JP3392769B2 - Switching power supply - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a so-called AC-D.
The present invention relates to a switching power supply device that is preferably implemented as a C converter or a DC-DC converter.

[0002]

2. Description of the Related Art Used in portable small electronic devices and the like, a direct current obtained by rectifying and smoothing a commercial alternating current or a direct current from a battery is switched at a high frequency of, for example, several hundreds of kHz to make a small transformer. 2. Description of the Related Art A switching power supply device, which is designed to convert a voltage into a desired voltage with high efficiency, is widely used.

As a typical configuration of such a switching power supply device, the secondary side output voltage is detected by a voltage detection circuit, and the control circuit controls the switching pulse width of the main switching element according to the detection result. 2. Description of the Related Art A pulse width modulation (PWM) type switching power supply device for obtaining a desired secondary side output voltage is widely used.

As another typical configuration of the switching power supply device, the excitation energy accumulated in the transformer during the on period of the main switching element is output to the secondary side circuit during the off period, and the output is completed. A ringing choke converter (RCC) for turning on the main switching element again by feeding back a ringing pulse generated in the control winding of the transformer to the control terminal of the main switching element via a DC cut capacitor. Switching power supplies of the type are also widely used.

In the RCC type switching power supply device, as the load becomes heavier, the off period and the on period are automatically lengthened, that is, the switching frequency is lowered and the secondary side output voltage is maintained at a predetermined constant voltage. So P
A low-cost power supply that does not require a complicated control circuit such as a WM-type switching power supply device and that does not require a power supply circuit for operating the control circuit and generating a voltage that serves as a pulse width reference. Suitable for equipment.

FIG. 10 is an electric circuit diagram of a typical prior art switching power supply device 1 of such an RCC system. A direct current obtained by rectifying commercial alternating current by a main power supply circuit (not shown) is input between the input terminals p1 and p2. The DC current is smoothed by the smoothing capacitor c1, and the smoothing capacitor c1 outputs a main power supply voltage between the high-level side main power supply line 2 and the low-level side main power supply line 3.

A transformer n is provided between the main power lines 2 and 3.
The primary winding n1 and the main switching element q are connected in series. The main switching element q is realized by, for example, a bipolar transistor or a field effect transistor, and is shown as a field effect transistor in the example of FIG. A starting circuit 4 composed of voltage dividing resistors r1 and r2 is also connected between the main power supply lines 2 and 3.

When the power is turned on, that is, when the power supply voltage is applied between the input terminals p1 and p2, the output voltage of the smoothing capacitor c1, that is, the main power supply voltage rises, and the voltage division value by the voltage dividing resistors r1 and r2. However, when the threshold voltage of the main switching element q becomes, for example, 3 V or more, the main switching element q is turned on, the voltage in the upward direction in FIG. 10 is applied to the primary winding n1, and the excitation energy is accumulated. . As will be described later, the main switching element q is
When turned off, the exciting energy induces an upward voltage in the secondary winding n2. Also at this off time,
The vibration generated by the leakage inductance between the primary winding n1 and the other windings n2 and n3 is provided in parallel between the drain and source of the main switching element q, and is generated from the series circuit of the resistor r3 and the capacitor c2. It is absorbed and removed by the snubber circuit 5.

The DC current induced in the secondary winding n2 is given to the smoothing capacitor c3 via the diode d1, smoothed by the smoothing capacitor c3, and then output via the output power supply lines 6 and 7. Output from the terminals p3 and p4 to a load circuit (not shown). The output power line 6,
A voltage detection circuit 8 is interposed between the seven. The voltage detection circuit 8 is configured to include a voltage dividing resistor, a photocoupler pc, and the like, and the light emitting diode d2 of the photocoupler pc is driven to light at a brightness corresponding to the output voltage, and the value of the output voltage is changed. Feedback is given to the primary side.

The main switching element q is connected to the control winding n3.
Is turned on, a voltage is induced in the same upward direction as the primary winding n1, and the induced current is a direct current cut capacitor c.
4 and a bias resistor r4 to be applied to the gate of the main switching element q, whereby the gate potential of the main switching element q is further raised, and the main switching element q is maintained in the on state.

Further, the current induced in the control winding n3 when the main switching element q is on is
4 and the bias resistor r4, the photocoupler pc
Via the phototransistor tr2 of the capacitor c5
Given to one terminal. The other terminal of the capacitor c5 is connected to the low-level main power supply line 3, and therefore the higher the secondary output voltage, the larger the charging current, and the faster the terminal voltage of the capacitor c5 rises. To do. The charging voltage of the capacitor c5 is given to the base of a control transistor tr1 interposed between the gate and source of the main switching element q, and the output voltage thereof is a threshold voltage of the control transistor tr1, for example, 0.
When the voltage is 6 V or higher, the control transistor tr1 is turned on, whereby the gate potential of the main switching element q is rapidly lowered, and the main switching element q is driven off.

Therefore, the higher the secondary side output voltage, that is, the lighter the load, the faster the output voltage of the capacitor c5 rises, and the faster the main switching element q is driven off. The capacitor c5 also has a control winding n3
The current induced by is given through the resistor r5.
Accordingly, even if the output voltage of the smoothing capacitor c3 on the secondary side is low due to a short circuit between the output terminals p3 and p4, the on period of the main switching element q is limited to a predetermined period, and the main switching element q is protected. Has been planned.

Further, in the control winding n3, when the number of turns of the control winding n3 and the secondary winding n2 is the same as the reference numeral, and the secondary side output voltage is vo, the main switching element q is When turned off, in the downward direction of FIG. 10, (n3 /
The voltage of n2) vo is induced, whereby the charge of the capacitor c5 is extracted, and the reset operation for the next on operation of the main switching element q is performed.

After turning off the main switching element q, 1
When the output of the excitation energy accumulated in the secondary winding n1 to the secondary side ends, ringing occurs mainly between the parasitic capacitance c6 of the control winding n3 and the control winding n3, and the parasitic The electrostatic energy stored at the voltage (n3 / n2) vo in the capacitance c6 is released, converted into the excitation energy of the control winding n3 after 1/4 cycle of vibration, and then the parasitic capacitance c6 is charged again. Therefore, an upward electromotive voltage of the voltage (n3 / n2) vo is generated in the control winding n3. The electromotive voltage, which is a ringing pulse, is set to be equal to or higher than the threshold voltage of the main switching element q, and the electromotive voltage turns on the main switching element q again.
Thus, the main switching element q is continuously driven on / off at the switching frequency corresponding to the load, and the desired secondary output voltage is output.

[0015]

In the switching power supply device, most of the loss is due to the power consumption required for extracting the electric charge accumulated in the parasitic capacitance between the drain and source of the main switching element and the iron loss of the transformer. Yes, these generally increase as the switching frequency increases.
Therefore, as described above, in the switching power supply device 1, the lighter the load is, the higher the switching frequency is. Therefore, the lighter the load is, the more the ratio of the loss to the converted power is increased, and the lower the power conversion efficiency is. There is a problem.

On the other hand, as other conventional techniques for solving such a problem, there are, for example, Japanese Patent Laid-Open No. 9-47023 and Utility Model Registration No. 3039391. In the prior art disclosed in Japanese Patent Laid-Open No. 9-47023, another control transistor is provided in parallel with a control transistor for driving the main switching element off, and when the load is light, the control winding of the control winding generated when the main switching element is off is provided. The induced voltage is instantaneously taken into a capacitor through a transistor that turns off in cooperation with the main switching element, and the other control transistor is turned on by the capacitor to keep the off state of the main switching element, thereby switching frequency. Is configured to be low.

