JP2000245150A - Switching power circuit and device for switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power circuit which allows switching loss to be further reduced under light load. SOLUTION: This switching power circuit is designed such that under steady- state load, the voltage of a connecting point 10 is higher than a threshold and the voltage of a connecting point 7 is lower than the threshold, because of feedback from an output detection circuit 20. Therefore, during an oscillation frequency quiescent period, circuit 11 does not operate and an oscillation circuit 13 continuously outputs triangular waves. Under light load, the voltage of the connecting point 10 is lower than the threshold, and the voltage of the connecting point 7 is higher than the threshold because of feedback from the output detection circuit 20. Therefore, the oscillation frequency quiescent period circuit 11 is actuated, and the oscillation circuit 13 outputs triangular waves provided with the quiescent period of oscillation. As a result, a switching element Q1 performs a switching operation such that it remains out of operation in an interrupted state for a certain period of time.

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 circuit for supplying a stabilized DC voltage to industrial and consumer electronic equipment.

[0002]

2. Description of the Related Art In the United States, the standard setting of the Energy Star Computer Program was established in 1993 so that the power consumption of a personal computer during standby was 30 W or less. In Japan, the power consumption during standby of a VTR was reduced in 1995. With the worldwide trend toward low power consumption, such as a regulation to cut by 10%, there is a demand for energy saving of switching power supplies used in electronic devices.

FIG. 9 shows a conventional switching power supply circuit 10.
1 is shown. In the switching power supply circuit 101, the AC voltage input to the input terminals P1 and P2 is first rectified by the rectification bridge circuit 2, and the smoothing capacitor C
It is smoothed by one. This DC voltage is the power line 3
The VC of the converter 15 is applied by applying the voltage between
Power is supplied to a terminal K5 which is a C terminal, a charging current flows from a constant current source TD1 to a capacitor C3 connected to a terminal (control terminal) K3, and a constant current source TD
The voltage at the connection point 7 between 1 and the capacitor C3 is input to the input terminal F4 of the PWM comparator 12.

The DC voltage is also applied to a series circuit including a diode D2, a pull-up resistor R1, and a phototransistor Q2 connected to a terminal K4, and a connection point 1 between the pull-up resistor R1 and the phototransistor Q2.
A voltage of 0 is input to the input terminal F2 of the PWM comparator 12. Further, the DC reference voltage Vref1 is input from the reference voltage source 14 to the input terminal F3 of the PWM comparator 12.

[0005] The PWM comparator 12 has a cycle of a signal input from the oscillation circuit 13 to the input terminal F1 and the input terminal F1.
A pulse having a duty based on the lowest voltage among the three voltages input to 2.F3.F4 is generated and output. At the time of startup, the voltage between the terminals of the capacitor C3, that is, the control terminal voltage CA at the terminal K3 gradually rises from 0, so that a pulse having a duty determined by the voltage input to the input terminal F4 is output and soft start is performed.

After this pulse is made constant by the control circuit 6, it is input to the gate of the switching element Q1 connected between the terminals K1 and K2, and the gate pulse turns on / off the switching element Q1. You. When the switching element Q1 is turned on, a current flows through the primary winding 5a of the pulse transformer 5 and the excitation energy is accumulated. When the switching element Q1 is cut off, the energy is released by the induced electromotive force in the secondary winding 5b. The flowing current is rectified and smoothed by the diode D1 and the smoothing capacitor C2, and a stabilized DC voltage is output from between the output terminals P3 and P4.

After the start, the voltage between the terminals of the capacitor C3 gradually rises, and when the charging is completed and a steady state is reached, the voltage at the node 10 input to the input terminal F2 or the reference voltage input to the input terminal F3. The voltage of the voltage Vref1 becomes the lowest. On the other hand, on the secondary side, the output voltage is detected by the output detection circuit 20 connected between the power supply lines 8 and 9. When the output voltage is higher (lower) than a predetermined value, the light emission intensity of the light emitting diode D3 is increased ( Decrease) to decrease (increase) the impedance of the light emitting diode D3 and the phototransistor Q2 forming the photocoupler. As a result, the voltage at the connection point 10 decreases (increases), and the connection point 1
When the voltage of 0 is lower than the reference voltage Vref1, the PWM comparator 12 outputs a pulse adjusted so that the duty becomes smaller (increased) in accordance with the voltage decrease (increase). Thus, the output voltage is made constant.

Since the switching power supply circuit 101 is lightly loaded during standby, if the switching operation of the switching element Q1 during this period is performed at the same frequency as that during heavy load, the ratio of switching loss to the total power consumption is reduced. growing. Therefore, the voltage at the connection point 10 is input to the oscillation frequency lowering circuit 91, and the output detection circuit 20 detects a high output voltage that is determined to be a light load, and the voltage at the connection point 10 drops below a specified value. Then, the oscillation frequency of the oscillation circuit 13 is reduced.

As another configuration example for reducing the power consumption at the time of light load, as disclosed in Japanese Patent Application Laid-Open No. HEI 8-111975, a switching power supply circuit having a power factor improving circuit has the above-mentioned structure at light load. In some cases, the operation of the power factor correction circuit is stopped to reduce the power consumption corresponding to the operation.

In the conventional switching power supply circuit, low power consumption at light load has been achieved in this manner.

