JPH0880041A - Switching power device - Google Patents

Abstract

PURPOSE: To improve efficiency within all load ranges. CONSTITUTION: The series circuit of a diode DA and a resistor RA is connected in parallel with a resistor RB. When a switching element Q1 is turned on, the switching element Q1 is turned on by impedance only of the resistor RB. When the switching element Q1 is turned off, the switching element Q1 is turned off by the parallel synthetic impedance of the resistor RB and the resistor RA. That is, when the switching element Q1 is turned off, the switching element Q1 is turned off by impedance lower than the case of the resistor RB.

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 using a ringing choke converter (RCC) system.

[0002]

2. Description of the Related Art FIG. 3 shows a specific circuit diagram of a conventional FET type ringing choke converter (RCC) type switching power supply device. As a conventional example of this type, for example, Japanese Patent Publication No. 4-9034 can be cited. An AC power supply AC is connected to an input end of a diode bridge DB ₁ for rectification via a fuse F and a line filter LF, and a smoothing capacitor C ₁ is connected to an output end of the diode bridge DB ₁ . .

The inverter circuit includes output transformers T and FE.
A switching element Q ₁ composed of T, a starting resistor R ₁ ,
It is composed of R ₂ etc. A rectifying diode D ₁ and a smoothing capacitor C ₃ are connected to both ends of the output winding N ₂ of the output transformer T.

Further, a voltage detection circuit and a control circuit as a stable control of the output voltage and an overcurrent protection circuit are provided.
The voltage detection circuit provided on the output side of the inverter circuit includes resistors R ₇ and R _{8 for} dividing and detecting the output voltage, a light emitting diode PD on the light emitting side of the photocoupler PC ₁ , a shunt regulator IC _{1 and the} like. . Further, the control circuit provided on the feedback winding N _B side of the output transformer T of the inverter circuit includes a phototransistor PT which forms a pair with the light emitting diode PD of the photocoupler PC ₁ , resistors R _{3 to} R ₅ , and a feedback winding N _B. A resistor R _B connected between _one end of _B and the gate of the switching element Q ₁ via a capacitor C ₄ , a diode D ₂ , a transistor Q ₂ connected in parallel between the gate and source of the switching element Q ₁ , and this transistor Q. capacitor C _2, connected between the _two base-emitter resistor R
₉ and a Zener diode D _{3 and the} like.

Next, the operation of the circuit shown in FIG. 3 will be described. First, at the time of start-up when the power is turned on, a voltage is applied to the gate of the switching element Q ₁ via the resistors R ₁ and R ₂ , and the switching element Q ₁ is turned on.
When the switching element Q ₁ is turned on, the power supply voltage is applied to the primary winding N _P of the output transformer T, and the feedback winding N _P
A voltage is generated in _B in the same direction as the primary winding N _P. The generated voltage charges the capacitor C ₂ via the resistor R ₃ .

At the time of startup, the output voltage is close to zero and the phototransistor PT of the photocoupler PC ₁
Is a cutoff state, and the capacitor C ₂ is charged only by the current flowing through the resistor R ₃ . At this time, since the capacitor C ₂ is not charged with electric charge, it is charged in a short time. When exceeding the forward voltage between the base and emitter of the transistor Q _2, the transistor Q ₂ is turned on.

When the transistor Q ₂ turns on, the collector potential of the transistor Q ₂ becomes L level, the gate of the switching element Q ₁ becomes L level, and the switching element Q ₁ is turned off. Therefore, at startup,
The ON period of the switching element Q ₁ can be kept small.

When the switching element Q ₁ is turned off, the energy stored in the output transformer T when the switching element Q ₁ is turned on is released through the output winding N ₂ . The voltage, which is this energy, is rectified by the diode D ₁ and smoothed by the capacitor C ₃ , so that power is supplied to the load.

When the electric charge of the capacitor C ₂ is discharged through the Zener diode D ₃ and the resistor R ₉ , the transistor Q ₂ is turned off and the switching element Q ₁ is turned on. When the switching element Q ₁ is turned on, the output transformer T is turned on again.
A voltage is applied to the primary winding N _P of the output transformer T to store energy in the output transformer T.

When the output voltage rises by repeating such an oscillating operation, the electric charge in the capacitor C ₂ is reversed in the opposite direction due to the voltage generated in the feedback winding N _B of the output transformer T during the off period of the switching element Q _1. Be charged. Therefore, a longer charging time is required than when the electric charge is empty, and the ON period of the switching element Q ₁ becomes longer. After the output voltage rises, the photo coupler PC ₁
The phototransistor PT also goes from the cutoff state to the active state, the collector current of the phototransistor PT controls the charging time of the capacitor C ₂ , and the ON period of the switching element Q ₁ corresponding to a predetermined output voltage is obtained. .

