JPH04368492A - Inductive load driving circuit - Google Patents

Abstract

PURPOSE:To operate an inductive load in non-active region and to lower the switching frequency of ON/OFF operation by providing a driving means, means for ON/OFF controlling the driving means, a current regenerating means, and a current detecting means thereby forming a loop for feeding the output back to the control means. CONSTITUTION:Upon turn ON of input signal, a switching element Q2 is turned ON and a base current IB flows through a switching element Q1. Consequently, a switching element Q3 has an emitter voltage VE=REIB. Upon turn ON of the switching element Q2, the switching element Q1 is also turned ON. Consequently, collector current IC flows through the switching element Q1 thus starting a motor. Upon start of the motor, the collector current IC increases and the switching element Q2 has a base voltage VB>=VE+VBE. At that time, the switching element Q3 is turned ON while the switching element Q2 is turned OFF.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for driving an inductive load such as a motor.

0002

2. Description of the Related Art FIGS. 3 and 4 show typical conventional inductive load drive circuits. In the circuit configuration shown in Figure 3, when the input turns on (high level), the switching element Q
5 is turned on, the base current IB of the switching element Q1 flows, and the switching element Q1 is turned on. Therefore, a collector current IC flows, starting the motor M, which is an inductive load. After starting, when the collector current IC becomes IC RC ≧VBE4, the switching element Q4 is turned on and the base current IB of the switching element Q1 is reduced. Therefore, the collector current IC is limited and VCE1
increases, and the switching element Q1 composed of a transistor operates in the active region.

In the circuit configuration shown in FIG. 4, when the input is turned on (high level), switching elements Q1 and Q2 are turned on, collector current IC flows, and the load is activated. After startup, the collector current IC is IC RC ≧
When VBE is reached, the switching element Q3 is turned on and the collector voltage of the switching element Q3 is brought to a low level, so that the switching element Q2 is turned off, and therefore the switching element Q1 is turned off. As a result, the collector current IC decreases and I
When C RC ≦VBE, switching element Q3
turns off, and the switching elements Q1 and Q
2 is in the on state. Thereafter, current is similarly supplied to the load while the switching elements Q1, Q2, and Q3 are repeatedly turned on and off, but the value of the collector current IC that performs the on and off operations is determined by VBE/RC.

0004

[Problems to be Solved by the Invention] In the circuit configuration shown in FIG. 3, since the switching element for driving the load is used in the active region, that is, the collector current is limited, the switching element The collector-base voltage (VCE) increases, the power consumption of the switching element itself increases, and there are drawbacks such as heat generation.

Furthermore, in the circuit configuration of FIG. 4, unlike the circuit configuration of FIG. 3, the switching element that drives the load is used in the inactive region of the on or off state, but the on/off operations are the same. Collector current value (VBE/RC)
Since the switching is performed based on , the repetition frequency of switching is high, and there are also drawbacks such as heat generation of the switching elements.

[0006] It is therefore an object of the present invention to eliminate the above-mentioned drawbacks, to operate in the non-active region and to have a low repetition frequency of switching on/off operations (preferably eventually to the steady state of the non-active region). The purpose of the present invention is to provide an inductive load drive circuit (operating with

[0007]

[Means for Solving the Problems] In order to achieve the above-mentioned objects, the present invention provides a drive means for driving an inductive load, a control means for controlling on/off of the drive means, and a control means for controlling the drive means on and off. It has a regeneration means for regenerating the current flowing through the inductive load, and a current detection means provided between the regeneration means and the inductive load to detect the current flowing through the inductive load, and the output from the detection means is controlled by the control means. The present invention employs an inductive load drive circuit characterized by forming a feedback loop that feeds back to the inductive load.

[0008] Here, the control means has a hysteresis characteristic, and an on/off condition for the hysteresis characteristic of the control means is determined in relation to a current limit value flowing to the inductive load and a current value flowing to the current detection means. Preferably, the driving means ultimately remains in the on state, and the inductive load is driven in a steady state.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a diagram showing signal, voltage, and current waveforms at various parts of the circuit of FIG.

