JP3672452B2 - Power supply circuit and power supply device using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a power supply circuit that receives AC power and supplies DC power to various loads, and a power supply device using the power supply circuit.
[0002]
[Prior art]
In recent years, there has been an increasing social demand for energy saving for electronic devices. Especially for electronic devices that are energized all day long, such as video tape recorders (VTRs), copiers, facsimiles, etc., and in which the standby mode lasts longer than in the operation mode, low power consumption in the standby mode is achieved to save energy. Power consumption is being promoted. In addition to the reduction in power consumption in such an electronic device, energy loss in a standby mode of a power supply device that supplies power to the electronic device is also being promoted.
In recent years, as electronic devices become more complex, the need to supply highly accurate DC power has increased. Power supply devices that can supply highly accurate DC power are used in information communication equipment such as personal computers, facsimiles, mobile phones, and copiers.
[0003]
Hereinafter, a conventional power supply device will be specifically described with reference to FIG. FIG. 2 is a circuit diagram showing a circuit configuration of a conventional switching power supply device.
In FIG. 2, the AC power supply 100 supplies AC power to the full-wave rectifier circuit 20. The full-wave rectifier circuit 20 and the input capacitor 30 rectify and smooth the AC voltage from the AC power supply 100 into a DC voltage.
The switching circuit 40 is configured by elements such as a switching transistor and a power MOSFET, and converts an input DC voltage into a high-frequency AC voltage by an on / off operation. The transformer 50 has a primary winding 50a, a secondary winding 50b, and a control winding 50c. In the switching circuit 40, the high-frequency AC voltage obtained by the switching operation is input to the primary winding 50 a of the transformer 50.
[0004]
The diode 60 and the output capacitor 70 connected to the secondary winding 50 b of the transformer 50 rectify and smooth the AC voltage generated in the secondary winding 50 b and supply DC power to the load 80. The control drive circuit 90 controls the switching circuit 40 that adjusts the DC power output to the load 80. The diode 250 and the capacitor 110 connected to the control winding 50 c of the transformer 50 rectify and smooth the AC voltage generated in the control winding 50 c and supply it as a power source for the control drive circuit 90. The resistor 31 is a starting resistor, and supplies power to the control drive circuit 90 at the time of starting when no voltage is generated in each winding of the transformer 50.
[0005]
The operation of the conventional power supply device will be described below.
The AC power supply 100 supplies AC power to the full-wave rectifier circuit 20. The full-wave rectifier circuit 20 and the input capacitor 30 perform full-wave rectification to smooth the AC voltage of the AC power supply 100 to a DC voltage.
The switching circuit 40 converts a DC voltage into a high-frequency AC voltage by the on / off operation. This high-frequency AC voltage is input to the primary winding 50a of the transformer 50, transformed from the secondary winding 50b, and output. The high-frequency AC voltage generated in the secondary winding 50b is rectified and smoothed by the diode 60 and the output capacitor 70 to form a DC voltage. This DC voltage is supplied to the load 80. The DC voltage supplied to the load 80 is adjusted by the on / off ratio of the switching circuit 40.
[0006]
The control drive circuit 90 detects the output DC voltage, compares it with a reference voltage, and detects an error. The control drive circuit 90 outputs a pulse signal having an on / off ratio adjusted to correct the error to the switching circuit 40.
The AC voltage generated in the control winding 50 c is rectified and smoothed by the diode 250 and the capacitor 110, and is supplied as a power source for the control drive circuit 90. The circuit of the starting resistor 31 supplies power to the control drive circuit 90 at the time of starting when no voltage is generated in each winding of the transformer 50.
At the time of a light load typified by the standby mode, one of the causes of energy loss of the conventional power supply device is power loss in the starting resistor 31. For this reason, the resistance value of the starting resistor 31 is desired to be increased, but the resistance value of the starting resistor 31 cannot be increased so as to smoothly start the conventional power supply device.
[0007]
In contrast to the conventional power supply device having the above configuration, a power supply circuit for a power supply device that does not use a starting resistor has been used.
Hereinafter, a power supply circuit for a conventional power supply apparatus that does not use a starting resistor will be described in detail with reference to FIG. FIG. 3 is a circuit diagram showing a circuit configuration of a conventional power supply circuit.
The AC power supply 101 supplies AC power to the full-wave rectifier circuit 200. The full-wave rectifier circuit 200 is configured as a bridge by four diodes 210, 220, 230, and 240. The full-wave rectifier circuit 200 and the input capacitor 300 are smoothed by full-wave rectifying the AC voltage of the AC power supply 101 into a DC voltage.
