JPH0325094B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a transistor switch with a low conduction voltage.

(Summary of the Invention) The present invention provides a transistor circuit comprising a first transistor of a first conductivity type, second and third transistors of a second conductivity type, and a PN junction element. The emitter of the first transistor is connected to the first main terminal, the base thereof is connected to the collector of the third transistor, the collector of the first transistor is connected to the collector of the second transistor, and the collector of the first transistor is connected to the collector of the second transistor. The base of the second transistor is connected to the gate terminal, the emitter of the second transistor is connected to the base of the third transistor,
The emitter of the third transistor is connected to the second main terminal, and the emitter of the first transistor is connected to the second main terminal.
The conduction voltage is lowered by connecting the PN junction elements in parallel between the collectors.

(Prior Art and Problems to be Solved by the Invention) Conventionally, a semiconductor switch having a PNPN four-layer structure has been commonly used as a semiconductor element that can switch and control large currents or high voltages and is easy to integrate. Figure 11 shows an example of this type of semiconductor switch, and as is well known,
PNPN switch _Q1 is equivalently a PNP transistor
It can also be expressed by Q _P and NPN transistor Q _N. In order to turn on the switch _Q1 in FIG. 11, a gate drive current _IG is supplied from outside the figure via the gate terminal _T3 . Then, the current flows into the base of the NPN transistor Q _N through the diode D ₂ installed to give directionality to the gate current, and the transistor Q _N is turned on. This allows the PNP transistor to act as the collector current of _QN .
The base current of Q _P flows, and as a result, the transistor Q _P is turned on, the entire switch Q ₁ is turned on, and the main current I _A flows from outside the figure through the anode terminal T ₁ and the cathode terminal T ₂ to the outside of the figure. From this point on, even if the supply of _IG is stopped, the base current of _QN is supplied as the collector current of _QP , so switch _Q1 remains on. Also, the gate current required to ignite switch Q ₁ only needs to be V _GK /R ₁ or more and does not depend on I _A (however, V _GK is the conduction voltage of the base-emitter junction of Q _N) . (R ₁ is the value of resistor R _1. ) Here, resistor R ₁ is inserted to prevent the breakdown voltage between the collector and emitter of Q _N from decreasing, and this causes the switch to turn off. , the forward breakdown voltage between T ₁ and T ₂ can be ensured. Hereinafter, the resistors R ₂ to _{R 5} , R ₄ ′, and R ₅ ′ are also used to ensure the CE breakdown voltage of the corresponding NPN transistor. On the other hand, the reverse breakdown voltage when the switch is turned off is ensured by increasing the emitter-base breakdown voltage of the diode D ₁ and the PNP transistors Q _P and Q ₄ . Also, for this reason Q _P
Q ₄ has a so-called lateral structure. Therefore,
For example, if R ₁ = 5KΩ, even though _IA of 100mA flows (since V _GK ~0.8V), _IG only needs 0.3mA. Also, when switch Q ₁ is on, the voltage between T ₁ and _{T 2} (so-called switch conduction voltage) is Q _N and
Since both Q and _P are in the saturated state, it is approximately equal to the conduction voltage of one stage of PN junction (~0.8V), which is a sufficiently small value. However, in the configuration of FIG. 11, as mentioned above, since there is a positive feedback operation between Q _P and Q _N , I _A cannot be stopped simply by stopping I _G , and Q ₁ To turn off the PNPN switch, use external means to change the value of I _A to
It is necessary to reduce it to a value smaller than the so-called holding current of _Q1 .

FIG. 12 shows a conventional example proposed to eliminate the above-mentioned drawbacks in the PNPN switch.

In FIG. 12, NPN transistors Q ₅ , Q ₆
To turn on the switch consisting of a PNP transistor Q ₄ and a gate current I _G through the gate terminal T ₃
supply. This causes diode D ₂ and
I _G flows into the base of transistor Q 6 through R ₄ or the base-emitter junction of transistor Q ₅ , turning on transistor _{Q 6 .} This results in
The base current of the transistor _Q4 flows as the collector current of the transistor _Q6 , and the transistor _Q4 is turned on. The collector current of transistor _Q4 is
It passes through transistor _Q5 , which is previously turned on, to the base of transistor _Q6 , thereby turning on the entire switch.

