JPH0767335A - Switching power supply device - Google Patents

Abstract

PURPOSE:To reduce the switching loss of a switching power supply device, by holding a second switching element in OFF-state during a predetermined period while driving a first switching element during the period determined through a time constant circuit. CONSTITUTION:When a transistor(Tr) Q2 is turned on, a switching element (SW) Q1 is turned off. At this time, positive voltages are generated respectively in output windings N2, N3 of an output transformer T whose winding polarities are opposite respectively to a primary winding Np of the output transformer T, and then, transistors TrQ4, Q3 are turned on, and thereby, a capacitor C6 is charged. By the charged voltage of the capacitor C6, transistors TrQ5, Q6 are turned on, and then, the transistors TrQ1, Q4 are turned off. Further, this state is held during a fixed period until the charge of the capacitor C6 is discharged to some extent according to the time constant deiterminated by the capacitor C6 and resistors R13-R15. By the adjustment of the time constant, the OFF-time of the switching element SWQ1 can be longer than a given time. Therefore, the switching frequency of the switching element SW Q1 cannot exceed, a given frequency.

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 device using a ringing choke converter (RCC) system.

[0002]

2. Description of the Related Art FIG. 11 shows a conventional FET type ringing.
It is a concrete circuit diagram of a switching power supply device of a choke converter (RCC) system. As a conventional example of this type, for example, Japanese Patent Publication No. 4-9034 can be cited. An AC power supply AC is connected to an input end of a diode bridge DB ₁ for rectification via a fuse F and a line filter LPF.
_A smoothing capacitor C ₁ is connected to the output terminal of ₁ .

The inverter circuit includes output transformers T and FE.
Switching element Q _{1 made of} T, start-up resistors R ₁ , R
It is composed of ₂ mag. A smoothing circuit including a rectifying diode D ₁ , a constant voltage zener diode ZD ₁ , and capacitors C ₃ and C ₄ is connected to both ends of the output winding N ₂ of the output transformer T.

Further, the inverter circuit is provided with a voltage detection circuit and a control circuit as a stable control of the output voltage and an overcurrent protection circuit. The voltage detection circuit provided on the output side of the inverter circuit has a resistor R that divides and detects the output voltage.
₇ , R ₈ , a light emitting diode PD on the light emitting side of the photocoupler PC ₁ , a shunt regulator IC _{1 and the} like. The control circuit provided on the feedback winding N _B side of the output transformer T of the inverter circuit includes a phototransistor P which forms a pair with the light emitting diode PD of the photocoupler PC _1.
T, resistor R ₃ to R _5, the diode D _2, D _7, the Zener diode ZD _2, is composed of a transistor Q ₂ and the like which are connected in parallel between the gate and source of the switching element Q _1.

Next, the operation of the circuit shown in FIG. 11 will be described. First, at the time of start-up when the power is turned on, a voltage is applied to the gate of the switching element Q ₁ via the resistors R ₁ and R ₂ , and the switching element Q ₁ is turned on. When the switching element Q ₁ is turned on, a power supply voltage is applied to the primary winding N _P of the output transformer T, and a voltage is generated in the feedback winding N _B in the same direction as the primary winding N _P. The generated voltage charges the capacitor C ₂ through the series circuit of the resistor R _{3, the} diode D ₇ , the resistor R ₅ , and the zener diode ZD ₂ .

[0006] Capacitor C ₂ is gradually charged, exceeds the forward voltage between the base and emitter of the transistor Q _2, the transistor Q ₂ is turned on. When the transistor Q ₂ turns on, the collector potential of the transistor Q ₂ becomes L level, the gate of the switching element Q ₁ becomes L level, and the switching element Q ₁ is turned off.

When the switching element Q ₁ is turned off, the energy stored in the output transformer T when the switching element Q ₁ is turned on is released through the output winding N ₂ . The voltage, which is this energy, is rectified by the diode D ₁ and smoothed by the capacitors C ₃ and C ₄ , and power is supplied to the load.

When the electric charge of the capacitor C ₂ is discharged through the resistor R ₃ , the transistor Q ₂ turns off and the switching element Q ₁ turns on. When the switching element Q ₁ is turned on, a voltage is applied to the primary winding N _P of the output transformer T again, and energy is stored in the output transformer T.
By repeating such an operation, the inverter circuit is activated and shifts to a steady state.

