JP3203922B2 - DC power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power supply used as a power supply for various electronic devices.

[0002]

2. Description of the Related Art In recent years, DC power supplies have been replaced by switching power supplies in accordance with miniaturization of equipment. However, although the basic output circuit of the multi-output DC power supply is stabilized, other outputs are not sufficiently stabilized, so that a dropper circuit is required, but the power loss is large.

Conventionally, this type of DC power supply has been configured as shown in FIG. 3 to solve the above problem. Hereinafter, the configuration will be described.

As shown in FIG. 1, a DC power supply 1 includes a first switching element 2 and a primary winding N of a switching transformer 3.
1 and a rectifying / smoothing circuit 6 composed of a diode 4 and a capacitor 5 is connected to the secondary winding N2 of the switching transformer 3. An auxiliary output circuit 7 is connected to the tertiary winding N3 of the switching transformer 3, and the auxiliary output circuit 7 includes a rectifying / smoothing circuit 11 including a diode 8, a capacitor 9, and a second switching element 10.
The charging circuit 15 includes a reference voltage source 12, an error amplifier 13, and a charging / discharging capacitor 14 connected to the rectifying / smoothing circuit 11. The tertiary winding N3 and the resistor 16 of the switching transformer 3 connected to the charging / discharging capacitor 14. The discharge circuit 17 and the voltage across the charge / discharge capacitor 14
And an auxiliary circuit 18a for driving the switching element 10 of FIG. A voltage detecting circuit 21 including a reference voltage source 19 and an error amplifier 20 is connected to the rectifying / smoothing circuit 6, and the output of the voltage detecting circuit 21 controls the first switching element 2 via a driving circuit 18b. The basic output circuit 22 is configured. Loads 23 and 24 are connected to the basic output circuit 22 and the auxiliary output circuit 7, respectively.
Is set lower than the voltage applied to the load 23 times the turns ratio of the switching transformer 3 (N3 / N2).

The operation of the above configuration will be described.
When the switching element 2 is ON, the switch transformer 3
When the charge / discharge capacitor 14 is discharged through the diode 25 and the resistor 16, the second switching element 10 is turned on and the first switching element 2 is turned off, the secondary winding of the switching transformer 3 is turned on. Since the winding voltage of the line N2 is lower than the voltage applied to the load 23,
The diode 4 becomes non-conductive, and the power stored in the switching transformer 3 is smoothed by the capacitor 9 and supplied to the load 24. The charge / discharge capacitor 14 is charged by the error amplifier 13 through the resistor 26, the second switching element 10 is turned off by the drive circuit 18 a, the power stored in the switching transformer 3 is smoothed by the capacitor 15, When the power supplied and stored in the switching transformer 3 is exhausted, the first switching element 2 is turned on, and the same operation is repeated.

This operation will be described in detail with reference to FIGS. 4 (a) to 4 (e). In FIG. 4 (a), a broken line a indicates that the tertiary winding N3 of the switching transformer 3 when the load 23 is large. The solid line b indicates the voltage of the tertiary winding N3 of the switching transformer 3 when the load 23 is small, and the ON periods of the first switching element 2 are t ₁ and t ₂ , respectively. FIG. 4B shows the charge / discharge capacitor 14.
During the period in which the first switching element 2 is turned on, the diode 25 is turned on and the resistor 1 is turned on.
6, the charge / discharge capacitor 14 is discharged. Here, when the load 23 changes, the first switching element 2
4A, the discharge voltage of the charge / discharge capacitor 14 fluctuates greatly as shown in FIG. 4B. From this state, when the charging of the charge / discharge capacitor 14 is started next (the first switching element 2 is turned off and the diode 25 is also turned off), when the load 23 increases rapidly, FIG. ) Takes the charging characteristic shown by the one-dot chain line c. This is because if the load 24 does not change, the terminal voltage of the load 24 is the same, and the output of the error amplifier 13 is the same, so that the load is charged via the resistor 26. As a result, the drive signal of the second switching element 10 becomes wider than the original signal d, as shown in FIG. Then, the capacitor 9 and the load 24
4 becomes overcharged as shown by the one-dot chain line c in FIG. Therefore, in the next cycle, the state becomes shorter than d in FIG. 4D in order to correct and control this state, and the stability of the control system is poor. Therefore, a resistor 27 and a capacitor 28 are connected between the input terminal and the output terminal of the error amplifier 13 to stabilize the operation of the auxiliary output circuit 7, and a resistor 29 and a capacitor 30 are connected between the input terminal and the output terminal of the error amplifier 20. Thus, the operation of the basic output circuit 22 is stabilized.