Further, in order to turn off the switch consisting of transistors _Q4 to _Q6 , it is sufficient to simply stop supplying the gate current _IG . In other words, by stopping the gate current I _G , the transistor Q ₅ is turned off as the supply of base current is stopped, thereby turning off the transistor Q5.
Q ₆ off → Q ₄ off, and the entire switch turns off.

When the switch is in the on state, the transistor
Q ₄ to _{Q 6} are all in a saturated state, and the on-voltage V _po between terminals T ₁ to _{T 2} is given by the following equation. (however,
The main current of T ₁ →T ₂ is L _A as in Fig. 11. ) V _po = V _BE6 + I _C4 (r _C4 + r _C5 ) = V _BE4 + I _C6・r _C6 where V _BEi : Base-emitter conduction voltage of Qi (i=4,6) r _Cj : Qj (j=4~ 6) Collector saturation resistance I _Ci : Collector current of Qi On the other hand, I _A = I _C4 + I _C6 and V _BE4 ~ V _BE6 ~ 0.8V, so in the end V _po ~ V _BE6 + (r _C4 + r _C5 )・r _C6 /r _C4 +r _C5 +r _C6・I _A. and usually (if integrated)
Since the NPN transistor has a vertical structure, the current amplification factor is large (30 to 200 for the common emitter current amplification factor in the non-saturated state).On the other hand, the PNP transistor has a lateral structure, so the current amplification factor is small (in the non-saturated state With emitter grounding current amplification factor
0.1~0.5).

Generally, when the collectors of two transistors of different conductivity types are connected, the potential of the collector is set to a value close to the emitter potential of the transistor with a larger current amplification factor. In particular, when the ratio of current amplification factors is about two digits or more as described above, the collector potential becomes equal to the emitter potential of the transistor with the larger current amplification factor.

Therefore, in the above formula, r _C5 = 0 (∵r _C5 ×I _C5 = 0)
In the end, we get V _po ~ _{V BE6} +r _C4・r _C6 /r _C4 +r _C6 I _A (1).

Also, since r _Cj is on the order of several tens of Ω, V _po and I _A
The relationship has a slope of several tens of Ω. For example, if r _C4 = r _C5 = r _C6 = 40 Ω, when I _A is 40 mA, V _po will be approximately V _BE6 + 0.8 V, which is quite large, equivalent to two PN junctions.

The configuration shown in Figure 11 is equivalent to setting r _C5 = 0Ω, but since Q _N and Q _P are integrated, r _C4 and r _C6 are extremely small (usually several Ω or less). ).

In other words, in the configuration shown in Figure 12, the dependence of V _po on I _A is large; in the region where I _A is small, V _po is equal to the conduction voltage of one stage of PN junction, but in the region where I _A is large, V _po is The drawback was that the conduction voltage for two stages of junctions was exceeded.

FIG. 13 shows an example of a conventional configuration capable of eliminating the drawbacks in the large current region shown in FIG. 12, in which NPN transistors Q ₂ and Q ₃ are also connected in a so-called Darlington connection. (Here diode D ₁ is T ₁ at switch-off
- This is to ensure reverse voltage resistance between _T2 . ) To turn on the switch with the configuration shown in Figure 13,
A gate current I _G is supplied via the gate terminal T ₃ . As a result, NPN transistor Q ₂ is turned on, and the emitter current of transistor Q ₂ flows into the base of transistor _{Q 3 .}
is also turned on, and as a result, the entire switch is turned on.

To turn off the switch, simply stop the _IG supply. The stop of I _G stops the base current of transistor Q ₂ and turns off transistor Q ₂ , which turns off transistor Q ₃ ,
The entire switch is turned off.

Now, T ₁ − when the switch is in the on state
The conduction voltage across T ₂ is, since transistor Q ₂ is in saturated operation and transistor Q ₃ is in non-saturated operation,
It is given by the following formula.