Here, the output voltage on the load side is always divided by the resistors R ₇ and R ₈ to be detected, and the divided detection voltage is compared with the reference voltage of the shunt regulator IC _1. There is. Then, the variation of the output voltage is amplified by the shunt regulator IC ₁ and the current flowing through the light emitting diode PD of the photocoupler PC ₁ is changed, so that the phototransistor PT of the photocoupler PC ₁ of the photocoupler PC ₁ is changed according to the light emission amount of the light emitting diode PD. By changing the impedance and changing the charging time constant of the capacitor C ₂ , control is performed so that the output voltage becomes constant.

When the output voltage rises, a large amount of current flows through the light emitting diode PD of the photocoupler PC ₁ ,
The charging time constant of the capacitor C ₂ is shortened via the phototransistor PT, the transistor Q ₂ is turned on quickly, the switching element Q ₁ is turned off, and the on period of the switching element Q ₁ is shortened to reduce the output voltage. Control to lower. When the output voltage decreases, the reverse operation described above is performed to control the output voltage to increase, and the constant voltage control is performed to keep the output voltage constant.

Further, when the load current becomes large, the output voltage decreases, and the light emitting diode P of the photocoupler PC ₁
The current flowing through D becomes small, and the charging time constant of the capacitor C ₂ becomes a maximum in parallel with the resistor R ₃ , the diode D ₇ , the resistor R ₅ , and the zener diode ZD ₂ series circuit, and the load current is further exceeded. Very switching element Q
The ON period width of ₁ does not increase, which is a so-called foldback characteristic. That is, overcurrent control is performed.

[0012]

Here, in the ringing choke converter circuit as shown in FIG. 11, the oscillation frequency f is generally expressed by the following equation. f = (D ² V ₁ ) / (2L ₁ P ₁ ) where D is the duty, P ₁ is the input power, L ₁ is the inductance value of the primary winding N _P , and V ₁ is the input voltage. From the above equation, when the input power P ₁ decreases, the oscillation frequency f increases (the fluctuation of f is large).

Further, when the input power P ₁ is small, the switching loss of the switching element Q ₁ becomes large and the efficiency becomes poor, and the loss of the switching element Q ₁ at this time is almost the switching loss (the switching element Q 1). _The loss due to the on-resistance R _DS of ₁ is small). Most of the loss when the input power P ₁ is small, that is, when the output power is small, is switching loss. Therefore, in order to attenuate the loss, a method of reducing the switching loss of the switching element Q ₁ itself. And a method of reducing the number of times of switching of the switching element Q ₁ .

Incidentally, FIG. 12 is a concrete circuit diagram of another conventional switching power supply device, which is substantially the same as the case of FIG. 11, but only the different circuit configuration will be explained. First, the secondary side of the output transformer T is a diode D for rectification.
The configuration of the smoothing circuit connected via ₁ is the capacitor C
₃ , C ₄ and choke coil L ₁ . The time constant circuit connected to the feedback winding N _B side of the output transformer T and charging the capacitor C ₂ is slightly different.
That is, the resistor R ₃ is connected in parallel to the series circuit of the resistor R ₅ and the Zener diode ZD ₂ .

The operation of the circuit shown in FIG. 12 is as shown in FIG.
Since it is basically the same as the circuit of No. 1, its explanation is omitted.

The present invention has been provided in view of the above points, and a switching power supply device for reducing the loss and increasing the efficiency by preventing the oscillation frequency of the switching element from increasing above a certain frequency. Is provided.

[0017]

The present invention provides an output transformer T having a primary winding N _P , an output winding N ₂ and a feedback winding N _B, and a primary winding N _P of the output transformer T. A switching element Q ₁ for oscillation whose one end is connected and a control terminal is connected to the feedback winding N _B , and an output winding N ₂ of the output transformer T.
In a switching power supply device of a ringing choke converter system including a rectifier circuit connected to, a control means for suppressing the switching frequency of the switching element Q _{1 from} exceeding a certain frequency is provided.
An output winding N provided on the output transformer T by the control means.
_{The second} output winding N ₃ wound in the same polarity as ₂ and this _second winding
A first switch element Q _{4 which} is turned on by a voltage generated in the output winding N ₃ of the second switch element, and a second switch element Q ₃ which is turned on by the ON operation of the first switch element Q ₄ .
A time constant circuit comprising a capacitor C ₆ and a resistor R _{1 3} to R _{1 5} which is charged by the on operation the second switching element Q _3, a predetermined time the first switching element Q ₄ by the time constant circuit Third switch element Q ₅ to be turned off
And a fourth switch element Q ₆ which maintains the switching element Q ₁ in the off state for a predetermined time by setting the control terminal of the switching element Q ₁ to the L level by the time constant circuit.

