JPH05236743A - Switching power source unit - Google Patents

Abstract

PURPOSE:To stabilize voltage control even against a wide range of load variation. CONSTITUTION:The title power unit has a light load stabilization circuit 50 which incorporates a switch circuit 51 for connecting or separating a dummy load 40 to or from a secondary DC power source 30 and a voltage detection circuit 31 for detecting whether a secondary DC power supply voltage V2 exceeds a set value and is constituted so that the load 40 can be connected to the power source 30 when the voltage V2 exceeds the set value due to a light load and the load 40 can be separated from the power source 30 when the voltage V2 does not exceed the set value.

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.

[0002]

2. Description of the Related Art FIG. 2 shows a general configuration of an RCC type switching power supply device. In the figure, the rectifier circuit 1
1, switching element 12, self-oscillation type voltage control circuit 1
The primary DC power supply 10 having 3 and the like, and the secondary DC power supply 30 having the diode D2, the voltage signal generating circuit 31 and the like,
They are coupled via a pulse transformer 20 having a primary winding CL11 and a secondary winding CL2.

On the primary side of the rectifying circuit 11, a switch 2,
The AC power supply 1 is input via the noise filter 3. C0 on the secondary side is a smoothing capacitor. The other primary winding CL12 of the pulse transformer 20, the diode D1 and the capacitor C1 connected to the primary winding CL12 generate the control power supply Vc of the voltage control circuit 13.

On the other hand, a feedback signal generating circuit 32 for generating a feedback signal Vf is connected to the voltage signal generating circuit 31 on the side of the secondary DC power supply 30. C2
1, C22 are capacitors.

In the RCC type switching power supply device, when the switch 2 is turned on, the control power supply Vc is generated and the voltage control circuit 13 can control the switching element 12 to be turned on and off at a constant duty ratio. The feedback signal Vf is fed back to the voltage control circuit 13 by the cooperation of the voltage signal generation circuit 31 and the feedback signal generation circuit 32.

Therefore, the primary DC power supply voltage V1 and the secondary DC power supply voltage V2 have the relationship shown in FIG. 3, and the amount of power corresponding to the load 100 connected to the secondary DC power supply 30 becomes
1 via pulse transformer 20 (CL11, CL2)
It is supplied from the secondary side to the secondary side.

When the load 100 fluctuates, the self-excited oscillation type voltage control circuit 13 changes the switching element 12 according to the change of the secondary DC power supply voltage V2, that is, the feedback signal Vf.
The secondary DC power supply voltage V2 can be stabilized by changing the ON-OFF cycle time T shown in FIG.
That is, the secondary DC power supply voltage (output voltage) V2 can be stabilized by the self-excited oscillation action.

However, when the load 100 becomes extremely small, the ON-OFF duty ratio is constant, so that the oscillation frequency becomes extremely high as shown in FIG.
Stabilization becomes difficult. The ON-OFF cycle time in this case is T '. Thus, conventionally, the dummy load 40 is connected to the secondary DC power supply 30 side to secure the minimum load necessary for stabilization and suppress the oscillation frequency from rising extremely.

Further, in FIG. 2, the voltage control circuit 13 has a P
In the case of the WM type, as shown in FIG. 5 and FIG.
Since the output voltage is stabilized by changing the OFF duty ratio, the ON duty ratio becomes extremely small at the minimum load, which makes stabilization difficult. Therefore, also in the case of the PWM type voltage control circuit 13, as shown in FIG. 2, the dummy load 40 is connected in order to secure the minimum load necessary for stabilization and prevent the ON duty ratio from becoming extremely small. ing.

[0010]

However, when the difference between the maximum load and the minimum load is large, for example, when it is used as a power supply device for a carrier driving device of a printer, if the dummy load 40 is increased for stabilization at the minimum load. However, it is difficult to save power because the power is constantly consumed, and the power efficiency at the maximum load decreases.