Here, in a steady state, the output voltage on the load side is always divided by the resistors R ₇ and R ₈ to be detected, and the divided detection voltage and the shunt regulator IC are detected.
₁ is compared with the reference voltage. Then, the variation of the output voltage is amplified by the shunt regulator IC ₁ and the current flowing through the light emitting diode PD of the photocoupler PC ₁ is changed, so that the phototransistor PT of the photocoupler PC ₁ of the photocoupler PC ₁ is changed according to the light emission amount of the light emitting diode PD. By changing the impedance and changing the charging time constant of the capacitor C ₂ , control is performed so that the output voltage becomes constant.

In the steady state, the capacitor C ₂ is charged mainly by the resistor R ₅ , the diode D ₂ and the photocoupler PC _1.
Is charged via the phototransistor PT. Also,
The charged electric charge of the capacitor C ₂ is discharged through the resistor R ₃ .

When the output voltage rises, a large amount of current flows through the light emitting diode PD of the photocoupler PC ₁ ,
Since the impedance of the phototransistor PT is lowered, the charging time constant of the capacitor C ₂ is shortened, the transistor Q ₂ is turned on quickly, and the switching element Q ₁ is turned off to shorten the ON period of the switching element Q ₁ .
Control to reduce the output voltage. When the output voltage decreases, the reverse operation described above is performed to control the output voltage to increase, and the constant voltage control is performed to keep the output voltage constant.

The control in the case of an abnormal current such as an overcurrent or a short circuit current is performed as follows. That is,
As the output current increases, the current flowing through the light emitting diode PD of the photocoupler PC ₁ is narrowed down. Therefore, the current flowing through the phototransistor PT is also reduced,
The charging time of the capacitor C ₂ becomes longer. Therefore, the time until the transistor Q ₂ is turned on becomes long, the on period of the switching element Q ₁ becomes long, and an attempt is made to flow a large amount of output current.

However, after the current flowing through the phototransistor PT becomes zero and is cut off, the capacitor C ₂ is charged only on the resistor R ₃ side, and the capacitor C ₂ and the resistor C ₂ are charged during the ON period of the switching element Q _1. It cannot be increased beyond the value determined by the time constant of R ₃ , and the output current becomes the limit. When the load impedance further decreases, the output voltage also starts to decrease, but when the output voltage decreases, the voltage generated in the feedback winding N _B of the output transformer T during the OFF period of the switching element Q ₁ also decreases. Therefore, the capacitor C
Decreases the charge accumulated in the reverse direction _2, the charging time of the capacitor C ₂ at the time of the on-switching element Q ₁ is shortened, the ON period of the switching element Q ₁ is shortened.

As described above, the ON period of the switching element Q ₁ continues to be shortened until the load impedance finally becomes zero (short circuit), so that the output voltage with respect to the output current is suppressed and a so-called fold curve is formed. Draw overcurrent protection control.

[0017]

In the circuit of the conventional example shown in FIG. 3, when the switching element Q ₁ is turned on, one end of the feedback winding N _B of the output transformer T and the gate G of the switching element Q ₁ are connected. Resistance R interposed between
Voltage is applied via _B. Further, when the switching element Q ₁ is turned off, the current is drawn through the resistor R _B. Then, by changing the resistance value of the resistor R _B , the drain of the switching element Q ₁
Adjusting waveform and efficiency between sources

[0018]

[Table 1]

As shown in Table 1, when the value of the resistor R _B connected to the gate G of the switching element Q ₁ is increased,
The loss at turn-on is small and the loss at turn-off is large. Further, when the value of the resistor R _B is reduced, the loss at turn-on becomes large and the loss at turn-off becomes small. Therefore, when the value of the resistor R _B is set to be large or small, there are advantages and problems at turn-on and turn-off. Therefore, it is difficult to improve efficiency in all load ranges.

The present invention has been made in view of the above points, and provides a switching power supply device for improving efficiency in all load ranges.

[0021]

Therefore, the first aspect of the present invention is described.
In the switching power supply device described, an output transformer T having a primary winding N _P , an output winding N ₂ and a feedback winding N _B ,
A switching element Q ₁ for oscillation, one end of which is connected to the primary winding N _P of the output transformer T, and a control terminal G is connected to the feedback winding N _B via a resistor R _B and a capacitor C ₄ , and the output transformer. Rectifier circuit D connected to the output winding N ₂ of T
In the switching power supply apparatus having a ₁ and the value of the resistor R _B is set to a value that is a slow rise of the voltage applied to the control terminal G when to turn on the switching element Q _1, the turn-off of the switching element Q ₁ It is characterized in that control means D _A, R _A for lowering the impedance of the resistor R _B are sometimes provided.

According to another aspect of the switching power supply device of the present invention, as the control means, a diode D _A having a control terminal G side of the switching element Q ₁ as an anode and a resistor R _{A are used.}
And a series circuit, and the series circuit is connected in parallel with the resistor R _B.

