JP3423163B2 - Overcurrent protection device for electrical equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates are those which relate to a device to prevent from being over power the driven body such as a stepping motor driven by a pulse voltage.

[0002]

2. Description of the Related Art In recent years, various electric devices have been driven and controlled by a microcomputer. Figure 8
FIG. 3 is a conceptual diagram of a device for controlling a motor (3) driven by a pulse voltage by a microcomputer. Motor (3)
The driver circuit (2) that supplies the pulse voltage to the CPU is controlled by the CPU (1) in which the control program is stored. If the driver circuit (2) fails for some reason and the pulse voltage continues to remain at the H level, the motor (3) will overheat, causing seizure and the like. Therefore, from the conventional motor
As a measure (3) for preventing overheating, a thermal fuse (9) is provided as shown in FIG.

There is also a CPU (1) provided with a time measuring means called a watchdog timer. Here, the watchdog timer is a well-known measuring means that measures the operation duration of the motor (3) and, when the operation duration reaches a certain time or longer, shifts to another operation. That is, when the motor (3) is energized, the CPU (1)
When the watchdog timer is activated and the watchdog timer detects that the H level voltage has been applied to the motor (3) for a certain time or longer, the CPU (1) stops the power supply to the motor (3). .

[0004]

In order to prevent overheating of the motor (3), the one using the temperature fuse (9) is
When (3) is overheated and the thermal fuse (9) is blown, the operation cannot be restarted unless the thermal fuse (9) is replaced. Replacing the thermal fuse 9 is generally troublesome. Further, in the case of controlling by the CPU (1) equipped with the watchdog timer, there is a bug in the control program of the CPU (1), and the watchdog timer does not operate normally in such CPU (1). . Also, C
When static electricity or the like is applied to the PU (1), the CPU (1) may not operate normally due to electrostatic breakdown. That is, the CPU (1) provided with the watchdog timer is not always accurate as a means for preventing overheating of the motor (3). An object of the present invention is to more accurately prevent over-power supply of a motor or the like.

[0005]

A driven body driven by a pulse voltage, a driver circuit (2) for supplying a pulse voltage to the driven body, and a C for controlling the operation of the driver circuit (2).
An overfeed prevention device is provided for an electric device including PU (1). The over-feed prevention device is connected to the driven body,
In synchronization with the rise of the pulse voltage flowing through the driven body,
A first multivibrator (5) that generates a reference time pulse that continues to be at the H level for a limit time T1 that can maintain normal operation of the driven body, and the reference time pulse and the pulse voltage that flows through the driven body are input, and the reference time is input. The level of the pulse voltage flowing through the driven body at the time of the falling edge of the pulse is judged, and when the level of the pulse voltage is at the H level, the power supply from the driver circuit (2) to the CPU (1) should be stopped. A second multivibrator (6) for issuing a reset signal of Flow through the driven body to the first multivibrator (5)
When the pulse voltage is input multiple times, the second multi-by
The vibrator (6) finally enters the first multivibrator (6).
Reference time generated in synchronization with the rising edge of the applied pulse
The subsequent operation is performed based on the inter-pulse. Also, CP
After receiving the reset signal from the second multivibrator (6), U (1) issues a power supply return signal to the driver circuit (2) after the elapse of the recoverable time.

[0006]

[Operation and effect] The second multivibrator (6) judges the level of the pulse voltage flowing through the driven body at the fall of the reference time pulse, and when the level of the pulse voltage is the H level, the CPU (1) In contrast, the driver circuit (2)
Signal to stop the power supply from. Therefore, it is possible to detect whether the power supply to the driven body is excessive by simply comparing the level of the pulse voltage flowing through the driven body with the level of the reference time pulse for control. A control program that is more complicated than that of
It becomes unnecessary and can detect over-power supply accurately. In addition, the driver circuit (2) automatically recovers after the elapse of the recoverable time after the CPU (1) receives the reset signal from the second multivibrator (6), so that the thermal fuse (9) is used. Compared to the conventional configuration, the driver circuit (2) does not take much time to restore.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION One embodiment of the present invention will be described below.
It will be described with reference to the drawings. FIG. 1 is a block diagram of the inside of an apparatus in which the overpower supply prevention device according to this example is incorporated. As in the conventional case, the motor (3) is connected to the driver circuit (2) for supplying power to the motor (3), and the driver circuit (2) is a CPU.
The operation is controlled by (1). The CPU (1) has a timer means for measuring a time sufficient to restore the operation of the motor (3) after receiving a reset signal as described later.
(7) is connected. The motor (3) is used for operating a card reader as a driven device, for example, but the description of the entire structure of the reader is omitted.

