JPH11275857A - Switching power source circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power source circuit which is capable of reducing the power consumption of a load as a whole and the number of item parts. SOLUTION: When the load of a switching power source circuit is small and the secondary-side voltage V0 of the circuit becomes a certain value VsH or higher, the output of a comparator CoH2 becomes 'H', and the output of a drive circuit 1 which drives a primary-side switching element Q2 is turned off by means of a photocoupler PC2 . Consequently, the power supply to the secondary side is discontinued, and the secondary-side voltage V0 drops as a capacitor C14 discharges. When the voltage V0 becomes a certain value VsL or lower, the output of the comparator CoH2 becomes 'L'. Since the photocoupler CP2 turns on the output of the drive circuit 1 when the output of the comparator CoH2 becomes 'L', the turning on/off operations of the switching element Q2 are restarted, and the voltage V0 rises. By repeating these operations, intermittent oscillation is maintained. When the secondary-side load current increases and the voltage drop is larger than a certain reference voltage, the intermittent operations are stopped so as to turn off the power supply to the comparator CoH2 .

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 incorporated in electric equipment such as microcomputers and word processors, electronic equipment, and the like.

[0002]

2. Description of the Related Art As the above-mentioned switching power supply circuit,
There is known a device capable of intermittent oscillation to reduce power consumption during standby. FIG. 9 shows a general circuit configuration of a conventional example of the circuit system.

[0003] In this switching power supply circuit, the commercial power supply is applied to the input terminal 100, the commercial power source is first through the resistor R ₁ which also serves as a rush current limiting fuse, through the noise filter L _1. After power supply for control through the noise filter L ₁ is rectified and smoothed with capacitor C ₂ by passing connexion diode D _2, D ₃ and capacitor C _3, further zener
Overvoltage is limited by the diode Z _1. A drive circuit 101 composed of a timer IC oscillates at a certain frequency, and drives a MOSFET (Q ₁ ) as a switching element.

The main power supply having passed through the noise filter L ₁ is rectified by a diode D ₁ and then smoothed by a capacitor C ₄ . The secondary side of the transformer T ₁ is rectified by the Schottky barrier diode Z ₂ and smoothed by the LC π-type filter (C ₉ , L ₂ , C ₁₀ ). On the output side of the π-type filter, a comparator C using an OP amplifier for voltage detection
oH ₁ is provided, and a slight positive feedback is applied to give a hysteresis characteristic. The output terminal of the comparator CoH ₁ is connected to a photodiode side of the photocoupler PC _1. Transistor side of the photo coupler PC ₁ is connected to a reset terminal of the drive circuit 101 (RES). A three-terminal regulator 102 is provided immediately before the output terminal 103. The three-terminal regulator 102 removes a ripple generated by intermittent oscillation.

[0005] When the voltage V ₀₁ of by the comparator CoH ₁ connexion detected secondary side becomes a certain value VsH, the output of the comparator CoH ₁ becomes H, on the photo-coupler PC ₁ connected to the output terminal Then, the oscillation is stopped by turning off the drive circuit 101 including the timer IC. When the oscillation stops, the voltage will not be transmitted from the transformer T ₁ secondary, the voltage of the secondary side is reduced. Becomes the secondary side of the voltage V ₀₁ is the value VsL (<VsH), the voltage of the turn output becomes L comparators CoH _1, the reset terminal of the drive circuit 101 photocoupler PC ₁ is turned off (RES) is increased And oscillation resumes. Then, the voltage on the secondary side increases again. The above operation is repeated to maintain intermittent oscillation.

Note that C ₁ , C ₅ , C ₆ ,
C ₇ , C ₈ , C ₉ , C ₁₀ and C ₁₁ are capacitors,
_{R 2, R 3, R 4} , R 5, R 6, R 7, R 8, R 9, R 10 and R ₁₁ is the resistance.

FIG. 10 shows a timing chart of this series of operations. (A) shows the secondary side voltage V ₀₁ ,
(B) the output of the comparator CoH _1, (c) a MOS
The operation of the FET will be described.

If power is intermittently supplied to the secondary side in this manner, power consumption on the primary side can be reduced, and power consumption during standby can be reduced.

