JPH033453B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a current limiting circuit that can be used in a current control circuit of a brushless motor or the like.

Configuration of a conventional example and its problems FIG. 1 is a wiring diagram showing a conventional example of a current limiting circuit for a brushless motor. In the figure, the voltage-current converter 1 has input terminals 17 and 18 and an output terminal 19.
and has. One end of the resistor 3 and the anode of the diode 2 are connected to the output terminal 19. resistance 3
The other end is connected to the base of the transistor 6 and one end of the resistor 5 at the connection point 4 . The emitters of the transistors 10 and 11 are connected in common, and an emitter current is supplied from a constant current source 8.

The emitter 20 of the transistor 6 is connected to the base of the transistor 10, and is also connected to the constant current source 7.
The emitter current is supplied from. The collector of the transistor 11 is connected to an output circuit 16, and the output terminal of the output circuit 13 is connected in series with a load 16 and a resistor 15 for detecting load current. resistance 1
The terminal 14 of the transistor 5 on the load 16 side is connected to the base of the transistor 12, and the emitter of the transistor 12 is connected to the base of the transistor 11, and an emitter current is supplied from the constant current source 9.

When a load current command voltage is input between the input terminals 17 and 18, a current according to the command is output to the output terminal 19, and a voltage is generated by the resistors 3 and 5. This voltage is divided by resistors 3 and 5 and the connection point 4
The voltage becomes the base voltage of the transistor 6. Transistors 6, 10, 11, and 12 operate as error amplifiers and drive output circuit 13 so that the voltages at the base of transistor 6 and the base of transistor 12 are equal. A voltage from a load current detection resistor 15 is applied to the base of the transistor 12 . Voltage V ₁₉ of output terminal 19, resistance 3,
If the values of 5 and 15 are respectively R ₃ , R ₅ , and R ₁₅ and the load current is I, the following equation holds true.

I=R ₅ · V ₁₉ /R ₁₅ (R ₃ + R ₅ )... (1) Since diode 2 is connected to output terminal 19, voltage V ₁₉ is the forward voltage of diode 2 V _D
It never exceeds. That is, V ₁₉ is limited by V _D.

On the other hand, if the transfer conductance of the voltage-current converter 1 is gm, and the load current command voltage is V, then
Since V ₁₉ ≦V _D , V ₁₉ = (R ₃ + R ₅ )・gm・V... (2), I=R ₅ /R ₁₅・gm・V... (3).

V > V _D / (R ₃ + R ₅ )・gm... (4) Since V ₁₉ = V _D , I=R ₅・V _D /R ₁₅ (R ₃ + R ₅ )... ( 5) Therefore, the maximum value of the load current is limited to the value determined by equation (5) depending on the diode voltage V _D.

However, the forward voltage of the diode has large element variations even when it is integrated into an integrated circuit, and it also fluctuates due to temperature, so the limit value of the load current cannot be controlled accurately.

OBJECTS OF THE INVENTION The present invention eliminates the drawbacks of the above-mentioned conventional examples, and provides a current limiting circuit that is suitable for integrated circuit implementation and can realize a load current limit value with high accuracy.

Structure of the Invention In the current limiting circuit of the present invention, a voltage that commands a load current is applied to the base of one of two transistors of the same conductivity type whose emitters are commonly connected, and a voltage that commands a load current is applied to the other base. By applying , and using the voltage on the low voltage side of one of these bases as one input of the error amplifier, and inputting the voltage to the other input according to the load current, The load current from the output circuit driven by the output of the error amplifier to the load is limited to a value corresponding to the limiting voltage.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 2 is a wiring diagram showing one embodiment of the present invention in a brushless motor drive circuit. In the figure, a voltage-current converter 1 has input terminals 17 and 18 and an output terminal 19. A resistor 5 and the base of a transistor 6 are connected to the output terminal 19.
The emitters of the transistors 10 and 11 are commonly connected, and an emitter current is supplied from a constant current source 8. The emitter 20 of the transistor 6 is connected to the emitter of the transistor 23 and the base of the transistor 10, and is supplied with emitter current from the constant current source 7. The collector of the transistor 11 is connected to the output circuit 13, and the collector of the transistor 11 is connected to the output circuit 13.
A load 16 and a resistor 15 for detecting load current are connected to the output of
are connected in series. The base of the transistor 12 is connected to the terminal 14 of the resistor 15 on the load 16 side, and the emitter of the transistor 12 is connected to the base of the transistor 11, and emitter current is supplied from the constant current source 9. . Transistors 6, 10, 11, 12, 23
The collector and one ends of the resistors 5 and 15 are respectively grounded, and power supplies 21 and 22 are applied to the constant current sources 7, 8, 9 and the output circuit 13, respectively. The base of the transistor 23 is connected to a current limiting terminal 24, to which a limiting voltage 25 is applied.

