JP2000014148A - Switching power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized and unexpensive switching power supply device having a high-conversion efficiency. SOLUTION: In a switching power supply device 21 provided with a main switch 4 for switching an input current through an inductive element 2a, and a control circuit 10 for controlling the main switch 4, a DC voltage generated on the basis of energy accumulated in the inductive element 2a by the switching performed by the main switch 4 is supplied to the control circuit 10 as an operating power source through the inductive element 2a.

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 having a control circuit for controlling switching of a main switching element, and more particularly to a switching power supply capable of achieving high conversion efficiency even at a low input voltage. Things.

[0002]

2. Description of the Related Art As a switching power supply device capable of generating a DC voltage of a predetermined voltage based on a low input voltage of this type,
A flyback type power supply device 41 shown in FIG. 6 is conventionally known. The power supply device 41 includes a switching transformer 42 including a primary winding 42a and secondary windings 42b and 42c. The power supply 41
Is supplied to the primary winding 42a of the transformer 42 via the primary winding 42a, the input DC VIN being a low voltage of about 3 to 5 V output from the DC power supply 3 by being turned on / off in accordance with the switching signal SS. F to switch
ET4, a control circuit 10 for controlling the switching of the FET 4 by outputting a switching signal SS to the gate of the FET 4, a diode 9 for supplying the input DC VIN of the DC power supply 3 to the control circuit 10 at startup.
And a resistor 10 for supplying a DC voltage generated by the switching by the FET 4 to the control circuit 10. The power supply device 41 includes a diode 11 and a capacitor 1 on the secondary winding 2b side, which generate an output voltage VO by rectifying and smoothing the induced voltage of the secondary winding 2b.
2, a diode 13 and a capacitor 14 are provided on the secondary winding 2c side to rectify and smooth the induced voltage of the secondary winding 2c to generate a power supply for operating the control circuit 10.

In this power supply device 41, an input DC VIN from a DC power supply 3 is supplied to a control circuit 10 via a diode 9 at the initial stage of operation, so that the control circuit 1
0 starts. Next, the control circuit 10 outputs a high-level switching signal SS to control the FET 4 to be in an ON state, so that a current I11 flows in the primary winding 2a in the direction shown in FIG. In this case, currents in the opposite directions to the currents I12 and I13 shown in FIG. On the other hand, when the control circuit 10 sets the switching signal SS to the low level to control the FET 4 to the off state, the currents I12 and I13 based on the flyback voltages induced in the respective secondary windings 2b and 2c generate the secondary windings 2b and 2c. Is output from each. Thus, the output voltage V rectified and smoothed by the diode 11 and the capacitor 12 is generated.
O is output outside the device. At the same time, a DC voltage V11 rectified and smoothed by the diode 13 and the capacitor 14 is generated by the control circuit 10 via the resistor 43.
Supplied to

In this case, generally, the on-resistance of the FET 4 increases as the voltage value of the switching signal SS, which is the driving voltage, at the high level decreases, so that when the operating power supply of the control circuit 10 is at a low voltage, FET4
The conduction loss is extremely large. On the other hand, the control circuit 1
The voltage value of the switching signal SS output from 0 is determined according to the voltage value of the operating power supply. Therefore, when the control circuit 10 continues to operate using the input DC VIN as the operating power supply even after the start, a large amount of power is always lost by the FET 4. For this reason,
In the power supply device 41, the voltage value of the DC voltage V11 generated based on the induced voltage of the secondary winding 2c is higher than the voltage value of the input DC VIN, and is sufficient to operate the FET 4 with low conduction loss. It is specified in advance so as to have a high voltage. As a result, the conduction loss of the FET 4 can be reduced, thereby improving the conversion efficiency of the entire device.

[0005]

However, the conventional power supply device 41 has the following problems. That is, in the power supply device 41, in order to improve the conversion efficiency of the entire device in a normal state after the switching by the FET 4 is started, the secondary winding 42c as the operating power supply winding of the control circuit 10 is connected to the transformer 42. Rectification
A smoothing diode 13 and a capacitor 14 are provided. For this reason, there is a problem that the size of the device is increased due to the increase in the size of the transformer 42 and the number of components. In particular, in the case of a micro power supply that is built in a small power-saving electronic device or the like and generates a DC power supply of a predetermined voltage by boosting a low voltage of about 3 to 5 V, an increase in the size of the device is a fatal disadvantage. In today's stiff price competition, the secondary winding 2c and the diode 1
There is a problem that an increase in cost due to the arrangement of the capacitor 3 and the capacitor 14 hinders the sales strategy.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and has as its main object to provide a switching power supply device capable of achieving downsizing and cost reduction while maintaining high conversion efficiency. I do.