[0011]

However, in the conventional switching power supply circuit 101, the oscillation frequency of the oscillation circuit 13 cannot be reduced to an audible frequency range of 20 kHz or less. There is a problem that there is a limit in reducing power consumption by reducing power consumption. Further, in the switching power supply circuit disclosed in JP-A-8-111975,
When the operation of the power factor correction circuit is stopped, power is supplied to the switching element for turning on / off the current flowing through the primary winding of the transformer without passing through the power factor correction circuit, and the power is supplied during light load. Switching losses remain unreduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has as its object to provide a switching power supply circuit capable of further reducing switching loss at a light load, and a switching power supply device used therein. Is to provide.

[0013]

According to a first aspect of the present invention, there is provided a switching power supply circuit for switching a DC voltage input to a primary side of a transformer and applying a pulse to a secondary side. Switching means for outputting as
Output means for outputting a DC voltage obtained by smoothing the pulse to a load, and feedback of the output voltage from the output means, an oscillation signal output from an oscillation means for performing an oscillating operation, and the output voltage fed back; And a control means for controlling the switching means to perform a switching operation at a predetermined frequency and duty based on the switching power supply circuit, further comprising: a load state detection means for detecting a magnitude of a load; When the load state detecting means detects a light load which is a load equal to or less than a predetermined value, a switching pause means for temporarily suspending the oscillating operation of the oscillating means and providing a pause period in which the switching operation is kept in a cut-off state is provided. It is characterized by:

According to the above invention, this switching power supply circuit used as a DC-DC converter, etc.
In a steady state, the switching frequency of the switching means and its duty are determined based on the oscillation signal output from the oscillation means and the output voltage fed back from the output means. The magnitude of the load connected to the means is detected. When a light load is detected by the load state detecting means due to the switching power supply circuit being in a standby state or the like, the switching suspending means temporarily suspends the oscillating operation of the oscillating means on the basis of the detection result, thereby enabling the switching means to operate. A quiescent period in which the switching operation is kept in the cutoff state is provided.

As a result, when the load is light, the switching loss in the switching means is greatly reduced, and the loss in the control means is suppressed, so that the power consumption of the entire switching power supply circuit is greatly reduced. Therefore, according to such a configuration, there is no need for a complicated structure such as providing a plurality of converter circuits and selectively using them according to the load state. Can respond. As a result, low power consumption of the switching power supply circuit can be realized with a low cost and small circuit configuration.

According to a second aspect of the present invention, there is provided a switching power supply circuit according to the first aspect, wherein the load state detecting means detects a load from a current level flowing through the output means. It is characterized by detecting the size of.

According to the above invention, the load state detecting means detects the magnitude of the load by detecting the level of the current flowing through the output means, for example, from the voltage between the terminals of the resistor inserted into the output means. Therefore, when the current level is lower than the predetermined secondary-side current level of the switching power supply circuit, it is determined that the load is light, and the switching pausing unit provides a pause period for the switching operation of the switching unit. On the other hand, when the current level is equal to or higher than the predetermined secondary current level of the switching power supply circuit, it is determined that the load is a steady load, and a normal switching operation is performed.

Thus, it is only necessary to select whether or not to operate the circuit for setting the idle period of the switching operation in the normal circuit under the two load states of the steady load and the light load. The power supply circuit can have a simple configuration.

According to a third aspect of the present invention, there is provided a switching power supply circuit according to the first aspect, wherein the load state detecting means determines a load from a current level flowing through the switching means. It is characterized by detecting the size of.

According to the above invention, the load state detecting means detects the level of the load by detecting the level of the current flowing through the switching means from, for example, the voltage between the terminals of a resistor inserted in series with the switching means. I do. Therefore,
When the current level is less than a predetermined primary drain current level of the switching power supply circuit, it is determined that the load is light, and the switching operation of the switching unit is provided with a pause period by the switching pause unit. On the other hand, when the current level is equal to or higher than the predetermined drain current level of the switching power supply circuit, it is determined that the load is a steady load, and a normal switching operation is performed.

Thus, it is only necessary to select whether or not to operate the circuit for setting the idle period of the switching operation in the normal circuit under the two load states of the steady load and the light load. The power supply circuit can have a simple configuration.

According to a fourth aspect of the present invention, there is provided a switching power supply circuit according to the first aspect, wherein the load state detecting means is configured to detect a load from the output voltage fed back. It is characterized in that the size is detected.

According to the above invention, the load state detecting means detects the load size from the output voltage fed back, utilizing the fact that the magnitude of the load corresponds to the output voltage of the output means. To do. Therefore, when the feedback voltage level is equal to or higher than the predetermined voltage level, it is determined that the load is light, and the switching pausing unit provides a pausing period for the switching operation of the switching unit. On the other hand, when the feedback voltage level is lower than the predetermined voltage level, it is determined that the load is a steady load, and a normal switching operation is performed.

Thus, it is only necessary to select whether or not to operate the circuit for setting the idle period of the switching operation in the normal circuit under the two load states of the steady load and the light load. The power supply circuit can have a simple configuration.

According to a fifth aspect of the present invention, there is provided a switching power supply circuit according to the first or fourth aspect of the present invention, wherein the load state detecting means determines a load from the duty cycle level. It is characterized by detecting the size of.

According to the above-mentioned invention, the fact that the magnitude of the load corresponds to the cycle level of the duty of the switching operation controlled by the control means is used to provide the load state detection means with the duty of the controlled duty. The magnitude of the load is detected from the cycle level. Therefore, when the duty cycle level is less than the predetermined cycle level, it is determined that the load is light, and the switching pause unit provides a pause period for the switching operation of the switching unit. On the other hand, when the duty cycle level is equal to or higher than the predetermined cycle level, it is determined that the load is a steady load, and a normal switching operation is performed.

