JPH11235030A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power supply which can improve energy conversion efficiency in waiting. SOLUTION: A current limiter capacitor C11 is connected between one end of output terminal of an AC power supply 1 and one end of an input terminal of a rectifier block 4, and a triac 3 is connected in parallel to the current limiter capacitor C11. In waiting, the triac 3 is turned OFF and the AC voltage input via the current limiter capacitor C11 from the AC power supply 1 is rectified by the rectifier block 4. In this case, the rectifier block 4 side is limited by the current limiter capacitor C11. After the DC voltage filtered by the filter capacitor C4 is converted to a high frequency voltage by turning OFF the switching transistor 5 with the control circuit 6, it is then converted to the high frequency voltage of the predetermined voltage with a transformer T and a DC voltage can be outputted by filtering the converted high frequency voltage with the diode D6 and filter capacitor C5.

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 capable of reducing power consumption during a standby operation.

[0002]

2. Description of the Related Art Conventionally, as a switching power supply,
There is a type that converts a rectified and smoothed DC current from a commercial AC power supply to a desired DC voltage with high efficiency by using a switching element and a small transformer that turns on and off at a high frequency of several hundred kHz. In the electronic equipment using this switching power supply, in order to increase the speed of transition from the standby operation state in which the power consumption is reduced to the normal operation state and to improve the convenience, in the standby operation state, the setting of the electronic apparatus side in the normal operation is set. While maintaining the state, the function for receiving the remote control operation signal is operated, and a small amount of electric power for operating the function such as displaying the setting state of the electronic device during normal operation is reduced from the switching power supply device to the electronic device body. Supplied to

As a switching power supply device having improved energy conversion efficiency when supplying power to the electronic device body in the standby operation state, there has been proposed a switching power supply device having a lower switching frequency during standby operation than during normal operation.

FIG. 6 is a circuit diagram of a switching power supply for lowering the switching frequency during the standby operation. In FIG. 6, in a normal operation state, an alternating current supplied from a commercial AC power supply 1 is rectified through a fuse 2, a line filter L, a triac 3, and a rectifying block 4 (diodes D1 to D4), and is rectified. After being smoothed by the capacitor C4, the current flows to the ground GND via the primary winding Ta of the transformer T and the switching transistor 5 PWM (pulse width modulation) controlled by the control unit 6.
A capacitor C1 is connected between the input terminals of the line filter L, and a capacitor C1 is connected between the output terminals of the line filter L.
2, the switching noise is prevented from leaking outside through the power supply line by the line filter L, the capacitor C1, and the capacitor C2.

The control circuit 6 performs switching based on a secondary output voltage detection signal transmitted through a secondary output voltage detection circuit 7 and a photocoupler PC1 (diode section PC1a, transistor section PC1b). Transistor 5
By controlling the timing of the switching operation, the secondary-side output voltage is stabilized. Immediately after the AC voltage from the AC power supply 1 is input to this switching power supply device, the triac 3 is not biased to a positive voltage. The current is the resistance R1 and the rectifier block 4
And gradually flows to the smoothing capacitor C4 side to suppress the rapid charging current (rush current) flowing into the smoothing capacitor C4.

When the charging voltage of the smoothing capacitor C4 becomes equal to or higher than a predetermined value, the control circuit 6 and the switching transistor 5 start a switching operation, so that the secondary winding Tc of the transformer T switches the diode D5 and the resistor R4. A positive voltage is applied to the gate of the triac 3 via the resistor R3 and the triac 3 is turned on. Thereafter, the AC current from the AC power supply 1 is supplied to the rectifying block 4 via the triac 3.

[0007] The switching frequency of the switching power supply is switched to, for example, the following two stages by the voltage of a control signal input to the control input terminal CNT. During normal operation, the electronic device main body to which power is supplied from the switching power supply holds a control signal input to the control input terminal CNT at a predetermined voltage level, and operates the switching power supply at a high switching frequency. do it,
Outputs large current. On the other hand, when the electronic device main body is in a standby operation, the control signal input to the control input terminal CNT is switched to another voltage level, and the switching power supply device is operated at a low switching frequency to output a small current.

[0008] The most important factor in reducing the loss when the switching frequency is reduced will be described below.

A stray capacitance C22 exists between the primary winding Ta of the transformer T and the drain of the switching transistor 5, and a parasitic capacitance C23 exists between the drain of the switching transistor 5 and the ground GND.
Is present, and each time the switching transistor 5 is turned on, the charge stored in the floating capacitance C22 and the parasitic capacitance C23 is rapidly released. Also, one of the transformers T
A parasitic capacitance C21 exists between both ends of the next winding Ta, and is charged rapidly each time the switching transistor 5 is turned on. Energy due to the charging and discharging currents of the parasitic capacitances C21 and C23 and the floating capacitance C22 is wasted in the switching transistor 5.

FIG. 7 to FIG. 9 are circuit diagrams of main parts for explaining the above-mentioned charge / discharge. 7 to 9, the switching transistor 5 is replaced with a switch in order to clarify the conductive state (ON or OFF) of the switching transistor 5.

FIG. 7 shows the charged state of the parasitic capacitances C21 and C23 and the floating capacitance C22 when the switching transistor 5 is off. In this state, the parasitic capacitance C
21 has a charging voltage of 0 V, and has a stray capacitance C22 and a parasitic capacitance C2.
The charging voltage of No. 3 is the same charging voltage EB as the smoothing capacitor C4.

When the switching transistor 5 is turned on from the state shown in FIG. 7 as shown in FIG. 8, the charges charged in the stray capacitance C22 and the parasitic capacitance C23 as shown by the arrows are:
While being discharged rapidly via the switching transistor 5, the parasitic capacitance C21 is rapidly charged via the switching transistor 5.

The loss due to the charging / discharging current mainly occurs in the switching transistor 5, and the loss PC at this time is:

(Equation 1) Here, CF = c21 + c22 + c23 c21: capacitance value of parasitic capacitance C21 c22: capacitance value of stray capacitance C22 c23: capacitance value of parasitic capacitance C23 EB: charging voltage of smoothing capacitor C4 fs: switching frequency of switching transistor 5 .

When the charging / discharging is completed, the parasitic capacitance C21,
As shown in FIG. 9, the charging voltage of C23 and the stray capacitance C22 is
The charging voltage of the parasitic capacitance C21 becomes the same as the charging voltage EB of the smoothing capacitor C4, the stray capacitance C22 and the parasitic capacitance C23 become 0 V, and the current flows through the primary winding Ta of the transformer T as shown by the arrow. It flows (accurately, it starts from the state of FIG. 8, but is expressed in this way for convenience).

As described above, in the switching power supply device, the switching frequency is reduced during the standby operation, so that the loss amount PC is reduced in proportion to the switching frequency, as is apparent from the equation (1).

[0016]

In recent years, interest in energy saving has been increasing, and there has been an increasing demand for lower power consumption to further reduce the power consumption during the standby operation of the electronic device as described above. However,
The switching power supply that lowers the switching frequency during the standby operation has a problem in that there is a limit in increasing the energy conversion efficiency.

An object of the present invention is to provide a switching power supply that can improve energy conversion efficiency during standby operation.

[0018]

According to a first aspect of the present invention, there is provided a switching power supply device comprising: a rectifier for rectifying an AC voltage from an AC power supply to a DC voltage; and a rectifier connected between an output terminal of the rectifier. A smoothing capacitor for smoothing the DC voltage rectified by the rectifier, and a DC-AC converter for converting the DC voltage to a high-frequency voltage by turning on and off the DC voltage smoothed by the smoothing capacitor. Unit, a transformer for converting the high-frequency voltage converted by the DC-AC converter to a predetermined voltage, and a smoothing unit for smoothing the high-frequency voltage converted to the predetermined voltage by the transformer to a DC voltage. A switching power supply device, wherein a current-limiting reactance element connected between one end of an output terminal of the AC power supply and one end of an input terminal of the rectifying unit; It is characterized in that a first switching element connected in parallel with the current limiting reactance element.