The motor (3) is a two-phase stepping motor, and the coils (30) and (30) in the motor (3) corresponding to each phase are supplied with equal voltage pulse voltages having different phases. . Both ends of each coil (30) (30) are connected to the driver circuit (2). In FIG. 1, the voltage from the driver circuit (2) passes through the coil (30) from the ends a and b of the coils (30) and (30), respectively.
It flows to the output terminals c and d. Both ends of the coil (30) are also connected to the over-feed prevention circuit (4) which is a characteristic part of this example.
The over-feeding prevention circuit (4) may be supplied with an electric signal passing through one end of the coil (30).

FIG. 2 is an internal block diagram of the overpower supply prevention circuit (4). The over-feeding prevention circuit (4) includes first and second multivibrators (5) (6) each having the same internal configuration,
The output of the multivibrator (5) is input to the second multivibrator (6). The first multivibrator (5) has five input terminals (50) (51) (52) (53) (54) and an output terminal (55), and the second multivibrator (6) has five input terminals (6).
It is equipped with 0) (61) (62) (63) (64) and output terminal (65). Each multivibrator (5) (6) and terminal (50) (5) to which a square wave is applied
A capacitor and a resistor that determine the time constant of the oscillation output wave are connected between 1) (60) and (61), and the first multivibrator is connected.
(5) has a time constant of T1 due to capacitor C1 and resistor R1.
In the second multivibrator (6), the time constant is set to T2 by the capacitor C2 and the resistor R2. As will be described later, the time constant T1 is larger than T2, and T1 is the motor
This is the limit time during which the normal operation of the motor (3) can be maintained even if the H level of the pulse voltage is continuously applied to (3). That is,
The continuous application of DC voltage to the motor (3) does not overheat the motor (3) and cause abnormalities such as smoking or ignition, which does not affect the performance of the motor (3). As such, it is time to anticipate safety. Each resistor R1, R2
A diode (83) is connected in parallel with the diode (83) to prevent an overcurrent from being applied to the multivibrator (5) (6) when the capacitors C1 and C2 are discharged.

Input terminals of each multivibrator (5) (6)
The inputs from (53) and (63) are inverted in the multivibrator (5) and (6) and ORed with the inputs from the input terminals (52) and (62), respectively.
Connected. The input terminal of the first multivibrator (5) (5
2) is grounded, and the input terminal (53) has the coil (3
The outputs from both ends of (0) and (30) are input as one via the diode (82). The remaining input terminal (54) has a constant voltage V with noise removed by the capacitor (81).
A is entered.

The input terminal (6) of the second multivibrator (6)
The output from the first multivibrator (5) is input to 2), and the constant voltage VA is input to the input terminal (63). Outputs from both ends of the combined coils (30, 30) are input to the input terminal (64) of the second multivibrator (6). The output of the second multivibrator (6) is input to the collector follower transistor (8) at the base, and when a voltage is applied to the base of the transistor (8), the transistor (8) goes through the inversion (80) to the CPU (1). To H level reset signal to stop the power supply to the motor (3). If the CPU (1) detects 0 level as a reset signal, the inversion (80) does not have to be provided. First, second
The multivibrator (6) is formed by forming Schmitt trigger circuits and the like in multiple stages, and both multivibrator (5) (6)
Are stored in one IC. The applicant has proposed Toshiba's TC74HC123AP / AF as such an IC, and this TC74HC123AP / AF is an existing IC. This example is characterized in that this IC is used to detect over-power supply of the motor (3). The signals applied to the terminals (52) (53) (54) (62) (63) (64) of both multivibrators (5) (6),
Fig. 6 shows the relationship with the signals output from the output terminals (55) and (65).
Shown in the table. In the table of FIG. 6, X means that the input may be H level or L level. In addition, both the multi-vibrator (5) (6), the input terminal (52) (62) or (5
3) When the pulse falling edge is input to any of (63),
This is the trigger state, that is, the operation start state.

