JPH0534763B2 - - Google Patents

Description

[Detailed description of the invention]

<Field> The present invention relates to a protection circuit for a driven circuit, and more particularly to a protection circuit for monitoring the operation of a driven circuit that operates in response to a control signal and cutting off power supply when an abnormality is detected. <Prior art and background> Conventionally, when the resistance (impedance) of a driven circuit becomes abnormal due to abnormal operation or failure of the driven circuit, secondary failure of the driven circuit itself, power supply wiring, etc. that occurs afterwards is prevented. Tame fuse,
Protection circuits such as breakers have been installed. However, if the operation of the driven circuit is controlled by a control signal, such as a drive circuit for a printing magnet in an impact line printer, the driven circuit may change depending on the input conditions given to the driven circuit. The resistance (impedance) that should appear depends on the timing of the input signal, including the duration, and also on the state, in the sense that it should not operate in response to an input signal that indicates a non-operating state. However, there are various operating states that must be taken to be normal, and depending on the control signal, a state with conduction is normal or a state with no conduction is normal, so it is simply a matter of the resistance of the driven circuit. An abnormality cannot be determined only from the fact that it is small or there is no continuity. In addition, in such a configuration, if there is an abnormality on the control signal side, the abnormal state may be automatically recovered, and a configuration such as a fuse in which the protection circuit cannot be recovered once activated is inconvenient. Therefore, a conventional protection circuit used for this purpose has a configuration as shown in FIG. 1, for example. FIG. 1 is an explanatory diagram of a conventional example. The voltage VD in the figure is connected to the output terminal of a power supply (not shown), and a circuit formed by a diode D ₁ and a resistor R ₁ is connected to the current detection section 1. A dividing resistor that divides the potential difference between the two ends of the detection section by dividing the potential at each end.
The comparator 2 is configured to input the values divided by R ₇ , R ₈ and R ₃ , R ₆ as respective comparison inputs, and the comparator operates when the potential difference between both ends of the current detection section 1 is greater than a predetermined value.

[0] is input, and [1] is input when the current is below a predetermined value, that is, when no current flows.
The state signal and the output of the retriggerable multi 3, which is repeatedly triggered by the hammer set signal (HMST), which is one of the control signals, are input to the NAND gate 4, and the operation of the printing magnet is performed using this output as a condition. A forced reset transistor that controls the input signals of the control circuit 5 of the hammer driver and the magnet drive transistor Tr ₆ of the hammer driver.
When the output of NAND gate 4 is [1], Tr ₇ is turned on to forcibly reset the input of transistor Tr ₆ , and connected to the input terminal of NAND gate 6 along with the inverted signal (*RLON) of the signal that sets the relay-on mode. Both inputs are output according to the output logic state.

Only when it is [0], transistor _Tr5 is turned on and relay RL1 is operated. Note that the control circuit 5 is configured so that the printable status signal PE is [1] and the logic output of the NOR gate 4 is

The above * in the state of [0]
At the same time as issuing the RL1ON status signal, the hammer set signal HMST is retriggerable.
Issued to. With this configuration, the current cutting circuit 7 is composed of the contact rl1 of the RL1, a capacitor C forming a sparkler, a diode D resistor _R0 , and an added resistor _R2 , and the logic output of the NOR gate 4 is

When the above PE signal is [0] and [1],
Conducted. Then, the control circuit 5 selects the timing to be driven based on the data to be printed (PDATA) and the synchronization signal (PSE) corresponding to the moving type, and selectively drives the transistor Tr ₆ (actually, there are multiple transistors). to print. In this case, the current flowed outside the scheduled time, that is, the output of the retriggerable multi

If the current is flowing in the current detection section 1 even though it is [0], the output *E of the comparator 2 is still

