JP2000075943A - Power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a power unit which has excellent power efficiency. SOLUTION: This power unit has a 1st power source part including a chopping transistor 2, a 2nd power source part including a chopping transistor 18, and a discharge lamp turning-on circuit part including a chopping transistor 35. In this case, a current detector 31 detects the current flowing to a load resistance 8 and a voltage comparator 32 compares it with a reference voltage 33. When the load current is below a specific level, a transistor 30 is turned off with the output of the voltage comparator 32. Consequently, a control circuit of the 2nd power source part and a driving circuit of the chopping transistor 18 are powered off and the 2nd power source part stops operating. Thereafter, the load resistance 8 at light load time is supplied power by the 1st power source part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply, and more particularly to a power supply suitable for use in information equipment.

[0002]

2. Description of the Related Art The power consumption of a power supply device used in information equipment tends to increase as the performance and function of the equipment increase. On the other hand, conventionally, this increase in power consumption has been dealt with by a power supply device in which a plurality of power supply units are arranged in parallel.

In this type of power supply device, measures have been taken to suppress the ripple of the input current. As described in Japanese Patent Application Laid-Open No. 58-136266, for example, in a DC-DC converter in which switching regulator circuits each having a semiconductor switch are connected in parallel, the phase difference of each semiconductor switch is approximately 180 degrees. This is realized by performing on / off control with.

[0004]

However, in the prior art, there is a description of a control method effective for reducing the ripple current, but no technique for suppressing power consumption is disclosed. The increase in the power consumption of the load can be easily dealt with by increasing the number of parallel power supply units. However, it is desired that the power supply device itself reduce the power consumption and improve the power efficiency. In the switching regulator circuit of the related art, since the operation of each switching regulator circuit continues even when the load becomes very light, the power loss in the drive circuit of the switching elements constituting the switching regulator circuit becomes relatively large, and Therefore, the power efficiency at light load decreases. This is easy to overlook, but it is true. Therefore, the present inventor pays particular attention to the fact that the information devices are not always in the same load state, and wondered if the difference in the degree of the load state can be linked to the suppression of the reduction in power efficiency. Thus, the inventor has found a new problem of improving the power efficiency of the power supply device.

Accordingly, it is an object of the present invention to provide a power supply having good power efficiency.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a power supply unit comprising: a plurality of power supply units connected in common to connect an input terminal and an output terminal thereof to perform parallel operation; And a control unit for stopping the operation of at least one of the power supply units. Specifically, for example, when the load current is equal to or less than a predetermined value, the operation of at least one power supply unit is stopped. When the number of power supply units operated in parallel decreases, the drive circuit loss and the control circuit loss of the switching elements decrease accordingly, and the overall conversion efficiency improves.

Further, this type of parallel power supply section has a chopper circuit. If the power supply apparatus includes a lighting circuit section for a discharge lamp having a similar chopper circuit, each of the chopper circuits has a predetermined phase difference. Operate with. As a result, flickering of the discharge lamp can be suppressed.

[0008] Such a power supply device is suitable for a power supply including a discharge lamp lighting circuit section used for a liquid crystal backlight of a portable information device, a personal computer, or the like. As the backlight device, a load parallel power supply unit in which input terminals and output terminals of a plurality of power supply units having a chopper circuit are commonly connected, and a plurality of power supply units according to a load state of the parallel power supply unit A control unit for stopping the operation of at least one power supply unit, a discharge lamp used for a backlight of a display screen, and a discharge lamp lighting circuit unit having a chopper circuit connected to an input terminal. It is configured to operate with a predetermined phase difference.

In this way, a plurality of power supply units are connected in common,
The power supply method of stopping or restoring the operation of at least one of the plurality of power supply units according to the load state of the power supply unit reduces power consumption of the power supply device and improves power efficiency. Improvement can be achieved.

[0010]

FIG. 1 is a diagram showing one embodiment of a power supply device according to the present invention. In the present embodiment, a first power supply unit and a second power supply unit connected in parallel are provided as load power supply units. The load in this case is, for example, a built-in CPU for a portable information device or a personal computer.

The first power supply section includes a chopping transistor 2, a choke coil 3, a resistor 4, a base resistor 5 of the chopping transistor, a diode 6, an error amplifier 11, a reference voltage source 12, a capacitor 13, and a voltage connected to the DC power supply 1. It comprises a comparator 14, a sawtooth wave generator 15, a transistor 16, and a resistor 17.

A second power supply section connected in parallel with the first power supply section;
Chopping transistor 1 connected to DC power supply 1
8, diode 19, choke coil 20, resistor 21,
Chopping transistor base resistor 22, error amplifier 23, reference voltage source 24, capacitor 25, voltage comparator 26, sawtooth generator 27, resistor 28, transistor 2
9 is comprised.