A second aspect of the present invention is characterized in that, in the circuit configuration of the _{first aspect} , a capacitor C ₇ is connected between the control terminal of the switching element Q ₁ and the ground.

Further, in claim 3, an output transformer T having a primary winding N _P , an output winding N ₂ and a feedback winding N _B , and one end of which is connected to the primary winding of the output transformer T. In a switching power supply device of a ringing choke converter system, which includes an oscillating switching element Q ₁ having a control terminal connected to a feedback winding N _B and a rectifying circuit connected to an output winding N ₂ of an output transformer T. A control means for suppressing the switching frequency of the switching element Q _{1 from} exceeding a certain frequency, the control means being wound in the same polarity as the output winding N ₂ provided in the output transformer T; Second output winding N ₃ , a first switching element Q _{4 which} is turned on by the voltage generated from the feedback winding N _B of the output transformer T when the switching element Q ₁ is turned on, and the first switch The second switch element Q ₃ which is turned on by the ON operation of the element Q ₄ and the first and second switch elements Q ₄ , which are generated by the reverse voltage generated in the feedback winding N _B when the switching element Q ₁ is turned off, Q ₃
During the time lag until the switch turns off, the capacitor C ₆ and the resistor R _{1 3} charged via the second switch element Q ₃ by the voltage generated in the second output winding N ₃ are charged.
A time constant circuit consisting to R _{1 5,} the switching element Q ₁ maintains the predetermined time on operation by the time constant circuit
The control terminal is set to the L level, and the third switching element Q ₆ keeps the switching element Q ₁ in the off state for a predetermined time.

Further, in the circuit configuration of the third aspect according to claim 4, it is characterized by connecting a capacitor C ₇ between the control terminal and ground of the switching element Q _1.

[0021]

According to the present invention, the fourth switching device Q ₆ is driven for a predetermined time by the time in the time constant circuit to keep the switching device Q ₁ in the off state for a predetermined time,
The switching frequency of the switching element Q ₁ is set not to exceed a certain frequency. Therefore, it is possible to reduce the switching loss when the output power is small, and therefore it is possible to improve the efficiency when the load is light.

According to claim 2, a capacitor C ₇ is provided between the control terminal of the switching element Q ₁ and the ground.
Since the switching element Q ₁ is turned on after a predetermined time elapses by the time constant circuit, the capacitor C ₇ delays the rise of the voltage to the control terminal of the switching element Q _{1 and} the switching element Q ₁ is connected. The off time of Q ₁ can be made longer. Therefore, the switching frequency of the switching element Q ₁ under a light load can be further reduced, and the efficiency can be further improved under a light load.

According to claim 3, the time in the time constant circuit that to maintain the switching element Q ₁ by driving the third switching element Q ₆ predetermined time in a predetermined time off, of the switching element Q ₁ The switching frequency does not exceed a certain frequency. Therefore, it is possible to reduce the switching loss when the output power is small, and therefore it is possible to improve the efficiency when the load is light.

According to claim 4, a capacitor C ₇ is provided between the control terminal of the switching element Q ₁ and the ground.
Since the switching element Q ₁ is turned on after a predetermined time elapses by the time constant circuit, the capacitor C ₇ delays the rise of the voltage to the control terminal of the switching element Q _{1 and} the switching element Q ₁ is connected. The off time of Q ₁ can be made longer. Therefore, the switching frequency of the switching element Q ₁ under a light load can be further reduced, and the efficiency can be further improved under a light load.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a specific circuit diagram of the switching power supply device of the present invention. The same elements as those in the related art shown in FIG. 11 are designated by the same reference numerals, and the description thereof will be omitted. The gist of the present invention will be described in detail.

As shown in FIG. 1, the output transformer T has a second
The output windings N ₃ provided in both ends of the diode D ₃ of the output winding N _3, resistor R ₉ to R _{1 1} of connecting a series circuit, a diode D ₄ from one end of the second output winding N ₃ Is connected to the emitter of the transistor Q ₃ via. Moreover, the base of the transistor Q ₃ are via a resistor R _{1 2} is connected to the collector of the transistor Q _4, the base of the transistor Q ₄ are are connected to the connection point of the resistors R _{1 0} and R _{1 1.}

A capacitor C ₆ is connected between the collector of the transistor Q _{3 and} the emitter of the transistor Q ₄ , and a resistor R _{1 3} , a diode D ₅ , resistors R _{1 4} and R ₄ are connected in parallel with the capacitor C _6. connected _{1 5} of the series circuits, respectively. The resistance R _{1 4} and R _{1 5} the connection point and the transistors Q _5, Q ₆ of the base and the respectively connected. The collector of one transistor Q ₅ is connected to the connection point of the resistors R ₉ and R _{1 0.} The collector of the other transistor Q ₆ is connected to the gate of the switching element Q ₁ via the diode D ₆ .

