JP3497075B2 - Switching power supply circuit - Google Patents

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 an electric device such as a microcomputer or a word processor, an electronic device or the like.

[0002]

2. Description of the Related Art As the switching power supply circuit described above,
There is known a device capable of reducing power consumption during standby by intermittently oscillating. FIG. 9 shows a general circuit configuration of a conventional example of the circuit system.

In this switching power supply circuit, a commercial power supply is applied to an input terminal 100, and the commercial power supply first passes through a resistor R ₁ which also serves as a rush current limiter and a fuse, and a noise filter L ₁ . The power supply for control that has passed through the noise filter L ₁ passes through the capacitor C ₂ and is rectified and smoothed by the diodes D ₂ and D ₃ and the capacitor C _3.
The diode Z ₁ limits the overvoltage. The drive circuit 101 composed of the timer IC oscillates at a certain frequency, and this drives the MOSFET (Q ₁ ) which is a switching element.

The main power source passing through the noise filter L ₁ is rectified by the diode D ₁ and then smoothed by the capacitor C ₄ . The secondary side of the transformer T ₁ is rectified by a Schottky barrier diode Z ₂ and smoothed by an 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 arranged to give a hysteresis characteristic by applying a slight positive feedback. The photodiode side of the photocoupler PC ₁ is connected to the output terminal of the comparator CoH ₁ . The transistor side of the photocoupler PC ₁ is connected to the reset terminal (RES) of the drive circuit 101. A three-terminal regulator 102 is provided immediately in front of the output terminal 103, and the three-terminal regulator 102 removes the ripple generated by the intermittent oscillation.

When the secondary side voltage V ₀₁ detected by the comparator CoH ₁ reaches a certain value VsH, the output of the comparator CoH ₁ becomes H, and the photocoupler PC ₁ connected to its output terminal is turned on. Then, the drive circuit 101 including the timer IC is turned off to stop the oscillation. When the oscillation stops, the voltage is not transmitted from the transformer T ₁ to the secondary side, and the voltage on the secondary side decreases. When the secondary side voltage V ₀₁ reaches a certain value VsL (<VsH), the output of the comparator CoH ₁ becomes L this time, the photocoupler PC ₁ is turned off, and the voltage of the reset terminal (RES) of the drive circuit 101 rises. Then the oscillation resumes. Then, the voltage on the secondary side rises again. The above operation is repeated to maintain the intermittent oscillation.

It should be noted that C ₁ , C ₅ , C ₆ , and
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) is the output of the comparator CoH ₁ , and (c) is a MOS
The operation of the FET is shown.

If power is supplied to the secondary side intermittently in this way, the power consumption on the primary side can be small, so that the 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, a loss occurs in the three-terminal regulator which is indispensable for obtaining a constant voltage, resulting in an efficiency loss. Is not good. In other words, the efficiency during normal operation is sacrificed in order to suppress the power consumption during standby, and it cannot be said that total power consumption can be reduced in all cases. In addition, the number of components for the power supply configuration, such as the reset timer IC and the three-terminal regulator, increases, leading to a problem that the power supply becomes large in size and high in cost.

The present invention has been made to solve the problems of the prior art, and an object of the present invention is to provide a switching power supply circuit which can reduce the total power consumption and the number of parts. To do.

[0011]

A switching power supply circuit according to the present invention includes a comparator with hysteresis, which detects a load on the secondary side and switches between standby and normal power supply operation .
A capacitor for performing the soft start function and the capacitor
Input the voltage signal of the capacitor and the voltage signal of the triangular wave.
A palletizer is provided, and in the standby state, the photocoupler performs on / off control of the switching element provided on the primary side based on the output of the comparator with hysteresis to perform intermittent oscillation, and in the normal power supply operation, the intermittent oscillation is stopped. To perform the normal power supply operation and increase the voltage when the power supply is started.
The voltage of the capacitor and the voltage of the triangular wave
Compare the output voltage of the comparator based on the voltage difference between the two.
The ON time of the switching element is
A longer or shorter off time may
Intermittent oscillation occurs in the tart, thereby achieving the above object.