With this, it is only necessary to select whether or not to operate the circuit for setting the idle period of the switching operation in the normal circuit under the two load states of the steady load and the light load. The power supply circuit can have a simple configuration.

According to a sixth aspect of the present invention, there is provided a switching power supply circuit according to any one of the first, second, and fourth aspects of the present invention, wherein the load state is detected by the load state detection means. The magnitude of the load is input to the switching suspending means from a control terminal of the control means provided so as to be converted into a voltage and input outside the control means.

According to the above invention, the magnitude of the load detected by the load state detecting means is converted into a voltage,
The signal is input to a control terminal provided in the control means, and is input to the switching suspending means. Accordingly, for example, when the control terminal voltage level is equal to or higher than the predetermined voltage level, it is determined that the load is light, and the switching operation of the switching means is provided with a pause period by the switching pause means, while the control terminal voltage level is lower than the predetermined voltage level. In some cases, it may be determined that the load is a steady load, and a normal switching operation may be performed.

Thus, it is only necessary to select whether or not to operate the circuit for setting the idle period of the switching operation in the normal circuit under the two load states of the steady load and the light load. The power supply circuit can have a simple configuration.

According to a seventh aspect of the present invention, there is provided a switching power supply device, wherein at least the switching means and the control means of the switching power supply circuit according to any one of the first to sixth aspects are in one package. It is characterized by being sealed inside.

According to the above invention, the switching power supply circuit according to any one of claims 1 to 6 is constituted by using a switching power supply device in which at least switching means and control means are sealed in one package. Therefore, the mounting area can be made very small.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIGS. 1 to 3 show an embodiment of a switching power supply circuit according to the present invention.
This will be described below.

FIG. 1 shows a configuration of a switching power supply circuit 1 according to the present embodiment. The switching power supply circuit 1 includes an input unit including a rectifier bridge circuit 2 and a smoothing capacitor C1, a voltage conversion unit including a converter 15 and a pulse transformer 5, a diode D1, and a smoothing capacitor C1.
2 and an output detection circuit 20, an output detection circuit 20, a light emitting diode D3, a phototransistor Q2, a capacitor C3, a diode D4, a resistor R2, a Zener diode ZD1,
And a feedback section including a phototransistor Q3, and is used as a DC-DC converter.

The input section rectifies a commercial AC voltage inputted between the input terminals P1 and P2 with a rectifying bridge circuit 2 composed of diodes, and smoothes the rectified bridge voltage with a smoothing capacitor C1 to obtain a DC voltage. It is output between 3 and 4.

In the voltage converter, the pulse transformer (transformer) 5 has a number of turns set to 1 according to the voltage conversion ratio.
It has a secondary winding 5a and a secondary winding 5b. The converter 15 includes a switching element (switching means) Q1 composed of an N-channel type power MOSFET, a diode D2, a pull-up resistor R1, a constant current source TD1,
Zener diode ZD2 and oscillation frequency idle period circuit 1
1. Oscillation circuit 13, PWM comparator 12, Reference voltage source 14
A switching control circuit (control means) comprising the control circuit 6; The converter 15 is a device molded in one package, and includes a terminal K1 to which a drain of the switching element Q1 is connected, a terminal K2 to which a source is connected, and a terminal (control terminal) K3 for inputting a control signal from outside. , A terminal K4 as a GND-side power supply terminal and a terminal K5 as a VCC (power supply) terminal.

The primary winding 5a of the pulse transformer 5 and the switching element Q1 of the converter 15 are connected in series, and the switching operation of the switching element Q1 by the gate pulse output from the control circuit 6 causes the primary The current flowing through the winding 5a is converted into a pulse. The diode D2 and the pull-up resistor R1 are connected in series between the terminals K5 and K4, and the connection between the pull-up resistor R1 and a phototransistor Q2 described later connected between the terminal K4 and the power supply line 4. Point 10 is the PWM comparator 1
2 input terminal F2. Further, the constant current source T
D1 is connected between terminals K5 and K3, and zener diode ZD2 is connected between terminal K3 and the ground line. A connection point 7 between the constant current source TD1 and a capacitor C3 described later connected between the terminal K3 and the power supply line 4 is connected to the input terminal F4 of the PWM comparator 12.

The connection points 10 and 16 are connected to the oscillation frequency idle period circuit 11, and the oscillation frequency idle period circuit 11 outputs the oscillation circuit 13 based on the voltage at the connection points 10 and 16.
A control signal is output to the oscillating circuit 13 as to whether or not to suspend the oscillation. The oscillation circuit 13 includes the oscillation frequency idle period circuit 11
As long as the control signal for instructing the suspension of the oscillation is not input, an oscillation signal of a predetermined frequency is continuously generated and output.

The output terminal of the oscillation circuit 13 is a PWM comparator 1
2 of the PWM comparator 12
Is the period of the oscillation signal input to the input terminal F1, the voltage at the node 10 input to the input terminal F2, the reference voltage Vref of the reference voltage source 14 input to the input terminal F3.
1 and a pulse having a duty corresponding to the lowest voltage among the voltages at the connection point 7 input to the input terminal F4, and outputs the generated pulse to the control circuit 6. The control circuit 6 controls the voltage value of the pulse output from the PWM comparator 12 to a level at which the gate of the switching element Q1 can be driven, and outputs the level to the gate.

The output section (output means) is connected to the primary winding 5 of the pulse transformer 5 when the switching element Q1 is cut off.
a, the excitation energy passed to the secondary winding 5b is 2
The current flowing due to the induced electromotive force of the next winding 5b is rectified by the diode D1 and is smoothed by the smoothing capacitor C2.
And output as a stabilized DC voltage between the output lines 8 and 9. The output voltage is the output terminal P3 / P4
It is supplied to the load from between.

