JP5235847B2 - Heater drive circuit - Google Patents

Description

  The present invention relates to a heater drive circuit for energizing and driving an electric heater.

  There are various types of heating apparatuses that use an electric heater (hereinafter simply referred to as “heater”). For example, an electric carpet includes a heater driving circuit that energizes and drives one or more heaters arranged in the carpet body. In this heater drive circuit, one or more heater energizing relay contacts are provided on a one-to-one basis in an energizing path to one or more heaters that are branched from a temperature fuse, and each coil of the one or more heater energizing relays is provided. ON / OFF control of energizing transistors that individually control energization to the power supply is performed according to the start / stop of operation instructed by the user, thereby energizing and stopping one or more heaters. .

  However, in this heater drive circuit, when the contact of the energizing relay is welded, or when the energizing transistor is short-circuited, the energizing relay is held in the ON operation state that closes the energization path to the heater. Therefore, the heater remains energized regardless of the user's intention to use, which causes a safety problem.

  Therefore, for example, in Patent Document 1, when the energization relay is turned ON due to the contact welding of the energization relay or the short circuit failure of the energization transistor, the thermal resistor is forcibly energized, and the thermal fuse is heated to generate the temperature fuse. There has been proposed a method of cutting off the power to the heater by fusing.

Japanese Patent Publication No. 5-20653

  However, the technique described in Patent Document 1 is insufficient as a method for solving the problem because the heater is continuously energized until the thermal fuse is blown. Further, when replacing the service, it is necessary to replace not only the board on which the heater drive circuit is mounted but also the wiring into which the thermal fuse is inserted, which places a heavy burden on the user.

  The present invention has been made in view of the above, and when an ON failure of the energizing relay due to contact welding of the energizing relay or a short circuit failure of the energizing transistor is detected, the heater can be quickly supplied without fusing the thermal fuse. An object of the present invention is to obtain a heater drive circuit capable of stopping the energization of the heater.

  In order to achieve the above-described object, the present invention provides one or more energizing relays whose contacts are connected to respective energizing paths from a commercial power source to one or more electric heaters, and the coils of the one or more energizing relays. The one or more energization switching elements that control energization of the current and the one or more energization switching elements between the start of operation and the stop of operation specified by the user are turned on, and the contact points of the one or more energization relays are A heater driving circuit comprising a control circuit for performing a heater operation mode for controlling the circuit in a closed state; a shut-off relay whose contact is connected to an energization path between the commercial power supply and the one or more energization relay contacts; , A heater switching element for detecting a heater current flowing between the commercial power source and the one or more electric heaters; The control circuit is complementary to the one or more energization switching elements and the shut-off switching element both or one of when the operation start instruction is input and when the operation stop instruction is input. Based on the comparison between the current value detected by the heater current detection circuit at that time and the determination value, whether or not each of the one or more energization relays and the disconnection relay has an ON failure is determined. When an ON failure is detected in any one of the relays, an abnormal stop process for opening one of the other relay contacts is performed.

  According to the present invention, when an ON failure occurs in either one of the interruption relay and the energization relay, the energization to the heater can be forcibly stopped quickly by the other normal relay. There is no abnormal state where the heater continues to be energized regardless of the intention, and there is an effect of enabling safe heater control.

1 is a circuit diagram showing a configuration of a heater drive circuit according to Embodiment 1 of the present invention. FIG. 2 is a flowchart for explaining the control procedure of the first operation example of ON failure detection. FIG. 3 is a timing chart for explaining an ON failure detection operation performed by the control procedure shown in FIG. FIG. 4 is a flowchart for explaining the control procedure of the second operation example of ON failure detection. FIG. 5 is a timing chart for explaining the ON failure detection operation performed by the control procedure shown in FIG. FIG. 6 is a flowchart for explaining the control procedure of the third operation example of ON failure detection. FIG. 7 is a timing chart for explaining the ON failure detection operation performed by the control procedure shown in FIG. FIG. 8 is a timing chart for explaining another operation example of the heater drive circuit shown in FIG. 1 as the second embodiment of the present invention.

  Embodiments of a heater drive circuit according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited by this embodiment.

Embodiment 1 FIG.
1 is a circuit diagram showing a configuration of a heater drive circuit according to Embodiment 1 of the present invention. As shown in FIG. 1, in this embodiment, the case where the two heaters 1a and 1b are energized and driven will be described. However, the contents of the description can be applied without problems even when there is one heater or when there are three or more heaters.

  In FIG. 1, one end of a commercial power source 2 is connected to one end of a contact 4 a of a cutoff relay and one input terminal of a power circuit 5 through a power switch (not shown) and a temperature fuse 3. In the illustrated example, one end of each of the contact points 6a and 7a of the two energizing relays is connected in parallel to the other end of the contact point 4a of the interrupting relay. One end of each of the heaters 1a and 1b is connected to the other end of each of the contact points 6a and 7a of the energizing relay, and each other end of each of the heaters 1a and 1b is commonly connected to the other end of the commercial power source 2. . A heater current detection circuit 8 is provided on a connection line between the other ends of the heaters 1 a and 1 b and the other end of the commercial power supply 2. The other end of the commercial power supply 2 is connected to the other input terminal of the power supply circuit 5.