The switching power supply circuit of the present invention includes a comparator with hysteresis that switches between standby and normal power supply operation based on a signal input from the outside, and a soft switch.
A capacitor for performing the start function and the capacitor
Comparator for inputting voltage signal and triangular wave voltage signal
In the standby state, the photocoupler performs on / off control of the switching element provided on the primary side based on the output of the comparator with hysteresis to perform intermittent oscillation, and during the normal power supply operation, the intermittent oscillation is stopped. The normal power supply operation, and the voltage rises when the power supply is started.
The comparator compares the voltage of the capacitor and the voltage of the triangular wave.
Of the output pulse width of the comparator based on the voltage difference between the two
The increase in the ON time of the switching element
Soft start
The above-mentioned object is achieved by intermittent oscillation .

A switching power supply circuit of the present invention includes a switching element on the primary side, a drive circuit for driving the switching element, and a comparator with hysteresis that switches between standby and normal power supply operation based on a signal input from the outside. And the soft start function
The voltage signal of the capacitor and the voltage signal of the triangular wave
And a comparator for inputting, and in the standby state, the photocoupler controls the power supply to the drive circuit based on the output of the comparator with hysteresis to adjust the switching operation of the switching element to perform intermittent oscillation. During the normal power supply operation, the intermittent oscillation is stopped and the normal power supply operation is performed, and the voltage rises when the power supply is started.
The rising voltage of the capacitor and the triangular wave voltage are compared with each other.
The comparator compares the output of the comparator based on the voltage difference between the two.
When the switching element is turned on by increasing the force pulse width
The longer the time, or the shorter the off time,
Intermittent oscillation occurs at the start, which achieves the above object.

[0014]

A signal input from the outside to switch between the standby time and the normal power supply operation is given to the comparator with hysteresis, the comparator with hysteresis is turned on during the standby to perform the intermittent oscillation, and during the normal power supply operation. the normal supply operation may be I row off the comparator with hysteresis.

The switching power supply circuit of the present invention has a secondary
Side load is detected and switched between standby and normal power supply operation
A hysteresis-equipped comparator and 1 from the secondary side
And a comparator for inputting the feedback signal and the triangular wave signal to the next side, the hysteresis when該待machine
Based on the output of the comparator with
The ON / OFF control of the switching element provided on the secondary side
Performs intermittent oscillation and stops the intermittent oscillation when the normal power supply is operating
Then, a normal power supply operation is performed, the comparator compares the feedback signal corresponding to the voltage on the secondary side with the lowest voltage of the triangular wave signal, and the first voltage is higher than the latter voltage during standby. the switching element provided in the following side by on-off control is performed the intermittent oscillation, the voltage of the front's normal supply operation is stopped the the intermittent oscillation in low the normal supply operation than the voltage of the rear's line have, the above-mentioned by the
The purpose is achieved .

The switching power supply circuit of the present invention is external
Based on the signal input from
A comparator with hysteresis to switch to and whether it is the secondary side
Input the feedback signal to the primary side and the triangular wave signal.
And a comparator for operating the
Based on the output of the comparator with cis
ON / OFF control of the switching element provided on the primary side
Intermittently oscillates during normal power supply operation.
Stop and perform normal power supply operation, depending on the voltage of the secondary side
The feedback signal and the minimum voltage of the triangular wave signal
The comparator compares and the former voltage is higher than the latter voltage.
The switching element provided on the primary side during high standby
ON / OFF control to perform the intermittent oscillation, and the former voltage
Is lower than the latter voltage, the intermittent voltage is applied during normal power supply operation.
Oscillation is stopped and normal power supply operation is performed.
The above object is achieved. Switching power supply circuit of the present invention
Is a switching element on the primary side and the switching element
Based on the drive circuit that drives the
Hysteresis that switches between standby and normal power operation
Comparator with cis and fee from secondary side to primary side
Comparator that inputs the feedback signal and triangular wave signal
And a comparator with hysteresis during the standby
The photocoupler to the drive circuit based on the output of
Switching of the switching element by controlling the power supply
Intermittent oscillation is performed by adjusting the operation to operate the normal power supply.
At times, the intermittent oscillation is stopped and normal power supply operation is performed.
The feedback signal and the triangular wave according to the voltage on the secondary side
The comparator compares the minimum voltage of the signal with the voltage of the former.
When the pressure is higher than the latter voltage, it is provided on the primary side during standby.
The switching element is turned on / off to control the intermittent oscillation.
The voltage of the former is lower than the voltage of the latter.
When the power supply is operating, the intermittent oscillation is stopped and normal power supply operation is performed.
Therefore, the above-mentioned object is achieved. An externally input signal for switching between the standby time and the normal power supply operation is given to the comparator with hysteresis, the comparator with hysteresis is turned on to perform the intermittent oscillation during the standby, and the hysteresis is included during the normal power supply operation. turns off the comparator I line the normal supply operation
Good .

