JPH0512767Y2 - - Google Patents

Description

[Detailed explanation of the invention] [Purpose of the invention] (Field of industrial application) The invention is a heater power supply circuit for a semiconductor gas sensor,
More specifically, a heater for a semiconductor gas sensor includes a transistor connected in series between the heater coil of the semiconductor gas sensor and a DC power source, and a voltage divider consisting of a pair of series-connected resistors that provides a base voltage to the transistor. Regarding power supply circuits.

(Prior Art) In a semiconductor gas sensor, an element portion made of a semiconductor coated with a catalyst is constantly heated by a heater. The heater coil is usually powered from a simple constant-voltage heater power supply circuit. Figure 3 shows such a conventional heater power supply circuit. A heater coil 11 of a gas sensor 10 is connected to a DC power supply _V2 via a transistor 12. The output terminal of the gas sensor 10 is connected to a constant-voltage DC power supply _V1 via a resistor 13, and a sensor output voltage _VS is taken from the output terminal. In this example, a front-end transistor 14 is provided in the stage preceding the transistor 12, which is connected to the constant-voltage DC power supply _V1 via a resistor 15. A connection point B between the transistor 14 and the resistor 15 is connected to the base of the transistor 12. The connection point B between the transistor 14 and the resistor 15 is connected to the base of the transistor 12.
A voltage divider consisting of resistors 16 and 17 is provided in the preceding stage of the input terminal 4, with both ends connected to a DC power source _V1 and an intermediate voltage dividing output point A connected to the base of a transistor 14.

In this circuit, the internal effective resistance of the transistor 14 is determined by the voltage at point A, and B
The voltage at the point is determined, and the internal effective resistance of transistor 12 is determined accordingly. The voltage V _H of the heater coil 11 is a constant value corresponding to a value obtained by dividing the voltage of the DC power supply V ₂ according to the ratio of the resistance value of the heater coil 11 and the internal effective resistance of the transistor 12 (Fig. 4). reference).

(Problems to be solved by the invention) Due to the characteristics of semiconductor gas sensors, gas and moisture adsorbed during a non-energized state are desorbed at the initial stage of energization.
As seen in the sensor output voltage V _S in Figure 4,
The sensor characteristics require a relatively long time T ₁ to reach steady state. Therefore, from power on,
Time until gas sensor returns to normal operating state T ₁
In most cases, sensors were left in a malfunctioning state, or circuit technology was used to forcibly stop sensor operation.

The present invention aims to eliminate such inconveniences.

[Structure of the idea]

(Means for solving the problem) In the present invention, a capacitor is connected in parallel to one of a pair of resistors constituting a voltage divider so that the internal effective resistance of the transistor becomes transiently small when the power is turned on. It is characterized by the fact that

(Function) By connecting a capacitor according to the present invention, the internal effective resistance of the transistor is small immediately after power is turned on, and then gradually decreases according to a time constant determined by the capacitance of the capacitor and the resistance value of the voltage divider resistor. becomes stable at a point determined by the original voltage divider constant. Along with this, overvoltage is applied to the heater coil of the gas sensor immediately after the power is turned on.
After that, it gradually decreases to the rated voltage. Therefore, according to the present invention, it is possible to enter the correct operating state in a shorter time.

(Embodiment) FIG. 1 shows an embodiment of the present invention.
The difference between this embodiment and the circuit shown in FIG. 3 is that in this embodiment, a capacitor 18 is connected in parallel to a resistor 17, and a diode 19 is connected in parallel to the resistor 16 in a direction that matches the direction of the discharge current of the capacitor 18. This is what is being done. The rest is completely the same as the one in Figure 3.

According to the circuit configuration shown in Fig. 1, when the power is turned on, A
The potential at the point gradually decreases from the potential of the constant voltage DC power supply _V1 according to a time constant determined approximately by the product of the capacitance of the capacitor 18 and the resistance value of the resistor 16, and finally, as in the case of FIG. , 17. This transition changes the transistor 14 from being almost non-conductive (high internal effective resistance) to a predetermined conductive state, and correspondingly, the transistor 12 is initially highly conductive (low internal effective resistance).
The value is then changed to a predetermined value. Therefore, as shown in FIG. 2, the voltage V _H of the heater coil 11 becomes an overvoltage immediately after the power is turned on, and thereafter gradually decreases to the rated voltage determined by the resistors 16 and 17 according to the above-mentioned time constant. . The time _T2 until the rated voltage is reached can be adjusted as appropriate by changing the time constant. In this way, by transiently applying an overvoltage to the heater coil 11 immediately after power is turned on, excess gas, moisture, etc. are rapidly removed from the gas sensor 10. The initial stabilization time T ₃ of the sensor output voltage V _S can also be significantly shortened compared to the conventional method (T ₁ ).

In the circuit of the present invention, transient overvoltage application is automatically performed simply by adding a capacitor.

Diode 19 is the capacitor 1 when the power is cut off.
8 is useful for discharging.

In the embodiment, a two-stage amplification type is shown in which the pre-transistor 14 is placed in front of the transistor 12, but the number of stages of this transistor may be three or more, or in some cases, it may be one stage. Good too. Also, the final stage transistor 12 determines which of the resistors 16 and 17 the capacitor is connected in parallel with.
For example, when the transistor 14 is an NPN type unlike the one shown, the capacitor 18 may be connected in parallel to the resistor 16. In any case, the heater coil 11
The final stage transistor 12 connected in series with the transistor 12 may operate as described above. For example, the same function as described above can be achieved by using a one-stage system in which the transistor 14 is omitted and the connection point A between the resistors 16 and 17 is directly connected to the base of the transistor 12.

[Effect of idea]

As described above, according to the present invention, by simply connecting an additional capacitor, moisture, gas, etc. adsorbed during rest can be rapidly desorbed without affecting the steady-state characteristics, and the initial stabilization time can be reduced. It is possible to shorten the time.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing one embodiment of the present invention;
The figure is a graph for explaining the characteristics of the circuit of the same embodiment, FIG. 3 is a circuit diagram of a conventional heater power supply circuit, and FIG. 4 is a graph for explaining the characteristics of the circuit. 10... Gas sensor, 11... Heater coil,
12, 14...transistor, 13, 15, 1
6, 17...Resistor, 18...Capacitor, V ₁ ,
V ₂ ...DC power supply.

Claims (1)

[Claims for Utility Model Registration] A semiconductor comprising a transistor connected in series between the heater coil of a semiconductor gas sensor and a DC power supply, and a voltage divider consisting of a pair of series-connected resistors that provides a base voltage to the transistor. In the heater power supply circuit of the gas sensor, a capacitor is connected in parallel to one of the pair of resistors constituting the voltage divider so that the internal effective resistance of the transistor becomes transiently small when the power is turned on. Heater power supply circuit for semiconductor gas sensor.