JPH02254920A - Protection circuit - Google Patents

Abstract

PURPOSE:To perform the protection assuredly against overcurrent or malfunction by checking the current flowing to a load and by interrupting the current supply to the load when the conduction is kept for not less than a predetermined time where the voltage corresponding to this current exceeds the specified reference voltage. CONSTITUTION:In a comparator 12 specified reference voltage Vr is given to an input (-) and this reference voltage Vr is compared with the detected voltage given to a (t) input. As a result, if the detected voltage Vd exceeds the reference voltage Vr, an output signal SG will be '1'. This output signal SG is given to a timer circuit 13. The timer circuit 13 measures the time when the output signal SG of the comparator 12 keeps '1' to the timer circuit 13. When this measured time gets to the predetermined timer operating time preset to the timer circuit 13, an output signal '1' is outputted. A power relay 14 is thereby energized to open a contact RB and the current supplied to the collector of a transistor Tr2 is interrupted.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a protection circuit used in a winding current supply circuit such as a step motor or a solenoid, and particularly relates to a protection circuit used in a winding current supply circuit such as a step motor or a solenoid. The present invention relates to an arrangement in which the supply of the current can be promptly cut off when the current is generated.

[Prior Art] For example, an example of a winding current supply circuit in a unipolar step motor is shown in FIG. The current supply circuit 30 supplies a predetermined constant current to the phase excitation circuit 20, and includes a transistor Tr2, a resistor R2, and a fuse H. The transistor Tr2 has a collector connected to the power supply Vcc, and a base supplied with a base voltage vb from the constant current control circuit 15. This base voltage vb controls the current WI (arrow) flowing from the power supply Vcc through the collector-emitter, that is, the emitter current. The emitter current of the transistor Tr2 is supplied to the phase excitation circuit 20 via a resistor R2 and a fuse H.

The phase excitation circuit 20 excites each phase of the motor,
It includes an excitation winding for each phase and an excitation transistor corresponding to each winding. The switching of each phase excitation transistor is sequentially controlled according to an excitation pulse signal PS for each phase given from a phase excitation control circuit 16. Due to this switching operation, the current WI sequentially flows as the winding currents 1 to I4 for each phase in accordance with the input pulse signal PS, and each phase is excited.

In general, step motors are small in size and are designed to obtain large torque.
A large current is supplied to the winding 0, and as time passes during which this large current is supplied, the temperature of the winding increases and the electrical resistance of the winding also increases. Furthermore, since a large current flows through each phase excitation transistor, drift may occur due to heat generation in these transistors, which may cause changes in characteristics. Further, even if electrical and electronic components are within standard values, they tend to deteriorate if high voltage/large current is supplied for a relatively long period of time. especially,
If the temperature of the components increases due to heat generation as the power supply time elapses, a protection circuit is required to prevent power supply from exceeding a predetermined time in order to prevent deterioration or burnout of the components. Therefore, in order to prevent winding burnout due to heat generation,
A protection circuit is provided to prevent winding current from being supplied for more than a predetermined time. Conventionally, fuse H has functioned as such a protection circuit.

[Problems to be Solved by the Invention] However, in protection circuits using fuses, it is difficult to select the optimal type of fuse that appropriately corresponds to the relationship between the current supplied to the phase excitation circuit and the fuse's blowing characteristics. There was a problem that. That is, for example,
When 5A is supplied to a fuse with a maximum capacity of 5A, it is difficult to know how long it will take for the power supply to blow out, as even fuses of the same standard are affected by variations in the characteristics of each fuse and the environment such as ambient temperature. It was not possible to accurately understand and use it as a protection circuit. Therefore, if such a fuse is used as a protection circuit in a winding current supply circuit, it may not be possible to cut off the winding current supply at any precise time, which may lead to component deterioration or burnout. There was a problem.