One end of the capacitor 310 is connected to one terminal on the AC side of the full-wave rectifier circuit 200, and the other end of the capacitor 310 is connected to the positive terminal of the capacitor 320 through the diode 140. The negative terminal of the capacitor 320 is connected to the other end of the capacitor 310 via the diode 150.
[0008]
The operation of the power supply circuit for the conventional power supply device shown in FIG. 3 will be described below.
In FIG. 3, the AC voltage of the AC power supply 101 is full-wave rectified and smoothed to a DC voltage by the full-wave rectifier circuit 200 and the input capacitor 300. When the AC line connected to the full-wave rectifier circuit 200 is at a high potential, the current flows from the AC power source 101 to the capacitor 310 connected to one end of the AC line of the full-wave rectifier circuit 200, and the diode 140 and the full-wave rectifier circuit 200. To the AC power supply 101 through the diode 240. At this time, the capacitor 320 is charged together with the capacitor 310.
Conversely, when the AC line connected to the full-wave rectifier circuit 200 swings to a negative potential, current flows from the AC power source 101 to the diode 220, the input capacitor 300, the diode 150, and the capacitor 310 of the full-wave rectifier circuit 200. At this time, the electric charge charged in the capacitor 310 is discharged. This discharge loop is indicated by a broken line in FIG.
As described above, the capacitor 310 repeats the charging / discharging operation, so that the power from the AC power supply 101 is supplied to the capacitor 320 through the capacitor 310 and charged.
[0009]
[Problems to be solved by the invention]
In the power supply circuit for the conventional power supply device shown in FIG. 3, when the AC line to which the capacitor 310 is connected swings to a negative potential, the discharge current of the capacitor 310 flows in the direction of charging the input capacitor 300.
With recent energy savings in electronic devices, light loads in the standby mode are progressing. When the power supply circuit shown in FIG. 3 is employed in such an electronic device, the load on the input capacitor 300 is further reduced. For this reason, when the discharge power from the input capacitor 300 becomes smaller than the charge power to the input capacitor 300, there is a problem that the potential of the input capacitor 300 rises abnormally.
It is an object of the present invention to provide a power supply circuit with little power loss and a power supply device using the same without causing the potential of the input capacitor to rise abnormally even when the load is light.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a power supply device according to the present invention includes an AC power source that outputs an AC voltage, a full-wave rectifying and smoothing circuit that converts an AC voltage from the AC power source into a DC voltage, and the full-wave rectifying and smoothing circuit. output DC voltage converter for supplying a load by converting a predetermined power mode, the electrical characteristic which is connected to one end of each of the respective AC lines of the AC power supply and the first capacitor is substantially equal to the second The other end of each of the first capacitor and the second capacitor is connected to each line on the input side, and the negative line on the output side is connected to the negative line on the output side of the full-wave rectifying and smoothing circuit full-wave rectifier circuit of the diode bridge configuration, the third connected to the output side each line of the full-wave rectifier circuit of a diode bridge configuration capacitor, said first capacitor and the second The power supply circuit having a capacitor and said third capacitor and said full-wave rectifier circuit as a power supply at startup, control drive circuit for driving the converter to control the power mode to be supplied to the load, and, said converter A power supply circuit that charges the third capacitor during normal operation and serves as a power source for the control drive circuit .
According to the present invention, it is possible to provide a power supply device that does not abnormally increase the potential of the input capacitor of the full-wave rectifying / smoothing circuit even during an extremely light load, and that has less power loss. The power supply device according to the present invention may be configured such that the capacities of the first capacitor and the second capacitor are substantially the same, and the charge / discharge currents of each other are balanced.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of a power supply circuit and a power supply apparatus using the same according to the present invention will be described with reference to the accompanying drawings.
[0013]
Example 1
FIG. 1 is a circuit diagram showing a circuit configuration of a power supply device using the power supply circuit according to the first embodiment of the present invention.
In FIG. 1, an AC power source 1 supplies AC power to a full-wave rectifier circuit 2 having a bridge configuration of diodes 21, 22, 23, and 24 and a full-wave rectifier circuit 11 having a bridge configuration of diodes 14, 15, 16, and 17. Supply. The full-wave rectifying / smoothing circuit includes a full-wave rectifying circuit 2 and an input capacitor 3, and converts an AC voltage from the AC power source 1 into a DC voltage.
