JP2500714B2 - Solenoid abnormality detection circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solenoid abnormality detecting circuit for detecting abnormality of a solenoid energized by pulse width modulation.

[0002]

2. Description of the Related Art FIG. 5 is a circuit diagram showing a configuration example of a conventional solenoid abnormality detecting circuit. In this figure, 1 is a pulse width modulation signal generating circuit for generating a pulse width modulation signal, and 2 is
And 3 are voltage dividing resistors, 4 and 5 are Darlington-connected transistors that are turned on / off by a pulse width modulation signal, 6 is a solenoid for driving keys and pedals of an automatically playing piano, and 7 is for protecting the solenoid 6. Is a diode, 8 is a capacitor for preventing noise generated in the solenoid 6, and 9 is a diode. These circuit elements 1 to 9 are provided with the number of keys and pedals, for example, about 90, and the diodes 9 _{a to} 9 _c are
It is shown that these circuit elements 1 to 9 are connected in parallel to the connection point a.

Further, 10 is a diode, 11 to 14 are resistors, 15 is a diode, and 16 is a capacitor. Of these circuit elements, the circuit elements 14 to 16 are analog integrator circuits having a time constant of about several seconds. I am configuring. 17
Is a comparator, 18 and 19 are predetermined reference voltages V
A resistor for setting _ref , 20 is a capacitor, and 21 is an output terminal for outputting an abnormality detection signal. The value of the resistor 11 is about 1/100 of the value of the resistor 13, and the value of the resistor 12 is 1/2 of the value of the resistor 13, for example.
0, the value of the resistor 14 is, for example, 2 of the value of the resistor 13.
Double the amount. In this case, the power supply voltage V _DD is 120
[V], the power supply voltage V _CC is 5 [V], and the value of the resistor 11 is 1
[KΩ], the value of the resistor 12 is 4.7 [kΩ], the value of the resistor 13 is 100 [kΩ], the value of the resistor 14 is 220 [kΩ],
The capacitance of the capacitor 16 is 10 [μF], the value of the resistor 18 is 12 [kΩ], and the value of the resistor 19 is 10 [kΩ].

In such a structure, when the pulse width modulation signal is generated in the pulse width modulation signal generation circuit 1, the transistors 4 and 5 are turned on / off by this signal.
The solenoid 6 is turned off, and the pulse width modulation signal is "H".
Energized during the level. Then, while the transistor 5 is off, the potential at the connection point a, that is, the collector potential of the transistor 5 is substantially the power supply voltage V _DD (120 [V]).
Therefore, the potential at the connection point b is the divided voltage (about 4.78) of the resistors 12 and 13 of the power supply voltage V _CC (5 [V]).
[V]), the diodes 9 and 10 are non-conductive. As a result, the capacitor 16 is charged via the power supply voltage V _CC (5 [V]), the resistor 12, and the diode 15. In this case, the charging time is almost resistance 1
2 and the time constant determined by the respective values of the capacitor 16.

On the other hand, while the transistor 5 is on, the potential at the connection point a, that is, the collector potential of the transistor 5 is almost 0 [V], but the potential at the connection point b is equal to the power supply voltage V _CC (5 [ V]) remains approximately equal to the divided voltage by resistors 12 and 13 (about 4.78 [V]), so that diodes 9 and 10 are conductive. As a result, the potential at the connection point b is divided by the resistors 11 and 12 of the power supply voltage V _CC (5 [V]) (about 0.87).
[V]) is almost equal to that of [V], the charge charged in the capacitor 16 while the transistor 5 is off is equal to the resistance 1
4, the resistor 11, the diodes 10 and 9 and the transistor 5 are discharged. The discharge time in this case depends on the time constant determined by the respective values of the resistor 14 and the capacitor 16.

In a normal state, the charging and discharging operations of the capacitor 16 described above are repeated according to the pulse width modulation signal output from the pulse width modulation signal generation circuit 1, so the potential of the capacitor 16 is always set in advance. The reference voltage V _ref (about 2.73 [V]) is higher than the reference voltage.
Therefore, it indicates that the output terminal 21 is normal.
An H "level signal is output.

