JPWO2005067134A1 - Power transistor protection circuit for motor drive circuit, motor drive circuit, and semiconductor device - Google Patents

Abstract

A power transistor protection circuit for a motor drive circuit and a motor drive circuit capable of preventing the power transistor from being destroyed when there is a disconnection between the output terminal of the power transistor and the other end of the exciting coil of the motor. Another object is to provide a semiconductor device. The present invention includes a terminal open detection circuit, a disconnection detection circuit, and a drive stop circuit. The first invention of the present invention detects a terminal open detection when a power transistor is operating to output a drive current. The other terminal of each exciting coil whose circuit is not connected to the output terminal or the line to which it is connected (one of them) and the output terminal corresponding to each exciting coil or the line to which this is connected (whichever) It is detected whether the space between is open. Further, as disconnection detection, it is detected that the terminal open detection circuit is not in the open state, and thereafter the open state is detected. In the second aspect of the invention, the terminal open detection circuit detects either an open state or a connection state between one and the other when the power transistor is performing a drive current output operation. As the disconnection detection, the disconnection state is detected when the open state is detected a plurality of times in response to detection of either the open state or the connection state by the terminal open detection circuit. [Selection] Figure 1

Description

  The present invention relates to a power transistor protection circuit of a motor drive circuit, a motor drive circuit, and a semiconductor device. More specifically, in a stepping motor driver of unipolar (half wave) drive, a gap between an output terminal of a power transistor and an excitation coil of a motor is provided. The present invention relates to a power transistor protection circuit for a motor drive circuit that can prevent the power transistor from being destroyed when it is disconnected.

A unipolar stepping motor driver (pulse motor driver) rotates the projection shape by a predetermined rotation angle by sequentially exciting the stator side of the motor by one-phase driving, one-phase-two-phase driving, or two-phase driving. Rotate the child.
The driver that drives the drive current to excite each stator has a power transistor (output stage transistor) corresponding to each phase in series with the coil (excitation coil) connected to the power line and wound around the stator. Each is provided. The power transistors provided for each phase are turned ON / OFF at a predetermined timing, whereby the stator is sequentially excited and the stepping motor is driven.
When a power transistor of a certain phase is turned on, the drive current is increased sequentially during the ON period due to a transient phenomenon of a predetermined time constant determined by the inductance of the exciting coil of that phase and the impedance of the power transistor or the like. In order to limit the amount of increase to a predetermined value, the power transistor is controlled to turn off after a predetermined period of time so that no overcurrent flows through the power transistor. Therefore, the power transistor is normally pulse-driven by chopping each phase with “H” (HIGH level) and “L” (LOW level) logic value pulses that are turned ON / OFF.

As one of such pulse drive controls, a chopper-controlled three-phase motor driver that controls the ON period with a timer circuit and a protection circuit for the IGBT power transistor are well known (Patent Document 1).
JP 11-112313 A

The power transistor protection circuit as described above is generally an overcurrent protection circuit or a current limiting circuit. However, when the motor-driven driver is an IC, since the motor excitation coil terminal is connected to the output terminal, poor connection between the output terminal and the motor is likely to occur. Further, since a motor or the like has a rotor, disconnection of the exciting coil or the like also occurs.
In addition, in a motor drive circuit or the like, one of the output terminals of the power transistor may be instantaneously opened due to noise, drive state, etc., and it is an error to detect disconnection by detecting the open state of the terminal. Detection is likely to occur and affects the driving operation of the motor drive circuit, making it impractical. Therefore, there is no protection circuit against this type of disconnection.
In the stepping motor driver, the motor continues to be driven even when connection failure or disconnection of the exciting coil occurs at one of the output terminals. At this time, since no back electromotive force is generated in the exciting coil connected to the open terminal, the current flowing through the other exciting coil increases and the driver continues to drive the motor in an overloaded state as a whole. Is done. As a result, the power transistor is destroyed, and the IC itself is destroyed.
The object of the present invention is to solve such problems of the prior art, and the power transistor is destroyed when there is a disconnection between the output terminal of the power transistor and the other end of the excitation coil of the motor. It is an object of the present invention to provide a power transistor protection circuit, a motor drive circuit, or a semiconductor device for a motor drive circuit that can prevent the above.

