The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2010-079486, filed Mar. 30, 2010, which is incorporated herein by reference.
The present invention relates to a relay driving circuit for driving an electromagnetic relay.
Electromagnetic relays are used more often than semiconductor relays for safety relays in combustion furnaces. This is because the ability to withstand noise and the ability to withstand the environment, which are the distinctive features of the electromagnetic relay, are more important than rapid response time and long service life, which are the distinctive features of semiconductor relays. Conventionally, circuits that use capacitors, as illustrated in
In the circuit illustrated in
Even in the circuit illustrated in
A distinctive feature of these circuits is that they are able to circumvent danger, by turning the relay OFF, if there is a failure in any of the components included in the circuit. For example, in order to maintain the relay in the ON state, continuous pulses must be supplied from the microcontroller, and if the supply of the pulses were to stop due to a failure in the microcontroller, the relay would be turned OFF. The design is such that the relay will reliably turn OFF if there is a failure in any other component as well.
However, in the circuit illustrated in
Additionally, in the circuit illustrated in
Given this, the object of the present invention is to provide a relay driving circuit able to achieve stabilized operations.
In order to achieve an object such as set forth above, the relay driving circuit according to the present invention includes a transformer; a direct-current (DC) power supply that is connected to the primary coil of the transformer; a modulating circuit for modulating, based on a control signal from the outside, the power supplied to the first coil of the transformer from the DC power supply; and a supplying circuit for supplying, to an electromagnetic relay that is provided with a mechanical contact point, electric power induced between the terminals of a secondary coil of the transformer.
In the relay driving circuit set forth above, the modulating circuit may be structured from a switching element, that is turned ON/OFF by a pulse circuit, connected in series with the primary coil of the transformer and with the DC power supply.
Additionally, in the relay driving circuit set forth above, the providing circuit may be further provided with a rectifying circuit for rectifying the voltage produced between the terminals of the secondary coil and providing this voltage to the electromagnetic relay.
The present invention is able to achieve stabilized operation as a result of reducing the ripple component in the voltage between the relay terminals due to the ability to provide an adequate relay driving current through modulating, based on a control signal from the outside, the power that is supplied to the primary coil of a transformer, from a DC power supply that is connected to the DC power supply, and the power that is induced between the terminals of the secondary coil of the transformer is supplied to an electromagnetic relay that is provided with a mechanical contact point.
Furthermore, it is possible to increase the power efficiency through the ability to provide power to the relay without charging/discharging the capacitors by turning the transistor ON/OFF based on a control signal. Since the power is supplied to the relay by a transformer through modulating, based the control signal, the power that is supplied to the primary coil of the transformer is all that is required.
Moreover, the double isolation between the device that is being driven using the relay (the load) and the DC power supply, through the use of the transformer and the electromagnetic relay, makes it possible to minimize the effects on the DC power supply side even if a fault were to occur in the load, resulting in the ability to provide a stabilized circuit.
Forms exemplifying the present invention are explained in detail below in reference to the drawings.
As illustrated in
A DC power supply 2 is connected in series with the primary-side circuit. Additionally, a switching element 3, a fuse 4, a feedback circuit 5, and a resistor R1 are connected in series between the transformer 1 and the DC power supply 2, and a diode D1, and a resistor R2 and a capacitor C1, which are each connected in series with the diode D1, are connected in parallel between the transformer 1 and the DC power supply 2. A pulse signal from a microcontroller is inputted into the switching element 3 through a resistance R3.
In the secondary-side circuit, a relay 6 is connected in series, through a diode D2 for rectification on one end, and through a resistor R4 on the other end. In addition, a smoothing capacitor C2 is connected in parallel between the transformer 1 and the relay 6. Here the diode D2 and the smoothing capacitor C2 structure a rectifying circuit. The rectifying circuit has a function of applying, to the relay 6, a virtual DC current by regulating, to a constant voltage, the terminal voltage applied from the secondary side of the transformer 1 to the relay 6. If this rectifying circuit were not provided, then the pulse voltage, converted by the switching element 3, would be inputted directly into the relay 6, and while it would be possible to perform an operation wherein the relay would be turned ON/OFF continuously and repetitively if the pulse voltage were at a relatively low frequency, if the frequency were relatively high, then the electric current required for driving the relay 6 could not be applied during the entire cycle, so there would be the risk that the relay 6 would be stuck in the OFF state.