[0009]

However, in this type of switching power supply circuit, since intermittent oscillation occurs even under normal load, the loss in a three-terminal regulator, which is indispensable to obtain a constant voltage, occurs. Is not good. That is, efficiency in normal operation is sacrificed in order to suppress power consumption during standby, and it cannot be said that power consumption can be reduced in all cases. In addition, the number of components for a power supply configuration, such as a reset timer IC and a three-terminal regulator, is increased, which leads to a problem that the power supply is increased in size and cost is increased.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems of the prior art, and has as its object to provide a switching power supply circuit capable of reducing the total power consumption and the number of components. I do.

[0011]

According to a first aspect of the present invention, there is provided a switching power supply circuit comprising means for detecting a load on a secondary side and switching between a standby state and a normal power supply operation. The switching element provided is turned on / off to perform intermittent oscillation, and at the time of normal power supply operation, the intermittent oscillation is stopped to perform normal power supply operation, thereby achieving the above object.

A switching power supply circuit according to a second aspect of the present invention controls on / off of a switching element provided on a primary side during a standby state based on a signal input from outside to switch between a standby state and a normal power supply operation. The intermittent oscillation is performed, the intermittent oscillation is stopped at the time of the normal power supply operation, and the normal power supply operation is performed, thereby achieving the above object.

According to a third aspect of the present invention, there is provided a switching power supply circuit comprising a switching element on a primary side and a drive circuit for driving the switching element, and a signal for switching between a standby state input from the outside and a normal power supply operation. On the basis of,
During standby, intermittent oscillation is performed by controlling power supply to the drive circuit and adjusting the switching operation of the switching element, and during normal power supply operation, the intermittent oscillation is stopped and normal power supply operation is performed. Objective is achieved.

According to a fourth aspect of the present invention, there is provided a switching power supply circuit including: a capacitor for performing a soft start function; and a comparator for inputting a voltage signal of the capacitor and a voltage signal of a triangular wave. The comparator compares the rising voltage of the capacitor with the voltage of the triangular wave, and the on-time of the switching element becomes longer or the off-time becomes shorter due to the increase in the output pulse width of the comparator based on the voltage difference between the two. By that
It is characterized by intermittent oscillation by soft start.

According to a fifth aspect of the present invention, there is provided a switching power supply circuit, wherein a signal input from outside for switching between a standby state and a normal power supply operation is supplied to the comparator. During power supply operation, the comparator is turned off to perform normal power supply operation.

According to a sixth aspect of the present invention, there is provided a switching power supply circuit including a comparator for inputting a feedback signal from the secondary side to the primary side and a triangular wave signal, the feedback signal and the triangular wave corresponding to the voltage on the secondary side. The comparator compares the signal with the lowest voltage, and in a standby state, when the former voltage is higher than the latter voltage, the switching element provided on the primary side is turned on / off to perform intermittent oscillation, and the former voltage becomes the latter voltage. At the time of the normal power supply operation lower than the voltage, the intermittent oscillation is stopped and the normal power supply operation is performed, thereby achieving the above object.

According to a seventh aspect of the present invention, there is provided a switching power supply circuit which supplies to the comparator a signal for switching between a standby state and a normal power supply operation, which is input from the outside. During power supply operation, the comparator is turned off to perform normal power supply operation.

Hereinafter, the operation of the present invention will be described.

First, the basic operation of the switching power supply circuit of the present invention will be described. Using the function of stopping the on / off operation of the switching element of the circuit of the power supply control part on the primary side, stopping the on / off operation of the primary side when the voltage on the secondary side exceeds a certain value, and a certain value The power supply operation is performed intermittently by starting the on / off operation when
Reduce power consumption during standby. When the power supply operation is not in the standby state, the element for detecting the voltage on the secondary side is turned off, thereby performing a normal power supply operation and preventing a decrease in efficiency. Further, whether or not the apparatus is in the standby state may be determined by a signal from a microcomputer (hereinafter, referred to as a set microcomputer) of an electric device or an electronic device in which the switching power supply circuit of the present invention is set.

Next, the specific operation of the present invention will be described.

The switching power supply circuit of claim 1 will be described with reference to FIG. When the load is small, the secondary side voltage V
_{When 0} becomes equal to or more than a certain value VsH, the output of the comparator CoH ₂ with hysteresis becomes H (= high level),
Turns off the output of the drive circuit 1 for driving the photo main switching element of the coupler PC ₂ on the primary side (MOSFET) Q _2. Then, there is no power supply to the secondary side, a voltage with the discharge of the capacitor C ₁₄ for smoothing the output voltage is reduced.

