JP2865850B2 - Thermal flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a control and circuit system of a constant-temperature hot-wire air flow meter, and in particular, to a reverse voltage state (a voltage when a power supply voltage is reversely connected). It relates to a durable control and circuit system.

[Conventional technology]

The electronic circuit of a conventional constant-temperature hot-wire air flow meter is often configured as shown in FIG. A hot wire (called a hot wire and made of platinum or the like) 2 is always controlled at a constant temperature by a circuit composed of operational amplifiers 6, 9, a transistor 10, resistors 3, 4, 5, 7, 8, and the like. You. When the wind hits the hot wire, this resistance value changes, and the whole circuit controls this value to be a constant value (constant resistance value means constant temperature).

At this time, the voltage V ₀ generated across the resistor 3 is a function of the flow rate of the wind hitting the hot wire 14, and the flow rate can be known from this voltage. The resistance _CW is a cold wire (cold wire) for compensating for temperature and the like, and the resistance 8 is an auxiliary resistance.

The diode 13 and the resistor 14 are protection circuits when the voltage source (corresponding to a battery of an automobile, etc.) 1 is connected in reverse.
Without this, the hot wire 2 often burns out. FIG. 3 is an equivalent circuit around the transistor 10 when the voltage source 1 is reversely connected in the circuit of FIG. 2. The reverse voltage of the voltage source 1 is represented by resistors 3, 2, 14 and a diode 13. Is applied to the transistor 10.

Transistor 10 is often connected in Darlington (composite) as shown in transistors 15 and 16 in order to increase the current amplification factor, and resistors 18 and 19 are added to reduce the influence of temperature and the like. At this time, the diodes 17 and 20 are parasitic due to manufacturing restrictions on the device. Therefore, most of the voltage applied to the transistor 10 is applied to the diode 17. At this time, if there is no protection circuit by the diode 13 and the resistor 14, most of the reverse voltage is applied to the resistor 2 and the hot wire is heated and may be burned out. Diode 13, resistor 14
Is connected in parallel with the resistor 2 and acts to reduce the heating of the resistor 2, so that burnout can be prevented.

[Problems to be solved by the invention]

The above-mentioned prior art has a drawback that the circuit element for reverse connection protection is optically necessary, and the circuit is complicated.

An object of the present invention is to propose a circuit system that does not require a reverse connection protection circuit.

[Means for solving the problem]

An object of the present invention is to provide an electronic circuit for controlling the temperature of a heating resistor placed in a fluid to be constant and a temperature compensation resistor for detecting the temperature of the fluid. The temperature of the body is changed, and this change is captured as an output of an electronic circuit as a flow rate of a fluid, and the electronic circuit is constituted by at least a resistor group, an operational amplifier, and a transistor, and the transistor is provided with a reverse voltage blocking function. The voltage blocking function is realized by using a Darlington (composite) transistor as the transistor and eliminating the second-stage base-emitter resistance and collector-emitter diode of the transistor in the thermal flowmeter. Two p's on the surface
The region is diffused, a base terminal is taken out from the first p region, the n ⁺ region is diffused into each of the two p regions, and the first n ⁺ region and the second p region are connected by a conductor. 2 n ⁺
The region is taken out of the emitter terminal, and p ⁺
This is achieved by diffusing the region, diffusing the n ⁺ region on the other surface of the single crystal n region, and taking out the collector terminal from the region.

[Action]

In this circuit configuration, the reverse voltage characteristic of the transistor 10 becomes extremely good, and the current when the reverse voltage is applied can be considerably reduced as compared with the method shown in FIG.