When a load current command voltage is input between the input terminals 17 and 18, a current according to the command is output to the output terminal 19, and a voltage is generated by the resistor 5. Since the emitters of the transistors 6 and 23 are connected in common, the voltage of the emitters depends on the base voltage of the lower voltage side of each base. When the emitter voltage of the transistor 12, that is, the base voltage of the transistor 11, is lower than the voltage of the base 20 of the transistor 10, the drive current of the output circuit 13 increases, and the voltage at the terminal 14 of the load current detection resistor 15 increases. As a result, the base voltage and emitter voltage of transistor 12 increase, and the voltage between the bases of transistors 10 and 11 decreases. In this manner, the emitter voltage of transistor 12 tracks the voltage at the base 20 of transistor 10. When the base voltage of the transistor 6 is lower than the base voltage of the transistor 23, the voltage at the base 20 of the transistor 10 is determined by the base voltage of the transistor 6. Therefore, if the current values of the constant current sources 7 and 9 are the same, the transistor The base-emitter voltages of 6 and 12 are equal. Therefore, the voltage at terminal 14 follows the base voltage of transistor 6, that is, the voltage at resistor 5. When the voltage of the resistor 5 rises and becomes higher than the base voltage of the transistor 23, that is, the limit voltage 25 of the current limit terminal 24, the transistor 6 is cut off, and the voltage at the base 20 of the transistor 10 is determined by the base voltage of the transistor 23. Become. Therefore, terminal 14
The voltage follows the limiting voltage.

Now, load current command voltage is V, voltage current converter 1
The transfer conductance of is gm, the resistance values of resistors 5 and 15 are R ₅ and R ₁₅ respectively, and the voltage of output 19 is V ₁₉ ,
If the limit voltage is V ₂₄ and the load current is I, then V ₁₉ = R ₅・gm・V... (6) Therefore, I=R ₅ /R ₁₅ gm・V (V≦V ₂₄ /R ₅・gm)… (7) I=V ₂₄ /R ₁₅ (V>V ₂₄ /R ₅・gm)… (8)

Therefore, the load current I is limited by the limiting voltage of the current limiting terminal 24. Since this limiting voltage can be provided in the form of a constant voltage source or resistance division of the power supply voltage, temperature dependence can be eliminated even when integrated, and sufficiently high accuracy can be achieved.

Since transistor 6 or 23 and transistor 12 operate with the same emitter current, their respective base-emitter voltages and their temperature characteristics are well matched, and the relationship between load current command voltage or load current limit voltage and load current is No fluctuations occur due to

Although the constant current sources 7 and 9 are current sources having the same current value, these are not necessarily necessary for the operation of the transistors 6, 23, and 12, and can be omitted.

In this embodiment, transistors 6, 10, 1
Although PNP type transistors are used in Embodiments 1, 12, and 23, it is clear that all of these transistors can be changed to NPN types without impairing the spirit of the present invention.

Although detailed explanation of the output circuit 13 has been omitted in the description of the embodiments, it is important to note that the present invention can be applied not only to brushless motors but also to various other current control circuits, and that the gist of the present invention may be changed. It goes without saying that there are many variations and applications.

Effects of the Invention As explained above, the present invention can realize a current limiting circuit with a simple configuration and suitable for integration into an integrated circuit.
In particular, it is possible to apply the limit voltage from a voltage source that is independent of the load current command voltage and eliminates temperature dependence, and the relationship between the limit voltage and load current does not fluctuate due to temperature. Extremely useful.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing a conventional example of a current limiting circuit.
FIG. 2 is a circuit diagram showing one embodiment of the present invention. 1...Voltage-current converter, 2...Diode,
3, 5, 15...Resistance, 6, 10, 11, 12,
23... Transistor, 7, 8, 9... Constant current source, 24... Current limiting terminal.

Claims (1)

[Claims] 1. First and second transistors of the same conductivity type whose emitters are commonly connected and connected to one input of the differential amplifier, and whose emitters are connected to the other input of the differential amplifier. a third transistor of the same conductivity type as the first transistor connected to the input; an output circuit driven by the output of the differential amplifier; and a voltage proportional to the load current of the third transistor. A current detecting means connected to be applied to the input, and a power supply means for supplying a load current command voltage to the base of the first transistor and also supplying a load current limiting voltage to the base of the second transistor. A current limiting circuit characterized by: 2. The power supply means includes a voltage-current conversion means and a resistor to which the output current of the voltage-current conversion means is supplied, and supplies the voltage obtained across the resistor to the base of the first transistor to convert the voltage to the base of the first transistor. 2. The current limiting circuit according to claim 1, wherein the current limiting circuit is configured so that the input voltage to the current converting means is the load current command voltage.