If the output of the comparator with hysteresis CoH ₂ is set to L when the voltage V ₀ on the secondary side falls below a certain value VsL, the photocoupler PC ₂ at this time outputs the output of the drive circuit 1. On, so MO
The ON / OFF operation of the SFET (Q ₂ ) resumes, and the voltage on the secondary side rises. By repeating this, the intermittent oscillation is maintained as in FIG. If the load current of the secondary side is increased, putting a voltage drop across the sensing resistor R ₁₄ to the load current detection comparator 2, the power of the comparator with hysteresis CoH ₂ when the voltage drops below a certain reference voltage is greater The intermittent operation is stopped by turning it off.

[0023] In the switching power supply circuit according to claim 2, comparator with hysteresis CoH ₃ as shown in FIG. 2
Is controlled by the microcomputer 4 of the set, and is turned on during standby with a light load, and turned off during normal operation with a heavy load. By doing so, there is no intermittent oscillation during normal power supply operation, and no protection function works. In addition, since it is not necessary to form a circuit for detecting the load current on the secondary side in the power supply, the size of the power supply can be reduced, and at the same time, the loss in the current detection resistor can be eliminated.

The switching power supply circuit of claim 3 will be described with reference to FIG.

When a standby signal is input from the microcomputer 5 in the set, the comparator CoH ₄ with hysteresis for detecting the secondary side voltage V ₀ operates. Output voltage of the secondary side is the certain value or more, the comparator CoH ₄ becomes H, and turns on the photo-coupler PC _4. Then M on the primary side
The output of the circuit for driving the OSFET (Q ₃ ) is cut off, the switching operation stops, and the power supply to the secondary side stops. And a capacitor C for smoothing the output voltage.
_The voltage drops with the discharge of ₁₈ . When the voltage on the secondary side falls below a certain value, the output of the comparator CoH ₄ becomes L (=
Circuit outputs to off the photocoupler PC ₄ goes low) drive the primary side of the MOSFET (Q _3), the switching operation is started.

Then, the voltage on the secondary side increases. This series of operations is repeated to maintain intermittent oscillation. When a signal indicating that the set is not in the standby state is input, the comparator C
The oH ₄ is turned off so that the intermittent operation is not performed, and the normal power supply operation starts. Since it is not necessary to form a circuit for detecting the load current on the secondary side in the power supply, the power supply can be miniaturized, and at the same time, the loss in the current detection resistor can be eliminated.

The soft start circuit according to claim 4 is
This will be described with reference to FIG.

When power is turned on, V
Power is supplied to CC, and the charging current supplied from the internal constant current source to the soft start capacitor C ₁₉ causes the voltage of the soft start capacitor C ₁₉ to rise. The pulse width control comparator PWM ₁ outputs the voltage of the capacitor C ₁₉ gently rising and the dead time control voltage (DE
T) Output when the voltage of the triangular wave oscillator 7 is lower than the lowest voltage among the feedback voltages from the secondary side. Power On the output of the pulse width control comparator PWM ₁ and the voltage of the capacitor C ₁₉ becomes the lowest is widening the pulse width with the voltage rise of the capacitor.
As a result, the ON time of the MOSFET (Q ₄ ) increases, a soft start is applied, and the output gradually increases.

FIG. 5 is a timing chart showing this series of operations. That is, when the voltage of the capacitor for the soft start rises, the switching operation of the MOSFET (Q ₄ ) starts, and when the voltage of the capacitor falls, the switching operation of the MOSFET (Q ₄ ) stops.

FIG. 6 shows a switching power supply circuit provided with the soft start circuit shown in FIG. This figure 6
In, the primary-side MOSFET (Q ₄₎ starts to turn on and off, since there is power supply from the transformer T ₅ 2
The voltage on the secondary side rises. The output of the comparator with hysteresis CoH ₂ becomes more than a certain value this voltage becomes H, dropping the voltage of the capacitor C ₁₃ by turning on the photocoupler PC _2. Then, the switching operation of the MOSFET (Q ₄ ) stops. Primary MOSFET (Q
Since ₄₎ on and off disappears the power supply from the transformer T ₅ is stopped, the capacitor C ₁₄ for smoothing the output voltage
, The secondary-side voltage decreases.