The switching circuit 4 is configured by elements such as a switching transistor and a power MOSFET, and converts an input DC voltage into a high-frequency AC voltage by an on / off operation. The transformer 5 has a primary winding 5a, a secondary winding 5b, and a control winding 5c. In the switching circuit 4, the high-frequency AC voltage obtained by the switching operation is input to the primary winding 5 a of the transformer 5. Further, an AC voltage that is insulated and transformed is output to the secondary winding 5b and the control winding 5c of the transformer 5.
[0014]
The diode 6 and the output capacitor 7 connected to the secondary winding 5 b of the transformer 5 rectify and smooth the AC voltage generated in the secondary winding 5 b and supply DC power to the load 8. As described above, the converter 4, the transformer 5, the diode 6, and the output capacitor 7 constitute a converter that converts the output of the full-wave rectifying / smoothing circuit into DC power and supplies it to the load 8. The control drive circuit 9 controls the switching circuit 4 that adjusts the DC power output to the load 8. The diode 25 and the third capacitor 11 connected to the control winding 5 c of the transformer 5 rectify and smooth the AC voltage generated in the control winding 5 c and supply it as a power source for the control drive circuit 9.
One end of each of the first capacitor 12 and the second capacitor 13 is connected to the AC power source 1 and has the same electrical characteristics. A first capacitor 12 and a second capacitor 13 are connected to each input terminal of the full-wave rectifier circuit 11 bridged by the diodes 14, 15, 16, and 17. A third capacitor 10 is connected to the output terminal and is configured to charge the third capacitor 10.
[0015]
Next, the operation of the power supply device according to the first embodiment will be described.
The AC power source 1 supplies AC power to the full-wave rectifier circuit 2. The AC voltage of the AC power source 1 is full-wave rectified and smoothed by the full-wave rectifier circuit 2 and the input capacitor 3 connected to the output terminal, and converted into a DC voltage.
The switching circuit 4 converts the input DC voltage into a high-frequency AC voltage by an on / off operation. This high-frequency AC voltage is input to the primary winding 5a of the transformer 5, and the transformed high-frequency AC voltage is output from the secondary winding 5b. The high-frequency AC voltage generated in the secondary winding 5 b is rectified and smoothed by the diode 6 and the output capacitor 7, output as a DC voltage, and supplied to the load 8. The DC voltage output from the power supply device is adjusted by the on / off ratio of the switching circuit 4.
[0016]
The control drive circuit 9 detects a DC voltage supplied to the load 8 and compares it with a reference voltage. The control drive circuit 9 outputs a pulse signal having an on / off ratio adjusted so as to correct an error between the detected DC voltage and the reference voltage.
The AC voltage generated in the control winding 5 c is rectified and smoothed by the diode 25 and the third capacitor 10 and becomes a power source for the control drive circuit 9.
[0017]
Next, a power supply circuit that supplies power to the control drive circuit 9 in the power supply device according to the first embodiment will be described. In this power supply circuit, AC power is supplied from the AC power supply 1 to the control drive circuit 9 as follows.
First, when the AC line to which the first capacitor 12 is connected is rising at a high potential, the current is AC power source 1 → first capacitor 12 → diode 14 → third capacitor 10 → diode 17 → second capacitor. 13 → Flows along the AC power source 1 As a result, the first capacitor 12 and the third capacitor 10 are charged, and the second capacitor 13 is discharged.
[0018]
Next, when the potential of the AC line of the full-wave rectifier circuit 2 to which the first capacitor 12 is connected becomes equal to the potential of the input capacitor 3, the full-wave rectifier circuit 2 becomes conductive and the input capacitor 3 is charged. At the same time as the input capacitor 3 is charged, current flows through the path of the AC power source 1 → the first capacitor 12 → the diode 14 → the third capacitor 10 → the diode 24 of the full-wave rectifier circuit 2 → the AC power source 1. As a result, the first capacitor 12 and the third capacitor 10 are charged.
Next, when the potential of the AC line to which the first capacitor 12 is connected decreases and becomes lower than the potential of the input capacitor 3, the full-wave rectifier circuit 2 becomes non-conductive, and the current flows from the AC power source 1 to the second capacitor 13. The current flows through the path of the diode 16 → the third capacitor 10 → the diode 15 → the first capacitor 12 → the AC power supply 1. As a result, the first capacitor 12 is discharged, and the second capacitor 13 and the third capacitor 10 are charged.
