JPH0351626A - Drive circuit for solenoid valve for combustion device - Google Patents

Abstract

PURPOSE:To take a measure to meet the occurrence of a short circuit trouble to an element current passage by a method wherein when a fuel feed flow passage is to be closed, a cutoff command signal is outputted to all semiconductor power switching elements from a control circuit. CONSTITUTION:When a solenoid valve 12 is kept in a closed state, a significant signal of a level L is outputted from a solenoid valve control circuit 11, a pair of photo couplers PC1 and PC2 are both in an ON-state, and a pair of power transistors Q1 and Q2 are both in an OFF-state. In this case, even when a short circuit trouble occurs to the first pnp transistor Q1, the collector terminal voltage of the other transistor Q2 holding a normal OFF-state is brought into a state to be approximately equal to a source voltage V<+> and therefore, the potential is inputted to the base of a pnp transistor Q4. As a result, the transistor Q4 is energized and a base potential enough for ensurance of an OFF-state is inputted to the transistor Q2 without depending upon the state of a parallel photo coupler PC2.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a drive circuit for a 1M1 valve that opens and closes a fuel supply flow path in various combustion equipment, and in particular, a semiconductor switching element is used to open and close a solenoid valve drive current. This invention relates to an improvement that enables self-diagnosis of a short-circuit failure in the element when the element is used, and prevents a solenoid valve from being erroneously turned on by one ton of drive. [Prior Art] Gas water heaters and other types of combustion equipment naturally require a drive current to supply fuel to the combustion section only when it is to be used, and to ensure that the fuel supply is cut off when not in use. A solenoid valve is required to selectively open and close the fuel supply channel depending on the presence or absence of fuel. However, conventionally, in order to supply a driving current to this electromagnetic valve when fuel should be supplied and to cut off the driving current when fuel should be cut off, a relay contact of an electromagnetic relay was inserted in series with the electromagnetic valve. It was done by turning it on and off. That is, as shown in FIG. 2, the conventional drive circuit for the electric 611 valve 12 is simply an electromagnetic relay Rv and a bibolar driver transistor q. For example, from the solenoid valve control circuit 11, a relatively high level
When a significant fuel supply command signal is output at "H", driver transistor q turns on and the power supply potential VC
The power supply for the control circuit system of C supplies power to the excitation coil in Relay Ro to close the relay contact, thereby causing the solenoid valve drive power supply of power supply potential v4 to drive the solenoid valve l2.
Current is supplied. Of course, in such equipment, for safety, solenoid valve 1
2 is designed to open the fuel supply flow path when it receives a driving current, and when the driving current is stopped, it returns to the closed state due to its built-in mechanical spring force. ing. In the figure, the solenoid valve control circuit 11 is designated as "c p u", but for example, in modern water heaters, microcomputers are often used for combustion control, so the solenoid valve control circuit l1 This function is often performed by this microcomputer, so
This is a general notation for such a microcomputer. In other words, the solenoid valve control circuit 11 is
It can be thought of as a schematic representation of the functions that a computer (CPU) performs regarding the control of the solenoid valve l2 in hardware. As stated in advance, this point is exactly the same in the summary of the present invention and in the embodiments of the present invention that will be described later. [Problems to be Solved by the Invention] Regarding the conventional solenoid valve drive circuit as described above, the problem to be addressed in the present invention is that the solenoid valve 12 is directly turned on/off.
This is due to the presence of relay Rv which is controlling off. In other words, since this type of relay rotor is an electromechanical element, there are many causes of failure and the shape tends to be large.
This becomes a factor that prevents miniaturization of the entire device. Therefore, if possible, it would be better to avoid their use and use semiconductor power switching elements, which are much smaller than such relays and have an order of magnitude lower failure rate. Furthermore, even with existing technology, it is not impossible in terms of circuits. For example, by using semiconductor power switching devices that are already available, such as bipolar power transistors, insulated gate bipolar power transistors, or MIS or MOS field effect power transistors, If the IE flow path (emitter-collector current path or source-drain current path) is inserted in series with a solenoid valve and driven by a suitable driver circuit, the electromagnetic valve can be used without any circuit problems using conventional technology. A valve drive circuit can be obtained. Despite this, until now there has been hesitation in incorporating these semiconductor power switching devices into actual products. The reason for this is as follows. As mentioned above, this type of semiconductor power switching element has a much lower failure rate than a relay, which is an electromechanical element and includes a moving part. However, the problem is that if a failure were to occur, it would generally result in a short-circuit failure. When a short-circuit failure occurs, the solenoid valve remains open even though the combustion control circuit issues a command to close the fuel flow path, resulting in raw fuel leakage, which is the most important thing to avoid in this type of combustion equipment. ．． That point,
With electromagnetic relays, there are many failures where the contacts remain open, so at least the probability of supplying unintended drive current to the itin valve is small, which improves the safety of the combustion equipment as a whole. If so-called fail-safe is important, such relays will inevitably be chosen over semiconductor devices. In view of these circumstances, the present invention aims to make the semiconductor power switching element, which has been desired to be adopted in the past, to a state where it can be practically used as an IEiii valve driving means. [Means for Solving the Problems] In order to achieve the above object, the present invention provides an electric wire for driving a solenoid valve. First, the element current paths of a plurality of semiconductor power switching elements are interposed in series in the supply line of the fuel supply line, and then, when the fuel supply passage is to be opened,
A conduction command fX should be given from the control circuit to all of these multiple semiconductor power switching elements to make the element current paths of all of these semiconductor power switching elements conductive and conversely close the fuel supply channel. when,
A cut-off command signal is given to all semiconductor power switching elements from the control circuit. However, even if a semiconductor power switching element is used, according to the conventional concept, one semiconductor power switching element inserted in series with the electric 6fl valve is usually sufficient, but in the present invention, As mentioned above, there are at least two or more.