Therefore, the structure for reducing the power consumption becomes complicated, the cost increases, the advantage of the RCC method is diminished, and the process of charging the capacitor depends on the storage time of the transistor. However, there is a problem that designing is difficult due to large variations among devices.

The utility model registration No. 3039391
In the prior art shown in the publication, a delay capacitor for blunting the ringing pulse is interposed in parallel with the control transistor when the load is light.

Therefore, as described in the seventh line to the eighth line of paragraph 0025 of the publication, the switching cycle can be extended only during the period in which ringing occurs, and the load cycle at the time of light load is reduced. There is a problem that the switching frequency cannot be significantly reduced compared to the switching frequency under heavy load.

An object of the present invention is to provide a switching power supply device having a simple structure and capable of enhancing power conversion efficiency.

[0021]

According to a first aspect of the present invention, there is provided a switching power supply device, wherein the excitation energy accumulated in a transformer during an on period of a main switching element is output to an output circuit on a secondary side during an off period. The ringing pulse generated in the control winding of the transformer after the output is completed
In a ringing choke converter type switching power supply device that feeds back to the control terminal of the main switching element via the capacitor and drives the main switching element on, the switching power supply device includes a first resistor and a first control switching element. includes a series circuit connected to the output side of the first capacitor and a second resistor interposed between said first capacitor and said main switching element, the
A series circuit includes the first capacitor and the second resistor.
And the first control switching element is driven on during a light load , and the first switching element is driven by a voltage induced in the control winding during an on period of the main switching element during the light load. A charge is accumulated in the first capacitor, and when the ringing pulse is generated, the first
Reverse bias is generated by the charge of the capacitor
The main switching element is prevented from being driven on.

According to the above construction, at the time of heavy load which is a normal load, the first control switching element is turned off, and the ringing pulse causes the first capacitor and the second capacitor to have no influence of the series circuit. It is given to the control terminal of the main switching element via a resistor, the main switching element is driven on, and the switching operation is continuously performed.

On the other hand, when the load is light, the series circuit is connected between the first capacitor and the second resistor,
A larger amount of current induced in the control winding flows through the first capacitor, and charges are accumulated. At this time, the potential of the control terminal of the main switching element is maintained by the second resistance, and the main switching element maintains the on state even if the series circuit is inserted by turning on the first control switching element. be able to. When the main switching element is turned off and the excitation energy is released and a ringing pulse is generated, the ringing pulse is reverse-biased by the charging voltage of the first capacitor and the main switching element is controlled via the second resistor. Since it is given to the terminal, on-driving of the main switching element by the ringing pulse is blocked.

Therefore, once the main switching element performs the switching operation at a light load, the next switching operation is performed in the same manner as when the power is turned on. That is, when the starting voltage obtained by resistance division of the main power supply voltage or the like causes the potential of the control terminal of the main switching element to gradually change and reaches a threshold voltage at which the main switching element is turned on, the main switching element is turned on. turn on.

In this way, when the load is light, the restart of the main switching element due to the ringing pulse as in the case of the heavy load is stopped, and the restart is gently performed in the same manner as when the power is turned on. The switching frequency can be reduced. This suppresses the loss that increases in proportion to the switching frequency, such as the power required to extract the charge accumulated in the stray capacitance between the drain and source of the main switching element, and obtains high power conversion efficiency even at light load. be able to.

Further, such reduction of the switching frequency at the time of light load can be realized by a simple structure of the series circuit including the first resistor and the first control switching element and the second resistor. It can be realized with a low-cost configuration.

A switching power supply device according to a second aspect of the present invention comprises a series circuit of a second capacitor and third to fifth resistors, which is interposed between main power supply lines and a fourth power supply line.
Of the starter circuit in which the connection point between the resistance of the second resistance and the fifth resistance is connected to the control terminal of the main switching element, the auxiliary power supply winding provided in the transformer, and the output of the auxiliary power supply winding are rectified.
A smoothing sub-power supply circuit and a first diode for preventing backflow that gives an output of the sub-power supply circuit to a connection point between the third resistor and the fourth resistor are provided, and a predetermined time from power-on Until the time elapses, the main switching element is turned on by the divided voltage of the main power supply voltage by the starting circuit.
It is characterized in that the main switching element is activated by the divided voltage of the sub power supply circuit after the predetermined time has elapsed since the power was turned on.

According to the above configuration, when the output voltage of the smoothing capacitor of the sub power supply circuit becomes a voltage sufficient for starting the main switching element after a predetermined time has passed since the power was turned on, the second voltage is set in this state. A voltage substantially corresponding to the difference between the main power supply voltage and the output voltage of the sub power supply circuit is generated in the capacitor, and the main switching element can be turned on by the divided voltage of the output voltage of the sub power supply circuit. It is possible to prevent the inflow of current from the main power supply.

Therefore, as shown in claim 1,
Restart the main switching element in the same way as when turning on the power.
Even if the main power supply voltage is divided by the fifth resistor, the main switching element is activated by the divided voltage of the main power supply voltage of, for example, several hundreds V, only when the power is turned on. After the lapse of the predetermined time, the main switching element is activated by the divided voltage of the output voltage of the sub power supply circuit of, for example, about 10V. As a result, it is possible to reduce power consumption due to the third to fifth resistors that are voltage dividing resistors, and it is possible to further improve efficiency.

Furthermore, a switching power supply device according to a third aspect of the invention comprises a series circuit of a second capacitor and third to fifth resistors, which is interposed between main power supply lines and has a fourth resistor. And a fifth resistor, the connection point of which is connected to the control terminal of the main switching element, a second diode for extracting an output from one terminal of the control winding of the transformer, and the second circuit. A choke coil to which an output of a diode is given, a smoothing capacitor that smoothes a current passing through the choke coil, and a flywheel that connects a connection point between the second diode and the choke coil to the other terminal of the control winding. A sub power supply circuit having a diode, and an output of the sub power supply circuit connected to the third resistor and the fourth resistor.
A first diode for preventing backflow applied to a connection point with the resistor, and the main switching element is operated by a divided voltage of the main power supply voltage by the start-up circuit until a predetermined time elapses after the power is turned on. Is turned on, and the main switching element is turned on by the divided voltage of the sub power supply circuit after the lapse of the predetermined time from power-on.

According to the above arrangement, the smoothing capacitor is charged via the second diode and the choke coil while the main switching element is on.
When the main switching element is turned off, the exciting current in the choke coil charges the smoothing capacitor via the flywheel diode.

Therefore, when the output voltage of the smoothing capacitor of the sub power supply circuit becomes a voltage sufficient for starting the main switching element after a lapse of a predetermined time after the power is turned on, in this state, the second capacitor is connected to the main power supply. A voltage substantially corresponding to the difference between the voltage and the output voltage of the sub power supply circuit is generated, and the main switching element can be turned on by the divided voltage of the output voltage of the sub power supply circuit. Can be blocked.