[0019]
When the potential of the AC line of the full-wave rectifier circuit 2 is inverted and the potential of the AC line becomes equal to the potential of the input capacitor 3, the full-wave rectifier circuit 2 becomes conductive and the input capacitor 3 is charged. At the same time as the input capacitor 3 is charged, current flows through the path of the AC power source 1 → the second capacitor 13 → the diode 16 → the third capacitor 10 → the diode 23 of the full-wave rectifier circuit 2 → the AC power source 1. As a result, the second capacitor 13 and the third capacitor 10 are charged.
By repeating the above operation, the third capacitor 10 is supplied with power from the AC power supply 1 via the first capacitor 12 and the second capacitor 13. The charge / discharge currents in the first capacitor 12 and the second capacitor 13 are balanced with each other, and the input capacitor 3 is not charged.
Since the power supply circuit according to the first embodiment operates as described above, it is possible to reliably prevent the voltage of the input capacitor 3 from rising abnormally at an extremely light load.
[0020]
In the power supply device according to the first embodiment, the power supply circuit including the first capacitor 12, the second capacitor 13, the third capacitor 10, and the bridge circuit 11 is used as a starting power supply for the control drive circuit 9. In the above description, power is supplied from the control winding 5c of the transformer 5 to the power supply during normal operation. However, the power supply circuit according to the present invention can function as a power supply circuit even when the power supply circuit configured by the first capacitor 12, the second capacitor 13, the third capacitor 10, and the bridge circuit 11 is used alone. It is. In this case, the voltage of the third capacitor 10 is Ec, the peak value of the AC voltage supplied from the input power supply 1 is Ei, the load current of the third capacitor 10 is Io, the first capacitor 12 and the second capacitor 13. Are equal to C and the frequency is f, the voltage Ec of the third capacitor 10 has a relationship represented by the following formula (1).
[0021]
Ec = Ei-Io / (2Cf) --- (1)
[0022]
When the power supply circuit configured as described above is used alone, the third capacitor 10 is charged with full waves from the AC power supply 1. Therefore, when the same power is supplied as compared with the conventional power supply circuit (FIG. 3) that is charged with half-wave, the capacitances of the first capacitor 12 and the second capacitor 13 are half, The ripple voltage superimposed on the voltage Ec of the third capacitor 10 is reduced.
[0023]
【The invention's effect】
As is apparent from the detailed description of the embodiments, the present invention has the following effects.
According to the power supply device using the power supply circuit according to the present invention, the starting resistor is unnecessary, and the first and second capacitors connected to the AC power supply are configured to balance the charge / discharge currents. Therefore, there is no path for charging the input capacitor, and the voltage does not rise abnormally at the very light load.
In addition, the power supply circuit according to the present invention is configured to supply power at full wave as compared with the conventional half-wave rectification power supply circuit, and therefore, the electrostatic capacitance of the first capacitor and the second capacitor. The advantageous effect that the capacitance can be kept low and the ripple voltage superimposed on the voltage of the capacitor as the output voltage is also reduced is obtained.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing a circuit configuration of a switching power supply device using a power supply circuit according to a first embodiment of the present invention.
FIG. 2 is a circuit diagram showing a circuit configuration of a conventional switching power supply device.
FIG. 3 is a circuit diagram showing a circuit configuration of a conventional power supply circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 AC power supply 2 Full wave rectifier circuit 3 Input capacitor 4 Switching circuit 5 Transformer 6 Diode 7 Output capacitor 8 Load 9 Control drive circuit 10 Third capacitor 11 Full wave rectifier circuit 12 First capacitor 13 Second capacitor

Claims (1)

AC power supply that outputs AC voltage,
A full-wave rectifying / smoothing circuit for converting an AC voltage from the AC power source into a DC voltage;
A converter for converting a DC voltage output from the full-wave rectifying and smoothing circuit into a predetermined power form and supplying the converted voltage to a load;
First and second capacitors electrical properties connected to one ends to each AC line of the AC power supply are substantially equal,
Diode bridge configuration in which the other end of each of the first capacitor and the second capacitor is connected to each line on the input side, and the negative line on the output side is connected to the negative line on the output side of the full-wave rectifying and smoothing circuit Full-wave rectifier circuit,
A third capacitor connected to each line on the output side of the full-wave rectifier circuit having the diode bridge configuration;
A power supply circuit having the first capacitor, the second capacitor, the third capacitor, and the full-wave rectifier circuit is used as a power source at the time of start-up, and the converter is controlled to control the form of power supplied to the load. A control drive circuit for driving, and
A power supply circuit that charges the third capacitor during normal operation of the converter and serves as a power source for the control drive circuit;
A power supply device comprising:

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