Next, the operation will be described. In the steady state, a voltage is applied to the gate of the switching element Q ₁ via the resistors R ₁ and R ₂ , and the switching element Q ₁ is turned on. When the switching element Q ₁ is turned on, a current flows through the output transformer T and the feedback winding N _B has the primary winding N 1.
Voltage is applied in the same direction as _P. And photo coupler PC
_Due to the current flowing through ₁ , electric charge is accumulated in the capacitor C ₂ , and the transistor Q ₂ is turned on.

[0029] When the transistor Q ₂ is turned on, lowers the voltage of the gate of the switching element Q _1, the switching element Q ₁ is turned off. At this time, the output transformer T 1
A positive voltage is generated in the output winding N ₂ and the output winding N ₃ which are wound in the opposite polarity with respect to the next winding N _P.

In the output winding N ₂ of the output transformer T, ideally, ΔT = (I _2P V) / L ₂ (I _2P is the secondary side current, V is the output voltage, ΔT is the switching element Q ₁ The energy stored in the output transformer T is discharged at ΔT indicated by (OFF period of), and the switching element Q ₁ is turned on immediately after that (at the time of light load, this Δ
The oscillation frequency increases because T is short).

However, here, when the switching element Q ₁ is turned off, a positive voltage is generated in the output winding N ₃ of the output transformer T to turn on the transistor Q ₄ . When the transistor Q ₄ is turned on, the transistor Q ₃ is turned on, the capacitor C ₆ is charged, and a voltage is generated across the capacitor C ₆ . The voltage across the resistor R _{1 4} and R ₁ divided voltage by ₅ the transistor Q ₅ of the capacitor C _6,
Transistors Q ₅ , applied to the bases of Q ₆ respectively,
Q ₆ turns on.

By turning on the transistor Q ₆ ,
The gate of the switching element Q ₁ is set to L level to turn off the switching element Q ₁ . At the same time, the transistor Q ₅ is turned on to bring the base of the transistor Q ₄ to the L level and turn off the transistor Q ₄ . Further, turning off the transistor Q ₄ turns off the transistor Q ₃ .

Then, the capacitor C ₆ and the resistors R _{13 to} R ₃
The time constant of _{1 5,} until some degree discharge the capacitor C _6, keep this certain time state. This time, that is, the capacitor C _6, resistors R _{1 3} ~R _{1 5} by adjusting the time constant of the time constant circuit formed by the turn-off time of the switching element Q _1, it is a certain or more it can. Therefore, it is possible to prevent the switching frequency of the switching element Q _{1 from} exceeding a certain frequency.

As described above, in this embodiment, in the ringing choke converter circuit, the switching element Q
_In order to reduce the number of switching times of 1, the switching frequency does not exceed a certain frequency by creating a dwell time during which current does not flow on the primary side and the secondary side of the output transformer T. . Accordingly, the turn-off period of the switching element Q _1, by providing a certain or higher, it is possible to reduce the switching times of the switching elements Q _1, as a result, it is possible to reduce the loss of light load.

The rest period is not constant depending on the input voltage, the load state, the oscillation waveform of the switching element Q ₁ at that time, and the turn-off period of the switching element Q ₁ is not completely fixed. Further, although the FET is used as the switching element Q ₁ , it can be similarly applied to the case where a transistor is used.

FIG. 2 shows the experimental results of the present invention. The solid line shown in FIG. 2 is the present invention, and the broken line is the conventional example (FIG. 11). As shown in the figure, when the output power was 5 W, the efficiency was about 61% in the conventional example, but could be about 70% in the present invention. Therefore, in the present invention, the efficiency is particularly good when the load is light.

(Second Embodiment) FIG. 3 shows a specific circuit diagram of the second embodiment. This embodiment is different from the previous embodiment in that the circuits on the base side of the transistors Q ₅ and Q ₆ are slightly different. That is, the base of the transistor Q ₅ is a divided output of resistor R _{1 6} and R _{1 7} so as to apply, also, to the base of the transistor Q ₆ is a divided output of resistor R _{1 8} and R _{1 9} I am trying to apply. And
The common connection point of the resistors R _{1 6} and R _{1 8} is connected to the cathode of the diode D _5.

