JP3614832B2 - Self-excited step-down switching power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a self-excited step-down switching power supply apparatus and relates to a circuit that can simplify the configuration of a transformer.
[0002]
[Prior art]
A circuit shown in FIG. 2 is known as a self-excited step-down switching power supply using two active elements. In this circuit, along with obtaining a NPN transistor Q _1, the current gain required for Q ₂ Darlington connected transistor Q via the resistor R _1, a capacitor C ₁ to feedback signals generated in the third winding L _F of the transformer ₂ is applied to the base of No. ₂ to cause self-excited oscillation.
[0003]
On the other hand, to connect one end of the secondary winding L _S of the transformer to ground, with the other end is connected to via a diode D ₁ to the emitter of the transistor Q _1, is connected to the output terminal V _O. Thus, the flyback voltage generated in the secondary winding L _S is rectified by the diode D ₁ and smoothed by the capacitor C ₂ to obtain an output, thereby constituting a self-excited step-down switching power supply device.
[0004]
In such a configuration, in the above circuit,
▲ 1 ▼ requires at least 3 winding the transformer, in addition to the transformer is complicated, the primary winding L _P and the secondary winding L _S is required to be essentially the same number of turns, the transformer design There is no freedom.
▲ 2 ▼ flyback voltage generated in the primary winding _{L P} with the secondary winding _{L S} to direct the output through a diode _{D 1,} the primary winding _L P, the secondary winding _{L S} A large spike voltage is generated by the leakage inductance generated in the meantime and various distributed capacitances, resulting in noise problems and breakdown voltage breakdown problems of the transistors Q ₁ and Q ₂ .
▲ 3 ▼ switching speed is slowed by the Darlington connection of the transistor, deterioration in efficiency due it, fever, problems such destruction of the transistor Q ₁ is generated.
[0005]
[Problems to be solved by the invention]
The present invention provides a self-excited step-down switching power supply device that eliminates the need for a secondary winding of a transformer, that is, simplification of transformer specifications, ensuring design freedom, noise reduction, and high efficiency. It is to provide.
[0006]
[Means for Solving the Problems]
The present invention solves the above-mentioned problems by adopting a complementary configuration for the switching element.
[0007]
That is, in a self-excited step-down switching power supply device in which a power control element and an inductance component are connected in series between input and output terminals,
The collector or drain of the main power control element and the emitter or source of the drive element of the main power control element are connected via the main winding of the inductance component to form a complementary Darlington connection power control element. One end of the feedback signal detection winding is connected to the input terminal side of the main power control element, and the other end of the feedback signal detection winding is connected to the base or gate of the main power control element to constitute a feedback circuit. It has characteristics.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
The point of the present invention is that
(1) Darlington connection between NPN transistor and PNP transistor (or N-type MOSFET and P-type MOSFET)
(2) Positive feedback of the signal generated in the feedback signal detection winding to perform self-excited oscillation to the base or gate of the main power control element,
There is.
[0009]
【Example】
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the present invention, and elements having the same functions are denoted by the same reference numerals as those in FIG. The primary winding L _P of the main switching element Q _1, the transformer between the input terminal V _IN and the output terminal V _O are connected in series. However, the primary winding functions as a simple inductance element.
[0010]
Transistor Q ₁ is formed of a PNP transistor, the driving transistor Q ₂ is formed of a NPN transistor, and a Darlington connection collector base and the transistor Q ₂ of the transistor Q ₁ is connected. The emitter of the transistor Q ₂ is connected between the output terminal V _O and the capacitor C _2.
[0011]
One end of the feedback signal detector winding L _F of the transformer is connected to the input side of the transistor Q _1, the other end is connected via a capacitor C _1, resistors R ₁ to the base of the transistor Q _1. The constant voltage diode ZD is connected between the transistor Q ₂ based and ground. As described above, the basic configuration of the step-down switching power supply is the same as the conventional one, but the configuration of the switching element and the method of applying the feedback signal are different from the conventional one.
[0012]
By adopting such a circuit configuration, the operation will be different from the conventional one, and the point to solve the above problem will be described. In the conventional circuit shown in FIG. 2, by using elements of the same polarity (NPNs) for each of the transistors Q ₁ and Q ₂ , an apparently one NPN transistor having a large current amplification factor is produced. . The collector is connected to the primary winding L _P, it had gained synthesized and output voltage energy of the secondary winding L _S in the emitter follower output.
[0013]
In the present invention, an apparently one NPN transistor is configured using the transistors Q ₁ and Q ₂ having complementary polarities (PNP and NPN). As a result, since the conventional emitter output is changed to the collector output, the conventionally used secondary winding L _S becomes unnecessary. By eliminating the need for the secondary winding, it is possible to eliminate the spike voltage, simplify the transformer structure, and increase the degree of design freedom.
[0014]
Further, since the feedback voltage for the self-excited oscillation by the feedback signal detector winding signal generated L _F is applied to the base of the transistor Q _1, when the off-going of the transistor Q ₁ between the base and emitter of the transistor Q ₁ is A reverse voltage is applied. As a result, the switching speed is improved and high efficiency can be achieved.
[0015]
In the above example, the transistor is a bipolar element, but the same configuration can be achieved using a MOSFET. Further, by making all the polar parts have opposite polarities, it is possible to cope with negative input and negative output. Furthermore, in the example of FIG. 1, the output voltage is almost determined by the Zener diode ZD, but if the shunt regulator IC and the resistors RA and RB are connected as shown in FIG. Or can be variable.
[0016]
【The invention's effect】
According to the present invention, since a complementary element is used for the transistor (switching element), the output form becomes a collector follower and the secondary winding of the transformer can be eliminated, so that the structure of the transformer can be simplified and the design can be simplified. It is easy to secure the degree of freedom. This also eliminates the occurrence of spike voltages, eliminating noise problems and device destruction problems.
[0017]
In addition, since the feedback signal for oscillation is positively fed back to the control terminal of the main switching element, the switching speed of the switching element is improved, the problem of heat generation is solved, and high efficiency can be realized.
[Brief description of the drawings]
FIG. 1 is a circuit diagram showing an embodiment of the present invention. FIG. 2 is a circuit diagram showing a conventional self-excited step-down switching power supply. FIG. 3 is a circuit diagram showing another embodiment of the invention.
Q ₁ , Q ₂ : Transistor L _P : Primary winding L _{F of} transformer: Detection winding of transformer

Claims (3)

In a self-excited step-down switching power supply in which a power control element and an inductance component are connected in series between input and output terminals,
The collector of the main power control element and the emitter of the drive element that drives the main power control element are connected via the main winding of the inductance component to form a complementary Darlington connection power control element,
The feedback signal detection winding of the inductance component is connected to the input terminal side of the main power control element, and the other end of the feedback signal detection winding is connected to the base of the main power control element to constitute a feedback circuit. A self-excited step-down switching power supply device. In a self-excited step-down switching power supply in which a power control element and an inductance component are connected in series between input and output terminals,
The drain of the main power control element and the source of the drive element that drives the main power control element are connected via the main winding of the inductance component to form a complementary Darlington connection power control element,
The feedback signal detection winding of the inductance component is connected to the input terminal side of the main power control element, and the other end of the feedback signal detection winding is connected to the gate of the main power control element to constitute a feedback circuit. A self-excited step-down switching power supply device. The self-excited step-down switching power supply device according to claim 1 or 2, wherein a control terminal of the drive element is connected to a shunt regulator, and an error signal input terminal of the shunt regulator is connected to a connection point of a dividing resistor.

Images