Therefore, as shown in claim 1,
Restart the main switching element in the same way as when turning on the power.
Even if the main power supply voltage is divided by the fifth resistor, the main switching element is activated by the divided voltage of the main power supply voltage of, for example, several hundreds V, only when the power is turned on. After the lapse of the predetermined time, the main switching element is activated by the divided voltage of the output voltage of the sub power supply circuit of about several tens of volts. As a result, it is possible to reduce power consumption due to the third to fifth resistors that are voltage dividing resistors, and it is possible to further improve efficiency.

Since the smoothing capacitor is charged through the impedance element such as the choke coil, it is affected by the secondary side output current value. For example, the higher the output current value, the higher the charging voltage. Therefore, when the load becomes large, the on period of the main switching element becomes long, and the secondary-side output current value becomes high, the voltage given by the sub power supply circuit for starting the on of the main switching element becomes high, and The on-timing of the main switching element is advanced and the switching frequency is increased. In this way, it is possible to cope with large load fluctuations when the load is light. Furthermore, it is not necessary to increase the number of taps of the transformer for supplying power to the sub power supply circuit.

Further, the switching power supply device according to a fourth aspect of the present invention further includes a fourth diode for discharging, which is provided in parallel with the third to fifth resistors and in the reverse bias direction. To do.

According to the above construction, when the power supply voltage of the main power supply drops after the power supply is cut off, the main power supply-fifth to third resistors-
Along with the second capacitor-main power supply path, the main power supply-fourth diode-second capacitor-main power supply path,
A discharge path for the second capacitor is formed.

Therefore, even if the time from power-off to power-on is short, the second capacitor is surely discharged, and at power-on again, the output voltage of the smoothing capacitor of the sub-power supply circuit is not lowered. It can be surely started by the divided voltage of the main power source.

Further, in the switching power supply device according to the invention of claim 5, instead of the second capacitor, a transistor provided between one main power supply line and a third resistor, and a base of the transistor. For connecting to the other main power supply line, a series circuit composed of a sixth resistor and a third capacitor, and for connecting the connection point of the sixth resistor and the third capacitor to the one main power supply line. And a fifth diode of the above.

According to the above configuration, the charging current of the third capacitor is 1 / think of the charging current of the second capacitor when the current amplification factor of the transistor is hfe.
It can be hfe.

Therefore, the capacitor can be downsized.

When the power supply voltage of the main power supply drops after the power supply is cut off, the discharge path of the third capacitor is formed by the path of main power supply-third capacitor-fifth diode-main power supply.

Therefore, even if the time from power-off to power-on is short, the third capacitor is surely discharged, and when power is turned on again, the output voltage of the smoothing capacitor of the sub-power supply circuit is not lowered. It can be surely started by the divided voltage of the main power source.

The switching power supply device according to the invention of claim 6 is characterized in that the first control switching element is controlled by using a charging voltage of a smoothing capacitor of the sub power supply circuit.

According to the above construction, when the smoothing capacitor of the sub power supply circuit is charged through the impedance element such as the choke coil, the charging voltage is equal to the secondary side output current. Since the value corresponds to the value, it is possible to determine the lightness of the load from the charging voltage and control the first control switching element.

Therefore, it is not necessary to provide a special configuration for detecting the operation mode of the on-board equipment, and it is possible to automatically control the first control switching element by judging the load lightness only on the primary side. Therefore, the cost can be reduced.

In the switching power supply device according to the present invention, the voltage detection circuit detects the secondary side output voltage of the transformer,
In the switching power supply device in which the main switching element switches the primary current of the transformer in response to the detection result to obtain a desired secondary current of a constant voltage, between the secondary output lines. A second control switching element for timing control, which is interposed in series with the voltage detection circuit, and a bias circuit for applying the output of the secondary auxiliary winding of the transformer to the control terminal of the second control switching element. It may be configured .

According to the above configuration, when the output voltage is induced on the secondary side, the bias voltage is applied to the control terminal of the switching element by the bias circuit, and the voltage detection circuit is connected between the secondary side output lines. It

Therefore, the voltage detection circuit can be activated only for the minimum period necessary for detecting the secondary side output voltage, and the power consumption of the voltage detection circuit including the light emitting diode of the photocoupler and the voltage dividing resistor can be reduced. Can be reduced
The power conversion efficiency can be improved.

[0049]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows an RC according to the first embodiment of the present invention.
3 is an electric circuit diagram of a C type switching power supply device 11. FIG. A direct current obtained by rectifying commercial alternating current by a main power supply circuit (not shown) is input between the input terminals P1 and P2. The DC current is smoothed by the smoothing capacitor C11, and the smoothing capacitor C11 outputs a main power supply voltage between the main power supply line 12 on the high level side and the main power supply line 13 on the low level side.

A series circuit of the primary main winding N11 of the transformer N and the main switching element Q is connected between the main power supply lines 12 and 13. The main switching element Q
Is realized by, for example, a bipolar transistor, a field effect transistor, or the like. In the example of FIG. 1, the field effect transistor is shown. The main power line 12,
In addition, the capacitor C2 and the voltage dividing resistors R3 to R
5 and a starting circuit 14 composed of a diode D4 are connected.

When the power is turned on, that is, the power supply voltage is applied between the input terminals P1 and P2, the output voltage of the smoothing capacitor C11, that is, the main power supply voltage rises, and the voltage dividing resistors R4 and R5 of the starting circuit 14 thereof. When the voltage division value between them becomes the threshold voltage Vth of the main switching element Q, for example, 3 V or more, the main switching element Q turns on and the primary main winding N
11, the voltage in the upward direction in FIG. 1 is applied,
Excitation energy is stored. As will be described later, when the main switching element Q is turned off, an upward voltage is induced in the secondary main winding N21 by the excitation energy. Further, at the time of this off, the vibration generated by the leakage inductance between the primary main winding N11 and other windings N12, N13, N21, N22 described later is parallel to the drain-source of the main switching element Q. Is provided,
It is absorbed and removed by the snubber circuit 15 formed of a series circuit of the resistor R11 and the capacitor C12.

The direct current induced in the secondary main winding N21 passes through the diode D12 and the smoothing capacitor C13.
To the output terminal P3 via the output power supply lines 16 and 17, after being smoothed by the smoothing capacitor C13.
Output from P4 to a load circuit (not shown). A voltage detection circuit 18 is interposed between the output power supply lines 16 and 17. The voltage detection circuit 18 is configured to include a voltage dividing resistor, a photocoupler PC1 and the like, and the light emitting diode D13 of the photocoupler PC1 is driven to light at a brightness corresponding to the output voltage, and the value of the output voltage is changed. 1
Feedback to the next side.

In the control winding N12, when the main switching element Q is on, a voltage is induced in the same upward direction as the primary main winding N11, and the induced current flows through the DC cut capacitor C1 and the bias resistor R2. Is applied to the gate of the main switching element Q via the gate, thereby further raising the gate potential of the main switching element Q, and the main switching element Q is maintained in the on state.

Further, the current induced in the control winding N12 when the main switching element Q is turned on is transmitted from the capacitor C1 and the bias resistor R2 to the photocoupler P2.
It is given to one terminal of the capacitor C14 via the phototransistor TR11 of C1. This capacitor C
The other terminal of 14 is the low-level main power supply line 1
Therefore, as the secondary side output voltage becomes higher than a predetermined set voltage, the charging current increases,
The terminal voltage of the capacitor C14 rises quickly. The charging voltage of the capacitor C14 is the main switching element Q.
Control transistor TR interposed between the gate and source of
When the output voltage reaches the threshold voltage of the control transistor TR12, for example, 0.6 V or more, the control transistor TR12 becomes conductive, and the gate potential of the main switching element Q rapidly decreases. , The main switching element Q is driven off.

