JPS6114690B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a turn-off method capable of shortening the turn-off time of a Darlington-connected transistor.

In general, a typical transistor circuit in which two NPN transistors are Darlington connected is shown in Figure 1, and such a circuit consists of two Darlington connected main switching transistors.
Q ₁ , drive stage transistor Q ₂ , and resistors connected between the base and emitter of these transistors, respectively.
R ₁ , R ₂ , and a resistor connected to the drive signal terminal Td
It consists of R ₀ . In a transistor circuit having such a configuration, no reverse bias voltage is applied when turning off the transistors Q ₂ and Q ₁ , and therefore the turn-off characteristics including the temperature characteristics cannot be improved.

In order to improve the turn-off characteristics of the transistor circuit as shown in Fig. 1, as shown in Fig. 2, an arm in which a chain yoke L and a resistor _R3 are connected in series between the base and emitter of the main switching transistor _Q1 is used. Connected transistor circuits have already been proposed. To explain the operation of this circuit, even if the drive current is removed from the drive signal terminal Td, the drive stage transistor _Q2 remains conductive during its accumulation time; in this state, the main switching transistor
Of course, _Q1 is also conducting. Then, as the storage time of the drive stage transistor Q ₂ passes and the transition to its full time occurs, the collector current of the transistor Q ₂ begins to decrease, and when the current flowing through the choke L begins to decrease, the main switch Since a reverse bias voltage is applied between the base and emitter of the switching transistor _Q1 , the main switching transistor _Q1 is also turned off.

In this way, if no reverse bias voltage is applied between the base and emitter of the drive stage transistor Q ₂ when it is turned off, even if the turn-off characteristics of the main switching transistor Q ₁ are good,
The turn-off characteristics of the Darlington-connected transistor circuit greatly depend on the turn-off characteristics of the drive stage transistor _Q2 , and the turn-off time of the transistor circuit cannot be reduced much. Also the main switching transistor
Since there is no reverse bias voltage between the base and emitter of the driving stage transistor Q ₂ when Q ₁ is turned off, the voltage between the collector and emitter of transistor Q ₂ increases due to the increase in the voltage V _CE between the collector and emitter of transistor Q ₁ as it turns off. Transistor Q ₂ may become conductive again due to current flowing through the capacitor, which is undesirable.

Although not shown, in the transistor circuit shown in Fig. 2, it is also possible to add a series connection body between the base and emitter of the drive stage transistor Q ₂ , which is a series connection of a chain yoke and a resistor, which is separate from the chain yoke L. In this case, the drive stage transistor Q ₂
When the main switching transistor Q 1 is turned off, a reverse bias voltage is applied between its base and emitter, but when the main switching transistor Q ₁ is turned off, the base and emitter of the drive stage transistor Q ₂ may be released from the reverse bias voltage state. So I know it's not good.

In order to eliminate all the above-mentioned drawbacks, the present invention inductively couples the base-emitters of the main switching transistor and the drive stage transistor to each other through an inductance, and when the drive stage transistor is turned off, the inductance is turned off. While putting the base-emitter in a reverse bias voltage state, due to the action of the inductance, until the main switching transistor is turned off,
It is characterized by maintaining the base and emitter of the drive stage transistor in a reverse bias state, and also applying a reverse bias voltage between the base and emitter of the main switching transistor.

Examples of the present invention will be described below.

First, in FIGS. 3 to 7, the same symbols as those shown in FIGS. 1 and 2 indicate members corresponding to these members. The yoke L in FIG. 3 has first and second windings N 1 and N ₂ closely wound around the same core, and the first winding N ₁ has _a resistor R _{3 .}
The main switching transistor is connected in series with
The _second winding N ₂ is connected in series with a resistor R ₄ and connected between the base and emitter of the drive stage transistor Q ₂ . Therefore, the bases and emitters of transistors Q ₁ and Q ₂ are inductively coupled to each other by a single chain yoke L.

Next, an embodiment of the turn-off method according to the present invention will be described while explaining the operation of such a circuit.