According to the switching power supply device of the first aspect, during the normal operation, the first switching element connected in parallel with the current limiting reactance element is turned on, so that the AC voltage from the AC power supply is reduced. The AC voltage input through one switching element is rectified by a rectifying unit and smoothed by a smoothing capacitor connected between output terminals of the rectifying unit. Then, by turning on and off the DC voltage smoothed by the smoothing capacitor by a DC-AC converter, the DC voltage is converted into a high-frequency voltage, and then the transformer converts the high-frequency voltage from the DC-AC converter into a high-frequency voltage. Convert to a predetermined voltage. The high-frequency voltage converted to a predetermined voltage by the transformer is smoothed by the smoothing unit to be a DC voltage. On the other hand, at the time of standby operation, by turning off the first switching element connected in parallel to the current limiting reactance element, it is connected between one end of the output terminal of the AC power supply and one end of the input terminal of the rectifier. The AC voltage from the AC power supply is input to the rectifier through the current limiting reactance element, and the AC current input to the rectifier is limited by the current limiting reactance element. By using, for example, a capacitor as the current-limiting reactance element and appropriately setting the capacitance of the capacitor, the charging voltage of the smoothing capacitor is reduced to about の of that in the normal operation when the electronic apparatus main body enters the standby operation. Can be reduced to the level of By doing so, it is possible to reduce charge / discharge losses of various parasitic capacitances and stray capacitances generated when the switching element used in the DC-AC converter performs a switching operation, and it is possible to improve power conversion efficiency.

Further, by using the method of improving the power conversion efficiency of the switching power supply of the present invention together with a method of reducing the switching frequency in the standby operation mode, for example, a greater effect can be obtained by a synergistic effect of these. be able to.

According to a second aspect of the present invention, in the switching power supply of the first aspect, the switching power supply is connected between a first switching element controller for turning off the first switching element during a standby operation and an output terminal of the rectifier. A second switching element connected to the rectifier side with respect to the smoothing capacitor; and a second switching element connected between one end of the second switching element and one end of the smoothing capacitor connected to the one end. A backflow preventing diode arranged so that electric charges charged in the smoothing capacitor are not discharged through the second switching element when the switch is on, and a charging voltage of the smoothing capacitor during a standby operation is a predetermined voltage. And a charging voltage control unit that controls on / off of the second switching element. That.

According to the switching power supply device of the second aspect, during the standby operation, the first switching element control section turns off the first switching element connected in parallel to the current limiting reactance element, and The second switching element connected between the output terminals of the rectifying unit and closer to the rectifying unit than the smoothing capacitor is turned on / off by the charging voltage control unit so that the charging voltage of the smoothing capacitor becomes a predetermined voltage. At this time, when the second switching element is on, the smoothing capacitor is connected to the second switching element by a backflow prevention diode arranged between one end of the second switching element and one end of the smoothing capacitor connected to the one end. The charged electric charge is prevented from being discharged through the second switching element. Therefore, by controlling the on / off of the second switching element, the charging voltage of the smoothing capacitor can be further reduced from about half the level in normal operation,
The power conversion efficiency can be particularly improved. In addition, since it is not necessary to employ an element having a large current rating as the second switching element and a small and inexpensive transistor can sufficiently cope with it, the power conversion efficiency in the standby operation mode can be improved at a very low cost. Furthermore, the charging voltage of the smoothing capacitor is finely set to a more effective value by turning on and off the second switching element while limiting the charging current to the smoothing capacitor during the standby operation by the current limiting reactance element. it can.

According to a third aspect of the present invention, in the switching power supply of the second aspect, the voltage across the smoothing capacitor is detected, and the voltage across the smoothing capacitor is set to an upper limit of a predetermined range. A charging voltage determination unit that determines whether the voltage is equal to or less than the lower limit value of the predetermined range. When it is determined that the voltage is equal to or more than the upper limit of the range, the second switching element is turned on, and when the charging voltage determination unit determines that the voltage across the smoothing capacitor is equal to or less than the lower limit of the predetermined range, The second switching element is turned off.

According to the switching power supply device of the third aspect, during a standby operation, the first switching element control section turns off the first switching element connected in parallel to the current limiting reactance element, and The charging voltage judging unit detects the voltage at both ends of the smoothing capacitor, that is, the charging voltage, and when the charging voltage judging unit judges that the charging voltage of the smoothing capacitor is equal to or higher than the upper limit of a predetermined range, the charging voltage The second switching element is turned on by the control unit. Then, the current limited by the current limiting reactance from the AC power supply is:
Since the current flows through the second switching element, the smoothing capacitor is not charged and supplies power to the electronic device main body side, and the charging voltage of the smoothing capacitor drops. on the other hand,
When the charging voltage of the smoothing capacitor drops and the charging voltage determining unit determines that the charging voltage of the smoothing capacitor is equal to or lower than the lower limit of the predetermined range, the charging voltage control unit turns off the second switching element. . Then, the current from the AC power supply limited by the current limiting reactance flows to the smoothing capacitor side via the rectifying unit and the backflow preventing diode, and the smoothing capacitor is charged, and the charging voltage of the smoothing capacitor is reduced. Rise. Thus, the charging voltage of the smoothing capacitor can be kept within the predetermined range, and the charging voltage of the smoothing capacitor during the standby operation can be reliably maintained at the optimum value.

According to a fourth aspect of the present invention, in the switching power supply of the second aspect, the voltage between the output terminals of the rectifier is detected to detect the voltage between the output terminals of the rectifier. A charging voltage determining unit configured to determine whether a voltage between output terminals of the rectifying unit is equal to or higher than an upper limit value of a predetermined range or a voltage between output terminals of the rectifying unit is equal to or lower than a lower limit value of the predetermined range. The voltage control unit turns on the second switching element when the charging voltage determination unit determines that the voltage between the output terminals of the rectification unit is equal to or higher than the upper limit value of the predetermined range during the standby operation, and When the voltage determining unit determines that the voltage between the output terminals of the rectifying unit is equal to or less than the lower limit of the predetermined range, the voltage determining unit turns off the second switching element.

According to the switching power supply device of the fourth aspect, during the standby operation, the first switching element control section turns off the first switching element connected in parallel with the current limiting reactance element, and The charging voltage determining unit detects a voltage between the output terminals of the rectifying unit, and when the charging voltage determining unit determines that the voltage between the output terminals of the rectifying unit is equal to or higher than an upper limit value of a predetermined range, the charging voltage control. The second switching element is turned on by the unit.
Then, the current limited by the current limiting reactance flows from the AC power supply through the second switching element, so that the smoothing capacitor is not charged and supplies power to the electronic device body side, and the smoothing capacitor is not charged. Charging voltage drops. On the other hand, when the charging voltage of the smoothing capacitor drops and the charging voltage determining unit determines that the voltage between the output terminals of the rectifying unit is equal to or lower than the lower limit of a predetermined range, the charging voltage control unit controls the second switching. Turn off the device. Then, the current from the AC power supply limited by the current limiting reactance flows to the smoothing capacitor side via the rectifying unit and the backflow preventing diode, and the smoothing capacitor is charged, and the charging voltage of the smoothing capacitor is reduced. Rise. Thus, the charging voltage of the smoothing capacitor can be kept within the predetermined range, and the charging voltage of the smoothing capacitor during the standby operation can be reliably maintained at the optimum value.

According to a fifth aspect of the present invention, in the switching power supply of the first aspect, a first switching element controller for turning off the first switching element during a standby operation, and a voltage across the smoothing capacitor. And a third switching element connected between one of the input terminals of the rectifying unit and ground, and a charging voltage determining unit for detecting the charging voltage of the smoothing capacitor.
A fourth switching element connected between the other of the input terminals of the rectifying unit and ground, and a charging voltage of the smoothing capacitor within a predetermined range based on a determination result of the charging voltage determining unit during a standby operation. So that the third and fourth
And a charging voltage control section for controlling on / off of each of the switching elements.