On the other hand, no matter how carefully the size of the dummy load 40 is determined in consideration of the above problems, the dummy load 40 limits the increase of the oscillation frequency and the like, so that the capacitance of the pulse transformer 20 is limited. -The size cannot be reduced, which hinders miniaturization of the device.

An object of the present invention is to provide a switching power supply device which can stabilize the voltage even when the load fluctuates in a wide range, consumes less power, and achieves downsizing of the device.

[0013]

A switching power supply device according to the present invention is a primary DC power supply side primary winding having a voltage control circuit and a secondary DC power supply side secondary winding having a voltage signal generating circuit. In order to stabilize the voltage of the secondary DC power supply while connecting the transformer with the transformer and feeding back the voltage signal from the secondary DC power supply side to the voltage control circuit to ON-OFF control the switching element on the primary DC power supply side. And a switch circuit arranged so that the dummy load can be connected to and separated from the secondary DC power supply.
A voltage detection circuit for detecting whether or not the secondary DC power supply voltage exceeds a set voltage, and connecting a dummy load to the secondary DC power supply when the secondary DC power supply voltage exceeds the set voltage due to a light load, and It is characterized in that a light load stabilizing circuit configured to be separated from the secondary DC power source is provided in other cases.

[0014]

According to the present invention having the above-described structure, when the load is larger than the size capable of stabilizing and controlling the secondary DC power supply voltage, the switch circuit of the light load stabilizing circuit is turned off and the dummy resistor is separated from the secondary DC power supply. ing. Therefore, power consumption by the dummy resistor does not occur. In addition, the power efficiency can be kept high even if the maximum load is exceeded. On the other hand, when the load fluctuates to a light load, the oscillation frequency is high when the voltage control circuit is the self-excited oscillation type, and the ON duty ratio is small when the voltage control circuit is the PWM type and the control becomes unstable, and the secondary DC power supply voltage The voltage rises above the set voltage. Then, the voltage detection circuit detects this and activates the switching circuit to connect the dummy load to the secondary DC power supply side. Therefore, since the load apparently increases, the oscillation frequency becomes low or the ON duty ratio becomes large, so that the control can be stabilized. Since the substantial load in this case is the minimum load, the power consumption is also very small and does not pose a problem.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the present switching power supply device is of the RCC system whose basic configuration is the same as that of the conventional example (FIG. 2 described above), is provided with a light load stabilizing circuit 50, and has a large (small) load 100. In some cases, it is formed so that it can be automatically detected and the dummy load 40 can be separated (connected).

The same or common components as those of the conventional example (FIG. 2) are designated by the same reference numerals, and the description thereof will be simplified or omitted.

In FIG. 1, on the side of the secondary DC power supply 30,
A light load stabilizing circuit 50 including a switch circuit (transistor) 51 connected in series with the dummy load 40 and a voltage detection circuit 52 is provided.

The voltage detection circuit 52 is composed of a Zener diode ZD and voltage dividing resistors R1 and R2. When the voltage exceeds a set voltage, the transistor (51) is turned on, and in the other cases, it is turned off. There is.

Since the dummy load 40 is separated from the secondary DC power source 30 when the load 100 is large,
First, the value of the dummy load 40 can be selected large without considering the problems of increased power consumption at the maximum load and reduced power supply efficiency. Secondly, it is possible to select a small value within a range where control stabilization can be achieved even with respect to the minimum side fluctuation of the load 100. That is, the pulse transformer 20 can be downsized by increasing the oscillation frequency as much as possible.
Therefore, it suffices to appropriately select and determine in consideration of both matters.

In such an RCC type switching power supply device, if the load 100 is large, the light load stabilizing circuit 50 separates the dummy load 40 from the secondary DC power supply 30. on the other hand,
When the load 100 becomes small (light load), the oscillation frequency rises, the control becomes unstable, and the secondary DC power supply voltage V2 rises. Then, when the voltage detection circuit 52 exceeds the set voltage, the transistor (51) is turned on to connect the dummy load 40 to the secondary DC power supply 30. Therefore, since the apparent load (100) increases, the oscillation frequency is suppressed and the secondary DC power supply voltage V2 can be stabilized at a constant level.

