JPS5854282A - Driving circuit for proportional valve - Google Patents

Abstract

PURPOSE:To reduce a loss of a collector of a transistor which drives a proportional valve and to restrain a rise in interior temperature of the device by adopting a switching system for a drive circuit wherein intermittent electric current is directly supplied to a solenoid coil. CONSTITUTION:A comparator 21 which is composed of an arithmetic amplifier receives a control voltage VA at the noninverted input terminal and a terminal voltage VB of a resistance 23 which detects a valve current flowing through a solenoid coil 22 at the inverted input terminal, while inverting its output dependently on the relationship between the intensities of both the voltages VA and VB to turn on or off a transistor 24. A transistor 26 is turned on and off in company with the on and off actions of the transistor 24 and directly supplies the solenoid coil 22 with an intermittent current. The switching frequency of the transistor 26 depends on a delay of the input or output response of the arithmetic amplifier and the time constant.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a drive circuit that arbitrarily adjusts and sets the opening degree of a proportional valve.

A proportional valve changes its valve opening in an analog manner according to the valve current flowing through the solenoid coil. For example, it adjusts the flow rate of fluid such as gas supplied to combustion equipment in an analog manner, and It is used to make the quantity i+lJ Ij.

As an example of a device using this type of proportional valve, FIG. 1 shows the basic configuration of a gas instantaneous water heater in which the amount of combustion gas is continuously controlled by a proportional valve. Briefly explaining the operation of this gas instantaneous water heater 1, when the faucet is opened to dispense hot water, the flow switch 5 installed at the water intake of the heat exchanger 4 detects running water, and the detection signal is sent to the combustion control device. 2
, the combustion control device 2 opens the original pulp 6 provided in the gas pipe line and supplies gas to the burner 8 via the gas governor 7° proportional valve 3. At the same time that gas starts to be supplied to the burner 8, the ignition transformer 9 is driven, the ignition electrode 10 sparks, and the burner 8 is ignited. An increase in the temperature of the hot water after ignition is detected by a thermistor 11 provided at the outlet of the heat exchanger 4. A control voltage of a predetermined level corresponding to the temperature difference between wAm and the set temperature is created from this detection signal, the set temperature in the combustion control device 12, the detection signal of the flow switch 5, etc., and this control voltage is used for driving as described below. When input to the circuit, the proportional valve 3 is supplied with a predetermined valve current corresponding to the level of the control voltage by this drive circuit, and the valve opening is changed in an analog manner, mI! The amount of combustion in the burner 8 is controlled so as to keep the amount constant.

An ignition detection rod 12 is provided to detect the ignition of the burner 8, and an alarm 13 is used to notify the outside when an ignition error occurs.

FIG. 3 shows a drive circuit for controlling the proportional valve 3.

This drive circuit uses a differential amplifier 16 to amplify the difference between the control voltage and the terminal voltage of a resistor 15 that detects the valve current flowing through the solenoid coil 14, and uses its output to adjust the base current of the transistor 17. As a result, solenoid coil 1
4 valve current controls wJi! It is controlled according to the level of li pressure, and the valve WIA degree of the proportional valve changes in an analog manner.

However, in such a circuit configuration of the drive circuit, current always flows through the transistor 17, so its collector loss is large, and a heat sink is usually required. Therefore, when designing a printed circuit board, there are restrictions such as the inability to place electronic components with low heat resistance near the transistors and their heat sinks. In addition, when such a printed circuit board is mounted on a device, the temperature inside the device increases and has a negative impact on other electronic components, so special heat dissipation measures are required, which increases costs and This made it difficult to downsize the device.

This invention was made in view of these conventional problems, and by using a switching system for the drive circuit, it drastically reduces the collector loss of the transistor that drives the proportional valve, and also improves the efficiency when mounting the device. The purpose of this invention is to provide a drive circuit that can suppress the rise in hot water temperature within the device, eliminate the need for a special radiator, and contribute to miniaturization of the device.

Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

In FIG. 3, a comparator 21 composed of an operational amplifier has a non-inverting input terminal inputted with the above-mentioned control voltage VA, and an inverted input terminal inputted with a terminal voltage VB of a resistor 23 that detects the valve current flowing through the solenoid coil 22. , the output is inverted depending on the magnitude relationship between the voltages VA and VB, and the transistor 24 is turned on and off.

Note that a normal comparator circuit is equipped with a hysteresis circuit to ensure stable operation.
In this embodiment, no particular provision is made, and a predetermined hysteresis characteristic is obtained by utilizing the input/output response delay of the operational amplifier itself.

The flag of the transistor 24 is input to the base of the transistor 26 via the resistor 25, and the transistor 26 turns ON/OFF as the transistor 24 turns ON/OFF.
L, an intermittent current is directly supplied to the solenoid coil 2.2.

Further, a diode 27 is connected in parallel to the series circuit consisting of the solenoid coil 22 and the valve current detection resistor 23.
This constitutes one closed circuit.

