JP2528421B2 - Driving circuit for switching semiconductor device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive circuit for a switching semiconductor element such as a switching transistor or GTO in various power supply circuits.

[0002]

2. Description of the Related Art Conventionally, as a relatively efficient drive circuit for a switching semiconductor element, there is one using current feedback as shown in FIG. 3 (for example, Japanese Patent Laid-Open No. 51-70181).
Issue).

Explaining this circuit, 1 is a main transistor used as a main switching semiconductor element,
2 is a drive switch for turning on / off the main transistor 1, 3 is a short-circuiting winding N ₁ which is a first winding, a driving winding N ₂ which is a second winding, and a third winding. A certain feedback winding N ₃
In the drive transformer, the black dots in the figure indicate the same polarity end of each winding. Further, 4 is a diode which conducts at the initial stage of conduction of the drive switch 2 to form a short circuit loop, 5 is a resistor for flowing an exciting current of the drive transformer 3, 6'is a control power source input terminal, 7 and 7'is DC input terminal, 8 is a current transformer having a current feedback winding N _a and a current output winding N _b which are connected in series to the feedback winding N ₃ of the drive transformer 3, and 10 is a diode for preventing reverse current. 15 is a main transformer having a primary winding N _p and a secondary winding N _s , 16 and 17 are rectifiers for rectifying the voltage between the secondary windings N _s , and 18 and 19 are smoothing circuits. The reactors, capacitors, 20 and 20 ′ are DC output terminals.

In such a circuit configuration, when the main transistor 1 is turned off, the drive switch 2 is closed,
A short circuit winding N ₁ of the drive transformer 3 is supplied with a current having a magnitude depending on the current of the main circuit and a short circuit current, and a reverse bias voltage is applied between the base and emitter of the main transistor 1 via the drive winding N _2. Turn off faster.

Now, with respect to the structure for accelerating turn-on of the main transistor 1 which is a problem of the present invention, the drive transformer 3 is only provided with the feedback winding N ₃ . As is well known, the action of this feedback winding N ₃ is given to the base of the main transistor 1 by applying a positive feedback current corresponding to a large main circuit current flowing through the main transistor 1 by the transformation action of the drive transformer 3. It speeds up turn-on.

[0006]

However, in such a conventional circuit, only the positive feedback current corresponding to the magnitude of the main circuit current is supplied to the base of the main transistor 1, and the feedback current is reduced. Since the switching cannot be performed, if the amount of the positive feedback current is increased in order to turn on the main transistor 1 at a high speed, the accumulation time becomes long and the turn-off takes time. Further, if the positive feedback current amount is reduced in order to shorten the accumulation time, there is a problem that turn-on becomes slow.

[0007]

According to the present invention, in order to eliminate such a drawback of the prior art, the positive feedback winding of the first transformer 3 and the secondary winding of the second transformer 8 are provided. Are connected in series via a backflow prevention element to form a closed loop, and are connected in series with the secondary winding of the second transformer 8 and in parallel with the backflow prevention element by one or more third The amount of positive feedback current can be changed by connecting the winding to one or more switch elements and selectively opening and closing the one or more switch elements.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, one embodiment of the present invention will be described with reference to FIGS. In Figure 1, members corresponding to Figure 3 denoted by the same symbols, transformer 8 has a first winding N _a serially connected to the main current path of the main transistor 1 serving as the main switching semiconductor device It has a second winding _Nb and a third winding _{Nb '} that are electromagnetically coupled to this, and constitutes a current feedback means. The third winding N _{b ′} has a second winding N _b when the switching element S ₂ for switching the feedback amount is closed.
_b is connected in series. When the switch element S ₂ is open, the second winding N _b is connected to the diode 9 for backflow prevention, the third winding N ₃ of the drive transformer ₃ and an external control circuit (not shown). It forms a closed loop with the switching element S ₁ whose opening and closing is controlled by a signal. In parallel with the winding N _b , as a device for discharging the excitation energy, for example, a diode, a resistor,
A circuit 11 composed of a Zener diode or the like is connected, and a winding N _b is connected via a diode 10 for preventing backflow.
And the winding N ₁ of the drive transformer 3 are connected to form a positive feedback path and a negative feedback path in the form of sharing the winding N _b .

