JP2833012B2 - Transistor with current detection function - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a transistor having a current detection function, and includes a main transistor unit and a main transistor unit that can accurately detect a current without being affected by a change in current value or temperature. The collector of the sense transistor section is common, and the base and the emitter are independent of each other, so that an individual base current is applied to each base from an external circuit so that current detection can be performed.

[Industrial applications]

The present invention relates to a transistor having a current detection function of detecting the magnitude of a main current, and is applied to various transistors such as a bipolar transistor, an electrostatic induction transistor, and a field effect transistor.

[Conventional technology]

2. Description of the Related Art Conventionally, a multi-emitter transistor in which a collector and a base are shared and a large number of emitters are provided has been known. When such a multi-emitter type transistor is provided with a current detecting function, most of the above-mentioned many emitters are used. It has been used as an emitter for a main transistor part for flowing a main current, while the remaining few emitters have been used as emitters for a sense transistor part for current detection. In this case, in principle, a small current (detection current) proportional to the magnitude of the main current flowing through the main transistor portion flows through the sense transistor portion. Therefore, the magnitude of this detection current is determined by an external current detection circuit or the like. It is possible to detect the magnitude of the main current by measuring at.

[Problems to be solved by the invention]

In the above-mentioned conventional transistor with a current detection function, the main transistor portion and the sense transistor portion have a common collector and a base as described above, and have only separate emitters. Therefore, when detecting current, if the current value or temperature changes, the base-emitter voltage of each of the main transistor section and the sense transistor section changes due to the influence of the emitter wiring resistance, and the ratio of the base current applied to each changes. Will change. Then, the ratio between the main current and the detection current is accordingly reduced, and it becomes difficult to accurately detect the magnitude of the main current based on the magnitude of the detection current. The current detection function could not be obtained.

The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a transistor with a current detection function that can accurately detect a current without being affected by a change in a current value or a temperature. Is to do.

[Means for solving the problem]

A transistor with a current detection function according to the present invention includes a main transistor portion for flowing a main current, and a sense transistor portion for detecting a current flowing in the main transistor portion. The two transistor portions have a common collector, and have a base and a base. It is characterized in that the emitters are made independent.

The present invention is intended to include not only a bipolar transistor but also an electrostatic induction transistor and a field-effect transistor. In this case, the expressions “emitter”, “base”, and “collector” respectively include It includes “source”, “gate”, and “drain”.

[Action]

According to the present invention, the main transistor portion and the sense transistor portion are provided with independent bases, respectively, so that a base current can be individually transferred to the bases from an external circuit. Therefore, if the ratio of these base currents is kept constant, the ratio of the base current will always be constant even if the current value or temperature changes, and a detection current proportional to the main current can always be obtained. Good current detection becomes possible.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic diagram showing a configuration of a bipolar transistor with a current detection function according to one embodiment of the present invention.

The transistor according to the present embodiment includes a main transistor portion for flowing a main current and a sense transistor portion for detecting a current flowing in the main transistor portion, and only a collector is common to the two transistor portions. The emitter and the base are provided independently of each other. That is, as shown in FIG. 1, the collector C is a collector common to the two transistor portions, while
The emitter is the emitter for the main transistor section (hereinafter
The main emitter referred to as) E and the emitter (hereinafter for the sense transistor portion, respectively provided independently as sense emitter referred to as) E _S, further base may base for the main transistor unit (hereinafter, referred to as the main base) and B The bases for the sense transistor section (hereinafter, referred to as sense bases) B _S are provided independently of each other.

In the above configuration, the entire collector current I _C flows through the common collector C, while the emitter current corresponding to the base current (hereinafter referred to as the main base current) I _B flowing into the main base B flows through the main emitter E. (hereinafter, referred to as main emitter current) I _E flows, base current credited to sense the base B _S is the sense emitter E _S (hereinafter, referred to as sense base current) micro emitter current corresponding to I _BS (hereinafter, It referred to as the sense emitter current) I _ES flows. And if the ratio of the two base currents I _B and I _BS is constant,
The ratio between the two emitter currents _IE and _IEs is also constant.