In order to achieve such an object, the power transistor protection circuit, motor drive circuit or semiconductor device configuration of the motor drive circuit according to the first aspect of the present invention is a power transistor that outputs a drive current to an excitation coil of a motor via an output terminal. In a power transistor protection circuit in a motor drive circuit having a plurality corresponding to a plurality of excitation coils,
A terminal open detection circuit, a disconnection detection circuit, and a drive stop circuit are provided.
The terminal open detection circuit is connected to an excitation coil having either one of the other terminal of each excitation coil not connected to the output terminal and a line to which the other terminal is connected and the other terminal. Between the output terminal and the line to which the output terminal is connected and each corresponding to the plurality of power transistors, and the power transistors perform the drive current output operation. Sometimes detect whether one of the other and the other is open,
The disconnection detection circuit detects that the terminal open detection circuit detects that there is no open state between one and the other, and then detects any open state by detecting that it is in the open state. Is,
The drive stop circuit stops the drive operation of the motor drive circuit when a disconnection state is detected by the disconnection detection circuit.
According to a second aspect of the present invention, the terminal open detection circuit detects an open state or a connection state between one of the power transistors and the other when the power transistor is performing a drive current output operation. Yes,
The disconnection detection circuit detects a disconnection state when an open state is detected a plurality of times in response to detection of either an open state or a connection state by the terminal open detection circuit.

Thus, according to the first aspect of the present invention, when the power transistor performs the output operation of the drive current, the other terminal of each exciting coil whose terminal open detection circuit is not connected to the output terminal or the line to which this terminal is connected. It is detected whether or not between any one of them and the output terminal corresponding to each exciting coil or the line (any other) to which this is connected. Further, as a disconnection detection, it is detected that the terminal open detection circuit is not in the open state, and thereafter the open state is detected.
Thus, according to the first aspect of the present invention, the power transistor detects that the terminals are not in an open state first, and thereafter detects that the terminals are in an open state. To detect a change from an open state to an open state. In the first aspect of the present invention, whether or not the open state between the terminals continues substantially until the subsequent output of the drive current by setting the detection condition that the terminals are not in the open state and in the open state. To detect.
On the other hand, in the second invention, the terminal open detection circuit detects either an open state or a connection state between one and the other when the power transistor is performing the drive current output operation. As the disconnection detection, the disconnection state is detected when the open state is detected a plurality of times in response to the detection of either the open state or the connection state by the terminal open detection circuit.
In the above detection, as a matter of course, the open state is set when the connection state is not established, and the connection state is established when the open state is not established.
By determining the disconnection state under these multiple conditions, disconnection is not erroneously detected, and disconnection can be reliably detected without affecting the drive operation of the motor drive circuit. Thus, the drive operation of the motor drive circuit can be stopped when the wire is disconnected.
Moreover, when the power transistor is operating to output the drive current, it is detected that it is always open or not open. At this time, the drive current is flowing through the motor coil, so instantaneous noise and drive are detected. Not easily affected by changes in state. In particular, if it is detected whether or not it is in an open state near a voltage value corresponding to the limit current value of the drive current, it is difficult to be affected by instantaneous noise and instantaneous open state. Can be detected.
As a result, when there is a disconnection between the output terminal of the power transistor and the other end of the exciting coil of the motor, it can be detected immediately, and thus the power transistor can be prevented from being destroyed.