According to the switching power supply device of the fifth aspect, during the standby operation, the first switching element control section turns off the first switching element connected in parallel to the current limiting reactance element, and the first switching element control section turns off the first switching element. The charging voltage determination unit determines the voltage at both ends of the smoothing capacitor, that is, the charging voltage, and based on the determination result of the charging voltage determination unit, for example, when the charging voltage of the smoothing capacitor is equal to or more than the upper limit of a predetermined range. The third and fourth switching elements are turned on by the charging voltage controller. Then, the current limited by the current limiting reactance from the AC power supply flows through the third and fourth switching elements, and no current is output from the rectifying unit, so that the smoothing capacitor is not charged and the electronic device is not charged. Power is supplied to the main body, and the charging voltage of the smoothing capacitor drops.
On the other hand, the charging voltage of the smoothing capacitor drops, and based on the determination result of the charging voltage determining unit, for example, when the charging voltage of the smoothing capacitor is equal to or less than a lower limit value of a predetermined range, the charging voltage control unit The third and fourth switching elements are turned off. Then, the current from the AC power supply limited by the current limiting reactance flows to the smoothing capacitor side via the rectifier, and the smoothing capacitor is charged, and the charging voltage of the smoothing capacitor increases.

Therefore, the backflow prevention diode is not used, and the loss due to the forward voltage drop of the backflow prevention diode is eliminated, so that the power conversion efficiency can be further improved. In addition, since it is not necessary to employ an element having a large current rating as the third and fourth switching elements, and a low-cost small transistor is sufficient, the power conversion efficiency in the standby operation mode can be improved at low cost. be able to. Further, the third and fourth switching elements are turned on and off while the charging current to the smoothing capacitor during the standby operation is limited by the current limiting reactance element, so that the charging voltage of the smoothing capacitor becomes more effective. Can be set finely.

According to a sixth aspect of the present invention, in the switching power supply of the first aspect, a first switching element controller for turning off the first switching element during a standby operation, and a voltage across the smoothing capacitor. And a charging voltage determining unit that determines a charging voltage of the smoothing capacitor, and a charging voltage of the smoothing capacitor that falls within a predetermined range based on a determination result of the charging voltage determining unit during a standby operation. And a charging voltage control unit that controls on / off of the first switching element.

According to the switching power supply device of the sixth aspect, during the standby operation, the first switching element control section turns off the first switching element connected in parallel with the current limiting reactance element, and The charging voltage determination unit determines the voltage at both ends of the smoothing capacitor, that is, the charging voltage, and based on the determination result of the charging voltage determination unit, for example, when the charging voltage of the smoothing capacitor is equal to or more than the upper limit of a predetermined range. The first switching element is turned off by the charging voltage control unit. Then, the smoothing capacitor is charged by the current limited by the current limiting reactance from the AC power supply, and power is supplied to the electronic device body. At this time, the reactance of the current-limiting reactance element is set so that the current supplied through the current-limiting reactance element is smaller than the current discharged from the smoothing capacitor to the DC-AC converter. By,
The charging voltage of the smoothing capacitor drops. On the other hand, the charging voltage of the smoothing capacitor drops, and based on the determination result of the charging voltage determining unit, for example, when the charging voltage of the smoothing capacitor is equal to or less than a lower limit value of a predetermined range, the charging voltage control unit The first switching element is turned on. Then, the current from the AC power supply flows to the smoothing capacitor side via the first switching element and the rectifier,
The smoothing capacitor is charged, and the charging voltage of the smoothing capacitor increases. Thus, the charging voltage of the smoothing capacitor can be kept within the predetermined range, and the charging voltage of the smoothing capacitor during the standby operation can be reliably maintained at the optimum value.

Therefore, the backflow blocking diode is not used, and the loss due to the forward voltage drop of the backflow blocking diode is eliminated, so that the power conversion efficiency can be further improved. Further, the charging voltage of the smoothing capacitor is finely set to a more effective value by turning on and off the first switching element while limiting the charging current to the smoothing capacitor during the standby operation by the current limiting reactance element. it can.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a switching power supply according to the present invention will be described in detail with reference to the illustrated embodiments.

(First Embodiment) FIG. 1 is a circuit diagram of a flyback type PWM (pulse width modulation) control switching power supply according to a first embodiment of the present invention.

As shown in FIG. 1, in this switching power supply, one end of an output terminal of a commercial AC power supply 1 is connected to one end of an input terminal of a line filter L via a fuse 2, and the output of the AC power supply 1 The other end of the terminal is connected to the other end of the input terminal of the line filter L. A capacitor C1 is connected between the input terminals of the line filter L, and a capacitor C2 is connected between the output terminals of the line filter L. The capacitors C1 and C2 and the line filter L prevent switching noise from leaking to the outside via the power supply line (measures against unnecessary radiation).

One end of the output terminal of the line filter L is connected to one end of a current limiting capacitor C11 as a current limiting reactance element, and the other end of the current limiting capacitor C11 is connected to the cathode of a diode D1. ing. Connect the anode of the diode D1 to ground GND.
Connected to On the other hand, the other end of the output terminal of the line filter L is connected to the cathode of the diode D2, and the anode of the diode D2 is connected to the anode of the diode D1. The anode of the diode D3 is connected to the cathode of the diode D1, the anode of the diode D4 is connected to the cathode of the diode D2, and the cathode of the diode D3 is connected to the cathode of the diode D4. A rectification block 4 as a rectification unit is configured.

A triac 3 as a first switching element is connected in parallel to the current limiting capacitor C11. Connection point A between the gate of triac 3, the cathode of diode D1, and the anode of diode D3
Is connected to a resistor R2. The gate of the triac 3 is connected to the collector of the transistor section PC2b of the photocoupler PC2, and the emitter of the transistor section PC2b is connected to the connection point A. The connection point A between the cathode of the diode D1 and the anode of the diode D3 is connected to one end of the secondary winding Tc of the transformer T. In addition, resistors R3 and R4 are connected to the gate of the triac 3.
Are connected in series from the triac 3 side, a cathode of a diode D5 is connected to one end of the resistor R4 opposite to the resistor R3, and an anode of the diode D5 is connected to the other end of the secondary winding Tc of the transformer T. Connected. The positive terminal of the capacitor C3 is connected to the connection point between the resistors R3 and R4, and the negative terminal of the capacitor C3 is connected to the connection point A between the cathode of the diode D1 and the anode of the diode D3.

A positive terminal of a smoothing capacitor C4 is connected to a connection point B between the cathode of the diode D3 and the cathode of the diode D4.
Is connected to the ground GND. A transformer T is connected to the positive terminal of the smoothing capacitor C4.
Is connected to one end of the primary winding Ta. The drain of the switching transistor 5 is connected to the other end of the primary winding Ta of the transformer T.
Are connected to the ground GND. The switching signal from the control circuit 6 is input to the gate of the switching transistor 5. The control circuit 6 includes:
The power supply voltage Vcc is applied, and the ground GND is connected. The switching transistor 5 and the control circuit 6 constitute a DC-AC converter.

The anode of the diode D6 is connected to one end of the secondary winding Tb of the transformer T, and the positive terminal of the smoothing capacitor C5 is connected to the cathode of the diode D6. The negative terminal of the smoothing capacitor C5 is connected to the other end of the secondary winding Tb of the transformer T. The output terminal 8a is connected to the positive terminal of the smoothing capacitor C5, and the output terminal 8b is connected to the negative terminal of the smoothing capacitor C5. The diode D6 and the smoothing capacitor C5 constitute a smoothing unit.

A secondary output voltage detection circuit 7 for detecting a secondary output voltage is connected between the output terminal 8a and the output terminal 8b. One end of the output terminal of the secondary output voltage detection circuit 7 is connected to the anode of the diode portion PC1a of the photocoupler PC1, and the other end of the output terminal of the secondary output voltage detection circuit 7 is connected to the diode of the photocoupler PC1. The cathode of the unit PC1a is connected. The collector of the transistor section PC1b of the photocoupler PC1 is connected to the input terminal for the secondary side output voltage detection signal of the control circuit 6, and the emitter of the transistor section PC1b is connected to the ground GN.
Connected to D.

The control input terminal CNT to which a control signal is input is connected to the cathode of the diode section PC2a of the photocoupler PC2. The above photocoupler PC
One end of the resistor R5 is connected to the anode of the second diode section PC2a, and the power supply voltage Vcc is applied to the other end of the resistor R5. The other end of the resistor R5 is connected to the positive terminal of the capacitor C6, and the negative terminal of the capacitor C6 is connected to the ground GND. The photocoupler PC2, the resistor R5 and the capacitor C6 constitute a first switching element control unit.