When this voltage falls below a certain value, the output of the comparator with hysteresis CoH ₂ becomes L, the photocoupler PC ₂ is turned off and the voltage of the capacitor C ₁₉ rises, so that the primary side switching element Q ₄ Resumes on / off. In this way, the intermittent operation is maintained.

In claim 5, the power supply of the comparator shown in FIG. 6 is controlled by a set microcomputer, that is, the secondary side circuit in FIG. 6 is configured in the same manner as in FIG. Therefore, it is turned on during standby with a light load, and turned off during normal operation with a heavy load. Also in this case, since it is not necessary to form a circuit for detecting the load current on the secondary side in the power supply, the power supply can be reduced in size, and at the same time, the loss in the current detection resistor can be eliminated.

In claim 6, as shown in FIG.
The voltage of the feedback terminal 8 is controlled instead of the voltage of the capacitor of the fourth aspect. Function of the feedback terminals 8, by changing the duty of the switching element (MOSFET) Q ₆ of the primary side in accordance with a variation in the secondary-side voltage, which constant voltage of the secondary side as in FIG 5 It is. When the voltage of the capacitor C ₂₃ for soft-start is constant, the switching operation starts in the higher feedback voltage from the secondary side MOSFET (Q _6), if the voltage is lower than the minimum voltage of the triangular wave oscillator 7 The switching operation of the MOSFET (Q ₆ ) stops (see FIG. 8).

Therefore, when the voltage on the secondary side is higher than a certain value, the comparator with hysteresis CoH ₂ is turned on to turn on the photocoupler PC ₂ . This reduces the feedback voltage to reduce the MOSFET (Q ₆ )
Is stopped, and when the secondary voltage drops to a certain value, the comparator CoH ₂ is turned off to turn off the photocoupler PC ₂ . As a result, the feedback voltage is increased to start the switching operation of the MOSFET (Q ₆ ), and the intermittent oscillation is continued.

[0035] In claim 7, the circuit of the secondary side of FIG. 7 as the same configuration as FIG. 2, that is to control the power of the comparator CoH ₂ according to claim 6 in the microcomputer of the set, ON when the load is light stand, Turn off during normal operation with heavy load. Since it is not necessary to form a circuit for detecting the load current on the secondary side in the power supply, the power supply can be miniaturized, and at the same time, the loss in the current detection resistor can be eliminated.

[0036]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described specifically.

(Embodiment 1) FIG. 1 is a block diagram showing a switching power supply circuit according to Embodiment 1. In addition,
A on the left side in FIG. 1 has the same configuration as A in FIG.
Description is omitted.

[0038] The switching power supply circuit, when the load is small, becomes more than a certain voltage V ₀ which secondary value VsH, the output of the comparator with hysteresis CoH ₂ is H
To be to turn off the output of the drive circuit 1 for driving the photo main switching element of the coupler PC ₂ on the primary side (MOSFET) Q _2. Then, there is no power supply to the secondary side, a voltage with the discharge of the capacitor C ₁₄ for smoothing the output voltage is reduced. The value V which is the voltage V ₀ which secondary
If the output of the comparator CoH ₂ is set to L when the output becomes less than sL, the photocoupler P
Since C ₂ is turned on the output of the drive circuit 1, MOSF
The on / off operation of ET (Q ₂ ) resumes, and the voltage on the secondary side rises.

By repeating this, the intermittent oscillation is maintained as in FIG. When the load current on the secondary side increases,
Put the voltage drop across the sensing resistor R ₁₄ to the load current detection comparator 2, when the voltage drops below a certain reference voltage is large so as to turn off the comparator CoH _2,
Stop the intermittent operation.

Therefore, according to the present embodiment,
It is possible to reduce the power consumption until the load power increases after the operation starts, with a smaller number of components than in the conventional power supply circuit. Further, at the time of a normal load, high efficiency operation which is an original merit of the switching power supply can be performed without impairing the conventional protection function. As described above, both the standby state of the light load and the normal load state, that is, the power consumption of the power supply circuit is reduced in total.