[0038] In this embodiment, the voltage dividing ratio of the resistors R _{1 6} and R _{1 7,} by varying the voltage dividing ratio of the resistors R _{1 8} and R _{1 9,} for example, a transistor the time the transistor Q ₅ is turned on Q _By delaying the time when ₆ turns on, the charging time of capacitor C ₆ is increased and transistor Q ₆
Can be increased, that is, the time when the switching element Q ₁ is turned off can be increased. That is, by increasing the turn-off time of the switching element Q ₁ and reducing the number of times of switching, it is possible to further improve the efficiency under light load.

(Third Embodiment) FIG. 4 shows a specific circuit diagram of the third embodiment. In this embodiment, a capacitor C ₇ is connected in parallel between the gate and source of the switching element Q _{1 in} the circuit shown in FIG. In this embodiment, when the charge of the capacitor C ₆ is completely discharged and the transistor Q ₆ is turned off, the resistors R ₁ and R are added to the gate of the switching element Q _1.
Although the voltage is applied via ₂ , the rising of the gate voltage of the switching element Q ₁ is delayed by the capacitor C ₇ .

That is, by increasing the off period of the switching element Q ₁ by the capacitor C _{7, the} number of times of switching of the switching element Q ₁ is changed from the previous embodiment.
It is possible to further reduce the loss at a light load. FIG. 5 shows the relationship between the output power and the switching frequency f, and lowers the switching frequency f when the capacitor C ₇ is connected to the gate of the switching element Q ₁ as compared with the case where the capacitor C ₇ is not provided. You can In addition, RCC shows the case where the control of the present invention is not performed, and the switching frequency is considerably increased under a light load.

FIG. 6 shows the relationship between the output power and the efficiency in this embodiment, the solid line represents this embodiment, and the broken line represents the conventional example (FIG. 11). As shown in the figure, the efficiency can be particularly improved when the load is light. In the case of the present embodiment, the efficiency can be improved by about 3 to 4% as compared with the embodiment shown in FIG.

(Fourth Embodiment) FIG. 7 shows a fourth embodiment. This embodiment corresponds to the conventional example shown in FIG. Similar to the above-mentioned embodiment, in this embodiment, the same elements as those in the conventional example of FIG. FIG. 8 shows the voltage waveform of each part of this embodiment.

As shown in FIG. 7, the output transformer T has a second
Output winding N ₃ is provided. And the output transformer T
Between the one end of the feedback winding N _{B and the} other end of the second output winding N ₃ of the diode D ₃ and the zener diode ZD.
_1, and a series circuit of a resistor R _{1 0} and resistor R _{1 1} are connected in parallel. Also, the second output winding N of the output transformer T
Transistor Q ₃ from one end of ₃ through diode D ₄
Connected to the emitter. The base of the transistor Q ₃ is connected to the collector of the transistor Q ₄ via the resistor R _{1 2.} The base of the transistor Q ₄ is the resistor R 4.
It is connected to the _{1 0} and R _{1 1} at the connection point.

[0044] A capacitor C ₆ between the emitter of the collector of the transistor Q ₄ of the transistor Q _3, in parallel with the capacitor C _6, and a resistor R _{1 3,} the resistor R _{1 4} and the resistor R _{1 5} Each series circuit is connected. Also connected to the resistor R _{1 4} resistor R _{1 5} and a base of the connection point between the transistor Q _6. Further, the collector of the transistor Q ₆ is connected to the gate of the switching element Q ₁ via the diode D ₆ .

Next, the operation will be described with reference to FIG. Here, FIG. 8 shows the voltage waveform of each part of FIG. 7, and FIG.
7A to 7I show voltage waveforms at points a to i in FIG. Further, in FIG. 8, the horizontal axis represents the entire waveform of 2.0 μ / di.
In v, GND is all measured as the potential of the emitter of the transistor Q ₄ .

In the steady state, a voltage is applied to the gate of the switching element Q ₁ via the resistors R ₁ and R ₂ , and the switching element Q ₁ is turned on. When the switching element Q ₁ is turned on, a current flows through the output transformer T, and a voltage is applied in the same direction as the primary winding N _P of the feedback winding N _B (see AB in FIG. 8B). And the diode D
_3, the Zener diode ZD _1, resistors R _{1 0,} R _{1 1} a voltage is applied to the base of the transistor Q ₄ through, the transistor Q ₄ is turned on (FIG. 8 (c) ~ (e)
A-B).

