JPH08116671A - Switching power supply - Google Patents

Abstract

PURPOSE: To enhance the efficiency by reducing the switching loss of a switching element when the input power is low. CONSTITUTION: Under a light load, a capacitor C5 is charged and a transistor Q5 is turned on. When a switching element Q1 is turned off, the gate thereof is held at L level for a predetermined period by the transistor Q5 thus delaying turn-ON thereof. Consequently, the switching frequency of the switching element Q1 is limited to some level or below under light load by means of a control circuit 1. As a result, switching loss of the switching element Q1 is reduced under light load and the efficiency is enhanced. When the load becomes heavier, a Zener diode ZD4 is turned on by a surge voltage to reduce the charging amount of the capacitor C5 thus quickening the discharge. Consequently, the time for limiting turn off of the switching element Q1 is shortened and the switching frequency is increased.

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. 7 shows a specific circuit diagram of a conventional FET type ringing choke converter (RCC) type switching power supply device. 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, and a smoothing capacitor C ₁ is connected to an output end of the diode bridge DB 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 rectifying / smoothing circuit including a rectifying diode D _{1 and a} capacitor C ₃ 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, resistors R _{3 to} R ₅ , a diode D ₂ , a transistor Q ₂ connected in parallel between the gate and source of the switching element Q ₁ , a capacitor C ₂ connected in parallel between the base and emitter of this transistor Q ₂ , etc. It is configured.

Next, the operation of the circuit shown in FIG. 7 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, the power supply voltage is applied to the primary winding N _P of the output transformer T, and the feedback winding N _P
A voltage is generated in _B in the same direction as the primary winding N _P. The generated voltage charges the capacitor C ₂ via the diode D ₂ and the resistor R ₃ .

[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 capacitor C ₃ , and power is supplied to the load.

When the charge of the capacitor C ₂ is discharged through the resistor R ₅ or the like connected in parallel and becomes lower than the forward voltage,
The transistor Q ₂ is turned off, and the energy stored in the output transformer T is released to the secondary side, whereby the switching element Q ₁ is turned 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, the charging time constant of the capacitor C ₂ becomes the maximum of the value of the resistor R ₃ , and the ON period width of the switching element Q ₁ does not increase even if the load current is further exceeded. It becomes a characteristic. That is, overcurrent control is performed.

[0012]

Now, in a ringing choke converter circuit as shown in FIG. 7,
Generally, the oscillation frequency f is 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 (η) becomes poor, and the loss (loss) of the switching element Q ₁ at this time is almost turned on. It is a turn-off switching loss (the loss due to the ON resistance R _DS of the switching element Q ₁ is small). When the input power P ₁ is small, that is, when the output power Po is small, the efficiency (η) is poor because the loss of the switching element Q ₁ is large. Since the loss when the output power Po is small is mostly the loss of the switching element Q ₁ , in order to reduce this loss, the turn-on / turn-off loss (switching loss) of the switching element Q ₁ and the switching There is a method of reducing the number of times of switching of the element Q ₁ itself.

The present invention has been made in view of the above points, and provides a switching power supply device for reducing switching loss of a switching element when input power is small and improving efficiency. This is the purpose.

[0015]

Therefore, in a switching power supply according to claim 1 of the present invention, an output transformer T having a primary winding N _P , an output winding N ₂ and a feedback winding N _B1 , and the output described above. A switching element Q ₁ for oscillation, one end of which is connected to the primary winding N _P of the transformer T and a control terminal of which is connected to the feedback winding N _B1 , and a rectifying circuit D connected to the output winding N ₂ of the output transformer T. _In the switching power supply device of the ringing choke converter system including ₁ and 1, the first transistor Q ₇ is turned on by the voltage generated from the feedback winding N _B1 of the output transformer T when the switching element Q ₁ is turned on. When, a second transistor Q ₆ is turned driven by turning on the first transistor Q _7, generated from the second feedback winding N _B2 provided in the output transformer T during the off switching element Q ₁ Voltage and capacitor C ₅ to charge through the second transistor Q ₆ was maintained turned on driven by the charging electric charge of the capacitor C ₅ to the control terminal of the switching element to Q ₁ when turned off a predetermined period L level With the third transistor Q ₅ , a control circuit 1 for suppressing the switching frequency of the switching element Q ₁ so as not to exceed a certain frequency at a light load is provided.
When the load becomes heavy, the second transistor Q ₆
The surge voltage that appears on the output side of the
Is provided with a zener diode ZD ₄ that regulates the voltage appearing on the output side of the transistor Q ₆ to a predetermined voltage, and by turning on the zener diode ZD ₄ , the charge amount of the capacitor C ₅ of the control circuit 1 is reduced. It is characterized in that the discharge of charges is accelerated to shorten the turn-off time limit of the switching element Q ₁ .