Further, in the present invention, the current path of each of the plurality of semiconductor power switching devices arranged in series with each other is individually monitored by a short-circuit detection circuit, and when the device current path should be in a non-conducting state, In other words, if there is an element that is short-circuited when a cut-off command signal is given from the control circuit, the short-circuit detection circuit detects this and switches on other semiconductor power devices that have not caused the short-circuit failure. Forcibly maintains the switching element in a cut-off state. In addition, in the above, other semiconductor power switching elements that are maintained in a cut-off state by the short circuit detection circuit are those that have caused a short circuit failure when a total of three or more semiconductor power switching elements are used in series. Of the two or more semiconductor power switching elements remaining after excluding the semiconductor power switching element, it is sufficient that it is at least one, but conversely, it may be all of the remaining semiconductor power switching elements. Further, as described above, although the present invention is generally configured with a plurality of (ie, two or more) semiconductor power switching elements, it is actually sufficient to use only two.

[Function] In the present invention, in the drive electric cable supply line of the solenoid valve,
Since they both have multiple semiconductor power switching elements that receive on/off commands from the control circuit, this alone increases safety. In other words, when the solenoid valve is to be operated to close the fuel supply channel without applying a driving electric channel to the solenoid valve, a cutoff command f3 is naturally given to all semiconductor power switching elements from the control circuit. Therefore, if there is a normal semiconductor power switching element among these multiple semiconductor power switching elements that has not caused a failure, the current path of that element will normally be in a non-conducting state. Even if a short-circuit failure occurs in all of the semiconductor power switching devices in the device, the drive current supply line will not be closed and the drive current will not close because the current paths of these multiple devices are all inserted in series with the solenoid valve. It will never become possible.

Considering this, it goes without saying that the more semiconductor power switching elements inserted in series, the more
Although the failure rate decreases, in general, the minimum number of two is sufficient even within the limit of multiple according to the present invention. The probability that both of the semiconductor power switching devices will suffer a short-circuit failure at the same time is so low that it can be almost ignored.