The first power supply unit and the second power supply unit connected in parallel are connected to a load resistor 8. A smoothing capacitor 7 and output voltage detecting resistors 9 and 10 are provided at both ends of the load resistor 8.
Are respectively connected. The connection point between the detection resistors 9 and 10 is connected to error amplifiers 11 and 23. A current detector 31 is provided between the choke coils 3 and 20 and the load resistor 8. The input terminal of the voltage comparator 32 is connected to the current detector 31 and the reference voltage source 33, and the output terminal is connected to the transistor 30. The transistor 30 and the voltage comparator 32 constitute a control unit that stops the operation of at least one of the plurality of power supply units according to the load state of the power supply device.

Further, as shown in FIG. 1, the power supply device can include a lighting circuit section of a discharge lamp 46 used for a liquid crystal backlight of, for example, a portable information device or a personal computer. The lighting circuit section is a chopping transistor 3
5, choke coil 36, diode 37, resistor 38,
Chopping transistor base resistor 39, base resistor 40, switching transistors 41 and 42, resonance capacitor 43, transformer 44, ballast capacitor 4
5, detection resistor 47 for current flowing through the discharge lamp, diode 4
8, smoothing capacitor 49, resistors 50 and 51, error amplifier 52, reference voltage source 53, capacitor 54, transistor 55, resistor 56, sawtooth generator 57, voltage comparator 5
8. This lighting circuit is connected to a discharge lamp 46 built in the liquid crystal backlight.

FIG. 2 (a) shows an output waveform diagram of the sawtooth wave generators 15, 27, 57. In the figure, a dotted sawtooth wave is generated by the generator 15, a broken sawtooth wave is generated by the generator 27, and a solid sawtooth wave is generated by the generator 5.
No.7. Also, the dotted straight line in the figure indicates the output of the error amplifier 11, the broken line indicates the output of the error amplifier 23, and the solid line indicates the output of the error amplifier 52. Hereinafter, the operation of each unit will be described.

First, regarding the first power supply section, the DC voltage of the DC power supply 1 is chopped by the chopping transistor 2 and then smoothed by the choke coil 3 and the smoothing capacitor 7 to a DC voltage lower than the voltage of the DC power supply 1. Is converted. The converted DC voltage is supplied to the load resistor 8. At the same time, the output voltage divided by the detection resistors 9 and 10 is fed back to the error amplifier 11. The error amplifier 11 outputs a voltage corresponding to the difference between the fed back voltage and the voltage of the reference voltage source 12 to the voltage comparator 14.

The error amplifier 1 input to the voltage comparator 14
1 is compared with the voltage waveform of the sawtooth generator 15. During a period when the output voltage of the error amplifier 11 is lower than the voltage waveform of the sawtooth wave generator 15, the chopping transistor 2 operates so as to be turned on as shown in FIG. If the output of the power supply section 1 decreases for some reason, the output voltage of the error amplifier 11 decreases, and the ON duty of the chopping transistor 2 increases. Therefore, the output voltage of the power supply unit 1 is increased, and control is performed so that the output voltage becomes constant.

The second power supply operates in the same manner as the first power supply. However, as shown in FIG. 2A, the voltage waveform of the sawtooth wave generator 27 of the second power supply unit is shifted by 120 degrees from the voltage waveform of the sawtooth wave generator 15 of the first power supply unit. .
Although the current waveforms of the chopping transistors 2 and 18 become triangular as shown in FIG. 2C, the peaks of the current waveforms of the chopping transistors 2 and 18 are shifted because the phases of the sawtooth wave generators 15 and 27 are shifted. The parts do not overlap. Therefore, the instantaneous value of the input current of the entire device becomes small, and the voltage fluctuation of the DC power supply 1 becomes small.

Here, if the load current supplied to the load resistor 8 is extremely small as compared with the normal state, the output power naturally has a small value. However, regardless of the load current, the error amplifier 11
And 23, and the power consumed by the control circuits such as the voltage comparators 14 and 26 and the drive circuits of the chopping transistors 2 and 18 are constant, so that the efficiency (output power /
Input power). When the load current is small, it is not necessary to operate both the first power supply unit and the second power supply unit.
Even when the power supply unit is stopped, a sufficient load current can be supplied by the first power supply unit. Therefore, the load current is detected by the current detector 31 and compared with the reference voltage 33 by the voltage comparator 32. When the load current is lower than the predetermined level, the transistor 30 is turned off. Thus, power supply to the control circuit of the second power supply unit and the drive circuit of the chopping transistor 18 is stopped. Therefore, power consumption is reduced and power efficiency is improved.

Next, the operation of the discharge lamp lighting circuit will be described. The operation is basically the same as the operation of the first and second power supply units described above, except that a portion on the secondary side from the choke coil 36 is different. The DC voltage is converted to an AC voltage by feeding back an AC voltage generated by a resonance phenomenon generated between the transformer 44 and the resonance capacitor 43 to the switching transistors 41 and 42 to alternately turn ON and OFF to continue the oscillation, thereby continuing the oscillation. You. This AC voltage is applied to the transformer 4
The voltage is increased in proportion to the turn ratio of 4 and a high voltage is applied to the discharge lamp 46. When the discharge lamp 46 starts discharging by a high voltage, a current flows through the tube current detection resistor 47, and a voltage corresponding to the tube current is generated. This voltage is rectified and smoothed by a diode 48 and a smoothing capacitor 49 and fed back to an error amplifier 52 via resistors 50 and 51 as a DC voltage proportional to the tube current. Is controlled to flow constantly. After stabilization, the output voltage of the transformer 44 and the ballast capacitor 45
In addition, a current corresponding to the impedance of the discharge lamp 46 flows stably.

