JPS62233095A - Drive circuit for inductive load - Google Patents

Abstract

PURPOSE:To keep the current flowing to the load within the specified limits for any input of chopping frequency driving signal. CONSTITUTION:A current control circuit 2 changes the output in accordance with the frequency of chopping actuation. In a proper chopping actuation, the voltage VR2 is inputted to the terminal of a comparator IC3 which is decided by the partial pressure ratio between resistances R3 and R2 connected in parallel and a resistance R4 connected in series. In the meantime, when the current value is below n-times in which it is impossible to actuate the chopping, the voltage inputted to the comparator IC3 is decided by the partial resistances R3 and R2, so that the value will rise as compared with the case in the abovementioned chopping actuation. On this account, when it is impossible to actuate the chopping by high speed operation, the increase of supply current to a coil L is ensured and the sufficient torque can be obtained without fail.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention involves periodically applying a predetermined voltage to an inductive load such as a coil using a pulse signal, etc., and chopping the current flowing through the inductive load. The present invention relates to an inductive load drive circuit that maintains an inductive load within a certain range by a circuit.

[Conventional technology]

Currently, examples of devices that use this type of circuit include stepping motors. This stepping motor is applied to a variety of devices, such as a printer carrier drive, and is capable of accurately controlling the rotational phase and rotational speed in accordance with drive pulses. However, this stepping motor has a problem in that when the frequency of the drive pulse is increased and the rotation speed is increased, the torque suddenly decreases when the rotation exceeds a certain certain frequency. In other words, until a certain frequency is reached, due to the chopping operation of the chopping circuit provided in the drive circuit, there is a current flowing through the coil as shown in Figure 5(a) - it is maintained within a certain range. , when the frequency becomes north of a certain value, the fifth (
b) The chopping circuit does not work as shown in the figure and flows into the coil. The current value suddenly decreases and the torque decreases significantly. Therefore, conventionally, when driving at a frequency similar to a certain constant where the '1π current suddenly decreases, the current supplied to the coil is increased so that a constant torque can always be obtained at any frequency. In this case, the frequency at which the current should be increased and the current value thereof are set in advance in the drive circuit.

[Problem that the invention seeks to solve]

However, in conventional inductive load drive circuits,
The frequency at which the current flowing through the coil suddenly decreases was set in advance to a certain value, and the current supplied to the coil was increased when operating above this frequency, so when coils with different inductances were connected, the current There is a problem in that the current increasing operation is always performed at a constant frequency even though the frequencies at which the current suddenly decreases are different, and an appropriate constant current supply operation cannot be performed. In other words, the rising and falling curves of the current flowing through the coil are determined by the inductance of the coil as shown in FIG. 6, and the chopping period T is determined by this curve. Therefore, if the inductance changes, the frequency at which the chopping operation becomes impossible, that is, the frequency at which the current flowing through the coil suddenly decreases, also changes, causing the problem described in F. Therefore, when the above drive circuit is applied to, for example, a stepping motor, sufficient torque may not be obtained depending on the inductance of the motor coil. Therefore, the frequency at which the current is increased had to be reset for each bowl motor.

This invention was made by paying attention to the above problem, and it is possible to maintain the current flowing through an inductive load within a certain range even if a drive signal having any frequency is manually applied. An object of the present invention is to provide an inductive load drive circuit that can always obtain a constant torque regardless of the rotational speed of a motor even when applied.

Means for Solving Problem C) This invention provides a detection means for detecting the number of times of chopping by a chopping circuit, and a current to be supplied to an inductive load depending on whether the number of times of chopping is less than or equal to a certain number of times. and current increasing means for increasing the current.

[Effect]

In this invention, by detecting the number of chopping operations, it is possible to detect whether or not the chopping circuit is operating properly, and if the chopping circuit is not operating properly, the current 'Y supplied to the inductive load is increased. , the current flowing through the inductive load can be maintained within a certain range.

The explanation will be based on.

FIG. 1 is a circuit diagram showing the configuration of an inductive load drive circuit according to an embodiment of the present invention. This circuit consists of a chopping circuit l that maintains the current flowing through an inductive load such as a coil in a stepping motor within a certain range, and a counter IC as a detection means that detects the number of chopping operations by the chopping circuit l. , If the number of detections by this counter [c2 is greater than a certain number of times,
Consisting of a current control circuit 2 as a current control means for controlling the current supplied to the inductive load to increase the current supplied to the inductive load, the chopping circuit 1 includes transistors Tr,...
Tr2. Tr3, current detection resistor R1, and comparator summer C3
, diodes D, , D2 and Zener diode Z
It is constructed of a snubber circuit etc. equipped with D.

In addition, the current control circuit 2 includes a D flip-flop ■01, an AND gate G, inverters IC4 and IV, and a resistor R3.
and voltage dividing resistors R2 and R4.

Next, the operation of the inductive load drive circuit having the above configuration will be explained.

FIGS. 2 and 3 are flowcharts showing the chopping operation, and FIG. 2 is a flow chart showing the chopping operation.
is turned off (step 2-1), and the current (2) flowing through the coil becomes 0 (step 2-2). Therefore, the voltage VR, generated across the current detection resistor R1 becomes 0 (step 2-3), and the voltage vR2 generated across the voltage dividing resistor R1 becomes 0 (step 2-3).
Since the magnitude relationship with VR2) VR, Comparison 3IC
, , a high level signal (H signal) is output (
Step 2-4). As a result, transistor TR3 becomes O
The transistor TR4 at the next stage is also turned on (steps 2-5 and 2-6).