According to another aspect of the switching power supply device of the present invention, an output transformer T having a primary winding N _P , an output winding N ₂ and a feedback winding N _B1, and a primary winding N _{P of the} output transformer T. A switching element Q ₁ for oscillation whose one end is connected to the feedback winding N _B1 and a control terminal is connected to the feedback winding N _B1 , and an output transformer T _1.
In the switching power supply device of the ringing choke converter system having the rectifier circuit D ₁ connected to the output winding N ₂ of the output transformer N, the feedback winding N _B1 of the output transformer T generates when the switching element Q ₁ is turned on. And a first transistor Q ₇ driven on by a voltage
The second transistor Q ₆ which is turned on by turning on the transistor Q ₇ and the voltage generated when the switching element Q ₁ is turned off are output from the second feedback winding N _B2 provided in the output transformer T. in the capacitor C ₅ to charge through Q _6, the third transistor Q ₅ to maintain the on-driven by electric charge of the capacitor C ₅ to the control terminal of the switching element to Q ₁ when turned off a predetermined period L level A control circuit 1 is provided to suppress the switching frequency of the switching element Q ₁ so that it does not exceed a certain frequency when the load is light, and a surge appears on the output side of the second transistor Q ₆ when the load becomes heavy. the Zener diode ZD ₇ which is turned with the rise of the voltage provided, the fourth transistor being turned on driven by turning on the Zener diode ZD ₇ The Q ₈ is provided, the fourth transistor Q ₈ which is the on-drive and regulates the voltage at the output side of the second transistor Q ₆ to a predetermined voltage,
It is characterized in that the charge amount of the capacitor C ₅ of the control circuit 1 is reduced to accelerate the discharge of the charged electric charge and shorten the turn-off time limit of the switching element Q ₁ .

[0017]

According to the switching power supply device of the first aspect of the present invention, the second transistor Q ₆ is turned on by the first transistor Q ₇ which is turned on due to the time lag when the switching element Q ₁ is turned off. The capacitor C ₅ is charged via the capacitor C _5, the third transistor Q ₅ is turned on by the charge stored in the capacitor C ₅ , and the control terminal of the switching element Q ₁ at the time of turning off is maintained at the L level for a predetermined period. When the load is light, the control circuit 1 suppresses the switching frequency of the switching element Q ₁ so as not to exceed a certain frequency. As a result, the switching loss of the switching element Q ₁ under a light load can be reduced and the efficiency can be improved. Further, when the load becomes heavy to some extent, the surge voltage appearing on the output side of the second transistor Q ₆ becomes large, and the Zener diode ZD ₄ is turned on by this increased surge voltage, and the Zener diode ZD ₄ The capacitor C ₅ is charged with a voltage regulated to a predetermined Zener voltage V _Z4 . Therefore, the charging voltage becomes lower than that in the case where the Zener diode ZD ₄ is not provided, so that the discharging time of the charging charge of the capacitor C ₅ is shortened, and as a result, the turn-off limit time of the switching element Q ₁ is shortened and the switching frequency is reduced. Get higher Therefore, the operation returns to the normal operation of the ringing choke converter, and high efficiency can be maintained even when the load becomes heavy.