  The heater current detection circuit 8 is an insulation type in the illustrated example, and includes a current transformer 9 in which a primary winding is inserted in a connection line between the other ends of the heaters 1a and 1b and the other end of the commercial power supply 2, and a diode. A rectifier circuit 10 having a bridge configuration, resistors R1 and R2 constituting a voltage dividing circuit, and a smoothing electrolytic capacitor C1 are provided.

  The secondary winding of the current transformer 9 is connected to each input terminal of the rectifier circuit 10, and a voltage dividing circuit (R1, R1) is connected between the positive output terminal of the rectifier circuit 10 and the negative output terminal connected to the circuit ground. R2) is connected. The divided voltage output from the voltage dividing circuit (R1, R2) is smoothed by the electrolytic capacitor C1 and input to the current monitoring port a of the control circuit (hereinafter referred to as “microcomputer”) 11. In short, the heater current detection circuit 8 converts the heater current taken in by the current transformer 9 into a voltage by the rectifier circuit 9 and the electrolytic capacitor C1, and inputs the voltage to the current monitoring port a of the microcomputer 11.

  When the power switch is turned on, the power supply circuit 5 is applied with the commercial power supply 2 to generate two DC power supplies 12 and 13. The DC power source 12 is, for example, a DC 12V power source, and the DC power source 13 is a DC 5V power source.

  An operation control signal indicating an operation start instruction and its stop instruction is input to the user instruction monitoring port b of the microcomputer 11 from a switch (not shown) operated by the user or a remote controller (not shown). The control output ports c, d, e of the microcomputer 11 are connected to control terminals (base terminals) of switching elements (npn transistors in the illustrated example) Q1, Q2, Q3 via resistors R3, R5, R7. Is connected.

  The base terminals of the transistors Q1, Q2, and Q3 are connected to circuit ground via resistors R4, R6, and R8, respectively. The emitter terminals of the transistors Q1, Q2, and Q3 are directly connected to the circuit ground. The collector terminal of the transistor Q1 is generated by the power supply circuit 5 via the coil 4b of the interrupting relay, and the collector terminals of the transistors Q2 and Q3 are respectively generated via the coils 6b and 7b of the energizing relay. It is connected to a DC power supply 12 of DC12V. Reflux diodes D1, D2, and D3 are connected in reverse parallel to the coil 4b for the interruption relay and the coils 6b and 7b for the energization relay, respectively.

  That is, the transistor Q1 corresponds to the cutoff switching element, and when the control output port c of the microcomputer 11 becomes a high level and the base current is supplied, the transistor Q1 is turned on to energize the coil 4b of the cutoff relay. The contact 4a of the breaking relay is closed (ON). The transistors Q2 and Q3 correspond to energization switching elements. When the control output ports d and e of the microcomputer 11 are at a high level and a base current is supplied, the transistors Q2 and Q3 are turned on and energized relay coils 6b and 7b. Are energized and the contacts 6a and 7a of the energizing relay are closed (ON), respectively.

  When the power switch is turned on and the DC power supply 13 of DC 5V is applied from the power supply circuit 5, the microcomputer 11 is, for example, a user instruction monitoring port as shown in the first to third operation examples of ON failure detection. As a part of energization drive control to the heaters 1a and 1b in accordance with the user instruction indicated by the operation control signal input to b, the interruption relays (4a and 4b) and the energization relays (6a and 6b) (7a and 7b) The control program which performs abnormal stop processing using a normal relay when a failure is detected is detected.

  Hereinafter, the control operation performed by the microcomputer 11 will be specifically described focusing on the ON failure detection operation according to this embodiment. The ON failure is a short-circuit failure of the contacts 4a, 6a, and 7a as described above. This occurs when the contacts 4a, 6a, 7a are welded or when the transistors Q1, Q2, Q3 are short-circuited.

(First operation example)
FIG. 2 is a flowchart for explaining the control procedure of the first operation example of ON failure detection. FIG. 3 is a timing chart for explaining an ON failure detection operation performed by the control procedure shown in FIG. In FIG. 3, the input timing of the heater operation start instruction and the heater operation stop instruction to the user instruction monitoring port b, and the cutoff relays (4a, 4b) and energization relays (6a, 6b) controlled on the basis thereof. ) (7a, 7b) ON / OFF state (FIGS. 3 (1), (2) and (3)) and the presence or absence of heater current input to the current monitoring port a (FIG. 3 (4)). ing. These also apply to FIGS. 5, 7, and 8 described later. In FIG. 3, times T1 and T2 are ON failure detection times. Times t1 and t2 are predetermined times for preventing the occurrence of an arc at the relay relay 4a.

  In FIG. 2, when the power switch is turned on and the DC power supply 13 of DC 5V is applied from the power supply circuit 5, the microcomputer 11 sets the control output ports c, d, e to low level and sets the shut-off relays (4a, 4b) and the energizing relays (6a, 6b, 7a, 7b) are both turned OFF (ST1), and the system waits for a heater operation start instruction to be input to the user instruction monitoring port b (ST2).