The operation of the overpower supply prevention circuit (4) will be described below. FIGS. 3 (a), 4 (a) and 5 (a) show pulse voltage waveforms that should flow through the motor (3) as shown in FIGS. 3 (b), 4 (b) and 5 (b).
Shows the voltage waveform output from the first multivibrator (5), and FIGS. 3 (c), 4 (c) and 5 (c) show the voltage waveform output from the second multivibrator (6), respectively. It is a figure.
3 (a), 4 (a), and 5 (a) show three types of voltage waveforms that may flow through the motor (3). In addition, in FIG. 3, FIG. 4, and FIG.
The voltage flowing through each of the points is shown. First, assume that the voltage waveform applied to the input terminal (53) of the first multivibrator (5) is as shown in FIG. 3 (a). The width of the H level of the pulse voltage flowing through the motor (3) is shorter than the time T1 and does not hinder the operation of the motor (3). First
When the rising edge of the pulse voltage is input to the input terminal (53) of the multivibrator (5), the input terminal (52) is grounded as described above and remains at the L level.
Since the H level voltage VA is continuously applied to (54),
This corresponds to Z0 in the table of FIG. 6, and a reference time pulse whose H level continues for a time T1 is output from the output terminal (55) of the first multivibrator (5). This time T1 is determined by the capacitor C1 and the resistor R1 connected to the input terminals (50) and (51) as described above.

The second multivibrator (6) receives the reference time pulse from the output terminal (55) of the first multivibrator (5). Since the H level voltage is continuously applied to the input terminal (64), the output is at the L level as indicated by Z1 in FIG. As described above, the second multivibrator (6)
The trigger is activated at the falling edge of the pulse signal input to the input terminal (62). However, as shown in FIG. 3A, when the reference time pulse falls after the time T1 has elapsed,
The voltage flowing through the motor (3) is at the L level, and the voltage at the L level is applied to the input terminal (64) of the second multivibrator (6), which corresponds to Z2 in the table of FIG. 2 Multivibrator (6) does not work. Therefore, since the transistor (8) located after the second multivibrator (6) does not operate, the reset signal is not issued to the CPU (1), and the power supply to the motor (3) is normal. I understand.

Next, as shown in FIG. 4A, it is assumed that pulses having a short H level time continuously flow through the motor (3). Although only two pulses are shown in FIG. 4A for convenience of explanation, it goes without saying that the number of pulses is repeated. Similarly to the above, since the input terminal (52) of the first multivibrator (5) is grounded and the L level is applied and the pulse voltage of FIG. 4 (a) is applied to the input terminal (53), When the rising edge of the first pulse is detected, as shown by Z0 in the table of FIG.
A reference time pulse lasting 1 is output. However,
Within time T1, the motor (3) receives the next pulse,
Since the second pulse shown in (a) is applied, the first multivibrator (5) detects the rising edge of the pulse, outputs the reference time pulse again, and starts time counting. That is, the reference time pulse output from the first multivibrator (5) continues to be at the H level for the limit time T1 from the rising edge of the pulse finally applied to the motor (3) in FIG. 4B. . In this case, when the reference time pulse falls, the voltage flowing through the motor (3) is
As shown in (a) and (b), since it is at the L level, the second multivibrator (6) is triggered in the same manner as above, but it is applied to the input terminal (64) of the second multivibrator (6). The applied voltage is L level. Therefore, as indicated by Z2 in the table, the second multivibrator (6) does not operate and the reset signal is not issued from the transistor (8).

Next, as shown in FIG. 5 (a), it is assumed that a pulse voltage whose H level time is T1 or more flows through the motor (3). As described above, the time T1 is the limit time for maintaining normal operation even if the H-level voltage continues to flow to the motor (3). Therefore, if the H-level voltage flows beyond the time T1, the motor (3) will The motor may be damaged.
Power supply to (3) must be temporarily stopped. At this time,
The over-feed prevention circuit (4) operates as follows. First, in the same manner as above, to the input terminal (53) of the first multivibrator (5),
When the rising edge of the pulse voltage flowing through the motor (3) is input, the first multivibrator (5) outputs a reference time pulse. When the reference time pulse falls after the limit time T1 has elapsed, this fall is input to the input terminal (62) of the second multivibrator (6) and the second multivibrator (6) is triggered. Second multivibrator
The constant voltage VA of H level is always applied to the input terminal (63) of (6) as in the above.

