JP2003319642A - Switching power supply device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a switching power supply device wherein loss which occurs in an auxiliary power circuit is reduced. <P>SOLUTION: The switching power supply device comprises a main circuit portion including a switching element 11 which switches an input voltage Vin supplied to between input terminals 1 and 2 and thereby produces a pulse output and output circuits 12, 13, and 14a which generate output voltages Vo based on the pulse output; a control circuit 17 which controls the switching operation of the switching element 11; and the auxiliary power circuit which extracts an intermediate voltage Vcc1 substantially proportional to the output voltage Vo and generates an operating voltage Vcc2 for the control circuit 17 based thereon. The auxiliary power circuit varies the ratio of the output voltage Vo to the intermediate voltage Vcc1 according to the operating state of the main circuit portion. Thus, loss which occurs in the auxiliary power circuit is effectively reduced. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply device, and more particularly to a switching power supply device having a voltage drooping characteristic.

[0002]

2. Description of the Related Art Conventionally, switching power supply devices have been used in various products such as computers, home electric appliances and automobiles.

FIG. 3 is a circuit diagram of a conventional general switching power supply device.

The conventional switching power supply device shown in FIG.
An input capacitor connected between the input terminals 1 and 2 for reducing the input voltage Vin applied between the input terminals 1 and 2 to generate an output voltage Vo and supplying the output voltage Vo between the output terminals 3 and 4. 10, a switching element 11 and a rectifying element 12 connected in series between the input terminals 1 and 2, an output capacitor 13 connected between the output terminals 3 and 4, and a connection point of the switching element 11 and the rectifying element 12. A transformer 14 having a primary winding 14a (choke coil) connected to the output terminal 3, a diode 15 having an anode connected to one end of a secondary winding 14b of the transformer 14, and a transformer 1
Smoothing capacitor 16 connected between the other end (output terminal 4) of the secondary winding 14b of No. 4 and the cathode of the diode 15.
A control circuit 17 for controlling the switching operation of the switching element 11, a drive circuit 18 for supplying the output of the control circuit 17 to the switching element 11, and a three-terminal regulator 19 for supplying the operating voltage Vcc2 to the control circuit 17. ing.

The secondary winding 14b of the transformer 14, the diode 15, the smoothing capacitor 16 and the three-terminal regulator 1
Reference numeral 9 constitutes an auxiliary power supply circuit 5 for generating the operating voltage Vcc2 of the control circuit 17. As shown in FIG. 3, the three-terminal regulator 19 includes an input terminal 19a, an output terminal 19b, and a reference terminal 19c. Operating voltage Vcc2 between the reference voltage and the reference terminal 19c.
Generate. The operating voltage Vcc2 generated by the auxiliary power supply circuit 5 is applied between the power supply terminal 17a and the ground terminal 17b of the control circuit 17, and the control circuit 17 becomes operable by the operating voltage Vcc2. Generally, an IC (integrated circuit) is used as the control circuit 17, and it becomes operable when a voltage equal to or higher than a predetermined minimum operating voltage Vcc (min) is applied between the power supply terminal 17a and the ground terminal 17b. Therefore, 3 terminal regulator 19
Output voltage (operating voltage Vcc2) is the minimum operating voltage Vc
It is set to be c (min) or more.

The control circuit 17 is further provided with an input terminal 17c and an output terminal 17d.
The output voltage Vo supplied to the input terminal 17c is monitored, and the duty of the control signal s is controlled so that the output voltage Vo becomes a desired voltage. The control signal s is output from the output terminal 17d and supplied to the drive circuit 18. The drive circuit 18 generates a drive signal S based on this, and supplies this to the switching element 11.

Therefore, the switching element 11 can be repeatedly turned on / off with a duty substantially matching the duty of the control signal s, whereby the output voltage Vo can be generated between the output terminals 3 and 4.