[0], but at this time, the output of the NOR gate becomes [1], forcibly resetting the coil drive signal and disconnecting relay RL1, and after relay RL1 is disconnected under this condition, this relay is controlled. It is memorized in the circuit (error state set), and from then on *
Avoid issuing RLION. The operation is restarted when the operator resets the state in which *RLION is not issued. However, with this configuration, in the case of a temporary abnormality such as a malfunction of the control circuit, it is possible to restart the operation, but if a circuit element, for example, the transistor Tr ₆ (the actual device has one for each printed digit) is broken, etc. The only way to determine the failure condition is to see that the relay is disconnected again after resetting and reactivating it.As the operator tries to reactivate the relay several times to check the condition, the relay contact rI1 wears out. I had a problem with doing this. <Purpose and Features> The present invention has been made in view of the above, and its purpose is to ensure the life of the relay contact by preventing the relay from operating again even after a reset in the case of a reproducible failure. The present invention is characterized in that, in order to achieve the above object, a circuit is provided between a driven circuit that is selectively driven by a control signal and a power supply,
In a protection circuit that includes a current detection means for monitoring the operation of the driven circuit and controlling the opening/closing of the supplied power, a switching control switch, and a resistor connected in parallel to the switch, the circuit remains driven even after the switch is opened. The present invention includes means for monitoring the resistance of the circuit, and performs control so as to prohibit the re-operation of the on-off switch while the resistance is different from the control state corresponding to the control signal. <Embodiment> FIG. 2 is an explanatory diagram of an embodiment of the present invention. 7′, which is the resistance monitoring circuit 8 on the coil side.
The other configuration is the same as in FIG. 1 except that . And the resistance monitoring circuit 8 is a transistor Tr ₄
, resistors R ₄ , R ₅ , R ₉ and a diode. The base input is the potential obtained by dividing the power supply voltage VD by resistors R ₄ and R ₅ , and the current detection section of comparator 2 is connected from the collector through resistor R ₉ . The collector terminal is connected to the comparison potential input terminal of the downstream _detection terminal in _FIG . is connected to the downstream side of the current cutting circuit 7' via a diode, and the transistor Tr ₄ of the resistance monitoring circuit 8 is connected to the downstream side of the current cutting circuit 7'.
The potential at both ends of the current cutting circuit 7' is constantly monitored, and when there is conduction on the load side such as a coil and current flows, the potential on the emitter side decreases and the potential on the base side relatively increases, so it turns ON. Since the potential of the signal at one input terminal of the comparator 2 is lowered, the output signal *E of the comparator 2 is

becomes [0], the output of NOR gate 4 becomes [1], and the output of retriggerable multi 3 becomes [0].

When it is [0], a condition is created to disconnect relay RL1. Even if this condition is activated, if there is no continuity, the above condition will not hold, so the other conditions will be exactly the same as the configuration shown in Figure 1 above, and the relay setting point rI1 will be turned on during operation. Naturally, when the voltage is on, the emitter potential of transistor Tr ₄ does not drop, so the current monitoring circuit 8 side for comparator 2 does not operate. Therefore, comparator 2 is controlled by the divided potential of resistors R ₃ and R ₅ . The same operation as in Fig. 1 is performed. In the configuration shown in Fig. 2, if current continues to flow through the coil even after the period set by the retriggerable multi 3, which sets the period for excitation of the coil, the current detecting circuit 1 detects the current. is detected and the output *E of comparator 2 is

Set it to [0], and the retriggerable multi 3 side is no longer in the hammer set period, so output

Since it is set to [0], the output of NOR gate 4 becomes [1], which forcibly resets the input of the drive circuit on the coil side, and the input condition of NAND gate 6 collapses, so the output becomes [1] and relay RL1 is turned off. Therefore, the set point rI1 is disconnected. When the contact rI1 is disconnected, a voltage drop occurs by the amount of current flowing through the resistor _R2 , so the potential at the emitter of the transistor _Tr4 decreases and turns on.
In the end, the comparator 2 receives the comparison output *E from the resistance monitoring circuit 8.

Logic output in the form of continuation of the condition to make it [0]

[0]
Therefore, unlike in the case of the configuration shown in Figure 1, even if the operator performs a reset operation this time, relay RL1 will not turn on unless the cause of the current flow is removed. This means that the reloading operation will not be executed. Therefore, the relay contact rI1
The contact only cuts off the current that flows once when the current becomes abnormal, and does not operate the next time it is turned on again, so the contact life is guaranteed and a spark killer circuit like the one shown in Figure 1 is not required. In the configuration shown in FIG. 2, the operator can perform a reset and re-throw operation and determine whether it is a temporary malfunction if the power can be turned on again, or a reoccurring failure if the power cannot be turned on again. <Effects> As explained above, according to the present invention, reproducibility is improved in the protection circuit that monitors whether the current flowing through the magnetic coil side of the printing device is flowing normally and cuts off the supply if abnormality occurs. In the case of a certain failure, the relay will not operate even if the relay is turned on again, so it is possible to reliably prevent wear and tear on the relay contacts that would otherwise occur if the relay is turned on again in the event of a failure, improving the life and reliability of the protection circuit. This produces a characteristic effect.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a conventional example, and Fig. 2 is an explanatory diagram of an embodiment of the present invention. circuit, 6 is a NAND gate, 7 and 7' are current cutting circuits,
8 is a resistance monitoring circuit.

Claims (1)

[Claims] 1 A current detection means provided between a driven circuit that is selectively driven by a control signal and a power source, and that monitors the operation of the driven circuit and controls the opening/closing of the supplied power, a switch for opening/closing control, and a parallel connection to the switch. The protection circuit has means for monitoring the resistance of the driven circuit even after the switch is opened, and the protection circuit has a means for monitoring the resistance of the driven circuit even after the switch is opened, and while the resistance is different from the control state corresponding to the control signal, the on-off switch A monitoring protection circuit characterized by controlling to prohibit re-operation.