According to another aspect of the switching power supply device of the present invention, the second transistor Q ₆ is turned on by the first transistor Q ₇ which is turned on due to the time lag when the switching element Q ₁ is turned off. The capacitor C ₅ is charged via the capacitor C _5, the third transistor Q ₅ is turned on by the charge stored in the capacitor C ₅ , and the control terminal of the switching element Q ₁ at the time of turning off is maintained at the L level for a predetermined period. When the load is light, the control circuit 1 suppresses the switching frequency of the switching element Q ₁ so as not to exceed a certain frequency. As a result, the switching loss of the switching element Q ₁ under a light load can be reduced and the efficiency can be improved. Further, when the load becomes heavy to some extent, the surge voltage appearing on the output side of the second transistor Q ₆ becomes large, and the Zener diode ZD ₇ is turned on by this increased surge voltage, and this Zener diode ZD ₇ becomes Turning on turns on the fourth transistor Q ₈ . By turning on the fourth transistor Q ₈ , the voltage appearing on the output side of the second transistor Q ₆ is regulated to a predetermined voltage, and the capacitor C ₅ is charged with this regulated voltage. Therefore, since the charging voltage becomes lower than that in the case where the fourth transistor Q ₈ is not provided, the discharging time of the charged electric charge of the capacitor C ₅ becomes shorter, and as a result, the turn-off limit time of the switching element Q ₁ becomes shorter and the switching becomes shorter. The frequency becomes higher. Therefore, the operation returns to the normal operation of the ringing choke converter, and high efficiency can be maintained even when the load becomes heavy.

[0019]

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. It should be noted that the same elements as those of the related art shown in FIG. In the present invention, when the switching loss of the switching element Q ₁ is reduced, the switching frequency rises, so the loss does not actually decrease. Therefore, the number of times of switching is reduced when the load is light, and the operation is similar to that of a conventional inverter (RCC) when the load is heavy.

As shown in FIG. 1, the output transformer T has a second
A feedback winding N _B2 of the control circuit 1 and the starting circuit 3
Is provided. In the output transformer T, the same feedback winding N _B as in the conventional case is denoted by the symbol N _B1 . Here, the inverter circuit side and points P1 to P7 in the control circuit 1 and the starting circuit 3 are shown to be connected to each other.

The starting resistors R ₁ and R on the inverter circuit side
₂ is connected to the starting circuit 3 side via points P6 and P7, and is disconnected after the switching element Q ₁ is started. The control circuit 1, the transistor Q ₄ to Q _7, resistors R ₁₄ to R _22, capacitors C _4, C
₅ , diodes D _{4 to} D ₇ , zener diode ZD ₂
~ ZD ₆ etc. And the transistor Q
The collector of ₅ is connected to the gate of the switching element Q ₁ of the inverter circuit via the diode D ₅ and the point P5. Further, P1 is connected to the feedback winding N _B1 of the output transformer T on the side where a positive voltage is generated when the switching element Q ₁ is turned on. P2 is connected to the side of the second feedback winding N _B2 of the output transformer T where the positive voltage is generated when the switching element Q ₁ is turned off.
Note that P3 is the ground. Further, P4 is a resistor R ₉ ,
It is connected to the gate of the switching element Q ₁ through the diode D ₃ .

Further, a voltage is applied to the base of the transistor Q ₇ from P1 via a diode D ₇ , a resistor R ₂₁ , a zener diode ZD _{6 and the} like, and the emitter of the transistor Q ₆ is applied. , Diode D ₆
A voltage is applied from P2 via the.
The Zener diode ZD ₆ and the resistor R ₂₁ may be replaced with each other. Similarly, the Zener diode ZD ₅ and the resistor R ₂₀ may be replaced with each other.

The starting circuit 3 includes a transistor Q
₃ , resistors R _{11 to} R ₁₃ , and the like.

Here, FIGS. 2 to 4 are operation waveform diagrams of each part of the circuit shown in FIG. 1 in the steady state. V _{ds of} FIG. 2 (a)
Is the drain-source voltage of the switching element Q ₁ , V _{1 in} (b) is the potential at the connection point between the resistor R ₂₁ of the control circuit 1 and the diode D _7, and V in FIG. 2 (c). ₁₁ is the potential at the connection point between the Zener diode ZD ₆ and the resistor R ₂₁ , V _{12 in} (d) is the base potential of the transistor Q ₇ ,
V _{13 in} (e) is the collector potential of the transistor Q ₆ ,
V _{14 in} (f) indicates the base potential of the transistor Q ₅ .

Further, the Vg is a gate voltage of the switching element to Q ₁ (b) of FIG. 3, the Id is a drain current of the switching element to Q ₁ (c), 2-order Io is the output transformer T of the (d) Side output currents are shown. Further, the V _B2 is a second voltage between the feedback winding N _B2 of the output transformer T of the (b) of FIG. 4, the V _B1 is the voltage between the feedback winding N _B1 of the output transformer T of the (c), V _{N2 in} (d) indicates the voltage across the output winding N ₂ of the output transformer T, respectively. Note that V _{ds in} FIGS. 3 (a) and 4 (a) is the same as V _ds in FIG. 2 (a).
Similar to _ds , it is the drain-source voltage of the switching element Q ₁ .