When the load 24 of the auxiliary output circuit 7 is close to no load and the charge / discharge current to the charge / discharge capacitor 14 decreases as indicated by a two-dot chain line e in FIG.
Since the drive signal to the switching element 10 is delayed as shown in FIG. 4C, a pulse-like voltage is generated immediately after the first switching element 2 is turned off as shown in FIG. Noise occurs.

The output voltage applied to the load 24 is kept constant by turning on and off the second switching element 10 by the above operation. The output voltage applied to the load 24 is compared with the detected voltage and the reference voltage source 19, amplified and amplified.
The ON period of the first switching element 2 is controlled by the signal fed back to b, and is always kept constant.

[0009]

In the conventional DC power supply as described above, when the load 23 of the basic output circuit 22 fluctuates, the change affects the charge / discharge capacitor 14 of the auxiliary output circuit 7. To reduce the effect, the error amplifier 1
A capacitor and a resistor are required between the input terminal and the output terminal of each of the terminals 3, 20. Also, there is a problem that the ripple voltage of each output voltage becomes large and the response to the load fluctuation is deteriorated. Had the disadvantage of increasing noise.

An object of the present invention is to solve the above-mentioned problems and to provide a DC power supply device that is highly stable, inexpensive, and has little noise.

[0011]

To achieve the above object, the present invention provides a switching transformer in which a series circuit of a DC power supply and a first switching element is connected to a primary winding,
A first connected to a secondary winding of the switching transformer ;
A basic output circuit configured to control the first switching element by detecting an output voltage of the rectifying / smoothing circuit, and a primary output circuit connected to a secondary winding or another winding of the switching transformer.
And a second rectifying / smoothing circuit including a diode, a capacitor, and a second switching element. The auxiliary output circuit is connected to the rectifying / smoothing circuit and includes a reference voltage source. A charging / discharging circuit including an error amplifier and a charging / discharging capacitor; a timing detecting circuit for detecting a period during which the first switching element is conducting from an output voltage of the switching transformer;
A third switching element for discharging the charge / discharge capacitor with an output of the timing detection circuit, and a drive circuit for driving the second switching element by a voltage across the charge / discharge capacitor are provided as means for solving the problem. I have.

[0012]

According to the present invention, the charging / discharging capacitor for controlling the auxiliary output circuit is not affected even when the load of the basic output circuit fluctuates. This eliminates the need for a capacitor and a resistor between the output terminal and the output terminal, thereby reducing the ripple voltage of each output voltage and improving the response to a load change. Further, even when the load on the auxiliary output circuit is small, it is possible to perform stable control with little noise and little loss and no loss.

[0013]

An embodiment of the present invention will be described below with reference to FIG. The same components as those in the above-described conventional example are denoted by the same reference numerals, and description thereof is omitted.

As shown in FIG. 1, the auxiliary output circuit 31 includes a rectifying / smoothing circuit 11, a reference voltage source 12, and a transistor 3.
Error amplifier 34 and charge / discharge capacitor 1
4, the voltage of the tertiary winding N3 of the switching transformer 3 is interposed between the resistors 36 and 37, and the DC component is cut through the capacitor 38 to reduce the resistance of the resistors 39 and 4.
0, a bias voltage is applied, a timing detection circuit 44 detects an on-period of the first switching element 2 by an inverter 41, a resistor 42, and a diode 43; It comprises a third switching element 46 for discharging 14, and a drive circuit 50 having transistors 47, 48 and 49 and driving the second switching element 10 by the voltage across the charge / discharge capacitor 14.

The auxiliary output circuit 31 may be connected to the secondary winding N2 of the switching transformer 3, or may be provided in two or more. The voltage applied to the load 24 is
Of the switching transformer 3 (N3
/ N2) times lower. This is because the voltage of the secondary winding N2 of the switching transformer 3 of the basic output circuit 22 is low while the diode 8 of the auxiliary output circuit 31 and the second switching element 10 are on, so that the diode 4 is turned off. That's why.