Here, the turns ratio of the transformer 14 is determined by the relationship between the output voltage Vo and the operating voltage Vcc2 of the control circuit 17. Specifically, when the number of turns of the primary winding 14a is N1 and the number of turns of the secondary winding 14b is N2, 3
Input terminal 19a of terminal regulator 19 and reference terminal 19
The intermediate voltage Vcc1 applied between the control circuit 1 and the control circuit 1 is Vcc1 = Vo × N2 / N1.
7 operating voltage Vcc2 or higher (strictly speaking, operating voltage Vcc
The winding ratio of the transformer 14 may be determined so that the voltage drops by the 2 + 3 terminal regulator 19).

On the other hand, the switching power supply device may be required to have a characteristic (voltage drooping characteristic) such that the output voltage Vo droops at the time of overcurrent. In this case, in order to ensure that the control circuit 17 operates even when the output voltage Vo droops, the minimum output voltage during drooping is Vo (mi
n), the primary winding 14a and the secondary winding 14b are satisfied so that Vcc2 <Vo (min) × N2 / N1 is satisfied.
It is necessary to set the turns ratio with.

[0010]

However, the primary winding 14a and the secondary winding 14b are set so that Vcc2 <Vo (min) × N2 / N1 is satisfied.
If the winding ratio is set to, the intermediate voltage Vcc1 between the input terminal 19a and the reference terminal 19c becomes extremely high during normal operation, and thus the loss generated in the three-terminal regulator 19 becomes very large. was there.

Specifically, the output voltage Vo at the normal time is
Is 14V, the minimum output voltage Vo (min) when drooping
Is 8 V and the operating voltage Vcc2 of the control circuit 17 is 12 V, it is necessary to set N2 / N1 to 1.5 or more, as is clear from the above formula. Since Vcc1 becomes 21 V or higher, the 3-terminal regulator 19 needs to lower the voltage by 9 V or higher.

As described above, the conventional switching power supply device has a problem that a large loss occurs in the auxiliary power supply circuit 5 during normal operation.

Therefore, an object of the present invention is to provide a switching power supply device in which the loss generated in the auxiliary power supply circuit is reduced.

[0014]

The object of the present invention is to:
Control a switching operation of a main circuit unit including a switching element that generates a pulse output by switching an input voltage supplied between input terminals and an output circuit that generates an output voltage based on the pulse output, and a switching operation of the switching element. Control circuit and an auxiliary power supply circuit that takes out an intermediate voltage substantially proportional to the output voltage and generates an operating voltage of the control circuit based on the intermediate voltage. The auxiliary power supply circuit operates the main circuit section. This is achieved by a switching power supply device characterized in that the ratio of the output voltage and the intermediate voltage is changed according to the state.

A preferred embodiment of the present invention has a voltage droop characteristic.

In a further preferred aspect of the present invention, the auxiliary power supply circuit has a first ratio (intermediate voltage / output voltage) of the output voltage and the intermediate voltage in a normal state.
And the ratio of the output voltage to the intermediate voltage (intermediate voltage / output voltage) is set to a second value different from the first value when the voltage droops.

In a further preferred aspect of the present invention, the second ratio is larger than the first ratio.

[0018] In a further preferred aspect of the present invention, the auxiliary power supply circuit has a secondary winding magnetically coupled to a smoothing inductor included in the output circuit, and the secondary winding is provided based on a voltage generated in the winding. Generate an intermediate voltage.

[0019] In a further preferred aspect of the present invention, the secondary winding includes at least first and second windings connected in series, and the voltage generated in the first winding during the normal time is included. Based on the voltage generated in the first and second windings at the time of the voltage droop, the intermediate voltage is generated.

In a further preferred aspect of the present invention, the operating state of the main circuit portion is determined based on the output voltage.

According to the switching power supply device of the present invention having the above structure, it is possible to effectively suppress the loss generated in the auxiliary power supply circuit.

[0022]

DETAILED DESCRIPTION OF THE INVENTION Referring to the accompanying drawings,
A preferred embodiment of the present invention will be described in detail.

FIG. 1 is a circuit diagram of a switching power supply device 100 according to a preferred embodiment of the present invention. In FIG. 1, the same components as those of the conventional switching power supply device shown in FIG. 3 are designated by the same reference numerals, and overlapping description will be omitted.

As shown in FIG. 1, the switching power supply device 100 according to this embodiment is different from the conventional switching power supply device shown in FIG.
4c is added and the circuit configuration of the auxiliary power supply circuit is changed.