The operation of the present invention will be described below.

First, the basic operation of the switching power supply circuit of the present invention will be described. When the voltage on the secondary side exceeds a certain value, the on / off operation on the primary side is stopped by 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. The power supply operates intermittently by starting the on / off operation when
Reduces power consumption during standby. When the power supply operation is not in the standby mode, the element for detecting the voltage on the secondary side is turned off to perform the normal power supply operation and prevent the efficiency from decreasing. Further, whether or not the standby state is set 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.

A switching power supply circuit according to a first embodiment described later will be described with reference to FIG. When the load is small,
When the secondary side voltage V ₀ exceeds a certain value VsH, the output of the comparator CoH ₂ with hysteresis becomes H (= high level), and the photocoupler PC ₂ turns on the primary side main switching element (MOSFET) Q ₂ . The output of the drive circuit 1 to be driven is turned off. Then, the power supply to the secondary side is lost, and the capacitor C ₁₄ that smoothes the output voltage is used.
The voltage decreases with the discharge of.

If the output of the comparator CoH ₂ with hysteresis is set to L when the secondary side voltage V ₀ becomes lower than a certain value VsL, the photocoupler PC ₂ outputs the output of the drive circuit 1 at this time. Is turned on, so MO
The on / off operation of the SFET (Q ₂ ) restarts, 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, the voltage drop of the detection resistor R ₁₄ is put into the load current detection comparator 2, and when the voltage drop is larger than a certain reference voltage, the power supply of the comparator CoH ₂ with hysteresis is turned on. It is turned off to stop the intermittent operation.

In the switching power supply circuit according to the second embodiment described later , as shown in FIG. 2, the power supply of the comparator CoH ₃ with hysteresis is controlled by the set microcomputer 4.
It is turned on during standby when the load is light, and turned off during normal operation when the load is heavy. In this way, there is no possibility of intermittent oscillation during normal power supply operation or failure of the protection function. Further, 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,
At the same time, it is possible to eliminate the loss in the resistance for current detection.

A switching power supply circuit according to a third embodiment described later will be described with reference to FIG.

When a standby signal is input from the set microcomputer 5, the hysteresis-equipped comparator CoH ₄ for detecting the secondary side voltage V ₀ operates. When the voltage on the secondary side is higher than a certain value, the output of the comparator CoH ₄ becomes H and the photocoupler PC ₄ is turned on. Then M on the primary side
The output of the circuit that drives the OSFET (Q ₃ ) is cut off, the switching operation is stopped, and the power supply to the secondary side is lost. And a capacitor C for smoothing the output voltage
_The voltage drops with the discharge of ₁₈ . When the voltage on the secondary side becomes lower than a certain value, the output of the comparator CoH ₄ becomes L (=
It becomes a low level) and the circuit for driving the primary side MOSFET (Q ₃ ) by turning off the photocoupler PC ₄ is output, and the switching operation is started.

Then, the voltage on the secondary side rises. By repeating this series of operations, intermittent oscillation is maintained. 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 is started. 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 resistance for current detection can be eliminated.

A soft start circuit according to a fourth embodiment described later will be described with reference to FIG.

When the 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. Pulse width control comparator PWM ₁ is the voltage of the capacitor C ₁₉ to gradually increase, 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. Since the voltage of the capacitor C ₁₉ becomes the lowest when the power supply is started, the output of the pulse width control comparator PWM ₁ widens the pulse width as the voltage of the capacitor rises.
As a result, the ON time of the MOSFET (Q ₄ ) increases and 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 soft start increases, the switching operation of the MOSFET (Q ₄ ) starts, and when the voltage of the capacitor decreases, the switching operation of the MOSFET (Q ₄ ) stops.