FIG. 1 is a block diagram of a unipolar driving stepping motor driver to which the power transistor protection circuit of the motor drive circuit of the present invention is applied, and FIG. 2 is a timing chart of the operation of the power transistor protection circuit.
In FIG. 1, reference numeral 10 denotes a unipolar stepping motor driver IC having four exciting coils. For this, single-phase drive circuits 1a, 1b, 1c and 1d are provided, and excitation coils 11a, 11b, 11c and 11d of the stepping motor 11 are connected to the output terminals 2a, 2b, 2c and 2d, respectively. Yes.
These exciting coils 11a, 11b, 11c, and 11d are connected to a power supply line 13 of a power source (battery) 12 and receive power supply therefrom. A flywheel diode D is connected in parallel to each of the exciting coils 11a, 11b, 11c, and 11d.
The power supply 12 supplies power to the voltage regulator circuit (REG) 2 inside the IC through the terminal 2e, and supplies a predetermined voltage, for example, 3V power, stabilized to the internal power supply line + VDD through the REG2. Send to various internal circuits.
Since the single-phase drive circuits 1a, 1b, 1c, and 1d are configured by the same circuit, the details are shown only in the single-phase drive circuit 1a. Hereinafter, the single-phase drive circuit 1a will be described, and the single-phase drive circuits 1b, 1c, and 1d are the same and will not be described.

The single-phase driving circuit 1a will be described. The single-phase driving circuit 1a includes an N-channel MOSFET power transistor 3, a power transistor protection circuit 4, a current limiting circuit 5, and a reference voltage generating circuit 6. For convenience of explanation, the current limiting circuit 5 of each single-phase driving circuit is outside the dotted frame of the single-phase driving circuit 1a.
The power transistor 3 has a drain connected to the output terminal 2a and outputs an excitation current to the output terminal 2a. The source side of the power transistor 3 is connected to an output current detection resistor Rs attached outside the IC via a terminal 2f, and is grounded via this. The output current of the output terminal 2a is a current that is sunk from the exciting coil 11a to the output terminal 2a.
The power transistor protection circuit 4 includes a terminal open detection circuit 4a that detects an open state of the power supply line 12a of the battery 12 and the output terminal 2a, and a disconnection detection circuit 4b.
The terminal open detection circuit 4a detects the voltage between the output terminal 2a and the terminal (the other terminal) on the power supply line 13 side of the exciting coil 11a, thereby detecting that the terminals are open. The resistor voltage divider circuit 44, the resistor voltage divider circuit 45, and the comparator 46. The resistance voltage dividing circuit 44 is composed of resistors R1 and R2 connected between the output terminal 2a and the ground GND. The resistance voltage dividing circuit 45 includes resistors R3 and R4, one of which is connected to the power supply line 13 via the terminal 2i and the other of which is connected to the ground GND.
The (+) input of the comparator 46 is connected to the connection point of the resistor of the resistance voltage dividing circuit 44 and receives the divided voltage Va at the connection point. The (−) input is connected to the connection point of the resistor of the resistance voltage dividing circuit 45 and receives the divided voltage Vb at the connection point. Here, when the output of the power transistor 3 is generated and has a predetermined drive current value, the output terminal 2a has a voltage value corresponding to the current value, and therefore Va> Vb. At this time, the output of the comparator 46 changes from “H” to “L”. That is, the comparator 46 generates a significant output detection pulse of “L” indicating that an output current is generated when “L” (see FIG. 2D). This output detection pulse is a detection signal that the terminal open detection circuit 4a outputs to indicate that the output terminal 2a and the other terminal of the exciting coil 11a are connected. In other words, this output detection pulse indicates that these terminals are not open. Accordingly, when the output detection pulse is not generated when the power transistor 3 is outputting the drive current, these terminals are in an open state.
Here, as shown in FIG. 2D, the voltage of the divided voltage Vb is set to a voltage value (5% to 20% lower) close to the limit current value of the drive current. In this way, when the power transistor 3 is outputting the drive current, it is detected whether or not the output terminal 2a is in an open state, and when the drive current is close to the voltage value corresponding to the limit current value. If it is detected whether or not the terminal is in an open state, the detection of the terminal open state is less likely to be affected by noise or instantaneously the open state because the drive current continues to flow through the motor coil.