In the feedback section (load state detecting means), the output detection circuit 20 is provided between the output lines 8 and 9 and detects, for example, the output voltage and output current of the output section. The light emitting diode D3 is connected between the output line 8 and the output detection circuit 20, and is adjusted to have a light emission intensity corresponding to the output voltage or output current detected by the output detection circuit 20. The phototransistor Q2 is connected between the terminal K4 of the converter 15 and the power supply line 4 and forms a photocoupler with the light emitting diode D3. The impedance of the phototransistor Q2 changes according to the intensity of light received from the light emitting diode D3. As a result, the detection result of the output detection circuit 20 is fed back to the voltage at the connection point 10.

The capacitor C3 is connected to the terminal K of the converter 15.
3 and a power supply line 4. The resistor R2, one end of which is connected to the power supply line 3, is connected to a parallel circuit of the Zener diode ZD1 and the phototransistor Q3, one end of which is connected to the power supply line 4, and the connection between the resistor R2 and the parallel circuit. The diode D4 is connected between the connection point and one end of the capacitor C3 on the terminal K3 side with the point side as the anode. The phototransistor Q3 forms a photocoupler with a light emitting diode (not shown) provided in the output detection circuit 20, and performs an ON / OFF operation based on a detection result of the output detection circuit 20. As a result, the detection result of the output detection circuit 20 is fed back to the voltage of the capacitor C3, that is, the voltage of the connection point 7.

The operation of the switching power supply circuit 1 having the above configuration will be described below. The AC voltage applied between the input terminals P1 and P2 is first rectified by the rectifying bridge circuit 2 and smoothed by the smoothing capacitor C1. When this DC voltage is applied between the power supply lines 3 and 4, power is supplied to the terminal K5 of the converter 15, and a charging current flows from the constant current source TD1 to the capacitor C3 via the resistor R2 and the diode D4. As it flows,
The voltage at the connection point 7 is input to the input terminal F4 of the PWM comparator 12.

The DC voltage is also applied to a series circuit including a diode D2, a pull-up resistor R1, and a phototransistor Q2.
The signal is input to the input terminal F2 of the comparator 12.

The PWM comparator 12 has a duty cycle based on the period of the oscillation signal input from the oscillation circuit 13 to the input terminal F1 and the lowest voltage among the three voltages input to the input terminals F2, F3 and F4. The pulse is generated and output. At the time of startup, the voltage between the terminals of the capacitor C3, that is, the control terminal voltage CA at the terminal K3 gradually rises from 0, so that a pulse having a duty determined by the voltage input to the input terminal F4 is output and soft start is performed. This pulse is made into a constant voltage by the control circuit 6 and then inputted to the gate of the switching element Q1, and the switching pulse of the switching element Q1 is turned on / off by this gate pulse. When the switching element Q1 is turned on, a current flows through the primary winding 5a of the pulse transformer 5 and the excitation energy is accumulated.
Is discharged by the induced electromotive force, the current flowing by this electromotive force is applied to the diode D1 and the smoothing capacitor C2.
Rectified and smoothed, and a stabilized DC voltage is output from between the output terminals P3 and P4.

After the start, the voltage between the terminals of the capacitor C3 gradually rises, and when the charging is completed and a steady state is reached, the voltage at the connection point 10 input to the input terminal F2 or the reference voltage input to the input terminal F3. The voltage of the voltage Vref1 becomes the lowest. On the other hand, when the output voltage detected by the output detection circuit 20 on the secondary side is higher (lower) than a predetermined value, the light emitting intensity of the light emitting diode D3 is increased (decreased) to decrease (increase) the impedance of the phototransistor Q2. . As a result, the voltage at the connection point 10 decreases (increases),
When the voltage at the connection point 10 is lower than the reference voltage Vref1, the PWM comparator 12 outputs a pulse adjusted so that the duty is reduced (increased) in accordance with the voltage decrease (increase). Thus, the output voltage is made constant.

When the load is a steady load larger than a predetermined value, the light emitting diode of the output detection circuit 20 is controlled to emit light, and as a result, the phototransistor Q3 is turned on.
State, and the voltage at the node 7 becomes the Zener diode Z
It becomes equal to the Zener voltage of D2. The oscillation frequency idle period circuit 11 has a threshold value for determining the operation or non-operation. At this time, the voltage at the connection point 10 is higher than the threshold value, and the voltage at the connection point 7 is lower than the threshold value. The logic is such that the oscillation frequency idle period circuit 11 does not operate with this setting. As a result, a control signal for normally operating the oscillation circuit 13 is output from the oscillation frequency pause period circuit 11, and the oscillation circuit 13 continuously outputs, for example, a triangular wave as shown in FIG.

On the other hand, when the load becomes a light load smaller than the predetermined value, the light emitting diode of the output detection circuit 20 is controlled so as not to emit light. As a result, the phototransistor Q3 is turned off and the Zener diode ZD1 is turned on. , The voltage at the connection point 7 rises to (the Zener voltage of the Zener diode ZD1) − (the voltage of the diode D4). At this time, the voltage at the connection point 10 is set to be lower than the threshold value, and the voltage at the connection point 7 is set to be higher than the threshold value. It has become. As a result, the oscillation frequency idle period circuit 11 outputs a control signal for providing an idle period to the oscillation of the oscillation circuit 13, and the oscillation circuit 13 outputs the oscillation idle period during a light load as shown in FIG. Outputs the provided triangular wave. Accordingly, accordingly, the switching element Q1 performs a switching operation in which the switching element Q1 is stopped in a state of being cut off for a certain period.