Next, the operation will be described, but in order to make the operation of the present invention easy to understand, it will be described separately at the time of starting, and at the time of light load and heavy load.

At the time of start-up A When the voltage of the AC power supply AC is input, the voltage is rectified and smoothed by the diode bridge DB ₁ and the capacitor C _1. First, the Zener diode ZD ₁ , the resistor R ₂ ,
A current flows through the resistor R _{11 from} the base / emitter of the transistor Q ₃ , the resistor R ₁₃ , the point P5, and the resistor R ₁₀ to the ground to turn on the transistor Q ₃ .
By turning on this transistor Q ₃ , this time the Zener diode ZD ₁ , the resistor R ₁ , the point P 7, the resistor R
₁₂ , a sufficient voltage is applied to the gate of the switching element Q ₁ through the collector / emitter of the transistor Q ₃ , the resistor R ₁₃ , and the point P 5, and the switching element Q ₁ is turned on and activated.

The voltage generated in the feedback winding N _B1 of the output transformer T charges the capacitor C ₂ via the diode D ₂ and the resistor R ₃ , and the charged voltage is between the base and emitter of the transistor Q _2. When the saturation voltage is exceeded, the transistor Q ₂ turns on. When transistor Q ₂ is turned on, the gate voltage of the switching element Q ₁ is the L level, the switching element Q ₁ is turned off. Capacitor C
_When the electric charge of ₂ is discharged and the transistor Q ₂ is turned off, the above operation is repeated and the starting resistor R ₁ and the transistor Q ₂ are turned on.
_The switching element Q ₁ is turned on via ₃ etc. to start the inverter circuit.

After startup, in the case of a light load When the control circuit 1 operates, the capacitor C ₄ is charged from the point P2 through the transistor Q ₆ and the diode D ₄ . The capacitor C ₄ is composed of an electrolytic capacitor, and in a steady state, the capacitor C 4
₄ has been charged. Voltage across V ₁₅ of the capacitor C ₄ is, transistor Q ₄ through the Zener diode ZD ₂ upon reaching a certain level or more where there is turned on, by pulling the base current of the transistor Q ₃ and the transistor Q ₃ is turned off. The Zener diode ZD ₂ provided on the base side of the transistor Q ₄
May not be required. Further, the positions of the Zener diode ZD ₂ and the resistor R ₁₄ may be exchanged.

Further, since the transistor Q ₃ is turned off, no voltage is applied to the gate of the switching element Q ₁ from the power source side through the resistor R ₁ and the point P5. In other words, the starting circuit 3 has the switching element Q ₁ after the switching element Q ₁ shifts to the steady state.
It is designed to be separated from the gate. On the other hand, the voltage across the capacitor C ₄ is used to switch the switching element Q ₁ from the point P4 through the resistor R ₉ and the diode D _3.
A voltage is applied to the gate of to turn on next.

B At light load When the switching element Q ₁ is turned on [T ₁ (Fig. 2
In a steady state, a voltage is applied from the feedback winding N _B1 of the output transformer T to the gate of the switching element Q ₁ .
Here, the voltage V _B1 generated in the feedback winding N _B1 is expressed by the following equation. V _B1 = (N _B1 / N _P ) · V _ds At the same time, the transistor Q ₇ is turned on from P1 via the diode D ₇ , the resistor R ₂₁ , and the zener diode ZD ₆ . When the transistor Q ₇ is turned on, the transistor Q ₆ is also turned on. However, at this time, the point P2 is negative because the voltage of the second feedback winding N _B2 is applied, and no current flows.

When the switching element Q ₁ is on [T ₁
-T ₂ (see FIG. 2)] In this period, the transistors Q ₇ and Q ₆ are in the ON state, but a negative voltage is generated in the above-mentioned second feedback winding N _B2 of the output transformer T. Therefore, the capacitor C ₅ is not charged.