In the above configuration, FIGS.
The operation will be described with reference to the first switching element.
When the child 2 is on, power is stored in the switching transformer 3.
available. At that time, a switch as shown in FIG.
The voltage of the tertiary winding N3 of the
And cuts the DC component through the capacitor 38,
When a bias voltage is applied by the resistors 39 and 40, the inverter
The output of 41 shows a voltage of the opposite polarity, and the resistor 42 and the diode
As shown in FIG.
2 (b), the first switching element 2 is turned off.
Only the time period can be detected. Here, the broken line a in FIG.
23 shows a case where the load 23 is large, and a solid line b shows a case where the load 23 is small.
The ON period of the first switching element 2
To t₁, T_TwoAnd And, of the inverter 41
Output to the third switching element 46 via the resistor 45
In addition, as shown in FIG.
The charge / discharge capacitor 14 is discharged. After that,
The capacitor 14 is charged, and the third switching element 4
6 is turned off, and the voltage of the load 24 is lower than that of the reference voltage source 12.
Until the error rises, the error constituted by the transistors 32 and 33
The charging period t of FIG._ThreeDuring charging and discharging
A charging current flows to the capacitor 14. Here, the load 23
Is large and small, the charge / discharge capacitor 14
Charging period t _ThreeIs not affected at all. This is charging and discharging
The capacitor 14 is switched by the third switching element 46
This is because the battery is always discharged to a constant voltage.

This is because even if the load 23 of the basic output circuit 22 changes suddenly, the auxiliary output circuit 31 is not affected, and the whole power supply circuit operates stably. As a result, the error amplifier 2
The filters of 0 and 34 are not required, the ripple voltage is small, and the response to a load change is quick.

Next, the transistor 47 is switched by the voltage across the charge / discharge capacitor 14, and the second switching element 10 is driven by the resistors 51, 52 and the transistors 48, 49 as shown in FIG. Drive with Then, the first switching element 2 is turned off, the second switching element 10 is turned on, and the diode 8 is also turned on. Secondary winding N of switching transformer 3
2 is lower than the voltage applied to the load 23, the diode 4 becomes non-conductive, and the electric power stored in the switching transformer 3 becomes the second switching element 10 and the diode 8 as shown in FIG. Is on, smoothed by the capacitor 9 and supplied to the load 24. When the voltage of the load 24 rises and charging of the charging / discharging capacitor 14 ends, the second switching element 10 turns off, and when the power stored in the switching transformer 3 runs out, the first switching element (2) turns on. And the same operation is repeated.

The output voltage applied to the load 24 is kept constant by turning on and off the second switching element 10 by the above operation. The output voltage applied to the load 23 is compared with the detected voltage and the reference voltage source 19, amplified and amplified.
b, the first switching element 2
Is controlled to be always constant.

[0020]

As is apparent from the above embodiments, according to the present invention, the third switching for discharging the charge / discharge capacitor by the output of the timing detection circuit for detecting the period during which the first switching element is conducting. Since the element is provided, it does not affect the charge / discharge capacitor that controls the auxiliary output circuit even when the load of the basic output circuit fluctuates. As a result, a capacitor is connected between the input terminal and the output terminal of the error amplifier. A resistor is not required, the ripple voltage of each output voltage is reduced, and the response to load fluctuation is improved.Furthermore, even when the load of the auxiliary output circuit is small, a stable and inexpensive DC power supply with less noise and less loss can get.

[Brief description of the drawings]

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

2A to 2F are operation time charts of the DC power supply.

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

4A to 4E are time charts of the DC power supply.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 DC power supply 2 first switching element 3 switching transformer 6 rectifying and smoothing circuit 8 diode 9 capacitor 10 second switching element 11 rectifying and smoothing circuit 12 reference voltage source 14 charge / discharge capacitor 22 basic output circuit 31 auxiliary output circuit 34 error amplifier 35 Charging circuit 44 Timing detection circuit 46 Third switching element 50 Drive circuit N1 Primary winding N2 Secondary winding N3 Tertiary winding

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H02M 3/28 H02J 1/00 306

Claims (1)

(57) [Claims] 1. A switching transformer in which a series circuit of a DC power supply and a first switching element is connected to a primary winding, and a switching transformer connected to a secondary winding of the switching transformer .
A basic output circuit configured to control the first switching element by detecting an output voltage of the first rectifying / smoothing circuit; and an auxiliary connected to at least one secondary winding or another winding of the switching transformer. An output circuit, wherein the auxiliary output circuit is connected to the rectifying / smoothing circuit, the second rectifying / smoothing circuit including a diode, a capacitor, and a second switching element. A charging / discharging circuit including a discharging capacitor; a timing detecting circuit for detecting a period during which the first switching element is conducting from an output voltage of the switching transformer; and discharging the charging / discharging capacitor with an output of the timing detecting circuit. A third switching element to be driven, and a drive for driving the second switching element by a voltage across the charge / discharge capacitor. DC power supply apparatus constituted by the road.