First, the drive base current Ib is supplied to the drive signal terminal Td, and the drive stage transistor _Q2 and the main switching transistor _Q1 are turned off. The base-emitter forward voltages V _BE1 and V _BE2 of these transistors Q ₁ and Q ₂ are constant in their steady state of conduction.

At this time, assuming that the number of turns of the first and second windings of the yoke L is equal, the current _{I 1 flowing} through the first winding N 1
is V _BE1 /R ₃・(1-e-R ₃・R ₄ /R ₃ +R ₄
・1/L ₀ t) and increases with a time constant of L ₀ /R ₃・R ₄ /R ₃ +R ₄ , while the current I ₂ flowing through the second winding N ₂ is V _BE2 /R ₄・(1-e-R ₃・R ₄ /R ₃ +R ₄
・1/L ₀ t), and increases with the time constant of L ₀ /R ₃ ·R ₄ /R ₃ +R ₄ . The currents I _N1 and I _N2 become constant at current values of V _BE1 /R ₃ and V _BE2 /R ₄ , respectively. Note that L ₀ is the inductance of the chain yoke L.

Next, when the drive signal current Ib is cut off, the current flowing in the direction of the arrow shown in the second winding _N2 of the yoke L flows as a reverse current through the emitter-base of the drive stage transistor _Q2 . the transistor
Since the storage carrier at the base-emitter junction of Q ₂ is forcibly swept, the storage time is sufficiently shortened. Then, when the storage carrier disappears and transitions to fall time, the second winding _N2 of the yoke L is connected to the base of the drive stage transistor _Q2 until the drive stage transistor _Q2 is at least reliably turned off for reasons described later. Since the emitter is reliably maintained in a reverse bias voltage state, the fall time of transistor _Q2 can also be shortened. In other words, the turn-off time of the drive stage transistor _Q2 is significantly shortened.

On the other hand, when the drive stage transistor Q ₂ transitions to full time, the collector current of the transistor Q ₂ decreases and the main switching transistor
The amount of base current supplied to Q ₁ also decreases, and at the same time, the current I _N1 flowing through the first winding N ₁ of the chain yoke L also begins to decrease. When the current I _N1 starts to decrease, the first and second windings N ₁ and N ₂ of the yoke L induce a voltage whose polarity is negative on the black dot side and positive on the opposite side,
These voltages reverse bias the bases and emitters of transistors Q ₁ and Q ₂ , respectively. Therefore, the constants of each member are set so that the voltage induced in the first winding _N1 of the main switching transistor Q1 can provide a reverse bias between the base and emitter of the main switching transistor _Q1 until the turn-off is completed. By doing so, the turn-off time of the main switching transistor _Q1 can be reliably and significantly shortened. Further, the first and second windings N ₁ and N ₂ B are tightly wound around the same core, and as described above, the main switching transistor Q ₁
Since a reverse bias voltage is applied between the base and emitter of the drive stage transistor Q ₂ until it turns off, the fall time of the drive stage transistor Q ₂ can be reliably and significantly shortened _. The overall time can also be significantly shortened.

Therefore, according to this embodiment, the turn-off time, especially the fall time, of the Darlington connection type transistor circuit can be reliably and significantly shortened.

Next, the transistor circuit shown in Figure 4 is a PNP
A first transistor, in which the main switching transistor Q ₁ and the driving stage transistor Q ₂ are connected in complementary Darlington type and NPN type transistors, respectively, and the base and emitters of these transistors are tightly wound around the same core of the yoke L. Second winding N ₁ , N ₂
are connected to each other. The polarity of the first winding N ₁ is such that when the current flowing through the winding N ₁ decreases with the transition of the fall time of the driving stage transistor Q ₂ , the base side of the main switching transistor Q ₁ is positive, the emitter It is set to apply a reverse bias voltage with negative side. In this circuit, Q ₃ is a transistor that opens and closes the drive signal current Ib, and E ₀ is a driving DC power supply.

Next, FIG. 5 shows another transistor circuit in which the present invention can be implemented, in which the main switching transistors include two transistors Q ₁ , connected in parallel with each other.
Q' ₁ , and the first winding N ₁ of the yoke L is commonly connected between the base and emitters of these transistors Q ₁ and Q' ₁ .