  When the user instructs the heater operation start (ST2: Yes), the control output port c is held at a low level, and according to the heater operation start instruction, both or either of the control output ports d and e are set to a high level. Then, both or one of the energizing relays (6a, 6b) (7a, 7b) is turned on (ST3), and counting of the ON failure detection time T1 is started (ST4). 3 (2) and 3 (3) show a case where both the energizing relays (6a, 6b) (7a, 7b) are simultaneously turned on. In the following, it is assumed that both the energizing relays (6a, 6b) (7a, 7b) are simultaneously turned ON / OFF in accordance with the notation in FIG.

  The microcomputer 11 determines that the heater current input to the current monitoring port a is determined in advance for ON failure detection within the determination time until the ON failure detection time T1 is counted (ST5: No). It is determined whether or not the value is exceeded (ST6). Note that the determination value is a predetermined value that is not zero in consideration of noise.

  In ST6, when it is detected that the heater current input to the current monitoring port a is equal to or larger than the determination value (ST6: Yes), the microcomputer 11 determines that the interruption relay (4a, 4b) is ON failure, An abnormal stop process for turning off the energizing relays (6a, 6b) (7a, 7b) is executed (ST7), and this procedure is terminated.

  On the other hand, when it is detected in ST6 that the heater current input to the current monitoring port a is smaller than the determination value (ST6: No), the microcomputer 11 determines that the interruption relays (4a, 4b) are normal. Then, after the count of the ON failure detection time T1 is finished (ST5: Yes), the energization relays (6a, 6b) (7a, 7b) are turned off (ST8).

  Then, the microcomputer 11 turns on the interrupting relays (4a, 4b) after elapse of the predetermined time t1 (ST9), and further turns on the energization relays (6a, 6b) (7a, 7b) after elapse of the predetermined time t2. (ST10), a heater operation mode for energizing the heaters 1a and 1b is executed (ST11). At this time, the microcomputer 11 monitors the input of the operation stop instruction to the user designated monitoring port b in the process of executing the heater operation mode (ST11) (ST12).

  In addition, it is determined that the interrupting relays (4a, 4b) are normal, and when switching to the heater operation mode (ST11), the energizing relays (6a, 6b) (7a, 7b) are once turned off (from ST8). Since the interruption relays (4a, 4b) are turned on (ST9), and then the energization relays (6a, 6b) (7a, 7b) are turned on (ST10), the contact 4a of the interruption relays (4a, 4b) It is possible to suppress arc generation in

  When the operation stop instruction is input to the user designated monitoring port b (ST12: Yes) while the microcomputer 11 is executing the heater operation mode (ST11), the energization relays (6a, 6b) (7a, 7b) ) Is turned OFF (ST13), and counting of the ON failure detection time T2 is started (ST14).

  The microcomputer 11 determines that the heater current input to the current monitoring port a is determined in advance for ON failure detection within the determination time until the ON failure detection time T2 is counted (ST15: No). It is determined whether or not the value is exceeded (ST16).

  When it is detected in ST16 that the heater current input to the current monitoring port a is equal to or larger than the determination value (ST16: Yes), the microcomputer 11 turns on the energization relays (6a, 6b) (7a, 7b). It is determined that there is a failure, an abnormal stop process for turning off the interrupting relays (4a, 4b) is executed (ST17), and this procedure is terminated.

  On the other hand, when it is detected in ST16 that the heater current input to the current monitoring port a is smaller than the determination value (ST16: No), the microcomputer 11 performs energization relays (6a, 6b) (7a, 7b). Is determined to be normal, waits for the count of the ON failure detection time T2 to end (ST15: Yes), turns off the interrupting relays (4a, 4b) (ST18), returns to ST2, and instructs to start the next operation Wait for input.

  To summarize the above, as shown in FIG. 3, all the relays are turned off and the input of the heater operation start instruction is waited. When the heater operation start instruction is input, the interruption relays (4a, 4b) are turned off. Hold and set the energizing relays (6a, 6b) (7a, 7b) to the ON state within the ON failure detection time T1, and monitor the heater current at that time to turn on the disconnecting relays (4a, 4b). Judgment is made.

  If an ON failure is detected in the interruption relays (4a, 4b) within the ON failure detection time T1, the energization relays (6a, 6b) (7a, 7b) are turned OFF at that time, and an abnormal stop occurs. If the relays (4a, 4b) are normal, as shown in FIG. 3, it is normal after the predetermined time t1, t2 is set and the arc generation at the contact 4a of the interrupting relay (4a, 4b) is suppressed. Transition to the heater operation mode.

  When the heater operation stop instruction is input, only the energization relays (6a, 6b) (7a, 7b) are turned OFF, and the heater current is monitored within the ON failure detection time T2 to detect the energization relays (6a, 6b). ) (7a, 7b) to determine whether there is an ON failure. If an ON failure of the energizing relays (6a, 6b) (7a, 7b) is detected within the ON failure detection time T2, the shut-off relays (4a, 4b) are turned OFF at that time and an abnormal stop occurs. When the relays (6a, 6b) (7a, 7b) are normal, as shown in FIG. 3, the interruption relays (4a, 4b) are turned OFF when the ON failure detection time T2 has elapsed, and the next heater operation starts. It will be in the state of waiting for input of an instruction.