The disconnection detection circuit 4b includes a comparator 4c and an octal counter 4d. The octal counter 4d receives the clock CLK sent from the clock generation circuit 14 via the terminal 2h. The (+) input of the comparator 4c receives the comparison reference voltage VR from the reference voltage generating circuit 6 provided in common to the single-phase drive circuits 1a, 1b, 1c, and 1d, and the (−) input is the terminal open detection circuit 4a. Receives a detection voltage signal from. The output of the comparator 4c is connected to the reset terminal R of the octal counter 4d. The reference voltage generating circuit 6 can be adjusted in voltage by laser trimming or the like. By this voltage adjustment, the voltage VR is set so that the comparators 4c of the single-phase drive circuits 1a, 1b, 1c, and 1d generate reset signals.
This reset signal is used as a falling trigger signal when the comparator 4c falls from “H” to “L” when the comparator 46 changes from “H” to “L” and then changes to “H”. Is done.
The disconnection detection circuit 4b receives the detection voltage signal from the terminal open detection circuit 4a, and detects the disconnection by counting the clock CLK with the octal counter 4d that the open state continues for a certain period. That is, the disconnection detection signal is generated when the octal counter 4d finishes counting (counts up by 8 or more). As a result, a disconnection detection signal is generated during a period in which the power transistor 3 does not output the drive current. As a result, the disconnection detection signal is not affected by noise during operation of the power transistor 3.
By the way, the period TG of the gate drive pulse for driving the power transistor 3 is TG <8 × T, and T is the period of the clock CLK. Here, the period TG is set to a period of about 6 counts (6 × T) of the octal counter 4d, for example.
The comparator 4 c generates an “H” output pulse (reset pulse) and resets the octal counter 4 d only when the comparator 46 generates an “L” output detection pulse. As a result, the octal counter 4d starts counting from “0”. Since the next gate drive pulse is generated before 8 × T, the output current of the power transistor 3 is thereby generated. As long as this occurs, the octal counter 4d continues to be reset. As a result, the 8-count end signal of the octal counter 4d is not generated.

Here, when a disconnection occurs between the terminal of the exciting coil 11a on the power supply line 13 side and the connection terminal 2a, the divided voltage of the resistance voltage dividing circuit 44 becomes the ground GND potential, and therefore the output generated by the comparator 46. Even if the gate drive pulse is generated, the detection pulse remains “H” when no output current is generated in the power transistor 3 (see the latter half waveform in FIG. 4E). Therefore, the output pulse (reset pulse) of the comparator 4c remains “L”, and the octal counter 4d is not reset by the output pulse of the comparator 4c. As a result, when the output current of the power transistor 3 is not generated, an 8-count end signal of the octal counter 4d is generated. This 8-count end signal is used as a disconnection detection signal.
Reference numeral 41 denotes a drive stop signal generation circuit which includes an OR gate 42 and a latch circuit 43. Then, the latch circuit 43 receives the 8-count end signal “H” at the final stage of the octal counter 4d of the single-phase drive circuits 1a, 1b, 1c, 1d via the OR gate 42 as a disconnection detection signal. As a result, the latch circuit 43 receives the 8-count end signal “H” as “1”, and latches the logical sum signal for the exciting coils 11a to 11d in accordance with the clock CLK.
When the disconnection detection signal (“1”) is latched, “1” is applied from the latch circuit 43 to the phase excitation signal generation circuit 9 as the drive stop signal SP. As a result, the phase excitation signal generation circuit 9 stops its operation. Note that when the reset signal “1” is input to the reset terminal R of the latch circuit 43 via the terminal RS, the value of the latch circuit 43 is cleared to “0”. In the initial state, the latch circuit 43 is set to “0” by this reset signal.
Therefore, when a disconnection occurs between the terminal of the exciting coil 11a on the power supply line 13 side and the connection terminal 2a, an 8-count end signal ("H") is generated as a disconnection detection signal from the octal counter 4d, and the latch circuit “1” is latched in 43, and the operation of the phase excitation signal generation circuit 9 stops. As a result, the stepping motor driver IC 10, particularly the power transistor 3, does not need to be destroyed.
By the way, the disconnection detection signal may use an overflow signal or carry signal of the octal counter 4d.