Therefore, as the secondary side output voltage becomes higher than the set voltage, that is, as the load becomes lighter, the charging voltage of the capacitor C14 rises faster, the main switching element Q is driven off faster, and the set voltage becomes higher. The lower the value, that is, the heavier the load, the longer the charging time of the capacitor C14 and the longer the on time of the main switching element Q. The capacitor C14 also has a control winding N
The current induced by 12 is given through the resistor R12. Thus, even if the output voltage of the smoothing capacitor C13 on the secondary side is low due to a short circuit between the output terminals P3 and P4, the on period of the main switching element Q is limited to a predetermined period, and the main switching element Q is protected. Has been planned.

In the control winding N12, the number of turns of the control winding N12 and the secondary main winding N21 is the same as the reference numeral, and when the secondary side output voltage is Vo, the main switching element Q Is turned off, in the downward direction of FIG.
A voltage of (N12 / N21) Vo is induced, whereby the charge of the capacitor C14 is extracted, and the reset operation for the next on operation of the main switching element Q is performed.

After turning off the main switching element Q, 1
When the output of the excitation energy accumulated in the next main winding N11 to the secondary side ends, ringing occurs mainly between the parasitic capacitance C15 of the control winding N12 and the control winding N12, and Voltage (N12 / N21) on parasitic capacitance C15
The electrostatic energy accumulated at Vo is released, converted into the excitation energy of the control winding N12 after ¼ cycle of vibration, and thereafter, in order to charge the parasitic capacitance C15 again,
An upward electromotive voltage of the voltage (N12 / N21) Vo is generated in the control winding N12. The electromotive voltage that is a ringing pulse is set to be equal to or higher than the threshold voltage Vth of the main switching element Q, and the electromotive voltage turns on the main switching element Q again. In this way, automatically, the main switching element Q is continuously driven on / off at the switching frequency corresponding to the load, and the desired secondary output voltage is output.

The switching power supply device 11 of the present invention includes:
When a device equipped with the switching power supply device 11 is in a non-standby state and is under heavy load, the normal R as described above is used.
In addition to the configuration for performing CC operation, the following configuration is provided to reduce the switching frequency when the mounted device is in a standby state and at a light load. From the device side, a control signal is given to the control terminal P5. The control terminal P5 and the output power line 17 on the low level side
Between the light emitting diode D1 of the photocoupler PC2
4 and the resistor R13 are connected in series. Therefore, when the control signal becomes high level during non-standby,
The light emitting diode D14 is turned on, and the heavy load state is output to the primary side.

On the other hand, on the primary side, between the connection point P6 of the capacitor C1 and the bias resistor R2 and the main power supply line 13 on the low level side, a diode D1 for preventing backflow is provided.
1, a Zener diode D15, a resistor R1, and a control transistor TR1 are connected in series. A power supply voltage from a sub-power supply circuit 19, which will be described later, is divided by the resistor R14 and the phototransistor TR13 of the photocoupler PC2 and applied to the base of the control transistor TR1.

Accordingly, in the non-standby state, the phototransistor TR13 is turned on and the control transistor TR13 is turned on.
1 turns off, and the normal RCC operation as described above is performed without the influence of the series circuit.

On the other hand, in the standby state of the device,
The control signal to the control terminal P5 becomes low level, the light emitting diode D14 turns off, and the phototransistor TR1
3 is turned off, the control transistor TR1 is turned on, and the series circuit is connected between the connection point P6 and the main power supply line 13. The bias resistor R2 is selected to be 680Ω, for example, while the resistor R1 is selected to be 150Ω, for example. Therefore, when the main switching element Q is on, a large amount of current flows in the series circuit while maintaining the main switching element Q in the on state, which causes the capacitor C1 to have a positive charge on the side of the control winding N12 and no electric charge. Accumulate.

Therefore, even if the ringing pulse is generated during standby, the ringing pulse is generated by the capacitor C.
Only the voltage between terminals 1 is reverse-biased and given to the main switching element Q.
On startup is blocked. As a result, in the switching power supply device 11 of the present invention, the switching power supply device 11 of the present invention is substantially different from the above-described conventional switching power supply device 1 in that a simple configuration of the resistor R1 and the control transistor TR1 is added. A switching frequency of about 80 kHz is 4 in the switching power supply device 1 during standby.
The switching power supply device 11 of the present invention can be lowered to about several kHz, whereas the power conversion efficiency in the standby mode can be significantly increased, while it has been increased to 100 to 500 kHz.

Further, in the present invention, the transformer N is provided with a sub power supply winding N13. The sub power supply winding N1
Similarly to the secondary main winding N21, a voltage is induced in the upper direction of the main switching element Q when the main switching element Q is off, and the voltage is applied to the diode 3 by the diode D16 and the smoothing capacitor C16.
After being smoothed by the sub power supply circuit 19 consisting of
It is output for driving the control transistor TR1 via the resistor R14, and is also a diode D1 for preventing backflow.
Is output to the connection point P7 between the voltage dividing resistors R3 and R4 of the starting circuit 14. Correspondingly, the capacitor C2 is provided in the starting circuit 14.

Therefore, when the power is turned on when the voltage across the terminals of the capacitor C2 is substantially zero, the voltage divided by the voltage dividing resistors R3 to R5 of the main power supply voltage of, for example, several hundred V is applied to the gate of the main switching element Q. Will be given.

On the other hand, when a predetermined time elapses after the power is turned on, the capacitor C16 is charged to a predetermined power supply voltage, for example, about 10 V, and the capacitor C16 is charged.
2 is charged to a voltage substantially corresponding to the difference between the main power supply voltage and the output voltage of the sub power supply circuit 19. Therefore, as described above, the main switching element Q is not activated by the ringing pulse in the standby state, and the activation circuit 14 is activated.
Even when the voltage for starting up is output from the above, it is possible to prevent the current from flowing from the main power source side to the voltage dividing resistors R3 to R5, and to make the main switching element Q have a relatively low voltage. It can be driven by the divided voltage of the output voltage of the sub power supply circuit 19. As a result, power consumption by the voltage dividing resistors R3 to R5 can be reduced, and higher efficiency can be achieved.

The capacitor C2 and the voltage dividing resistor R
Connection point P8 with the main power supply line 13 on the low level side
A discharge diode D4 is provided in parallel with the voltage dividing resistors R3 to R5 and in the reverse bias direction. Therefore, when the main power supply voltage drops, the smoothing capacitor C11-the main power supply line 13-the voltage dividing resistor R5.
~ R3-capacitor C2-main power line 12-smoothing capacitor C11-with the path of the smoothing capacitor C11-
Main power supply line 13-Diode D4-Capacitor C2-
A discharge path of the capacitor C2 is formed by the path of the main power supply line 12 and the smoothing capacitor C11. by this,
Even if the time from power-off to power-on is short, the capacitor C2 can be surely discharged, the potential of the connection point P8 can be raised almost equal to the main power supply voltage, and the main switching element Q can be reliably started. it can.