(Second operation example)
FIG. 4 is a flowchart for explaining the control procedure of the second operation example of ON failure detection. FIG. 5 is a timing chart for explaining the ON failure detection operation performed by the control procedure shown in FIG. In FIG. 3, times T3 and T4 are ON failure detection times. Times t3 and t4 are predetermined times for preventing the occurrence of an arc at the contact point 4a of the interrupting relay.

  In FIG. 4, when the power switch is turned on and the DC power supply 13 of DC 5V is applied from the power supply circuit 5, the microcomputer 11 sets both the control output ports c, d, e to a low level and disconnects the relays (4a, 4b) and the energizing relays (6a, 6b, 7a, 7b) are both turned OFF (ST20), and the system waits for the heater operation start instruction to be input to the user instruction monitoring port b (ST21).

  When the user gives an instruction to start the heater operation (ST21: Yes), first, the control output port c is set to a high level and the cutoff relays (4a, 4b) are turned ON (ST22). According to the operation start instruction, both or one of the control output ports d and e are set to a high level, and both or one of the energizing relays (6a, 6b) (7a, 7b) is turned on (ST23). The heater operation mode is executed (ST24). 5 (2) and (3) show a case where both the energizing relays (6a, 6b) (7a, 7b) are simultaneously turned on. In the following, it is assumed that both the energizing relays (6a, 6b) (7a, 7b) are simultaneously turned ON / OFF in accordance with the notation in FIG.

  In the process of executing the heater operation mode (ST24), when the microcomputer 11 inputs an operation stop instruction to the user-specified monitoring port b (ST25: Yes), the energizing relays (6a, 6b) (7a, 7b) ) Is turned OFF (ST26), and counting of the ON failure detection time T3 is started (ST27).

  The microcomputer 11 determines that the heater current input to the current monitoring port a is determined in advance for failure detection within the determination time until the ON failure detection time T3 is counted (ST28: No). It is determined whether or not (ST29).

  In ST29, when it is detected that the heater current input to the current monitoring port a is equal to or larger than the determination value (ST29: Yes), the microcomputer 11 turns on the energizing relays (6a, 6b) (7a, 7b). It is determined that there is a failure, an abnormal stop process for turning off the interrupting relays (4a, 4b) is executed (ST30), and this procedure is terminated.

  On the other hand, when it is detected in ST29 that the heater current input to the current monitoring port a is smaller than the determination value (ST29: No), the microcomputer 11 switches the energizing relays (6a, 6b) (7a, 7b). Is determined to be normal, waits for the count of the ON failure detection time T3 to end (ST28: Yes), and then the shut-off relays (4a, 4b) are turned off (ST31). Then, after the elapse of the predetermined time t4, the energizing relays (6a, 6b) (7a, 7b) are turned on (ST32), and counting of the ON failure detection time T4 is started (ST33).

  The microcomputer 11 determines that the heater current input to the current monitoring port a is determined in advance for failure detection within the determination time until the ON failure detection time T4 is counted (ST34: No). It is determined whether or not (ST35).

  In ST35, when it is detected that the heater current input to the current monitoring port a is equal to or larger than the determination value (ST35: Yes), the microcomputer 11 determines that the interruption relay (4a, 4b) is ON failure, An abnormal stop process for turning off the energizing relays (6a, 6b) (7a, 7b) is executed (ST36), and this procedure is terminated.

  On the other hand, when it is detected in ST35 that the heater current input to the current monitoring port a is smaller than the determination value (ST35: No), the microcomputer 11 determines that the interruption relays (4a, 4b) are normal. After waiting for the count of the ON failure detection time T4 to end (ST34: Yes), the process returns to ST21 and waits for the input of the next operation start instruction.

  ST22 and ST23, and ST31 and ST32 are processes for suppressing arc generation at the contact point 4a of the interrupting relay (4a, 4b), respectively.

  To summarize the above, as shown in FIG. 5, all relays are turned off and the input of the heater operation start instruction is waited. When the heater operation start instruction is input, first, the interruption relays (4a, 4b) The heater is turned on after the elapse of a predetermined time t3, and the normal relay heater (6a, 6b) (7a, 7b) is turned on to suppress arc generation at the contact point 4a of the interrupting relay (4a, 4b). Transition to operation mode. When a heater operation stop instruction is input, only the energizing relays (6a, 6b) (7a, 7b) are turned off, and the heater current is monitored within the ON failure detection time T3 to detect the energizing relays (6a, 6b). ) It is determined whether or not there is an ON failure in (7a, 7b).

  If an ON failure of the energizing relays (6a, 6b) (7a, 7b) is detected within the ON failure detection time T3, the shut-off relays (4a, 4b) are turned OFF at that point and an abnormal stop occurs. If the relays (6a, 6b) (7a, 7b) are normal, as shown in FIG. 5, first, when the ON failure detection time T3 has elapsed, the interruption relays (4a, 4b) are turned OFF, and the predetermined time t4 By turning on the energizing relays (6a, 6b) (7a, 7b) after the elapse of time, arc generation at the contact point 4a of the breaking relays (4a, 4b) is suppressed, and the energizing relays (6a, 6b) (7a 7b), the heater current is monitored within the ON failure detection time T4 when the ON state is ON, and it is determined whether or not the interruption relays (4a, 4b) are ON.