Nevertheless, in the present invention, the safety of this type of combustion equipment is not ensured solely by the theory of numbers, that is, by the number of semiconductor power switching elements; It also detects short-circuit failures in semiconductor power switching devices. In other words, the short-circuit detection circuit monitors the individual element current paths of multiple semiconductor power switching elements provided in series, and when a cut-off command signal is given to all semiconductor power switching elements from the control circuit. If there is an element that is in a short-circuit state without properly blocking the element canal passage, it will force the other elements to be in a cut-off state. Therefore, it is possible to reliably open the supply line of the solenoid valve drive current that includes the element current paths of these semiconductor power switching elements in series, and prevent the solenoid valve from accidentally opening the fuel supply flow path. It is almost completely suppressed. [Embodiment] FIG. 1 shows a preferred embodiment of a solenoid valve drive circuit constructed according to the present invention. Solenoid valve control circuit 1
! As already explained with reference to FIG. 2, the solenoid valve control circuit I1 and the solenoid valve l2 may be ones that have been conventionally provided in this type of combustion equipment. As indicated by "CPU", a microcomputer can also perform this function. However, from the point of view of safety as already mentioned, unlike the conventional method which purposely used a t6Ti relay Rv instead of a semiconductor power switching element, although it has various other advantages, the present invention In the case, the solenoid valve l
As a selective drive means of 2, such semiconductor power
A plurality of switching elements are actively used, and in the illustrated embodiment, a PnP transistor q1 and an npn transistor q. is used. That is, in the line that selectively supplies N driving current to the solenoid valve l2 from the power supply potential v0, there is an element canal path (emitter-collector main current line) of each of these PnP} transistor Q+ and npn transistor q2. ) are installed in series, and in particular, in the illustrated embodiment, the first transistor q, is inserted into the hot side of the solenoid valve l2, and the second transistor q7 is inserted into the cold side or the ground (GND) side. I'm here.

In the following, each component will be explained while following the operation of the device according to the first illustrated embodiment, but the normal operation will be explained first. When the solenoid valve control circuit 1l should apply electric power to the solenoid valve 12 to open a fuel supply channel (not shown), it is defined at a relatively high level "H" (outputs a signal W, and stops the fuel supply. When the flow path should be closed, the signal level is set to a relatively low level "L".As will be understood from the later explanation, the signal emitted by this control circuit l1, when it is at the "H" level, Then, the transistor Q+, which is the -5th second semiconductor power switching element. Assuming that the emitted signal changes from the previous "L" level to the "H" level as shown in FIG. 1, this signal is inverted by the inverter G and becomes the "HI" level. is applied to the bases of a pair of npn} transistors Qs, Qs.Then, these pair of npnl-transistors Qs, q.
As will be explained later, the element is turned off from its previously on state, and its emitter-collector element current path becomes non-conductive.

Then, with respect to the power supply potential VCC, these pair of transistors Qs . A pair of photocoupler pc, , PC2 inserted in series with the element current path of Qs
Power is no longer supplied to the human-powered side light emitting diode, and the output side transistor turns off. This results in a circuit in the first pnp power transistor Q1 whose base is substantially pulled down to ground via the resistor R, so that the first transistor A base current flows from the resistor R toward ground (GND) through the emitter and base of q1, and this turns on.

On the other hand, by similarly turning off the output side transistor of the second photocoupler Pc2, the second power
Also in the npn transistor Q, which is a transistor, a base current flows from the power supply hot side terminal at the potential v0 to the ground via the resistor R4, the base and emitter of the transistor q, and this turns on. Therefore, since the element current paths of these pairs of power transistors Q+, (12) inserted in series in the solenoid valve l2 are conductive together, the 74 solenoid valve l2 receives a drive power from an N source of potential V'. A fuel supply channel (not shown) must be opened.