The phase of the sawtooth wave generator 57 used here is shifted from the sawtooth wave generators 15 and 27 by 120 degrees. Therefore, as shown in FIG. 2C, the peak of the current flowing through the chopping transistor 35 does not overlap with the peak of the current flowing through the chopping transistors 2 and 18 of the first and second power supply units.

When the lighting circuit section and the first and second power supply sections operate asynchronously, the peak of the current of the chopping transistor of the lighting circuit section does not overlap with the peak of the current of the chopping transistor of the power supply section. Since the cases come alternately, the voltage of the DC power supply 1 fluctuates each time. This variation affects the operation of the lighting circuit section,
In an extreme case, flicker may occur in the discharge lamp 46. In the present invention, the flicker does not occur because the current peaks of the lighting circuit section and the power supply section do not overlap.

As described above, in the present invention, an efficient power supply device can be obtained by operating the power supply unit at a light load, and a lighting device for a liquid crystal backlight with a small ripple current can be realized. .

[0024]

According to the present invention, a power supply having good power efficiency can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a power supply device according to the present invention.

FIG. 2A is a diagram showing an output waveform of a sawtooth wave generator;
(B) is a diagram showing ON and OFF states of the chopping transistor, and (c) is a diagram showing a current waveform of the chopping transistor.

[Explanation of symbols]

 2 chopping transistor 8 load resistance 18 chopping transistor 35 chopping transistor 30 transistor 31 current detector 32 voltage comparator 33 reference voltage source 46 discharge lamp

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenji Kawabata Heating Lighting Division, Hitachi, Ltd. 6-16, Shinmachi, Ome City, Tokyo (72) Inventor Takashi Okada 6-16, Shinmachi, Ome City, Tokyo (2) Inventor Ryuichi Ikeda 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Pref. Multimedia Systems Development Division, Hitachi, Ltd. (72) Motohiro Sugino Yokohama, Kanagawa 292 Yoshida-cho, Totsuka-ku, Ichitochi, Japan Multimedia System Development Division, Hitachi, Ltd. Inventor Keiji Suzuki 1623-14 Shimotsuruma, Yamato City, Kanagawa Prefecture・ F-term in the Yamato Plant of M Co., Ltd. (reference) EE10 EE30 EE72 EE79 FD01 FD31 FF02 FG02 XX24 XX29 XX35

Claims (10)

[Claims] An input terminal and an output terminal of a plurality of power supply units are connected in common so that parallel operation can be performed, and a parallel power supply unit among the plurality of power supply units according to a load state. And a control unit for stopping the operation of at least one power supply unit. 2. The power supply device according to claim 1, wherein the operation of the at least one power supply unit is stopped when a load current is equal to or less than a predetermined value. 3. The power supply unit according to claim 1, wherein each of the plurality of power supply units has a chopper circuit, and each of the chopper circuits is configured to perform a parallel operation with a predetermined phase difference. Power supply. 4. A parallel power supply unit configured so that input terminals and output terminals of a plurality of power supply units having a chopper circuit are commonly connected to perform parallel operation, and a chopper circuit connected to the input terminal. A power supply device comprising: a discharge lamp lighting circuit unit having the control unit; and a control unit that stops operation of at least one of the plurality of power supply units according to a load state of the parallel power supply unit. . 5. The power supply device according to claim 4, wherein each of the chopper circuits is configured to operate with a predetermined phase difference. 6. The power supply unit according to claim 4, wherein the parallel power supply unit stops operation of at least one of the plurality of power supply units when a load current is equal to or less than a predetermined value. Or the power supply device according to 5. 7. A parallel power supply unit configured to be able to perform parallel operation by connecting input terminals and output terminals of a plurality of power supply units having a chopper circuit in common, and a chopper circuit connected to the input terminal. And a chopper circuit configured to operate with a predetermined phase difference. 8. A parallel power supply unit for a load in which input terminals and output terminals of a plurality of power supply units having a chopper circuit are connected in common, and a power supply unit for the plurality of power supply units according to a load state of the parallel power supply unit A control unit for stopping the operation of at least one of the power supply units, a discharge lamp used for a backlight of a display screen, and a lighting circuit unit for the discharge lamp having a chopper circuit connected to the input terminal, A backlight device, wherein each of the chopper circuits is configured to operate with a predetermined phase difference. 9. An input terminal and an output terminal of the plurality of power supply units are commonly connected, and operation of at least one of the plurality of power supply units is stopped according to a load state of the power supply unit. Or a power supply method characterized by resuming. 10. The power supply method according to claim 9, wherein said load state is obtained based on a magnitude of a load current in said plurality of power supply units.