According to this embodiment, however, the light load stabilizing circuit 50 consisting of the switching circuit 51 and the voltage detecting circuit 52 is provided, and the load 100 becomes smaller, the oscillation frequency becomes higher, and control stabilization becomes difficult. If dummy resistor 4
Since it is configured to connect 0 and separate it in the other cases, the secondary DC power supply voltage V2 can be stabilized even if there is a minimum to maximum fluctuation of the load 100, and power saving and predetermined power supply efficiency can be maintained. can do.

Further, the dummy load 40 can be selected so as to have the maximum value within the allowable range, because it is not necessary to consider the power consumption at the maximum load and the reduction of the power supply efficiency. Therefore, the control can be further stabilized even with the minimum load. On the other hand, it suffices that the control can be stabilized with the minimum load when the load 100 fluctuates, so that the dummy load 40 is set to the minimum value within the allowable range to maintain the oscillation frequency high, and the pulse transformer 20 can be miniaturized. That is, the applicability is wide.

Further, since the voltage detecting circuit 52 is formed of the Zener diode ZD and the voltage dividing resistors R1 and R2, selection of the set voltage and the like are easy and the applicability is wide and the handling is easy.

The present invention is a PWM type voltage control circuit 1
In case of 3, it is applied as it is.

[0025]

According to the present invention, a light load stabilizing circuit including a switch circuit and a voltage detection circuit is provided on the secondary DC power supply side, and when the load is large, the dummy load is separated and the light load is provided. Since the dummy load is connected to prevent the oscillation frequency from extremely increasing or the ON duty ratio to be minimized, the voltage can be stabilized even at the minimum load.
In addition, the power consumption at the maximum load can be reduced and the power efficiency can be kept high.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional example.

FIG. 3 is a diagram for explaining an operation of a conventional example (self-excited oscillation type).

FIG. 4 is a diagram for explaining a problem of a conventional example (self-excited oscillation type).

FIG. 5 is a diagram for explaining the operation of a conventional example (PWM type).

FIG. 6 is a diagram for explaining a problem of a conventional example (PWM type).

[Explanation of symbols]

 1 AC power supply 2 Switch 10 Primary DC power supply 11 Rectifier circuit 12 Switching element 13 Voltage control circuit 20 Pulse transformer CL11 Primary winding CL2 Secondary winding 30 Secondary DC power supply 31 Voltage signal generation circuit 40 Dummy load 50 Light load stability Circuit 51 switch circuit 52 voltage detection circuit 100 load

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toyoyasu Kusaka 570, Ohito, Ohito-cho, Takata-gun, Shizuoka Tokyo Electric Co., Ltd. Ohito factory (72) Inventor Yoshiaki Matsumoto 570, Ohito, Ohito-cho, Shizuoka Prefecture Tokyo Electric Corporation Ohi Plant

Claims (1)

[Claims] 1. A primary DC power supply side primary winding having a voltage control circuit and a secondary DC power supply side secondary winding having a voltage signal generation circuit are transformer-coupled, and from the secondary DC power supply side. Is fed back to the voltage control circuit to control ON-OFF of the switching element on the primary DC power supply side, and the voltage of the secondary DC power supply is stabilized, and a dummy load is formed on the secondary DC power supply side. A switching power supply device provided with a switch circuit arranged so that the dummy load can be connected to and separated from the secondary DC power supply; and a voltage detection circuit for detecting whether or not the secondary DC power supply voltage exceeds a set voltage. If the secondary DC power supply voltage exceeds the set voltage due to a light load, the dummy load is connected to the secondary DC power supply, and if there is a residual load, 2
A switching power supply device comprising a light load stabilizing circuit configured to be separated from the next DC power supply.