When the switch element S ₂ is closed, the third winding N _{b ′} joins the second winding N _b to form the above-mentioned closed loop. It should be noted that reference numerals 12 and 13 are backflow prevention diodes, and the backflow prevention diode 13 can be omitted when the switch element S ₂ is composed of a unidirectional switching semiconductor element such as an ordinary controlled rectifier.

First, the turn-on of the main transistor 1 will be described. At this time, the switch element S ₂ is open.

It is assumed that the drive switch 2 is closed and the main transistor 1 is off before the time t ₁ . In FIG. 2, when the drive switch 2 that has been closed until now is opened at time t ₁ (FIG. 2 (c)), the drive transformation is performed by the current flowing through the input winding N ₁ and the drive switch 2 until then. The energy stored in the container 3 is discharged from the drive winding N _{2 with} a polarity that forward biases the main transistor 1, and a forward base current (FIG. 2B) flows through the base of the main transistor 1. On the other hand, at time t ₁ , the switch element S ₁
A positive feedback path is formed by closing. Therefore, when the main transistor 1 starts to turn on, a positive feedback is given to the base of the main transistor 1 by the flowing current through the current feedback means 8, the diode 9, the third winding N ₃ and the switch element S ₁ , and the main transistor 1 1 rapidly reaches saturation.

[0012] forward base current _{I B1} passing through the main transistor 1 at this _{time, I B1 = I H + (} n a / n b) × (n 3 / n 2) × (I c -I g) ··· It becomes (1). However, _{I H;} excitation current of the drive transformer 3 in terms of winding _{N 2, n a;} number of turns of the windings _{N a, n b;} number of turns of the winding _{N b, n 2;} number of turns of the drive winding _{N 2} , n _3; current feedback winding _{n 3} turns, _{I c;} a magnetizing current, the current was converted to the winding _{n a} feedback means 8; main current at saturation of the main switching transistor 1, _{I g.}

[0013] Then switching element _S feedback current winding _N b is ₂ in the closed state, _'flows through both, the positive current feedback _{ratio, {n a / (n b} + n b' N b)} × (N ₃ / n ₂ ) ... (2) As is clear from the above equation, when the switch element S ₂ is closed, the current feedback ratio is smaller than when it is not closed, and when the switch element S ₂ is open, the feedback current is equal to the winding N _b. Since it only flows through the side, the current feedback ratio increases. Therefore, when the main transistor 1 is turned on, the switch element S ₂ is initially opened to increase the positive current feedback ratio to rapidly rise, and then the switch element S ₂ is closed to decrease the positive current feedback ratio. By the
It is also possible to reduce the amount of charge stored in the base of the main transistor 1 and shorten the storage time to further speed up the turn-off.

Further, in the case of a switching semiconductor element in which the amplification factor h _FE changes significantly depending on the flowing current, the switching element S ₂ should be selectively opened or closed according to the magnitude of the current flowing through the switching semiconductor element. Thus, the switching speed can be effectively improved by adjusting the positive and negative current feedback factors.

In any case, the fact that the positive current feedback amount can be switched broadens the choice of conditions for turning on the switching semiconductor element, which is advantageous for switching the switching semiconductor element.

The turn-off of the main transistor 1 will be described next. As shown in FIGS. 2C and 2D, the drive switch 2 is closed at time t ₂ and the switch element S ₁ which has been closed until now is opened. Along with this, the current flowing in the current feedback winding N ₃ is negatively fed back to the base terminal of the main transistor 1 via the diode 10, the input winding N ₁ and the drive switch 2, and the reverse base current I _B2 flows. The reverse base current _{I B2} is, _I B2 _{= I} H - become _{(n a / n b) ×} (n 1 / n 2) × (I c -I g) ··· (3). However, n ₁ is the number of turns of the input winding N ₁ .