Furthermore, in the present invention, the transformer N is provided with a secondary auxiliary winding N22. A control transistor TR2 is interposed in series with the voltage detection circuit 18 between the output power supply lines 16 and 17 in relation to the secondary sub winding N22. The secondary auxiliary winding N22 includes
As with the control winding N12, the main switching element Q is turned on.
A voltage is sometimes induced, and the voltage is given to the base of the control transistor TR2 via the bias circuit of the diode D17 and the resistor R15. The base of the control transistor TR2 is also connected to the output power line 17 on the low level side via the resistor R16.

Therefore, the main switching element Q is turned on.
The voltage detection circuit 18 can be activated only during the period during which the detection data is required for control, and power consumption by the light emitting diode D13 and the voltage dividing resistor of the photocoupler PC1 can be reduced. Therefore, the power conversion efficiency can be further improved.

2 and 3 are waveform charts for explaining the operation of the switching power supply device 11 configured as described above. 2 shows a standby state, and FIG. 3 shows a non-standby state. In both figures, (a) represents the drain-source voltage of the main switching element Q, (b) represents the potential at the connection point P6 between the resistor R2 and the capacitor C1, and
(C) represents the gate-source voltage of the main switching element Q.

Referring to FIG. 2, at time t0, the gate-source voltage of the main switching element Q changes to the threshold voltage Vt.
When reaching h, the main switching element Q is turned on.
As a result, the drain-source voltage of the main switching element Q becomes zero. Further, since a current is injected from the control winding N12 into the gate of the main switching element Q via the capacitor C1 and the bias resistor R2, the gate voltage of the main switching element Q is the stray capacitance of the main switching element Q. And the bias resistance R2 causes the gate current to be integrated to increase. Furthermore, a current also flows from the connection point P6 to the control transistor TR1 side, the capacitor C1 is charged with a large charging current, and the voltage across the terminals thereof increases. Therefore, the potential at the connection point P6 becomes the time t0. It suddenly rises and then descends.

At time t1, when the control transistor TR12 is turned on, the gate voltage of the main switching element Q sharply drops and the main switching element Q turns off.
To do. At this time, the potential at the connection point P6 is equal to the control winding N
This is the sum of the negative voltage induced by 12 and the charging voltage of the capacitor C1, which is significantly lower than that under heavy load. After that, the excitation energy is discharged over the period T2, and the charge stored in the capacitor C1 is gradually discharged through the voltage dividing resistor R5 having a high resistance value, and the potential at the connection point P6 gradually rises. Go on.

At the time t2, when the release of the excitation energy is completed, ringing occurs over the period T3 until the time t3. However, due to the reverse bias of the capacitor C1, the threshold voltage Vth is not reached even with the peak value of the ringing pulse, and the operation is suspended for the period T4 after the time t3.

After the time t2, the capacitor C
1-Control winding N12-Main power supply line 13-Voltage dividing resistor R5
-The path of the bias resistor R2-the capacitor C1, the path of the capacitor C1-the control winding N12, the smoothing capacitor 16-the diode D1-the voltage dividing resistor R4-the bias resistor R2-the capacitor C1, and the discharge of the capacitor C1 and the reverse direction Charging is done. However, since the voltage dividing resistors R4 and R5 have high resistance, the charging / discharging proceeds slowly, and the gate voltage of the main switching element Q and the potential at the connection point P6 gradually rise. After that, again at time t0
In, when the gate voltage reaches the threshold voltage Vth, the main switching element Q is turned on, and the same operation as described above is performed.

On the other hand, in the non-standby state, referring to FIG.
The on period T of the main switching element Q is from time t0 to t1.
1, the period from time t1 to t2 is the exciting energy emission period T2, and the period from time t2 to t0 is the ringing occurrence period T3. Therefore, the main switching element Q is driven on by the ringing pulse.

As described above, by changing the resistance value of the resistor R1, it is possible to change the charging voltage of the capacitor C1 when the main switching element Q is on, that is, the reverse bias voltage, and the voltage dividing resistor R4. , R5, the charge and discharge currents in the two paths can be changed, and the gate voltage of the main switching element Q and the slope of the potential rise at the connection point P6, and thus the switching frequency, can be changed. be able to.

For example, when the required power during standby is large, the resistance values of the voltage dividing resistors R4 and R5 are reduced to reduce the charging / discharging time constants during the idle periods T3 and T4, whereby the main switching element is reduced. The gate-source voltage of Q quickly reaches the threshold voltage Vth, and the switching cycle can be shortened, so that the switching frequency can be increased. On the other hand, when the required power is small, the switching frequency can be lowered by increasing the resistance values of the voltage dividing resistors R4 and R5. Further, when the pause period becomes too long and the switching frequency overlaps with the audible frequency range, the capacitance value of the capacitor C14 is decreased and the resistance value of the resistor R12 is decreased to reduce the charging voltage of the capacitor C14. By shortening the on period of the main switching element Q so that the excitation energy stored in the transformer N can be reduced for each switching operation, and the switching noise can be kept below the audible level. can do.

Here, the resistance values of the voltage dividing resistors R3 to R5 can be determined as follows. When the input voltage to the input terminals P1 and P2 is Vin, the output voltage of the smoothing capacitor C16, that is, the sub-power supply circuit 19 is Vs, and the resistance values of the voltage dividing resistors R3 to R5 are indicated by the same reference numerals, the power is turned on. At the start of operation by Vin × [R5 / (R3 + R4 + R5)]> Vth (1) During steady operation in the standby state Vs × [R5 / (R4 + R5)]> Vth (2) Further, the Zener diode D15 is in the standby state. When the control transistor TR1 is turned on, the resistance value of the voltage dividing resistor R5 becomes the value of the series circuit of the bias resistor R2 and the resistor R1 and the parallel circuit of the voltage dividing resistor R5 in the above equations 1 and 2. This is a Zener diode for compensation provided in order to prevent that these Equations 1 and 2 cannot be satisfied. Therefore, the Zener voltage is selected to be equal to or higher than the threshold voltage Vth and equal to or lower than the induced voltage of the control winding N12 when the main switching element Q is on. However, if the above formulas 1 and 2 can be satisfied even in the standby state according to the design specifications, the Zener diode D15 may be deleted, that is, the diode D11 and the resistor R1 may be short-circuited. .

Furthermore, a diode D1 for preventing backflow is provided.
1 is off of the main switching element Q during standby
At the time, that is, during the period T2 to T4 in FIG. 2, the control transistor TR1-resistor R1-zener diode D
It is provided to prevent a current from flowing through the connection point P6 along the path of 15 and release of the negative bias to the gate of the main switching element Q.

Therefore, for example, the supply of the base current to the control transistor TR1 is stopped except during the on period T1 of the main switching element Q, and the base current is pulled out during the remaining off periods T2 to T4. By devising the base current supply circuit, the off period T
When it is possible to reliably prevent the current flowing through the path from 2 to T4, the backflow prevention diode D11 can be omitted.

A control transistor TR2 is inserted in series with the voltage detection circuit 18 between the output power supply lines 16 and 17, and the voltage induced in the secondary auxiliary winding N22 is passed through the diode D17 and the resistors R15 and R16. The switching power supply device 1 has a configuration in which the voltage detection circuit 18 is activated only during a period in which detection data is required for control by applying the voltage to the base of the control transistor TR2.
The present invention is not limited to the RCC type switching power supply device such as No. 1 and can be suitably used as a method for reducing power consumption in a switching power supply device of another system such as the PWM system described above.