FIG. 6 shows a switching power supply circuit including the soft start circuit shown in FIG. This Figure 6
At the time, when the primary side MOSFET (Q ₄ ) starts to turn on and off, power is supplied from the transformer T _5.
The voltage on the secondary side rises. Then, when this voltage exceeds a certain value, the output of the comparator CoH ₂ with hysteresis becomes H, and the photocoupler PC ₂ is turned on to drop the voltage of the capacitor C ₁₃ . Then, the switching operation of the MOSFET (Q ₄ ) is stopped. Primary side MOSFET (Q
_When the on / off of ₄ ) is stopped, the power supply from the transformer T ₅ is lost, so a capacitor C ₁₄ for smoothing the output voltage is used.
The secondary side voltage decreases with the discharge of.

When this voltage becomes lower than a certain value, the output of the comparator CoH ₂ with hysteresis 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 Restarts on and off. In this way, the intermittent operation is maintained.

A switching power source according to a fifth embodiment described later.
In the source circuit, the power supply of the comparator shown in FIG. 6 is controlled by the set microcomputer, that is, the circuit on the secondary side of 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 provide 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.

A switching power source according to a sixth embodiment described later.
In source circuit, as shown in FIG. 7, exemplary forms described below
The voltage of the feedback terminal 8 is controlled instead of the voltage of the capacitor according to the state 4 . The function of the feedback terminal 8 is to change the duty of the switching element (MOSFET) Q ₆ on the primary side according to the fluctuation of the voltage on the secondary side to make the voltage on the secondary side constant as in FIG. Is. When the voltage of the capacitor C ₂₃ for soft start is constant, the switching operation of the MOSFET (Q ₆ ) starts if the feedback voltage from the secondary side is high, and if this 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 exceeds a certain value, the comparator CoH ₂ with hysteresis is turned on and the photocoupler PC ₂ is turned on. This reduces the feedback voltage to reduce the MOSFET (Q ₆ )
When the secondary side voltage drops to a certain value, the comparator CoH ₂ is turned off and the photocoupler PC ₂ is turned off. As a result, the feedback voltage is raised to start the switching operation of the MOSFET (Q ₆ ) and the intermittent oscillation is continued.

A switching power source according to a seventh embodiment described later.
In the power source circuit , the circuit on the secondary side of FIG. 7 has the same configuration as that of FIG. 2, that is, the power source of the comparator CoH _{2 according to} the sixth embodiment described later is controlled by the set microcomputer, and the load is light. It is turned on during standby and turned off during normal operation with a 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 downsized, and at the same time, the loss in the resistance for current detection can be eliminated.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below.

(First Embodiment) FIG. 1 is a block diagram showing a switching power supply circuit according to the first embodiment. In addition,
A on the left side of FIG. 1 has the same configuration as A of FIG.
The description is omitted.

In this switching power supply circuit, when the secondary side voltage V ₀ exceeds a certain value VsH when the load is small, the output of the hysteresis-equipped comparator CoH ₂ becomes H.
Then, the photocoupler PC ₂ turns off the output of the drive circuit 1 for driving the main switching element (MOSFET) Q ₂ on the primary side. Then, the power supply to the secondary side is lost, and the voltage drops as the capacitor C ₁₄ that smoothes the output voltage discharges. Secondary voltage V ₀ is a certain value V
If the output of the comparator CoH ₂ is set to L when it becomes sL or less, the photocoupler P at this point
Since C ₂ turns on the output of drive circuit 1, MOSF
The on / off operation of ET (Q ₂ ) restarts, and the voltage on the secondary side rises.

By repeating this, the intermittent oscillation is maintained as in the case of FIG. If the load current on the secondary side increases,
The voltage drop of the detection resistor R ₁₄ is put into the load current detection comparator 2, and when the voltage drop is larger than a certain reference voltage, the power supply of the comparator CoH ₂ is turned off.
Stop the intermittent operation.

Therefore, in the case of this embodiment,
It is possible to reduce the power consumption until the load power increases after starting the operation with a smaller number of components than the conventional power supply circuit. Furthermore, under normal load, high efficiency operation, which is an original advantage of the switching power supply, is possible without impairing the conventional protection function. As described above, the power consumption of the power supply circuit can be reduced both when the light load is on standby and when the load is normal, that is, 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, and R ₁₂ , R ₁₃ , R ₁₅ and R are shown.
₁₆ is a resistance and V _S is a reference voltage.

