JPH0249047B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a transistor circuit that has a high collector-emitter breakdown voltage and a large current amplification factor even in a minute current range.

(Prior art and problems to be solved by the invention) As is well known, in a transistor, the collector-emitter breakdown voltage BV _CEO when the base is open is the collector-base junction breakdown voltage BV _CBO when the emitter is open.
is smaller than , and the two are related by the following equation.

BV _CEO = BV _CBO /n√+1 Here, β is the common emitter current amplification factor of the transistor, and in silicon, it is usually assumed that 2=2 to 4. (For example, 108 of "Integrated Circuits - Design Principles and Manufacturing" by Kindai Kagakusha, by Odagawa et al.
(See page) In other words, it is explained that B _CEO becomes smaller than BV _CBO due to the current amplification effect of the transistor.

As a result, under conditions where a large voltage is applied between the collector and emitter when the transistor is in the off state, resistor 2 should be connected between the base and emitter of transistor 1 as shown in Figure 6. This is the method that has traditionally been used. In other words, by inserting resistor 2, the base
A bypass circuit for reverse current I _BC of the collector junction is provided to prevent the current I _BC from flowing into the base-emitter junction and turning on the transistor. As a result, transistor 1 remains off, the current amplification effect is suppressed, and the voltage BV _CEO value is
It is possible to get closer to BV _CBO . (I _BC is usually smaller than the order of 10 ^-12 amperes in an integrated case.) However, in the method shown in Figure 6, a portion of the base input current bypasses resistor 2 when the transistor is on. Therefore, there is a drawback that the current amplification factor of the transistor 1 apparently decreases for a minute base input current. In order to prevent this, the value of the resistor 2 may be increased, but this increases the size of the resistor, making integration difficult. For example, for an input current on the order of several μA, the value of resistor 2 should be set to several MΩ or more, but generally it is several 100 K.Ω.
It is considered difficult to integrate resistors of this type.

(Means for Solving the Problems) The present invention was proposed to improve these drawbacks, and it is possible to increase the current amplification factor to the minute current range without impairing the breakdown voltage between the collector and emitter of the transistor. The purpose is to provide a transistor circuit that can be kept large.

In order to achieve the above object, the present invention comprises first and second transistors of the same conductivity type,
The emitter of the transistor and the emitter of the second transistor are connected, the base of the first transistor and the collector of the second transistor are connected, and the collector of the first transistor and the base of the second transistor are connected to each other. Collector-base junction breakdown voltage when the emitter of the first transistor is open
The gist of the invention is a transistor circuit characterized in that it is connected via a PN junction element having a breakdown voltage equal to the BV _CBO voltage.

Furthermore, the present invention includes first and second transistors of the same conductivity type and a third transistor of a complementary conductivity type, and the emitter of the first transistor and the second
The base of the first transistor is connected to the collector of the second transistor, and the breakdown characteristic is equal to the withstand voltage of the collector of the first transistor and the base-collector junction of the first transistor. and the anode of the diode connected to the third
, the collector of the transistor is connected to the base of the second transistor, and the base-emitter breakdown characteristics and base-collector breakdown characteristics of the third transistor are connected to the collector of the first transistor. - The gist of the invention is a transistor circuit characterized by matching the base open breakdown characteristic and further setting the forward/reverse emitter ground current amplification factor of the third transistor to be small.

Next, examples of the present invention will be described. It should be noted that the embodiments are merely illustrative, and it goes without saying that various changes and improvements can be made without departing from the spirit of the present invention.

FIG. 1 shows a first embodiment of the present invention, in which 1 and 3 indicate NPN transistors, and 4 indicates a diode. The emitter of the first transistor 1 and the emitter of the second transistor 3 are connected at a terminal 12, and the base of the first transistor 1 and the collector of the second transistor 3 are connected. Further, the collector of the first transistor and the cathode of the diode 4 are connected at a terminal 11, and the anode of the diode 4 is connected to the base of the second transistor.

Next, the operation will be explained.