The current limiting circuit 5 includes a comparator 5a and a reference voltage generation circuit 5b. The (+) input terminal of the comparator 5a is connected to the terminal 2f, and the reference voltage generation circuit 5b is provided outside the IC, and is connected to the (−) input terminal of the comparator 5a via the terminal 2g, so that the reference voltage VREF is supplied. (-) Add to the input terminal. Assuming that the terminal voltage of the resistor Rs for detecting the output current (the voltage at the terminal 2f) is Vs, the drive current (output current) of the power transistor 3 is increased, and the output current is such that the voltage Vs exceeds the reference voltage VREF. When it occurs in the transistor 3, in other words, when the output current reaches a specified value, the comparator 5a generates the detection pulse S. The detection pulse S is applied to the chopping pulse generation circuit 7 to turn off the chopping pulse P of “H” (from “H” to “L”) and to drive the OFF timer circuit 8. As a result, the power transistor 3 is turned off (the operation will be described later).
The stop time (“L” period) of the chopping pulse P is counted by the OFF timer circuit 8 for setting the OFF time, and the chopping pulse P changes from “L” to “H” after a certain period, for example, 15 μsec. The chopping pulse P is, for example, a pulse that becomes “H” during a period selected in a range of about 30 μsec to 50 μsec. That is, the chopping pulse P is generated as a chopping pulse when the “H” pulse becomes “L” according to the detection pulse S and becomes “H” after a certain time.
As a result, the current limiting circuit 5 stops the driving current and limits the output current of the power transistor 3 when the terminal voltage Vs of the resistor Rs exceeds the voltage VREF. In this respect, the current limiting circuit 5 is provided also as an overcurrent protection circuit for the motor drive circuit.

The chopping pulse P of “H” in the steady state is sent to the phase excitation signal generation circuit 9, and, for example, the phase excitation signal generation circuit 9 ANDs the “H” of the gate drive pulse of the single-phase drive circuit 1a by AND gate. Logic is adopted and output to the gate of the power transistor 3 (see FIGS. 2A and 2B). Therefore, a chopping pulse (corresponding to the chopping pulse P) for cutting off the transistor 3 at a predetermined frequency is applied to the power transistor 3 from the phase excitation signal generation circuit 9 during the “H” period of the gate drive pulse. . When the chopping pulse P is “L”, the gate drive pulse is “L”, the power transistor 3 is turned off, and the drive current to the excitation coil 11a of the stepping motor 11 is stopped.
Here, since each exciting coil is provided with the flywheel diode D in parallel, each current flowing through each exciting coil 11a, 11b, 11c, 11d is in the OFF period when the chopping pulse P is "L". It flows through the flywheel diode D. That is an average current determined by the relationship between the ON period and the OFF period due to the chopping pulse P.

Here, the chopping pulse generation circuit 7 and the OFF timer circuit 8 are provided in common to the single-phase drive circuits 1a, 1b, 1c, and 1d, and the single-phase drive circuits 1a, 1b, A chopping pulse P is generated for each of the excitation coil drives 1c and 1d and sent to the phase excitation signal generation circuit 9.
The phase excitation signal generation circuit 9 drives the gates of the power transistors 3 of the single-phase drive circuits 1a, 1b, 1c, and 1d in accordance with single-phase drive, one-phase and two-phase drive, and two-phase drive. This circuit generates a pulse at a predetermined timing, and generates “H” and “L” gate drive pulses. Further, the “H” period of each gate pulse is chopped by the respective chopping pulses P in order to limit the drive current. Note that the cycle of the chopping pulse P is smaller than the cycle of the clock CLK.

FIG. 2 is a timing chart of the operation of the power transistor protection circuit 4.
FIG. 2A shows a gate drive pulse of the single-phase drive circuit 1a, and the power transistor 3 is chopped and driven during this period of “H”. FIG. 2B shows the chopping pulse P, and during this “H” period, the drive current flows through the exciting coil 11 a of the stepping motor 11, so the output voltage Vout of the output terminal 2 a is 2 (c).
Here, it is assumed that the power transistor 3 of the single-phase drive circuit 1a generates an output current in response to the gate drive pulse of FIG. In this case, the comparator 46 changes from "H" to "L" when the divided voltage Va obtained by dividing the voltage according to the voltage of the output terminal 2a exceeds the divided voltage Vb (see FIG. 2D). Since it becomes an output, as shown in FIG. 2 (e), the output pulse is "H", "L", "H", "L" according to the voltage Vout of the output terminal 2a in FIG. 2 (c). Output detection pulse. Since the cycle of the chopping pulse P is smaller than that of the clock CLK, the comparator 4c generates an output of “H” (reset pulse) in response to the output pulse of the output detection pulse “L” of the comparator 46, and is 8 The decimal counter 4d is reset. As a result, the latch circuit 43 remains at the initial value “0”, and the phase excitation signal generation circuit 9 continues to operate without generating the drive stop signal SP.