In FIG. 1, T ₂ is a transformer, nB is an auxiliary winding, D ₄ and D ₅ are diodes, C ₁₂ and C ₁₃ are capacitors, R ₁₂ , R ₁₃ , R ₁₅ and R
₁₆ resistance, V _S is the reference voltage.

(Embodiment 2) FIG. 2 is a block diagram showing a secondary side of a switching power supply circuit according to Embodiment 2. The primary side is the same as in FIG. 1, and the description is omitted.

In this switching power supply circuit, as shown in FIG. 2, the power supply of the comparator CoH ₃ with hysteresis is controlled by the set microcomputer 4, and is turned on during standby with a light load and turned off during normal operation with a heavy load. By doing so, there is no intermittent oscillation during normal power supply operation, and no protection function works. In addition, since it is not necessary to form a circuit for detecting the load current on the secondary side in the power supply, the size of the power supply can be reduced, and at the same time, the loss in the current detection resistor can be eliminated.

Note that T _{3 in} FIG. 2 is a transformer and D ₆
Is a diode, C ₁₅ is a capacitor, and R ₁₇ and R
₁₈ is a resistor. PC ₃ is a photocoupler,
A photocoupler (not shown) on the light receiving side is provided on the primary side.

(Embodiment 3) FIG. 3 is a block diagram showing a switching power supply circuit according to Embodiment 3. In addition,
A on the left side of FIG. 3 has the same configuration as A of FIG.
Description is omitted.

In this switching power supply circuit, when a standby signal is input from the microcomputer 5 of the set, the comparator CoH ₄ with hysteresis for detecting the secondary-side voltage V ₀ operates. Output voltage of the secondary side is the certain value or more, the comparator CoH ₄ becomes H, and turns on the photo-coupler PC _4. Then, the output of the circuit for driving the primary-side MOSFET (Q ₃ ) is cut off, the switching operation is stopped, and power supply to the secondary side is stopped. Then, the voltage decreases with the discharge of the capacitor _C18 for smoothing the output voltage. When the voltage on the secondary side falls below a certain value, the output of the comparator CoH ₄ becomes L, a circuit for turning off the photocoupler PC ₄ and driving the MOSFET (Q ₃ ) on the primary side is output, and the switching operation starts. I do.

Then, the voltage on the secondary side increases. This series of operations is repeated to maintain intermittent oscillation. When a signal indicating that the set is not in the standby state is input, the comparator C
The oH ₄ is turned off so that the intermittent operation is not performed, and the normal power supply operation starts.

Also in the third embodiment, since it is not necessary to form a circuit for detecting the load current on the secondary side in the power supply, the power supply can be downsized, and at the same time, the loss in the current detection resistor can be eliminated. be able to.

[0049] Incidentally, 6 drive circuit in FIG. 3, T ₄ are trans, D ₇ and D ₈ are diodes, C ₁₆ and C ₁₇ are capacitors, R ₁₉ and R ₂₀ is the resistance.

(Embodiment 4) FIG. 6 is a block diagram showing a main part of a switching power supply circuit according to Embodiment 4.

On the primary side of this switching power supply circuit,
The soft start circuit shown in FIG. 4 is provided. The soft start circuit, when power is turned on, power to the VCC is supplied via the starting resistor, the charging current supplied to the soft-start capacitor C ₁₉ from internal constant current source,
The voltage of the soft-start capacitor C ₁₉ is increased. Pulse width control comparator PWM ₁ is the voltage of the capacitor C ₁₉ to gradually increase, the dead-time control voltage (DET), than the lowest voltage among the feedback voltage from the secondary side, when the voltage of the triangular wave oscillator 7 is low Output to Pulse width control comparator PWM because the power supply startup voltage of the capacitor C ₁₉ becomes the lowest
The output of ₁ increases the pulse width as the voltage of the capacitor rises. As a result, the ON time of the MOSFET (Q ₄ ) increases, a soft start is applied, and the output gradually increases. In addition, soft start is MOSFET
The case where the OFF time of (Q ₄ ) is performed may be reduced.

FIG. 5 is a timing chart showing this series of operations. That is, when the voltage of the capacitor for the soft start rises, the switching operation of the MOSFET (Q ₄ ) starts, and when the voltage of the capacitor falls, the switching operation of the MOSFET (Q ₄ ) stops.