In the switching power supply having the above configuration, in the normal operation mode, the alternating current supplied from the commercial AC power supply 1 is rectified through the fuse 2, the line filter L, the triac 3, and the rectification block 4 to be smoothed. Of the transformer T after being smoothed by the
The current flows to the ground GND via the next winding Ta and the switching transistor 5 that is turned on / off. The control circuit 6 performs an arithmetic processing on the secondary output voltage detection signal transmitted through the secondary output voltage detection circuit 7 and the photocoupler PC1 and the internal oscillation signal, and performs switching of the switching transistor 5. By controlling the operation timing by PWM, the secondary side output voltage is stabilized.

When the switching power supply starts to be started, the triac 3 is off because the induced voltage of the secondary winding Tc is zero, so that the current from the AC power supply 1 is supplied to the current limiting capacitor C11. Is supplied to the smoothing capacitor C4 via the rectifying block 4. Then, the voltage across the smoothing capacitor C4 gradually rises, thereby preventing a rapid rush current from flowing from the AC power supply 1 when the power is turned on. Further, as the charging voltage of the smoothing capacitor C4 gradually rises, after the power supply voltage Vcc for internal control of the switching power supply rises, the control circuit 6 starts operating. 5, the DC voltage is output from the output terminals 8a and 8b, and a voltage is induced in the secondary winding Tc with the start of the startup of the switching power supply. A voltage is applied to the gate of the triac 3 via R3, and the triac 3 is turned on. In this state, when the control signal input to the control input terminal CNT from the electronic device main body (not shown) is set to the high (High) level in the normal operation mode, the triac 3 is turned on and the normal operation is performed. When the control signal is set to the low level in the standby operation mode, the triac 3 is turned off to perform a light output standby operation.

[Explanation of Operation in Normal Operation Mode] In the normal operation mode, since the control signal input to the control input terminal CNT is held at a high level, the photocoupler PC2
No current flows through the diode portion PC2a, and the phototransistor portion PC2b is off. Therefore, the gate of the triac 3 is connected to the secondary winding Tc,
A positive voltage is applied via the diode D5 and the resistor R3, and the triac 3 is turned on.

[Explanation of Operation in Standby Operation Mode] In the standby operation mode, when the control signal input to the control input terminal CNT is lowered to a low level, a current flows through the diode portion PC2a of the photocoupler PC2 and the phototransistor portion P
Since C2b is turned on, the gate of triac 3 goes low, and triac 3 is turned off. Therefore, the AC current supplied from the AC power supply 1 is
Since the power is supplied to the circuit after the rectifier block 4 via the current limiting capacitor C11 and the passing power is limited by the current limiting capacitor C11, the charging voltage of the smoothing capacitor C4 starts to decrease, and after a while, the charging voltage is increased. The value reaches the equilibrium point and stabilizes at this equilibrium point.

At this time, the current limiting capacitor C11
That is supplied to the smoothing capacitor C4
Is

(Equation 2) Here, EA: voltage value (effective value) of the AC power supply 1 fa: frequency of the AC power supply 1 EB: charging voltage of the smoothing capacitor C4 c11: capacitance value of the current limiting capacitor C11

FIG. 10 shows the electric power PI and the charging voltage EB in the above equation (2).
Is shown by a solid line, and the vertical axis is power PI,
The horizontal axis is the charging voltage EB of the smoothing capacitor C4. The solid line indicating the relationship between the power PI and the charging voltage EB draws a hyperbola.For example, when the charging voltage EB is zero, even if the charging current is supplied to the smoothing capacitor C4 via the current limiting capacitor C11, Since this is the product of the current value and the charging voltage EB, the power is zero. Conversely, when the charging voltage EB is EB = ^{21 /} 2EA, the current supplied through the current limiting capacitor C11 becomes zero, and thus the power also becomes zero. As a result, when the charging voltage EB is EB = EA / ^21/2 , the power PI becomes the maximum power, and the value PIM at this time is obtained.
AX is

(Equation 3) Required by

In FIG. 10, since the main body of the electronic device requests a constant light output from the switching power supply in the standby operation mode, the power PZ required for the light output and the charging voltage EB of the smoothing capacitor C4 are determined. Is indicated by a dotted line. The curve shown by the dotted line indicates that the lower the charging voltage EB, the lower the power PZ. In FIG. 10, two points where the dotted line and the solid line intersect are the equilibrium point EHA and the equilibrium point EHB, of which the equilibrium point EHB
Is not a true equilibrium point for the following reasons.

That is, assuming that the power PZ is operated at the equilibrium point EHB, if the power PZ slightly increases momentarily for some reason, the power operates in the following order (1) to (4). (1) The discharge current of the smoothing capacitor C4 increases instantaneously. (2) The charging voltage EB of the smoothing capacitor C4 decreases. (3) The power PI decreases along the solid curve in the diagram. (4) When the power PI decreases, the charging voltage EB becomes zero and the operation of the power supply stops according to the logical progress that the charging voltage EB further decreases.

Similarly, when it is assumed that the power PZ is operating at the equilibrium point EHA, if the power PZ increases momentarily for some reason, the power operates in the following order (11) to (14). (11) The discharge current of the smoothing capacitor C4 increases instantaneously. (12) The charging voltage EB of the smoothing capacitor C4 decreases. (13) The power PI increases along the solid curve in the diagram. (14) When the electric power PI increases, the charging voltage EB increases, and the operation is stably performed according to the logical progress of returning to the original value.

Further, when it is assumed that the operation is performed at the equilibrium point EHA, the operation is performed in the following order (21) to (24) even if the power PZ is momentarily reduced by some factor. (21) The discharge current of the smoothing capacitor C4 decreases instantaneously. (22) The charging voltage EB of the smoothing capacitor C4 increases. (23) The power PI decreases along the solid curve in the diagram. (24) The charge voltage EB stabilizes according to the logical progress of returning to the original value.

Therefore, the true equilibrium point is EHA,
In this switching power supply, the equilibrium point EHA, as (the EA effective value of the AC ^{voltage) EA / 2 1/2 <EHA <} 2 1/2 EA be in the range of, and possible EA / 2 ^{1 / 2} so that the capacitance c of the current limiting capacitor C11 is close to ^2.
By setting 11, power conversion efficiency in the standby operation mode is improved.

[0053] Thus, the 2 ^1/2 EA in the normal operation mode the charging voltage EB of the smoothing capacitor C4 when the electronic device main body enters the standby mode of operation ^1/2 (= EA / 2 1/2) near the This can reduce the charge and discharge loss of various parasitic capacitances and stray capacitances generated when the switching transistor 5 performs a switching operation, thereby improving power conversion efficiency. That is, in the standby operation mode, the current value supplied from the commercial power supply is limited by the current limiting capacitor C11 as a current limiting reactance element, and the charging voltage EB of the smoothing capacitor C4 is reduced.
Is reduced, the loss amount PC expressed by the above equation 1 is obtained.
Is reduced in proportion to the square of the charging voltage EB.

Further, the switching power supply of the first embodiment can be used in combination with a conventional method such as lowering the switching frequency in the standby operation mode, for example, and has a great effect of improving the power conversion efficiency by a synergistic effect. Can be obtained.

In the normal operation mode, the current limiting capacitor C1 serving as the current limiting reactance element is used.
1 is short-circuited by a triac 3 serving as a first switching element, whereby a current limiting capacitor C11
Releases the current limit state due to. The current limiting capacitor C11 is a conventional switching power supply (FIG. 6).
) Also serves as an impedance for preventing a rush current when the power is turned on.

(Second Embodiment) FIG. 2 is a circuit diagram of a flyback type PWM controlled switching power supply according to a second embodiment of the present invention. This switching power supply device has the same configuration as the switching power supply device of the first embodiment except for the stabilizing circuit 10, and the same components are denoted by the same reference numerals and description thereof is omitted.

In the switching power supply device of the first embodiment, the lower the charging voltage EB of the smoothing capacitor C4, the lower the charging efficiency EB in the standby operation mode. Since the point EHA cannot be reduced to EA / 2 ^1/2 or less, in the second embodiment, the equilibrium point EHA of the charging voltage EB of the smoothing capacitor C4 is set.
Is added to a stabilizing circuit 10 for lowering EA / 2 ^1/2 or less.

