, the loss in the voltage dividing resistors R ₁ and R ₂ of the input voltage detection circuit is reduced, and the signal input from the outside of the device By forcibly stopping the operation of the relay RL, the loss in the relay RL can be eliminated, and the power consumption of the switching power supply device 1 can be reduced.

[Comparison of loss]
The loss of the switching power supply according to Example 1 shown in FIG. 1 and the switching power supply according to Example 2 shown in FIG. 2 was measured, and the loss of the switching power supply shown in FIG. 5 was measured as a conventional example. The results are shown in Table 1.
The circuit constants of Examples 1 and 2 are the same as those described above: “voltage dividing resistor R ₁ = 120 [kΩ], voltage dividing resistor R ₂ = 68 [kΩ], breakdown voltage of constant voltage diode ZD = 8 .2 [V] The turns ratio n ₁ : n ₃ = 9: 1 ″ of the primary side winding T ₁ and the input voltage detection winding T ₃ .
The circuit constants of the conventional example are also similar to those described above, “voltage dividing resistor R ₁ = 400 [kΩ], voltage dividing resistor R ₂ = 44 [kΩ], breakdown voltage of constant voltage diode ZD = 20 [V]. ".

  As can be seen from Table 1, in Examples 1 and 2, the loss in the voltage dividing resistance could be greatly reduced in both cases of the AC 100 V system and the 200 V system (first effect). In addition to the first effect, Example 2 provided with the standby signal input terminal 7 was able to reduce the loss in the relay to zero (second effect).

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to the said structure.

For example, in each embodiment, an excitation current is passed through the control coil of the relay RL in “AC200V system”, and the choke coils L ₁ and L ₂ are connected “in series”, but the choke coils L ₁ and L ₂ are connected, By changing the configuration of the input voltage detection circuit, an excitation current may be passed in the “AC 100 V system”, and the choke coils L ₁ and L ₂ may be connected in “parallel”.

The circuit constant in each embodiment can be changed to another constant as appropriate.
For example, the loss in the voltage dividing resistor can be further reduced by increasing the resistance values of the voltage dividing resistors R ₁ and R ₂ .
Also, the turns ratio of the primary winding T ₁ and the input voltage detection winding T ₃ is able to reduce the losses in the larger voltage dividing resistors, at least, an input voltage detection winding T ₃ the number of turns by less than the number of turns of the primary winding T _1, it is possible to obtain the first effect of the present invention.

1 is a circuit diagram of a switching power supply device according to Embodiment 1. FIG. 6 is a circuit diagram of a switching power supply device according to Embodiment 2. FIG. It is a figure which shows the relationship between an input alternating voltage and the voltage of each part of an input voltage detection circuit. It is a circuit diagram of the conventional switching power supply device. It is a circuit diagram of the switching power supply device concerning a prior art example, (A) is a whole circuit diagram at the time of AC100V system, and (B) shows a relay peripheral part at the time of AC200V system.

Explanation of symbols

First switching power supply unit 2 AC power supply 3 power supply unit 3 'power unit 4 driven circuit 5 detecting unit 6 control unit 7 waiting signal input terminal _C, C 1 -C ₃ smoothing capacitor _D, D 1 to D ₃ rectifier diode L, L _{1, L 2} choke coil Q, _{Q 2} transistor _{Q 1} switching element _R 1, _{R 2} dividing resistor RL relay T transformer _{T 1} 1 primary winding _{T 2} output winding (secondary winding)
T ₃ Winding for detecting input voltage (secondary winding)
ZD constant voltage diode

Claims (5)

The input side is connected to the AC power line, the rectifying and smoothing means for rectifying and smoothing the input AC voltage to convert it into a DC voltage, two choke coils inserted in the AC power line, and the magnitude of the input AC voltage An input voltage detection circuit to detect, a switching means for switching the connection state of two choke coils in series or in parallel according to the magnitude of the input AC voltage detected in the input voltage detection circuit, and an output of the rectifying and smoothing means The DC voltage is switched by a switching element connected to the primary winding of the transformer, and the induced AC voltage induced in the secondary winding of the transformer by the switching is rectified and smoothed. A switching power supply unit including a power supply unit that converts the output DC voltage to be supplied to the driven circuit,
The input voltage detection circuit is connected to the secondary side winding of the transformer, and uses the DC voltage obtained by rectifying and smoothing the induced AC voltage induced in the secondary side winding. A switching power supply device that detects the magnitude of an AC voltage. The secondary side winding of the transformer has an output winding and an input voltage detection winding,
The power supply unit supplies the output DC voltage obtained by rectifying and smoothing the induced AC voltage induced in the output winding to the driven circuit and is induced in the input voltage detection winding. A DC voltage for detection obtained by rectifying and smoothing the induced AC voltage is supplied to the input voltage detection circuit;
2. The switching power supply device according to claim 1, wherein the input voltage detection circuit detects the magnitude of the input AC voltage based on the amount of the detection DC voltage.   3. The switching power supply device according to claim 2, wherein the number of turns of the input voltage detection winding is smaller than the number of turns of the primary side winding.   4. The switching power supply device according to claim 1, wherein the switching operation of the switching means is forcibly stopped by a signal input to the input voltage detection circuit from outside the device.   The switching power supply device according to claim 4, wherein the signal indicates that the driven circuit is in a low power consumption state.

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