  If an ON failure is detected in the interrupting relay (4a, 4b) within the ON failure detection time T4, the energizing relays (6a, 6b) (7a, 7b) are turned OFF at that time and an abnormal stop occurs. If the relays (4a, 4b) are normal, as shown in FIG. 5, the energization relays (6a, 6b) (7a, 7b) are turned OFF after the ON failure detection time T4 has elapsed, and the next heater operation starts. It will be in the state of waiting for input of an instruction.

(Third operation example)
FIG. 6 is a flowchart for explaining the control procedure of the third operation example of ON failure detection. FIG. 7 is a timing chart for explaining the ON failure detection operation performed by the control procedure shown in FIG. In FIG. 7, times T5 and T6 are ON failure detection times. Times t5 and t6 are predetermined times for preventing the occurrence of an arc at the contact point 4a of the interrupting relay.

  In FIG. 6, when the power switch is turned on and the DC power supply 13 of DC 5V is applied from the power supply circuit 5, the microcomputer 11 sets both the control output ports c, d, and e to a low level and sets the cutoff relays (4a, 4b) and the energizing relays (6a, 6b) (7a, 7b) are both turned OFF (ST40), and the system waits for the heater operation start instruction to be input to the user instruction monitoring port b (ST41).

  When the user gives an instruction to start the heater operation (ST41: Yes), first, both of the control output ports d and e are set to a high level according to the designation, and both the energizing relays (6a, 6b) (7a, 7b) are set. Alternatively, either one is turned on (ST42), and counting of the ON failure detection time T5 is started. 7 (2) and 7 (3) show a case where both the energizing relays (6a, 6b) (7a, 7b) are simultaneously turned on. In the following, it is assumed that both the energizing relays (6a, 6b) (7a, 7b) are simultaneously turned ON / OFF in accordance with the notation in FIG.

  The microcomputer 11 determines that the heater current input to the current monitoring port a is determined in advance for ON failure detection within the determination time until the ON failure detection time T5 is counted (ST44: No). It is determined whether or not the value is exceeded (ST45).

  In ST45, when it is detected that the heater current input to the current monitoring port a is equal to or larger than the determination value (ST45: Yes), the microcomputer 11 determines that the interruption relay (4a, 4b) is ON failure, An abnormal stop process for turning off the energizing relays (6a, 6b) (7a, 7b) is executed (ST46), and this procedure is terminated.

  On the other hand, when it is detected in ST45 that the heater current input to the current monitoring port a is smaller than the determination value (ST45: No), the microcomputer 11 determines that the interruption relays (4a, 4b) are normal. Then, after the count of the ON failure detection time T5 is finished (ST44: Yes), the energization relays (6a, 6b) (7a, 7b) are turned off (ST47), and the disconnecting relay (4a, 4b) is turned ON (ST48), and counting of the ON failure detection time T6 is started (ST49).

  The microcomputer 11 determines that the heater current input to the current monitoring port a is determined in advance for ON failure detection within the determination time until the count of the ON failure detection time T6 ends (ST50: No). It is determined whether or not the value is exceeded (ST51).

  When it is detected in ST51 that the heater current input to the current monitoring port a is equal to or larger than the determination value (ST51: Yes), the microcomputer 11 turns on the energization relays (6a, 6b) (7a, 7b). It is determined that there is a failure, an abnormal stop process for turning off the interrupting relays (4a, 4b) is executed (ST52), and this procedure is terminated.

  On the other hand, when it is detected in ST52 that the heater current input to the current monitoring port a is smaller than the determination value (ST52: No), the microcomputer 11 performs energization relays (6a, 6b) (7a, 7b). Is determined to be normal, and the energization relays (6a, 6b) (7a, 7b) are turned on (ST53) after waiting for the count of the ON failure detection time T6 to end (ST50: Yes), and the heater operation mode is executed. (ST54).

  In the process of executing the heater operation mode (ST54), when the microcomputer 11 inputs an operation stop instruction to the user designated monitoring port b (ST55: Yes), the energization relays (6a, 6b) (7a, 7b) ) Is turned off (ST55), and the relays (4a, 4b) are turned off after a predetermined time t6 (ST57), the process returns to ST41, and the next operation start instruction is awaited.

  Note that ST47 and ST48, and ST56 and ST57 are processes for suppressing arc generation at the contact point 4a of the interrupting relay (4a, 4b), respectively.

  To summarize the above, as shown in FIG. 7, all relays are turned OFF and the heater operation start instruction is waited for input. When the heater operation start instruction is input, the energization relay ( 6a, 6b) (7a, 7b) is turned ON, and the heater current is monitored within the ON failure detection time T5 during which it is continued to determine whether the interruption relay (4a, 4b) is ON.

  If an ON failure is detected within the ON failure detection time T5, the energizing relays (6a, 6b) (7a, 7b) are turned OFF at that point, and an abnormal stop occurs. If the relays (4a, 4b) are normal, as shown in FIG. 7, first, the energization relays (6a, 6b) (7a, 7b) are turned OFF when the ON failure detection time T5 has elapsed, and the predetermined time t5 is reached. After the elapse of time, the interrupting relays (4a, 4b) are turned on to suppress arc generation at the contact point 4a of the interrupting relays (4a, 4b), and the energizing relays (6a, 6b) (7a, 7b) are turned off. During the ON failure detection time T6 maintained in the state, the heater current is monitored to determine whether the energization relays (6a, 6b) (7a, 7b) are ON.