However, since a voltage is applied to the second output winding N ₃ of the output transformer T in the direction opposite to that of the primary winding N _P (see AB of FIG. 8A), the diode D ₄ is used. Blocked, capacitor C ₆ is not charged (A in FIG. 8 (g))
-See B). Then, the electric charge is accumulated in the capacitor C ₂ by the current flowing through the photocoupler PC ₁ , and the transistor Q ₂ is turned on.

[0048] When the transistor Q ₂ is turned on, lowers the voltage of the gate of the switching element Q _1, the switching element Q ₁ is turned off. At this time, the output transformer T 1
A positive voltage is generated in the output winding N ₂ and the output winding N ₃ wound in the opposite polarity to the next winding N _P (see point B in FIG. 8A).

In the output winding N ₂ of the output transformer T, ideally, ΔT = (I _2P V) / L ₂ (I _2P is the secondary side current, V is the output voltage, ΔT is the switching element Q ₁ The energy stored in the output transformer T is discharged at ΔT indicated by (OFF period of), and the switching element Q ₁ is turned on immediately after that (at the time of light load, this Δ
The oscillation frequency increases because T is short).

However, here, when the switching element Q ₁ is turned off, a positive voltage is generated in the second output winding N ₃ of the output transformer T (see point B in FIG. 8A). At this point, the transistor Q ₄ has already been turned on, and FIG.
Of the voltage represented by point B, the delay of the off transistor Q _4, upon turn-off, the transistor Q ₄ are not turned off immediately (see B-C of FIG. 8 (e)), also on-state transistor Q ₃ keep.

Therefore, the voltage generated in the second output winding N ₃ is applied to the collector of the transistor Q ₃ via the diode D ₄ (see BC in FIG. 8F).
The charging of the capacitor C ₆ is started (B-C in FIG. 8G).
reference). The voltage across the capacitor C ₆ is the resistance R _1
4 and R _{1 5} by dividing the voltage transistor Q ₆ is applied to the base of the transistor Q ₆ is turned on.

By turning on the transistor Q ₆ ,
The gate of the switching element Q ₁ is set to L level to maintain the OFF state of the switching element Q ₁ . On the other hand, since a reverse voltage is generated in the feedback winding N _B of the transistor Q ₄ (see BC in FIG. 8B), even if the ON state is maintained due to the above-mentioned delay, the delay of the delay occurs. After that, it is turned off (see point C in FIG. 8 (e)).

Further, the output transformer T is connected between C and D in FIG.
The feedback winding N _B has a positive and negative amplitude around the ground (GND) (V _B2 ), but is sufficiently smaller than the voltage (V _B1 ) between A and B in FIG. 8B. Therefore, the zener voltage (V _Z ) of the zener diode ZD ₁ is set so that V _B2 <V _Z <V _B1 so that the transistor Q ₄ cannot be turned on again.

[0054] Then, the capacitor C _6, resistors R _{1 3} to R
The time constant of _{1 5,} until some degree discharge the capacitor C _6, keep this certain time state. This time, that is, the capacitor C _6, resistors R _{1 3} ~R _{1 5} by adjusting the time constant of the time constant circuit formed by the turn-off time of the switching element Q _1, it is a certain or more it can. Therefore, it is possible to prevent the switching frequency of the switching element Q _{1 from} exceeding a certain frequency.

As described above, in this embodiment, in the ringing choke converter circuit, the switching element Q
_In order to reduce the number of switching times of 1, the switching frequency does not exceed a certain frequency by creating a dwell time during which current does not flow on the primary side and the secondary side of the output transformer T. . Accordingly, the turn-off period of the switching element Q _1, by providing a certain or higher, it is possible to reduce the switching times of the switching elements Q _1, as a result, it is possible to reduce the loss of light load.

The rest period is not constant depending on the input voltage, the load state, the oscillation waveform of the switching element Q ₁ at that time, and the turn-off period of the switching element Q ₁ is not completely fixed. Further, although the FET is used as the switching element Q ₁ , it can be similarly applied to the case where a transistor is used.

[0057]

[Table 1]

FIG. 9 shows the experimental result of this embodiment. The above Table 1 shows the conditions for the lines in FIG. As shown in FIG. 9, when the input voltage is 220V and the output power is 3W, FIG.
In the conventional example () shown in 2, the efficiency was about 41%, but in the present example (), the efficiency could be about 58%. Further, when the output power was 3 W, the efficiency fluctuated by 16% from 33% () to 49% () in the conventional example depending on the input voltage, but in the present embodiment, 52% () to 62% ().
And the fluctuation could be 10%. Therefore, in this embodiment, the efficiency is good at a light load, and the fluctuation of the efficiency due to the fluctuation of the input is small.