The operation of the relay driving circuit of this type of structure is explained next.
The switching element 3 repetitively turning ON/OFF when the continuous pulse is inputted from the microcontroller (not shown) causes the DC voltage, which is supplied from the DC power supply 2, to be converted into a pulse voltage that is synchronized with the continuous pulses, as illustrated in
The converted pulse voltage passes through the transformer 1 to propagate from the primary side to the secondary side thereof. At this time, the transformer 1, as illustrated in
The pulse voltage that is transmitted to the secondary side of the transformer 1 is again converted into a DC voltage, as illustrated in
If there is a failure in the microcontroller, the switching element, or the like, so that the pulses are not inputted continuously, then, in the present example, the driving voltage ceases to be supplied to the relay 6 in the secondary-side circuit. For example, if, due to a failure, there were a situation wherein only the low-level or high-level voltage were supplied to the transformer 1 from the primary-side circuit, then the power supply that is connected to the primary-side circuit would be the DC power supply 2, and thus the electric current in the secondary-side circuit would stop. In this way, in the present example, the supply of the driving voltage to the relay 6 in the secondary-side circuit, and, by extension, the operation of the relay 6, can be prevented when a fault occurs, and thus there is excellent safety.
Here, when comparing with the conventional relay driving circuit, in the conventional relay driving circuit only the power stored in the capacitor was used as the driving power supply for the relay, and thus, as illustrated in
Additionally, in the present example, as explained above, it is possible to provide, to the relay 6, the power that is stored in the inductor of the transformer 1 and in the capacitor, so that the driving current of the relay 6 is not controlled by the capacitance of the capacitor, thus making it possible to supply a large driving current to the relay 6, which reduces the ripple component in the voltage between the terminals of the relay 6, which, as a result, makes it possible to perform stabilized controlled. Furthermore, it is possible to increase the power efficiency through the ability to provide power to the relay 6 without charging/discharging the capacitor by turning the transistor ON/OFF based on a control signal, because the power is supplied to the relay 6 by a transformer 1 through modulating, based the control signal, the power that is supplied to the primary coil of the transformer 1.
Additionally, in the example, the provision of the transformer 1 isolates the primary side circuit, to which the microcontroller is connected, from the secondary-side circuit, to which they relay 6 is connected, thus making it possible to prevent the propagation of noise to the microcontroller side, which, as a result, makes it possible to perform stabilized controlled. That is, because there is double isolation between the microcontroller and the load, there is enhanced safety when a fault occurs, such as a short in the load. Furthermore, because the power supply is produced locally, there is no need for a driving power supply for the relay 6, making it possible to provide power also to circuitry other than the relay 6, such as for failure diagnostics. Above all, there is no need to use an electrolytic capacitor, or the like, as the driving power supply for the relay 6 when the power capacity of the relay 6 is small, which means that the service life of the circuit will not be dependent on the service life of the electrolytic capacitor which, as a result, can increase the service life of the circuit.
Additionally, the present example makes it possible to set the driving voltage for the relay 6 by controlling the switching frequency or duty ratio, enabling selection from a variety of relays. That is, it is necessary to use a switching element 3 or a DC/AC converter to cause the electric current that is supplied to the primary side of the transformer 1 to be a pulsed current or an AC current in order to drive the transformer 1 when using a DC power supply such as in the present example, or in other words, it is necessary to perform modulation. However, it is possible to change the voltage that is supplied by the secondary side of the transformer 1 to the relay 6, through using a modulating circuit to set, as appropriate, the electric current waveform that is supplied to the primary side of the transformer 1.
Additionally, the transformer 1 may be such that a voltage that is larger than the input voltage on the primary side is outputted, as the secondary side voltage, to the relay 6 (that is, the voltage may be stepped up). Conventionally, it has been necessary to select and use a relay that depends on the supply voltage. However, in the present example a supply voltage that is suitable to the relay is produced through the settings for the switching element 3 and the transformer 1, enabling the design of the circuit to be performed more easily.
Furthermore, in the present example, voltage regulation control can be performed through feeding back the output voltage to the microcontroller, to achieve stabilized relay control and diagnostics.
The present invention can be applied to a variety of devices that are provided with electromagnetic relays.
Number | Date | Country | Kind |
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2010-079486 | Mar 2010 | JP | national |