In this state, when a driving pulse is applied manually, the transistor TR turns on (step 3-1), and the current flowing through the coil increases (step 3-2), which generates a current across the current detection resistor VR. The voltage VR1 increases (step 3-4). The comparator IC3 compares this voltage VR with the voltage VR2 generated across the voltage dividing resistor R2 (
Step 3-5), if VR, > VR2, then
IC, ++7) output continues to output an H signal (step 3-6), turn on transistors TR, TR2, step 3-7), repeat steps 3-3 to 3-7, and coil. The current IL flowing to the current IL continues to increase. Eventually, the voltage VR increases due to an increase of the current +4, and when it reaches VR, ) VR, a signal is output from the comparator IC (step 3-r). As a result, transistors TR, TR2 are turned off (step 3-
9) The current flowing through the coil is interrupted by 1°, and the voltage VR generated across the current detection resistor R3 (Step 8)
, also decreases (step 3-!l) , (- and then
When VRl<VR2tort, an H signal is output from the comparator IC3, and the operations from step 3-3 onward are repeated again. The above operation is the conventional chopping operation, and if the frequency of the drive pulse is within a certain value, this operation will reduce the current flowing through the coil to the fifth
It can be maintained within a certain range as shown in Figure (a).

However, as mentioned earlier, when the frequency of the drive pulse exceeds a certain value or reaches F, this chopping operation becomes impossible and the current flows through the coil. , suddenly decreases, so in this embodiment, the current IL is corrected by the operation shown in the flowchart of FIG.

That is, the n-ary counter C2 counts the number of H signals sent out from the comparator 11c3 over one cycle of the drive pulse, that is, the number of chopping operations, and (Step 4-
1) If the count has reached the proper number of chopping operations n times, and the H signal has not been reached, a low level signal (L signal) is output to the D flip-flop IC1 (step 4-2). In D flip-flop IC,
If the counter IC3 outputs an H signal, an L signal is output via the inverter IV (step 4).
-4). As a result, the output of the inverter IC becomes L level (step 4-4), and the resistor R3 and the voltage dividing resistor R2 are connected in parallel. Therefore, during proper chopping operation when the count value is n times or more, the resistors R3 and R2 are connected in parallel, and the resistor R is connected in series with them.
The voltage VR generated across the resistor R1 due to the voltage division ratio with 4,
A comparison is made with

On the other hand, when the chopping operation is disabled when the count value is n or more, the D flip-flop IC.

A read signal is output (step 4-7), and the output of inverter IC4 becomes H level (step 4-8).
. As a result, the voltage VR2 input to one input terminal of the comparison Brc3 is determined only by the voltage dividing resistors R4 and R2, so its value increases compared to the above-described chopping operation. Therefore, the magnitude relationship between this voltage VR2 and the voltage VR generated across the current detection resistor R1 is VR2
) VR, and an H level signal is output from the comparison 3tc3, and ■I increases (step 4-10).

As shown below, in this embodiment, during high-speed driving when the number of current rises due to chopping operation is n times or more, this is detected and the current supplied to the call L is automatically increased, and the chopping operation is performed. It is possible to compensate for the sudden decrease in current caused by inoperability. Therefore, for example, when this circuit is used to drive a stepping motor, no matter what inductance the coil built in the motor has, the current supplied to coil L will certainly increase when chopping is disabled due to high-speed operation. 1 and always have enough torque! can do.

In the above embodiment, the current supplied to the coil is increased when the number of chopping operations becomes less than a certain number (0 times), but the current supplied to the coil is increased depending on the frequency of the drive pulse. , it is also possible to increase the current stepwise.

Note that the number of chopping times n for increasing the current supplied to the coil can be set to a desired value, and the counter value may be determined by the CPU. Roughly speaking, if you want to set n=0 and increase the supply current depending on whether the chopping operation has completely stopped, you can simply use a flip-flop without using the counter IC3. Good too.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to maintain the current flowing through an inductive load within a certain range even if a drive signal having any frequency is manually applied, and for example, when applied to a stepping motor, etc. , the effect is that constant torque can always be obtained regardless of the rotational speed of the motor.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram showing an embodiment of the present invention. FIGS. 2 and 3 are flowcharts showing the operation of the chopping circuit in FIG. Figure 3 shows the drive pulses when they are applied manually. Figure 4 is a flowchart showing the operation of the counter and current control circuit shown in Figure 1, and Figure 5 is a waveform diagram of the current supplied to the coil by the chopping circuit.
(b) shows the case where the human power driving pulse is a low frequency, and (b) shows the case where the same pulse is a high frequency. FIG. 6 is a diagram showing the rise time of the drive current that changes depending on the inductance of the coil, where (a) shows the time when the inductance is low, and FIG. 6 (b) shows the time when the inductance is high. l...Chopping circuit 2--Current control circuit IC2...Counter L as a detection means ---
----- Coil IE1 diagram as an inductive load Figure 4

Claims (1)

[Claims] An inductive load drive circuit that periodically applies a predetermined voltage to an inductive load and maintains the current flowing through the inductive load within a certain range by a chopping circuit, wherein the chopping circuit performs chopping. An inductive load drive circuit comprising a detection means for detecting the number of times, and a current control means for increasing the current supplied to the inductive load when the number of times of detection is less than a certain number of times.