When the switching element Q ₁ is turned off [T ₂ (see FIG. 2)] Here, the secondary side of the output transformer T is the photocoupler PC ₁
Is fed back to the phototransistor PT on the primary side by the light emitting diode PD of the diode D ₂ and the resistor R ₄
, The capacitor C ₂ is charged through the time constant circuit of the phototransistor PT. Then, by charging the capacitor C _2, the transistor Q ₂ is turned on and the switching element Q ₁ is turned off. In this case, the voltage V _B1 of the feedback winding N _B1 of the output transformer T is inverted negatively, so that the transistors Q ₇ and Q ₆ are turned off. However, there is a time lag (T _{2 to} T _{3 in} FIG. 2) until the transistors Q ₇ and Q ₆ are completely turned off, and during this time, from the second feedback winding N _B2 that is positively inverted, The capacitor C ₅ is charged via the point P2 and the transistor Q ₆ . In addition,
Voltage V _B2 generated in the second feedback winding N _B2 is expressed by the following equation. V _B2 = (N _B2 / N ₂ ) ・ V _N2

At this time, if it is desired to keep the transistor Q ₇ on for more than the above time lag, the transistor Q ₇
Add a capacitor between the base and emitter of. Also,
The Zener diode ZD ₅ is inserted in order to improve the turn-off of the transistor Q ₆ . Further, the Zener diode ZD ₅ may be omitted.

When the switching element Q ₁ is off [T ₂
~ T ₁ (see FIG. 2)] Eventually, the transistor Q ₆ is turned off, and the charging of the capacitor C ₅ is completed. The charging voltage to the capacitor C ₅ is divided by the Zener diode ZD ₃ and the resistors R ₁₆ and R _17, and when the divided voltage becomes equal to or higher than the forward voltage between the base and the emitter of the transistor Q ₅ , the transistor Q ₅ is turned on. ₅ turns on. The Zener diode ZD ₃ may be omitted. When the transistor Q ₅ is turned on, the gate of the switching element Q ₁ is set to the L level via the point P ₅ to keep the switching element Q ₁ off and delay the turn-on. That is, the intermittent operation is performed.

At this time, the Zener diode ZD ₆
Is the feedback winding N _B1 during the off period of the switching element Q _1.
Since the voltage V _B1 generated at the ringing occurs around the ground (see FIG. 4C), it is inserted to prevent the transistor Q ₇ from turning on even when it is positively swung.

Then, the charge of the capacitor C ₅ is changed to the resistance R ₁₈
The transistor Q ₅ is turned off at the time point T ₄ when it is discharged through the above. During this period, no current flows in the primary side or the secondary side of the output transformer T. Usually an inverter circuit (RCC)
Can be turned off by the kick voltage from the secondary side, but the feedback winding N _B1 of the output transformer T is almost zero at this time.
Since it is V, even if the transistor Q ₆ is turned off, it cannot be turned on immediately. Therefore, the voltage charged in the capacitor C ₄ is charged to the gate of the switching element Q ₁ from the resistor R ₉ and the diode D ₃ via the point P 4, and when it reaches the threshold voltage V _th , it turns on. That is, the switching frequency can be adjusted by the resistor R ₉ . Then, the above is repeated.

As a result, the input power is small (the output power is small).
Therefore, even if the switching frequency of the switching element Q ₁ tries to increase, the operation of the control circuit 1 maintains the OFF period of the switching element Q ₁ for a certain period or longer. That is, when the load is light, the switching frequency of the switching element Q ₁ does not exceed a certain frequency, that is, when the load is light, the switching frequency is considerably lower than the switching frequency in the normal operation of the inverter circuit. The switching loss can be reduced when is small, and the efficiency at light load is improved.

C Under heavy load Under heavy load, the surge voltage generated in the second feedback winding N _B2 of the output transformer T becomes large, so that it is output to the collector side of the transistor Q ₆ via the point P2. Voltage (surge voltage) also increases. The Zener diode ZD ₄ on the collector side of the transistor Q ₆
The zener voltage is V _Z4, when the collector-side potential of the transistor Q ₆ and V _13, at light load, V ₁₃ <V
As will be _Z4, also setting the Zener voltage V _Z4 of the Zener diode ZD ₄ such that V _13> V _Z4 in the heavy load.