FIG. 4 shows the second embodiment of the present invention.
The explanation is based on the following.

FIG. 4 is an electric circuit diagram of the switching power supply device 21 according to the second embodiment of the present invention. This switching power supply device 21 corresponds to the switching power supply device 1 described above.
Similar to 1 and corresponding parts are designated by the same reference numerals, and description thereof will be omitted. It should be noted that the switching power supply device 21 has a modified starter circuit. Instead of the capacitor C2 in the starter circuit 14 described above, the starter circuit 14a includes a transistor TR14 and a resistor R2.
6 and a capacitor C3 are used.

The PNP transistor TR14 constitutes a series circuit together with the voltage dividing resistors R3 to R5, and is interposed between the main power supply lines 12 and 13. This transistor T
The emitter of R14 is the main power line 12 on the high level side.
, The collector is connected to the voltage dividing resistor R3, and the base is connected to the main power supply line 13 on the low level side via the series circuit of the resistor R6 and the capacitor C3. A connection point P9 between the resistor R6 and the capacitor C3 is connected to the main power supply line 12 on the high level side via a discharging diode D5 similar to the diode D4.

Therefore, when the power is turned on and the main power supply voltage is applied, the base of the transistor TR14 is biased to approximately 0V by the discharged capacitor C3, the transistor TR14 is turned on, and the above equation 1 is applied.
As shown by, the divided voltage of the main power supply voltage Vin can be applied to the gate of the main switching element Q to turn on the main switching element Q. At the same time when the power is turned on, the charging of the capacitor C3 is started, and the sub power supply circuit 1
After the elapse of the predetermined time in which the smoothing capacitor C16 in 9 is charged to a predetermined charging voltage, the voltage across the terminals of the capacitor C3 is substantially equal to the main power supply voltage. As a result, the transistor TR14 is turned off,
In the standby state, the main switching element Q continues to be turned on by the divided voltage of the charging voltage of the smoothing capacitor C16 as described above.

When the power is cut off, the smoothing capacitor C1
1, the smoothing capacitor C11-
Main power supply line 13-Capacitor C3-Diode D5-
A discharge path of the capacitor C3 is formed by the path of the main power supply line 12 and the smoothing capacitor C11, and the reset operation as described above is performed in preparation for the re-input of power.

In the start-up circuit 14a thus constructed, when the current amplification factor of the transistor TR14 is set to hfe, the capacitance of the capacitor C3 is set to the above-mentioned capacitor C2.
Can be made 1 / hfe, and the capacitor in the starting circuit can be miniaturized.

FIG. 5 shows the third embodiment of the present invention.
The following is a description based on FIG.

FIG. 5 is an electric circuit diagram of a switching power supply device 31 according to the third embodiment of the present invention. This switching power supply device 31 is similar to the switching power supply devices 11 and 21 described above, and corresponding parts are designated by the same reference numerals and the description thereof will be omitted.

In this switching power supply device 31, the control transistor TR2 in the switching power supply devices 11 and 21 described above and the secondary auxiliary winding N2 for driving the control transistor TR2.
2, the configuration for on / off driving of the voltage detection circuit 18 including the diode D17 and the resistors R15 and R16 is omitted. Therefore, although the power consumption by the voltage detection circuit 18 increases, it is suitable for a low-cost configuration, and the transformer Na of the switching power supply device 31 can also suppress an increase in the number of taps.

Further, in this switching power supply device 31, the sub power supply circuit 19a includes the smoothing capacitor C16.
And two diodes D2 and D3 and choke coil L
And is configured. The diode D2 controls the control winding N12 while the main switching element Q is on.
Extract the induced current from one terminal of the choke coil L
The smoothing capacitor C16 is charged via. The flywheel diode D3 connects the connection point P10 between the choke coil L and the diode D2 to the other terminal of the control winding N12. Therefore, when the main switching element Q is turned off and the polarity direction of the induced voltage in the control winding N12 is reversed, the diode D2 is turned off, and the exciting current in the choke coil L passes through the smoothing capacitor C16 via the flywheel diode D3. To charge. The inductance of the choke coil L is selected so that the exciting current becomes zero by the time when the main switching element is next turned on in the non-standby state.

In the sub power supply circuit 19a thus constructed, the number of taps can be reduced by removing the sub power supply winding N13 from the transformer Na.

In the sub power supply circuit 19, the smoothing capacitor C16 is charged by the flyback method, and the rectified voltage of the sub power supply winding N13 is smoothed by the smoothing capacitor C16.
Since the charging voltage E _O of the smoothing capacitor C16 is not directly influenced by the secondary side output current value, refer to the numbers of turns of the secondary winding N21 and the auxiliary power supply winding N13, respectively. When represented by the same symbols, E _O = Vo × (N13 / N21) ... (3) It becomes a constant value, and the switching frequency during standby does not reflect the influence of the secondary side load fluctuation, and is a substantially constant value. Becomes

On the other hand, in the sub power supply circuit 19a,
Since the smoothing capacitor C16 is charged from the control winding N12 via the choke coil L, the charging voltage E
_O increases as the secondary-side output current value increases, that is, as the on period of the main switching element Q increases, and the switching frequency can be increased.

That is, the control transistor TR1 is turned on.
When the switching operation of the main switching element Q in the state where the load is relatively light is shown in FIG. 6A in the standby state, when the load becomes a little heavy, in the switching power supply devices 11 and 21, the smoothing capacitor Since C16 is directly charged by the rectified voltage of the sub power supply winding N13 and the charging voltage E _O has a constant value shown in the above Expression 3, the switching frequency remains constant and the on period becomes long. Eventually,
When the on period is limited by the resistor R12 as shown in FIG. 6 (b), even if the load becomes heavier than that, it cannot be dealt with.

On the other hand, in the switching power supply device 31, since the smoothing capacitor C16 is charged with the voltage of the output voltage of the control winding N12 through the choke coil L, the charging voltage E _O will be described in detail below. As I said, 2
The larger the secondary output current value is, the higher it becomes, and as shown in FIG. 6C, until the period limited by the resistor R12, o
As the n period becomes longer, the switching frequency also increases. Therefore, it is possible to cope with the load fluctuation even during standby.

FIG. 7 is an equivalent circuit diagram for explaining the operation of sub power supply circuit 19a. In FIG. 7, the starting circuit 14, the control transistor TR12 and the resistor R14 which consume current are represented by a constant resistance R _O , and the consumed current is I _O.
It is represented by. The positive pulse from the control winding N12, that is, the output time of the pulse in the forward direction to the diode D2 in FIG. 7, is T _IN , its voltage value is E _IN, and the switching cycle of the main switching element Q is T _S , When the charging voltage of the smoothing capacitor C16 is E _O , the current I flowing into the smoothing capacitor C16 via the pulse E _IN generated in the control winding N12 and the choke coil L.
_L becomes as shown in FIG. 8, and the average value I _LAV of the current I _L can be obtained from the following equation when the inductance of the choke coil L is represented by the same reference numeral.

