JPH0413696Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a current source circuit, and particularly to a constant current switching circuit that switches a constant current to either flow in or flow out.

(Prior Art) FIG. 1 shows a conventional example of this type of constant current circuit.
Reference numeral 10 denotes a constant current switching terminal, which is connected to the base of the switching transistor 7. The emitter of the transistor 7 is grounded, and the collector is connected to the anode side of the diode 6, the base of the constant current transistor 4, and the collector of the constant current transistor 5. The cathode of the diode 6 and the emitter of the transistor 4 are grounded to form a first current mirror circuit 20, and the collector of the transistor 4 is connected to the output terminal 3. transistor 5
Its emitter is connected to the power supply 1, its base is connected to the base of the transistor 2 and the cathode of a diode 8 whose anode is connected to the power supply, and is grounded via a resistor 9. The emitter of transistor 2 is connected to the power supply, and the collector is connected to output terminal 3, and transistors 2 and 5 and diode 8
This constitutes the second current mirror circuit 30.
Note that the emitter area of the transistor 4 is designed to be twice that of the diode 6.

Next, the operation of the above-mentioned circuit will be explained. first,
Consider a case where an input that makes the transistor 7 conductive is input to the current switching terminal 10. If the current flowing through the diode 8 and the resistor 9 is I, the second current mirror circuit 30 operates and a constant current I flows through the transistors 2 and 5, but since the transistor 7 is conductive, the first current mirror circuit 20 is not conductive, and therefore a constant current I flows out to the output terminal 3.

Next, consider the case where the current switching terminal 10 is grounded. Similarly to the above, the current mirror circuit 30 operates regardless of the input to the current switching terminal.
On the other hand, since the transistor 7 is not conductive, the current mirror circuit 20 operates. Therefore, since constant current I flows through transistor 2 and constant current 2×I flows through transistor 4, constant current I flows from the output terminal.
will flow in. However, it is assumed that the output terminal 3 is connected to a current path through which the output current can flow in or out.

(Problems to be Solved by the Invention) As described above, in this conventional example, the constant current I must always flow out from the transistor 2 regardless of the inflow or outflow of the output current.
When a constant current flows out, a current of 3×I flows through the entire circuit, and when a constant current flows in, a current of 4×I flows through the entire circuit.
current flows. Therefore, extra current always flows through the circuit, increasing power consumption.

The purpose of the present invention is to provide a constant current circuit with low power consumption and a constant current switching function.

(Means for Solving the Problems) A current source circuit according to the present invention includes a first current mirror circuit that draws current from an output terminal according to an input current to an input terminal, and an output current according to an input current to an input terminal. a second current mirror circuit that allows current to flow into a terminal; and the first and second current mirror circuits such that the input current to the first current mirror circuit becomes the input current to the second current mirror circuit. coupling means for coupling between the input terminals of the first current mirror circuit; and a coupling means coupled to the input terminal of the first current mirror circuit for inhibiting input current from being supplied to the first current mirror circuit in response to a control signal; means for forming a current path for supplying an input current to a second current mirror circuit via the coupling means; coupled to input terminals of the first and second current mirror circuits; Prohibiting the input current from being supplied to the second current mirror circuit in response to the input current being supplied, and supplying the input current to the first current mirror circuit via the coupling means. and means for forming a current path.

(Example) Hereinafter, an example of the present invention is shown in FIG. 2 and will be described in detail. Note that in FIG. 2, parts corresponding to those in FIG. 1 are given the same reference numerals and their explanations will be omitted. The main difference from FIG. 1 is that transistors 11, 13 and resistor 12 are added, and transistor 5 in FIG. 1 is deleted. That is, the current switching terminal 10 is connected to the base of the switching transistor 7, the collector of the transistor 7 is connected to the base of the transistor 4 and the anode of the diode 6, which constitute the first current mirror circuit 20, and further connected to the resistor 9. One end of the transistor 13 is connected to the base of a transistor 13 whose emitter is grounded. The other end of the resistor 9 is connected to the collector of the switching transistor 11, and further connected to the base of the transistor 2 constituting the second current mirror circuit 30 and the diode 8.
connected to the cathode of The emitter of the transistor 11 is connected to the power supply 1, and the base is connected to the power supply 1 via the resistor 12.
Connected to collector No. 3. Furthermore, transistor 2
The area ratio between the transistor 4 and the diode 8 is equal to that between the transistor 4 and the diode 6.

Next, the operation of FIG. 2 will be explained. Current switching terminal 1
When an input that makes transistor 7 conductive is input to 0, transistor 13 is not conductive, so transistor 11 is also not conductive. Therefore, current flows through the diode 8 and the resistor 9, and the current mirror circuit 3
0 works. At this time, the current mirror circuit 20 does not operate due to the conduction of the transistor 7, and the constant current I eventually flows out to the output terminal 3.

Next, when the current switching terminal 10 is grounded, that is, when the transistor 7 is turned off, current flows through the diode 8, the resistor 9, and the diode 6, which causes the transistor 13 to conduct and switch the switching transistor 11 is conductive, so the current mirror circuit 30 does not operate. On the other hand, the first current mirror circuit 20 operates. Therefore, a constant current I flows from the output terminal 3.

In this way, in the embodiment of the present invention, as is clear from the above explanation, there is no need to constantly pass an extra current through the circuit, and when a constant current is caused to flow out, a current of 2×I flows through the entire circuit. When flowing in, only a current of 3×I flows respectively.

(Effects of the Invention) As described above, according to the present invention, it is not necessary to constantly flow current as in the conventional example, and power consumption can be reduced.

In the embodiment used to explain the present invention, the collectors of the transistors 2 and 4 are connected to have one output terminal, but the same effect can be achieved even if they are separated and the output terminals are provided separately. Furthermore, it can be connected to a potential point other than the power source or ground.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a conventional constant current circuit, and FIG. 2 is a circuit diagram showing an embodiment of the present invention. In Figures 1 and 2, 1...power supply, 3...
Output terminal, 10...Current switching terminal, 2, 4, 5,
7, 11, 13... transistor, 6, 8... diode, 9, 12... resistor, respectively.

Claims (1)

[Scope of utility model registration request] a first current mirror circuit that draws current from the output terminal in accordance with the input current to the input terminal; a second current mirror circuit that draws current into the output terminal in accordance with the input current to the input terminal; coupling means for coupling between the input terminals of the first and second current mirror circuits so that the input current to the current mirror circuit becomes the input current to the second current mirror circuit; and coupled to an input terminal of the circuit for inhibiting input current from being supplied to the first current mirror circuit and supplying input current to the second current mirror circuit via the coupling means in response to a control signal; means for forming a current path coupled to the input terminals of the first and second current mirror circuits to cause the second current mirror circuit to flow in response to the input current being supplied to the first current mirror circuit; and means for forming a current path for prohibiting input current from being supplied to the mirror circuit and for supplying input current to the first current mirror circuit via the coupling means.