The last output detection pulse “L” of the comparator 46 generated at this time is generated in correspondence with the chopping pulse P in which the gate drive pulse in FIG. Then, the “L” output detection pulse of the comparator 46 generated next corresponds to the first chopping pulse P generated by the next gate drive pulse. The generation period of the “L” output detection pulse of the comparator 46 at this time is shorter than the period 8 × T in which the octal counter 4d counts for eight clocks. Therefore, the drive stop signal SP for the phase excitation signal generation circuit 9 is not generated from the latch circuit 43 as long as there is no disconnection between the terminal of the excitation coil 11a on the power line 13 side and the connection terminal 2a. The count period of the octal counter 4d may be a period longer than the last output detection pulse to the next first output detection pulse.
On the other hand, when there is a disconnection between the terminal of the exciting coil 11a on the power supply line 13 side and the connection terminal 2a due to poor connection with the stepping motor 11, the power transistor 3 of the single-phase drive circuit 1a is switched according to the gate drive pulse. No output current is generated even when driven. Therefore, as shown in the second half of FIG. 2C, the voltage Vout of the output terminal 2a is not generated. Therefore, the divided voltage Va becomes Va≈0V.

As a result, Va <Vb, and the output detection pulse generated from the comparator 46 remains “H”. As a result, the octal counter 4d counts the clock CLK without being reset. Therefore, when the next output current does not occur, since the output detection pulse of “L” is not generated from the comparator 46, an 8-count end signal (“H”) is generated from the octal counter 4d, which is the OR gate 42. This is latched as “1” in the latch circuit 43 via the. As a result, the operation of the phase excitation signal generation circuit 9 is stopped, so that the stepping motor driver IC 10 is not destroyed.
In this case, the 8-count end signal (disconnection detection signal) from the octal counter 4d is longer than the period in which a plurality of "L" output detection pulses are generated from the comparator 46 in the next output current generation period. Preferably. Therefore, here, the period until the end of the 8-count of the octal counter 4d is set to a value longer than the generation period of each gate drive pulse in each of the single-phase drive circuits 1a, 1b, 1c, and 1d. is doing. Thereby, it can be detected that the terminal open state continues for one period or more of the gate drive pulse.
The OR gate 42 receives an 8-count end signal (disconnection detection signal) obtained from the final stage of the octal counter 4d of the single-phase drive circuits 1a, 1b, 1c, and 1d as a logical sum, so that the single-phase drive circuit 1a, Even when an 8-count end signal (disconnection detection signal) is generated in the octal counter 4d of any one of 1b, 1c, and 1d, the operation of the phase excitation signal generation circuit 9 is stopped.

In the above embodiment, the period from the reset of the octal counter 4d to the end of the count of the octal counter 4d is 8 × T, and the period TG of the gate drive pulse is 6 × T. Therefore, if the detection signal indicating the connection state of the terminal open detection circuit 4a is not generated once, it is determined that the terminal open detection signal has been generated by the disconnection detection circuit 4b.
However, in the present invention, for example, the octal counter 4d can be a 13-digit counter or a counter that counts more. In this case, if the detection signal indicating the connection state of the terminal open detection circuit 4a is not continuously generated a plurality of times, it is assumed that the terminal open detection signal is generated a plurality of times continuously. 4b is determined to be disconnected. Thereby, determination of a disconnection can be made more reliable.
In other words, in the present invention, the disconnection determination may be made so that the period from the reset of the counter 4d to the end of counting exceeds twice the period TG of the gate drive pulse.
Note that the disconnection detection circuit 4b may determine that the disconnection is detected when the terminal open detection signal is detected a plurality of times even if it is not continuously detected.