According to this normal operating state, when the pair of power transistors Q+ and Q2 are both turned on and driving current is supplied to the solenoid valve l2, as will be seen in the explanation for the failure state later, the main The pair of transistors Q3 and Q4, each forming part of a short circuit detection circuit provided in accordance with the invention, together do not impair such normal operation in any way. That is, the transistor Q3 configured as a pnp transistor has a circuit configuration of C
The emitter-collector line is short-circuited between the base and emitter of the first power transistor Q1, so when the first power transistor Ql is initially turned on, the solenoid valve l2 is turned on. Then, the hot side potential V of the voltage &ii #I 2. Even if the voltage becomes a low value close to ground potential and is applied to the base of this transistor Q3 through the resistor R, the collector is Since the emitter voltage is clamped, conduction cannot occur. Similarly, the np whose collector emitter is connected between the base and emitter of the second power transistor q2
nl- transistor Q4 also has its base connected to the collector ffll+ of the second power transistor Q, via a resistor R,
, so the second power transistor Q2
When it turns on and its collector potential becomes low enough, it still cannot conduct. Next, to explain the case where the solenoid valve control circuit 1 cuts off the drive current to the solenoid valve l2 to block the fuel supply channel, the solenoid valve filJ control circuit 11 at this time:
As a cutoff command signal for the first and second power transistors Q+ and Qz, their output (g) is set to a relatively "L" level. When this happens, the output of the inverter G1 is inverted and becomes relatively "L" level. becomes “H” level, and a pair of np
nl-transistor Qs. Apply a significant base potential to both Qa to turn them on. Along with this, power is supplied from the power source of the potential VCC to the human-powered light emitting diodes of the first and second photocoupler PC, , PC to cause them to emit light,
Therefore, the built-in output transistor is also turned on. Then, this first Photo Cabra PC turned on. A potential v0 is generated across the resistor R, which had previously pulled down the base of the first power transistor q1 to approximately ground potential, through the output transistor of the first power transistor Q1. Since the voltage rises to that value, the corresponding transistor Q is turned off.

At the same time, the built-in output transistor of the second photocoupler PC2 is also turned on, so that until then the resistor R4
The base current that was being applied to the base of the second power transistor q2 through the transistor q2, which is the second power transistor, is bypassed by the transistor with a built-in photocoupler that is turned on, and therefore the second power transistor q is also turned on.・Turn off.

As a result, the solenoid valve 12 is cut off from the supply of driving electric power from the power source at the potential V°, and the not-shown fuel supply flow path is closed by the action of the built-in spring means (not shown). Under this normal operating condition, the first and second power
Regarding the turn-off of the transistors Q+, No misfortune will come.In the first place, the first and second Photo Cabra pc, , pc,
By turning on both output transistors, the base-emitter of the first and second power transistors Q+, Ch is short-circuited, and these transistors Q+, (h are turned off. In this state, the transistor Qs, which will be connected in parallel to the short circuit path caused by the photocoupler output transistor,
No matter what the on/off state of Q- is, it has no effect on the above operation. However, these transistors Q3 and Q4
When the n-valve l2 is closed, the drive Ii for this
A pair of power transistors Q+ . (If a short-circuit failure occurs in any one of h, it will function effectively as follows.

t When maintaining the solenoid valve l2 in the closed state, as described above, a significant signal at the "L" level is output from the solenoid valve control circuit l1, and as a result, both the pair of photocouplers PC+ and PC2 are closed. The on state, ie, their output transistors are in the conducting state, so that the pair of power transistors Q+.(h) are both designed to be in the off state.

However, in this case, if the first pnρ transistor q
A short-circuit failure occurs in 1, and the power transistor q
Even if conduction occurs between the collector and emitter of one power transistor Q2, according to the illustrated circuit structure, the collector terminal voltage of the other power transistor Q2, which normally maintains an off state, is approximately equal to the power supply potential v0, so the resistor This potential is applied to the base of the npn transistor Q4 via R2, and as a result, this transistor q4 becomes conductive by receiving supply of the element wire from the power supply potential v0 via the resistor R4, and therefore, the transistor q4 is connected in parallel to it. Regardless of the state of the photocoupler PC (that is, even if there is some failure), a low base potential is applied to the second power transistor Q2 to ensure its off state. In other words, as a backup function of the photocoupler PC2, it is ensured that the second power transistor q2 is in the OFF state. Therefore, even if the first power transistor q1 has a short-circuit failure, the second power transistor Q2
In other words, the forced shutoff command signal can be continuously given from the transistor Q4b), and the electric current is accidentally supplied to the solenoid valve l2, and raw fuel such as raw rice is discharged from the unexpectedly opened fuel supply channel. The risk of leakage can be kept to a sufficiently low level. In exactly the same way, in the event of a short-circuit fault in the direction of the second power transistor q, such a risk of raw fuel leakage can be prevented with a very high degree of certainty, i.e. The value of the resistor R1 provided between the collector emitter of q1 is determined by the solenoid valve l2.
If the resistance is set sufficiently higher than the expected resistance R1 (R.>>Rl). If a short-circuit fault occurs in the second power transistor Q, the hot fIll of the solenoid valve l2
Since the potential v0 of I, that is, the base potential of transistor q, can be set to a sufficiently low value close to ground potential, this transistor q3 can be turned on, and with respect to the first power transistor Q+, As a forced cut-off command signal from this transistor Q3, a high Haes potential can be continuously applied, and in other words, it functions as further backup for the photocoupler PCI at this time. Although the illustrated embodiment has been described in detail above, the number of semiconductor power switching elements used is arbitrary, and it is possible to expand the number of semiconductor power switching elements to three or more connected in series. Of course, in the case of the illustrated embodiment, semiconductor power switching elements are allocated to the hot side and cold side of valve iii 12, but these multiple semiconductor power switching elements are allocated only to the hot side or only for cold measurement. may be provided. Also, as a semi-i-body power switching element itself,
In the case shown, it is a current drive! Although a bibolar power transistor, which is a JJ-type element, is used, other voltage-driven devices such as the recently developed insulated gate bibolar transistor (IGBT), or MIS or MOS field effect power transistors are used.・Uses transistors, etc.
It is also possible to apply a potential as the gate potential to issue an OFF command when such a short-circuit failure is detected.