The stabilizing circuit 10 includes a reverse current blocking diode D11 having an anode connected to a connection point B between the cathode of the diode D3 and the cathode of the diode D4 and the cathode connected to the positive terminal of the smoothing capacitor C4. A transistor Q11 as a second switching element having a collector connected to the connection point B and an emitter connected to the ground GND;
The collector is connected to the base of the
The charge voltage control circuit includes a transistor Q12 connected to the ND, and a resistor R11 connecting the base of the transistor Q12 and the control input terminal CNT. Also,
The stabilizing circuit 10 includes the backflow preventing diode D11.
The emitter is connected to the cathode and the collector is connected to the resistor R12.
The transistor Q13 is connected to the base of the transistor Q11 via the
13 and the anode is ground G
A Zener diode ZD12 connected to the ND; a Zener diode ZD11 having a cathode connected to the cathode of the Zener diode ZD12; a diode having an anode connected to the anode of the Zener diode ZD11 and a cathode connected to the collector of the transistor Q11. D12.

In the normal operation mode (non-standby operation mode), the level of the control signal input to the control input terminal CNT is set to a high level by the electronic equipment main body (not shown) supplied with power from the switching power supply. Therefore, no current flows through the diode portion PC2a of the photocoupler PC2, and the transistor portion P2
C2b is in an off state, and the induced voltage of the secondary winding Tc of the transformer T is rectified and smoothed by the diode D5, the resistor R4 and the capacitor C3, and the triac 3 as the first switching element is passed through the resistor R3. , The triac 3 is turned on, and the current limiting capacitor C11 as a current limiting reactance element is short-circuited. A transistor Q12 to which a high-level control signal is applied to the base via the resistor R11.
Is turned on, the base of the transistor Q11 goes low, and the transistor Q11 is turned off. Therefore, the AC current from the AC power supply 1 is rectified by the rectifying block 4 without being subjected to current limitation by the current limiting capacitor C11, and charges the smoothing capacitor C4.

When the main body of the electronic equipment supplied with power from the switching power supply enters a standby operation mode, the control signal input to the control input terminal CNT is lowered to a low level. Then, a current flows through the diode section PC2a of the photocoupler PC2, and the transistor section P2
When C2b is turned on and the gate injection current of the triac 3 becomes zero and the triac 3 is turned off, the current supplied from the AC power supply 1 is supplied to the current limiting capacitor C11.
, The current is limited by the current limiting capacitor C11.

The Zener diode ZD12 sets the upper limit of the charging voltage of the smoothing capacitor C4. When the charging voltage of the smoothing capacitor C4 exceeds the Zener voltage of the Zener diode ZD12, the transistor Q13
Flows through the resistor R13 and the Zener diode ZD12, the collector current of the transistor Q13 flows into the base of the transistor Q11 via the resistor R12, turning on the transistor Q11 and turning on the output terminal of the rectifier block 4 (connection point). B) is connected to the ground G via the transistor Q11.
Connected to ND. At this time, since the control signal input to the control input terminal CNT is low level, the transistor Q
12 is off.

Then, the polarity of the AC power supply 1 is positive at the connection point A between the diode D1 and the diode D3,
When the connection point C between the diode D2 and the diode D4 has a negative polarity, a current flows from the connection point B between the diode D3 and the diode D3 in the order of the collector, the emitter, and the diode D2 of the transistor Q11. From the connection point B of D3 and the diode D4 to the transistor Q11
Since the current flows in the order of the collector, the emitter and the diode D1, the smoothing capacitor C4 is not charged. The Zener voltage of the Zener diode ZD11 sets the lower limit of the charging voltage of the smoothing capacitor C4. Therefore, the Zener voltage of the Zener diode ZD11 is set to a voltage lower than that of the Zener diode ZD12. When the transistor Q11 is turned on, the base current of the transistor Q13 is reduced by the resistance R13, the Zener diode ZD11, the diode D12, and the transistor Q11. It flows through the collector and the emitter of transistor Q11.

Then, even in the standby operation mode, the electronic device main body is continuously stored in the smoothing capacitor C4 during the period when the transistor Q11 is on in order to continuously request the switching power supply unit to supply a small amount of power. The charged charge is used for the switching operation. Therefore, the charging voltage of the smoothing capacitor C4 gradually drops,
When the charging voltage becomes equal to or lower than the Zener voltage of the Zener diode ZD11, the base current of the transistor Q13 becomes zero, so that the transistor Q13 is turned off and the transistor Q11 is turned off. And the rectification block 4
Output current charges the smoothing capacitor C4 via the backflow preventing diode D11,
Charging voltage gradually starts rising, and Zener diode Z
When the voltage exceeds the Zener voltage of D12, the transistor Q13
Is turned on, and the transistor Q11 is turned on. Thus, the on / off operation of the transistor Q11 is repeated.

The charging current (charging current of the smoothing capacitor C4) supplied through the current limiting capacitor C11 is discharged from the smoothing capacitor C4 to the switching circuit (the switching transistor 5 and the control circuit 6). It is necessary to set the capacitance value of the current limiting capacitor C11 so as to be larger than the current flowing. However, as the capacitance value increases, the collector current of the transistor Q11 tends to increase, and the conduction loss tends to increase. It is assumed that the capacitance value of the current limiting capacitor C11 is set to a minimum necessary value.

The present applicant conducted the experiment under the following experimental conditions and design specifications using the switching power supply circuit of the second embodiment.

[Experimental Conditions] AC input power supply voltage: 230 V (effective value) AC frequency: 50 Hz Output power: 0.1 W (a general value required when the electronic device body is in a standby operation mode) [Design specification] Circuit used: Circuit of the fourth embodiment shown in FIG. 5 Capacitance value of current limiting capacitor C11: 0.14 μF Type of transistor Q11: 2SC4002 (manufactured by Sanyo Electric Co., Ltd., shape TO-92) [Experimental result] AC input power: 0.4 W power Conversion efficiency: 25% As shown in the above experimental results, a good value of 0.4 W AC power consumption in the standby operation mode was obtained. On the other hand, in a general switching power supply, the AC power consumption is 1 W or more and the power conversion efficiency is 1 under the same conditions.
0% or less.

Therefore, when the electronic apparatus enters the standby operation mode, the charging voltage of the smoothing capacitor C4 can be reduced to an optimum value without being restricted by the first embodiment, and the power conversion efficiency can be further reduced. Can be improved.

It is not necessary to use a transistor rated for large current as the transistor Q11 as the second switching element used in the charging voltage control circuit of the smoothing capacitor C4, and a small and inexpensive transistor is sufficient. Therefore, the power conversion efficiency in the standby operation mode can be improved by adding a very low cost.

Further, while the charging current to the smoothing capacitor C4 in the standby operation mode is limited by the current limiting capacitor C11, the transistor Q11 is turned on and off to more effectively reduce the charging voltage EB of the smoothing capacitor C4. Value can be set finely.

The backflow preventing diode D11 is
When the transistor Q11 is turned on, the smoothing capacitor C4 functions to prevent discharging through the transistor Q11. As shown in FIG. 3, the collector of the transistor Q13 and the positive terminal of the smoothing capacitor C4 are connected to each other. The same effect can be obtained by using a stabilizing circuit 20 (the other components are the same as the stabilizing circuit 10) in which a backflow preventing diode D31 is connected therebetween.

(Third Embodiment) FIG. 4 is a circuit diagram of a flyback PWM switching power supply according to a third embodiment of the present invention. Note that this switching power supply has the same configuration as the switching power supply of the first embodiment except for the stabilizing circuit 30, and the same components are denoted by the same reference numerals and description thereof will be omitted.

In the second embodiment, the forward voltage drop of the reverse current blocking diodes D11 and D31 connected between the rectifying block 4 and the smoothing capacitor C4 shown in FIGS.
Since a loss occurs due to (VF), in the third embodiment, the above-described backflow prevention diode D11 is removed to reduce the loss.

