JP2572617Y2 - Switching regulator - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching regulator used in a monitor display device and the like, and more particularly, to a ringing choke converter type switching regulator.

[0002]

2. Description of the Related Art A conventional ringing choke converter type switching regulator is shown in FIG. 3 and will be described below.

In FIG. 1, (1) is a rectifying / smoothing circuit including a diode bridge (10), an inrush current prevention resistor (11), and a smoothing capacitor (12).
Is connected to an AC input terminal (not shown). A switching transistor (3) is connected in series to the input winding (N1) of the converter transformer (4), and its base is connected to the feedback winding (N3) and the detection winding (N4). When an AC input voltage is applied to (VIN), first, a base current flows through the starting resistor (21), and a collector current of the switching transistor (3) starts flowing. The windings (N1) and (N3) have the polarities as shown (dots indicate the winding direction of the windings, and the windings (N2) and (N2) when the transistor (3) is ON). (N
3), the voltage direction of (N4) is the diode (51),
(24) and (22) are turned off), so that a voltage is generated in the input winding (N1) and a voltage is generated in the feedback winding (N3), and the base current is reduced. The switching transistor (3) is turned on, with a positive feedback effect, such as increasing the collector current. At this time, a voltage is generated in the output winding (N2), but no current flows because the direction of the diode (51) is reversed. Therefore, switching transistor (3)
Increases linearly due to the inductance of the converter transformer (4). When the ON current of the switching transistor (3) increases to hfe (current amplification factor) times the base current of the switching transistor (3), the collector current stops increasing and the windings (N1) and (N3) are generated. The voltage decreases. Therefore, the base current of the switching transistor (3) starts to decrease, the collector current decreases, a positive feedback action reverse to the previous operation occurs, and the switching transistor (3) turns off. At this time, the energy stored in the converter / transformer (4) is released, a current flows through the diode (51), and the current is smoothed by the capacitor (52). Thus, a blocking oscillation circuit is formed, and the output winding (N2) of the converter transformer (4) is formed.
DC is supplied to the output terminal (VO) through the secondary output side rectifying / smoothing circuit (5) connected to the output terminal (VO).

A resistor (71), a diode (72),
The circuit (7) including the capacitor (73) is a circuit for setting the amount of base current of the switching transistor (3), and also has a function of preventing the current of the starting resistor (21) from flowing to the emitter side. .

The basic operation of the switching regulator of the ringing choke converter type has been described above. Next, stabilization control of the output voltage of this circuit will be described.

The output winding (N2) and the detection winding (N4) of the converter / transformer (4) are closely wound with each other, and a voltage change of the output winding (N2) occurs in the detection winding (N4). I do. Utilizing this phenomenon, the output voltage is stabilized by an output voltage stabilizing circuit (2) as shown in FIG.

First, the operation of the output voltage stabilizing circuit (2) when the output voltage VO rises will be described. converter·
The voltage generated in the detection winding (N4) of the transformer (4) is
The voltage is smoothed and rectified by the capacitor (23) through the diode (22) and becomes a detection voltage for voltage stabilization. Similarly, a feedback winding (N3) of the converter / transformer (4).
Is smoothed and rectified by the capacitor (25) through the diode (24). The detection voltage generated in the capacitor (23) is a Zener diode (2
6) and the voltage between the emitter and the base of the transistor (27) and the voltage divided by the resistor (29), the variable resistor (30) and the resistor (31) are compared with each other to turn on the transistor (27). When the transistor (27) is turned on, the resistance (2
The transistors (35) and (36) are turned on through 8), and the voltage charged in the capacitor (25) is discharged through the resistor (37). At this time, a current path flows from the capacitor (25) to the resistor (37) → the collector to the emitter of the transistor (36) → the resistor (40) → the current flows from the emitter of the switching transistor (3) to the base. Then, the base voltage of the switching transistor (3) is reverse-biased to turn off the switching transistor (3). Therefore, the ON period of the switching transistor (3) is shortened, the energy stored in the input winding of the converter transformer (4) is reduced, the energy released to the output winding is also reduced, and the voltage of the output terminal (VO) is reduced. Will decrease.

If the output voltage VO is too low, the output voltage VO is increased by the operation opposite to the above operation.

The variable resistor (30) changes the base voltage of the transistor (27) and changes the set value of the output voltage VO. Output voltage stabilization circuit (2)
In this case, a circuit composed of a resistor (32), a diode (33) and a capacitor (34)
5) A circuit for maintaining the operation of the output voltage stabilizing circuit (2) stably by supplying an appropriate reverse bias voltage to the bases of (36), and includes a resistor (40), a resistor (39), and a diode. The circuit constituted by (38) is configured to reduce the emitter current flowing through the switching transistor (3) when the power supply is turned on or when the load on the output winding side is short-circuited by the resistor (4).
0) is a circuit for preventing an excessive current flowing through the switching transistor (3), which is detected at 0), thereby preventing the switching transistor (3) from being destroyed.