[0023]

According to the switching power supply device of the first aspect of the present invention, when the switching element Q ₁ is turned on, the value of the resistor R _B is set to a value that makes the rise of the voltage applied to the control terminal G slow. Therefore, the loss at turn-on is small, and the switching element Q ₁
Since the impedance of the resistor R _B is lowered by the control means when turning off, the loss at turning off is small. Therefore, efficiency is improved in all load ranges.

Further, according to the switching power supply device of the second aspect, since the control means for lowering the impedance of the resistor R _B is constituted by the series circuit of the diode D _A and the resistor R _A , one diode, the resistor The efficiency can be improved by the low cost of one piece.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a specific circuit diagram of a switching power supply device according to an embodiment of the present invention. Since the overall configuration is the same as that of the conventional example shown in FIG. 3, the elements having the same functions are designated by the same reference numerals. The description will be omitted and the gist of the present invention will be described in detail.

[0026] That is, the resistance R _B as shown in FIG. 1,
It is characterized in that a series circuit of a diode D _A and a resistor R _A whose anode is on the gate G side of the switching element Q ₁ is connected in parallel. Then, when the switching element Q ₁ is turned on, it is turned on by the impedance of only the resistor R _{B, and} when it is turned off, the resistor R _B and the resistor R _B are turned on.
_The switching element Q ₁ is turned off by the parallel combined impedance with _A. That is, when the switching element Q ₁ is turned off, it is turned off with an impedance lower than that of the resistance R _B.

When the switching element Q ₁ is turned on, the voltage applied to the gate G of the switching element Q ₁ does not rise sharply due to the value of the resistor R _B , but rather has a gentle slope to increase the switching frequency. By doing so, switching loss is reduced and noise is reduced to improve efficiency. On the other hand, when the switching element Q ₁ is turned off, a large current flows through the gate G, so that the switching element Q ₁
Must be turned off rapidly. Therefore, in order to a value lower than the impedance value of the resistor R _B in the time of turn-off, via a diode D _A and a resistor R _A in parallel with the resistor R _B, a current of the gate G by the parallel combined impedance abruptly The switching element Q ₁ is turned off by pulling it out. Switching loss is reduced by rapidly turning off the switching element Q ₁ .

As a result, as shown in Table 1, it is possible to minimize the switching loss of the switching element Q ₁ by increasing the resistance value during turn-on and decreasing the resistance value during turn-off. FIG. 2 shows the relationship between load and efficiency, where the solid line is the conventional example and the broken line is the present invention, and as is clear from the figure, the efficiency is improved in all load ranges. Moreover, as a means for improving the efficiency, since the resistor R _B is constituted only by the series circuit of one diode D _A and one resistor R _A , the switching power supply (RCC) can be manufactured at low cost. It is possible to improve efficiency.

In the embodiment shown in FIG. 1, the case where the FET is used as the switching element Q ₁ has been described, but the present invention can be applied not only to the FET but also to a transistor.

[0030]

According to the switching power supply device of the first aspect of the present invention, when the switching element is turned on, the value of the resistance is set to a value that makes the rise of the voltage applied to the control terminal slow. The loss at turn-on is small, and the impedance of the resistor is lowered by the control means when turning off the switching element, so the loss at turn-off is small.
Therefore, efficiency is improved in all load ranges.

Further, according to the switching power supply device of the second aspect, since the control means for lowering the impedance of the resistor is constituted by the series circuit of the diode and the resistor, the cost of one diode and one resistor is reduced. It is possible to improve efficiency.

[Brief description of drawings]

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

FIG. 2 is a characteristic diagram showing a relationship between load and efficiency according to the embodiment of the present invention.

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

[Explanation of symbols]

T Output transformer N _P Primary winding N ₂ Output winding N _B Feedback winding Q ₁ Switching element G Gate (control terminal) R _A resistance R _B resistance D _A diode

Claims (2)

[Claims] 1. An output transformer (T) having a primary winding (N _P ), an output winding (N ₂ ) and a feedback winding (N _B ), and a primary winding of the output transformer (T) ( N _P) one end connected to the resistor in the feedback winding _{(N B) (R B)} , a capacitor (C
₄ ) A switching element for oscillation (Q ₁ ) connected to the control terminal (G) via a rectifier circuit (D ₁ ) connected to the output winding (N ₂ ) of the output transformer (T) in the switching power supply apparatus having the value of the resistor (R _B) is set to a value that is a slow rise of the voltage applied to the control terminal (G) when turning on the switching element (Q _1), the switching element ( _A switching power supply device characterized by comprising control means (D _A, R _A ) for lowering the impedance of the resistor (R _B ) when Q ₁ ) is turned off. 2. The control means comprises a series circuit of a diode (D _A ) having a control terminal (G) side of a switching element (Q ₁ ) as an anode and a resistance (R _A ) and the series circuit is formed. the resistor (R _B) and the switching power supply device according to claim 1, characterized in that connected in parallel.