The stabilizing circuit 30 includes a transistor Q21 as a third switching element having a collector connected to a connection point A between the cathode of the diode D1 and the anode of the diode D3 and an emitter connected to the ground GND.
A transistor Q22 whose collector is connected to the base of the transistor Q21 and whose emitter is connected to the ground GND; a resistor R21 connected between the base of the transistor Q22 and the control input terminal CNT;
A transistor Q24 as a fourth switching element having a collector connected to a connection point C between the cathode of the second D2 and the anode of the diode D4 and an emitter connected to the ground GND.
And a transistor Q25 having a collector connected to the base of the transistor Q24 and an emitter connected to the ground GND, and a resistor R25 connected between the base of the transistor Q25 and the control input terminal CNT. It has a part. Further, the stabilizing circuit 30 includes:
An emitter is connected to a connection point B between the cathode of the diode D3 and the cathode of the diode D4, and the collector is connected to a resistor R22.
, A collector connected to the base of the transistor Q24 via a resistor R24, a cathode connected to the base of the transistor Q23 via a resistor R23, and an anode connected to the base of the transistor Q23. A Zener diode ZD22 connected to the ground GND; and a Zener diode ZD having a cathode connected to the cathode of the Zener diode ZD22.
And a diode D21 having an anode connected to the anode of the Zener diode ZD21 and a cathode connected to the collector of the transistor Q21. The upper limit value and the lower limit value of the charging voltage of the smoothing capacitor C4 are set by the Zener voltages of the Zener diodes ZD22 and ZD21, respectively, as in the second embodiment.

In the switching power supply device having the above-described configuration, in the normal operation mode, the electronic device main body (not shown) raises the control signal input to the control input terminal CNT to a high level as in the second embodiment. As a result, the triac 3 is turned on, and a high-level control signal is applied to the base via the resistors R21 and R25, and the transistor Q2 is turned on.
2, Q25 is turned on, and transistor Q21 and transistor Q24 are turned off. Therefore, the current from the AC power supply 1 flows through the triac 3 as the first switching element, and the current limiting capacitor C11
Without the current limitation by the smoothing capacitor C
Flow into 4.

In the standby operation mode, as in the second embodiment, the electronic device main unit lowers the control signal input to the control input terminal CNT to a low level.
Are turned off, and the transistors Q22 and Q25 are turned off. The charging voltage of the smoothing capacitor C4 is the upper limit set value.
When the voltage is higher than (the Zener voltage of the Zener diode ZD22), the transistors Q21 and Q24 are respectively turned on. This ON state is maintained until the charging voltage of the smoothing capacitor C4 becomes lower than the lower limit set value (the Zener voltage of the Zener diode ZD21). continue. Then, the output current of the rectifying block 4 is blocked while the transistors Q21 and Q24 are on.

That is, the polarity direction of the AC power supply 1 is
When the connection point A between the diode D1 and the diode D3 is positive and the connection point C between the diode D2 and the diode D4 has a negative polarity, the current flows from the connection point A between the diode D1 and the diode D3 to the collector and the emitter of the transistor Q21. In the case of the opposite polarity, the current flows from the connection point C of the diode D2 and the diode D4 to the collector and the emitter of the transistor Q24 and then to the diode D1, thereby preventing the current from flowing into the smoothing capacitor C4. At this time, the diodes D3 and D4 prevent the charge charged in the smoothing capacitor C4 from being discharged through the transistors Q21 and Q24.

Therefore, when the electronic device body enters the standby operation mode, the charging voltage of the smoothing capacitor C4 can be reduced to the optimum value without being restricted by the first embodiment, and the power conversion efficiency can be further reduced. Can be improved. Further, since the loss due to the forward voltage drop due to the backflow preventing diodes D11 and D31 (shown in FIGS. 2 and 3) of the switching power supply of the second embodiment is eliminated,
The power conversion efficiency can be further improved.

It is not necessary to use a high-current-rated product for the transistor Q21 as the third switching element and the transistor Q24 as the fourth switching element. By adding the cost, it is possible to achieve an improvement in the power conversion efficiency in the standby operation mode.

Further, while the charging current to the smoothing capacitor C4 in the standby operation mode is limited by the current limiting capacitor C11, the transistors Q21 and Q24 are turned on and off, respectively, to reduce the charging voltage EB of the smoothing capacitor C4. More effective values can be finely set.

(Fourth Embodiment) FIG. 5 is a circuit diagram of a flyback PWM control switching power supply according to a fourth embodiment of the present invention. It should be noted that this switching power supply device has a circuit related to a control signal and a stabilizing circuit 40.
Except for this, the configuration is the same as that of the switching power supply device of the first embodiment, and the same components are denoted by the same reference numerals and description thereof is omitted.

In the standby mode of the fourth embodiment, the charging voltage of the smoothing capacitor C4 is
The charging voltage of the smoothing capacitor C4 is controlled to a predetermined voltage value by detecting at P1 and controlling the triac 3 as the first switching element on and off based on the detection result.

The stabilizing circuit 40 is connected between a resistor R40 having one end connected to a connection point B between the cathode of the diode D3 and the cathode of the diode D4, and between the other end of the resistor R40 and the ground GND. The resistor R41 and the resistor R
A collector is connected to a connection point between the resistor R41 and the resistor R41 through a resistor R42, and an emitter is connected to the ground GND. An inverting input terminal is connected to a connection point between the resistor R40 and the resistor R41. Supply voltage Vcc to input terminal
And the comparator CP1 having the ground input terminal connected to the ground GND.
The cathode is connected to the non-inverting input terminal of the Zener diode, and the Zener diode ZD41 whose anode is connected to the ground GND.
And a resistor R44 connected between the non-inverting input terminal of the comparator CP1 and the power supply input terminal, and a resistor R45 connected between the output terminal of the comparator CP1 and the base of the transistor Q41. I have. The output terminal of the comparator CP1 is an open drain or an open collector.

Further, one end of a resistor R46 is connected to the output terminal of the comparator CP1 of the stabilizing circuit 40, and the other end of the resistor R46 is connected to the diode part PC2 of the photocoupler PC2.
The cathode of a is connected. The diode section PC2a
Is connected to the collector of a transistor Q42, and the power supply voltage Vcc is applied to the emitter of the transistor Q42. The emitter of the transistor Q42 and the ground G
The capacitor C6 is connected to the ND. And
The control input terminal CNT is connected to the base of the transistor Q42. The photocoupler PC2, the transistor Q42 and the capacitor C6 constitute a first switching element control unit.

The operation of the switching power supply having the above configuration will be described below.

First, when the electronic device main body (not shown) is operating in the normal operation mode, the transistor Q42 is turned off in order to raise the control signal input to the control input terminal CNT to a high level. No current flows through the diode portion PC2a, the transistor portion PC2b of the photocoupler PC2 is turned off, a voltage is applied from the secondary winding Tc to the gate of the triac 3, and the triac 3 is turned on. Therefore, the current from the AC power supply 1 flows into the smoothing capacitor C4 without being limited by the current limiting capacitor C11, and charges the smoothing capacitor C4.

On the other hand, when the electronic apparatus body starts operating in the standby operation mode, the transistor Q42 is turned on to lower the control input terminal CNT to the low level. At this time, a current is supplied to the base of the transistor Q41 via the transistor Q42, the diode portion PC2a of the photocoupler PC2, the resistor R46, and the resistor R45, so that the transistor Q41 is turned on. Further, the transistor Q
Since the base current of 41 is limited to a small value by the resistor R45, the current value of the diode portion PC2a of the photocoupler PC2 is equal to or less than the current value (threshold level) required to turn on the transistor portion PC2b. Triac 3 is on.

The comparator CP1 compares the Zener voltage of the Zener diode ZD41 with the voltage obtained by dividing the charging voltage of the smoothing capacitor C4 by the resistors R40, R41 and R42, and satisfies the following equation (4). During this operation, the output of the comparator CP1 is lowered to a low level.

(Equation 4) VT: Zener voltage of Zener diode ZD41 r40: Resistance value of resistance R40 r41: Resistance value of resistance R41 r42: Resistance value of resistance R42 V4: Charging voltage of smoothing capacitor C4 The output of the comparator CP1 drops to a low level. And the threshold level (current value required to turn on) on diode section PC2a of photocoupler PC2
After the above current flows and the triac 3 is turned off, the current from the AC power supply 1 is supplied to the smoothing capacitor C4 via the current limiting capacitor C11.

In the standby operation mode, the switching circuit
(The switching transistor 5 and the control circuit 6) continue the switching operation, and continue the operation of supplying power to the electronic device body. At this time, the capacitance value of the current limiting capacitor C11 is set so that the current supplied through the current limiting capacitor C11 is smaller than the current discharged from the smoothing capacitor C4 to the switching circuit side. Therefore, the charging voltage of the smoothing capacitor C4 gradually decreases.