The auxiliary power supply circuit 20 includes the secondary windings 14b and 14c of the transformer 14 and the secondary winding 14b of the transformer 14.
15 having an anode connected to one end (one end of the secondary winding 14c) of the transformer 15 and a smoothing connected between the other end (output terminal 4) of the secondary winding 14b of the transformer 14 and the cathode of the diode 15. 2 of the condenser 16 and the transformer 14
A diode 25 whose anode is connected to the other end of the secondary winding 14c, a smoothing capacitor 26 connected between the other end (output terminal 4) of the secondary winding 14b of the transformer 14 and the cathode of the diode 25, It has a three-terminal regulator 19 and a switching circuit 30.

The three-terminal regulator 19 has the input terminal 19a, the output terminal 19b and the reference terminal 19 as described above.
c, which lowers the intermediate voltage Vcc1 appearing between the input terminal 19a and the reference terminal 19c, and outputs it to the output terminal 17b.
The operating voltage Vcc2 is generated between the reference voltage and the reference terminal 19c. The operating voltage Vcc2 is the power supply terminal 17 of the control circuit 17.
The voltage is applied between a and the ground terminal 17b, and the control circuit 17 becomes operable by the operating voltage Vcc2.
As described above, the output voltage (operating voltage Vcc2) of the three-terminal regulator 19 is the minimum operating voltage Vc of the control circuit 17.
It is set to be c (min) or more.

The switching circuit 30 includes a PNP type transistor 31, an NPN type transistor 32, and a comparator 3.
3, a diode 34 and resistors 40 to 49 and 46 '.

The transistor 31 is connected between the cathode of the diode 25 and the cathode of the diode 15, and the transistor 32 is connected between the base electrode of the transistor and the other end (output terminal 4) of the secondary winding 14b. It is connected to the. A resistor 40 is provided between the base and emitter of the transistor 31, and a resistor 41 is provided between the base electrode of the transistor 31 and the collector electrode of the transistor 32.
Is provided.

The comparator 33 has a non-inverting input terminal (+) and an inverting input terminal (-), and a detection voltage obtained by dividing the operating voltage Vcc2 by the resistors 42 and 43 at the non-inverting input terminal (+). V1 is supplied and inverting input terminal (-)
Is supplied with a detection voltage V2 obtained by dividing the output voltage Vo by the resistors 44 and 45. The detection voltage V1 is a voltage that is obtained by dividing the operating voltage Vcc2, which has been converted to a constant voltage by the three-terminal regulator 19, and is therefore a substantially constant voltage. On the other hand, the detection voltage V2 is a voltage obtained by dividing the output voltage Vo, and therefore decreases when the voltage droops. As for the relationship between the detection voltages V1 and V2, the resistance ratio of the resistors 42 to 45 is selected so that V1 <V2 is normally established.

The output terminal of the comparator 33 is a resistor 46.
It is connected to the output terminal 19b of the three-terminal regulator 19 via. The resistor 46 and the resistor 46 'are resistors used for giving the hysteresis to the comparator 33. Therefore, if there is no need to do so, they may be omitted. Also, the three-terminal regulator 19
Between the output terminal 19b and the reference terminal 19c of the resistor 4
7 to 49 are connected in series, and the resistors 47 and 48 are connected.
The anode of the diode 34 is connected to the connection point of the transistor 32, and the connection point of the resistors 48 and 49 is connected to the transistor 32.
The base electrode of is connected. The cathode of the diode 34 is connected to the output terminal of the comparator 33.

The type of the switching element 11 is not particularly limited, and is a bipolar transistor, FET (field effect transistor), IGBT (insulated gate bipolar transistor), BSIT (bipolar mode static induction transistor), BIMOS (bipolar). Any kind of switching element such as a field effect transistor) or a BJT (bipolar junction type transistor) can be used as long as it can generate a pulse output by switching the input voltage Vin supplied between the input terminals. I don't mind.