[0007]

To achieve the above object, a switching power supply according to claim 1 comprises a main switch for switching an input direct current through an inductive element;
A control circuit for controlling the main switch, the control circuit using a DC voltage generated based on energy accumulated in the inductive element by switching by the main switch as an operating power supply via the inductive element. Is supplied.

The switching power supply according to claim 2 is
2. The switching power supply device according to claim 1, further comprising: a unidirectional element that passes a current based on stored energy, and a capacitor that is charged by the current that has passed through the unidirectional element. It is characterized in that it is supplied to a control circuit as power.

The switching power supply according to claim 3 is
3. The switching power supply according to claim 2, further comprising: a field-effect transistor that is connected in parallel with the one-way element and passes a current based on energy stored when the main switch is in an off state to the capacitor. It is characterized by.

The switching power supply according to claim 4 is
4. The switching power supply according to claim 1, wherein the inductive element is a primary winding of a switching transformer.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a switching power supply according to the present invention will be described below with reference to the accompanying drawings. Note that the same components as those of the power supply device 41 are denoted by the same reference numerals, and redundant description will be omitted.

First, a basic configuration of a switching power supply according to the present invention will be described with reference to FIG. As shown in FIG. 1, the power supply device 1 is a flyback type switching power supply device, and includes a switching transformer 2. On the side of the primary winding 2a (corresponding to an inductive element in the present invention) of the transformer 2, an FET 4 corresponding to a main switch in the present invention, a diode 5, a capacitor 6 corresponding to a unidirectional element in the present invention, A resistor 7 is provided and these diodes 5,
The capacitor 6 and the resistor 7 form an RCD clamp circuit for clamping the voltage VA on the cathode side of the diode 5 to a predetermined voltage. A diode 11 and a capacitor 12 are disposed on the secondary winding 2b side of the transformer 2.

In the power supply device 1, the FET 4 is turned on when the switching signal SS input to the gate is controlled to a high level. At this time, the current I1 in the direction shown in FIG. 1 flows through the primary winding 2a of the transformer 2, whereby energy is accumulated in the transformer 2.
Next, the switching signal SS is controlled to a low level, so that the FET 4 is turned off. At this time, on the secondary winding 2b side of the transformer 2, a current I2 in the direction shown in the figure flows through a current path including the secondary winding 2b, the diode 11, the capacitor 12, and the secondary winding 2b.
As a result, the output voltage VO stabilized to the predetermined voltage is output to the outside of the device. At the same time, the primary winding 2 of the transformer 2
The voltage V1 in the direction shown in FIG. In this case, if the high-level duty ratio of the switching signal SS and the voltage of the input DC VIN output from the DC power supply 3 are set to the values D and VIN, respectively, and the forward voltage of the diode 5 is ignored, the diode 5 The voltage VA on the cathode side is expressed by the following equation. VA = VIN / (1-D) formula

If the turn ratio of the primary winding 2a and the secondary winding 2b of the transformer 2 is 1: 1 and the output voltage VO is the value VO, the following equation is established. VO = D · VIN / (1−D) formula The following formula is derived from the formula and the formula. VA = VIN + VO ···········

According to the above equation, the voltage VA on the cathode side of the diode 5 is clamped to the sum of the voltage VIN and the output voltage VO. If the turns ratio of the transformer 2 is N: 1, the voltage VA is clamped to a voltage value obtained by adding a voltage value N times the output voltage VO to the input DC voltage VIN. Accordingly, by supplying the charging voltage of the capacitor 6 charged to the voltage VA to the control circuit for controlling the switching of the FET 4,
The switching signal SS at the time of the high level can be maintained at a high voltage.

The primary winding 2 of the power supply 1 shown in FIG.
The circuit on the side a is equivalent to a boost converter circuit that generates a DC voltage obtained by boosting the input DC VIN as shown in FIG. In this case, the diode 5, the capacitor 6, and the resistor 7 function as an RCD clamp circuit. At this time, the resistor 7 acts as a load circuit for the capacitor 6, and consumes the charging energy of the capacitor 6. Therefore, the resistance 7
Is used as the power supply for operating the control circuit, the voltage VA can be used as the power supply for operating the control circuit without increasing the number of parts. As a result, the conversion efficiency of the device can be improved.