As a result, when the load is light, the switching loss in the switching element Q1 is significantly reduced, and the loss in the switching control circuit is suppressed by the provision of the idle period. Will be very small. Therefore, according to such a configuration, there is no need for a complicated structure such as providing a plurality of converter circuits and selectively using them according to the load state. Can respond. As a result, low power consumption of the switching power supply circuit can be realized with a low cost and small circuit configuration.

Next, the package form of the converter (switching power supply device) 15 will be described below. FIG. 3 shows a package structure of the converter 15. The switching control circuit including the diode D2, the pull-up resistor R1, the constant current source TD1, the zener diode ZD2, the oscillation frequency idle period circuit 11, the oscillation circuit 13, the PWM comparator 12, the reference voltage source 14, and the control circuit 6 It is formed in an integrated circuit chip 19, which is mounted on a ceramic substrate 17. The ceramic substrate 17 on which the integrated circuit chip 19 is mounted and the switching element Q1 are integrally sealed with resin or the like.

Power MOSFET (metal oxide semiconductor)
, The drain connected to the primary winding 5a of the pulse transformer 5 is connected from the lead frame 18 to the terminal K1. The terminal K2 is connected to the source of the switching element Q1 and the ground line of the converter 15, and the terminal K3 is connected to the terminal shown in FIG.
The control terminal voltage CA which is connected to the capacitor C3 and becomes an input signal to the control circuit 6 is input.
Further, the terminal K4 is connected to the collector of the phototransistor Q2, and the terminal K5 is connected to the power supply line 3.

The switching power supply circuit 1 is formed by using such a switching power supply device in which the switching element Q1 and the switching control circuit are sealed in one package.
, The mounting area can be made very small.

[Second Embodiment] The following will describe another embodiment of the switching power supply circuit of the present invention with reference to FIG. Components having the same functions as those described in the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

As shown in FIG. 4, the switching power supply circuit 21 of the present embodiment has the output detection circuit 11 in the switching power supply circuit 1 described in the first embodiment composed of an output voltage detection section and an output current detection section. It was done. In addition, the phototransistor Q5 receiving the feedback from the output current detector is connected to the oscillation frequency idle period circuit 11, the zener diode ZD2 is omitted, and only the capacitor C3 is connected outside the terminal K3. The configuration is such that the voltage at the connection point 7 is input only to the PWM comparator 12. Further, the voltage at the connection point 10 is also input only to the PWM comparator 12.

In the output detecting circuit 11, the output voltage detecting section includes the resistors R3 and R4 and the shunt regulator SR1.
The output voltage is detected and fed back to the voltage at the connection point 10. The resistors R3 and R4 are connected to the output lines 8.9
The voltage dividing resistors are connected in series between them, and their connection points are connected to the R terminal of the shunt regulator SR1. The shunt regulator SR1 is a light emitting diode D3
And the output line 9.

When the output voltage increases, the voltage divided by the resistors R3 and R4 increases, and the shunt regulator SR1 adjusts the output so as to reduce the cathode voltage of the light emitting diode D3. As a result, the light emission intensity of the light emitting diode D3 increases, the impedance of the phototransistor Q2 decreases, and the voltage at the connection point 10 decreases. On the other hand, when the output voltage decreases, the voltage division by the resistors R3 and R4 decreases, and the shunt regulator SR1 switches the light emitting diode D
The output is adjusted so as to increase the cathode voltage of No. 3.
As a result, the light emission intensity of the light emitting diode D3 decreases, the impedance of the phototransistor Q2 increases, and the voltage at the connection point 10 increases.

The output current detecting section includes resistors R5, R6, R7
R8, comparator 16, transistor Q4, and light emitting diode D5. The output current is detected and fed back from the phototransistor Q5 to the input voltage to the oscillation frequency idle period circuit 11. The resistor R7 is inserted on the output line 9 and one end thereof is connected to the non-inverting input terminal of the comparator 16. The resistors R5 and R6 are voltage-dividing resistors connected in series between the output line 8 and the other end of the resistor R7, and their connection points are connected to the inverting input terminal of the comparator 16. The resistor R8, the light emitting diode D5, and the transistor Q4 are connected in series between the output lines 8.9, and the base of the transistor Q4 is connected to the output terminal of the comparator 16. The light emitting diode D5 forms a photocoupler with the phototransistor Q5.

In a steady state where the output current, that is, the load current is larger than a predetermined secondary current level, the voltage at one end on the high potential side of the resistor R7 becomes larger than the voltage divided by the resistors R5 and R6. Outputs a high level voltage to turn on the transistor Q4. As a result, the cathode voltage of the light emitting diode D5 decreases, and the light emitting diode D5 emits light.
The state becomes the N state, and the input voltage from the phototransistor Q5 to the oscillation frequency pause period circuit 11 becomes Low level.

On the other hand, at a light load when the output current is smaller than the secondary current level, the voltage at one end on the high potential side of the resistor R7 becomes smaller than the voltage divided by the resistors R5 and R6, and the comparator 16 outputs a low level. To turn off the transistor Q4. As a result, the cathode voltage of the light emitting diode D5 increases, the light emitting diode D5 does not emit light, the phototransistor Q5 is turned off, and the oscillation frequency pause period circuit 1
The input voltage to 1 goes high.