When the output terminal of the comparator CP1 becomes low level, the supply of the base current of the transistor Q41 has already stopped, and the divided value of the charging voltage of the smoothing capacitor C4 by the resistor R40 and the resistor R41. But,

(Equation 5) In the relationship shown in the following expression, the output terminal of the comparator CP1 becomes high level, and the current of the diode part PC2a of the photocoupler PC2 becomes a small value and becomes equal to or less than the above-mentioned threshold level, so that the transistor part PC2b is turned off. The triac 3 is turned on.

When the triac 3 is turned on, the current from the AC power supply 1 flows into the smoothing capacitor C4 via the triac 3, so that the charging voltage of the smoothing capacitor C4 starts increasing, and the resistance R40, Resistor R41,
When the division ratio of the charging voltage of the smoothing capacitor C4 by the resistor R42 satisfies the relationship shown in Expression 4, the comparator CP1
Output is low level.

Thereafter, during the operation in the standby operation mode, the charging voltage of the smoothing capacitor C4 is calculated by the following equations (6) and (7).
The transition is made while reciprocating between the upper limit value V4H and the lower limit value V4L.

(Equation 6)

(Equation 7) By setting the upper limit value V4H and the lower limit value V4L to optimal values, the power conversion efficiency in the standby operation mode can be increased.

It is not necessary to employ a type having a high current rating for the comparator CP1 used in the charging voltage control circuit of the smoothing capacitor C4. An improvement in power conversion efficiency in the mode can be achieved.

As described above, the current limiting capacitor C
By turning on / off the triac 3 while limiting the charging current to the smoothing capacitor C4 in the standby operation mode by 11, the charging voltage EB of the smoothing capacitor C4 can be finely set to a more effective value.

In the second, third, and fourth embodiments, the optimum value of the charging voltage of the smoothing capacitor C4 is:
This is the minimum charging voltage that can supply the power supply amount required by the electronic device body in the standby operation mode at a predetermined switching frequency. The power conversion efficiency improves as the charging voltage of the smoothing capacitor C4 decreases.

[0095]

As is apparent from the above description, the switching power supply according to the first aspect of the present invention turns on the first switching element connected in parallel with the current limiting reactance element during normal operation, thereby providing the AC power supply. The rectifying unit rectifies the AC voltage input from the rectifier through the first switching element, smoothes the AC voltage with a smoothing capacitor connected between the output terminals of the rectifier, and smoothes the AC voltage with the smoothing capacitor. After the converted DC voltage is converted to a high-frequency voltage by the DC-AC converter, the high-frequency voltage from the DC-AC converter is converted to a predetermined voltage by a transformer, and the converted high-frequency voltage is converted by the smoothing unit. Turning off the first switching element connected in parallel with the current-limiting reactance element during standby operation while smoothing to a DC voltage. Therefore, the AC voltage from the AC power supply is input to the rectification unit via the current limiting reactance element connected between one end of the output terminal of the AC power supply and one end of the input terminal of the rectification unit, and the current limiting reactance element This limits the alternating current input to the rectifier.

Therefore, according to the switching power supply of the first aspect of the present invention, the electronic device main body enters a standby operation by appropriately setting the capacitance of the capacitor by using, for example, a capacitor for the current limiting reactance element. In this case, the charging voltage of the smoothing capacitor can be reduced to about half the level in normal operation. By doing so, it is possible to reduce charge / discharge losses of various parasitic capacitances and stray capacitances generated when the switching element used in the DC-AC converter performs a switching operation, and it is possible to improve power conversion efficiency.

Further, by using the method for improving the power conversion efficiency of the switching power supply of the present invention together with a method for lowering the switching frequency in the standby operation mode, for example, a greater effect can be obtained by a synergistic effect of these. be able to.

A switching power supply according to a second aspect of the present invention is the switching power supply according to the first aspect, wherein the first switching element control section connects the first current limiting reactance element in parallel with the current limiting reactance element during standby operation. With the switching element turned off, the second switching element connected between the output terminals of the rectifying unit and closer to the rectifying unit than the smoothing capacitor is charged to the charging voltage so that the charging voltage of the smoothing capacitor becomes a predetermined voltage. On / off control is performed by a control unit. At this time, the second switching element is turned on by a backflow prevention diode disposed between one end of the second switching element and one end of a smoothing capacitor connected to the one end. In this case, the charge charged in the smoothing capacitor was prevented from being discharged through the second switching element. It may further lowering than about half the level of the normal operation of the charging voltage of the smoothing capacitor, it is possible to particularly improve the power conversion efficiency. In addition, since it is not necessary to employ an element having a large current rating as the second switching element, and a small and inexpensive transistor can sufficiently cope with it, it is possible to improve power conversion efficiency during standby operation at a very low cost. it can. further,
The charging voltage of the smoothing capacitor is finely set to a more effective value by turning on and off the second switching element while limiting the charging current to the smoothing capacitor during the standby operation by the current limiting reactance element. Can be.

A switching power supply according to a third aspect of the present invention is the switching power supply according to the second aspect, wherein the first switching element control unit is connected in parallel with the current limiting reactance element during standby operation. In a state where one switching element is turned off, the charging voltage determining unit detects the voltage at both ends of the smoothing capacitor, that is, the charging voltage, and the charging voltage determining unit determines that the charging voltage of the smoothing capacitor is equal to or more than an upper limit value of a predetermined range. Is determined, the second switching element is turned on by the charging voltage control unit, a current limited by the current-limiting reactance flows from the AC power supply through the second switching element, and the smoothing capacitor is charged. Instead, power is supplied to the electronic device body, and while the charging voltage of the smoothing capacitor falls, When the voltage determination unit determines that the charging voltage of the smoothing capacitor is equal to or lower than the lower limit value of the predetermined range, the charging voltage control unit turns off the second switching element, and switches from the AC power supply limited by the current limiting reactance. Flows through the rectifying unit and the backflow preventing diode to the smoothing capacitor side to charge the smoothing capacitor and increase the charging voltage of the smoothing capacitor. The charging voltage of the smoothing capacitor during the standby operation can be reliably maintained at the optimum value.

According to a fourth aspect of the present invention, in the switching power supply of the second aspect, the first switching element control section connects in parallel with the current limiting reactance element during the standby operation. 1 In a state where the switching element is turned off, the voltage between the output terminals of the rectifying unit is detected by the charging voltage determining unit, and the charging voltage determining unit determines that the voltage between the output terminals of the rectifying unit is equal to or more than the upper limit of a predetermined range. If it is determined that there is, the second switching element is turned on by the charging voltage control unit, and the current limited by the current limiting reactance from the AC power supply is changed to the second current.
Flowing through the switching element, the smoothing capacitor supplies power to the electronic device main body without being charged, and the charging voltage of the smoothing capacitor drops, while the charging voltage determination unit operates between the output terminals of the rectifying unit. When it is determined that the voltage is equal to or lower than the lower limit value of the predetermined range, the charging voltage control unit turns off the second switching element, and the current from the AC power supply limited by the current limiting reactance is used to prevent the rectifying unit and the backflow. The current flows to the smoothing capacitor side via the diode, and the smoothing capacitor is charged, and the charging voltage of the smoothing capacitor rises. Therefore, the charging voltage of the smoothing capacitor can be set within a predetermined range, and the smoothing voltage during the standby operation can be reduced. The charging voltage of the storage capacitor can be reliably maintained at the optimum value.