Next, a specific configuration of a switching power supply to which the present invention is applied will be described with reference to FIG. Note that the same components as those of the power supply device 1 and the power supply device 41 are denoted by the same reference numerals, and redundant description will be omitted.

A power supply device 21 shown in FIG. 1 is a flyback switching power supply device of a so-called active clamp system, in which an FET 8 having a built-in body diode 8a is provided in place of the diode 5 in the power supply device 1. . Further, in addition to the configuration of the power supply device 1,
8 and a diode 9 for supplying the input DC VIN to the control circuit 10. A resistor 7 is provided between the drain of the FET 8 and the power input of the control circuit 10. Connected. In FIG. 1, the body diode 4a built in the FET 4 is shown.

In the power supply device 21, at the beginning of the operation start, the input DC VIN from the DC power supply 3 is supplied to the control circuit 10 via the diode 9, so that the control circuit 1
0 starts. Next, the control circuit 10 outputs a high-level switching signal Ss to control the FET 4 to the on state, so that the current I1 in the direction shown in the figure flows through the primary winding 2a of the transformer 2, and at this time, 2 stores energy. Next, the control circuit 10 controls the switching signal SS to a low level and outputs a high level switching signal S1 to the gate of the FET 8. As a result, the FET 4 and the FET 8 are controlled to the off state and the on state, respectively. At this time, the current I2 in the direction shown in FIG.
Flows through a current path composed of the secondary winding 2b, the diode 11, the capacitor 12, and the secondary winding 2b, and an output voltage VO stabilized to a predetermined voltage is output to the outside of the device.

At the same time, on the primary winding 2a side, a current I3 in the direction shown in the figure flows through a current path composed of the primary winding 2a, the source-drain of the FET 8, the capacitor 6, and the primary winding 2a. Thereby, the capacitor 6
The battery is charged to the voltage VA, and the charged voltage is supplied to the power input of the control circuit 10 via the resistor 7. For this reason,
The operating power supply voltage of the control circuit 10 is changed from the voltage VIN to the voltage V
As a result, the high level voltage of the switching signal SS rises to near the voltage VA.
4 is reduced. At this time, the power supply 1 charges the capacitor 6 via the diode 5, whereas the power supply 21 charges the capacitor 6 via the FET 8. Can be reduced. Also, the resistance 7
Since the charging energy of the capacitor 6 that has been lost due to the power is used as an operating power source of the control circuit 10, the charging energy of the capacitor 6 can be effectively used.

Subsequently, when the energy release of the transformer 2 is completed, the current based on the charging energy of the capacitor 6 flows in the opposite direction to the current I3, and the
Is reversely excited. Next, the control circuit 10 controls the switching signal S1 to a low level, thereby
8 is turned off. As a result, a current in a direction opposite to the current I1 flows through a current path including the source-drain of the FET 4, the primary winding 2a, and the DC power supply 3. As a result, the energy stored in the parasitic capacitor (not shown) in the FET 4 is regenerated to the DC power supply 3, so that the voltage between the terminals of the parasitic capacitor is maintained at or near 0V. Next, in this state, the control circuit 10 outputs the high-level switching signal SS to control the FET 4 to the on state. Thereby, a so-called zero volt switch is achieved, and power loss at the time of switching of the FET 4 is reduced. Thereafter, by repeating the above operation, the output voltage VO is continuously generated.

As described above, according to the power supply device 21, the voltage VA clamped to a predetermined voltage on the primary winding 2a side of the transformer 2 is supplied to the control circuit 10 as an operating power supply, thereby providing an input DC VIN. The high-level voltage of the switching signal SS can be maintained at a higher voltage as compared with the case where is used as an operating power supply. As a result, the conduction loss of the FET 4 as the main switch can be reduced, and the conversion efficiency of the entire device can be improved. Further, as compared with the conventional power supply device 41, parts such as the secondary winding 2c for generating the operation power supply of the control circuit 10, the rectifying / smoothing diode 13, and the capacitor 14 can be omitted. ,
The number of parts can be reduced, and the cost and size of the device can be reduced.