On the other hand, regarding the winding current of a DC solenoid,
Generally, the starting current is relatively small, and the power consumption increases as the power supply time passes. Therefore, fuses cannot provide sufficient protection, and if for some reason the winding current is supplied for more than a specified time, the windings and other parts will heat up as the power supply time elapses, creating a risk of smoke and burnout. There was the problem of inviting.

The present invention has been made in view of the above-mentioned points, and it is an object of the present invention to provide a protection circuit that can reliably protect against overcurrent or malfunction without using fuses.

[Means for Solving the Problems] A protection circuit according to the present invention includes a detection means for detecting a voltage according to a current applied to a load, and a voltage detected by the detection means and a predetermined base 1? ! and a timer means for measuring the time during which the level of the detected voltage exceeds the level of the reference voltage based on the output of the comparing means, and generating an output signal when this time lasts for a predetermined time or more. and means for cutting off the supply of the current to the load in response to the output signal of the timer means.

[Operation] The reference voltage of the comparison means is set corresponding to a predetermined current value at which abnormality should be detected. When detecting that an overcurrent is applied to a load, the setting is made in accordance with a predetermined overcurrent value to be detected. In that case.

When an overcurrent is applied, the output of the comparison means indicates that the current to the load has become an overcurrent, that is, the level of the detected voltage of the detection means has exceeded the level of the reference voltage;
The timer means measures the time during which the level of the detected voltage exceeds the level of the reference voltage, and generates an output signal when this time lasts for a predetermined time or more. The supply of the current to the load is cut off in response to the output signal of the timer means.

Therefore, according to the present invention, protection against overcurrent or malfunction can be reliably achieved without using fuses.

The object to be detected is not limited to overcurrent, but may be any appropriate current value corresponding to normal operation or abnormal operation.

For example, it is also possible to detect an abnormal operation such as when a drive current flows through a solenoid for a predetermined period of time or longer.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows an embodiment in which a protection circuit according to the present invention is applied to a winding current supply circuit of a unipolar step motor. In the figure, circuit elements having the same reference numerals as the circuit elements in FIG. 3 perform the same functions. The current supply circuit 40 includes a power relay 14, a transistor Tri,
Resistor R2, detector 11 and comparator 12. Timer circuit 13
It consists of etc. The transistor Tr2 functions as a current control element, and its collector is connected to the power supply Vcc via the normally closed contact RB of the power relay 14, and the base receives the base voltage vb as a control voltage from the constant current control circuit 15. The emitter is connected to one end of the resistor R2 and one input (+) of the detector 11.
is connected.

The other input (-) of the detector 11 and each winding of the phase excitation circuit 20 are connected to the other end of the resistor R2. That is, the current Ie, that is, the emitter current is supplied to the phase excitation circuit 20 via the resistor R2. The detector 11 detects the voltage generated across the resistor R2 due to the current Ie flowing through the resistor R2, and inputs the detected voltage Vd to one input of the comparator 12 (+
).

Comparison m12 has the other input (-) set to a predetermined reference voltage Vr.
is given, and this reference voltage Vr is compared with a detection voltage Vd given to the human force. As a result of this comparison, if the detection voltage Vd has not reached the reference voltage Vr, the output signal SG is "0", but if the detection voltage Vd exceeds the reference voltage Vr, the output signal SG becomes "1". Output signal S
G is given to the timer circuit 13.

The timer circuit 13 is configured so that the output signal SG of the comparator 12 is 11"
, that is, the detection voltage Vd is equal to the reference voltage V
It measures the duration of time exceeding r, and when this measured time reaches a predetermined timer operation time set in advance in the timer circuit 13, an output signal "1" is output. Note that it is convenient if the timer operating time can be set variably.

The output signal 1'1'' of the timer circuit 13 is applied as a relay control signal R8 to the base of the transistor Tri. The transistor Tri is a relay driver for driving the power relay 14 connected to the collector. When the relay control signal R8 given from the timer circuit 13 becomes "1".

Transistor Tri is turned on and relay 14 is energized.