In the switching power supply circuit 21 having the above configuration, the input voltage from the phototransistor Q5 to the oscillation frequency idle period circuit 11 becomes lower than the threshold value when the load is a steady load, and the oscillation frequency idle period circuit 11 does not operate. It has become. When the load is light, the input voltage from the phototransistor Q5 to the oscillation frequency idle period circuit 11 becomes higher than the threshold value, and the logic is such that the oscillation frequency idle period circuit 11 operates.

As described above, according to the switching power supply circuit 21 of the present embodiment, the circuit for setting the idle period of the switching operation for the two load states of the steady load and the light load is incorporated in the normal circuit. Since it is only necessary to select whether or not to operate, the switching power supply circuit can have a simple configuration.

Further, as in the first embodiment, the converter 15 of the present embodiment can be sealed in one package.

Third Embodiment A third embodiment of the switching power supply circuit of the present invention will be described below with reference to FIG. Note that components having the same functions as those described in the first and second embodiments are given the same reference numerals, and descriptions thereof are omitted.

As shown in FIG. 5, the switching power supply circuit 31 according to the present embodiment stores the current of the switching element Q1, that is, the primary side current in the converter 15 of the switching power supply circuit 1 described in the first embodiment. It has a primary side current detection circuit that detects and feeds back to the input voltage to the oscillation frequency idle period circuit 11. Along with this,
The zener diode ZD2 is omitted, and only the capacitor C3 is connected to the outside of the terminal K3, so that the voltage at the connection point 7 is input only to the PWM comparator 12. The primary side current detection circuit constitutes a part of the load state detection means.

The primary side current detection circuit includes resistors R9 and R10
And a capacitor C4. The resistor R9 is provided between the source of the switching element Q1 and the terminal K2, and a series circuit of the resistor R10 and the capacitor C4 is provided in parallel with the resistor R9. A connection point 32 between the resistor R10 and the capacitor C4 is connected to the oscillation frequency idle period circuit 11.

Since the primary side current flowing through the switching element Q1 corresponds to the secondary side output current, the primary side current detection circuit converts this primary side current into a voltage between terminals of the resistor R9. , Smoothed by the capacitor C4 and fed back to the voltage at the connection point 32. In the case of a steady load, since the primary current is larger than a predetermined primary drain current level, the voltage between the terminals of the resistor R9 is large, the voltage at the connection point 32 is high, and the oscillation frequency idle period circuit 11 is at a high level. Is input. In the case of a light load, the primary-side current is smaller than the primary-side drain current level, the voltage between the terminals of the resistor R9 is small, the voltage at the connection point 32 is low, and the oscillation frequency idle period circuit 11 Voltage is input.

In the switching power supply circuit 31 having the above configuration, the logic is such that the voltage at the connection points 10 and 32 both becomes higher than the threshold value when the load is steady and the oscillation frequency idle period circuit 11 does not operate. On the other hand, when the load is light, the voltages at the connection points 10 and 32 are both lower than the threshold value, so that the oscillation frequency idle period circuit 11 operates.

At the time of startup, there is a period in which the primary side current is small due to soft start and the voltage at the node 32 is lower than the threshold value. At this time, the voltage at the node 10 is reduced due to the low output voltage. Will be higher than the threshold,
The oscillation frequency idle period circuit 11 can be prevented from operating.

As described above, according to the switching power supply circuit 31 of the present embodiment, the circuit for setting the idle period of the switching operation for the two load states of the steady load and the light load is incorporated in the normal circuit. Since it is only necessary to select whether or not to operate, the switching power supply circuit can have a simple configuration.

Further, as in the first embodiment, it is needless to say that converter 15 in the present embodiment can be sealed in one package.

[Embodiment 4] Still another embodiment of the switching power supply circuit of the present invention will be described below with reference to FIG. Note that components having the same functions as those described in the first to third embodiments are given the same reference numerals, and descriptions thereof are omitted.

As shown in FIG. 6, the switching power supply circuit 41 of the present embodiment is configured such that the output detection circuit 11 of the switching power supply circuit 31 described in the third embodiment is connected to the resistors R3 and R4.
And a shunt regulator SR1 in which the primary side current detection circuit is omitted and the output voltage is fed back to the voltage at the connection point 10.

The operation of detecting the output voltage by the resistors R3 and R4 and the shunt regulator SR1 and feeding it back to the voltage at the connection point 10 is as described in the second embodiment. In this case, since the output voltage is low at the time of a steady load, the voltage at the connection point 10 becomes higher than the threshold value, and the logic is such that the oscillation frequency idle period circuit 11 does not operate. On the other hand, when the load is light, the output voltage increases.
The voltage at the connection point 10 is lower than the threshold value, and the logic is such that the oscillation frequency idle period circuit 11 operates.

As described above, according to the switching power supply circuit 41 of the present embodiment, the circuit for setting the idle period of the switching operation for the two load states of the steady load and the light load is incorporated in the normal circuit. Since it is only necessary to select whether or not to operate, the switching power supply circuit can have a simple configuration.

Further, as in the first embodiment, it is needless to say that converter 15 in the present embodiment can be sealed in one package.

[Fifth Embodiment] Still another embodiment of the switching power supply circuit of the present invention is described below with reference to FIG. Components having the same functions as the components described in the first to fourth embodiments are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 7, the switching power supply circuit 51 of the present embodiment comprises an output terminal of the PWM comparator 12 in the converter 15 of the switching power supply circuit 41 described in the fourth embodiment and an oscillation frequency idle period circuit. 11 is provided with a duty cycle detection circuit 52 for detecting the duty cycle of the pulse output from the PWM comparator 12. The duty cycle detection circuit 52 forms a part of the load state detection means.