(Fifth Embodiment) FIG. 10 shows a specific circuit diagram of the third embodiment. In this embodiment, in the circuit shown in FIG. 7, a capacitor C _{7 is provided} between the gate and source of the switching element Q _1.
Are connected in parallel. In this embodiment, when the charge of the capacitor C ₆ is completely discharged and the transistor Q ₆ is turned off, a voltage is applied to the gate of the switching element Q ₁ via the resistors R ₁ and R ₂ , but switching is performed by the capacitor C _7. The rise of the gate voltage of the element Q ₁ is delayed.

That is, by increasing the off period of the switching element Q ₁ by the capacitor C _{7, the} number of times of switching of the switching element Q ₁ is changed from the previous embodiment.
It is possible to further reduce the loss at a light load. FIG. 5 shows the relationship between the output power and the switching frequency f (note that FIG. 5 is a characteristic diagram in the case of the first embodiment, but the same result was obtained in the case of the present embodiment as well. In comparison with the case where the capacitor C ₇ is not provided, the capacitor C ₇ is used as the switching element Q.
_The switching frequency f can be further reduced when connected to the gate of ₁ . In addition, RCC shows the case where the control of the present invention is not performed, and the switching frequency is considerably increased under a light load.

FIG. 6 shows the relationship between the output power and the efficiency in this embodiment (note that FIG. 6 is a characteristic diagram in the case of the above-mentioned first embodiment, the same as in the case of FIG. 5 above). Since the same result was obtained in the case of the embodiment, FIG. 6 is used.),
The solid line is the present embodiment, and the broken line is the conventional example (FIG. 11). As shown in the figure, the efficiency can be particularly improved when the load is light. In the case of the present embodiment, the efficiency can be improved by 3 to 4% as compared with the embodiment shown in FIG.

[0062]

According to the present invention, an output transformer having a primary winding, an output winding and a feedback winding, and one end of which is connected to the primary winding of the output transformer and a control terminal is connected to the feedback winding. In the switching power supply device of the ringing choke converter system including the switching element for oscillation and the rectifying circuit connected to the output winding of the output transformer, the switching frequency of the switching element should not exceed a certain frequency. And a second output winding wound in the same polarity as the output winding provided in the output transformer, and the control means is turned on by the voltage generated in the second output winding. And a second switch element that is driven to be turned on by the ON operation of the first switch element, and is charged by the ON operation of the second switch element. A time constant circuit comprising a capacitor and a resistor is, a third switch element is turned off for a predetermined time the first switching element by the time constant circuit,
The time constant circuit makes the control terminal of the switching element L level and the fourth switch element keeps the switching element off for a predetermined time. The switching element of No. 4 is driven to maintain the switching element in the off state for a predetermined time so that the switching frequency of the switching element does not exceed a certain frequency. Therefore, it is possible to reduce the switching loss when the output power is small, and therefore it is possible to improve the efficiency at the time of a light load.

Further, according to the second aspect, since the capacitor is connected between the control terminal of the switching element and the ground, even if the switching element is turned on after a predetermined time has passed by the time constant circuit. The capacitor delays the rise of the voltage to the control terminal of the switching element, so that the off time of the switching element can be extended. Therefore, the switching frequency of the switching element under a light load can be further reduced, and the efficiency can be further improved under a light load.

According to the third aspect, the switching frequency of the switching element is set to a certain frequency by driving the third switching element for a predetermined time by the time in the time constant circuit and keeping the switching element in the off state for a predetermined time. I try not to exceed the above. Therefore, it is possible to reduce the switching loss when the output power is small,
Therefore, there is an effect that the efficiency at the time of light load can be improved.

Further, according to the second aspect, since the capacitor is connected between the control terminal of the switching element and the ground, even if the switching element is turned on after a predetermined time has passed by the time constant circuit. The capacitor delays the rise of the voltage to the control terminal of the switching element, so that the off time of the switching element can be extended. Therefore, the switching frequency of the switching element under a light load can be further reduced, and the efficiency can be further improved under a light load.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a relationship between output power and efficiency according to an embodiment of the present invention.

FIG. 3 is a specific circuit diagram of a switching power supply device according to a second embodiment of the present invention.