The operation of the drive circuit configured in this way will be explained.

Now, the control voltage VA and the terminal voltage V of the valve current detection resistor 23
If the magnitude relationship of B is VA>VB, the comparator 21
The output of becomes high level, the transistor 24 and the transistor 26 are turned ON sequentially, and the electric current lI■+ is applied to the solenoid coil 22. As a result, a valve current flows to the solenoid coil 22 via the transistor 26, and the terminal of the resistor 23 Voltage VB increases toward control voltage VA. At this time,
In a series circuit consisting of a solenoid coil 22 and a resistor 23, let the inductance of the solenoid coil 22 be 11 and its resistance value be R and the resistance value of the resistor 23 be R23.
As a result of the existence of a time constant 1- of T-1/(R+R32), the valve current temporarily increases according to this time constant T, so the proportional valve slowly increases its opening and the terminal voltage V
B also rises in a gentle curve. Then, when the terminal voltage VB becomes larger than the control voltage HVA, the output of the comparator 21 is inverted and becomes a low level, so the transistor 24 and the transistor 26 are sequentially turned off, and the current supply to the solenoid coil 22 is cut off. However, as is well known, inductance has current continuity, and due to this current continuity, a current tends to continue to flow through the solenoid coil 22, but this current flows through the closed circuit,
The area is determined according to the above time constant T. As a result, the proportional valve slowly decreases its opening, and the terminal voltage VB follows a gentle curve and descends toward the limiting voltage VA. and,
When the terminal voltage VB becomes lower than the control voltage VA, the comparator 21 performs an inverting operation and returns to the above-described operation.

As a result of repeating the above operations, the valve current becomes a waveform that includes ripple as shown in FIG. Determined by The above-mentioned increase or decrease in the valve opening of the proportional valve is a phenomenon in this ripple portion, but since the switching frequency of the transistor 26 is sufficiently higher than the response limit frequency of the proportional valve, the increase or decrease in the valve opening in this ripple portion is a phenomenon. It can be almost ignored. Therefore, the valve current is regarded as an averaged constant current, as shown by the broken line in the figure, and the proportional valve maintains a predetermined valve opening determined by the control voltage VA.

The valve opening degree of the proportional valve is changed by changing the magnitude of the control voltage VA, but as mentioned above, since the valve current is considered to be a substantially constant current, the valve opening degree is changed as the control voltage A changes. The current changes in an analog manner, and the valve opening of the proportional valve can be changed smoothly as before.

Note that when the transistor 26 reverses from OFF to ON, the diode 27 recovers from ON to OFF, but a short-circuit current flows through the diode during the recovery time at this time, deteriorating the efficiency of the power supply. It is better to use a high-speed one.

As explained in detail above, since the drive circuit for the proportional valve according to the present invention is of the switching type, the collector loss of the transistor that drives the proportional valve is only the loss during switching, and the loss is much lower than that of the conventional one. It can be reduced to about one-tenth of that.

As a result, constraints on printed circuit board design are significantly relaxed, and an increase in leakage inside the device during i* mounting is suppressed.

Therefore, the problem of heat resistance of electronic parts can be solved, the lifespan and reliability can be expected to be improved, and the device can be made smaller.

Furthermore, since the hysteresis characteristic during switching utilizes the response delay of the operational amplifier itself as a comparator, it is possible to simplify the circuit and reduce costs. .

[Brief explanation of the drawing]

Figure 1 is a block diagram of combustion equipment showing an application example of the proportional valve.
Fig. 2 is a circuit diagram showing a conventional proportional valve drive circuit, Fig. 3 is a circuit diagram showing a proportional valve drive circuit according to the present invention, and Fig. 4 is a schematic diagram illustrating the state of the valve current of the solenoid coil. It is. 3... Proportional valve 21... Comparator 22... Solenoid coil 23... Valve current detection resistor 26... Transistor 27. ...Diode patent applicant Tateishi Electric Co., Ltd.] Figure 1, Figure 2, Figure 3v! J Figure 4□0

Claims (1)

[Claims] (1) A drive circuit that controls the valve current flowing through the solenoid coil in response to the control voltage and changes the valve opening of the proportional valve in an analog manner, so that the control voltage is applied to one input terminal and the other input terminal is applied to the drive circuit. A comparator to which the terminal voltage of the resistor for detecting the valve current is input, a transistor connected in series with the solenoid coil between the power supply and driven ON/OFF by the output of the comparator, and when the transistor is turned OFF. , constitutes a series closed circuit with the solenoid coil and the valve current detection resistor,
and a diode that maintains the valve current flowing through the solenoid coil, with a time constant determined from the impedance of the solenoid coil and the valve current detection resistor.
A drive circuit for a proportional valve, characterized in that the valve current is an analog current having a magnitude corresponding equivalently to the control voltage.