Although a diode is generally used as the rectifying element 12, synchronous rectification may be performed by using a switching element having a control electrode such as a bipolar transistor or FET. A portion composed of the rectifying element 12, the primary winding 14a (choke coil) of the transformer 14 and the output capacitor 13 constitutes an output circuit, and generates an output voltage Vo which is a direct current based on the pulse output generated by the switching element 11. To do. In this specification, the switching element 11 and the output circuit (the rectifying element 12, the primary winding 14a, and the output capacitor 1
The part composed of 3) may be referred to as a "main circuit part".

FIG. 2 is a graph showing the voltage drooping characteristic of the switching power supply device 100.

As shown in FIG. 2, when the output current Io is less than or equal to Imax1 (output rated value), the switching power supply device 100 sets the output voltage Vo to a desired constant value (Vo).
When the output current Io exceeds Imax1 (output rated value), the output voltage Vo is drooped down. That is, it has a voltage drooping characteristic. If the output current Io is Imax2 (> Imax1) or less even during voltage droop, the switching power supply device 100 is required to operate normally. The output voltage when the output current Io is Imax2 is Vo (min) as shown in FIG. 2, which is the minimum output voltage.

The operation of the switching power supply device 100 will be described below.

First, in a normal state, the relationship between the detection voltages V1 and V2 is V1 <V2 as described above, so the output of the comparator 33 is at a low level. As a result, the diode 34 is turned on, and its anode voltage drops to the forward voltage of the diode 34. As a result, the transistors 31 and 32 are both turned off, and the intermediate voltage Vcc1 between the input terminal 19a of the three-terminal regulator 19 and the reference terminal 19c.
Is a voltage represented by Vcc1 = Vo × N2 / N1.

On the other hand, when the voltage droops, the detected voltage V
2 decreases, the output voltage Vo decreases below a predetermined value, the relationship between the detection voltages V1 and V2 changes to V1> V2, and the output of the comparator 33 is inverted to a high level. Therefore, the diode 34 is turned off, which turns on both the transistors 31 and 32. That is, the cathode of the diode 25 is connected to the input terminal 19a of the three-terminal regulator 19. Therefore, the intermediate voltage Vcc1 between the input terminal 19a of the three-terminal regulator 19 and the reference terminal 19c is a voltage represented by Vcc1 = Vo × (N2 + N3) / N1. That is, the ratio (Vcc1 / Vo) between the output voltage Vo and the intermediate voltage Vcc1 becomes larger than that in the normal state.

Therefore, when the output voltage value at which the output of the comparator 33 is inverted is Vo2 (<Vo1), Vcc2 <Vo2 × N2 / N1 and Vcc2 <Vo (min) × (N2 + N3) / N1 are satisfied. Primary winding 14a and secondary winding 14
By setting the turns ratio with b and 14c, the operating voltage Vcc2 can be set to a voltage equal to or higher than the minimum operating voltage Vcc (min) in both the normal time and the voltage droop.

In this case, the value of the output voltage Vo2 at which the output of the comparator 33 is inverted is set to the output voltage V2 in the normal state.
If it is set to a value sufficiently close to o1, it is possible to minimize a large loss in the three-terminal regulator 19 in normal times.

Explaining with specific numerical values, the output voltage Vo1 at the normal time is 14V, the output voltage Vo2 at which the output of the comparator 33 is inverted is 12V, the output voltage Vo (min) at the time of droop is 8V, and the control circuit 17 If the operating voltage of Vcc2 is 12V, N2 / N1 is set to 1
The above setting and (N2 + N3) / N1 may be set to 1.5 or more (strictly, it is necessary to consider the drop voltage by the terminal regulator 19). In this case, the intermediate voltage Vcc1 is 12 V or more in the normal time, and 3
While the step-down amount by the terminal regulator 19 can be minimized, the intermediate voltage Vc can be maintained even when the voltage droops.
It is possible to keep c1 at 12 V or higher.

As described above, in the switching power supply device 100 according to the present embodiment, the loss that normally occurs in the auxiliary power supply circuit 20 (three-terminal regulator 19) is greatly suppressed, and even when the voltage droops. The control circuit 17 can be operated normally. Therefore, it is particularly suitable as a switching power supply device that is expected to be frequently operated in an overcurrent state, for example, a switching power supply device for automobiles.