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

As shown in FIG. 2, this switching power supply circuit controls the power supply of the comparator CoH ₃ with hysteresis by the set microcomputer 4 to turn it on when the load is in a standby state and turn it off when the load is in a normal operation. In this way, there is no possibility of intermittent oscillation during normal power supply operation or failure of the protection function. Further, 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 resistance for current detection can be eliminated.

In FIG. 2, T ₃ is a transformer, and D ₆
Is a diode, C ₁₅ is a capacitor, and R ₁₇ and R
₁₈ is a resistance. Also, PC ₃ is a photo coupler,
A photo coupler (not shown) on the light receiving side is provided on the primary side.

(Third Embodiment) FIG. 3 is a block diagram showing a switching power supply circuit according to a third embodiment. In addition,
A on the left side of FIG. 3 has the same configuration as A of FIG. 9,
The description is omitted.

In this switching power supply circuit, the comparator CoH ₄ with hysteresis which detects the voltage V ₀ on the secondary side operates when a standby signal is input from the microcomputer 5 of the set. When the voltage on the secondary side is higher than a certain value, the output of the comparator CoH ₄ becomes H and the photocoupler PC ₄ is turned on. Then, the output of the circuit for driving the MOSFET (Q ₃ ) on the primary side is cut off, the switching operation is stopped, and the power supply to the secondary side is lost. Then, the voltage decreases as the capacitor C ₁₈ that smoothes the output voltage discharges. When the voltage on the secondary side becomes a certain value or less, the output of the comparator CoH ₄ becomes L, the photocoupler PC ₄ is turned off, the circuit for driving the MOSFET (Q ₃ ) on the primary side outputs, and the switching operation starts. To do.

Then, the voltage on the secondary side rises. By repeating this series of operations, intermittent oscillation is maintained. 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 is started.

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 source, the power source can be downsized, and at the same time, the loss in the resistance for current detection can be eliminated. be able to.

In FIG. 3, 6 is a drive circuit, T ₄ is a transformer, D ₇ and D ₈ are diodes, C ₁₆ and C ₁₇ are capacitors, and R ₁₉ and R ₂₀ are resistors.

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

On the primary side of this switching power supply circuit,
The soft start circuit shown in FIG. 4 is provided. When the power supply is turned on, this soft start circuit is supplied with power to VCC through the starting resistor, and by the charging current supplied from the internal constant current source to the soft start capacitor C ₁₉ ,
The voltage of the soft start capacitor C ₁₉ rises. The pulse width control comparator PWM ₁ operates when the voltage of the triangular wave oscillator 7 is lower than the lowest voltage of the voltage of the capacitor C ₁₉ which rises gently, the dead time control voltage (DET) and the feedback voltage from the secondary side. Output to. When the power supply is started, the voltage of the capacitor C ₁₉ becomes the lowest, so the pulse width control comparator PWM
The output of ₁ widens the pulse width as the voltage of the capacitor rises. As a result, the ON time of the MOSFET (Q ₄ ) increases and soft start is applied, and the output gradually increases. The soft start is MOSFET
The OFF time of (Q ₄ ) may be reduced.

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

In FIG. 6, the primary side MOSFET
When (Q ₄ ) starts turning on / off, the voltage on the secondary side rises because power is supplied from the transformer T ₅ . And
When this voltage exceeds a certain value, the output of the comparator CoH ₂ with hysteresis becomes H, and the photocoupler PC ₂ is turned on to drop the voltage of the capacitor C ₁₉ . Then MO
The switching operation of SFET (Q ₄ ) stops. When the on / off of the primary side MOSFET (Q ₄ ) is stopped, the power supply from the transformer T ₅ is stopped, so that the voltage on the secondary side decreases with the discharge of the capacitor C ₁₄ that smoothes the output voltage. Then, when this voltage becomes a certain value or less, the output of the comparator CoH ₂ becomes L, the photocoupler PC ₂ is turned off, and the voltage of the capacitor C ₁₉ rises. Therefore, the primary side switching element Q ₄ is turned on / off. Resume. In this way, the intermittent operation is maintained.

In FIG. 6, D ₅ is a diode, C ₁₃ is a capacitor, and R _{12 to} R ₁₆ are resistors.