The power relay 14 is a normally closed contact type, and the transistor T
When ri is off, it is in a deenergized state, contact RB is closed, and power is supplied from the power supply Vcc to the collector of the transistor Tr2. On the other hand, when the transistor Tr1 is on, the power relay 14 is energized, the contact RB is opened, and the current being supplied to the collector of the transistor Tr2 is cut off.

In this way, if an overcurrent exceeding the rating continues to flow for a predetermined period of time or more, the power is cut off, thereby protecting circuits, components, etc.

The protection circuit according to the present invention can be applied not only to a motor winding current supply circuit but also to other circuits. For example, if a solenoid coil is used in place of the phase excitation circuit 20 in FIG. If an overcurrent exceeding the rating continues to flow through the coil for a predetermined period of time or more, one circuit, component, etc. can be protected.

Furthermore, the present invention can be applied not only to protection against overcurrent but also to checking for normal operation. FIG. 2 shows an example of this. In FIG. 6, which checks the operation of a solenoid coil, circuit elements having the same reference numerals as those in FIG. 1 perform the same functions.

Normally closed contact RB of power relay 14 with respect to power supply Vcc
, solenoid coil SOL, and the collector-emitter of transistor Tr2 are connected in series. By controlling the base voltage vb of the transistor Tr2, the transistor Tr2 is turned on or off, and the solenoid coil SQL is energized or deenergized.

In FIG. 2, the collector voltage Vc of the transistor Tr2 corresponds to the current flowing through the solenoid coil SQL, which is a load, and this collector voltage Vc corresponds to the comparator 12.
It is given directly to the ten-man force.

If the transistor Tr2 is turned off, the solenoid coil 50 is deenergized and the collector voltage Vc is at a predetermined high level. When energizing the solenoid coil 50, the transistor Tr2 is turned on and its collector voltage V
c falls to a predetermined low level (approximately an "on" level). If a disconnection occurs in the solenoid coil 50, the collector voltage Vc always maintains a low level.

The reference voltage Vr applied to the comparator 12 is set to an appropriate level that distinguishes between on and off levels of the collector voltage Vc of the transistor Tr2. The comparator 12 outputs "110" when the collector voltage Vc applied to the voltage is on level, that is, low level, and outputs "1" when it is off level, that is, high level.

The timer circuit 13 may be configured to perform a time measurement operation using either when the input signal rises to I(I+) or when it falls to "0", and may be configured to perform a time measurement operation depending on design requirements. For example, when checking for an abnormality in the duration of the on level, that is, the low level, in this example, the timer start trigger may be set when the input signal falls to '0'.

For example, it is assumed that the solenoid coil 50 is a numbering solenoid that is repeatedly turned on and off at regular intervals. In that case, the set operating time of the timer circuit 13 corresponds to a predetermined on-time. During normal operation, the output R8 of the timer circuit 13 is "O" and the contact RB of the relay 14 remains closed. If the ON time continues for a predetermined time or more due to some abnormality, the output RS of the timer circuit 13 becomes "1", the relay 14 is energized, the contact RB is opened, and the power is cut off.

[Effects of the Invention] As described above, according to the present invention, the current flowing through the load is checked, and when the voltage corresponding to this current exceeds a predetermined reference voltage for a predetermined period or longer, the current supply to the load is stopped. Since we made it possible to cut off the
This provides an excellent effect in that protection against overcurrent or malfunction can be reliably realized.

14... Power relay 15... Constant current control circuit, 16... Phase excitation control circuit, 20... Phase excitation circuit, 40°... Current supply circuit, SQL... Solenoid coil.

Tri, Tr2...transistor, R2, R3...
resistance.

Claims (1)

[Scope of Claims] Detecting means for detecting a voltage according to the current applied to the load; Comparing means for comparing the voltage detected by the detecting means with a predetermined reference voltage; Based on the output of the comparing means. , timer means for measuring the time during which the level of the detected voltage exceeds the level of the reference voltage, and generating an output signal when this time continues for a predetermined time or more; and adjusting the current to the load in accordance with the output signal of the timer means. protection circuit with means for interrupting the supply.