As described above, in the switching regulator circuit of the ringing choke converter type, when the AC input voltage becomes large, the on-period timing of the switching transistor (3) is shortened to make the transformer (4).
The operation is performed to keep the amount of energy stored in the input winding (N1) constant. Therefore, the peak value of the current flowing through the input winding (N1) of the switching transistor (3) and the converter transformer (4) is constant,
The switching transistor (3) can operate stably.

[0011]

However, the above-mentioned conventional switching regulator is compatible with one AC input voltage (for example, 100 V for domestic ones), and is not affected by fluctuations in the AC input voltage. Corresponds only to about ± 10V. Therefore, it cannot be used for a device in which the AC input power supply changes greatly (for example, it is necessary to support an input voltage of 90 V to 264 V when adopted in a monitor device compatible with the whole world).

[0012] Because the converter transformer (4)
When the voltage input to the input winding (N1) changes greatly, the voltage of the feedback winding (N3) also changes greatly at the same ratio, but this voltage becomes the positive feedback base voltage of the switching transistor (3). Therefore, the base current supplied to the switching transistor (3) also changes greatly, and the operation of the switching transistor (3) that performs high-speed switching operation becomes unstable or the switching characteristics of the switching transistor (3) deteriorate. Temperature rise caused destruction.

The switching regulator of the present invention has been made in view of such circumstances. By controlling the base current of the switching transistor to an optimum value at all times in accordance with the input voltage, a wide variety of switching regulators are provided. It is an object of the present invention to provide a switching regulator that can always obtain a stable DC output voltage even when an input voltage is input.

[0014]

Means for Solving the Problems The switching / switching of the present invention.
The regulator connects the primary-side input winding and the primary-side feedback winding of the converter / transformer to form a blocking oscillation circuit, and has a rectifying / smoothing circuit on the secondary-side output winding of the converter / transformer. In a ringing choke converter type switching regulator connected, a collector is connected to a primary side input winding of the converter transformer and a base detects a voltage change of the secondary side output winding. A switching transistor connected to the primary-side detection winding and the primary-side feedback winding, and a base current supplied to the switching transistor according to the characteristics of the switching transistor by changing a set value of a voltage. Is defined as a characteristic in a positive direction, a constant current or a negative direction with respect to a change in the input voltage of the switching regulator. A control transistor having a collector and an emitter connected between an emitter of the switching transistor and the primary feedback winding and having a base connected to the primary detection winding via the zener diode; And a base current control circuit for the switching transistor, wherein a positive feedback voltage generated in the primary side feedback winding is supplied from the emitter of the switching transistor to the collector of the control transistor. The switching between emitters and via the primary feedback winding;
A negative voltage having a polarity which is supplied to a base of a transistor and has a polarity opposite to a positive feedback voltage generated in the primary side feedback winding and which is generated in the primary side detection winding, through the Zener diode. Supplying to the base of the control transistor lowers (or raises) the base voltage of the control transistor by raising (or lowering) the input voltage of the switching regulator, thereby reducing the current flowing between the collector and emitter of the control transistor. By increasing (or increasing), the base current of the switching transistor is decreased (or increased).

[0015]

By inputting the voltage generated in the detection winding of the converter / transformer to the base of the control transistor via the Zener diode, when the input voltage increases, the base current supplied to the switching transistor is reduced, On the other hand, when the power supply voltage decreases, the operation is performed so that the supplied base current increases.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the switching regulator according to the present invention will be described below with reference to FIG. The same parts as those in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted.

In FIG. 1, (6) is a base current control circuit for controlling the base current of the switching transistor (3). Even if the AC input voltage VIN greatly changes, the base of the switching transistor (3) is controlled. It operates so as to keep the base current supplied to the power supply constant. And
The base current control circuit (6) includes a resistor (61) and a capacitor (63) connected in series, a diode (62) and a control transistor (64) also connected in series.
And the resistor (65), and the resistor (6
6), a resistor (67), a Zener diode (68), and a diode (69). The collector of the control transistor (64) is connected to the emitter of the switching transistor (3).
The emitter side of 4) is connected to one end of a feedback winding (N3), and the base of the control transistor (64) is connected to one end of a detection winding (N4) via a Zener diode (68).

The diode (69) connected in series to the Zener diode (68) is a diode for preventing reverse voltage.

Next, the operation of the base current control circuit (6) will be described.