According to a fifth aspect of the present invention, there is provided the switching power supply device according to the first aspect, wherein the first switching element control section connects the first current limiting reactance element in parallel with the current limiting reactance element during standby operation. In a state where the switching element is turned off, based on the determination result of the charging voltage determining unit, for example, when the charging voltage of the smoothing capacitor is equal to or more than an upper limit value of a predetermined range, between one of the input terminals of the rectifying unit and ground. The third switching element connected and the fourth switching element connected between the other of the input terminals of the rectifying unit and the ground were respectively turned on by the charging voltage control unit, and were limited by the current limiting reactance from the AC power supply. A current flows through the third and fourth switching elements, and the smoothing capacitor is not charged and supplies power to the electronic device body side. The charging voltage of the smoothing capacitor drops while the charging voltage of the smoothing capacitor is lower than the lower limit value of the predetermined range, based on the determination result of the charging voltage determining unit. 3rd, 4th
Each of the switching elements is turned off, and the current from the AC power supply, which is limited by the current limiting reactance, flows to the smoothing capacitor side via the rectifier, and the smoothing capacitor is charged, and the charging voltage of the smoothing capacitor increases. Therefore, the backflow preventing diode is not used, and the loss due to the forward voltage drop of the backflow preventing diode is eliminated, so that the power conversion efficiency can be further improved. In addition, since it is not necessary to employ elements having a large current rating as the third and fourth switching elements, and a low-priced small transistor is sufficient, the power conversion efficiency during standby operation can be improved at low cost. Can be. Further, while the charging current to the smoothing capacitor during the standby operation is limited by the current limiting reactance element, the third and fourth switching elements are turned on and off, so that the charging voltage of the smoothing capacitor becomes more effective. It can be set finely.

A switching power supply according to a sixth aspect of the present invention is the switching power supply according to the first aspect, wherein the first switching element controller is connected in parallel with the current limiting reactance element by a first switching element controller during a standby operation. In a state where the switching element is turned off, for example, when the charging voltage of the smoothing capacitor is equal to or more than the upper limit of a predetermined range based on the determination result of the charging voltage determining unit, the first switching element is turned off by the charging voltage control unit, The smoothing capacitor is charged by the current limited by the current limiting reactance from the AC power supply, supplies power to the electronic device main body, and is discharged from the smoothing capacitor at that time to the DC-AC converter side. As the current supplied through the current limiting reactance element is smaller than the current,
By setting the reactance of the current limiting reactance element, the charging voltage of the smoothing capacitor drops, while the charging voltage of the smoothing capacitor drops. When the charging voltage of the capacitor for use is less than or equal to the lower limit value of the predetermined range, the first switching element is turned on by the charging voltage control unit, and the current from the AC power supply is smoothed via the first switching element and the rectifying unit. Since the current flows to the capacitor side, the smoothing capacitor is charged, and the charging voltage of the smoothing capacitor rises.Therefore, the charging voltage of the smoothing capacitor is set within a predetermined range, and the charging voltage of the smoothing capacitor during the standby operation is ensured. The value can be maintained at the optimum value, and the reverse current blocking diode can be used in order without using the reverse current blocking diode. Since the loss due to countercurrent voltage drop is eliminated, it is possible to further improve the power conversion efficiency. In addition, it is not necessary to employ an element having a large current rating in the charging voltage control unit, and the power conversion efficiency during standby operation can be improved at low cost. In addition, the charging voltage of the smoothing capacitor is finely set to a more effective value by turning on and off the first switching element while limiting the charging current to the smoothing capacitor during the standby operation by the current limiting reactance element. can do.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a switching power supply device according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a switching power supply device according to a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing an example of the switching power supply according to the second embodiment in which the arrangement of a backflow prevention diode is changed.

FIG. 4 is a circuit diagram of a switching power supply according to a third embodiment of the present invention.

FIG. 5 is a circuit diagram of a switching power supply device according to a fourth embodiment of the present invention.

FIG. 6 is a circuit diagram of a conventional switching power supply device.

FIG. 7 is a circuit diagram illustrating the influence of parasitic capacitance and stray capacitance around a switching transistor of the switching power supply device.

FIG. 8 is a circuit diagram illustrating the influence of parasitic capacitance and stray capacitance around a switching transistor of the switching power supply device.

FIG. 9 is a circuit diagram illustrating an influence of a parasitic capacitance and a stray capacitance around a switching transistor of the switching power supply device.

FIG. 10 is a diagram for explaining the relationship between the powers PI and PZ and the charging voltage EB of the smoothing capacitor C4 in the switching power supply according to the first embodiment of the present invention.

[Explanation of symbols]

1. AC power supply 2. Fuse 3. Triac 4.
Rectifier block, 5 ... transistor, 6 ... control circuit, 7 ...
Secondary side output voltage detection circuit, 8a, 8b ... output terminals, C1, C2
... capacitors, C3, C6 ... capacitors, C3, C5 ... smoothing capacitors, L ... line filters, T ... transformers, Ta ...
Primary winding, Tb, Tc Secondary winding, PC1, PC2 Photocoupler, PC1a, PC2a Diode section, PC1b, P
C2b: transistor section.

Claims (6)

[Claims] A rectifying unit for rectifying an AC voltage from an AC power supply into a DC voltage; a smoothing capacitor connected between output terminals of the rectifying unit for smoothing the DC voltage rectified by the rectifying unit; A DC-AC converter for converting the DC voltage to a high-frequency voltage by turning on and off the DC voltage smoothed by the smoothing capacitor; and converting the high-frequency voltage converted by the DC-AC converter to a predetermined voltage. A switching power supply, and a smoothing unit for smoothing a high-frequency voltage converted to a predetermined voltage by the transformer to a DC voltage, wherein one end of an output terminal of the AC power supply and an input of the rectifying unit. A current-limiting reactance element connected between one end of the terminal and a first switching element connected in parallel to the current-limiting reactance element; A switching power supply device comprising: 2. The switching power supply according to claim 1, wherein the first switching element is turned off during a standby operation.
A switching element control unit; a second switching element connected between the output terminals of the rectification unit and closer to the rectification unit than the smoothing capacitor; one end of the second switching element and the smoothing unit connected to the one end A backflow preventing diode arranged between the first switching element and one end of the second switching element so that the electric charge charged in the smoothing capacitor is not discharged through the second switching element when the second switching element is in an on state; A switching power supply device comprising: a charging voltage control unit that controls on / off of the second switching element so that a charging voltage of the smoothing capacitor becomes a predetermined voltage during a standby operation. 3. The switching power supply device according to claim 2, wherein a voltage across the smoothing capacitor is detected, and a voltage across the smoothing capacitor is equal to or more than an upper limit value of a predetermined range. A charging voltage determining unit that determines whether the voltage is equal to or less than a lower limit value, wherein the charging voltage control unit is configured such that, during a standby operation, the charging voltage determining unit determines that a voltage across the smoothing capacitor is equal to or greater than the upper limit value of the predetermined range. If it is determined that there is, the second switching element is turned on, and if the charging voltage determination unit determines that the voltage across the smoothing capacitor is equal to or less than the lower limit of the predetermined range, the charging voltage determination unit turns off the second switching element. A switching power supply device. 4. The switching power supply according to claim 2, wherein a voltage between output terminals of the rectifier is detected, a voltage between output terminals of the rectifier is detected, and an output terminal of the rectifier is detected. A charging voltage determining unit that determines whether a voltage between the output terminals of the rectifying unit is equal to or greater than an upper limit value of the predetermined range or less than a lower limit value of the predetermined range. When the charging voltage determination unit determines that the voltage between the output terminals of the rectification unit is equal to or greater than the upper limit of the predetermined range, the charging voltage determination unit turns on the second switching element, and the charging voltage determination unit determines A switching power supply unit that turns off the second switching element when it is determined that the voltage between the output terminals is lower than or equal to the lower limit value of the predetermined range. 5. The switching power supply according to claim 1, wherein the first switching element is turned off during a standby operation.
A switching element control unit, a charging voltage determining unit that detects a voltage between both ends of the smoothing capacitor and determines a charging voltage of the smoothing capacitor, and is connected between one of input terminals of the rectifying unit and ground. A third switching element, a fourth switching element connected between the other of the input terminals of the rectifier and the ground, and, during a standby operation, the smoothing based on the determination result of the charging voltage determination unit. A switching power supply device comprising: a charging voltage control unit that controls on / off of each of the third and fourth switching elements so that a charging voltage of a capacitor falls within a predetermined range. 6. The switching power supply device according to claim 1, wherein the first switching element is turned off during a standby operation.
A switching element control unit, a charging voltage determining unit that detects a voltage across the smoothing capacitor and determines a charging voltage of the smoothing capacitor, and a standby operation, based on a determination result of the charging voltage determining unit. And a charging voltage control unit that controls on / off of the first switching element so that the charging voltage of the smoothing capacitor falls within a predetermined range.