Under heavy load, the surge voltage becomes large, the collector potential V ₁₃ of the transistor Q _{6 and} the voltage V ₁₅ across the capacitor C ₄ become large, and V ₁₃ is V ₁₃ > V
_Since it becomes _Z4 , the potential of the collector of the transistor Q ₆ is
It is limited to a certain voltage V ₁₃ 'by the Zener diode ZD ₄ and the resistor R ₁₉ . Transistor Q ₆ is T shown in FIG.
_Since it is off at the time point of _3, the capacitor C ₅ is charged with the above voltage V ₁₃ 'up to that time point. Then, at that voltage, discharge is started by the resistors R ₁₈ , R ₁₆ and R ₁₇ . Therefore, the surge voltage outputted to the collector of the transistor Q ₆ becomes heavy load is increased, by the Zener diode ZD ₄ exceeds the Zener voltage V _Z4 of the Zener diode ZD ₄ are turned on, a large surge voltage It is charged at a lower voltage than in the case where the Zener diode ZD ₄ is not regulated and is not provided. As a result, when the Zener diode ZD ₄ is turned on, the capacitor C ₅
Zener diode ZD ₄ due to small charge
The discharge of the capacitor C ₅ is faster than that in the case where there is no.
As a result, the time limit for turning off the switching element Q ₁ becomes shorter and the switching frequency f becomes higher.

On the other hand, when the load is heavy, the surge voltage is large, so that the voltage charged in the capacitor C ₄ via the diode D ₄ also rises. Due to the increased voltage of the capacitor C ₄ , the point P4 and the resistance R ₉ The voltage applied to the gate of the switching element Q ₁ via the switch also increases. Therefore, in addition to the faster discharge of the capacitor C _5, the voltage applied to the gate of the switching element Q ₁ increases as the charging voltage of the capacitor C ₄ increases, and thus the switching element Q ₁ is quickly turned on. I will let you. As a result, the time limit for turning off the switching element Q ₁ is shortened and the switching frequency f is increased. Further, as the load increases, the surge voltage rises and the charging voltage of the capacitor C ₄ also rises,
As the turn-on timing of the switching element Q ₁ is advanced, the switching frequency f also increases. In this way, as the load becomes heavier, the inverter circuit behaves more like a normal inverter circuit (RCC). In this way, at the time of heavy load, operation similar to that of the conventional inverter is performed to maintain high efficiency.

(Second Embodiment) FIG. 5 shows a second embodiment. In the present embodiment, the cathode of the zener diode ZD ₇ is connected to the cathode side of the diode D ₄ , and the anode of this zener diode ZD ₇ is connected to the transistor Q via the resistor R _23.
Connected to the base of ₈ . And the transistor Q ₈
Is connected to the collector of the transistor Q ₆ via the resistor R ₂₅ . Also, the resistor R _{24 is connected} to the transistor Q ₈
It is connected between the base and emitter of. The Zener voltage V _Z7 of the Zener diode ZD ₇ is set to be lower than the voltage V ₁₅ across the capacitor C ₄ at light load, and accordingly, when the surge voltage becomes large at heavy load, the Zener voltage V _Z7 is set accordingly. The increased voltage V ₁₅ is V ₁₅ >
The zener voltage of the zener diode ZD ₇ is set so as to be V _Z7 .

Next, the operation will be described. At the time of starting or at a light load, it is the same as the previous embodiment, and the switching frequency of the switching element Q ₁ at the time of a light load is lowered to improve the efficiency. Since the operation under heavy load is different, the operation under heavy load will be described.

Under heavy load, the surge voltage becomes large, and the collector potential V ₁₃ of the transistor Q ₆ and the capacitor C ₄
Since the voltage V ₁₅ between both ends of the voltage V becomes large and V ₁₅ becomes V ₁₅ > V _Z7 , the Zener diode ZD ₇ is turned on and the transistor Q ₈ is turned on. When this transistor Q ₈ is turned on, the potential of the collector of the transistor Q ₆ changes to the resistance R
By the ₂₃ and the transistor Q _8, is limited to a certain voltage V ₁₃ '. Since the transistor Q ₆ is off at the time T ₃ shown in FIG. 2, the capacitor C ₅ is charged with the above voltage V ₁₃ ′ until that time. Then, at that voltage, discharge is started by the resistors R ₁₈ , R ₁₆ and R ₁₇ . Therefore, the surge voltage outputted to the collector of the transistor Q ₆ becomes heavy load is increased, by the Zener diode ZD ₇ exceeds the Zener voltage V _Z7 Zener diode ZD ₇ is turned on, a large surge voltage It is charged at a lower voltage compared to the case where the Zener diode ZD ₇ is not regulated and is not provided. As a result, when the Zener diode ZD ₇ is turned on, the capacitor C ₅ is discharged faster than when the Zener diode ZD ₇ is not used because the amount of charge of the capacitor C ₅ is small. as a result,
The turn-off time limit of the switching element Q ₁ becomes shorter and the switching frequency f becomes higher.