In the embodiment, the comparator 5a is provided in each of the single-phase drive circuits 1a, 1b, 1c, and 1d. However, the comparator 5a may be provided in common to a plurality of single-phase drive circuits. Good. In this case, for example, the output current value detection resistors Rs are shared by the comparators 5a of the single-phase drive circuits 1a and 1b and the comparators 5a of the single-phase drive circuits 1c and 1d. There can be two.
In the embodiment, the comparator 5 is one having two (+) input terminals. However, the internal circuit of the comparator 5 may be configured by two comparators in parallel. Also, this may use two comparators each having a (+) input terminal and a (−) input terminal.
Further, in the embodiment, the disconnection detection signal is the count end signal of the n-ary counter, but the present invention does not need to be based on the count end signal of the counter. In the present invention, the disconnection detection signal may be after the period until the output of the drive current generated next to the output of the drive current when the detection signal of the terminal open detection circuit is received and received. .
In addition, the power transistor Tr of the embodiment is a MOSFET transistor, but it is needless to say that it may be a bipolar transistor.
Further, in the embodiment, the motor driving circuit of the unipolar driving stepping motor driver IC has been described. However, the output circuit of the power transistor is used as a driving circuit for push-pull operation, and bipolar driving (both positive and reverse phase waves) is performed. It goes without saying that the present invention may be applied to a stepping motor driver IC for driving.

As described above, in the embodiment, the power transistor 3 is controlled to be turned off via the chopping pulse generation circuit 7 and the OFF timer circuit 8. However, if the power transistor 3 is turned off, the chopping pulse is generated. The circuit 7 and the OFF timer circuit 8 are not necessarily required for the present invention.
Further, in the embodiment, the stepping motor driver IC is described. However, any circuit can be used as long as the drive circuit has a current limiting circuit that limits the driving current by turning off the power transistor with a specified current value. Even so, the present invention can be applied.

FIG. 1 is a block diagram of a unipolar driving stepping motor driver according to an embodiment to which a power transistor protection circuit of a motor drive circuit of the present invention is applied. FIG. 2 is a timing chart of the operation of the power transistor protection circuit.

Explanation of symbols

1a, 1b, 1c, 1d ... single phase drive circuit,
2a, 2b, 2c, 2d ... output terminals,
3 N-channel MOSFET power transistor,
4 ... Power transistor protection circuit, 4a ... Terminal open detection circuit,
4b ... disconnection detection circuit, 4c, 46 ... comparator,
4d ... octal counter, 5 ... current limiting circuit,
5a ... comparator, 6 ... reference voltage generation circuit,
7 ... Chopping pulse generation circuit, 8 ... OFF timer circuit,
9: Phase excitation signal generation circuit,
10 ... Stepping motor driver IC,
11a, 11b, 11c, 11d ... exciting coils,
12 ... Power supply, 13 ... Clock generation circuit, 14 ... Clock generation circuit,
41: Drive stop signal generation circuit, 42: OR gate,
43 ... latch circuit, 44, 45 ... resistance voltage divider circuit,
Rs: resistance, D: flywheel diode.

Claims (14)