V _po = V _D1 + V _BE3 + I _C2・r _C2 I _A = I _C2 + I _C3 I _C3 = β ₃・(I _G + I _C2 ) where V _D1 : Conduction voltage of diode D ₁ V _BE3 : Base/emitter of Q ₃ Conduction voltage between I _C2 and I _C3 : Collector current of Q ₂ and Q ₃ r _C2 : Collector saturation resistance of Q ₂ β ₃ : Emitter ground current amplification factor of Q ₃ From the above formula, V _po = V _D1 + V _BE3 + r _C2・(I _A −β ₃ I _G /β ₃ +1 (2) Usually, β ₃ ≫ 1 (for example, 30 to 200), and r _C2
is several tens of Ω (for example, 30 Ω), and I _G is V _BE2 /R ₂
(For example, if the conduction voltage between the base and emitter of Q ₂ is V _BE2 , then V _BE2 = 0.8V, R ₂
= 5KΩ and I _G = 0.3mA), so r _C2・
β ₃ ·I _G /(β ₃ +1) is approximately 10 mA. On the other hand, r _C2 /(β ₃ +1) is several Ω or less.

In other words, in the configuration shown in Figure 13, V _po for I _A
The dependence of V po becomes smaller, and even in the large current region, the value of V _po can be approximately the conduction voltage of two PN junctions. However, even in the low current region, V _po is still equivalent to two stages of PN junctions, and there is a drawback that V _po is larger than the configuration shown in FIG. 12.

If the conduction voltage is large, it is necessary to increase the DC voltage applied to the entire device, and for this reason it is desirable that the conduction voltage be small.

This type of switch circuit has a simple circuit configuration, and once the signal to the gate is stopped,
Although it is desired that the current between the main terminals be thereby stopped and that the conduction voltage between the main terminals be small, no circuit has been proposed that satisfies these requirements at the same time.

(Means for Solving the Problems) The present invention was proposed to eliminate these drawbacks, and in the region where the main current I _A is small, the on-voltage (conduction voltage) is set to one stage of PN junction, The object is to provide a transistor circuit with two stages in a large area.

FIG. 1 shows a first embodiment of the transistor circuit of the present invention. In the figure, the emitter of the first transistor _Q4 of the first conductivity type is connected to the first main terminal _T1 , and its base is connected to the collector of the third transistor _Q6 of the second conductivity type, The collector of the first transistor Q ₄ and the collector of the second transistor Q ₅ of the second conductivity type are connected, and the base of the second transistor Q ₅ is connected to the gate terminal T ₃ via the diode D ₂ . , connect the emitter of the second transistor Q ₅ and the base of the third transistor Q ₆ , connect the emitter of the third transistor Q ₆ to the second main terminal T ₂ , and connect the emitter of the second transistor Q ₅ to the second main terminal T 2.
Connect a diode D ₃ in parallel between the emitter and collector of. R ₄ and R ₅ indicate resistance.

By configuring as shown in Fig. 1, in the region where the main current _IA is small, the potential difference between the emitter and collector of the transistor _Q4 is small, and the diode _D3 does not become conductive, so that the overall switch ( _T1 -
The conduction voltage (between T ₂ ) can be the same as that in FIG. That is, since the diode _D3 is in the off state, the configuration is electrically equivalent to the configuration shown in FIG. 12. On the other hand, as the main current I _A increases, the potential difference between the emitter and collector of transistor Q ₄ I _C4・r _C4
When the voltage becomes larger than the conduction voltage of one stage of the PN junction, the diode _D3 becomes conductive. In this state, the potentials of the collectors of NPN transistors Q ₅ and Q ₆ are both lower than the potential of the T ₁ terminal by one PN junction, and are almost equal. In other words, they are almost equivalent. In other words, in the region where _IA is large, the conduction voltage of the entire switch is approximately the value of two PN junctions,
It can be made smaller than the conventional example shown in FIG. For example, when r _C4 = 40Ω, if I _C4 is 20 mA or more, D ₃ turns on and the conduction voltage of the switch becomes PN.
There are two stages of joining. On the other hand, when switching off,
Reverse breakdown voltage can be ensured by increasing the breakdown voltage between the emitters and collectors of D ₃ and Q ₄ , and forward breakdown voltage can be ensured by increasing the breakdown voltage between the bases and collectors of transistors Q ₅ and Q ₆ .

FIG. 2 shows a second embodiment of the present invention.
Diode D ₃ in the figure is replaced with the emitter-base junction of PNP transistor Q ₇ , and the collector of Q ₇ is connected to terminal T ₂ . By configuring like this, when the switch is turned on,
Since T ₁ and T ₂ are short-circuited by transistor Q ₇ in a large I _A region, the conduction voltage of the switch can be further reduced compared to FIG. 1. To ensure the withstand voltage between T ₁ and _{T 2} when the switch is turned off, the breakdown voltage of transistors Q ₄ to _{Q 6} should be increased as shown in Figure 1, and the breakdown voltage between the base and emitter of transistor Q ₇ and between the base and collector should be increased. Increase the breakdown voltage of both junctions.