Here, the breakdown voltage of the diode 4 is made to match the BV _CBO of the transistor 1. Then, when transistor 1 is off, if a high voltage with the collector side being positive is applied between the collector and emitter of transistor 1, most of the high voltage will be applied between the collector and base of transistor 1. . On the other hand, the high voltage is also applied between the cathode of the diode 4 and the emitter of the transistor 3, but most of it is also applied between the cathode and anode of the diode 4. Therefore, due to the high voltage, a reverse current I _BC flows at the collector-base junction from the collector side to the base side of transistor 1.
On the one hand, the reverse current _ID of the anode-anode junction of the diode 4 flows into the base of the transistor 3. Therefore, when the common emitter current amplification factor of transistor 3 is _β3 , the base-collector junction area of transistor 1 and the anode-collector area of diode 4 are adjusted so that _β3・I _D ≧I _BC (1) is satisfied. Cathode junction area and current amplification factor β ₃ of transistor 3
By setting , all I _BC bypasses transistor 3 and does not pass through the base-emitter junction of transistor 1. As a result, transistor 1 continues to maintain the off state, causing the BV _CEO of transistor 1 to
BV can be brought closer to _BCO . Usually I _D and I _BC
is proportional to each joint area. Moreover, when integrated, β ₃ is about 30 to 300. Therefore, the ratio of the base-collector junction area of transistor 1 to the anode-cathode junction area of diode 4 is
If it is set to 30 or less, equation (1) will be satisfied. Furthermore, since the withstand voltage between the cathode of diode 4 and the emitter of transistor 3 is approximately equal to the withstand voltage between the cathode and anode of diode 4 (BV _CBO ), The breakdown voltage of transistor 1 is close to BV _BCO of transistor 1. On the other hand, to turn on transistor 1, it is sufficient to input current I _B to the base of transistor 1 from outside the figure. At this time, due to the above-mentioned reason, transistor 3
is on, but its collector current is β ₃ · _ID , which is on the order of 10 ⁻¹⁰ amperes at most, so it can be ignored for an input current of a few μA. In other words, according to the configuration shown in FIG. 1, the collector-emitter breakdown voltage of transistor 1 can be made comparable to the collector-base breakdown voltage, and the current amplification factor can be maintained even in the minute current range. be.

FIG. 2 shows a second embodiment of the present invention, in which the diode 4 in FIG. 1 is replaced with a base-collector junction of an NPN transistor 5. In FIG. Here, by matching the breakdown voltage conditions of the BV _BCO of the transistor 5 and the BV _BCO of the transistor 1, the same effect as explained in FIG. 1 can be achieved.

FIG. 3 shows a third embodiment of the present invention.
The diode 4 in the figure is replaced with a base-collector junction of a PNP transistor 6. Here, if the breakdown characteristics of the base-collector junction of the transistor 6 are made to match the breakdown characteristics of the base-collector junction of the transistor 1, the same effect as explained in FIG. 1 can be achieved.

FIG. 4 shows a fourth embodiment of the present invention, in which the diode 4 in FIG. 1 is replaced with a base-collector junction of a PNP transistor 7. However, in this case, it is necessary to reduce the size of the forward current amplifier of transistor 7.
Otherwise, the breakdown voltage of the terminal 11 and 12 will be determined by the BV _CEO of the transistor 7 itself. However, by making the transistor 7 a lateral (so-called lateral type) transistor, the base-collector breakdown characteristics of the transistor 7 can be matched with the base-collector breakdown characteristics of the transistor 1, and the forward-direction emitter-grounded current of the transistor 7 can be amplified. Reduce the rate (for example, around 1)
It is easy to set.

In FIG. 5, the diode 4 in FIG. 1 is replaced with a transistor 7, and the breakdown voltage between the collector and emitter of the transistor 1 is provided in both forward and reverse directions. That is, BV _CBO of transistor 1
A diode 8 having the same breakdown voltage as is connected in series to the collector of transistor 1, and the base-emitter breakdown characteristics and base-collector breakdown characteristics of transistor 7 are matched with the collector-base breakdown characteristics of transistor 1, and By setting the common emitter current amplification factors of the transistor 7 in both the forward and reverse directions to 1, the withstand voltages of the terminals 11 and 12 can be made comparable to the base-collector breakdown voltage BV _CBO of the transistor 1 in both the forward and reverse directions.