In the power transistor protection circuit in the motor drive circuit having a plurality of power transistors corresponding to the plurality of excitation coils, which output a drive current to the excitation coil of the motor via the output terminal,
A terminal open detection circuit, a disconnection detection circuit, and a drive stop circuit;
The terminal open detection circuit includes the excitation coil having one of the other terminal of each excitation coil not connected to the output terminal and a line to which the other terminal is connected and the other terminal. Are connected to the other of the output terminal to which the output terminal is connected or the line to which the output terminal is connected, and are respectively provided corresponding to the plurality of power transistors. Detecting whether or not there is an open state between any one and the other when the output operation of the flow,
The disconnection detection circuit detects a disconnection state by detecting that the terminal open detection circuit is not in an open state between the one and the other and then detecting that the terminal is in an open state. Is what
The drive stop circuit is a power transistor protection circuit that stops the drive operation of the motor drive circuit when a disconnection state is detected by the disconnection detection circuit.   The terminal open detection circuit generates a detection signal of either one of the one and the other being in an open state or not in an open state, and the disconnection detection circuit includes a plurality of disconnection detection circuits A plurality of disconnection detection circuits are provided corresponding to each of the power transistors, and each disconnection detection circuit receives the detection signal from the terminal open detection circuit provided corresponding to the power transistor corresponding to itself and enters the open state. The power transistor protection circuit according to claim 1, wherein a disconnection state is determined when it is detected that an open state is detected after the absence is detected.   The terminal open detection circuit detects a voltage between the one and the other, and the detection signal detects the connection state as not being in the open state. Item 3. A power transistor protection circuit according to Item 2.   4. The power transistor protection according to claim 3, wherein the disconnection detection signal is generated after the output operation of the drive current is completed by not receiving the detection signal when the power transistor is outputting the drive current. 5. circuit.   Each of the disconnection detection circuits has a counter for counting clocks having a period T by n (n is an integer of 2 or more), the counter is reset according to the detection signal, and the counter ends n counts from this reset. 5. The power transistor protection according to claim 4, wherein an n count end signal of the counter is used as the disconnection detection signal for a period longer than a period from the output of the drive current to a next output of the drive current generated. circuit.   The power transistor protection circuit according to claim 4, wherein the disconnection detection signal is generated when the detection signal is not received a plurality of times.   Each of the terminal open detection circuits includes a first comparator that compares a voltage between the one and the other, and the first comparator generates the detection signal as a detection pulse. 6. The power according to claim 5, wherein the disconnection detection circuit includes a second comparator that compares the detection pulse with a predetermined reference voltage, and generates a signal that resets the counter in accordance with an output of the second comparator. Transistor protection circuit.   The drive stop circuit has an OR gate and a latch circuit, receives each disconnection detection signal obtained from each disconnection detection circuit by the OR gate, latches it in the latch circuit, and according to the output of the latch circuit The power transistor protection circuit according to claim 6, wherein a signal for driving the power transistor is stopped.   The power transistor generates a drive current that sinks from the output terminal as an output current, the other terminal is connected to a power supply line, and the one of the voltages is obtained by dividing the voltage of the power supply line by a first resistance. A voltage divided by a voltage circuit, the voltage value of which is close to the voltage value when the drive current is limited, and the one of the other voltages is the second voltage of the output terminal. 8. The current limiting circuit according to claim 7, wherein the current limiting circuit is a voltage divided by a resistance voltage dividing circuit. In the power transistor protection circuit in the motor drive circuit having a plurality of power transistors corresponding to the plurality of excitation coils, which output a drive current to the excitation coil of the motor via the output terminal,
A terminal open detection circuit, a disconnection detection circuit, and a drive stop circuit;
The terminal open detection circuit includes the excitation coil having one of the other terminal of each excitation coil not connected to the output terminal and a line to which the other terminal is connected and the other terminal. Are connected to the other of the output terminal to which the output terminal is connected or the line to which the output terminal is connected, and are respectively provided corresponding to the plurality of power transistors. Detecting any one of the open state or the connection state between any one of the two and the other when the output operation of the flow,
The disconnection detection circuit detects a disconnection state when the open state is detected a plurality of times in response to detection of either the open state or the connection state by the terminal open detection circuit,
The drive stop circuit is a power transistor protection circuit that stops the drive operation of the motor drive circuit when a disconnection state is detected by the disconnection detection circuit.   The power transistor protection circuit according to claim 10, wherein the disconnection detection circuit is in the disconnection state by continuously being in the open state a plurality of times.   12. A motor drive circuit in which the motor drive circuit having the power transistor protection circuit according to claim 1 is formed as an IC, and a motor is driven by the output current of the power transistor.   The motor drive circuit according to claim 12, wherein the motor is a stepping motor.   14. A semiconductor device in which the motor drive circuit according to claim 12 is integrated into an IC.

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