(Fifth Embodiment) In the fifth embodiment, the secondary side of the switching power supply circuit shown in FIG. 6 is configured as shown in FIG.

This switching power supply circuit controls the power supply of the comparator CoH ₂ shown in FIG. 6 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 provide 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.

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

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. The function of the feedback terminal 8 is to change the duty of the switching element (MOSFET) Q ₆ on the primary side according to the fluctuation of the voltage on the secondary side to make the voltage on the secondary side constant as in FIG. Is. When the voltage of the capacitor C ₂₃ for soft start is constant, the switching operation of the MOSFET (Q ₆ ) starts if the feedback voltage from the secondary side is high, and if this 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 exceeds a certain value, the comparator CoH ₂ with hysteresis is turned on and the photocoupler PC ₂ is turned on. This reduces the feedback voltage to reduce the MOSFET (Q ₆ )
When the secondary side voltage drops to a certain value, the comparator CoH ₂ is turned off and the photocoupler PC ₂ is turned off. As a result, the feedback voltage is raised to start the switching operation of the MOSFET (Q ₆ ) and the intermittent oscillation is continued.

Also in this embodiment, the power supply can be downsized, and at the same time, the loss in the resistance for current detection 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 circuit on the secondary side of FIG. 7 has the same configuration as that of FIG. That is, the power supply of the hysteresis-equipped comparator CoH ₂ 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 in a standby state and turned off when the load is in a 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 resistance for current detection can be eliminated. .

[0064]

[Effects of the Invention] In recent years, when environmental problems are exclaimed on a global scale, there is an increasing international impetus to legalize not only the operating efficiency of electric devices but also the power consumption during standby. However, the target value of the power consumption during standby is 0.1 VA. However, according to the present invention, it is necessary to suppress the power consumption until the device starts operating and the load power increases. It can be realized with fewer parts. Furthermore, under normal load, high efficiency operation, which is an original advantage of the switching power supply, is possible without impairing the conventional protection function. As described above, the power consumption of the power supply circuit can be reduced both when the light load is on standby and when the load is normal, that is, in total.

[Brief description of drawings]

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

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

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

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

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

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

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

FIG. 8 is a timing chart showing the operation content of the switching power supply circuit according to the sixth embodiment.

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 of microcomputer 7 Triangle wave oscillator 8 Feedback terminal

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Atsushi Kanamori 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Prefecture 22-22 Sharp Corporation (72) Kenji Yamura 22-22 Nagaike-cho, Abeno-ku, Osaka City, Osaka Sharp shares In-house (56) Reference JP-A-4-42771 (JP, A) JP-A-4-12666 (JP, A) JP-A-4-29482 (JP, A) JP-A-7-163143 (JP, A) ) Japanese Patent Laid-Open No. 9-9616 (JP, A) Actual Development 4-10588 (JP, U) Actual Development 6-52391 (JP, U) (58) Fields investigated (Int.Cl. ⁷ , DB name) H02M 3/28 G06F 1/00

Claims (8)