  If an ON failure of the energizing relays (6a, 6b) (7a, 7b) is detected within the ON failure detection time T6, the shut-off relays (4a, 4b) are turned OFF at that point and an abnormal stop occurs. When the relays (6a, 6b) (7a, 7b) are normal, the relays for energization (6a, 6b) (7a, 7b) are turned on after the elapse of the ON failure detection time T6 as shown in FIG. Transition to heater operation mode. When a heater operation stop instruction is input, only the energization relays (6a, 6b) (7a, 7b) are turned off, and the interruption relays (4a, 4b) are turned off after a predetermined time t6. The arc generation at the contact point 4a of the interrupting relay (4a, 4b) is suppressed, and the input of the next heater operation start instruction is awaited.

  As described above, according to the first embodiment, the cutoff relay is provided on the power input side of one or more energization relays, and the circuit for monitoring the heater current is provided. The power relay is turned ON / OFF in a complementary manner, and based on the heater current at that time, it is judged whether there is any ON failure of the relay for relay and the relay for power shortage due to a short circuit failure of the transistor. Each ON failure can be detected.

  At that time, in a normal operation state where no ON failure is detected in both the interruption relay and the energization relay, as shown in the first to third operation examples, the ON / OFF of the interruption relay and the energization relay are turned on. Since a time difference is provided in the OFF operation to suppress the occurrence of arc at the contact of the interrupting relay, contact welding failure of the interrupting relay can be extremely reduced. In other words, it can be considered that the probability of ON failures occurring simultaneously in the interrupting relay and the energizing relay is extremely small.

  Therefore, if an ON failure occurs in one of the interrupting relay and the energizing relay, the normal relay of either one can quickly forcibly stop the energization of the heater, so it is irrelevant to the user's intended use. Thus, an abnormal state in which the heater is continuously energized is eliminated, and a heater drive circuit that enables safe heater control can be realized.

  In FIG. 1, an insulation type is shown as the heater current detection circuit 8. However, for example, a resistor for extracting the heater current is provided in a connection line between the other ends of the heaters 1 a and 1 b and the other end of the commercial power supply 2. You may comprise by the non-insulated type. The switching elements Q1, Q2, and Q3 are bipolar transistors, but may be MOS transistors.

Embodiment 2. FIG.
FIG. 8 is a timing chart for explaining another operation example of the heater drive circuit shown in FIG. 1 as the second embodiment of the present invention. In the second embodiment, another method of using the interrupting relay provided in the present invention will be described.

  The relay fixedly mounted on the circuit board by soldering self-heats during the ON period when the coil is energized. The soldering part is heated by this self-heating, and the temperature becomes higher than when the relay is OFF. The temperature difference generated in the soldering portion is called a thermal shock, and it is known that the soldering portion is likely to cause solder breakage due to the thermal shock. Specifically, in the case where the temperature difference is large, the larger the number of repetitions of energization / stop of the coil, the greater the thermal shock to the soldered portion, and the more likely the solder is cut.

  Therefore, in the second embodiment, as shown in FIG. 8, attention is paid to the fact that the interruption relays (4a, 4b) are turned off during the heater OFF period 20 in which the heater operation start instruction is input. During the heater OFF period 20, the energization relays (6a, 6b) (7a, 7b) are turned on. Heater current does not flow through the heaters 1a and 1b, but current flows through the coils 6b and 7b of the energizing relays (6a and 6b) (7a and 7b). Rises to a certain temperature higher than when the relay is OFF.

  Then, when the heater operation start instruction is input, the heater operation mode is executed after the elapse of the period 21 in which the arc generation at the contact 4a of the interrupting relay (4a, 4b) is suppressed, but the energizing relay (6a 6b) Since the temperature of the soldered portion of (7a, 7b) has been raised to a certain temperature in advance during the heater OFF period 20, the coil of the energizing relay (6a, 6b) (7a, 7b) during the heater operation mode. It is possible to reduce the temperature difference from the temperature of the soldered portion that rises when current flows through 6b and 7b. That is, since the thermal shock to the soldering portion is greatly reduced, it is possible to make it difficult to cause solder breakage.

  In addition, the second embodiment pays attention to the fact that the energizing relays (6a, 6b) (7a, 7b) are turned on during the heater OFF period 20, and whether the interruption relays (4a, 4b) are turned on or not. The determination is made according to the procedure described in the first embodiment. Naturally, when an ON failure of the interrupting relays (4a, 4b) is detected in the heater OFF period 20, the energizing relays (6a, 6b) (7a, 7b) are immediately turned OFF to execute an abnormal stop.

  In FIG. 8, when a heater operation start instruction is input when an ON failure of the interruption relays (4 a, 4 b) is not detected in the heater OFF period 20, the heater operation mode is changed after the arc generation suppression period 21 has elapsed. The case of execution is shown.