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

FIG. 5 is a diagram showing the relationship between output power and switching frequency according to the third embodiment of the present invention.

FIG. 6 is a diagram showing a relationship between output power and efficiency in Example 3 of the present invention.

FIG. 7 is a specific circuit diagram of a switching power supply device according to a fourth embodiment of the present invention.

FIG. 8 is a diagram showing voltage waveforms of respective portions in FIG. 7 of Embodiment 4 of the present invention.

FIG. 9 is a diagram showing a relationship between output power and efficiency in Example 4 of the present invention.

FIG. 10 is a specific circuit diagram of a switching power supply device according to a fifth embodiment of the present invention.

FIG. 11 is a specific circuit diagram of a conventional switching power supply device.

FIG. 12 is a specific circuit diagram of another conventional switching power supply device.

[Explanation of symbols]

T output transformer N _P 1 winding N ₂ output winding N ₃ second output winding N _B feedback winding Q ₁ switching element Q ₃ transistor (second switch element) Q ₄ transistor (first switch element ) Q ₅ transistor (third switch element) Q ₆ transistor (fourth switch element) C ₆ capacitors R _{1 3} to R _{1 5-resistance}

Claims (4)

[Claims] 1. An output transformer (T) having a primary winding (N _P ), an output winding (N ₂ ) and a feedback winding (N _B ) and a primary winding of the output transformer (T). A ringing choke including an oscillating switching element (Q ₁ ) having one end connected to a feedback winding and a control terminal connected to the feedback winding, and a rectifying circuit connected to an output winding (N ₂ ) of an output transformer (T).・
A converter type switching power supply device is provided with a control means for suppressing the switching frequency of the switching element (Q ₁ ) so as not to exceed a certain frequency, and the control means is provided in the output transformer (T). A second output winding (N ₂ ) wound in the same polarity as the wire (N ₂ )
₃ ), the first switch element (Q ₄ ) which is turned on by the voltage generated in the second output winding (N ₃ ), and the first switch element (Q ₄ ).
A switching element a second switching element which is ON-driven by ON operation of the _{(Q 4) (Q 3)} , a capacitor which is charged by the ON operation of the second switching element (Q ₃₎ (C ₆₎ and a resistor a time constant circuit consisting of _{(R 1 3) ~ (R} 1 5), a third switch element is turned off for a predetermined time the first switching element (Q ₄₎ the time constant circuit (Q _5), the characterized by being configured out with a fourth switching element that maintains the switching element (Q ₁₎ and the control terminal of the switching element (Q ₁₎ to L level for a predetermined time oFF state by the time constant circuit (Q ₆₎ Switching power supply. 2. The switching power supply device according to claim 1, further comprising a capacitor (C ₇ ) connected between the control terminal of the switching element (Q ₁ ) and the ground. 3. An output transformer (T) having a primary winding (N _P ), an output winding (N ₂ ) and a feedback winding (N _B ) and a primary winding of the output transformer (T). A switching element (Q ₁ ) for oscillation whose one end is connected and a control terminal is connected to the feedback winding (N _B ), and an output winding (N ₂ ) of the output transformer (T)
A ringing choke converter type switching power supply device having a rectifier circuit connected to the control circuit, the control device including a control unit for suppressing the switching frequency of the switching element (Q ₁ ) so as not to exceed a certain frequency, The control means includes a second output winding (N ₃ ) wound in the same polarity as the output winding (N ₂ ) provided in the output transformer (T), and the switching element (Q ₁ ) when the switching element (Q ₁ ) is turned on. The first switch element (Q ₄ ) which is turned on by the voltage generated from the feedback winding (N _B ) of the output transformer T, and the second switch element which is turned on by the ON operation of the first switch element (Q ₄ ). a switching element (Q _3), the switching element (Q ₁₎ feedback winding upon turning off of the (N _B) the first by reverse voltage generated in the second switching element (Q
₄ ), (Q ₃ ) is charged through the second switch element (Q ₃ ) by the voltage generated in the second output winding (N ₃ ) during the time lag until it turns off. capacitor time constant circuit consisting of (C ₆₎ and a resistor _{(R 1 3) ~ (R} 1 5), a control terminal of the time by constant circuit maintains a predetermined time on operation the switching element (Q ₁₎ L A switching power supply device comprising a third switch element (Q ₆ ) which is set to a level and maintains the switching element (Q ₁ ) in an off state for a predetermined time. 4. The switching power supply device according to claim 3, wherein a capacitor (C ₇ ) is connected between the control terminal of the switching element (Q ₁ ) and the ground.