(57) [Claims] 1. A comparator with hysteresis that detects a load on the secondary side and switches between standby and normal power supply operation.
And a capacitor for performing a soft start function,
Input capacitor voltage signal and triangular wave voltage signal
And a comparator, in which the photocoupler performs on / off control of the switching element provided on the primary side based on the output of the comparator with hysteresis to perform intermittent oscillation, and stops the intermittent oscillation during normal power supply operation. to have line normal supply operation, photoelectric of the capacitor increases the voltage when performing the power activation
The comparator compares the voltage and the voltage of the triangular wave,
By increasing the output pulse width of the comparator based on the difference
ON time of the switching element becomes longer or
Shorter run time causes intermittent oscillation with soft start
Switching power supply circuit that. 2. A comparator with hysteresis that switches between standby and normal power supply operation based on a signal input from the outside, and a capacitor for performing a soft start function.
And the voltage signal of the capacitor and the triangular wave voltage signal.
And a comparator for inputting power, and a photocoupler performs on / off control of a switching element provided on the primary side based on an output of the comparator with hysteresis to perform intermittent oscillation, and during the normal power supply operation, the intermittent oscillation is performed. gastric line normal supply operation is stopped, electricity of the capacitor to voltage rise when performing power activation
The comparator compares the voltage and the voltage of the triangular wave,
By increasing the output pulse width of the comparator based on the difference
ON time of the switching element becomes longer or
Shorter run time causes intermittent oscillation with soft start
Switching power supply circuit that. 3. A switching element on the primary side, a drive circuit for driving the switching element, a comparator with hysteresis that switches between standby and normal power supply operation based on a signal input from the outside, and a soft start machine.
And a voltage signal of the capacitor
And a comparator for inputting a triangular wave voltage signal, and in the standby state, the photocoupler controls the power supply to the drive circuit based on the output of the comparator with hysteresis to adjust the switching operation of the switching element. in performs intermittent oscillation, the usually have line normal supply operation is stopped the the intermittent oscillation at power operation, electric of said capacitor to a voltage increase when performing the power activation
The comparator compares the voltage and the voltage of the triangular wave,
By increasing the output pulse width of the comparator based on the difference
ON time of the switching element becomes longer or
Shorter run time causes intermittent oscillation with soft start
Switching power supply circuit that. 4. An externally input signal for switching between the standby time and the normal power supply operation is given to the comparator with hysteresis, and during the standby, the comparator with hysteresis is turned on to perform the intermittent oscillation and the normal power supply. The switching power supply circuit according to any one of claims 1 to 3, wherein the comparator with hysteresis is turned off during operation to perform normal power supply operation. 5. A comparator with hysteresis that detects the load on the secondary side and switches between standby and normal power supply operation.
And a feedback signal from the secondary side to the primary side and
And a comparator for inputting a triangular wave signal, performs intermittent oscillation photocoupler based on the output of the hysteresis comparator is turned on and off control of the switching element provided on the primary side at the time該待machine, the normal supply operation Sometimes the intermittent oscillation is stopped and normal power supply operation is performed.
The feedback signal and the triangle depending on the voltage of the secondary side.
The comparator compares the lowest voltage of the wave signal with the
Provided on the primary side during standby when the voltage is higher than the latter voltage
ON / OFF control of the switching element to perform the intermittent oscillation
And the voltage of the former is lower than the voltage of the latter.
During power supply operation, the intermittent oscillation is stopped and normal power supply operation is resumed.
Do switching power supply circuit. 6. A comparator with hysteresis that switches between standby and normal power supply operation based on a signal input from the outside, and a feedback signal from the secondary side to the primary side.
And a comparator for inputting a preliminary triangular wave signal, performs intermittent oscillation photocoupler based on the output of the hysteresis comparator is turned on and off control of the switching element provided on the primary side at the time該待machine, the During normal power supply operation, the intermittent oscillation is stopped and normal power supply operation is performed.
The feedback signal and the triangle depending on the voltage of the secondary side.
The comparator compares the lowest voltage of the wave signal with the
Provided on the primary side during standby when the voltage is higher than the latter voltage
ON / OFF control of the switching element to perform the intermittent oscillation
And the voltage of the former is lower than the voltage of the latter.
During power supply operation, the intermittent oscillation is stopped and normal power supply operation is resumed.
Do switching power supply circuit. 7. A switching element on the primary side, a drive circuit for driving the switching element, a comparator with hysteresis that switches between standby and normal power supply operation based on a signal input from the outside, and from the secondary side Primary side
Input the feedback signal and triangle wave signal to the
In the standby state, the photocoupler controls the power supply to the drive circuit based on the output of the comparator with hysteresis to adjust the switching operation of the switching element to perform intermittent oscillation, and the normal power supply. There line normal supply operation is stopped the the intermittent oscillation in operation, the feedback signal and the triangle corresponding to the voltage of the secondary side
The comparator compares the lowest voltage of the wave signal with the
Provided on the primary side during standby when the voltage is higher than the latter voltage
ON / OFF control of the switching element to perform the intermittent oscillation
And the voltage of the former is lower than the voltage of the latter.
During power supply operation, the intermittent oscillation is stopped and normal power supply operation is resumed.
Do switching power supply circuit. 8. An externally input signal for switching between the standby time and the normal power supply operation is given to the comparator with hysteresis, and during the standby, the comparator with hysteresis is turned on to perform the intermittent oscillation and the normal power supply. 8. The operation according to claim 5, wherein the comparator with hysteresis is turned off to perform normal power supply operation during operation.
Switching power supply circuit according to either.