[0098]

[Equation 1]

On the other hand, from the smoothing capacitor C16 to the constant resistance R
_The current I _O flowing out to _O is I _O = E _O / R _O (5), and I _LAV = I _O in the state where the charging voltage E _O of the smoothing capacitor C16 is stable. From 4, 5

[0100]

[Equation 2]

It becomes

Therefore, the main switching element Q is turned on.
It is understood that the charging voltage E _O of the smoothing capacitor C16 rises as the period T _IN during which the charging is performed increases.
Thus, as described above, the larger the secondary side output current value is,
The n period becomes longer, the switching frequency also increases, and it is possible to cope with load fluctuation even during standby.

In the above description, as shown in FIG. 8, the choke coil L is supplied during the off period of the positive pulse of the control winding N12.
Although the current flowing through the indicates a case disappear, so even if you do not disappear, the charging voltage E _O of the smoothing capacitor C16 in accordance with the load increase is increased.

FIG. 9 shows the fourth embodiment of the present invention.
The explanation is based on the following.

FIG. 9 is an electric circuit diagram of a switching power supply device 41 according to the fourth embodiment of the present invention. This switching power supply device 41 corresponds to the switching power supply device 3 described above.
Similar to 1 and corresponding parts are designated by the same reference numerals, and description thereof will be omitted. This switching power supply 4
In No. 1, paying attention to the fact that the smoothing capacitor C16 of the sub power supply circuit 19a of the switching power supply device 31 is charged to the voltage corresponding to the secondary side output current value, and the control is performed based on the output voltage of the smoothing capacitor C16. Transistor T
R1 is on / off driven.

That is, the base of the control transistor TR1 is the phototransistor T of the photocoupler PC2.
Instead of R13, it is connected to the main power supply line 13 on the low level side by a transistor TR15, and the base of the transistor TR15 has a Zener diode D18.
And the smoothing capacitor C16 via a resistor R17.
Output voltage is given.

Therefore, when the load on the secondary side becomes heavy and the charging voltage of the smoothing capacitor C16 becomes high and exceeds the Zener voltage of the Zener diode D18, the transistor T
A current flows through the base of R15 and the transistor TR15
Turns on. As a result, the base of the transistor TR1 becomes low level, and the transistor TR1 turns off.
Then, the operation is performed in the normal operation mode in the non-standby state.

On the other hand, when the load on the secondary side becomes lighter and the charging voltage becomes lower than the Zener voltage, the base current of the transistor TR15 becomes zero, and the transistor T15 becomes lower.
R15 is turned off, whereby the base of the transistor TR1 is biased by the resistor R14, the transistor TR1 is turned on, and the operation in the standby operation mode can be performed.

In this way, since the lightness of the load can be judged only on the primary side and the control transistor TR1 can be automatically controlled, it is possible to specially detect the operation mode of the mounted equipment such as the control terminal P5. Since it is not necessary to provide such a structure, the cost can be reduced.

[0110]

As described above, the switching power supply device according to the invention of claim 1 is a switching power supply device of the ringing choke converter system, when a heavy load is applied.
The ringing pulse is applied to the control terminal of the main switching element via the first capacitor and the second resistor to perform the normal switching operation to drive the main switching element on.
Even if a ringing pulse is generated by storing charge in the first capacitor by the voltage induced in the control winding at the time of n and the main switching element is turned off and the excitation energy is released, the ringing pulse is generated. Is reverse biased by the charging voltage of the first capacitor to prevent the main switching element from being driven on.

Therefore, at the time of light load, the restart of the main switching element due to the ringing pulse as at the time of heavy load is stopped, and when the main switching element once performs the switching operation at the time of the light load, the next switching operation is the power supply. The switching frequency of the main switching element can be lowered by gradually performing the same operation as when the switching element is turned on.
As a result, it is possible to suppress the loss that increases in proportion to the switching frequency, such as the power required to extract the charge accumulated in the drain-source stray capacitance, and obtain a high power conversion efficiency even at a light load.

Further, in order to reduce such a decrease in the switching frequency at the time of a light load, a second resistor for making a high impedance between the first capacitor and the main switching element, and the first capacitor are provided. It can be realized by a simple configuration with a series circuit including a first resistor and a first control switching element that connect a connection point with a second resistor to a main power supply line, and a low cost configuration can be realized. You can

Further, as described above, the switching power supply device according to the second aspect of the present invention is configured such that the second capacitor and the third to third capacitors are provided from the time when the power is turned on until the predetermined time elapses.
The main switching element is turned on by the divided voltage of the main power supply voltage by the starting circuit including a series circuit with the fifth resistor.
When the output voltage of the smoothing capacitor of the sub power supply circuit becomes a voltage sufficient for starting the main switching element after a predetermined time has elapsed since the power was turned on, the main switching element is activated by the divided voltage of the sub power supply circuit. At the same time as turning on, the inflow of current from the main power supply is blocked by a voltage that substantially corresponds to the difference between the main power supply voltage generated in the second capacitor and the output voltage of the sub power supply circuit.

Therefore, as described in claim 1, the restarting of the main switching element is performed in the same manner as when the power is turned on.
Even when the main power supply voltage is divided by the fifth resistor, the main switching element is turned on by the divided voltage of the main power supply voltage having a relatively high voltage only when the power is turned on.
After the predetermined time has passed, the main switching element is turned on by the divided voltage of the output voltage of the sub power supply circuit having a relatively low voltage, so that the third to fifth voltage dividing resistors are activated.
The power consumption due to the resistance can be reduced, and the efficiency can be further improved.

Furthermore, in the switching power supply device according to the invention of claim 3, as described above, from the power-on to the elapse of a predetermined time, the second capacitor and
A smoothing capacitor of the sub-power supply circuit is activated by turning on the main switching element by the divided voltage of the main power-supply voltage by a start-up circuit composed of a series circuit with third to fifth resistors, and a predetermined time has elapsed since the power was turned on. When the output voltage of the main switching element becomes a voltage sufficient to start the main switching element, the main switching element is turned on by the divided voltage of the sub power supply circuit, and the main power supply voltage and the sub power supply generated in the second capacitor. The voltage corresponding to the difference from the output voltage of the circuit blocks the inflow of current from the main power supply.

Therefore, as described in claim 1, the restarting of the main switching element is performed in the same manner as when the power is turned on.
Even when the main power supply voltage is divided by the fifth resistor, the main switching element is turned on by the divided voltage of the main power supply voltage having a relatively high voltage only when the power is turned on.
After the predetermined time has passed, the main switching element is turned on by the divided voltage of the output voltage of the sub power supply circuit having a relatively low voltage, so that the third to fifth voltage dividing resistors are activated.
The power consumption due to the resistance can be reduced, and the efficiency can be further improved.

In the sub power supply circuit, the smoothing capacitor is charged through the second diode and the choke coil while the main switching element is on.
When the main switching element is turned off, the smoothing capacitor is charged by the exciting current from the choke coil via the flywheel diode.

Therefore, since the smoothing capacitor is charged via the choke coil L, the smoothing capacitor is affected by the secondary side output current value, and the switching frequency changes corresponding to the secondary side output current value. As a result, it is possible to cope with a large load change when the load is light.
Furthermore, it is not necessary to increase the number of taps of the transformer for supplying power to the sub power supply circuit.

Further, in the switching power supply device according to the invention of claim 4, as described above, by the fourth diode for discharging provided in parallel with the third to fifth resistors and in the reverse bias direction, When the power supply voltage of the main power supply drops after the power supply is cut off, the discharge path of the second capacitor is formed by the path of the main power supply-the fourth diode-second capacitor-main power supply.