However, if the transistor 5 is short-circuited or if the transistor 5 is continuously turned on for some reason, that is, if the solenoid 6 is continuously energized for a long time, the discharge time of the capacitor 16 becomes long, so that the capacitor 16 is discharged. The potential becomes equal to or lower than the reference voltage V _ref , and the output terminal 21 indicates "L" indicating an abnormality.
A level abnormality detection signal is output. As a result, the control circuit (not shown) inputs the abnormality detection signal to the solenoid 6
To stop the solenoid 6 from burning.

[0008]

By the way, in the above-mentioned conventional solenoid abnormality detection circuit, the ON state of the transistor 5 is continuous, or the collector-emitter voltage V _{CE of} the transistor 5 is about 0 to 1.5 V. The short circuit condition is detected and an abnormality detection signal is output. However, among the failure modes of the transistor 5,
There are some cases where the collector-emitter is short-circuited, but the conventional circuit cannot detect this condition.
There is a problem that the solenoid 6 is burned out.

Further, in the automatic playing piano to which the above-mentioned conventional solenoid abnormality detecting circuit is applied, the power source of the entire device is still turned on, but the power source voltage V _DD applied to the solenoid is cut off when the operation is stopped. There are cases.
However, in the above-described conventional solenoid abnormality detection circuit, when the power supply voltage V _DD is cut off, the circuit operation becomes the same as the state in which the transistor 5 is turned on.
The electric charge charged in the capacitor 16 is the resistance 14 and the resistance 1.
Since it is discharged through the diode 1, the diodes 10 and 9 and the transistor 5, the potential of the capacitor 16 becomes equal to or lower than the reference voltage V _ref in this case as well, and the output terminal 21 indicates an abnormality of "L" level. The detection signal is output. The present invention has been made under such a background, and provides a solenoid abnormality detection circuit which can detect a half-short state of a transistor that drives a solenoid and which does not malfunction even when the power is cut off. To aim.

The solenoid abnormality detection circuit according to the first aspect of the present invention comprises a first charging / discharging means for charging / discharging according to energization / disconnection of the solenoid, which is energized / disconnected according to the pulse width modulation signal. The first charging / discharging means is provided only when the electric potential of the first charging / discharging means is compared with a predetermined electric potential to detect an abnormality in the energization of the solenoid, and only when a predetermined voltage or more is applied to the solenoid. And a second charging / discharging means for charging or discharging the means.

According to a second aspect of the present invention, there is provided a solenoid abnormality detecting circuit, comprising: first charging / discharging means for charging / discharging according to energization / disconnection of a solenoid, which is energized / disconnected according to a pulse width modulation signal. Detection means for comparing the electric potential of the first charging / discharging means with a predetermined electric potential to detect an abnormality in the energization of the solenoid; and the first charging / discharging means when a predetermined voltage or more is applied to the solenoid. A second charging / discharging means for charging / discharging, and a blocking means for blocking charging / discharging to / from the first charging / discharging means when the power applied to the solenoid is cut off. It has a feature.

[0012]

In the solenoid abnormality detection circuit according to the first aspect of the present invention, when the solenoid is energized / de-energized in response to the pulse width modulation signal, the first charging / discharging means turns on / off the solenoid. It is charged and discharged accordingly. As a result, the detecting means detects the energization abnormality of the solenoid by comparing the electric potential of the first charging / discharging means with the predetermined electric potential. Then, when the second charging / discharging means is applied to the solenoid at a predetermined voltage or higher, the first charging / discharging means is charged or discharged, and accordingly, the detecting means causes the first charging / discharging means to discharge. An abnormality in energization of the solenoid is detected by comparing the potential of the means with a predetermined potential.