In FIG. 6, the primary side MOSFET
When (Q ₄ ) starts turning on and off, the voltage on the secondary side rises because power is supplied from the transformer T ₅ . And
The output of the comparator with hysteresis CoH ₂ becomes more than a certain value this voltage becomes H, dropping the voltage of the capacitor C ₁₉ by turning on the photocoupler PC _2. Then MO
The switching operation of the SFET (Q ₄ ) stops. The on-off of the primary-side MOSFET (Q ₄₎ the power supply from the transformer T ₅ is eliminated is stopped, the voltage of the secondary side with the discharge of the capacitor C ₁₄ for smoothing the output voltage is reduced. Then, the output of the comparator CoH ₂ becomes below a certain value the voltage is L, and since the photocoupler PC ₂ is the voltage of the capacitor C ₁₉ is turned off is increased, the primary side switching element Q ₄ is turned on and off To resume. In this way, the intermittent operation is maintained.

[0054] D ₅ in FIG. 6 is a diode, C ₁₃ is a capacitor, R ₁₂ to R ₁₆ is a resistor.

(Embodiment 5) In Embodiment 5, the secondary side of the switching power supply circuit shown in FIG. 6 has the configuration shown in FIG.

In this switching power supply circuit, the power supply of the comparator CoH ₂ shown in FIG. 6 is controlled by the microcomputer 4 of the set shown in FIG. Therefore, it is turned on during standby with a light load, and turned off during normal operation with a heavy load. Also in this case, since it is not necessary to form a circuit for detecting the load current on the secondary side in the power supply, the power supply can be reduced in size, and at the same time, the loss in the current detection resistor can be eliminated.

(Embodiment 6) FIG. 7 is a block diagram showing a main part of a switching power supply circuit according to Embodiment 6.

In the sixth embodiment, the voltage of the feedback terminal 8 is controlled instead of the voltage of the capacitor used in the fourth embodiment. Function of the feedback terminals 8, by changing the duty of the switching element (MOSFET) Q ₆ of the primary side in accordance with a variation in the secondary-side voltage, which constant voltage of the secondary side as in FIG 5 It is. When the voltage of the capacitor C ₂₃ for soft-start is constant, the switching operation starts in the higher feedback voltage from the secondary side MOSFET (Q _6), if the voltage is lower than the minimum voltage of the triangular wave oscillator 7 The switching operation of the MOSFET (Q ₆ ) stops (see FIG. 8).

Therefore, when the voltage on the secondary side is higher than a certain value, the comparator CoH ₂ with hysteresis is turned on to turn on the photocoupler PC ₂ . This reduces the feedback voltage to reduce the MOSFET (Q ₆ )
Is stopped, and when the secondary voltage drops to a certain value, the comparator CoH ₂ is turned off to turn off the photocoupler PC ₂ . As a result, the feedback voltage is increased to start the switching operation of the MOSFET (Q ₆ ), and the intermittent oscillation is continued.

Also in this embodiment, the size of the power supply can be reduced, and at the same time, the loss in the current detecting resistor can be eliminated.

In FIG. 7, PWM ₃ is a pulse width control comparator, T ₆ is a transformer, D ₅ is a diode, C ₁₃ and C ₁₄ are capacitors, and R 12 to R 16 are resistors.

(Embodiment 7) In the switching power supply circuit of Embodiment 7, the secondary side circuit of FIG. 7 has the same configuration as that of FIG. That is, the power supply of the comparator CoH ₂ with hysteresis shown in FIG. 7 is controlled by the microcomputer 4 of the set shown in FIG. 2, and is turned on when the load is light standby and turned off during the heavy load normal operation.

In this case, since it is not necessary to form a circuit for detecting the load current on the secondary side in the power supply, the power supply can be downsized, and at the same time, the loss in the current detection resistor can be eliminated. .

[0064]

In recent years, environmental issues have been raised on a global scale. In recent years, there has been a growing international momentum to legislate regulations on not only the efficiency of operation of electrical equipment but also the power consumption during standby. Although the target value of the power consumption during standby is 0.1 VA, according to the present invention, the conventional power supply circuit suppresses power consumption until the device starts operating and the load power increases. It can be realized with a smaller number of parts. Further, at the time of a normal load, high efficiency operation which is an original merit of the switching power supply can be performed without impairing the conventional protection function. As described above, both the standby state of the light load and the normal load state, that is, the power consumption of the power supply circuit is reduced in total.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a switching power supply circuit according to a first embodiment.