On the other hand, when the load is heavy, the surge voltage is large, so the voltage charged in the capacitor C ₄ via the diode D ₄ also rises, and the increased voltage of the capacitor C ₄ causes the point P 4 and the resistance R _{9 to} rise. The voltage applied to the gate of the switching element Q ₁ via the switch also increases. Therefore, in addition to the faster discharge of the capacitor C _5, the voltage applied to the gate of the switching element Q ₁ increases as the charging voltage of the capacitor C ₄ increases, and thus the switching element Q ₁ is quickly turned on. I will let you. As a result, the time limit for turning off the switching element Q ₁ is shortened and the switching frequency f is increased. Further, as the load increases, the surge voltage rises and the charging voltage of the capacitor C ₄ also rises,
As the turn-on timing of the switching element Q ₁ is advanced, the switching frequency f also increases. In this way, as the load becomes heavier, the inverter circuit behaves more like a normal inverter circuit (RCC). In this way, at the time of heavy load, operation similar to that of the conventional inverter is performed to maintain high efficiency.

(Third Embodiment) FIG. 6 shows a specific circuit diagram of the third embodiment. In this embodiment, instead of charging the capacitor C ₄ from the collector of the transistor Q ₆ via the diode D ₄ as in the previous embodiment, the diode D is directly fed from the second feedback winding N _B2 of the output transformer T. _The capacitor C ₄ is charged via the capacitor ₄ . Since the operation is the same as that in the case of FIG. 5, the description is omitted.

In each of the above embodiments, the case where the FET is used as the switching element Q ₁ of the inverter circuit has been described, but the present invention is not limited to this. For example, a transistor may be used as the switching element Q ₁ .

[0048]

According to the switching power supply device of the first aspect of the present invention, the capacitor is provided via the second transistor which is turned on by the first transistor which is turned on due to the time lag when the switching element is turned off. Is charged, and the third transistor is turned on by the charge stored in this capacitor, and the control terminal of the switching element at the time of turning off is maintained at the L level for a predetermined period. The switching frequency is suppressed so that it does not exceed a certain frequency. As a result, the switching loss of the switching element under a light load can be reduced and the efficiency can be improved. Further, when the load becomes heavy to some extent, the surge voltage that appears on the output side of the second transistor increases, and the Zener diode is turned on by this increased surge voltage, and the Zener voltage of this Zener diode is regulated to a predetermined Zener voltage. The capacitor is charged by the applied voltage.
Therefore, the charging voltage is lower than that in the case without the Zener diode, so that the discharging time of the charging charge of the capacitor is shortened, and as a result, the turn-off limit time of the switching element is shortened and the switching frequency is increased. Therefore, the operation returns to the normal operation of the ringing choke converter, and high efficiency can be maintained even when the load becomes heavy.

According to the second aspect of the present invention, the capacitor is charged through the second transistor which is turned on by the first transistor which is turned on due to the time lag when the switching element is turned off. By driving the third transistor on by the charge of this capacitor and maintaining the control terminal of the switching element at the L level when the transistor is off for a predetermined period, the control circuit controls the switching frequency of the switching element when the load is light. , It is controlled so that it does not exceed a certain frequency.
As a result, the switching loss of the switching element under a light load can be reduced and the efficiency can be improved. When the load becomes heavy to some extent, the surge voltage that appears on the output side of the second transistor increases, and the increased surge voltage turns on the Zener diode. Transistor turns on. By turning on the fourth transistor, the voltage appearing on the output side of the second transistor is regulated to a predetermined voltage, and the regulated voltage charges the capacitor. Therefore, the charging voltage becomes lower than that in the case where the fourth transistor is not provided, so that the discharging time of the charging charge of the capacitor becomes faster, and as a result, the turn-off limit time of the switching element becomes shorter and the switching frequency becomes higher. Therefore, the operation returns to the normal operation of the ringing choke converter, and high efficiency can be maintained even when the load becomes heavy.

[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.

2 (a) to (f) are operation waveform diagrams of an embodiment of the present invention.

3A to 3D are operation waveform diagrams of an embodiment of the present invention.