FIG. 3 shows a third embodiment of the present invention.
The diode _D3 in the figure is replaced with the emitter-base junction of a PNP transistor _Q8 , and the collector of the transistor _Q8 is connected to the base of an NPN transistor _Q6 . By doing this, when transistor Q ₈ turns on in the large current region of I _A , the base current of transistor Q ₆ increases due to the collector current of transistor Q 8, and the collector current of transistor _{Q 6 increases} by that amount. .
In other words, the conduction voltage _Vpo of the switch is reduced. (This is because, as shown in equation (2) above, V _po is expressed by a linear function of I _A , and its coefficient is positive.) These are the results of experiments to determine the relationship between V _po and I _A of the transistor switches with the configurations shown in FIGS. 1, 2, and 3.

During the experiment, turn on _IA in the range of 0 to 50mA.
Each transistor switch is configured so that it can be turned off, and each transistor used in the experiment was prototyped using an integrated manufacturing process. 300V, NPN
The withstand voltage of the base-collector junction of a transistor is
A 300V one is used.

Curves C ₁ , C ₂ , C ₃ , C ₄ and C ₅ are the third
Figure (third example of the present invention), Figure 2 (second example of the same), Figure 1
(first example), FIG. 13, and FIG. 12. As can be seen from FIG. 4, the configuration according to the present invention (C ₁ to C ₃ ) exhibits the same V _po · I _A characteristics as the configuration in FIG. 12 when I _A is 30 mA or less, and when I _A is less than 30 mA, In large areas, it is better than the configuration shown in Figure 13.
Shows V _po −I _A characteristics.

FIG. 5 shows a modification of the configuration shown in FIG. 1 to reduce the number of constituent elements when making it bidirectional. In other words, the PNP transistor _Q9 is a combination of two lateral PNP transistors _Q4 shown in FIG. Here, transistor _Q9 is
For example, this can be realized by a structure as shown in FIG.
However, in Fig. 9, I is the separation region, S is the main surface, and P ₃
~ _P5 is a P-type region, _N4 is an N-type region, _B3 is a base terminal, _E3 and _E4 are emitter terminals, _C2 is a collector terminal, and _B3 , _E3 , _C2 , _E4 are respectively shown in Figure 5.
Corresponds to B ₃ , E ₃ , C ₂ , and E ₄ . In other words, when the switch in Figure 5 turns on in the forward direction, D ₂ ,
Q ₅ , Q ₆ and Q ₉ are turned on. At this time, the transistor _Q9 operates with _E3 as the emitter, _B3 as the base, and _C2 as the collector. _E4 also operates as a second collector. Therefore, the V _po -I _A characteristic can be improved compared to FIG. 1 by the amount that I _A is partially bypassed as the second collector current. Also, when the switch turns on in the opposite direction, D ₂ ′, Q ₅ ′,
Q ₆ ′ and Q ₉ are turned on. However, at this time, E ₄
becomes the emitter and E ₃ becomes the second collector.
(Since Fig. 9 has a lateral structure, the electrical characteristics of the transistor do not change even if E ₃ and E ₄ are replaced.) In Fig. 5, NPN transistors Q ₅ and Q ₅ ' or Q ₆ and Q It is also possible to further reduce the number of elements by integrating ₆ '. At this time, these transistors can be realized with a structure as shown in FIG. 8, for example. In Figure 8, I is the isolation region, S is the main surface, N ₁ to _{N 3} are N-type regions, P ₁ and P ₂ are P-type regions, C ₁ is the collector terminal, and B ₁
and B ₂ are base terminals, E ₁ and E ₂ are emitter terminals, and C ₁ , B ₁ , B ₂ , E ₁ shown in FIG. 5 respectively.
and corresponds to E ₂ .