That is, in the embodiments shown in FIGS. 1 to 4, the withstand voltage for this circuit is limited to the case where the direction of the applied voltage is positive at terminal 11 and negative at terminal 12, but in the embodiment shown in FIG. This has an effect that can be applied even when the terminal 12 is negative and the terminal 12 is positive.

As a specific experimental example of the present invention, the inventor verified that the withstand voltage between terminals 11 and 12 was verified using NPN transistors and PNP transistors having a BV _CBO of 300V for FIGS. 1 to 5. could be made equal to the BV _CBO of transistor 1. By the way, transistor 1 alone was about 1/2 of BV _CBO . (150V) We also confirmed that transistor 1 operates normally (same operation as transistor 1 alone, without additional parts such as transistor 3 and diode 4) with a current of at least 50 nA or more as the base input.

(Effects of the Invention) As described above, the present invention has the advantage that the current amplification factor can be maintained high even in the micro current region without impairing the breakdown voltage between the collector and emitter of the transistor.

[Brief explanation of the drawing]

FIG. 1 shows one embodiment of the transistor circuit of the present invention, FIGS. 2 to 5 show other embodiments of the invention, and FIG. 6 shows a conventional example. 1, 3, 5, 6, 7...transistor, 4, 8
...Diode, 2...Resistor, 11, 12...Terminal.

Claims (1)

[Claims] 1. A transistor comprising a first transistor and a second transistor of the same conductivity type, the emitter of the first transistor and the second transistor having the same conductivity type.
The base of the first transistor and the collector of the second transistor are connected, and the collector of the first transistor and the base of the second transistor are connected to the emitter of the first transistor. 1. A transistor circuit connected through a PN junction element having a breakdown voltage equal to the breakdown voltage BV _CBO voltage of the collector-base junction when open. 2. The transistor circuit according to claim 1, wherein the PN junction element is a diode arranged with opposite polarity from the collector of the first transistor to the base of the second transistor. 3 Using a third transistor of the same conductivity type as the first and second transistors as a PN junction element,
Connect the collector of the third transistor to the collector of the first transistor, connect the base of the third transistor to the base of the second transistor, and match the BV _CBO of the first and third transistors. A transistor circuit according to claim 1, characterized in that: 4 A third transistor of a conductivity type complementary to that of the first and second transistors is used as a PN junction element, and the collector of the first transistor and the third
The bases of the transistors are connected, the collectors of the third transistor and the bases of the second transistor are connected, and the breakdown characteristics of the base-collector junction of the third transistor and the base-collector junction of the first transistor are 2. The transistor circuit according to claim 1, wherein the transistor circuit has the same breakdown characteristics. 5 A third transistor of a conductivity type complementary to that of the first and second transistors is used as a PN junction element, and the collector of the first transistor and the third
The collector of the third transistor is connected to the base of the second transistor, and the base of the third transistor is connected to the emitter of the third transistor.
Claim 1, characterized in that the collector breakdown characteristics are made the same as the base-collector breakdown characteristics of the first transistor, and the forward emitter ground current amplification factor of the third transistor is set to be small.
Transistor circuit described in section. 6 Comprising first and second transistors of the same conductivity type and a third transistor of a complementary conductivity type, the emitter of the first transistor and the emitter of the second transistor are connected, and the emitter of the first transistor is connected to the emitter of the second transistor. The base and the collector of the second transistor are connected, the collector of the first transistor is connected to the cathode of a diode having a breakdown characteristic equal to the withstand voltage of the base-collector junction of the first transistor, and the anode of the diode is connected. is connected to the emitter of the third transistor, the collector of the transistor is connected to the base of the second transistor, and the base-emitter breakdown characteristics and base-collector breakdown characteristics of the third transistor are 1. A transistor circuit characterized in that the collector-base breakdown characteristics of a transistor are matched, and the forward and reverse emitter ground current amplification factors of a third transistor are set to be small.