[0017] (3) As apparent from the equation, the reverse base current _{I B2} mainly flows through the main transistor 1 current _{I c} is large, the reverse base current _{I B2} is also increased, smaller and smaller. Therefore, the negative current feedback ratio is given by equation (4). (N _a / n _b ) × (n ₁ / n ₂ ) ... (4) Then, if these values are set in accordance with the characteristics of the main transistor 1, a reverse base current suitable for high-speed turn-off drive is obtained. Is obtained. Next, when the switch element S ₂ is closed, a negative feedback current flows through both the windings N _a and N _{b ′} , so that the negative current feedback ratio is {n _a / (n _b + n _b ′)} × (N ₁ / n ₂ ) ... (5)

As is clear from the above equation, the switch element S
_{When 2} is closed, the negative current feedback amount is smaller than when it is not closed, and when the switch element S ₂ is open, the feedback current only flows through the winding N _b side, so that the negative current feedback is performed. The amount will increase. The same operation is repeated thereafter, but a large amount of electric power is not required because the drive power source only supplies the excitation energy of the drive transformer 3.

[0019]

As described above, according to the present invention, the magnitude of the positive or negative feedback current, which is approximately proportional to the magnitude of the main current flowing through the semiconductor element that is driven to perform switching, is further increased. Because you can switch selectively,
At least, it can be turned on at a high speed regardless of the characteristics of the switching semiconductor element, and the accumulation time can be shortened by appropriately changing the switching timing.

[Brief description of drawings]

FIG. 1 shows an embodiment of a drive circuit for a switching semiconductor device according to the present invention.

FIG. 2 is a waveform diagram for explaining the operation of the drive circuit shown in FIG.

FIG. 3 is a diagram showing a conventional circuit.

[Explanation of symbols]

1 ... Main switching semiconductor element 2 ... Drive switch 3 ... Drive transformer 4 ... Short circuit diode 5 ... Current limiting element 6 ... Reverse bias source 7, 7 '...・ Main current terminal 8 ・ ・ ・ Transformer for current feedback 9,10 ・ ・ ・ Backflow prevention diode 11 ・ ・ ・ Circuit including discharge element for discharging excitation energy 12,13 ・ ・ Diode S ₁ , S ₂ ..Switch elements

Claims (1)

(57) [Claims] 1. A driven main switching semiconductor device 1
A first winding N ₁ whose one end is connected to the DC power supply 6 through the current limiting means 5, a second winding N ₂ connected to the control terminal of the main switching semiconductor element 1, and a third for current feedback. First transformer 3 having a winding N ₃ of a primary winding, _a primary winding Na inserted in series in the main current path of the main switching semiconductor device 1, and a secondary winding electromagnetically coupled to the primary winding Na. A second transformer 8 having N _b , a driving switch 2 capable of connecting the other end of the first winding N ₁ of the first transformer 3 to the other end of the DC power supply 6, The secondary winding N _b of the transformer 8 and the third winding of the first transformer 3
Feedback switch S for selectively connecting to the winding N _{3 of
1} and, in the driving circuit of the switching semiconductor devices to provide a forward or reverse drive current to the control terminal of the selective main switching semiconductor device 1 comprises a first of said third winding N ₃ of the transformer 3 One end is selectively connected to the secondary winding N _b of the second transformer 8 through the feedback switch S ₁ and is connected in series with the secondary winding N _b of the second transformer 8 to prevent backflow.
2 is connected in series with the secondary winding N _b of the second transformer 8 and in parallel with the backflow prevention means 12 so that the third winding and the switch element are connected in series with each other. By selectively opening and closing the elements, the first side is fed from the secondary side of the second transformer 8 through the feedback switch S ₁ .
Of the positive feedback current through the _third winding N ₃ of the transformer ₃ and the positive feedback current of the selected amount from the second winding N _{2 of} the first transformer 3 is supplied to the main switching semiconductor. A driving circuit for a switching semiconductor element, which is applied to a control terminal of the element 1.