Further, in the solenoid abnormality detecting circuit according to the second aspect of the present invention, in addition to performing the same operation as the solenoid abnormality detecting circuit according to the first aspect of the invention, the power applied to the solenoid is cut off. In this case, the blocking means blocks charging or discharging of the first charging / discharging means, so that in this case, the detecting means does not detect an abnormality in the energization of the solenoid.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing the configuration of a solenoid abnormality detection circuit according to a first embodiment of the present invention. In this figure, parts corresponding to those in FIG. 5 are assigned the same reference numerals and explanations thereof are omitted. . In the solenoid abnormality detection circuit shown in this figure, the power source voltage V _{DD of the} solenoid 6 is
Resistances 22 and 23 are newly inserted between the terminal to which is applied and the cathode of the diode 9.

Further, a Zener diode 24 and a diode 25 are inserted between the cathode of the diode 9 and the terminal b, instead of the diode 10 and the resistor 11, and the cathode of the Zener diode 24 and the anode of the diode 25 are connected. A resistor 26 is inserted between the connection point of the above and the ground. The value of the resistor 26 is, for example, about 1/10 of the sum of the value of the resistor 22 and the value of the resistor 23. The critical voltage V _Z of the Zener diode 24 is
It can be changed according to the collector-emitter voltage V _CE of the transistor 5, and the values of the resistors 22, 23 and 26 can also be changed. Now, the power supply voltage V _DD = 120 [V]
When the collector-emitter voltage V _CE when the transistor 5 is in the short-circuited state is about 60 [V], the zener diode 24 has a critical voltage V _Z of 75.
Use [V]. The values of the resistors 22, 23 and 26 are 12 [kΩ] and 10 [kΩ], respectively.
And 2.2 [kΩ].

In such a structure, when the pulse width modulation signal is generated in the pulse width modulation signal generation circuit 1, the transistors 4 and 5 are turned on / off by this signal.
The solenoid 6 is turned off, and the pulse width modulation signal is "H".
Energized during the level. Then, while the transistor 5 is off, the potential of the connection point a, that is, the collector potential of the transistor 5 is substantially the power supply voltage V _DD [V] (120
[V]), and the potential at the connection point c becomes the critical voltage V _Z of the Zener diode 24 and the power supply voltage V _DD [V] (120
[V]) minus the critical voltage V _Z of the Zener diode 24 and the sum of the divided voltage (about 4.09 [V]) by the resistors 22 and 23 and the resistor 26 (about 79.1).
[V]), the diode 9 is non-conductive.

Further, the potential at the connection point d is the power supply voltage V
Zener diode 24 from _DD [V] (120 [V])
Of the resistors 22 and 23 of which the critical voltage V _Z of
And a voltage divided by the resistor 26 (about 4.09 [V]), and the potential at the connection point b is the power supply voltage V _CC [V] (5
[V]) divided voltage by resistors 12 and 13 (about 4.7)
8 [V]), the diode 25 is non-conductive. As a result, the capacitor 16 is charged via the power supply voltage V _CC [V], the resistor 12, and the diode 15. The charging time in this case depends on the time constant determined by the respective values of the resistor 12 and the capacitor 16.

On the other hand, while the transistor 5 is on, the potential at the connection point a, that is, the collector potential of the transistor 5 is almost 0 [V], but the potential at the connection point c is
The critical voltage V _Z of the Zener diode 24 and the power supply voltage V
Zener diode 24 from _DD [V] (120 [V])
Of the resistors 22 and 23 of which the critical voltage V _Z of
Since it remains the sum (about 79.1 [V]) of the divided voltage (about 4.09 [V]) by the resistor 26 and the resistor 26, the diode 9 becomes conductive.

As a result, the potential at the connection point c is about 0.7.
Since it becomes [V], the reverse current does not flow through the Zener diode 24. On the other hand, the potential at the connection point b is
Since it remains almost equal to the divided voltage (about 4.78 [V]) by the resistors 12 and 13 of the power supply voltage V _CC [V] (5 [V]), the diode 25 becomes conductive and
A forward current flows through the Zener diode 24.