In this case, since the duty cycle is long at the time of a steady load, the duty cycle detection circuit 52
Detects this, and outputs a High-level or Low-level voltage to the oscillation frequency detection circuit 11. on the other hand,
Since the duty cycle is short when the load is light, the duty cycle detection circuit 52 detects this, and when a high-level voltage is output during a steady load, L
When a low-level voltage is output under a steady load, a high-level voltage is output to the oscillation frequency detection circuit 11.

Therefore, at a steady load, the voltage at the node 10 becomes higher than the threshold value, and the output voltage from the duty cycle detection circuit 52 becomes higher (lower) than the threshold value, and the oscillation frequency idle period circuit 11 Is not working logic. When the load is light, the voltage at the node 10 becomes lower than the threshold value, and the output voltage from the duty cycle detection circuit 52 becomes lower (higher) than the threshold value. Has become.

At the time of startup, there is a period in which the duty cycle is short due to the soft start. At this time, the voltage at the node 10 becomes higher than the threshold value due to the low output voltage. It can be disabled.

As described above, according to the switching power supply circuit 51 of the present embodiment, the circuit for setting the idle period of the switching operation for the two load states of the steady load and the light load is incorporated in the normal circuit. Since it is only necessary to select whether or not to operate, the switching power supply circuit can have a simple configuration.

Further, as in the first embodiment, it is needless to say that converter 15 in the present embodiment can be sealed in one package.

[Embodiment 6] Still another embodiment of the switching power supply circuit of the present invention will be described below with reference to FIG. Note that components having the same functions as those described in the first to fifth embodiments are denoted by the same reference numerals, and description thereof is omitted.

As shown in FIG. 8, the switching power supply circuit 61 according to the present embodiment is the same as the switching power supply circuit 1 described in the first embodiment except that the output detection circuit 20 is the same as that described in the second embodiment. , And the voltage at the connection point 10 is input only to the PWM comparator 12.

That is, the resistors R5, R6, R7, R8,
The operation / non-operation of the oscillation frequency idle period circuit 11 is controlled only by the feedback of the output current detected by the output current detection unit including the comparator 16, the transistor Q4, and the light emitting diode D5.

In this case, at a steady load, the connection point 7
Is lower than the threshold value, so that the oscillation frequency idle period circuit 11 does not operate. On the other hand, when the load is light, the voltage at the node 7 becomes higher than the threshold value, and the logic is such that the oscillation frequency idle period circuit 11 operates.

As described above, according to the switching power supply circuit 61 of the present embodiment, the circuit for setting the idle period of the switching operation for the two load states of the steady load and the light load is incorporated in the normal circuit. Since it is only necessary to select whether or not to operate, the switching power supply circuit can have a simple configuration.

Further, as in the first embodiment, the converter 15 of the present embodiment can be sealed in one package.

[0089]

According to the first aspect of the present invention, there is provided a switching power supply circuit for switching a DC voltage input to a primary side of a transformer and outputting a pulse to a secondary side as described above, Output means for outputting a DC voltage obtained by smoothing the pulse to a load, and feedback of the output voltage from the output means, an oscillation signal output from an oscillation means for performing an oscillating operation, and the output voltage fed back; And a control means for controlling the switching means to perform a switching operation at a predetermined frequency and duty based on the switching power supply circuit, further comprising: a load state detection means for detecting a magnitude of a load; When the load state detecting means detects a light load that is equal to or less than a predetermined value, the oscillation operation of the oscillating means is stopped. Is stopped is configured to have a switching pause means for providing a pause period to be kept in the interrupted state to the switching operation.

Therefore, when the load is light, the switching loss in the switching means is greatly reduced, and the loss in the control means is suppressed, so that the power consumption of the entire switching power supply circuit is significantly reduced. Therefore, according to such a configuration, there is no need for a complicated structure such as providing a plurality of converter circuits and selectively using them according to the load state. Can respond. As a result, there is an effect that the power consumption of the switching power supply circuit can be reduced with a low cost and small circuit configuration.

As described above, in the switching power supply circuit according to the second aspect of the present invention, in the switching power supply circuit according to the first aspect, the load state detecting means determines the size of the load based on a current level flowing through the output means. Is detected.

Therefore, it is only necessary to select whether or not to operate the circuit for setting the idle period of the switching operation in the normal circuit under the two load states of the steady load and the light load. There is an effect that the power supply circuit can have a simple configuration.

According to a third aspect of the present invention, as described above, in the switching power supply circuit according to the first aspect, the load state detecting means determines the size of the load based on a current level flowing through the switching means. Is detected.

Therefore, it is only necessary to select whether or not to operate the circuit for setting the idle period of the switching operation in the normal circuit under the two load states of the steady load and the light load. There is an effect that the power supply circuit can have a simple configuration.

According to a fourth aspect of the present invention, as described above, in the switching power supply circuit according to the first aspect, the load state detecting means determines the magnitude of the load from the output voltage fed back. This is a configuration for detecting.

Therefore, it is only necessary to select whether or not to operate the circuit for setting the idle period of the switching operation in the normal circuit under the two load states of the steady load and the light load. There is an effect that the power supply circuit can have a simple configuration.

According to a fifth aspect of the present invention, as described above, in the switching power supply circuit according to the first or fourth aspect, the load state detecting means determines the magnitude of the load based on the duty cycle level. Is detected.

Therefore, it is only necessary to select whether or not to operate the circuit for setting the idle period of the switching operation in the normal circuit under the two load states of the steady load and the light load. There is an effect that the power supply circuit can have a simple configuration.

