JPH0240964A - Sit provided with current sensing function - Google Patents

Abstract

PURPOSE:To detect current flowing in a source for main current, with small current and low power consumption, by constituting the area of a source for current detection so as to be a specified fraction of the area of a source for main current. CONSTITUTION:A plurality of surface gate type electrostatic induction transistors are formed on a substrate 20. These semiconductor elements are divided by m:n; sources of (m) elements are connected with an electrode as a source S for main current; sources of (n) elements are connected with an electrode as a source SS for current detection. Drains and gates are commonly connected for all elements, and connected with electrodes as a drain D and a gate G, respectively. By making (m) large as compared with (n) in this constitution, a small part of drain current can be made to branch and flow into a resistor connected with the source SS, and an over-current protecting circuit can be constituted. Hence, the total current flowing through an electrostatic induction transistors can be detected by a very small current, and problems such as heat generation are not encountered because of low power consumption.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a SIT with a current sensing function, and aims to easily detect a current flowing through the SIT with a small current and almost no power loss. and a main current source are provided separately, and a surface gate type SIT with a multi-source structure is constructed such that the area of the current detection source is substantially one predetermined fraction of the area of the main current source.

[Industrial application field]

The present invention relates to a 5IT (static induction transistor) with a current sensing function, which detects the current flowing through the SIT with low power loss and, based on the detection, provides a control circuit etc. for protecting the SIT itself from damage due to overcurrent. This is related to applicable SIT.

[Conventional technology]

Overcurrent protection circuits have been devised to protect transistors, power FETs, SITs, and other power devices from damage caused by excessive currents, and such protection circuits have been applied to power circuits provided in various appliances or devices. In order to configure the overcurrent protection circuit, it is generally necessary to detect by some means whether or not an excessive current is flowing through the power element.

FIGS. 5 and 6 show conventional examples of power circuits to which the above-mentioned overcurrent protection circuit is applied.

In FIG. 5, a power supply l is connected to a power element 3 via a load 2.
The emitter is connected to the collector of a pieborer power transistor used as a power transistor, and the emitter is grounded via a resistor 7. One of the outputs of the drive circuit 4 that drives the power element 3 is connected to the base of the power element 3, and the other is grounded.

The voltage generated across the resistor 7 is input to a DC amplifier 6, and the output of the DC amplifier 6 is supplied as control power to the drive circuit 4 via a control circuit 5. Further, the control circuit 5 has a comparator, and a comparison reference voltage 10 is supplied to the comparator. Note that the power source 1
The negative side of is grounded.

The operation of the above configuration is such that the voltage drop across the resistor 7 is amplified by the DC amplifier 6, the output thereof is judged by the control circuit 5, and when it is judged that a current larger than expected is flowing, the A control signal is output to the drive circuit 4 to operate the power element 3 to reduce its base current. Therefore, it is possible to prevent excessive current from flowing through the power element 3.

In FIG. 6, a power supply l is connected to a power element 3 via a load 2.
It is connected to the collector of a bipolar power transistor, and its emitter is grounded via a current transformer 9. One of the outputs of a drive circuit 4 that drives the power element 3 is connected to the base of the power element 3, and the other is grounded. The voltage generated across the secondary winding of the current transformer 9 is input to an amplifier 8, and the output of the amplifier 8 is supplied via a control circuit 5 as a control input to the drive circuit 4.

Further, the control circuit 5 includes a comparator and the like, and a comparison reference voltage 10 is supplied to the comparator. Further, the negative side of the power source 1 is grounded.

The operation of the above configuration is such that the voltage generated across the secondary winding of the current transformer 9 is amplified by the amplifier 8, the control circuit 5 makes a decision based on the output, and as a result of the decision, the bipolar power transistor If a current of
The control circuit 5 outputs a control signal to the drive circuit 4 to operate the bipolar power transistor 3 to reduce its base current. Thus, it is possible to prevent excessive current from flowing through the bipolar power transistor 3.

[Problem to be solved by the invention]

Among the conventional circuits, the one shown in FIG. 5 has a problem in that the power loss consumed by the resistor 7 is large and heat is generated, whereas the one shown in FIG. 9. There is a problem that the circuit configuration of the amplifier 8, the control circuit 5, etc. becomes complicated.

The present invention was made in view of such problems.
The purpose of the present invention is to provide an SIT with a current sense function that has a sense function that can easily grasp the total current flowing through the SIT despite the small current and almost no power loss.
The use of the SIT also makes it easier to configure the protection circuit and the like.

[Means to solve the problem]

In order to achieve the above object, an SIT with a current sensing function of the present invention is a surface gate type SIT with a multi-source structure, in which a current detection source and a main current source are separately provided, and the area of the current detection source is reduced. The area is formed to be substantially one predetermined fraction of the area of the main current source.

[For production]

According to the SIT with a current sensing function of the present invention, since a current that is substantially an integer fraction of the current flowing through the main current source flows through the current sensing source, the current sensing function is based on the current flowing through the current sensing source. By obtaining a detection output and multiplying it by a constant, it is possible to know the current flowing through the main current source. If the ratio is selected to be large, it is possible to know the current flowing through the main current source with extremely small current and low power consumption.