In the circuit of FIG. 1, M represents a motor;
D1 indicates a regeneration diode, Q1, Q2, Q3
indicates a switching element made of, for example, a transistor, RB1 indicates the base resistance of the switching element Q1, RE and RB2 indicate resistances that determine the current limit value, and VE, VB, and VBE each indicate the resistance of the switching element Q3. Base voltage, emitter voltage, base-
It shows the emitter voltage, IC and IB show the collector current and base current of the switching element Q1, respectively, and IM shows the current flowing through the motor.

The current amplification factor of the switching element Q1 is h
FE, IB determines RB1 so that IB = IC /hFE. When the input signal is turned on, the switching element Q2 is turned on, and the base current IB of the switching element Q1 begins to flow. The emitter voltage VE of the switching element Q3 at this time is VE=RE IB. Also, due to the on state of switching element Q2, switching element Q
1 is also turned on. As a result, the switching element Q
1 of the collector current IC flows, and the motor is started.

After starting, the collector current IC increases as shown in FIG. 2, and the switching element Q2 at this time increases.
The base voltage VB (VB = IC RB2) is VB
≧VE +VBE is satisfied. In this state, switching element Q3 is turned on and switching element Q2 is turned off. When IC at this time is the current limit value IC MAX, the current limit resistance value RB2 is RB2 = (VE + VBE) / IC MAX
It is determined that

By turning off the switching element Q2, the base current IB stops flowing, and VE=0. Further, as a result, the switching element Q1 is turned off, but the motor M continues to rotate because a gradually decreasing regenerative current IM flows through the regenerative diode D1. This state continues until the current IM decreases and the switching element Q3 is turned off.

The condition for turning off is VB = IC RB2
≦VBE, and when switching element Q3 is turned off, switching elements Q1 and Q2 are turned on again. As a result, as mentioned above, the base current IB and the collector current IC begin to flow, and the collector current IC begins to flow again.
increases until IC MAX is reached. After repeating the same switching operation, as shown in Figure 2,
The current IM flowing through the motor becomes constant and the motor reaches a steady state.

[0015]

[Effects of the Invention] As explained in detail above, the present invention has the following features:
In an inductive load drive circuit, by providing hysteresis characteristics to the on/off operation of the switching element that drives the inductive load, the repetition frequency of the switching operation can be lowered, and ultimately the motor can be driven in a steady state. Furthermore, the switching element is configured to operate in a non-active region, thereby reducing power consumption.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

FIG. 2 is a diagram showing signal, voltage, and current waveforms at various parts of the circuit in FIG. 1;

FIG. 3 is a diagram showing a conventional circuit.

FIG. 4 is a diagram showing another conventional circuit.

[Explanation of symbols]

1 Drive circuit 2 Drive circuit control means 3 Feedback circuit M motor D1 Regeneration diode

Claims (5)

[Claims] 1. A drive means for driving an inductive load, a control means for controlling on/off of the drive means, a regeneration means for regenerating a current flowing through the inductive load when the drive means is off, and a current flowing through the inductive load. An inductive load drive circuit comprising: a current detection means provided between a regeneration means and an inductive load in order to detect the current, and a feedback loop for feeding back an output from the detection means to the control means. . 2. The inductive load drive circuit according to claim 1, wherein the control means has a hysteresis characteristic. 3. The inductive load drive circuit according to claim 2, wherein the on/off conditions for the hysteresis characteristic of the control means are determined in relation to a current limit value flowing through the inductive load and a current value flowing through the current detection means. An inductive load drive circuit characterized by: 4. In the inductive load drive circuit according to claim 2 or 3, the drive means ultimately remains in an on state and the inductive load is driven in a steady state. An inductive load drive circuit featuring: 5. The inductive load drive circuit according to claim 1, wherein the drive means is a switching element connected in series with the inductive load, and the control means turns on the drive means in accordance with the current flowing through the inductive load. - A switching element configured to turn off, and the regeneration means is a diode connected in parallel to the inductive load in a polarity direction that regenerates the current flowing through the inductive load when the drive means is off, and the regeneration means An inductive load drive circuit characterized in that the detection means is a resistance.