As a result, even if the voltage at the time of reverse connection is applied via the resistors 2, 3, etc., almost no current flows in the circuit, and the voltage at both ends of the resistor 2 becomes small, so that heating can be prevented.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIG. In FIG. 1, the same components as those in the conventional example (FIG. 2) are denoted by the same reference numerals and symbols. In the figure, the transistor 15 in the second stage of the transistor 101 has no base-emitter resistance and has no collector-emitter diode. The first stage resistor 19 is added because it is effective in preventing oscillation of the transistor. A transistor device having a circuit function such as the transistor element 101 can be realized by the structure shown in FIG. The figure shows a device cross section of a transistor, and includes a collector C (23), a base B (21), and an emitter E.
(22) is drawn out. The single silicon (single crystal) 24 is an n-type diffused semiconductor region, and the collector C is taken out by attaching an n ⁺ region 25 with a higher concentration to n. On the other hand, two p diffusion regions 26 and 2 are formed on the upper surface of n, and the end 21 of the base B is drawn out from this 26. Between these two p regions 26 and 2, there is ap ⁺ region 30 forming a resistor 19. region
26 and 2 have high-concentration n ⁺ regions 28 and 29, respectively, and the emitter E terminal 22 is drawn out from 29. The region 28 is connected to the p region 27 once it has been taken out to the outside by a conductor (aluminum). Such a device has the function of the transistor 101 in FIG. 1, and an equivalent circuit of this device can be considered as shown in FIG.

In FIG. 5, the second stage transistor 15 is in the regions 24, 27 and 29,
The first-stage transistor 16 has regions 24, 26, and 28, and the resistor 19 has regions
At 30, the diode 20 can be shaped in regions 24, 25, 30 respectively.

Since the device does not have the resistor 18 and the diode 17 described above, the current at the time of reverse voltage of the transistor 101 is drastically reduced (if the resistor 18 is provided without the diode 17, the transistor 18 is connected through the transistors 18 and 19). 16 performs the reverse operation,
Reverse current flows). That is, the device can reduce the reverse current at the time of the reverse voltage, and can have a function of blocking the reverse voltage. This embodiment has an effect that a transistor element can be relatively easily formed.

FIG. 6 shows another embodiment of the present invention, in which a bridge circuit comprising resistors 2, 3, _CW , 8, 7 and an operational amplifier 40 are used as a constant temperature control circuit. Transistor 101 is applied between the output of operational amplifier 40 and one end of the bridge and one end 1A of the power supply. In this embodiment, since the circuit configuration except for the resistor 2 and _CW becomes extremely simple, there is an effect that this portion is formed into an IC (integrated circuit).

〔The invention's effect〕

According to the present invention, when a power supply voltage such as a battery is reversely connected, reverse connection protection can be performed by the transistor itself, so that there is no need to add a protection circuit, and a reduction in circuit scale and improvement in reliability can be expected.

[Brief description of the drawings]

1 is a diagram showing a specific embodiment of the present invention, FIG. 2 is a diagram showing a conventional example, FIG. 3 is a diagram showing a circuit operation at the time of reverse connection in FIG. 2, and FIG. 4 is a diagram in FIG. FIG. 5 is a diagram showing a device structure of a transistor, FIG. 5 is a diagram showing an equivalent circuit of FIG. 4, and FIG.
The figure shows another embodiment of the present invention. 1 ... Power supply, 2 ... Hot wire, 3,4,5,7 ... Resistance,
6,9 …… Op amp, 10,101 …… Transistor.

Continuation of front page (56) References JP-A-60-86420 (JP, A) JP-A-54-76182 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01F 1 / 68 H01L 29/72

Claims (1)

(57) [Claims] An electronic circuit for controlling the temperature of a heating resistor placed in a fluid to be constant and a temperature compensating resistor for detecting the temperature of the fluid. The temperature of the resistor is changed, and the change is captured as an output of an electronic circuit as a flow rate of a fluid, and the electronic circuit is constituted by at least a resistor group, an operational amplifier, and a transistor, and the transistor has a reverse voltage blocking function. The reverse voltage blocking function is realized by a thermal flow meter which is realized by using a Darlington (composite) transistor as the transistor and eliminating the second-stage base-emitter resistance and collector-emitter diode of the transistor. The two p regions are diffused into the Darlington transistor surface, and the base terminal is taken out from the first p region. Each allowed diffused n ⁺ region, and a first n ⁺ region and the second p-region are connected by conductors, the second n ⁺ region removed emitter terminal, a p ⁺ region between the two p regions Diffusion, diffuse the n ⁺ region on the other surface of the single crystal n region,
A thermal flow meter, wherein a collector terminal is taken out of the region.