The present invention is not limited to the above embodiments, and various modifications can be made within the scope of the invention described in the claims, and these are also included in the scope of the present invention. It goes without saying that it is a thing.

For example, the circuit shown in FIG. 1 is an example of the switching power supply device to which the present invention can be applied, and the control circuit 17 is obtained by taking out a voltage proportional to the output voltage Vo.
The circuit configuration of the main circuit section is not particularly limited as long as it is a switching power supply device of the type that operates the. Therefore, the present invention can be applied to a switching power supply device having a circuit configuration different from that shown in FIG. 1, such as an insulation type. The present invention can be applied not only to the step-down type switching power supply device but also to the step-up type and step-up / down type switching power supply devices.

In the above embodiment, the switching circuit 30 is used to switch the operating state of the auxiliary power supply circuit 20 in two stages, but it is also possible to switch it in three or more stages. In this case, it is possible to further suppress the loss that occurs in the auxiliary power supply circuit 20 (three-terminal regulator 19).

[0045]

As described above, according to the present invention,
It is possible to significantly suppress the loss generated in the auxiliary power supply circuit 20 during normal operation, and it is possible to operate the control circuit normally even during voltage droop. Therefore, the switching power supply device according to the present invention is particularly suitable as a switching power supply device that is expected to be frequently operated in an overcurrent state, like a switching power supply device for an automobile.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a switching power supply device 100 according to a preferred embodiment of the present invention.

2 is a graph showing a voltage drooping characteristic of the switching power supply device 100. FIG.

FIG. 3 is a circuit diagram of a conventional general switching power supply device.

[Explanation of symbols]

1,2 input terminals 3,4 output terminals 5 Auxiliary power circuit 10 input capacitors 11 Switching element 12 Rectifying element 13 Output capacitor 14 transformers 14a Primary winding 14b, 14c secondary winding 15 diode 16 Smoothing capacitor 17 Control circuit 17a Power terminal 17b Ground terminal 17c input terminal 17d output terminal 18 Drive circuit 19 3-terminal regulator 19a input terminal 19b output terminal 19c Reference terminal 20 Auxiliary power circuit 25 diodes 26 Smoothing capacitor 30 switching circuit 31, 32 transistors 33 Comparator 40-49,46 'resistance 100 switching power supply

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kenichi Aonuma             1-13-1, Nihonbashi, Chuo-ku, Tokyo             -In DC Inc. F-term (reference) 5H730 AA14 AS01 BB03 BB13 DD02                       DD03 DD04 EE02 EE07 FD03                       VV01 XX33 XX49

Claims (7)

[Claims] 1. A main circuit unit including a switching element for generating a pulse output by switching an input voltage supplied between input terminals and an output circuit for generating an output voltage based on the pulse output, and the switching element. A control circuit for controlling the switching operation of, and an auxiliary power supply circuit for taking out an intermediate voltage substantially proportional to the output voltage and generating an operating voltage of the control circuit based on the intermediate voltage, the auxiliary power supply circuit, A switching power supply device, characterized in that a ratio between the output voltage and the intermediate voltage is changed according to an operating state of a main circuit section. 2. The switching power supply device according to claim 1, which has a voltage drooping characteristic. 3. The auxiliary power supply circuit sets the ratio of the output voltage and the intermediate voltage (intermediate voltage / output voltage) to a first value in the normal time, and sets the output voltage to the output voltage during the voltage droop. The switching power supply device according to claim 2, wherein a ratio (intermediate voltage / output voltage) to the intermediate voltage is set to a second value different from the first value. 4. The switching power supply device according to claim 3, wherein the second ratio is larger than the first ratio. 5. The auxiliary power supply circuit has a secondary winding magnetically coupled to a smoothing inductor included in the output circuit,
The switching power supply device according to claim 4, wherein the intermediate voltage is generated based on a voltage generated in the winding. 6. The secondary winding includes at least first and second windings connected in series, and the intermediate voltage is generated based on a voltage generated in the first winding in the normal time. The switching power supply device according to claim 5, wherein the intermediate voltage is generated based on the voltage generated in the first and second windings when the voltage droops. 7. The switching power supply device according to claim 1, wherein the operating state of the main circuit section is determined based on the output voltage.