4 (a) to (d) are operation waveform diagrams of an embodiment of the present invention.

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

FIG. 6 is a specific circuit diagram of a switching power supply device according to a third embodiment of the present invention.

FIG. 7 is a specific circuit diagram of a conventional switching power supply device.

[Explanation of symbols]

1 Control circuit T Output transformer N _P Primary winding N ₂ Output winding N _B1 Feedback winding N _B2 Second feedback winding D ₁ Diode (rectifier circuit) Q ₁ Switching element Q ₇ First transistor Q ₆ Second 2nd transistor Q ₅ 3rd transistor Q ₈ 4th transistor C ₅ Capacitor ZD ₄ Zener diode ZD ₇ Zener diode

Claims (2)

[Claims] 1. An output transformer (T) having a primary winding (N _P ), an output winding (N ₂ ) and a feedback winding (N _B1 ), and a primary winding of the output transformer (T) ( Switching element for oscillation (Q ₁ ) whose one end is connected to N _P ) and whose control terminal is connected to the feedback winding (N _B1 ), and rectification connected to the output winding (N ₂ ) of the output transformer (T) In a switching power supply device of a ringing choke converter system including a circuit (D ₁ ), a voltage generated from a feedback winding (N _B1 ) of an output transformer (T) when the switching element (Q ₁ ) is on oN driven first transistor is (Q _7), and the first transistor (Q ₇₎ on the on-driven second transistor is of (Q _6), first provided on the output transformer (T) 2 switching element from the feedback winding (N _B2) Q ₁₎ and capacitor voltages developed during off charge through the second transistor (Q ₆₎ of (C _5), the capacitor (C ₅₎ driven to turn on by the charging electric charge of the switching element in the OFF state (Q ₁ )
With a third transistor (Q ₅ ) for keeping the control terminal of L at L level for a predetermined period, a control circuit for suppressing the switching frequency of the switching element (Q ₁ ) so as not to exceed a certain frequency at a light load ( 1) is provided, the voltage at the output side of the second transistor (Q ₆₎ the second transistor is turned on with the increase of surge voltage at the output side of the (Q ₆₎ when the load has become heavier A zener diode (ZD ₄ ) that regulates to a predetermined voltage is provided, and by turning on the zener diode (ZD ₄ ), the charge amount of the capacitor (C ₅ ) of the control circuit (1) is reduced to discharge the charge. Fasten the switching element (Q ₁ )
The switching power supply device is characterized in that the turn-off time limit of is shortened. 2. An output transformer (T) having a primary winding (N _P ), an output winding (N ₂ ) and a feedback winding (N _B1 ), and a primary winding of the output transformer (T) ( Switching element for oscillation (Q ₁ ) whose one end is connected to N _P ) and whose control terminal is connected to the feedback winding (N _B1 ), and rectification connected to the output winding (N ₂ ) of the output transformer (T) In a switching power supply device of a ringing choke converter system including a circuit (D ₁ ), a voltage generated from a feedback winding (N _B1 ) of an output transformer (T) when the switching element (Q ₁ ) is on oN driven first transistor is (Q _7), and the first transistor (Q ₇₎ on the on-driven second transistor is of (Q _6), first provided on the output transformer (T) 2 switching element from the feedback winding (N _B2) Q ₁₎ and capacitor voltages developed during off charge through the second transistor (Q ₆₎ of (C _5), the capacitor (C ₅₎ driven to turn on by the charging electric charge of the switching element in the OFF state (Q ₁ )
With a third transistor (Q ₅ ) for keeping the control terminal of L at L level for a predetermined period, a control circuit for suppressing the switching frequency of the switching element (Q ₁ ) so as not to exceed a certain frequency at a light load ( 1) is provided, and a Zener diode (ZD ₇ ) that is turned on with an increase in surge voltage appearing on the output side of the second transistor (Q ₆ ) when the load becomes heavy is provided, and this Zener diode (ZD ₇ ) fourth transistor which is turned on driven by the oN (Q ₈₎ to provided by the on-driven fourth transistor (Q _8), a second transistor (Q ₆₎
The voltage appearing on the output side of the control circuit (1) is regulated to a predetermined voltage, the charge amount of the capacitor (C ₅ ) of the control circuit (1) is reduced to accelerate the discharge of the charge, and the switching element (Q ₁ ) is turned off. A switching power supply device characterized in that a time limit is shortened.