In the transistor circuits shown in FIGS. 4 and 5, even if the main switching transistor and the drive stage transistor are in a complementary relationship, it is difficult to apply a sufficiently good reverse bias voltage to both transistors at turn-off. I can do it.

The one in Fig. 6 has transistors Q ₂ and Q′ ₂ connected complementary to Darlington as drive stage transistors.
It is known that the Darlington transistor circuit having such a configuration has a low saturation voltage. Even in such a three-stage Darlington transistor circuit, both drive-stage transistors Q ₂ and Q' ₂ are turned off from the moment they shift to their own turn-off operation due to the action of the windings N ₁ to _{N 3} of the yoke L. The reverse bias voltage between the base and emitter is maintained until the switching transistor _Q1 completes turn-off. Therefore, the transistor Q′ ₂ ,
The storage time and fall time of both Q ₂ and Q ₁ are shortened, and the turn-off time as a transistor circuit is significantly shortened.

Next, in the transistor circuit of FIG. 7, the main switching transistor Q ₁ and the first drive stage transistor Q' ₂ are connected by the action of the first winding N ₁ of the yoke L.
A reverse bias voltage is applied between the base and emitter of the device. In a circuit with such a configuration, even if the drive current is removed from the drive signal terminal Td, the main switching transistor _Q1 is in a conductive state immediately after that, so the voltage of the first winding _N1 is approximately zero in DC terms. , and the stored carriers of the first drive stage transistor _Q'2 are therefore swept through the resistor _R'4 . The base-emitter of the first drive stage transistor Q' ₂ is sufficiently reverse biased by the voltage induced in the winding N ₁ when the main switching transistor Q ₁ is turned off. Such a configuration is economically advantageous since it is possible to use a chain having two windings. Further, the common use of the winding of the chiyoke can also be applied to a transistor circuit formed by removing the second driving stage transistor Q ₂ and connecting the transistors Q ₁ and Q' ₂ to Darlington as shown in FIG.

As described above, according to the present invention, since the base and emitter of the main switching transistor connected to Darlington and the drive stage transistor are inductively coupled by the chain yoke, when each transistor is turned off, the base and emitter of the main switching transistor and the drive stage transistor are inductively coupled. Although it has a simple configuration, it is possible to reliably apply a reverse bias voltage between the emitters and maintain the reverse bias state between the base and emitters of the drive stage transistor without fail when the main switching transistor is turned off. The turn-off time of such a transistor circuit can be reliably and significantly shortened, and it is also possible to prevent re-conduction during the turn-off operation period, especially after entering the fall time.

[Brief explanation of the drawing]

1 and 2 are diagrams for explaining a conventional transistor circuit turn-off method, and FIGS. 3 to 7 are diagrams showing transistor circuits for carrying out the transistor circuit turn-off method according to the present invention, respectively. be. Q ₁ , Q′ ₁ ……main switching transistor,
Q ₂ , Q' ₂ ... Drive stage transistor, L... Chiyoke, N ₁ , N ₂ , N' ₂ ... Winding of chiyoke, R ₀ , R ₁ ,
R′ ₁ , R ₂ , R′ ₂ , R ₃ , R′ ₃ .R ₄ , R′ ₄ ...Resistance, Td...
...Drive signal terminal.

Claims (1)

[Claims] 1. A method for driving a transistor circuit in which a main switching transistor and a drive stage transistor are connected in Darlington, in which the bases and emitters of the main switching transistor and the drive stage transistor are inductively coupled to each other by inductance via a resistor. , storing energy in the inductance when the main switching transistor and the driving stage transistor are turned on, and reverse biasing between the base and emitter of the driving stage transistor by the energy stored in the inductance when the driving stage transistor is turned off;
A method for turning off a transistor circuit, characterized in that when the main switching transistor is turned off, the base and emitters of the main switching transistor and the drive stage transistor are maintained in a reverse bias state by the action of energy stored in the inductance.