FIG. 6 shows an arrangement in which the number of constituent elements is reduced when making the configuration of FIG. 8 bidirectional. In other words, the PNP transistor in Figure 1
In Fig. ₆ , two PNP transistors Q7 are realized with one PNP transistor _Q7 . This takes advantage of the fact that when integrated, PNP transistors have a lateral structure, so even if the emitter and collector are swapped, the electrical characteristics do not change.
Other circuit elements are the same as those in FIG.

FIG. 7 shows an arrangement in which the number of circuit elements is reduced when making the configuration of FIG. 3 bidirectional. That is, two PNP transistors _Q8 in FIG. 3 are integrated into a PNP transistor _Q10 in FIG. 7, and _Q10 can be realized, for example, with a configuration as shown in FIG. 10. In Fig. 10, I is the separation region, S is the main surface, _N5 is the N-type region, and _P6 to _P9.
is a P-type region, B ₄ is a base terminal, C ₃ and C ₄ are collector terminals, E ₅ and E ₆ are emitter terminals, and B ₄ ,
C ₃ , C ₄ , E ₅ and E ₆ correspond to B ₄ , C ₃ , C ₄ , E ₅ and E ₆ shown in FIG. 7, respectively. In other words, the switch is turned on in the forward direction (D ₂ , Q ₅ ,
Q ₆ and Q ₉ are on), E ₅ is emitter,
B ₄ acts as the base and C ₃ acts as the collector. At this time, E ₆ operates as a second collector, and thereby a portion of the main current I _A is bypassed, and the V _po -I _A characteristic in FIG. 7 is improved compared to that in FIG. 3. The switch turns on in the opposite direction (D ₂ ′,
Q ₅ ', Q ₆ ', and Q ₉ are on), E ₆ operates as an emitter, B ₄ as a base, C ₄ as a collector, and E ₅ as a second collector. Other circuit elements are the same as those in FIG.

(Effects of the Invention) As explained above, according to the transistor switch circuit of the present invention, in the region where the main current is small, the conduction voltage is equivalent to one stage of PN junction, and in the region where the main current is large, the conduction voltage is equivalent to two stages. Therefore, it has the effect of reducing the conduction voltage over a wide range of main current.

[Brief explanation of drawings]

1 to 3 and 5 to 7 are examples of the transistor circuit of the present invention, FIG. 4 is a diagram showing a comparison of characteristics between a conventional circuit and a circuit according to the present invention, and FIG. 8 10 to 10 show simulated cross-sectional shapes of integrated transistors applicable to the present invention, FIG. 11 shows an equivalent circuit diagram of a conventional PNPN switch, and FIGS. 12 and 13 show circuit diagrams of conventional transistor circuits. Q _P , Q _N , Q ₁ to _{Q 10} , Q ₅ ′, Q ₆ ′...Transistor, D ₁ to _{D 3} , D ₂ ′, D ₃ ′... Diode, R ₁ to _{R 5} ,
R ₄ ′, R ₅ ′...Resistance, T ₁ to T ₃ , B ₁ to _{B 4} , C ₁ to _{C 4} ,
_E1 to _E6 ...terminal, I, _N1 to _N5 , _P1 to _P9 ...area, S...main surface.

Claims (1)

[Claims] 1. A first transistor of a first conductivity type, and a second transistor of a first conductivity type.
and a PN junction element, the emitter of the first transistor is connected to the first main terminal, and the base and collector of the third transistor are connected. the collector of the first transistor and the collector of the second transistor are connected, the base of the second transistor is connected to the gate terminal, and the emitter of the second transistor and the base of the third transistor are connected. , the emitter of a third transistor is connected to a second main terminal, and the PN junction element is connected in parallel between the emitter and collector of the first transistor. 2. Claim 1, wherein the PN junction element is a diode, one end of which is connected to the emitter of the first transistor, and the other end connected to the collector of the first transistor. The transistor circuit described. 3. The PN junction element is a fourth transistor of the first conductivity type, and the emitter and base of the fourth transistor are connected to the emitter and collector of the first transistor, respectively. 2. The transistor circuit according to claim 1, wherein the collector is connected to the emitter of the third transistor. 4. The PN junction element is a fifth transistor of the first conductivity type, and the emitter and base of the fifth transistor are respectively connected to the emitter and collector of the first transistor, and the emitter and base of the fifth transistor are connected to the emitter and collector of the first transistor, respectively. 2. The transistor circuit according to claim 1, wherein the collector is connected to the base of the third transistor.