When the AC input voltage VIN rises, the voltage applied to the input winding (N1) of the converter / transformer (4) increases, and the voltage of the feedback winding (N3) on the same magnetic field also has the same winding ratio. It becomes high with. Since this voltage is connected to the base of the switching transistor (3) in such a direction that a positive feedback action occurs, the positive feedback voltage generated in the feedback winding (N3) of the converter transformer (4) is A feedback from the converter / transformer (4) from the emitter of the transistor (3) through a circuit in which a capacitor (63) and a resistor (61), a diode (62), a control transistor (64) and a resistor (65) are connected in parallel; Switching transistor (3) through winding (N3)
Flows to the base. At this time, the switching of the detection winding (N4) of the converter transformer (4) is also performed from the anode side of the diode (22) through the detection winding (N4).
A negative voltage is generated in the base direction of the transistor (3). The negative voltage generated in the detection winding (N4) has the same ratio as that of the input winding (N1) of the converter transformer (4) and becomes similarly high. When this negative voltage becomes higher, it flows through the resistor (66), the resistor (67), the Zener diode (68), and the diode (69), so that the base voltage of the control transistor (64) is reduced. When the base voltage of the control transistor (64) decreases, the current flowing between the collector and the emitter of the control transistor (64) decreases. As a result, the base current of the switching transistor (3) can be reduced. At this time, the base current control circuit (6)
Since only the differentiated current flows through the capacitor (63) and the resistor (61), the base current of the switching transistor (3) can be reduced by controlling the collector current flowing through the control transistor (64). .

By changing the set value of the voltage of the Zener diode (68), the base current supplied to the switching transistor (3) is changed to the positive direction and the constant current or the negative direction as shown in FIG. The driving conditions can be freely set in accordance with the characteristics of the switching transistor (3).

Here, in order to make the base current have a positive characteristic, the voltage of the Zener diode (68) may be set to be high. In this case, the operation of the Zener diode (68) in response to a rise in the AC input voltage. Since the point is delayed and the decrease of the base voltage of the control transistor (64) is delayed, FIG.
In this case, as shown by the dotted line (A), the base current of the switching transistor (3) has a curve characteristic that gradually increases and rises with respect to the AC input voltage.
On the other hand, if the set value of the voltage of the Zener diode (68) is set low, the operating point of the Zener diode (68) becomes earlier with an increase in the AC input voltage, and the base voltage of the control transistor (64) falls earlier. Therefore, as shown by the alternate long and short dash line (B) or the alternate long and two short dashes line (C) in FIG. 2, the base current of the switching transistor (3) is constant or gentle with respect to the rise of the AC input voltage. It is possible to have a negative curve characteristic that decreases to

The optimum condition for the base current of the switching transistor (3) is that the current supplied to the base has a constant current characteristic, or that the ON period of the switching transistor (3) is short. In order to improve the switching-off characteristic due to the influence of the base storage carriers of the switching transistor (3), it is preferable that the base current is slightly reduced.

As described above, according to the switching regulator of this embodiment, the base current of the switching transistor (3) can always be controlled to an optimum value in accordance with the input voltage. Even if it changes, the operation of the switching transistor (3) can be prevented from becoming unstable or destroyed. In addition, the allowable range for the load fluctuation is widened. Furthermore,
According to the configuration of this embodiment, various input voltages can be handled with a simple circuit configuration, so that the demands for space saving, energy saving, and cost reduction can be satisfied, and the industrial use value is high.

[0025]

As described above, according to the switching regulator of the present invention, it is possible to provide a switching regulator that can always output a DC voltage stably even when various input voltages are input over a wide range. .

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of the switching regulator of the present invention.

FIG. 2 is a diagram showing a relationship between an AC input voltage and a generated voltage of a winding in the switching regulator of the present invention.

FIG. 3 is an overall configuration diagram of a conventional switching regulator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rectification smoothing circuit 2 Output voltage stabilization circuit 3 Switching transistor 4 Converter transformer 5 Secondary output side rectification smoothing circuit 6 Base current control circuit 64 Control transistor 68 Zener diode N1 Input winding N2 Output winding N3 Feedback winding N4 Detection winding

Claims (1)

(57) [Scope of request for utility model registration] A primary input winding and a primary feedback winding of a converter / transformer are connected so as to form a blocking oscillation circuit, and rectification and smoothing are performed on a secondary output winding of the converter / transformer. In a switching regulator of a ringing choke converter system connected with a circuit, a collector is connected to a primary input winding of the converter transformer, and a base changes in voltage of the secondary output winding. And a switching transistor connected to the primary side feedback winding and the primary side feedback winding, and changing the set value of the voltage to supply the voltage to the switching transistor in accordance with the characteristics of the switching transistor. A change in the base current is defined as a positive, constant current or negative characteristic with respect to a change in the input voltage of the switching regulator. And a control transistor having a collector and an emitter connected between the emitter of the switching transistor and the primary feedback winding and having a base connected to the primary detection winding via the Zener diode. A base current control circuit for the switching transistor, comprising: a positive feedback voltage generated in the primary side feedback winding from an emitter of the switching transistor to a collector of the control transistor. A positive voltage which is supplied to the base of the switching transistor between the emitters and the primary side feedback winding and is generated in the primary side detection winding and which is generated in the primary side feedback winding; A negative voltage having a reverse polarity to the voltage is applied to the control transistor through the Zener diode. The base voltage of the control transistor is reduced (or increased) by increasing (or decreasing) the input voltage of the switching regulator, and accordingly, the current flowing between the collector and the emitter of the control transistor is reduced (or A switching regulator characterized by decreasing (or increasing) the base current of the switching transistor by increasing (increase).