According to a sixth aspect of the present invention, as described above, in the switching power supply circuit according to any one of the first, second, and fourth aspects, the load of the load detected by the load state detection means is controlled. The magnitude is inputted to the switching suspending means from a control terminal of the control means provided so as to be converted into a voltage and inputted outside the control means.

Therefore, it is only necessary to select whether or not to operate the circuit for setting the idle period of the switching operation in the normal circuit under the two load states of the steady load and the light load. There is an effect that the power supply circuit can have a simple configuration.

According to a seventh aspect of the present invention, as described above, at least the switching means and the control means of the switching power supply circuit according to any one of the first to sixth aspects are enclosed in one package. This is a configuration that is stopped.

Therefore, since the switching power supply circuit is constituted by using the switching power supply device in which at least the switching means and the control means are sealed in one package, the mounting area can be made very small. Play.

[Brief description of the drawings]

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

2A is a waveform diagram illustrating an oscillation state of the oscillation circuit under a light load, and FIG. 2B is a waveform diagram illustrating an oscillation state of the oscillation circuit under a steady load.

FIG. 3 is a plan view showing a configuration of a converter package in the switching power supply circuit of FIG. 1;

FIG. 4 is a circuit block diagram illustrating a configuration of a switching power supply circuit according to a second embodiment of the present invention.

FIG. 5 is a circuit block diagram illustrating a configuration of a switching power supply circuit according to a third embodiment of the present invention.

FIG. 6 is a circuit block diagram illustrating a configuration of a switching power supply circuit according to a fourth embodiment of the present invention.

FIG. 7 is a circuit block diagram illustrating a configuration of a switching power supply circuit according to a fifth embodiment of the present invention.

FIG. 8 is a circuit block diagram illustrating a configuration of a switching power supply circuit according to a sixth embodiment of the present invention.

FIG. 9 is a circuit block diagram showing a configuration of a conventional switching power supply circuit.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 switching power supply circuit 5 pulse transformer (transformer) 6 control circuit (control means) 11 oscillation frequency idle period circuit (control means) 12 PWM comparator (control means) 13 oscillation circuit (control means) 14 reference voltage source (control means) 15 converter (device for switching power supply) 20 output detection circuit (load state detection means) 21 switching power supply circuit 31 switching power supply circuit 41 switching power supply circuit 51 switching power supply circuit 52 duty cycle detection circuit (load state detection means) 61 switching power supply circuit C2 Smoothing capacitor (output means) C3 Capacitor (load state detecting means) C4 Capacitor (load state detecting means) D1 diode (output means) D2 diode (control means) D3 Light emitting diode (load state detecting means) D4 diode (Control means) D5 Light emitting diode (Load state detecting means) K3 Control terminal Q1 Switching element (Switching means) Q2 Phototransistor (Load state detecting means) Q3 Phototransistor (Load state detecting means) Q4 Transistor (Load state detecting means) Q5 Phototransistor (load state detection means) R1 Pull-up resistor (control means) R2 Resistance (load state detection means) R3 Resistance (load state detection means) R4 Resistance (load state detection means) R5 Resistance (load state detection means) R6 resistance (Load state detecting means) R7 Resistance (Load state detecting means) R8 Resistance (Load state detecting means) R9 Resistance (Load state detecting means) R10 Resistance (Load state detecting means) SR1 Shunt regulator (Load state detecting means) TD1 Constant current Source (control means) ZD1 Zener -Diode (load condition detecting means) ZD2 Zener diode (control means)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tomohiro Suzuki 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Koji Kugawa 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside (72) Inventor Atsushi Kanamori 22-22 Nagaikecho, Abeno-ku, Osaka City, Osaka F-term (reference) 5H730 AA14 BB43 BB57 CC01 DD04 EE02 EE07 EE59 FD01 FD31 FD41 FD61 FF02 FF19 FG05 FG26 XC14 ZZ11

Claims (7)

[Claims] 1. A switching means for switching a DC voltage input to a primary side of a transformer and outputting a pulse to a secondary side, and an output means for outputting a DC voltage obtained by smoothing the pulse to a load. And feedback the output voltage from the output means to cause the switching means to perform a switching operation at a predetermined frequency and duty based on the oscillating signal output from the oscillating means performing the oscillating operation and the output voltage fed back. A switching power supply circuit having control means for controlling the load condition, comprising: a load state detecting means for detecting a magnitude of a load, wherein the control means detects a light load in which the load state detecting means is a load equal to or less than a predetermined value. A pause period during which the oscillating operation of the oscillating means is temporarily stopped and the switching operation is kept in a cutoff state A switching power supply circuit, comprising: a switching pause unit for providing a switching power supply. 2. The switching power supply circuit according to claim 1, wherein said load state detecting means detects a magnitude of a load from a current level flowing through said output means. 3. The switching power supply circuit according to claim 1, wherein said load state detecting means detects a magnitude of a load from a current level flowing through said switching means. 4. The switching power supply circuit according to claim 1, wherein said load state detecting means detects a magnitude of a load from said output voltage fed back. 5. The switching power supply circuit according to claim 1, wherein said load state detecting means detects a magnitude of a load from a cycle level of said duty. 6. The switching suspending means from a control terminal of the control means provided so that the magnitude of the load detected by the load state detecting means is converted into a voltage outside the control means and inputted. The switching power supply circuit according to claim 1, wherein the switching power supply circuit is input to the switching power supply circuit. 7. A switching power supply device according to claim 1, wherein at least said switching means and said control means of said switching power supply circuit are sealed in one package.