  When the heater operation stop instruction is input, the ON failure detection time 22 is set according to the procedure described in the first embodiment, and the ON failure of the energizing relays (6a, 6b) (7a, 7b) is determined. to decide. When an ON failure is not detected in the energizing relays (6a, 6b) (7a, 7b), the interruption relays (4a, 4b) are turned OFF after the ON failure detection time 22 has elapsed, and then the energizing relay (6a, 6b) After performing the arc generation suppressing procedure for turning on (7a, 7b), the process proceeds to the heater OFF period 20 described above.

  Although FIG. 8 shows the case where the determination of the ON failure of the energizing relays (6a, 6b) (7a, 7b) is performed at the timing when the heater operation stop instruction is input, the heater operation start instruction is input. The heater operation mode may be executed when the normal operation is performed.

  As described above, in the second embodiment, one or more energization relays are provided during the heater operation standby (when the heater is OFF) by using a configuration in which a cutoff relay is provided on the power input side of the one or more energization relays. Since the soldering part is preheated to a certain temperature by turning ON, the temperature difference from the temperature of the soldering part at the time of heater operation (when the heater is ON) can be reduced. The thermal shock to can be greatly reduced. That is, it is possible to extend the life of the soldering portion with the substrate of one or more energizing relays, and to improve the effectiveness of the ON failure detection operation according to the present invention.

  As described above, when the heater drive circuit according to the present invention detects the ON failure of the energizing relay due to the contact welding of the energizing relay or the short circuit failure of the energizing transistor, the heater drive circuit can be quickly supplied to the heater without blowing the thermal fuse. This is useful as a heater driving circuit that enables safe heater control.

1a, 1b heater (electric heater)
2 Commercial power supply 3 Thermal fuse 4a Contact for relay 4b Coil for relay 5 Power supply circuit 6a, 7a Contact for relay 6b, 7b Coil for relay 8 Heater current detection circuit 11 Control circuit (microcomputer)
Q1 transistor (switching element for blocking)
Q2, Q3 transistor (switching element for energization)

Claims (7)