Therefore, even if the time from power-off to power-on is short, the second capacitor is surely discharged, and at power-on again, the output voltage of the smoothing capacitor of the sub-power supply circuit which has dropped Instead, it can be surely started by the divided voltage of the main power source.

Furthermore, in the switching power supply device according to the invention of claim 5, as described above, a transistor is provided between one main power supply line and the third resistor instead of the second capacitor, The base of the transistor is connected to the other main power supply line by a series circuit composed of a sixth resistor and a third capacitor, and the connection point between the sixth resistor and the third capacitor is connected to the other of the one main line by a fifth diode. The charging current of the capacitor is set to 1 / hfe.

Therefore, the capacitor can be downsized.

When the power supply voltage of the main power supply drops after the power is cut off, the discharge path of the third capacitor is formed by the main power supply-third capacitor-fifth diode-main power supply path.

Therefore, even if the time from power-off to power-on is short, the third capacitor is surely discharged, and at power-on again, the output voltage of the smoothing capacitor of the sub-power supply circuit is not lowered. It can be surely started by the divided voltage of the main power source.

As described above, in the switching power supply device according to the invention of claim 6, the smoothing capacitor of the sub-power supply circuit is charged through the impedance element such as the choke coil as described in claim 3. In this case, since the charging voltage corresponds to the secondary side output current value, the weight of the load is determined from the charging voltage and the first control switching element is controlled.

Therefore, it is not necessary to provide a special structure for detecting the operation mode of the on-board equipment, and the lightness of the load is judged only on the primary side to automatically control the first control switching element. Therefore, the cost can be reduced.

[0127]

[0128]

[Brief description of drawings]

FIG. 1 is an electric circuit diagram of an RCC type switching power supply device according to a first embodiment of the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the switching power supply device shown in FIG. 1 during standby.

FIG. 3 is a waveform diagram for explaining an operation of the switching power supply device shown in FIG. 1 in a non-standby state.

FIG. 4 is an electric circuit diagram of an RCC type switching power supply device according to a second embodiment of the present invention.

FIG. 5 is an electric circuit diagram of an RCC type switching power supply device according to a third embodiment of the present invention.

FIG. 6 is a diagram for comparing the switching operation of the main switching element when the load changes in the standby state between the switching power supply device shown in FIGS. 1 and 4 and the switching power supply device shown in FIG.

FIG. 7 is an equivalent circuit diagram for explaining the operation of the sub power supply circuit in the switching power supply device shown in FIG.

8 is a waveform diagram for explaining the operation of the switching power supply device shown in FIG.

FIG. 9 is an electric circuit diagram of an RCC type switching power supply device according to a fourth embodiment of the present invention.

FIG. 10 is an electric circuit diagram of a typical prior art switching power supply device of RCC type.

[Explanation of symbols]

11, 21, 31, 41 Switching power supply device 12, 13 Main power supply line 14, 14a Startup circuit 15 Snubber circuit 16, 17 Output power supply line 18 Voltage detection circuit 19, 19a Sub power supply circuit C1 capacitor (first capacitor) C2 capacitor (Second Capacitor) C3 Capacitor (Third Capacitor) C11, C13, C16 Smoothing Capacitor C12, C14 Capacitor C15 Parasitic Capacitance D1 Diode (First Diode) D2 Diode (Second Diode) D3 Flywheel Diode D4 Diode (Fourth diode) D5 Diode (fifth diode) D11, D12, D16, D17 Diodes D13, D14 Light emitting diodes D15, D18 Zener diode L Choke coil N Transformer N11 Primary main winding N12 Control winding N13 Sub power supply winding N21 Secondary main winding N22 Secondary sub winding PC1, PC2 Photo coupler Q Main switching element R1 Resistance (first resistance) R2 Bias resistance (second resistance) R3 Voltage dividing resistance (Third resistance) R4 voltage dividing resistance (fourth resistance) R5 voltage dividing resistance (fifth resistance) R6 resistance (sixth resistance) R11 to R17 resistance TR1 control transistor (first control switching element) TR2 Control transistor (second control switching element) TR11, TR13 Phototransistor TR12 Control transistor TR14, TR15 Transistor

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H02M 3/28 H02M 3/338

Claims (6)

(57) [Claims] 1. A ringing pulse generated in the control winding of the transformer after the excitation energy accumulated in the transformer during the on period of the main switching element is output to the output circuit on the secondary side during the off period. Is fed back to the control terminal of the main switching element via a first DC-cutting capacitor to drive the main switching element on, and a switching power supply device of a ringing choke converter system comprising a first resistor and a first control The series circuit includes a switching element and includes a series circuit connected to the output side of the first capacitor, and a second resistor interposed between the first capacitor and the main switching element. , The first capacitor and the second capacitor
The first control switching element is connected to a resistor and is driven on at a light load, and the voltage is induced by the control winding during the on period of the main switching element at the light load. First
A charge is accumulated in the capacitor of the first capacitor, a reverse bias is generated by the charge of the first capacitor when the ringing pulse is generated, and on-driving of the main switching element is blocked. 2. A series circuit including a second capacitor and third to fifth resistors, which is interposed between main power supply lines and a fourth circuit.
Starter circuit in which a connection point between the resistance of the second resistance and the fifth resistance is connected to a control terminal of the main switching element, an auxiliary power supply winding provided in the transformer, and an output of the auxiliary power supply winding is rectified and smoothed. And a first diode for preventing backflow that gives the output of the sub power supply circuit to the connection point between the third resistor and the fourth resistor, and a predetermined time has elapsed since the power was turned on. Until that time, the main switching element is turned on by the divided voltage of the main power supply voltage by the starter circuit, and after the lapse of the predetermined time from power-on, the main switching is performed by the divided voltage of the sub power supply circuit. The switching power supply device according to claim 1, wherein the element is activated. 3. A series circuit comprising a second capacitor and third to fifth resistors, which is interposed between the main power supply lines and a fourth circuit.
A start-up circuit in which a connection point between the resistance of the second switching element and the fifth resistance is connected to a control terminal of the main switching element, a second diode for extracting an output from one terminal of a control winding of the transformer, A choke coil to which the output of the second diode is given, a smoothing capacitor for smoothing the current passing through the choke coil, and a connection point between the second diode and the choke coil are connected to the other terminal of the control winding. A sub-power supply circuit having a flywheel diode; and a first diode for preventing backflow that gives an output of the sub-power supply circuit to a connection point between the third resistor and the fourth resistor. Until the predetermined time elapses, the main switching element is turned on by the divided voltage of the main power supply voltage by the starter circuit, and the predetermined time is elapsed after the power is turned on. Over after the switching power supply device according to claim 1, characterized in that on activating the main switching element by the divided voltage of the secondary power supply circuit. 4. The switching power supply device according to claim 2, further comprising a fourth diode for discharging provided in parallel with the third to fifth resistors and in the reverse bias direction. 5. A transistor provided between one main power supply line and a third resistor instead of the second capacitor, and a sixth resistor connecting the base of the transistor to the other main power supply line. And a third circuit including a third capacitor, and a fifth diode for discharging, which connects a connection point between the sixth resistor and the third capacitor to the one main power supply line. The switching power supply device according to claim 2 or 3. 6. The switching power supply device according to claim 3, wherein the first control switching element is controlled by using a charging voltage of a smoothing capacitor of the sub power supply circuit.