The present invention is not limited to the configuration of the power supply 1 and the power supply 21 described above, but can be applied to a switching power supply of another system. For example,
A part of the configuration of the flyback type power supply device 1 shown in FIG. 1 can be modified and applied to the forward type power supply device 31 shown in FIG. In this case, the anode of the diode 11 is connected to the winding start terminal of the secondary winding 2b of the transformer 2 in the power supply device 1, the smoothing choke coil 32 is arranged between the cathode of the diode 11 and the capacitor 12, and the flywheel is connected. What is necessary is just to provide the diode 33 for wheeling. Since the operation of the power supply device 31 is basically based on the difference between the flyback method and the forward method, the same components as those of the power supply devices 1 and 21 are denoted by the same reference numerals, and their configurations and Description of the operation is omitted. Similarly, by changing a part of the configuration of the active power supply device 21 of the flyback type shown in FIG. 2, an active clamp type power supply device of the forward type can be formed.

Further, in the power supply device 21 according to the embodiment of the present invention, the voltage VA is supplied to the control circuit 10 via the resistor 7, but instead of the resistor 7, a switch element such as a diode or an FET is used. Of course, it can be used. Further, other components can be appropriately changed according to the specifications of the switching power supply device. For example, in the embodiment of the present invention, the main switch is an FET.
Although the example using 4 has been described, the present invention is not limited to this, and various switching elements such as transistors can be used. Further, in the embodiment of the present invention, the power supply device using the primary winding 2a of the transformer 2 as the inductive element in the present invention has been described. However, the present invention is not limited to this, and as shown in FIG. Can of course be applied to a boost converter using as an inductive element.

[0025]

As described above, according to the switching power supply of the first aspect, the control circuit uses the DC voltage generated based on the energy accumulated in the inductive element by the switching by the main switch as the operating power supply. By supplying, the high level voltage of the switching signal SS for driving the main switch can be made high, thereby reducing the conduction loss of the main switch and improving the conversion efficiency of the entire device. be able to. Further, since the power supply for operating the control circuit can be generated without using an auxiliary winding or the like, the size and cost of the device can be reduced.

According to the switching power supply device of the second aspect, the capacitor is charged through the one-way element, and the charging voltage is supplied to the control circuit as an operating power supply, so that a very small number of circuit components are provided. Thus, a power supply for operating the control circuit can be generated. In addition, when applied to a boost converter, a power supply for operating a control circuit can be generated only by its components, so that conduction loss of the main switch can be reduced without increasing costs.

Further, according to the switching power supply device of the third aspect, by charging the capacitor via the field effect transistor, the power loss at that time can be reduced.

According to the switching power supply device of the fourth aspect, since the primary winding of the switching transformer provided in the general switching power supply device is used, the switching power supply device is configured without adding another inductive element. As a result, a low-cost and compact switching power supply can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a power supply device 1 having a basic configuration to which the present invention is applied.

FIG. 2 is a circuit diagram of a primary winding 2a side of the power supply device 1.

FIG. 3 is an equivalent circuit diagram of the power supply device 1 in FIG.

FIG. 4 is a circuit diagram of a power supply device 21 according to another embodiment of the present invention.

FIG. 5 is a circuit diagram of a power supply device 31 according to still another embodiment of the present invention.

FIG. 6 is a circuit diagram of a conventional power supply device 41.

[Explanation of symbols]

 Reference Signs List 1 power supply device 2 transformer 2a primary winding 4 FET 5 diode 6 capacitor 7 resistor 8 FET 8a body diode 10 control circuit 21 power supply device 31 power supply device

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H730 BB23 BB43 BB57 DD04 DD41 EE02 EE07 EE08 EE10 FD01 VV01

Claims (4)

[Claims] 1. A switching power supply device comprising: a main switch for switching an input direct current via an inductive element; and a control circuit for controlling the main switch, wherein the inductive element is switched by the main switch. A DC voltage generated based on the energy stored in the control circuit as an operation power supply to the control circuit via the inductive element. 2. A power supply comprising: a one-way element for passing a current based on the stored energy; and a capacitor charged by the current passing through the one-way element. The switching power supply according to claim 1, wherein the switching power supply is supplied to the control circuit. 3. A field effect transistor, which is equivalently connected in parallel with the one-way element and passes a current based on the stored energy to the capacitor when the main switch is in an off state. The switching power supply device according to claim 2, wherein: 4. The switching power supply according to claim 1, wherein the inductive element is a primary winding of a switching transformer.