Furthermore, if a total of three or more semiconductor power switching elements are used in series, at least one of the remaining two or more semiconductor power switching elements excluding the semiconductor power switching element that has caused a short-circuit failure, It is sufficient if the configuration is such that a forced cut-off command signal is sent to one, but it may be configured to send a forced cut-off command signal to all the remaining ones.

However, as mentioned above, it is actually sufficient to use two semiconductor power switching elements as in the illustrated embodiment. The probability that two semiconductor power switching elements will cause a short-circuit failure at the same time is so low as to be almost negligible, and therefore, in this sense as well, the present invention is effective. Conversely, even if this is not the case, the number of semiconductor power switching elements is now two or more, and the risk of erroneous opening of the solenoid valve due to a short circuit failure is extremely low. Efforts are being made to ensure even greater safety.

[Effects] According to the present invention, the present invention is considered desirable due to its small size and low failure rate, but when it does fail, it often results in a short-circuit failure. This opens the door to the actual use of power switching elements as solenoid valve control means for this type of combustion equipment.In other words, even when semiconductor power switching elements are used as driving elements for electric 6F1 valves, combustion The safety of the device as a whole is not compromised at all, but rather can be significantly improved.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a preferred embodiment of a solenoid valve drive circuit for combustion equipment constructed according to the present invention. Figure 2 is a schematic diagram of a relay-based solenoid valve drive circuit that has been typically used in the past. It is. In the figure, 11 is a t magnetic valve control circuit, 12 is an electric 61 valve, and q. Q
, are bipolar power transistors as semiconductor power switching elements, Q3 and Qa are transistors forming part of a short circuit detection circuit, Qs and Qa are driver transistors for photocoupler, PC,
, P.C. is photocabra, Rl + R2 + R
3 + R4 +R, is the resistance, vo is the potential of the hot side terminal of the solenoid valve at any given time, and v0 is the potential of the power source for supplying the solenoid valve driving electric wire.

Claims (1)

[Scope of Claims] A drive circuit for a solenoid valve for a combustion device that opens a fuel supply flow path of the combustion device when receiving a drive current; wherein each element current path is provided in a supply line for the drive current to the solenoid valve. a plurality of semiconductor power switching elements interposed in series; a conduction command signal is sent to all of the plurality of semiconductor power switching elements when the fuel supply flow path should be opened, and a cutoff command signal is sent to all of the plurality of semiconductor power switching elements when the fuel supply flow path should be closed; a control circuit for outputting; individually monitoring the element current paths of the plurality of semiconductor power switching elements, and detecting any short-circuited element when receiving a cutoff command signal from the control circuit; , a short-circuit detection circuit that maintains other semiconductor power switching elements that have not caused a short-circuit failure in a cut-off state; and a drive circuit for a solenoid valve for combustion equipment.