In the transistor of this embodiment, since the two bases B and B _S are provided independently, a base current can be separately supplied to them from an external circuit. Therefore, if it is desired to detect the main emitter current I _E which is the main current, while maintaining the ratio of the main base current I _B and the sense base current I _BS supplied from the external circuit constant of the sense emitter current I _ES size Is detected by an external current detection circuit. Then, since the magnitude of the sense emitter current I _ES is proportional to the size of the main emitter current I _E, it is possible to know the magnitude of the main emitter current I _E.

According to the present embodiment, as described above, a constant ratio of base currents I _B and I _{BS are} supplied to the two independent bases B and B _S from an external circuit.
Therefore, even if the current value or the temperature changes, the ratio of the base currents I _B and I _BS can be always kept constant. Therefore, the main current (main emitter current I _E ) and the detection current (sense emitter current I _ES ) can always be maintained at a constant ratio without being affected by changes in the current value or temperature. it can always accurately detect the magnitude of the main emitter current I _E on the basis of the measured value of the current I _ES.

Next, FIG. 2 shows an example of an overcurrent protection circuit for protecting the transistor T itself from overcurrent using the transistor with a current detection function of the above embodiment.

In the figure, the collector C of a transistor T is a load 1
Is connected to the positive side of the DC power source 2 through a through a common terminal 3 of the main emitter E is connected to the negative side of the DC power source 2, The sense emitter E _S is the resistance R _S for detecting a current Connected to the common terminal 3 via Furthermore,
The base currents I _B and I _{BS of} a fixed ratio output from the transistor drive circuit 4 are respectively supplied to the main base B and the sense base B _S.

Further, the voltage generated across the current detecting resistor R _S connected to the sense emitter E _S is input to the DC amplifier 5, and the output voltage obtained here is amplified by the reference voltage V _REF of the reference voltage source 6. Is input to the judgment control circuit 7 together with the control signal. An output voltage corresponding to the result of the judgment by the judgment control circuit 7 is supplied to the control input terminal s of the transistor drive circuit 4 as a control signal.

The operation of the overcurrent protection circuit having the above configuration will be described below.

First, when a drive signal is input to the drive input terminal d of the transistor drive circuit 4, the transistor drive circuit 4 _applies a fixed ratio base current to the two bases B and BS of the transistor T.
Supply I _B and I _BS respectively. As a result, the transistor T is turned on and the main emitter current
I _E (≒ collector current I _C ) flows through the load 1. At this time, a small sense emitter current is also applied to the current detection resistor R _S.
When _IES flows, a voltage is generated across the resistor _RS that is exactly proportional to the magnitude of the main emitter current _IE . This voltage is amplified by K (K is a constant) by the DC amplifier 5.

The output voltage of the DC amplifier 5 is input to the judgment control circuit 7 and compared with the reference voltage _VREF . If, becomes excessive the main emitter current I _E and the load 1 is shorted for some reason, the output voltage of the DC amplifier 5 is higher than the reference voltage V _REF, the base current I _B of the determination control circuit 7 to the transistor T , _Reduce the supply of IBS. Such a negative feedback loop protects the transistor T, the load 1 and the DC power supply 2 from overcurrent.

Although FIG. 1 shows an npn-type bipolar transistor, it is needless to say that a pnp-type bipolar transistor may be used. Further, the present invention can be applied to an electrostatic induction transistor, a field effect transistor, and the like in addition to the bipolar transistor.

〔The invention's effect〕

According to the present invention, an independent base is provided for each of the main transistor section and the sense transistor section, and a base current is individually transferred from an external circuit to the base to perform current detection, thereby detecting a current value and a temperature. Accurate current detection that is not affected by the change is enabled.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a bipolar transistor with a current detection function according to an embodiment of the present invention, and FIG. 2 is a block diagram showing an example of an overcurrent protection circuit using the transistor of the embodiment. E ...... main emitter, E _S ...... sense emitter, B ...... main base, B _S ...... sense-based, C ...... collector.

Claims (1)

(57) [Claims] 1. A main transistor section for flowing a main current, and a sense transistor section for detecting a current flowing in the main transistor section, wherein the two transistor sections have a common collector, and a base and an emitter are independently formed. A transistor having a current detection function.