〔Example〕

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

FIG. 1 is an enlarged plan view showing the physical configuration of an SIT with a current sensing function according to the present invention. In the figure, a substrate 20
A plurality of semiconductor elements are formed thereon, and the unit structure of the semiconductor elements is a surface gate type SIT. These semiconductor elements are divided into man (man, the one shown is 499:1), and the sources of the m (many) semiconductor elements are connected to the electrode as the main current source S, and the n (small number) is connected to the electrode as a current detection source SS. The drain and gate are commonly connected to all the semiconductor elements and are connected to electrodes as drain D and gate G, respectively.

The SIT with current sensing function of the present invention is configured as described above, and its structure is as follows. However, Is is the current flowing through the main current source S, rSS is the current flowing through the current detection source SS, and Io is the current flowing through the nidrain D.

However, fine (the unit width of the semiconductor element is 3 μm or less)
In a surface gate type SIT constructed by paralleling a large number of semiconductor elements, the relationship between m and n is m)n (for example, m:
n=998: 2) can be easily realized.

For this reason, l5s(IpFor example, Is s = (2/
1000) In, the drain current I
By shunting a small portion of D to a resistor RS connected to the current detection source SS, an overcurrent protection circuit as described later can be constructed. Moreover, the resistance R
Since the current flowing through s is sufficiently small, the power loss and heat generation in the resistor Rs are small and can be almost ignored. Therefore, the resistor R5 can be built into the SIT with a current sensing function, and even in this case, heat generation does not become a problem.

FIG. 2 is a block configuration diagram of an overcurrent protection circuit for protecting the SIT itself from overcurrent using the SIT with current sensing function according to the present invention, and FIG. 3 is a more detailed diagram of the overcurrent protection circuit of FIG. It is a circuit diagram. In FIG. 2, the power supply 21 is connected to the load 2
The main current source electrode is directly connected to the common terminal 28, and the current detection source electrode is connected to the common terminal via the resistor 27. 28. One of the outputs of the drive circuit 24 that drives the power element is connected to the gate electrode of the power element 23,
The other end is connected to the common terminal 28. Said resistance 2
7 is input to a DC amplifier 26, the output of which is supplied via a decision control circuit 25 as a control input to the drive circuit 240. Also,
The judgment control circuit 25 includes a comparator, and a comparison reference voltage 29 is supplied to the comparator. Also,
The negative side of the power source 21 is connected to the common terminal 28, and the common terminal 28 is grounded. As shown in FIG. 3, the DC amplifier 26 is composed of an operational amplifier operating on a single power supply, and the judgment control circuit 25 is a comparator with an open collector output, and the portion consisting of a Zener diode, a resistor, and a capacitor is stable. This configuration provides a reference voltage for comparison. The drive circuit 24 is composed of an amplification circuit including a transistor Q1 and a current mirror circuit including transistors Q2 and Q3.

The operation of the above configuration will be explained below.

When a drive signal is input to the drive input terminal d of the drive circuit 24, the drive circuit 24 supplies a gate current Ia to the gate G of the power element 23. As a result, the power element 2
3 conducts, and a drain current In flows from the power source 21 through the load 22.

The drain current In flows through two sources, that is, the main current source S and the current detection source ss. At this time, a voltage is generated across the resistor 27 due to the current ISS flowing through the current detection source SS. The voltage is amplified by a factor of K (K is a constant) by the DC amplifier 26. The output voltage of the DC amplifier 26 is supplied to the decision control circuit and compared with the reference voltage 29. If the load 22 is short-circuited for some reason, the drain current 1o becomes excessive, and the output voltage of the DC amplifier 26 becomes higher than the reference voltage 29, the judgment control circuit 25 controls the drive circuit 24. Send a control signal to the input terminal. As a result, the drive circuit 24 reduces the amount of gate current supplied to the power device 23, and therefore reduces the drain current In. Through such a negative feedback loop, the power element 23, the load 22, and the power source 21
is protected from overcurrent.

Figure 4 shows an example of the configuration of an overcurrent protection circuit when an SIT with a P-channel current sensing function is used as the power element in Figure 2. Parts with the same functions as those in Figure 2 are given the same symbols. It was shown. Further, the operation is the same as that shown in FIG. 2 above. Note that the circuits shown in FIGS. 2 and 4 can also be configured as a monolithic SIT power IC except for the power supply and load.

〔Effect of the invention〕

As explained in detail above, according to the present invention, the total current flowing through the SIT can be detected with a minute current, and almost no power is consumed for the detection, so heat generation does not become a problem. do not have.

[Brief explanation of the drawing]

Fig. 1 is an enlarged view showing the physical configuration of the SIT with current sensing function according to the present invention, Fig. 2 is a block diagram of an overcurrent protection circuit using the SIT with current sensing function according to the present invention, and Fig. 3 is Figure 2 is a more detailed circuit diagram, Figure 4 is a block diagram showing another example of an overcurrent protection circuit, Figures 5 and 6 are block diagrams of an overcurrent protection circuit configured with conventional power elements. It is.

Claims (1)

[Claims] In a surface-gate SIT with a multi-source structure, a current detection source and a main current source are provided separately, and the area of the current detection source is formed to be a predetermined fraction of the area of the main current source. An SIT with a current sensing function that senses the current value of the main current source based on the current value flowing through the current detection source.