Therefore, the potential of the connection point b is the sum of the forward voltages of the diode 9, the zener diode 24 and the diode 25, that is, about 2.1.
Since it is substantially equal to [V], the charge charged in the capacitor 16 while the transistor 5 is off is the resistance 14,
It is discharged through the diode 25 and the resistor 26. The discharge time in this case is almost equal to that of the resistor 14 and the capacitor 1.
With a time constant determined by each value of 6.

In a normal state, the charging and discharging operations of the capacitor 16 described above are repeated according to the pulse width modulation signal output from the pulse width modulation signal generating circuit 1, so the potential of the capacitor 16 is always set in advance. _Is equal to or higher than the reference voltage V _ref . Therefore, an "H" level signal indicating normal is output from the output terminal 21.

However, if the transistor 5 is short-circuited or if the transistor 5 is continuously on for some reason, that is, if the solenoid 6 is continuously energized for a long time, the discharge time of the capacitor 16 becomes long, so that the capacitor 16 is discharged. The potential becomes equal to or lower than the reference voltage V _ref, and "L" indicating that there is an abnormality from the output terminal 21
A level abnormality detection signal is output. As a result, the control circuit (not shown) inputs the abnormality detection signal to the solenoid 6
To stop the solenoid 6 from being burnt.

When the transistor 5 is in a short-circuited state for some reason, that is, the transistor 5 has a predetermined resistance value,
For example, when a potential difference of about 60 [V] is generated between the collector and the emitter of
A voltage of about 40 [V] or higher is applied, but in such a case, the solenoid 6 starts to generate heat and is highly likely to burn.

Therefore, the solenoid abnormality detection circuit according to this embodiment prevents the solenoid 6 from being burnt out by the following operation. The transistor 5 is in a semi-shorted state for some reason, and the collector potential of the transistor 5, that is, the potential at the connection point a is, for example, 60.
When it is about [V], the potential at the connection point c is equal to the critical voltage V _Z of the Zener diode 24 and the power supply voltage V
Zener diode 24 from _DD [V] (120 [V])
Of the resistors 22 and 23 of which the critical voltage V _Z of
Since it remains the sum (about 79.1 [V]) of the divided voltage (about 4.09 [V]) by the resistor 26 and the resistor 26, the diode 9 becomes conductive.

As a result, the potential at the connection point c is approximately 60.
Since it becomes [V], the reverse current does not flow through the Zener diode 24. On the other hand, the potential at the connection point b is
Since the power supply voltage V _CC [V] (5 [V]) remains almost equal to the divided voltage (about 4.78 [V]) of the resistors 12 and 13, the diode 25 is turned on. No current flows through the Zener diode 24.

Therefore, the potential at the connection point b is equal to the resistance 1
2, the voltage determined by the diode 25 and the resistor 26,
That is, since it becomes about 1.3 [V], the capacitor 16
The electric charge charged in the capacitor is discharged through the resistor 14, the diode 25 and the resistor 26. Then, if the short-circuited state of the transistor 5 continues for a certain time or longer, the potential of the capacitor 16 becomes equal to or lower than the reference voltage V _ref, and an "L" level abnormality detection signal indicating an abnormality is output from the output terminal 21. . As a result, a control circuit (not shown) receives the abnormality detection signal, stops energization of the solenoid 6, and protects the solenoid 6 from burning.

Next, a second embodiment of the present invention will be described. 2 is a circuit diagram showing the configuration of a solenoid abnormality detection circuit according to a second embodiment of the present invention. In this figure, parts corresponding to those in FIG.
The description is omitted. In FIG. 2, 27 is a Zener diode having the same critical voltage V _Z as the Zener diode 24, 28 is a PNP type transistor, and 29 to 32.
Is a resistor for applying a bias to the transistor 28 in order to operate the transistor 28 at a predetermined operating point when the power supply voltage V _{DD is} cut off. As the transistor 28,
For example, the typical value of the base-emitter voltage V _BE is −0.6 [V], the typical value of the collector-emitter voltage V _CE is −0.07 [V], and the typical value of the direct current amplification factor h _FE is 200, the maximum value of the emitter-base voltage V _EB0 is -5 [V].