FIG. 2 is a block diagram illustrating a secondary side of a switching power supply circuit according to a second embodiment.

FIG. 3 is a block diagram illustrating a switching power supply circuit according to a third embodiment.

FIG. 4 is a block diagram illustrating a soft start circuit provided on a primary side of a switching power supply circuit according to a fourth embodiment.

FIG. 5 is a timing chart showing an operation content of the soft start circuit shown in FIG.

FIG. 6 is a block diagram illustrating a main part of a switching power supply circuit according to a fourth embodiment.

FIG. 7 is a block diagram illustrating a main part of a switching power supply circuit according to a sixth embodiment.

FIG. 8 is a timing chart showing the operation of the switching power supply circuit according to Embodiment 6.

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

10 is a timing chart showing intermittent oscillation of the switching power supply circuit shown in FIG.

[Explanation of symbols]

CoH _{2 to} CoH ₄ Comparator with hysteresis PC _{2 to} PC ₄ Photocoupler Q ₂ , Q ₃ , Q ₄ , Q ₆ Switching element (MOSFE
T) C ₁₂ ~C ₁₈ capacitor R ₁₄ detecting resistor _{T 2, T 3, T 4} , T 5, T 6 trans nB auxiliary winding D _5, D ₆ diodes _{R 12, R 13, R 15} ~R 19 resistance V _S reference voltage C ₁₉ , C ₂₃ Soft start capacitor PWM ₁ , PWM ₃ Pulse width control comparator 1, 6 Drive circuit 2 Load current detection comparator 4, 5 sets microcomputer 7 Triangular wave oscillator 8 Feedback terminal

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Jun Kanamori 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Kenji Hachimura 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka In the company

Claims (7)

[Claims] A means for detecting a load on a secondary side to switch between a standby state and a normal power supply operation, and performs intermittent oscillation by controlling on / off of a switching element provided on the primary side during a standby state; A switching power supply circuit that stops intermittent oscillation during normal power supply operation and performs normal power supply operation. 2. An intermittent oscillation is performed by controlling on / off of a switching element provided on a primary side in a standby mode based on a signal for switching between a standby mode and a normal power mode operation from an external source. Switching power supply circuit that stops oscillation and performs normal power supply operation. 3. A switching element on a primary side, and a drive circuit for driving the switching element, wherein the drive circuit is supplied to the drive circuit during standby based on a signal input from outside to switch between standby and normal power supply operation. A switching power supply circuit that performs intermittent oscillation by controlling the power supply of the switching element and adjusts the switching operation of the switching element, and stops the intermittent oscillation during normal power supply operation to perform normal power supply operation. 4. A capacitor for performing a soft-start function, and a comparator for inputting a voltage signal of the capacitor and a voltage signal of a triangular wave, wherein the voltage of the capacitor and the triangular wave whose voltage increases when power is turned on are increased. The comparator compares the voltage of the switching element and the output pulse width of the comparator based on the difference between the two voltages, so that the on-time of the switching element becomes longer or the off-time becomes shorter, so that intermittent oscillation by soft start is performed. The switching power supply circuit according to claim 1. 5. A signal input from outside for switching between a standby mode and a normal power supply operation is supplied to the comparator, and the comparator is turned on to perform intermittent oscillation during a standby state. The switching power supply circuit according to claim 4, which performs the power supply operation of (1). 6. A comparator for inputting a feedback signal from a secondary side to a primary side and a triangular wave signal.
The comparator compares the feedback signal according to the voltage on the next side with the lowest voltage of the triangular wave signal, and controls the switching element provided on the primary side in a standby state when the former voltage is higher than the latter voltage. A switching power supply circuit that performs intermittent oscillation and stops the intermittent oscillation during normal power supply operation when the former voltage is lower than the latter voltage and performs normal power supply operation. 7. A signal input from outside for switching between a standby state and a normal power supply operation is supplied to the comparator, and the comparator is turned on to perform intermittent oscillation during the standby state. 7. The switching power supply circuit according to claim 6, wherein the power supply operation is performed.