However, as shown in FIG. 5 (a), the motor (3)
The voltage flowing through is still at H level after the elapse of time T1 from the rise of the reference time pulse. Therefore, since the H level voltage is input to the input terminal (64) of the second multivibrator (6), the H level of the second multivibrator (6) is changed as shown by Z3 in the table of FIG. A pulse that lasts for time T2 is output. This time T2 is determined by the capacitor C2 and the resistor R2 as described above. The transistor (8) receives the pulse from the second multivibrator (6) as a base and is turned on to generate a reset signal. C
The PU (1) receives the reset signal, and the driver circuit (2)
To stop the power supply to the motor (3).

When the CPU (1) receives the reset signal from the transistor (8) (S1) as shown in the flow chart of FIG. 7, the CPU (1) stops supplying power to the motor (3).
(S2), as described above, the timer means (7) connected to the CPU (1) is operated (S3). By the timer means (7),
Elapsed recoverable time is detected (S4). The recoverable time refers to a time sufficient for the once overheated motor (3) to cool down and to operate normally again. This time depends on the characteristics of the motor (3) and may be less than the reference time T1. It may be T1 or more. When the CPU (1) does not receive the reset signal within the recoverable time, it judges that the motor (3) is not overheated again and issues a power supply recovery signal to drive the driver circuit (2).
The power supply from the motor to the motor (3) is restored (S5, S6). Needless to say, when the reset signal is detected again within the recoverable time, the timer means (7) starts to measure the recoverable time again from that point (S5).

The above description of the embodiments is for explaining the present invention, and should not be construed as limiting the invention described in the claims or reducing the scope. The configuration of each part of the present invention is not limited to the above-mentioned embodiment, and it goes without saying that various modifications can be made within the technical scope described in the claims. For example, in this example, the motor (3) is illustrated as the driven body driven by the pulse voltage, but a solenoid may be used.

[Brief description of drawings]

FIG. 1 is an internal conceptual diagram of an electric device.

FIG. 2 is an internal block diagram of an overpower supply prevention circuit.

3A is a diagram showing a voltage waveform flowing through a motor, FIG. 3B is a waveform diagram showing an output voltage from a first multivibrator, and FIG. 3C is a diagram showing a pulse voltage waveform applied to a transistor at the time of reset.

4A is a diagram showing a voltage waveform flowing through a motor, FIG. 4B is a diagram showing an output voltage waveform from a first multivibrator, and FIG. 4C is a diagram showing a pulse voltage waveform applied to a transistor at the time of reset.

5A is a diagram showing a voltage waveform flowing through a motor, FIG. 5B is a diagram showing an output voltage waveform from the first multivibrator, and FIG. 5C is a diagram showing a pulse voltage waveform applied to a transistor at the time of reset.

FIG. 6 is a table showing the relationship between the voltage applied to the terminals of the first and second multivibrators and the output voltage.

FIG. 7 is a flowchart showing the operation of the CPU when receiving a reset signal.

FIG. 8 is an internal block diagram of a conventional electric device.

[Explanation of symbols] (1) CPU (2) Driver circuit (5) First multivibrator (6) Second multivibrator

Claims (2)

(57) [Claims] 1. A driven body driven by a pulse voltage, and a driver circuit for supplying a pulse voltage to the driven body.
(2) and CPU (1) for controlling the operation of the driver circuit (2)
In a device for preventing over-feeding from a driver circuit (2), which is provided in an electric device having a driven body, the driven body is connected to a driven body and is synchronized with a rise of a pulse voltage flowing through the driven body. The first multivibrator (5) that generates a reference time pulse that continues to be at the H level for the limit time T1 that can maintain normal operation of the device, and the reference time pulse and the pulse voltage that flows through the driven body are input, and the rising of the reference time pulse is input. Judge the level of the pulse voltage flowing through the driven body when falling,
When the pulse voltage level is H level, the CPU (1)
On the other hand, a second multivibrator (6) which issues a reset signal to the effect that the power supply from the driver circuit (2) should be stopped is provided, and the first multivibrator (5) has a pulse flowing through the driven body.
The second multi-vibration
The data (6) was last input to the first multivibrator (5).
Pulse generated in synchronization with the rising edge of the pulse
Overfeed prevention device characterized by performing subsequent operations based on the looseness . 2. The CPU (1) is connected with a timer means (7) for measuring a recoverable time after receiving a reset signal from the second multivibrator (6), and the timer means (7). After the elapse of the recoverable time is detected by
The over-power supply prevention device according to claim 1, wherein the PU (1) issues a power supply return signal to the driver circuit (2).