When the power supply voltage V _DD is 120 [V] and the collector-emitter voltage V _CE when the transistor 5 is in the short-circuited state is 62.7 [V], the zener diode 24 The critical voltage V _Z is 62 [V] for and. Also, the resistor 2
The values 2, 23 and 26 are, for example, 12 each
[KΩ], 10 [kΩ], and 2.7 [kΩ].
Further, the values of the resistors 29 to 32 are, for example, 1 each.
5 [kΩ], 2.7 [kΩ], 1 [kΩ] and 1 [k
Ω].

In such a configuration, when a pulse width modulation signal is generated in the pulse width modulation signal generation circuit 1, the transistors 4 and 5 are turned on / off by this signal.
The solenoid 6 is turned off, and the pulse width modulation signal is "H".
Energized during the level. Then, while the transistor 5 is off, the potential of the connection point a, that is, the collector potential of the transistor 5 is substantially the power supply voltage V _DD [V] (120
[V]), and the potential at the connection point c becomes the critical voltage V _Z of the Zener diode 24 and the power supply voltage V _DD [V].
The resistances 22 and 23 and the resistance 2 of a voltage obtained by subtracting the critical voltage V _Z of the Zener diode 24 from (120 [V])
6 and divided voltage (about 6.3 [V]) and sum (about 6)
Since it is 8.3 [V]), the diode 9 is in a non-conducting state.

The potential at the connection point d is the power supply voltage V
Zener diode 24 from _DD [V] (120 [V])
Of the resistors 22 and 23 of which the critical voltage V _Z of
Is a divided voltage (about 6.3 [V]) by the resistor 26 and the resistor 26, and the potential at the connection point b is the power supply voltage V _CC [V] (5 [V]).
Voltage divided by resistors 12 and 13 (approximately 4.78
Higher than [V]), the diode 25 is non-conductive. As a result, the capacitor 16 has the power supply voltage V
It is charged via _CC [V], resistor 12 and diode 15. The charging time in this case depends on the time constant determined by the respective values of the resistor 12 and the capacitor 16.

At this time, the potential at the connection point e changes to the power supply voltage V _DD.
[V] (120 [V]) minus the critical voltage V _Z of the Zener diode 27, which is a divided voltage (about 8.8 [V]) by the resistors 29 and 30, and is applied to the emitter of the transistor 28. Is applied with the power supply voltage V _CC (5 [V]), the base-emitter voltage V _BE of the transistor 28 is approximately the potential at the connection point e (about 8.8).
Since the potential is about 3.8 [V], which is obtained by subtracting the power supply voltage V _CC (5 [V]) from [V]), the transistor 28 is in the cutoff state.

On the other hand, while the transistor 5 is on, the potential at the connection point a, that is, the collector potential of the transistor 5 is almost 0 [V], but the potential at the connection point c is
The critical voltage V _Z of the Zener diode 24 and the power supply voltage V
Zener diode 24 from _DD [V] (120 [V])
Of the resistors 22 and 23 of which the critical voltage V _Z of
And the divided voltage by the resistor 26 (about 6.3 [V]) remains (about 68.3 [V]), the diode 9
Becomes conductive.

As a result, the potential at the connection point c is about 0.7.
Since it becomes [V], the reverse current does not flow through the Zener diode 24. On the other hand, the potential at the connection point b is
Since it remains almost equal to the divided voltage (about 4.78 [V]) by the resistors 12 and 13 of the power supply voltage V _CC [V] (5 [V]), the diode 25 becomes conductive and
A forward current flows through the Zener diode 24.

Therefore, the potential of the connection point b is the sum of the forward voltages of the diode 9, the Zener diode 24 and the diode 25, that is, about 2.1.
Since it is substantially equal to [V], the charge charged in the capacitor 16 while the transistor 5 is off is the resistance 14,
It is discharged through the diode 25 and the resistor 26. The discharge time in this case is almost equal to that of the resistor 14 and the capacitor 1.
With a time constant determined by each value of 6.