One or more energization relays connected to each energization path from a commercial power source to one or more electric heaters, and one or more energization switching elements for controlling energization to the coils of the one or more energization relays A control circuit that performs a heater operation mode for turning on the one or more energization switching elements and controlling the contacts of the one or more energization relays in a closed state from an operation start to an operation stop specified by the user In a heater drive circuit comprising:
An interruption relay in which a contact is connected to an energization path between the commercial power source and the contact of the one or more energization relays;
An interruption switching element for controlling energization to the coil of the interruption relay;
A heater current detection circuit for detecting a heater current flowing between the commercial power source and the one or more electric heaters;
The control circuit includes:
In both or either of when entering the operation stop instruction at the time of input of the operation start instruction, the one or more energization switching element and the breaking switching element so as to become a complementarily turned on and off states Te, based on a comparison between the current value and the determination value the heater current detection circuit detects at that time, and detecting the presence or absence of the oN failure of the one or more electromagnetic relay and the cutoff relay, one of the relay When an ON failure is detected, an abnormal stop process is performed to open one of the other relay contacts, and a time difference is generated between the ON operation or OFF operation of the interrupting relay and the ON operation or OFF operation of the energizing relay. Provide
The heater drive circuit characterized by the above-mentioned. One or more energization relays connected to each energization path from a commercial power source to one or more electric heaters, and one or more energization switching elements for controlling energization to the coils of the one or more energization relays A control circuit that performs a heater operation mode for turning on the one or more energization switching elements and controlling the contacts of the one or more energization relays in a closed state from an operation start to an operation stop specified by the user In a heater drive circuit comprising:
An interruption relay in which a contact is connected to an energization path between the commercial power source and the contact of the one or more energization relays;
An interruption switching element for controlling energization to the coil of the interruption relay;
A heater current detection circuit for detecting a heater current flowing between the commercial power source and the one or more electric heaters;
With
The control circuit includes:
In one or both of the operation start instruction input and the operation stop instruction input, the one or more energization switching elements and the cutoff switching element are complementarily turned on and off, Based on the comparison between the current value detected by the heater current detection circuit at that time and the determination value, the presence or absence of each ON failure of the one or more energizing relays and the cutoff relay is detected, and either one of the relays is turned ON. When a failure is detected, the control circuit executes an abnormal stop process for opening one of the other relay contacts. When the operation start instruction is input, the shut-off switching element continues to be turned off. The one or more energization switching elements are turned on within the first ON failure detection time period and the comparison operation is performed to check whether the interruption relay is ON or not. If the normal ON failure detection time elapses, the one or more energization switching elements are turned off, and the cutoff switching element is turned on, and then the one or more energization switching elements are turned on. When the heater operation mode is turned on and the operation stop instruction is input, the one or more energization switching elements are turned off, and the shut-off switching element is turned on to detect a second ON failure. is continued in time, characteristics and be Ruhi over motor drive circuit that detects the presence of the ON failure of the one or more electromagnetic relay by performing the comparison operation. One or more energization relays connected to each energization path from a commercial power source to one or more electric heaters, and one or more energization switching elements for controlling energization to the coils of the one or more energization relays A control circuit that performs a heater operation mode for turning on the one or more energization switching elements and controlling the contacts of the one or more energization relays in a closed state from an operation start to an operation stop specified by the user In a heater drive circuit comprising:
An interruption relay in which a contact is connected to an energization path between the commercial power source and the contact of the one or more energization relays;
An interruption switching element for controlling energization to the coil of the interruption relay;
A heater current detection circuit for detecting a heater current flowing between the commercial power source and the one or more electric heaters;
With
The control circuit includes:
In one or both of the operation start instruction input and the operation stop instruction input, the one or more energization switching elements and the cutoff switching element are complementarily turned on and off, Based on the comparison between the current value detected by the heater current detection circuit at that time and the determination value, the presence or absence of each ON failure of the one or more energizing relays and the cutoff relay is detected, and either one of the relays is turned ON. When a failure is detected, the control circuit executes an abnormal stop process for opening one of the other relay contacts, and when the operation start instruction is input, the shut-off switching element is turned on, Thereafter, the heater operation mode is performed by turning on the one or more energization switching elements, and when the operation stop instruction is input, the one or more energization switches are operated. The switching element is turned off, and the on-off operation is continued within the third ON failure detection time for the blocking switching element to perform the comparison operation to detect the ON failure of the one or more energizing relays. If the third ON failure detection time has elapsed, the cutoff switching element is turned off, and then the one or more energization switching elements are turned on within the fourth ON failure detection time to perform the comparison operation. It was carried out, features and be Ruhi over motor drive circuit that detects the presence of the ON failure of the cutoff relay. One or more energization relays connected to each energization path from a commercial power source to one or more electric heaters, and one or more energization switching elements for controlling energization to the coils of the one or more energization relays A control circuit that performs a heater operation mode for turning on the one or more energization switching elements and controlling the contacts of the one or more energization relays in a closed state from an operation start to an operation stop specified by the user In a heater drive circuit comprising:
An interruption relay in which a contact is connected to an energization path between the commercial power source and the contact of the one or more energization relays;
An interruption switching element for controlling energization to the coil of the interruption relay;
A heater current detection circuit for detecting a heater current flowing between the commercial power source and the one or more electric heaters;
With
The control circuit includes:
In one or both of the operation start instruction input and the operation stop instruction input, the one or more energization switching elements and the cutoff switching element are complementarily turned on and off, Based on the comparison between the current value detected by the heater current detection circuit at that time and the determination value, the presence or absence of each ON failure of the one or more energizing relays and the cutoff relay is detected, and either one of the relays is turned ON. When a failure is detected, the control circuit executes an abnormal stop process for opening one of the other relay contacts. When the operation start instruction is input, the shut-off switching element continues to be turned off. The one or more energization switching elements are turned on within a fifth ON failure detection time period and the comparison operation is performed to check whether or not the interruption relay is ON. If normal, the one or more energization switching elements are turned off when the fifth ON failure detection time has elapsed, and then the shut-off switching element is turned on, and within the sixth ON failure detection time, A comparison operation is performed to detect the ON failure of the one or more energization relays. If normal, the one or more energization switching elements are turned on when the sixth ON failure detection time has elapsed. features and to Ruhi over motor drive circuit to implement the heater operation mode. One or more energization relays connected to each energization path from a commercial power source to one or more electric heaters, and one or more energization switching elements for controlling energization to the coils of the one or more energization relays A control circuit that performs a heater operation mode for turning on the one or more energization switching elements and controlling the contacts of the one or more energization relays in a closed state from an operation start to an operation stop specified by the user In a heater drive circuit comprising:
An interruption relay in which a contact is connected to an energization path between the commercial power source and the contact of the one or more energization relays;
An interruption switching element for controlling energization to the coil of the interruption relay;
A heater current detection circuit for detecting a heater current flowing between the commercial power source and the one or more electric heaters;
With
The control circuit includes:
In one or both of the operation start instruction input and the operation stop instruction input, the one or more energization switching elements and the cutoff switching element are complementarily turned on and off, Based on the comparison between the current value detected by the heater current detection circuit at that time and the determination value, the presence or absence of each ON failure of the one or more energizing relays and the cutoff relay is detected, and either one of the relays is turned ON. When a failure is detected, the control circuit executes an abnormal stop process for opening one of the other relay contacts, while turning off the shut-off switching element and waiting for input of the operation start instruction , features and be Ruhi over motor driving circuit that is turned on the one or more current-carrying switching element. The control circuit includes:
While waiting for the input of the operation start instruction, the comparison operation is performed to detect the presence or absence of an ON failure of the blocking relay, and if normal, the input of the operation start instruction is received and the one or more The energization switching element is turned off, the cutoff switching element is turned on, and then the one or more energization switching elements are turned on to execute the heater operation mode, and the operation stop instruction is input. The one or more energization switching elements are turned off, and the ON operation of the shut-off switching element is continued for a predetermined ON failure detection time to perform the comparison operation, and the one or more energization relays are turned on. The heater driving circuit according to claim 5, wherein presence or absence of a failure is detected. The control circuit includes:
While waiting for the input of the operation start instruction, the comparison operation is performed to detect the presence or absence of an ON failure of the blocking relay, and if normal, the input of the operation start instruction is received and the one or more The energization switching element is turned off, and then the shut-off switching element is turned on, and the comparison operation is performed within a predetermined ON failure detection time to detect the presence or absence of the one or more energization relays. If so, the heater driving circuit according to claim 5, wherein the one or more energization switching elements are turned on to shift to the heater operation mode.

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