At this time, the potential at the connection point e changes to the power supply voltage V _DD.
[V] (120 [V]) minus the critical voltage V _Z of the Zener diode 27, which is a divided voltage (about 8.8 [V]) by the resistors 29 and 30, and is applied to the emitter of the transistor 28. Is applied with the power supply voltage V _CC (5 [V]), the base-emitter voltage V _BE of the transistor 28 is approximately the potential at the connection point e (about 8.8).
Since it is the potential (about 3.8 [V]) obtained by subtracting the power supply voltage V _CC (5 [V]) from [V]), the transistor 28 remains in the cutoff state.

In a normal state, the charging and discharging operations of the capacitor 16 described above are repeated according to the pulse width modulation signal output from the pulse width modulation signal generation circuit 1, so the potential of the capacitor 16 is always set in advance. _Is equal to or higher than the reference voltage V _ref . Therefore, an "H" level signal indicating normal is output from the output terminal 21.

However, if the transistor 5 is short-circuited or if the transistor 5 is continuously turned on for some reason, that is, if the solenoid 6 is continuously energized for a long time, the discharge time of the capacitor 16 becomes long, so that the capacitor 16 is discharged. The potential becomes equal to or lower than the reference voltage V _ref, and "L" indicating that there is an abnormality from the output terminal 21
A level abnormality detection signal is output. As a result, the control circuit (not shown) inputs the abnormality detection signal to the solenoid 6
To stop the solenoid 6 from being burnt.

Further, as shown in FIG. 3, the transistor 5 is in a short-circuited state for some reason, and the collector potential of the transistor 5, that is, the potential at the connection point a falls from 120 [V], for example, at time t. ₁ to 6
When it becomes 2.7 [V], both ends of the solenoid 6 are
Since a voltage of about 57 [V] or higher is applied,
The solenoid 6 is generating heat.

At this time, the potential at the connection point c is the critical voltage V _Z of the Zener diode 24 and the power supply voltage V _DD [V].
The resistances 22 and 23 and the resistance 2 of a voltage obtained by subtracting the critical voltage V _Z of the Zener diode 24 from (120 [V])
6 and divided voltage (about 6.3 [V]) and sum (about 6)
Since it remains 8.3 [V]), the diode 9 becomes conductive. As a result, the potential at the connection point c is approximately 63.
Since the voltage is 4 [V], no reverse current flows through the Zener diode 24. On the other hand, the potential at the connection point b is the resistances 12 and 13 of the power supply voltage V _CC [V] (5 [V]).
Since it remains almost equal to the divided voltage (about 4.78 [V]) due to, the diode 25 becomes conductive. No current flows through the Zener diode 24.

Therefore, the potential at the connection point d becomes a voltage determined by the resistor 12, the diode 25 and the resistor 26, that is, about 1.6 [V], as shown in FIG. Since it becomes about 2.3 [V], the electric charge charged in the capacitor 16 is discharged through the resistor 14, the diode 25 and the resistor 26. When the short-circuited state of the transistor 5 continues for a certain time or longer,
The potential of the capacitor 16 becomes equal to or lower than the reference voltage _Vref , and the output terminal 21 outputs an "L" level abnormality detection signal indicating an abnormality. As a result, a control circuit (not shown) receives the abnormality detection signal, stops energization of the solenoid 6, and protects the solenoid 6 from burning.

At this time, the potential at the connection point e changes to the power supply voltage V _DD.
[V] (120 [V]) minus the critical voltage V _Z of the Zener diode 27, which is a divided voltage (about 8.8 [V]) by the resistors 29 and 30, and is applied to the emitter of the transistor 28. Is applied with the power supply voltage V _CC (5 [V]), the base-emitter voltage V _BE of the transistor 28 is approximately the potential at the connection point e (about 8.8).
Since it is the potential (about 3.8 [V]) obtained by subtracting the power supply voltage V _CC (5 [V]) from [V]), the transistor 28 remains in the cutoff state.

In the automatic playing piano to which this embodiment is applied, the power supply of the entire device is still turned on, but the power supply voltage V applied to the solenoid when the operation is stopped.
_May block _DD . Below, FIG. 2 in such a case
The operation of the circuit shown in will be described. As shown in FIG. 4, when the power supply voltage V _DD applied to the solenoid 6 is cut off at time t0, the voltage is reduced from 120 [V] to 0.
While gradually decreasing toward [V], the potential at the connection point a, that is, the collector potential of the transistor 5 also gradually decreases from 120 [V] to 0 [V] (power supply voltage V _DD (When the transistor 5 is off immediately before the cutoff).

Further, the power supply voltage V _DD changes from 120 [V] to 0.
The connection point c is gradually decreased toward [V].
Since also the potential go down gradually from about 68.3 [V] to 0 [V], as shown in FIG. 4, the power supply voltage V _DD
There when lowered to 65.7 [V] (time t _2), the Zener diode 24 is reverse current does not flow.

By the way, as the power supply voltage V _DD gradually decreases from 120 [V] to 0 [V], the potential at the connection point e also becomes 8.8 [V] as shown in FIG. ] To 0 [V] gradually, but 4.4
When it decreases to [V], the base-emitter voltage V _BE of the transistor 28 is almost equal to the potential of the connection point e (4.4).
The transistor 28 is turned on (time t ₁ ) because the potential (−0.6 [V]) is obtained by subtracting the power supply voltage V _CC (5 [V]) from [V]).

As a result, the collector current of the transistor 28 flows into the connection point d, so that the potential at the connection point d is prevented from lowering, as shown in FIG. 4, and does not fall below 3.65 [V]. Therefore, the potential of the capacitor 16 does not _fall below the reference voltage V _ref, and the "L" level abnormality detection signal indicating an abnormality is not output from the output terminal 21.

[0046]

As described above, according to the first aspect of the invention, it is possible to detect the half-short state of the transistor that drives the solenoid. As a result, the detection range of abnormal energization of the solenoid becomes wider, and it is possible to prevent the solenoid from burning more than before.
The reliability of the device is improved.

According to the second aspect of the invention, the power of the entire apparatus is still turned on. However, even when the power applied to the solenoid is cut off during the operation stop, the solenoid is stopped during the operation stop and the solenoid is stopped. It is distinguished from the operation
There is an effect that the circuit does not erroneously detect that the transistor is in a short state.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a solenoid abnormality detection circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a solenoid abnormality detection circuit according to a second embodiment of the present invention.

FIG. 3 is a diagram for explaining the operation of the circuit of FIG.

FIG. 4 is a diagram for explaining the operation of the circuit of FIG.

FIG. 5 is a circuit diagram showing a configuration example of a conventional solenoid abnormality detection circuit.

[Explanation of symbols]

5, 28 ... Transistor, 6 ... Solenoid, 22,
23, 26, 29 to 32 ... Resistance, 24, 27 ... Zener diode, 25 ... Diode.

Claims (2)

(57) [Claims] 1. A first charging / discharging means for charging / discharging according to energization / disconnection of a solenoid, which is energized / disconnected according to a pulse width modulation signal, and a potential of the first charging / discharging means. detecting means for detecting a current abnormality of the solenoid as compared to the potential of, if it is applied above a predetermined voltage to the solenoid
Only for charging or discharging the first charging / discharging means
And a charging / discharging means for the solenoid abnormality detecting circuit. 2. A first charging / discharging means for charging / discharging according to energization / disconnection of a solenoid that is energized / disconnected according to a pulse width modulation signal, and a potential of the first charging / discharging means is predetermined. Detecting means for detecting an abnormality in the energization of the solenoid by comparing with the potential of the second charging means, and second charging / discharging means for charging or discharging the first charging / discharging means when a predetermined voltage or more is applied to the solenoid. When the power applied to the solenoid is cut off,
A solenoid abnormality detection circuit comprising: a blocking unit that blocks charging or discharging of the first charging / discharging unit.